Editing Concrete

{{Short description|Composite construction material}}
{{Hatnote group|
{{About-distinguish|the construction material|Cement|Grout|Mortar (masonry){{!}}Mortar|Plaster}}
{{Other uses}}
}}
{{More citations needed|date=July 2022}}
{{Use dmy dates|date=November 2019}}
[[File:Bloczek betonowy.jpg|thumb|A single [[concrete block]], as used for construction]]

'''Concrete''' is a [[composite material]] composed of [[construction aggregate|aggregate]] bound together with a fluid [[cement]] that [[curing (chemistry)|cures]] to a [[solid]] over time. It is the second-most-used substance (after [[water]]),<ref>{{cite journal |last=Gagg|first=Colin R. |title=Cement and concrete as an engineering material: An historic appraisal and case study analysis |journal=Engineering Failure Analysis |date=May 2014 |volume=40 |pages=114–140 |doi=10.1016/j.engfailanal.2014.02.004}}</ref> the most–widely used building material,<ref>{{cite journal |last=Crow|first=James Mitchell |date=March 2008 |title=The concrete conundrum |url=https://rsc.org/images/Construction_tcm18-114530.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://www.rsc.org/images/Construction_tcm18-114530.pdf |archive-date=2022-10-09 |url-status=live |journal=[[Chemistry World]] |pages=62–66}}</ref> and the most-manufactured material in the world.<ref name="USGS2024">{{cite web |title=Cement Statistics and Information |url=https://usgs.gov/centers/national-minerals-information-center/cement-statistics-and-information |website=usgs.gov |publisher=[[United States Geological Survey]] |access-date=2025-03-21}}</ref>

When aggregate is mixed with dry [[Portland cement]] and [[water]], the mixture forms a fluid [[slurry]] that can be poured and molded into shape. The cement reacts with the water through a process called hydration,<ref>{{cite web |url=http://matse1.matse.illinois.edu/concrete/prin.html |title=Scientific Principles |website=matse1.matse.illinois.edu |access-date=2023-05-24}}</ref> which hardens it after several hours to form a solid matrix that binds the materials together into a durable stone-like material with various uses.<ref>{{cite book |first=Zongjin|last=Li |title=Advanced concrete technology |year= 2011 |publisher=[[Wiley (publisher)|John Wiley & Sons]] |isbn=978-0-470-90243-1}}</ref> This time allows concrete to not only be cast in forms, but also to have a variety of tooled processes performed. The hydration process is [[exothermic process|exothermic]], which means that [[room temperature|ambient temperature]] plays a significant role in how long it takes concrete to set. Often, additives (such as [[pozzolan]]s or [[superplasticizer]]s) are included in the mixture to improve the physical properties of the wet mix, delay or accelerate the curing time, or otherwise modify the finished material. Most structural concrete is poured with reinforcing materials (such as steel [[rebar]]) embedded to provide [[tensile strength]], yielding [[reinforced concrete]].

Before the invention of Portland cement in the early 1800s, [[lime (material)|lime]]-based cement binders, such as lime putty, were often used. The overwhelming majority of concretes are produced using Portland cement, but sometimes with other [[hydraulic cement]]s, such as [[calcium aluminate cements|calcium aluminate cement]].<ref>{{Cite web|url=http://www.industrialresourcescouncil.org/Applications/PortlandCementConcrete/tabid/381/Default.aspx|title=Portland Cement Concrete|last=Industrial Resources Council|date=2008|website=www.industrialresourcescouncil.org|language=en-US|access-date=15 June 2018}}</ref><ref>{{Cite web|url=https://www.fhwa.dot.gov/pavement/pubs/013683.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://www.fhwa.dot.gov/pavement/pubs/013683.pdf |archive-date=2022-10-09 |url-status=live|title=Portland Cement Concrete Materials|last=National Highway Institute|publisher=[[Federal Highway Administration]]}}</ref> Many other non-cementitious [[types of concrete]] exist with other methods of binding aggregate together, including [[asphalt concrete]] with a [[bitumen]] binder, which is frequently used for [[road surface]]s, and [[polymer concrete]]s that use polymers as a binder.

Concrete is distinct from [[Mortar (masonry)|mortar]].<ref>{{Cite book |last1=Limbachiya |first1=Mukesh C. |url=https://books.google.com/books?id=FOZTNlDN3cYC&dq=%22Concrete+is+distinct+from+mortar%22&pg=PA115 |title=Excellence in Concrete Construction through Innovation: Proceedings of the conference held at the Kingston University, United Kingdom, 9 - 10 September 2008 |last2=Kew |first2=Hsein Y. |date=2008-09-03 |publisher=CRC Press |isbn=978-0-203-88344-0 |pages=115 |language=en}}</ref> Whereas concrete is itself a building material, and contains both coarse (large) and fine (small) aggregate particles, mortar contains only fine aggregates and is mainly used as a bonding agent to hold [[brick]]s, [[tile]]s and other masonry units together.<ref>{{Cite book|last1=Allen|first1=Edward|title=Fundamentals of building construction: materials and methods|last2=Iano|first2=Joseph|publisher=John Wiley & Sons|year=2013|isbn=978-1-118-42086-7|edition=Sixth|location=Hoboken|page=314|oclc=835621943}}</ref> [[Grout]] is another material associated with concrete and cement. It also does not contain coarse aggregates and is usually either pourable or [[thixotropic]], and is used to fill gaps between masonry components or coarse aggregate which has already been put in place. Some methods of concrete manufacture and repair involve pumping grout into the gaps to make up a solid mass ''in situ''.
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== Etymology ==
The word concrete comes from the [[Latin]] word "{{lang|la|concretus}}" (meaning compact or condensed),<ref>{{cite web|title=concretus|url=http://latinlookup.com/word/12124/concretus|publisher=Latin Lookup|access-date=1 October 2012|archive-url=https://web.archive.org/web/20130512013931/http://latinlookup.com/word/12124/concretus|archive-date=12 May 2013}}</ref> the perfect passive participle of "{{lang|la|concrescere}}", from "{{lang|la|con}}-" (together) and "{{lang|la|crescere}}" (to grow).

==History==
===Ancient times===
Concrete floors were found in the royal palace of [[Tiryns]], Greece, which dates roughly to 1400 to 1200 BC.<ref>{{cite book|author1=Heinrich Schliemann|author2=Wilhelm Dörpfeld|author3=Felix Adler|title=Tiryns: The Prehistoric Palace of the Kings of Tiryns, the Results of the Latest Excavations|url=https://archive.org/details/bub_gb_pw4BAAAAMAAJ|year=1885|publisher=Charles Scribner's Sons|location=New York|pages=[https://archive.org/details/bub_gb_pw4BAAAAMAAJ/page/n266 190], 203–204, 215}}</ref><ref>{{cite arXiv|first =Amelia Carolina|last = Sparavigna|title = Ancient concrete works|eprint= 1110.5230|class = physics.pop-ph|year = 2011}}</ref> Lime mortars were used in Greece, such as in Crete and Cyprus, in 800 BC. The [[Assyria]]n Jerwan Aqueduct (688 BC) made use of [[waterproof concrete]].<ref>Jacobsen T and Lloyd S, (1935) "Sennacherib's Aqueduct at Jerwan," ''Oriental Institute Publications'' 24, Chicago University Press</ref> Concrete was used for construction in many ancient structures.<ref>{{Cite journal|title=Ancient Concrete Structures|author=Stella L. Marusin|journal=Concrete International|volume=18|issue=1|pages=56–58|date=1 January 1996|url= https://www.concrete.org/publications/internationalconcreteabstractsportal/m/details/id/9377}}</ref>

Mayan concrete at the ruins of [[Uxmal]] (AD 850–925) is referenced in ''Incidents of Travel in the Yucatán'' by [[John Lloyd Stephens|John L. Stephens]]. "The roof is flat and had been covered with cement". "The floors were cement, in some places hard, but, by long exposure, broken, and now crumbling under the feet." "But throughout the wall was solid, and consisting of large stones imbedded in mortar, almost as hard as rock."

Small-scale production of concrete-like materials was pioneered by the [[Nabataea|Nabatean]] traders who occupied and controlled a series of oases and developed a small empire in the regions of southern Syria and northern Jordan from the 4th century BC. They discovered the advantages of [[hydraulic lime]], with some self-cementing properties, by 700 BC. They built [[kiln]]s to supply mortar for the construction of [[rubble masonry]] houses, concrete floors, and underground waterproof [[cistern]]s. They kept the cisterns secret as these enabled the Nabataeans to thrive in the desert.<ref name="Gromicko-2016">{{Cite web|url=https://www.nachi.org/history-of-concrete.htm |title=The History of Concrete |last1=Gromicko|first1=Nick|last2=Shepard|first2=Kenton|date=2016|website=International Association of Certified Home Inspectors, Inc.|access-date=27 December 2018}}</ref> Some of these structures survive to this day.<ref name="Gromicko-2016" />

In the [[Ancient Egypt]]ian and later [[Roman Empire|Roman]] eras, builders discovered that adding [[Pozzolan|volcanic ash]] to [[Lime (material)|lime]] allowed the mix to set underwater. They discovered the [[Pozzolanic activity#Reaction|pozzolanic reaction]].<ref>{{Cite web |date=2023-01-06 |title=Riddle solved: Why was Roman concrete so durable? |url=https://news.mit.edu/2023/roman-concrete-durability-lime-casts-0106 |access-date=2024-10-25 |website=MIT News {{!}} Massachusetts Institute of Technology |language=en}}</ref>

===Classical era===
[[File:Rome (Italy, October 2019) - 275 (50589571796).jpg|thumb|Exterior of the [[Roman Pantheon]], finished 128 AD, the largest unreinforced concrete [[dome]] in the world.<ref>{{Cite web |title=Roman Concrete Research |first=David |last=Moore |url=http://www.romanconcrete.com/ |access-date=2022-08-13 |archive-url=https://web.archive.org/web/20141006012615/http://www.romanconcrete.com/|url-status=live |date=6 October 2014 |website= Romanconcrete.com|archive-date=6 October 2014 }}</ref>]]
[[File:Pantheon (Rome) - Dome.jpg|thumb|Interior of the Pantheon dome, seen from beneath. The concrete for the [[coffer]]ed dome was laid on moulds, mounted on temporary scaffolding.]]
[[File:Museo Foro Caesaragusta - Cloaca del foro 03.JPG|thumb|upright|''[[Opus caementicium]]'' exposed in a characteristic Roman arch. In contrast to modern concrete structures, the concrete used in Roman buildings was usually covered with brick or stone.]]

The Romans used concrete extensively from 300 BC to AD 476.<ref name=MAST>{{cite web|title=The History of Concrete|url=http://matse1.matse.illinois.edu/concrete/hist.html|publisher=Dept. of Materials Science and Engineering, University of Illinois, Urbana-Champaign|access-date=8 January 2013|url-status=live|archive-url=https://web.archive.org/web/20121127052951/http://matse1.matse.illinois.edu/concrete/hist.html|archive-date=27 November 2012}}</ref> During the Roman Empire, [[Roman concrete]] (or ''[[opus caementicium]]'') was made from [[quicklime]], [[pozzolana]] and an aggregate of [[pumice]].<ref>{{Cite book |last=Chiu |first=Y. C. |url=https://books.google.com/books?id=osNrPO3ivZoC&dq=During+the+Roman+Empire,+Roman+concrete+(or+opus+caementicium)+was+made+from+quicklime,+pozzolana+and+an+aggregate+of+pumice.&pg=PA50 |title=An Introduction to the History of Project Management: From the Earliest Times to A.D. 1900 |date=2010 |publisher=Eburon Uitgeverij B.V. |isbn=978-90-5972-437-2 |pages=50 |language=en}}</ref> Its widespread use in many [[Architecture of ancient Rome|Roman structures]], a key event in the [[history of architecture]] termed the [[Roman architectural revolution]], freed [[Roman engineering|Roman construction]] from the restrictions of stone and brick materials. It enabled revolutionary new designs in terms of both structural complexity and dimension.<ref>{{Cite book| last = Lancaster| first = Lynne| title = Concrete Vaulted Construction in Imperial Rome. Innovations in Context| publisher=Cambridge University Press| date = 2005| isbn = 978-0-511-16068-4}}</ref> The [[Colosseum]] in Rome was built largely of concrete, and the [[Pantheon, Rome|Pantheon]] has the world's largest unreinforced concrete dome.<ref>{{cite web |url=http://www.romanconcrete.com/docs/chapt01/chapt01.htm |title=The Pantheon |first=David |last=Moore |work=romanconcrete.com |date=1999 |access-date=26 September 2011 |url-status=live |archive-url=https://web.archive.org/web/20111001052926/http://www.romanconcrete.com/docs/chapt01/chapt01.htm |archive-date=1 October 2011  }}</ref>

<blockquote>Concrete, as the Romans knew it, was a new and revolutionary material. Laid in the shape of [[arch]]es, [[Vault (architecture)|vaults]] and [[List of Roman domes|domes]], it quickly hardened into a rigid mass, free from many of the internal thrusts and strains that troubled the builders of similar structures in stone or brick.<ref>D.S. Robertson (1969). ''Greek and Roman Architecture'', Cambridge, p. 233</ref></blockquote>

Modern tests show that ''opus caementicium'' had a similar compressive strength to modern Portland-cement concrete (c. {{convert|200|kg/cm2|MPa psi|abbr=on|disp=sqbr}}).<ref>{{Cite book |last=Cowan |first=Henry J. |title=The master builders: a history of structural and environmental design from ancient Egypt to the nineteenth century |date=1977 |publisher=Wiley |isbn=0-471-02740-5 |location=New York |oclc=2896326}}</ref> However, due to the absence of reinforcement, its [[Ultimate tensile strength|tensile strength]] was far lower than modern [[reinforced concrete]], and its mode of application also differed:<ref>{{Cite web|url=http://www.ce.memphis.edu/1101/notes/concrete/section_2_history.html|archive-url=https://web.archive.org/web/20170227213256/http://www.ce.memphis.edu/1101/notes/concrete/section_2_history.html|title=CIVL 1101|archive-date=27 February 2017|website=www.ce.memphis.edu}}</ref>

<blockquote>Modern structural concrete differs from Roman concrete in two important details. First, its mix consistency is fluid and homogeneous, allowing it to be poured into forms rather than requiring hand-layering together with the placement of aggregate, which, in Roman practice, often consisted of [[rubble]]. Second, integral reinforcing steel gives modern concrete assemblies great strength in tension, whereas Roman concrete could depend only upon the strength of the concrete bonding to resist tension.<ref>Robert Mark, Paul Hutchinson: "On the Structure of the Roman Pantheon", ''Art Bulletin'', Vol. 68, No. 1 (1986), p. 26, fn. 5</ref></blockquote>

The long-term durability of Roman concrete structures was found to be due to the presence of [[Pyroclastic rock|pyroclastic]] (volcanic) rock and ash in the concrete mix. The crystallization of [[strätlingite]] (a complex calcium aluminosilicate hydrate)<ref>{{cite journal |doi = 10.1111/j.1151-2916.1995.tb08910.x|title = 29Si and27Al MASNMR Study of Stratlingite|journal = Journal of the American Ceramic Society |volume = 78|issue = 7|pages = 1921–1926|year = 1995|last1 = Kwan|first1 = Stephen|last2 = Larosa|first2 = Judith |last3=Grutzeck |first3= Michael W.}}</ref> during the formation of the concrete and its merging with similar calcium–aluminium-silicate–hydrate structures helped give the Roman concrete a greater degree of fracture resistance compared to modern concrete.<ref>{{cite journal|title=Mechanical resilience and cementitious processes in Imperial Roman architectural mortar|first1=Marie D.|last1=Jackson|first2=Eric N.|last2=Landis|first3=Philip F.|last3=Brune|first4=Massimo|last4=Vitti|first5=Heng|last5=Chen|first6=Qinfei|last6=Li|first7=Martin|last7=Kunz|first8=Hans-Rudolf|last8=Wenk|first9=Paulo J. M.|last9=Monteiro|first10=Anthony R.|last10=Ingraffea|date=30 December 2014|journal=PNAS|volume=111|issue=52|pages=18484–18489|doi=10.1073/pnas.1417456111|pmid=25512521|pmc=4284584|bibcode = 2014PNAS..11118484J|doi-access=free}}</ref> In addition, Roman concrete is significantly more resistant to erosion by seawater than modern concrete; the aforementioned pyroclastic materials react with seawater to form Al-[[tobermorite]] crystals over time.<ref>{{cite journal|periodical=American Mineralogist|title=Phillipsite and Al-tobermorite mineral cements produced through low-temperature water-rock reactions in Roman marine concrete|volume=102|issue=7|pages=1435–1450 |author1=Marie D. Jackson |author2=Sean R. Mulcahy |author3=Heng Chen |author4=Yao Li |author5=Qinfei Li |author6=Piergiulio Cappelletti |author7=Hans-Rudolf Wenk |date=3 July 2017 |bibcode=2017AmMin.102.1435J|doi=10.2138/am-2017-5993CCBY|s2cid=53452767|url=https://cedar.wwu.edu/geology_facpubs/67|doi-access=free }}</ref><ref>{{cite news|url=https://www.telegraph.co.uk/science/2017/07/03/secret-roman-concrete-survived-tidal-battering-2000-years-revealed/|title=Secret of how Roman concrete survived tidal battering for 2,000 years revealed|url-status=live|archive-url=https://web.archive.org/web/20170704011801/http://www.telegraph.co.uk/science/2017/07/03/secret-roman-concrete-survived-tidal-battering-2000-years-revealed/ |work=The Telegraph|date=3 July 2017|archive-date=4 July 2017|last1=Knapton|first1=Sarah}}</ref> The use of hot mixing in preparation of concrete, leading to the formation of lime clasts in the final product, has been proposed to give the Roman concrete a [[Self-healing concrete|self-healing ability]].<ref>{{cite journal |last1=Seymour |first1=Linda M. |last2=Maragh |first2=Janille |last3=Sabatini |first3=Paolo |last4=Di Tommaso |first4=Michel |last5=Weaver |first5=James C. |last6=Masic |first6=Admir |title=Hot mixing: Mechanistic insights into the durability of ancient Roman concrete |journal=Science Advances |date=6 January 2023 |volume=9 |issue=1 |pages=eadd1602 |doi=10.1126/sciadv.add1602 |pmc=9821858 |pmid=36608117 |bibcode=2023SciA....9D1602S }}</ref><ref>{{Cite web |last=Starr |first=Michelle |date=2024-02-01 |title=We Finally Know How Ancient Roman Concrete Was Able to Last Thousands of Years |url=https://www.sciencealert.com/we-finally-know-how-ancient-roman-concrete-was-able-to-last-thousands-of-years |access-date=2024-02-01 |website=ScienceAlert |language=en-US}}</ref>

The widespread use of concrete in many Roman structures ensured that many survive to the present day. The [[Baths of Caracalla]] in Rome are just one example. Many [[Roman aqueduct]]s and bridges, such as the magnificent [[Pont du Gard]] in southern France, have masonry cladding on a concrete core, as does the dome of the [[Pantheon, Rome|Pantheon]].

===Middle Ages===
After the Roman Empire, the use of burned lime and pozzolana was greatly reduced. Low kiln temperatures in the burning of lime, lack of pozzolana, and poor mixing all contributed to a decline in the quality of concrete and mortar. From the 11th century, the increased use of stone in church and [[castle]] construction led to an increased demand for mortar. Quality began to improve in the 12th century through better grinding and sieving. Medieval lime mortars and concretes were non-hydraulic and were used for binding masonry, "hearting" (binding [[rubble masonry]] cores) and foundations. [[Bartholomaeus Anglicus]] in his ''De proprietatibus rerum'' (1240) describes the making of mortar. In an English translation from 1397, it reads "lyme ... is a stone brent; by medlynge thereof with sonde and water sement is made". From the 14th century, the quality of mortar was again excellent, but only from the 17th century was pozzolana commonly added.<ref>Peter Hewlett and Martin Liska (eds.), ''Lea's Chemistry of Cement and Concrete'', 5th ed. (Butterworth-Heinemann, 2019), pp. 3–4.</ref>

The ''[[Canal du Midi]]'' was built using concrete in 1670.<ref>{{cite book |last1=Rassia |first1=Stamatina Th |last2=Pardalos |first2=Panos M. |title=Cities for Smart Environmental and Energy Futures: Impacts on Architecture and Technology |date=15 August 2013 |publisher=Springer Science & Business Media |isbn=978-3-642-37661-0 |page=58 |url={{google books|plainurl=y|id=vFu6BAAAQBAJ|page=58}} |language=en}}</ref>

===Industrial era===
[[File:Smeaton's Lighthouse00.jpg|thumb|upright|[[Smeaton's Tower]] in [[Devon]], England]]

Perhaps the greatest step forward in the modern use of concrete was [[Smeaton's Tower]], built by British engineer [[John Smeaton]] in [[Devon]], England, between 1756 and 1759. This third [[Eddystone Lighthouse]] pioneered the use of [[hydraulic lime]] in concrete, using pebbles and powdered brick as aggregate.<ref name=InterNACHI>{{cite web|title=the History of Concrete|url=http://www.nachi.org/history-of-concrete.htm|publisher=The International Association of Certified Home Inspectors (InterNACHI)|author=Nick Gromicko|author2=Kenton Shepard|name-list-style=amp|access-date=8 January 2013|url-status=live|archive-url=https://web.archive.org/web/20130115151648/http://www.nachi.org/history-of-concrete.htm|archive-date=15 January 2013}}</ref>

A method for producing [[Portland cement]] was developed in England and patented by [[Joseph Aspdin]] in 1824.<ref>{{cite web|last=Herring|first=Benjamin|title=The Secrets of Roman Concrete|url=http://www.romanconcrete.com/Article1Secrets.pdf|publisher=Romanconcrete.com|access-date=1 October 2012|url-status=live|archive-url=https://web.archive.org/web/20120915054736/http://www.romanconcrete.com/Article1Secrets.pdf|archive-date=15 September 2012}}</ref> Aspdin chose the name for its similarity to [[Portland stone]], which was quarried on the [[Isle of Portland]] in [[Dorset]], England. His son [[William Aspdin|William]] continued developments into the 1840s, earning him recognition for the development of "modern" Portland cement.<ref>{{cite book|last1=Courland|first1=Robert|title=Concrete planet: the strange and fascinating story of the world's most common man-made material|date=2011|publisher=Prometheus Books|location=Amherst, NY|isbn=978-1-61614-481-4|url={{google books|plainurl=y|id=qRcwAQAAQBAJ|page=190}}|access-date=28 August 2015|url-status=live|archive-url=https://web.archive.org/web/20151104111744/https://books.google.com/books?id=qRcwAQAAQBAJ&pg=PT190|archive-date=4 November 2015}}</ref>

[[Reinforced concrete]] was invented in 1849 by [[Joseph Monier]].<ref>{{Cite web |title=The History of Concrete and Cement |url=https://www.thoughtco.com/history-of-concrete-and-cement-1991653 |website=ThoughtCo |language=en|date=9 April 2012 |access-date=2022-08-13}}</ref> and the first reinforced concrete house was built by François Coignet<ref name="britannia">{{cite web |url=https://www.britannica.com/EBchecked/topic/124672/Francois-Coignet |title=Francois Coignet – French house builder |access-date=23 December 2016}}</ref> in 1853.
The first concrete reinforced bridge was designed and built by [[Joseph Monier]] in 1875.<ref>« Château de Chazelet » [archive], notice no PA00097319, base Mérimée, ministère français de la Culture.</ref>

[[Prestressed concrete]] and [[Prestressed concrete#Post-tensioned concrete|post-tensioned concrete]] were pioneered by [[Eugène Freyssinet]], a French  [[structural engineer|structural]] and [[civil engineer]]. Concrete components or structures are compressed by tendon cables during, or after, their fabrication in order to strengthen them against [[Tension (physics)|tensile]] forces developing when put in service. Freyssinet [[patent]]ed the technique on 2 October 1928.<ref name="Billington1985">{{cite book| last = Billington| first = David| title = The Tower and the Bridge| publisher = Princeton University Press| location = Princeton| year = 1985| isbn = 0-691-02393-X| url = https://archive.org/details/towerbridgenewar00bill}}</ref>

==Composition==

Concrete is an artificial [[composite material]], comprising a matrix of cementitious binder (typically [[Portland cement]] paste or [[Bitumen|asphalt]]) and a dispersed phase or "filler" of [[#Aggregates|aggregate]] (typically a rocky material, loose stones, and sand). The binder "glues" the filler together to form a synthetic [[Conglomerate (geology)|conglomerate]].<ref name="matse">{{Cite web|title=Concrete: Scientific Principles |url=http://matse1.matse.illinois.edu/concrete/prin.html|access-date=2021-10-06|website=matse1.matse.illinois.edu}}</ref> Many [[types of concrete]] are available, determined by the formulations of binders and the types of aggregate used to suit the application of the engineered material. These variables determine strength and density, as well as chemical and thermal resistance of the finished product.

[[File:DB Museum rail and concrete sleeper cross section 2.jpg|thumb|[[Cross section (geometry)|Cross section]] of a concrete [[Railroad tie|railway sleeper]] below a rail]]

[[Construction aggregate]]s consist of large chunks of material in a concrete mix, generally a coarse [[gravel]] or crushed rocks such as [[limestone]], or [[granite]], along with finer materials such as [[sand]].

Cement paste, most commonly made of [[Portland cement]], is the most prevalent kind of concrete binder. For cementitious binders, [[water]] is mixed with the dry cement powder and aggregate, which produces a semi-liquid slurry (paste) that can be shaped, typically by pouring it into a form. The concrete solidifies and hardens through a [[Chemical reaction|chemical process]] called [[mineral hydration|hydration]]. The water reacts with the cement, which bonds the other components together, creating a robust, stone-like material. Other cementitious materials, such as [[fly ash]] and [[slag cement]], are sometimes added—either pre-blended with the cement or directly as a concrete component—and become a part of the binder for the aggregate.<ref name=flyash>{{cite journal |last1=Askarian |first1=Mahya |last2=Fakhretaha Aval |first2=Siavash |last3=Joshaghani |first3=Alireza |title=A comprehensive experimental study on the performance of pumice powder in self-compacting concrete (SCC) |journal=Journal of Sustainable Cement-Based Materials |date=22 January 2019 |volume=7 |issue=6 |pages=340–356 |doi=10.1080/21650373.2018.1511486 |s2cid=139554392 }}</ref> Fly ash and slag can enhance some properties of concrete such as fresh properties and durability.<ref name=flyash/> Alternatively, other materials can also be used as a concrete binder: the most prevalent substitute is [[Bitumen|asphalt]], which is used as the binder in [[asphalt concrete]].

Admixtures are added to modify the cure rate or properties of the material. [[#Mineral admixtures and blended cements|Mineral admixtures]] use recycled materials as concrete ingredients. Conspicuous materials include [[fly ash]], a by-product of [[Fossil fuel power plant|coal-fired power plants]]; [[ground granulated blast furnace slag]], a by-product of [[steelmaking]]; and [[silica fume]], a by-product of industrial [[electric arc furnace]]s.

Structures employing Portland cement concrete usually include [[#Reinforcement|steel reinforcement]] because this type of concrete can be formulated with high [[compressive strength]], but always has lower [[tensile strength]]. Therefore, it is usually reinforced with materials that are strong in tension, typically [[steel]] [[rebar]].

The ''[[types of concrete#Mix design|mix design]]'' depends on the type of structure being built, how the concrete is mixed and delivered, and how it is placed to form the structure.

===Cement===
{{main|Cement}}
[[File:Stockage de ciments.JPG|thumb|Several tons of bagged cement, about two minutes of output from a 10,000 ton per day [[cement kiln]]]]

Portland cement is the most common type of cement in general usage. It is a basic ingredient of concrete, [[mortar (masonry)|mortar]], and many [[plaster]]s.<ref>{{Cite web|last1=Melander|first1=John M.|last2=Farny|first2=James A.|last3=Isberner|first3=Albert W. Jr. |date=2003|title=Portland Cement Plaster/Stucco Manual|url=https://www.cement.org/docs/default-source/stucco/eb049.pdf?sfvrsn=540de3bf_2|url-status=live|access-date=2021-07-13|website=Portland Cement Association|archive-url=https://web.archive.org/web/20210412174321/https://www.cement.org/docs/default-source/stucco/eb049.pdf?sfvrsn=540de3bf_2 |archive-date=12 April 2021 }}</ref>  It consists of a mixture of calcium silicates ([[alite]], [[belite]]), [[tricalcium aluminate|aluminates]] and [[calcium aluminoferrite|ferrites]]—compounds, which will react with water. Portland cement and similar materials are made by heating [[limestone]] (a source of calcium) with clay or shale (a source of silicon, aluminium and iron) and grinding this product (called ''[[clinker (cement)|clinker]]'') with a source of [[sulfate]] (most commonly [[gypsum]]).

[[Cement kiln]]s are extremely large, complex, and inherently dusty industrial installations. Of the various ingredients used to produce a given quantity of concrete, the cement is the most energetically expensive. Even complex and efficient kilns require 3.3 to 3.6 gigajoules of energy to produce a ton of clinker and then [[Cement mill|grind it into cement]]. Many kilns can be fueled with difficult-to-dispose-of wastes, the most common being used tires. The extremely high temperatures and long periods of time at those temperatures allows cement kilns to efficiently and completely burn even difficult-to-use fuels.<ref>{{cite web|title=Cement Production|url=http://www.iea-etsap.org/web/E-TechDS/PDF/I03_cement_June%202010_GS-gct.pdf|publisher=IEA ETSAP – Energy Technology Systems Analysis Programme|access-date=9 January 2013|author=Evelien Cochez|author2=Wouter Nijs|name-list-style=amp|author3=Giorgio Simbolotti|author4=Giancarlo Tosato|location= |archive-url=https://web.archive.org/web/20130124004654/http://www.iea-etsap.org/web/E-TechDS/PDF/I03_cement_June%202010_GS-gct.pdf|archive-date=24 January 2013}}</ref> The five major compounds of calcium silicates and aluminates comprising Portland cement range from 5 to 50% in weight.

===Curing===
Combining [[water]] with a cementitious material forms a cement paste by the process of hydration. The cement paste glues the aggregate together, fills voids within it, and makes it flow more freely.<ref>{{cite web|last=Gibbons|first=Jack|title=Measuring Water in Concrete|date=7 January 2008 |url=http://www.concreteconstruction.net/concrete-construction/measuring-water-in-concrete.aspx|publisher=Concrete Construction|access-date=1 October 2012|url-status=live|archive-url=https://web.archive.org/web/20130511192721/http://www.concreteconstruction.net/concrete-construction/measuring-water-in-concrete.aspx|archive-date=11 May 2013}}</ref>

As stated by [[Abrams' law]], a lower water-to-cement ratio yields a stronger, more [[Reinforced concrete structures durability|durable]] concrete, whereas more water gives a freer-flowing concrete with a higher [[Workability|slump]].<ref>{{cite web|title=Chapter 9: Designing and Proportioning Normal Concrete Mixtures |url=http://www.ce.memphis.edu/1112/notes/project_2/PCA_manual/Chap09.pdf|work=PCA manual|publisher=Portland Concrete Association|access-date=1 October 2012|url-status=live|archive-url=https://web.archive.org/web/20120526015347/http://www.ce.memphis.edu/1112/notes/project_2/PCA_manual/Chap09.pdf|archive-date=26 May 2012}}</ref> The hydration of cement involves many concurrent reactions. The process involves [[polymerization]], the interlinking of the silicates and aluminate components as well as their bonding to sand and gravel particles to form a solid mass.<ref name="Hydration">{{cite web|title=Cement hydration|url=http://www.understanding-cement.com/hydration.html|publisher=Understanding Cement|access-date=1 October 2012|url-status=live|archive-url=https://web.archive.org/web/20121017144613/http://www.understanding-cement.com/hydration.html|archive-date=17 October 2012}}</ref> One illustrative conversion is the hydration of tricalcium silicate:

: [[Cement chemist notation]]: {{space|2}} C<sub>3</sub>S + H → C-S-H + CH + heat
: Standard notation: {{space|13}} Ca<sub>3</sub>SiO<sub>5</sub> + H<sub>2</sub>O → CaO・SiO<sub>2</sub>・H<sub>2</sub>O (gel) + Ca(OH)<sub>2</sub> + heat
: Balanced: {{space|27}} 2 Ca<sub>3</sub>SiO<sub>5</sub> + 7 H<sub>2</sub>O → 3 CaO・2 SiO<sub>2</sub>・4 H<sub>2</sub>O (gel) + 3 Ca(OH)<sub>2</sub> + heat
: {{space|44}} (approximately as the exact ratios of CaO, SiO<sub>2</sub> and H<sub>2</sub>O in C-S-H can vary)<ref name="Hydration" />

The hydration (curing) of cement is irreversible.<ref>{{cite book |doi=10.1016/B978-0-08-100773-0.00005-8 |chapter=Hydration, Setting and Hardening of Portland Cement |title=Lea's Chemistry of Cement and Concrete |date=2019 |last1=Beaudoin |first1=James |last2=Odler |first2=Ivan |pages=157–250 |isbn=978-0-08-100773-0 }}</ref>

===Aggregates===
{{main|Construction aggregate}}
[[File:Gravel 03375C.JPG|thumbnail|Crushed stone [[Construction aggregate|aggregates]]]]

Fine and coarse aggregates make up the bulk of a concrete mixture. [[Sand]], natural gravel, and [[crushed stone]] are used mainly for this purpose. Recycled aggregates (from construction, demolition, and excavation waste) are increasingly used as partial replacements for natural aggregates, while a number of manufactured aggregates, including air-cooled [[blast furnace]] slag and [[bottom ash]] are also permitted.<ref>{{Cite journal |last=Oikonomou |first=Nik. D. |date=2005-02-01 |title=Recycled concrete aggregates |url=https://www.sciencedirect.com/science/article/pii/S095894650400037X |journal=Cement and Concrete Composites |series=Cement and Concrete Research in Greece |volume=27 |issue=2 |pages=315–318 |doi=10.1016/j.cemconcomp.2004.02.020 |issn=0958-9465}}</ref>

The size distribution of the aggregate determines how much binder is required. Aggregate with a very even size distribution has the biggest gaps whereas adding aggregate with smaller particles tends to fill these gaps. The binder must fill the gaps between the aggregate as well as paste the surfaces of the aggregate together, and is typically the most expensive component. Thus, variation in sizes of the aggregate reduces the cost of concrete.<ref>{{Cite web |title=The Effect of Aggregate Properties on Concrete |url=https://www.engr.psu.edu/ce/courses/ce584/concrete/library/materials/Aggregate/Aggregatesmain.htm |access-date=2022-08-13 |website=www.engr.psu.edu|archive-url=https://web.archive.org/web/20121225184337/http://www.engr.psu.edu/ce/courses/ce584/concrete/library/materials/Aggregate/Aggregatesmain.htm |date=25 December 2012 |publisher=Engr.psu.edu|archive-date=25 December 2012 }}</ref> The aggregate is nearly always stronger than the binder, so its use does not negatively affect the strength of the concrete.

Redistribution of aggregates after compaction often creates non-homogeneity due to the influence of vibration. This can lead to strength gradients.<ref name="Veretennykov Yugov Dolmatov et al 2008">{{cite book |doi=10.1061/41002(328)17 |chapter=Concrete Inhomogeneity of Vertical Cast-in-Place Elements in Skeleton-Type Buildings |title=AEI 2008 |year=2008 |last1=Veretennykov |first1=Vitaliy I. |last2=Yugov |first2=Anatoliy M. |last3=Dolmatov |first3=Andriy O. |last4=Bulavytskyi |first4=Maksym S. |last5=Kukharev |first5=Dmytro I. |last6=Bulavytskyi |first6=Artem S. |pages=1–10 |isbn=978-0-7844-1002-8 }}</ref>

Decorative stones such as [[quartzite]], small river stones or crushed glass are sometimes added to the surface of concrete for a decorative "exposed aggregate" finish, popular among landscape designers.

===Admixtures===
Admixtures are materials in the form of powder or fluids that are added to the concrete to give it certain characteristics not obtainable with plain concrete mixes. Admixtures are defined as additions "made as the concrete mix is being prepared".<ref name=text>{{cite book|isbn=978-0-7277-3611-6 |doi=10.1680/pc.36116.185 |chapter=Admixtures and Special Cements |title=Portland Cement: Third edition |author1=Gerry Bye |author2=Paul Livesey |author3=Leslie Struble |year=2011|doi-broken-date=1 November 2024 }}</ref> The most common admixtures are retarders and accelerators. In normal use, admixture dosages are less than 5% by mass of cement and are added to the concrete at the time of batching/mixing.<ref name="FHWA Admixtures">{{cite web |author=U.S. Federal Highway Administration |author-link=Federal Highway Administration |title=Admixtures |url=http://www.fhwa.dot.gov/infrastructure/materialsgrp/admixture.html |access-date=25 January 2007 |date=14 June 1999 |archive-url=https://web.archive.org/web/20070127132641/http://www.fhwa.dot.gov/infrastructure/materialsgrp/admixture.html |archive-date=27 January 2007 }}</ref> (See {{section link||Production}} below.) The common types of admixtures<ref>{{cite web |author=Cement Admixture Association |url=http://www.admixtures.org.uk/types.asp |title=Admixture Types |access-date=25 December 2010 |archive-url=https://web.archive.org/web/20110903081932/http://www.admixtures.org.uk/types.asp |archive-date=3 September 2011 }}</ref> are as follows:

* [[Accelerant|Accelerators]] speed up the hydration (hardening) of the concrete. Typical materials used are [[calcium chloride]], [[calcium nitrate]] and [[sodium nitrate]]. However, use of chlorides may cause corrosion in steel reinforcing and is prohibited in some countries, so that nitrates may be favored, even though they are less effective than the chloride salt. Accelerating admixtures are especially useful for modifying the properties of concrete in cold weather.
* [[Air entrainment|Air entraining agents]] add and entrain tiny air bubbles in the concrete, which reduces damage during [[Weathering|freeze-thaw]] cycles, increasing [[Reinforced concrete structures durability|durability]]. However, entrained air entails a tradeoff with strength, as each 1% of air may decrease compressive strength by 5%.<ref>{{cite web |last1=Hamakareem |first1=Madeh Izat |title=Effect of Air Entrainment on Concrete Strength |url=https://theconstructor.org/concrete/effect-air-entrainment-concrete-strength/8427/ |website=The Constructor |date=14 November 2013 |access-date=13 November 2020}}</ref> If too much air becomes trapped in the concrete as a result of the mixing process, [[defoamer]]s can be used to encourage the air bubble to agglomerate, rise to the surface of the wet concrete and then disperse.
* Bonding agents are used to create a bond between old and new concrete (typically a type of polymer) with wide temperature tolerance and corrosion resistance.
* [[Corrosion inhibitor]]s are used to minimize the corrosion of steel and steel bars in concrete.
* Crystalline admixtures are typically added during batching of the concrete to lower permeability. The reaction takes place when exposed to water and un-hydrated cement particles to form insoluble needle-shaped crystals, which fill capillary pores and micro-cracks in the concrete to block pathways for water and waterborne contaminates. Concrete with crystalline admixture can expect to self-seal as constant exposure to water will continuously initiate crystallization to ensure permanent waterproof protection.
* [[Pigment]]s can be used to change the color of concrete, for aesthetics.
* [[Plasticizer]]s increase the workability of plastic, or "fresh", concrete, allowing it to be placed more easily, with less consolidating effort. A typical plasticizer is lignosulfonate. Plasticizers can be used to reduce the water content of a concrete while maintaining workability and are sometimes called water-reducers due to this use. Such treatment improves its strength and durability characteristics.
* [[Superplasticizer]]s (also called high-range water-reducers) are a class of plasticizers that have fewer deleterious effects and can be used to increase workability more than is practical with traditional plasticizers. Superplasticizers are used to increase compressive strength. It increases the [[#Sample analysis—workability|workability]] of the concrete and lowers the need for water content by 15–30%. 
* Pumping aids improve pumpability, thicken the paste and reduce separation and bleeding.
* [[Retarder (chemistry)|Retarders]] slow the hydration of concrete and are used in large or difficult pours where partial setting is undesirable before completion of the pour. Typical retarders include [[sugar]], [[sodium gluconate]], [[citric acid]], and [[tartaric acid]].<ref>{{Citation |last=Bensted |first=John |title=14 - Special Cements |date=1998-01-01 |work=Lea's Chemistry of Cement and Concrete (Fourth Edition) |pages=783–840 |editor-last=Hewlett |editor-first=Peter C. |url=https://linkinghub.elsevier.com/retrieve/pii/B9780750662567500266 |access-date=2024-11-03 |place=Oxford |publisher=Butterworth-Heinemann |doi=10.1016/b978-075066256-7/50026-6 |isbn=978-0-7506-6256-7}}</ref>

===Mineral admixtures and blended cements===
{{Components of Cement, Comparison of Chemical and Physical Characteristics}}

Inorganic materials that have [[pozzolan]]ic or latent hydraulic properties, these very [[Granularity|fine-grained]] materials are added to the concrete mix to improve the properties of concrete (mineral admixtures),<ref name = "FHWA Admixtures"/> or as a replacement for [[Portland cement]] (blended cements).<ref>{{cite book | author=Kosmatka, S.H. |author2=Panarese, W.C. | title = Design and Control of Concrete Mixtures | publisher=[[Portland Cement Association]] | date = 1988 | location = Skokie, IL | pages = 17, 42, 70, 184 | isbn = 978-0-89312-087-0 }}</ref> Products which incorporate [[limestone]], [[fly ash]], [[Ground granulated blast-furnace slag|blast furnace slag]], and other useful materials with [[Pozzolanic activity|pozzolanic properties]] into the mix, are being tested and used. These developments are ever growing in relevance to minimize the impacts caused by cement use, notorious for being one of the largest producers (at about 5 to 10%) of global [[greenhouse gas emissions]].<ref name=mit>{{Cite web |title=Paving the way to greenhouse gas reductions |url=https://news.mit.edu/2011/concrete-pavements-0829 |access-date=2022-08-13 |website=MIT News {{!}} Massachusetts Institute of Technology |language=en|archive-url=https://web.archive.org/web/20121031015018/http://web.mit.edu/newsoffice/2011/concrete-pavements-0829.html |archive-date=31 October 2012 |date=28 August 2011}}</ref> The use of alternative materials also is capable of lowering costs, improving concrete properties, and recycling wastes, the latest being relevant for [[circular economy]] aspects of the [[Construction Industry|construction industry]], whose demand is ever growing with greater impacts on raw material extraction, waste generation and [[landfill]] practices.
* [[Fly ash]]: A by-product of coal-fired [[power station|electric generating plants]], it is used to partially replace Portland cement (by up to 60% by mass). The properties of fly ash depend on the type of coal burnt. In general, siliceous fly ash is [[Pozzolanic activity|pozzolanic]], while [[calcareous]] fly ash has latent hydraulic properties.<ref>{{cite web |author=U.S. Federal Highway Administration |author-link=Federal Highway Administration |title=Fly Ash |url=http://www.fhwa.dot.gov/infrastructure/materialsgrp/flyash.htm |access-date=24 January 2007 |date=14 June 1999 |archive-url=https://web.archive.org/web/20070621161733/http://www.fhwa.dot.gov/infrastructure/materialsgrp/flyash.htm |archive-date=21 June 2007 }}</ref>
* [[Ground granulated blast furnace slag]] (GGBFS or GGBS): A by-product of [[Steelmaking|steel production]] is used to partially replace [[Portland cement]] (by up to 80% by mass). It has latent hydraulic properties.<ref>{{cite web | author = U.S. Federal Highway Administration | author-link = Federal Highway Administration | title = Ground Granulated Blast-Furnace Slag | url = http://www.fhwa.dot.gov/infrastructure/materialsgrp/ggbfs.htm | access-date = 24 January 2007 | archive-url = https://web.archive.org/web/20070122083859/http://www.fhwa.dot.gov/infrastructure/materialsgrp/ggbfs.htm | archive-date = 22 January 2007 | df = dmy-all }}</ref>
* [[Silica fume]]: A by-product of the production of [[silicon]] and [[ferrosilicon]] [[alloy]]s. Silica fume is similar to fly ash, but has a particle size 100 times smaller. This results in a higher surface-to-volume ratio and a much faster [[Pozzolanic activity|pozzolanic reaction]]. Silica fume is used to increase strength and [[Reinforced concrete structures durability|durability]] of concrete, but generally requires the use of superplasticizers for workability.<ref>{{cite web | author = U.S. Federal Highway Administration | author-link = Federal Highway Administration | title = Silica Fume | url = http://www.fhwa.dot.gov/infrastructure/materialsgrp/silica.htm | access-date = 24 January 2007 | archive-url = https://web.archive.org/web/20070122022403/http://www.fhwa.dot.gov/infrastructure/materialsgrp/silica.htm | archive-date = 22 January 2007 | df = dmy-all }}</ref>
* High reactivity [[metakaolin]] (HRM): Metakaolin produces concrete with [[Strength of materials|strength]] and [[durability]] similar to concrete made with silica fume. While silica fume is usually dark gray or black in color, high-reactivity metakaolin is usually bright white in color, making it the preferred choice for architectural concrete where appearance is important.
* [[Carbon nanofiber]]s can be added to concrete to enhance compressive strength and gain a higher [[Young's modulus]], and also to improve the electrical properties required for strain monitoring, damage evaluation and self-health monitoring of concrete. Carbon fiber has many advantages in terms of mechanical and electrical properties (e.g., higher strength) and self-monitoring behavior due to the high [[Ultimate tensile strength|tensile strength]] and high [[electrical conductivity]].<ref>{{cite journal |last1=Mullapudi |first1=Taraka Ravi Shankar |last2=Gao |first2=Di |last3=Ayoub |first3=Ashraf |title=Non-destructive evaluation of carbon nanofibre concrete |journal=Magazine of Concrete Research |date=September 2013 |volume=65 |issue=18 |pages=1081–1091 |doi=10.1680/macr.12.00187 }}</ref>
* Carbon products have been added to make concrete electrically conductive, for deicing purposes.<ref>{{cite journal |last1=Tuan |first1=Christopher |last2=Yehia |first2=Sherif |title=Evaluation of Electrically Conductive Concrete Containing Carbon Products for Deicing |journal=ACI Materials Journal |date=1 July 2004 |volume=101 |issue=4 |pages=287–293 |url=https://digitalcommons.unomaha.edu/civilengfacpub/26/ }}</ref>
* New research from Japan's [[University of Kitakyushu]] shows that a washed and dried recycled mix of used diapers can be an environmental solution to producing less landfill and using less sand in concrete production. A model home was built in Indonesia to test the strength and durability of the new diaper-cement composite.<ref>{{Cite news |last=Kloosterman |first=Karin |date=23 May 2023 |title=Tiny house built from diapers and concrete |url=https://www.greenprophet.com/2023/05/diaper-concrete-house/ |access-date=6 October 2024 |work=Green Prophet}}</ref>

==Production==
[[File:Concrete plant in Mansfield, Ohio.jpg|thumb|upright|[[Concrete plant]] showing a [[concrete mixer]] being filled from ingredient silos]]
[[File:Concrete mixing plant, Birmingham, Alabama, view 2.jpg|thumb|upright|Concrete mixing plant in [[Birmingham, Alabama]], in 1936]]

Concrete production is the process of mixing together the various ingredients—water, aggregate, cement, and any additives—to produce concrete. Concrete production is time-sensitive. Once the ingredients are mixed, workers must put the concrete in place before it hardens. In modern usage, most concrete production takes place in a large type of industrial facility called a [[concrete plant]], or often a batch plant. The usual method of placement is casting in [[formwork]], which holds the mix in shape until it has set enough to hold its shape unaided.

Concrete plants come in two main types, ready-mix plants and central mix plants. A ready-mix plant blends all of the solid ingredients, while a central mix does the same but adds water. A central-mix plant offers more precise control of the concrete quality.  Central mix plants must be close to the work site where the concrete will be used, since hydration begins at the plant.

A concrete plant consists of large hoppers for storage of various ingredients like cement, storage for bulk ingredients like aggregate and water, mechanisms for the addition of various additives and amendments, machinery to accurately weigh, move, and mix some or all of those ingredients, and facilities to dispense the mixed concrete, often to a [[concrete mixer]] truck.

Modern concrete is usually prepared as a viscous fluid, so that it may be poured into forms.  The forms are containers that define the desired shape. Concrete [[formwork]] can be prepared in several ways, such as [[slip forming]] and [[steel plate construction]]. Alternatively, concrete can be mixed into dryer, non-fluid forms and used in factory settings to manufacture [[precast concrete]] products.

Interruption in pouring the concrete can cause the initially placed material to begin to set before the next batch is added on top. This creates a horizontal plane of weakness called a ''cold joint'' between the two batches.<ref>{{Cite web |title=Cold Joints |url=https://www.concrete.org.uk/fingertips-nuggets.asp?cmd=display&id=372 |website=www.concrete.org.uk|archive-url=https://web.archive.org/web/20160304074543/http://www.concrete.org.uk/fingertips-nuggets.asp?cmd=display&id=372 |archive-date=4 March 2016 |publisher= [[The Concrete Society]]|access-date= 30 December 2015}}</ref> Once the mix is where it should be, the curing process must be controlled to ensure that the concrete attains the desired attributes. During concrete preparation, various technical details may affect the quality and nature of the product.

===Design mix===
''Design mix'' ratios are decided by an engineer after analyzing the properties of the specific ingredients being used. Instead of using a 'nominal mix' of 1 part cement, 2 parts sand, and 4 parts aggregate, a civil engineer will custom-design a concrete mix to exactly meet the requirements of the site and conditions, setting material ratios and often designing an admixture package to fine-tune the properties or increase the performance envelope of the mix. Design-mix concrete can have very broad specifications that cannot be met with more basic nominal mixes, but the involvement of the engineer often increases the cost of the concrete mix.

Concrete mixes are primarily divided into nominal mix, standard mix and design mix.

Nominal mix ratios are given in volume of <math>\text{Cement : Sand : Aggregate}</math>. Nominal mixes are a simple, fast way of getting a basic idea of the properties of the finished concrete without having to perform testing in advance.

Various governing bodies (such as [[British Standards]]) define nominal mix ratios into a number of grades, usually ranging from lower [[compressive strength]] to higher compressive strength. The grades usually indicate the 28-day cure strength.<ref>{{cite web |url=http://www.civilology.com/grades-of-concrete/ |title=Grades of Concrete with Proportion (Mix Ratio)| date=26 March 2018}}</ref>

===Mixing===
{{See also|Volumetric concrete mixer|Concrete mixer}}

Thorough mixing is essential to produce uniform, high-quality concrete.

{{em|Separate paste mixing}} has shown that the mixing of cement and water into a paste before combining these materials with [[Construction aggregate|aggregates]] can increase the [[compressive strength]] of the resulting concrete.<ref>{{Cite web |title=Concrete International |url=https://www.concrete.org/publications/concreteinternational.aspx |access-date=2022-08-13 |archive-url=https://web.archive.org/web/20070928092034/http://www.concreteinternational.com/pages/featured_article.asp?ID=3491 |archive-date=28 September 2007|website=concrete.org|date=1 November 1989}}</ref> The paste is generally mixed in a {{em|high-speed}}, shear-type mixer at a [[Water-cement ratio|w/c]] (water to cement ratio) of 0.30 to 0.45 by mass. The cement paste premix may include admixtures such as accelerators or retarders, [[Plasticizer|superplasticizers]], [[pigment]]s, or [[silica fume]]. The premixed paste is then blended with aggregates and any remaining batch water and final mixing is completed in conventional concrete mixing equipment.<ref>{{cite web | title=ACI 304R-00: Guide for Measuring, Mixing, Transporting, and Placing Concrete (Reapproved 2009) | url=https://www.concrete.org/store/productdetail.aspx?ItemID=30400}}</ref>

Resonant acoustic mixing has also been found effective in producing ultra-high performance cementitious materials, as it produces a dense matrix with low porosity.<ref>{{Cite book |last1=Vandenberg |first1=Aileen |last2=Wille |first2=Kay |chapter=The Effects of Resonant Acoustic Mixing on the Microstructure of UHPC |date=2019-06-02 |title=Second International Interactive Symposium on UHPC |chapter-url=https://www.iastatedigitalpress.com/uhpc/article/id/9636/ |journal=International Interactive Symposium on Ultra-High Performance Concrete |volume=2 |issue=1 |doi=10.21838/uhpc.9636 |issn=0000-0000|doi-access=free }}</ref>

===Sample analysis—workability===
{{Main|Concrete slump test}}
[[File:Cannon Renewal Project - October 2016 (30662609012).jpg|thumb|Concrete floor of a [[parking garage]] being placed]]
[[File:Concreteathruz.jpg|thumb|Pouring and smoothing out concrete at Palisades Park in Washington, DC]]

Workability is the ability of a fresh (plastic) concrete mix to fill the form/mold properly with the desired work (pouring, pumping, spreading, tamping, vibration) and without reducing the concrete's quality. Workability depends on water content, aggregate (shape and size distribution), cementitious content and age (level of [[hydration reaction|hydration]]) and can be modified by adding chemical admixtures, like superplasticizer. Raising the water content or adding chemical admixtures increases concrete workability. Excessive water leads to increased bleeding or [[Segregation in concrete|segregation of aggregates]] (when the cement and aggregates start to separate), with the resulting concrete having reduced quality. Changes in gradation can also affect workability of the concrete, although a wide range of gradation can be used for various applications.<ref>{{cite book |last1=Sarviel |first1=Ed |title=Construction Estimating Reference Data |date=1993 |publisher=Craftsman Book Company |isbn=978-0-934041-84-3 |url={{google books|plainurl=y|id=TopgKO4x_2kC}}|page=74 |language=en}}</ref><ref>{{cite journal |last1=Cook |first1=Marllon Daniel |last2=Ghaeezadah |first2=Ashkan |last3=Ley |first3=M. Tyler |title=Impacts of Coarse-Aggregate Gradation on the Workability of Slip-Formed Concrete |journal=Journal of Materials in Civil Engineering |date=1 February 2018 |volume=30 |issue=2 |doi=10.1061/(ASCE)MT.1943-5533.0002126 }}</ref> An undesirable gradation can mean using a large aggregate that is too large for the size of the formwork, or which has too few smaller aggregate grades to serve to fill the gaps between the larger grades, or using too little or too much sand for the same reason, or using too little water, or too much cement, or even using jagged crushed stone instead of smoother round aggregate such as pebbles. Any combination of these factors and others may result in a mix which is too harsh, i.e., which does not flow or spread out smoothly, is difficult to get into the formwork, and which is difficult to surface finish.<ref>{{cite web |url=https://www.concretenetwork.com/aggregate/ |title=Aggregate in Concrete – the Concrete Network |access-date=15 January 2017 |url-status=live |archive-url=https://web.archive.org/web/20170202232307/https://www.concretenetwork.com/aggregate/ |archive-date=2 February 2017  }}</ref>

Workability can be measured by the [[concrete slump test]], a simple measure of the plasticity of a fresh batch of concrete following the [[ASTM]] C 143 or EN 12350-2 test standards. Slump is normally measured by filling an "[[Duff Abrams|Abrams cone]]" with a sample from a fresh batch of concrete. The cone is placed with the wide end down onto a level, non-absorptive surface. It is then filled in three layers of equal volume, with each layer being tamped with a steel rod to consolidate the layer. When the cone is carefully lifted off, the enclosed material slumps a certain amount, owing to gravity. A relatively dry sample slumps very little, having a slump value of {{convert|1|to|2|in|mm|spell=in}} out of {{convert|1|ft|mm|spell=in}}. A relatively wet concrete sample may slump as much as {{convert|8|in|mm|spell=in}}. Workability can also be measured by the [[flow table test]].

Slump can be increased by addition of chemical admixtures such as plasticizer or [[superplasticizer]] without changing the [[water-cement ratio]].<ref>{{cite journal |last1=Ferrari |first1=L. |last2=Kaufmann |first2=J. |last3=Winnefeld |first3=F. |last4=Plank |first4=J. |title=Multi-method approach to study influence of superplasticizers on cement suspensions |journal=Cement and Concrete Research |date=October 2011 |volume=41 |issue=10 |pages=1058–1066 |doi=10.1016/j.cemconres.2011.06.010 }}</ref> Some other admixtures, especially air-entraining admixture, can increase the slump of a mix.

High-flow concrete, like [[self-consolidating concrete]], is tested by other flow-measuring methods. One of these methods includes placing the cone on the narrow end and observing how the mix flows through the cone while it is gradually lifted.

After mixing, concrete is a fluid and can be pumped to the location where needed.

===Curing===
[[File:Curing-concrete.jpg|thumb|A concrete slab being kept hydrated during water curing by submersion (ponding)]]

====Maintaining optimal conditions for cement hydration====
Concrete must be kept moist during curing in order to achieve optimal strength and [[Reinforced concrete structures durability|durability]].<ref>"Curing Concrete" Peter C. Taylor CRC Press 2013. {{ISBN|978-0-415-77952-4}}. eBook {{ISBN|978-0-203-86613-9}}</ref> During curing [[hydrate|hydration]] occurs, allowing calcium-silicate hydrate (C-S-H) to form. Over 90% of a mix's final strength is typically reached within four weeks, with the remaining 10% achieved over years or even decades.<ref>{{cite web | title=Concrete Testing | url=http://technology.calumet.purdue.edu/cnt/rbennet/concrete%20lab.htm | access-date=10 November 2008 | archive-url=https://web.archive.org/web/20081024193802/http://technology.calumet.purdue.edu/cnt/rbennet/concrete%20lab.htm | archive-date=24 October 2008 | df=dmy-all }}</ref> The conversion of [[calcium hydroxide]] in the concrete into [[calcium carbonate]] from absorption of [[carbon dioxide|CO<sub>2</sub>]] over several decades further strengthens the concrete and makes it more resistant to damage. This [[carbonation]] reaction, however, lowers the pH of the cement pore solution and can corrode the reinforcement bars.

Hydration and hardening of concrete during the first three days is critical. Abnormally fast drying and shrinkage due to factors such as evaporation from wind during placement may lead to increased tensile stresses at a time when it has not yet gained sufficient strength, resulting in greater shrinkage cracking. The early strength of the concrete can be increased if it is kept damp during the curing process. Minimizing stress prior to curing minimizes cracking. High-early-strength concrete is designed to hydrate faster, often by increased use of cement that increases shrinkage and cracking. The strength of concrete changes (increases) for up to three years. It depends on cross-section dimension of elements and conditions of structure exploitation.<ref name="Veretennykov Yugov Dolmatov et al 2008"/> Addition of short-cut polymer fibers can improve (reduce) shrinkage-induced stresses during curing and increase early and ultimate compression strength.<ref>{{Cite web|url=http://www.minifibers.com/documents/ADMIXUS-Admixtures-for-Cementitious-Applications.pdf|archive-url=https://web.archive.org/web/20161017073633/http://www.minifibers.com/documents/ADMIXUS-Admixtures-for-Cementitious-Applications.pdf|title="Admixtures for Cementitious Applications."|archive-date=17 October 2016}}</ref>

Properly curing concrete leads to increased strength and lower permeability and avoids cracking where the surface dries out prematurely. Care must also be taken to avoid freezing or overheating due to the [[exothermic]] setting of cement. Improper curing can cause [[Spalling#Spalling in mechanical weathering|spalling]], reduced strength, poor [[abrasion (mechanical)|abrasion]] resistance and [[fracture|cracking]].

====Curing techniques avoiding water loss by evaporation====
During the curing period, concrete is ideally maintained at controlled temperature and humidity. To ensure full hydration during curing, concrete slabs are often sprayed with "curing compounds" that create a water-retaining film over the concrete. Typical films are made of wax or related hydrophobic compounds. After the concrete is sufficiently cured, the film is allowed to abrade from the concrete through normal use.<ref>{{cite web |url=http://www.daytonsuperior.com/docs/default-source/tech-data-sheets/section-05---curing-compounds.pdf?sfvrsn=3 |title=Home |access-date=12 November 2015 |url-status=live |archive-url=https://web.archive.org/web/20151208184425/http://www.daytonsuperior.com/docs/default-source/tech-data-sheets/section-05---curing-compounds.pdf?sfvrsn=3 |archive-date=8 December 2015  }}</ref>

Traditional conditions for curing involve spraying or ponding the concrete surface with water. The adjacent picture shows one of many ways to achieve this, ponding—submerging setting concrete in water and wrapping in plastic to prevent dehydration. Additional common curing methods include wet burlap and plastic sheeting covering the fresh concrete.

For higher-strength applications, [[accelerated curing]] techniques may be applied to the concrete. A common technique involves heating the poured concrete with steam, which serves to both keep it damp and raise the temperature so that the hydration process proceeds more quickly and more thoroughly.

==Alternative types==
{{main|Types of concrete}}

===Asphalt===
{{main|Asphalt concrete}}

''Asphalt concrete'' (commonly called ''asphalt'',<ref>{{cite book |title=The American Heritage Dictionary of the English Language |year=2011 |publisher=Houghton Mifflin Harcourt |location=Boston |isbn=978-0-547-04101-8 |page=106 }}</ref> ''blacktop'', or ''pavement'' in North America, and ''tarmac'', ''bitumen macadam'', or ''rolled asphalt'' in the [[United Kingdom]] and [[Republic of Ireland|Ireland]]) is a [[composite material]] commonly used to surface [[road surface|roads]], [[parking lot]]s, [[airport]]s, as well as the core of [[embankment dam]]s.<ref>{{cite web|url=http://www.waterpowermagazine.com/story.asp?storyCode=472 |title=Asphalt concrete cores for embankment dams |publisher=International Water Power and Dam Construction |access-date=3 April 2011 |archive-url=https://web.archive.org/web/20120707001414/http://www.waterpowermagazine.com/story.asp?storyCode=472 |archive-date=7 July 2012 }}</ref> Asphalt mixtures have been used in pavement construction since the beginning of the twentieth century.<ref>{{cite journal |last1=Polaczyk |first1=Pawel |last2=Huang |first2=Baoshan |last3=Shu |first3=Xiang |last4=Gong |first4=Hongren |title=Investigation into Locking Point of Asphalt Mixtures Utilizing Superpave and Marshall Compactors |journal=Journal of Materials in Civil Engineering |date=September 2019 |volume=31 |issue=9 |doi=10.1061/(ASCE)MT.1943-5533.0002839 |s2cid=197635732 }}</ref> It consists of [[Construction aggregate|mineral aggregate]] [[Binder (material)|bound]] together with [[Bitumen|asphalt]], laid in layers, and compacted. The process was refined and enhanced by Belgian inventor and U.S. immigrant [[Edward De Smedt]].<ref>{{cite book|url={{google books|plainurl=y|id=6iS8BwAAQBAJ|page=120}}|title=Roads Were Not Built for Cars: How Cyclists Were the First to Push for Good Roads & Became the Pioneers of Motoring |last=Reid |first=Carlton |date=2015 |publisher=Island Press |isbn=978-1-61091-689-9|page=120|language=en}}</ref>

The terms ''asphalt'' (or ''asphaltic'') ''concrete'', ''bituminous asphalt concrete'', and ''bituminous mixture'' are typically used only in [[engineering]] and construction documents, which define concrete as any composite material composed of mineral aggregate adhered with a binder. The abbreviation, ''AC'', is sometimes used for ''asphalt concrete'' but can also denote ''asphalt content'' or ''asphalt cement'', referring to the liquid asphalt portion of the composite material.

=== Graphene enhanced concrete ===
Graphene enhanced concretes are standard designs of concrete mixes, except that during the cement-mixing or production process, a small amount of chemically engineered [[graphene]] {{nowrap|(typically < 0.5% by weight)}} is added.<ref>{{cite journal |last1=Dalal |first1=Sejal P. |last2=Dalal |first2=Purvang |title=Experimental Investigation on Strength and Durability of Graphene Nanoengineered Concrete |journal=Construction and Building Materials |date=March 2021 |volume=276 |page=122236 |doi=10.1016/j.conbuildmat.2020.122236 |s2cid=233663658 }}</ref><ref>{{cite journal |last1=Dalal |first1=Sejal P. |last2=Desai |first2=Kandarp |last3=Shah |first3=Dhairya |last4=Prajapati |first4=Sanjay |last5=Dalal |first5=Purvang |last6=Gandhi |first6=Vimal |last7=Shukla |first7=Atindra |last8=Vithlani |first8=Ravi |title=Strength and feasibility aspects of concrete mixes induced with low-cost surfactant functionalized graphene powder |journal=Asian Journal of Civil Engineering |date=January 2022 |volume=23 |issue=1 |pages=39–52 |doi=10.1007/s42107-021-00407-7|s2cid=257110774 }}</ref> These enhanced graphene concretes are designed around the concrete application.

=== Microbial ===
Bacteria such as ''[[Bacillus pasteurii]]'', ''[[Bacillus pseudofirmus]]'', ''Bacillus cohnii'', ''Sporosarcina pasteuri'', and ''[[Arthrobacter crystallopoietes]]'' increase the compression strength of concrete through their biomass. However some forms of bacteria can also be concrete-destroying.<ref>{{cite book |last1=Falkow |first1=Stanley |last2=Rosenberg |first2=Eugene |last3=Schleifer |first3=Karl-Heinz |last4=Stackebrandt |first4=Erko |title=The Prokaryotes: Vol. 2: Ecophysiology and Biochemistry |date=13 July 2006 |publisher=Springer Science & Business Media |isbn=978-0-387-25492-0 |page=1005 |url={{google books|plainurl=y|id=kyAZ47ZrazkC|page=1005}} |language=en}}</ref>  Bacillus sp. CT-5. can reduce corrosion of reinforcement in reinforced concrete by up to four times. ''Sporosarcina pasteurii'' reduces water and chloride permeability. ''B. pasteurii'' increases resistance to acid.<ref>{{cite journal |last1=Metwally |first1=Gehad A. M. |last2=Mahdy |first2=Mohamed |last3=Abd El-Raheem |first3=Ahmed El-Raheem H. |title=Performance of Bio Concrete by Using Bacillus Pasteurii Bacteria |journal=Civil Engineering Journal |date=August 2020 |volume=6 |issue=8 |pages=1443–1456 |doi=10.28991/cej-2020-03091559 |doi-access=free }}</ref>  ''[[Bacillus pasteurii]]'' and ''B. sphaericuscan'' induce calcium carbonate precipitation in the surface of cracks, adding compression strength.<ref name=raju>{{Cite book|last=Raju|first=N. Krishna|url={{google books |plainurl=y|id=41ekDwAAQBAJ|page=1131}}|title=Prestressed Concrete, 6e|date=2018|publisher=McGraw-Hill Education|isbn=978-93-87886-25-4|page=1131}}</ref>

=== Nanoconcrete ===
[[File:Decorative cameo plate.jpg|thumbnail|Decorative plate made of Nano concrete with High-Energy Mixing (HEM)]]

[[Nanoconcrete]] (also spelled "nano concrete"' or "nano-concrete") is a class of materials that contains Portland cement particles that are no greater than 100 μm<ref>{{cite book|chapter-url={{google books|plainurl=y|id=eRVAAAAAQBAJ|page=485}}|title=Proceedings of the International Symposium on Engineering under Uncertainty: Safety Assessment and Management (ISEUSAM-2012)|last1=Tiwari|first1=AK|last2=Chowdhury|first2=Subrato|date=2013|publisher=Springer India|others=Cakrabartī, Subrata; Bhattacharya, Gautam|isbn=978-81-322-0757-3|location=New Delhi|page=485|chapter=An over view of the application of nanotechnology in construction materials|oclc=831413888}}</ref> and particles of silica no greater than 500 μm, which fill voids that would otherwise occur in normal concrete, thereby substantially increasing the material's strength.<ref>{{Cite journal |last1=Thanmanaselvi |first1=M |last2=Ramasamy |first2=V |date=2023 |title=A study on durability characteristics of nano-concrete |journal=Materials Today: Proceedings |volume=80 |pages=2360–2365 |doi=10.1016/j.matpr.2021.06.349 |issn=2214-7853}}</ref> It is widely used in foot and highway bridges where high flexural and compressive strength are indicated.<ref name=raju/>

=== Pervious ===
{{Main|Pervious concrete}}

Pervious concrete is a mix of specially graded coarse aggregate, cement, water, and little-to-no fine aggregates. This concrete is also known as "no-fines" or porous concrete. Mixing the ingredients in a carefully controlled process creates a paste that coats and bonds the aggregate particles. The hardened concrete contains interconnected air voids totaling approximately 15 to 25 percent. Water runs through the voids in the pavement to the soil underneath. Air entrainment admixtures are often used in freeze-thaw climates to minimize the possibility of frost damage. Pervious concrete also permits rainwater to filter through roads and parking lots, to recharge aquifers, instead of contributing to runoff and flooding.<ref>{{Cite web|title=Ground Water Recharging Through Pervious Concrete Pavement |url=https://www.researchgate.net/publication/277231494|access-date=2021-01-26|website=ResearchGate|language=en}}</ref>

=== Polymer ===
{{main|Polymer concrete}}

Polymer concretes are mixtures of aggregate and any of various polymers and may be reinforced. The cement is costlier than lime-based cements, but polymer concretes nevertheless have advantages; they have significant tensile strength even without reinforcement, and they are largely impervious to water. Polymer concretes are frequently used for the repair and construction of other applications, such as drains.

=== Plant fibers ===
Plant fibers and particles can be used in a concrete mix or as a reinforcement.<ref>{{Cite journal |last1=Onuaguluchi |first1=Obinna |last2=Banthia |first2=Nemkumar |date=2016-04-01 |title=Plant-based natural fibre reinforced cement composites: A review |url=https://www.sciencedirect.com/science/article/abs/pii/S0958946516300269 |journal=Cement and Concrete Composites |volume=68 |pages=96–108 |doi=10.1016/j.cemconcomp.2016.02.014 |issn=0958-9465}}</ref><ref>{{Cite journal |last1=Wu |first1=Hansong |last2=Shen |first2=Aiqin |last3=Cheng |first3=Qianqian |last4=Cai |first4=Yanxia |last5=Ren |first5=Guiping |last6=Pan |first6=Hongmei |last7=Deng |first7=Shiyi |date=2023-09-20 |title=A review of recent developments in application of plant fibers as reinforcements in concrete |url=https://www.sciencedirect.com/science/article/abs/pii/S095965262302423X |journal=Journal of Cleaner Production |volume=419 |pages=138265 |doi=10.1016/j.jclepro.2023.138265 |bibcode=2023JCPro.41938265W |issn=0959-6526}}</ref><ref>{{Cite journal |last1=Yan |first1=Libo |last2=Kasal |first2=Bohumil |last3=Huang |first3=Liang |date=2016-05-01 |title=A review of recent research on the use of cellulosic fibres, their fibre fabric reinforced cementitious, geo-polymer and polymer composites in civil engineering |url=https://www.sciencedirect.com/science/article/abs/pii/S1359836816001025 |journal=Composites Part B: Engineering |volume=92 |pages=94–132 |doi=10.1016/j.compositesb.2016.02.002 |issn=1359-8368}}</ref> These materials can increase ductility but the lignocellulosic particles hydrolyze during concrete curing as a result of alkaline environment and elevated temperatures<ref>{{Cite journal |last1=Li |first1=Juan |last2=Kasal |first2=Bohumil |date=July 2023 |title=Degradation Mechanism of the Wood-Cell Wall Surface in a Cement Environment Measured by Atomic Force Microscopy |url=https://ascelibrary.org/doi/10.1061/JMCEE7.MTENG-14910 |journal=Journal of Materials in Civil Engineering |language=en |volume=35 |issue=7 |doi=10.1061/JMCEE7.MTENG-14910 |issn=0899-1561}}</ref><ref>{{Cite journal |last1=Li |first1=Juan |last2=Kasal |first2=Bohumil |date=2022-08-10 |title=The immediate and short-term degradation of the wood surface in a cement environment measured by AFM |journal=Materials and Structures |language=en |volume=55 |issue=7 |pages=179 |doi=10.1617/s11527-022-01988-8 |issn=1871-6873|doi-access=free }}</ref><ref>{{Cite journal |last1=Li |first1=Juan |last2=Kasal |first2=Bohumil |date=2022-04-11 |title=Effects of Thermal Aging on the Adhesion Forces of Biopolymers of Wood Cell Walls |journal=Biomacromolecules |language=en |volume=23 |issue=4 |pages=1601–1609 |doi=10.1021/acs.biomac.1c01397 |issn=1525-7797 |pmc=9006222 |pmid=35303409}}</ref> Such process, that is difficult to measure,<ref>{{Cite journal |last1=Li |first1=Juan |last2=Bohumil |first2=Kasal |date=2021-02-05 |title=Repeatability of Adhesion Force Measurement on Wood Longitudinal Cut Cell Wall Using Atomic Force Microscopy |url=https://wfs.swst.org/index.php/wfs/article/view/2971 |journal=Wood and Fiber Science |language=en |volume=53 |issue=1 |pages=3–16 |doi=10.22382/wfs-2021-02 |issn=0735-6161}}</ref> can affect the properties of the resulting concrete.

=== Sulfur concrete ===
{{Main|Sulfur concrete}}

Sulfur concrete is a special concrete that uses sulfur as a binder and does not require cement or water.

=== Volcanic ===
Volcanic concrete substitutes volcanic rock for the limestone that is burned to form clinker. It consumes a similar amount of energy, but does not directly emit carbon as a byproduct.<ref>{{Cite web|last=Lavars|first=Nick|date=2021-06-10|title=Stanford's low-carbon cement swaps limestone for volcanic rock|url=https://newatlas.com/materials/stanfords-low-carbon-cement-volcanic-rock/|url-status=live|access-date=2021-06-11|website=New Atlas|language=en-US|archive-url=https://web.archive.org/web/20210610065226/https://newatlas.com/materials/stanfords-low-carbon-cement-volcanic-rock/ |archive-date=10 June 2021 }}</ref> Volcanic rock/ash are used as supplementary cementitious materials in concrete to improve the resistance to sulfate, chloride and alkali silica reaction due to pore refinement.<ref>{{cite journal |last1=Celik |first1=K. |last2=Jackson |first2=M.D. |last3=Mancio |first3=M. |last4=Meral |first4=C. |last5=Emwas |first5=A.-H. |last6=Mehta |first6=P.K. |last7=Monteiro |first7=P.J.M. |title=High-volume natural volcanic pozzolan and limestone powder as partial replacements for portland cement in self-compacting and sustainable concrete |journal=Cement and Concrete Composites |date=January 2014 |volume=45 |pages=136–147 |doi=10.1016/j.cemconcomp.2013.09.003 |hdl=11511/37244 |s2cid=138740924 |url=https://www.escholarship.org/uc/item/6mq3j474 }}</ref> Also, they are generally cost effective in comparison to other aggregates,<ref name=Lemougna>{{cite journal |last1=Lemougna |first1=Patrick N. |last2=Wang |first2=Kai-tuo |last3=Tang |first3=Qing |last4=Nzeukou |first4=A.N. |last5=Billong |first5=N. |last6=Melo |first6=U. Chinje |last7=Cui |first7=Xue-min |title=Review on the use of volcanic ashes for engineering applications |journal=Resources, Conservation and Recycling |date=October 2018 |volume=137 |pages=177–190 |doi=10.1016/j.resconrec.2018.05.031 |bibcode=2018RCR...137..177L |s2cid=117442866 }}</ref> good for semi and light weight concretes,<ref name=Lemougna/> and good for thermal and acoustic insulation.<ref name=Lemougna/>

Pyroclastic materials, such as pumice, scoria, and ashes are formed from cooling magma during explosive volcanic eruptions. They are used as supplementary cementitious materials (SCM) or as aggregates for cements and concretes.<ref>{{cite book |doi=10.1016/b0-12-369396-9/00153-2 |chapter=Pyroclastics |title=Encyclopedia of Geology |date=2005 |last1=Brown |first1=R.J. |last2=Calder |first2=E.S. |pages=386–397 |isbn=978-0-12-369396-9 }}</ref> They have been extensively used since ancient times to produce materials for building applications. For example, pumice and other volcanic glasses were added as a natural pozzolanic material for mortars and plasters during the construction of the Villa San Marco in the Roman period (89 BC – 79 AD), which remain one of the best-preserved otium villae of the Bay of Naples in Italy.<ref>{{cite journal |last1=Izzo |first1=Francesco |last2=Arizzi |first2=Anna |last3=Cappelletti |first3=Piergiulio |last4=Cultrone |first4=Giuseppe |last5=De Bonis |first5=Alberto |last6=Germinario |first6=Chiara |last7=Graziano |first7=Sossio Fabio |last8=Grifa |first8=Celestino |last9=Guarino |first9=Vincenza |last10=Mercurio |first10=Mariano |last11=Morra |first11=Vincenzo |last12=Langella |first12=Alessio |title=The art of building in the Roman period (89 B.C. – 79 A.D.): Mortars, plasters and mosaic floors from ancient Stabiae (Naples, Italy) |journal=Construction and Building Materials |date=August 2016 |volume=117 |pages=129–143 |doi=10.1016/j.conbuildmat.2016.04.101 }}</ref>

===Waste light===
{{main|Waste light concrete}}

Waste light is a form of polymer modified concrete. The specific polymer admixture allows the replacement of all the traditional aggregates (gravel, sand, stone) by any mixture of solid waste materials in the grain size of 3–10&nbsp;mm to form a low-compressive-strength (3–20&nbsp;N/mm<sup>2</sup>) product<ref>{{cite web |title=MASUKO light concrete |url=http://www.masuko.hu/eindex.php |access-date=13 November 2020 |archive-date=15 November 2020 |archive-url=https://web.archive.org/web/20201115055625/http://www.masuko.hu/eindex.php |url-status=dead }}</ref> for road and building construction. One cubic meter of waste light concrete contains 1.1–1.3&nbsp;m<sup>3</sup> of shredded waste and no other aggregates.

===Recycled Aggregate Concrete (RAC)===
{{unreferenced section|date=October 2024}}

Recycled aggregate concretes are standard concrete mixes with the addition or substitution of natural aggregates with recycled aggregates sourced from construction and demolition wastes, disused pre-cast concretes or masonry. In most cases, recycled aggregate concrete results in higher water absorption levels by capillary action and permeation, which are the prominent determiners of the strength and durability of the resulting concrete. The increase in water absorption levels is mainly caused by the porous adhered mortar that exists in the recycled aggregates. Accordingly, recycled concrete aggregates that have been washed to reduce the quantity of mortar adhered to aggregates show lower water absorption levels compared to untreated recycled aggregates.

The quality of the recycled aggregate concrete is determined by several factors, including the size, the number of replacement cycles, and the moisture levels of the recycled aggregates. When the recycled concrete aggregates are crushed into coarser fractures, the mixed concrete shows better permeability levels, resulting in an overall increase in strength. In contrast, recycled masonry aggregates provide better qualities when crushed in finer fractures. With each generation of recycled concrete, the resulting compressive strength decreases.

==Properties==
{{Main|Properties of concrete}}

Concrete has relatively high [[compressive strength]], but much lower [[tensile strength]].<ref>{{Cite web | url=https://www.civil-engg-world.com/2009/04/relation-between-compressive-and.html | title=Relation Between Compressive and Tensile Strength of Concrete | access-date=6 January 2019 | archive-url=https://web.archive.org/web/20190106104521/https://www.civil-engg-world.com/2009/04/relation-between-compressive-and.html | archive-date=6 January 2019 }}</ref> Therefore, it is usually [[reinforced concrete|reinforced]] with materials that are strong in tension (often steel). The elasticity of concrete is relatively constant at low stress levels but starts decreasing at higher stress levels as matrix cracking develops. Concrete has a very low [[coefficient of thermal expansion]] and shrinks as it matures. All concrete structures crack to some extent, due to shrinkage and tension. Concrete that is subjected to long-duration forces is prone to [[Creep (deformation)|creep]].

Tests can be performed to ensure that the properties of concrete correspond to specifications for the application.

[[File:Concrete Compression Testing.jpg|thumb|upright|Compression testing of a concrete cylinder]]

The ingredients affect the strengths of the material. Concrete strength values are usually specified as the lower-bound compressive strength of either a cylindrical or cubic specimen as determined by standard test procedures.

The strengths of concrete is dictated by its function. Very low-strength—{{convert|14|MPa|psi|-2|abbr=on}} or less—concrete may be used when the concrete must be lightweight.<ref name=lightweight>{{cite web|title=Structural lightweight concrete|url=http://www.concreteconstruction.net/Images/Structural%20Lightweight%20Concrete_tcm45-345994.pdf|work=Concrete Construction|publisher=The Aberdeen Group|date=March 1981|archive-url=https://web.archive.org/web/20130511221842/http://www.concreteconstruction.net/Images/Structural%20Lightweight%20Concrete_tcm45-345994.pdf|archive-date=11 May 2013}}</ref> Lightweight concrete is often achieved by adding air, foams, or lightweight aggregates, with the side effect that the strength is reduced. For most routine uses, {{convert|20|to|32|MPa|psi|-2|abbr=on}} concrete is often used. {{convert|40|MPa|psi|-2|abbr=on}} concrete is readily commercially available as a more durable, although more expensive, option. Higher-strength concrete is often used for larger civil projects.<ref name=American>{{cite web|title=Ordering Concrete by PSI|url=http://www.americanconcreteofiowa.com/aspx/diy.aspx?id=30|publisher=American Concrete|access-date=10 January 2013|archive-url=https://web.archive.org/web/20130511142813/http://www.americanconcreteofiowa.com/aspx/diy.aspx?id=30|archive-date=11 May 2013}}</ref> Strengths above {{convert|40|MPa|psi|-2|abbr=on}} are often used for specific building elements. For example, the lower floor columns of high-rise concrete buildings may use concrete of {{convert|80|MPa|psi|-2|abbr=on}} or more, to keep the size of the columns small. Bridges may use long beams of high-strength concrete to lower the number of spans required.<ref name=Russel /><ref name=NRMCA>{{cite web|title=Concrete in Practice: What, Why, and How?|url=http://www.nrmca.org/aboutconcrete/cips/33p.pdf|publisher=NRMCA-National Ready Mixed Concrete Association|access-date=10 January 2013|url-status=live|archive-url=https://web.archive.org/web/20120804024341/http://www.nrmca.org/aboutconcrete/cips/33p.pdf|archive-date=4 August 2012}}</ref> Occasionally, other structural needs may require high-strength concrete. If a structure must be very rigid, concrete of very high strength may be specified, even much stronger than is required to bear the service loads. Strengths as high as {{convert|130|MPa|psi|-2|abbr=on}} have been used commercially for these reasons.<ref name=Russel>{{cite web|title=Why Use High Performance Concrete?|url=http://www.silicafume.org/pdf/reprints-whyhpc.pdf|work=Technical Talk|access-date=10 January 2013|author=Henry G. Russel, PE|url-status=live|archive-url=https://web.archive.org/web/20130515033211/http://www.silicafume.org/pdf/reprints-whyhpc.pdf|archive-date=15 May 2013}}</ref>

===Energy efficiency===
The cement produced for making concrete accounts for about 8% of worldwide {{CO2}} emissions per year (compared to, ''e.g.'', global aviation at 1.9%).<ref name=chathamhouse>{{Cite web|url=https://reader.chathamhouse.org/making-concrete-change-innovation-low-carbon-cement-and-concrete |title=Making Concrete Change: Innovation in Low-carbon Cement and Concrete|website=Chatham House|date=13 June 2018|access-date=17 December 2018 |archive-url=https://web.archive.org/web/20181219161129/https://reader.chathamhouse.org/making-concrete-change-innovation-low-carbon-cement-and-concrete |archive-date=19 December 2018 |url-status=live}}</ref> The two [[Cement#CO2 emissions|largest sources]] of {{CO2}} are produced by the cement manufacturing process, arising from (1) the decarbonation reaction of [[limestone]] in the [[cement kiln]] (T ≈ 950&nbsp;°C), and (2) from the combustion of [[fossil fuel]] to reach the [[sintering]] temperature (T ≈ 1450&nbsp;°C) of [[cement clinker]] in the kiln. The energy required for extracting, crushing, and mixing the raw materials ([[construction aggregate]]s used in the concrete production, and also [[limestone]] and [[clay]] feeding the [[cement kiln]]) is lower. Energy requirement for transportation of [[ready-mix concrete]] is also lower because it is produced nearby the construction site from local resources, typically manufactured within 100 kilometers of the job site.<ref>{{cite web|last1=Rubenstein|first1=Madeleine|date=9 May 2012|title=Emissions from the Cement Industry|url=http://blogs.ei.columbia.edu/2012/05/09/emissions-from-the-cement-industry/|url-status=live|archive-url=https://web.archive.org/web/20161222053719/http://blogs.ei.columbia.edu/2012/05/09/emissions-from-the-cement-industry/|archive-date=22 December 2016|access-date=13 December 2016|website=State of the Planet|publisher=Earth Institute, Columbia University}}</ref> The overall [[embodied energy]] of concrete at roughly 1 to 1.5 megajoules per kilogram is therefore lower than for many structural and construction materials.<ref>{{cite web|date=22 February 2013|title=Concrete and Embodied Energy – Can using concrete be carbon neutral|url=http://strineenvironments.com.au/factsheets/concrete-and-embodied-energy-can-using-concrete-be-carbon-neutral/|url-status=live|archive-url=https://web.archive.org/web/20170116174733/http://strineenvironments.com.au/factsheets/concrete-and-embodied-energy-can-using-concrete-be-carbon-neutral/|archive-date=16 January 2017|access-date=15 January 2017}}</ref>

Once in place, concrete offers a great energy efficiency over the lifetime of a building.<ref>{{cite web|last1=Gajda|first1=John|year=2001|title=Energy Use of Single-Family Houses with Various Exterior Walls|url=https://www.healthyheating.com/Page%2055/Downloads/Wall_Systems.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://www.healthyheating.com/Page%2055/Downloads/Wall_Systems.pdf |archive-date=2022-10-09 |url-status=live}}</ref> Concrete walls leak air far less than those made of wood frames.<ref>{{cite book|title=Green Building with Concrete|year= 2015|publisher=Taylor & Francis Group|isbn=978-1-4987-0411-3}}{{page needed|date=October 2021}}</ref> Air leakage accounts for a large percentage of energy loss from a home. The thermal mass properties of concrete increase the efficiency of both residential and commercial buildings. By storing and releasing the energy needed for heating or cooling, concrete's thermal mass delivers year-round benefits by reducing temperature swings inside and minimizing heating and cooling costs.<ref name="Features and Usage of Foam Concrete">{{cite web|title=Features and Usage of Foam Concrete|url=http://www.chinaconcretepump.com/Foam-Concrete-Machine.html/|archive-url=https://archive.today/20121129122814/http://www.chinaconcretepump.com/Foam-Concrete-Machine.html/|archive-date=29 November 2012}}</ref> While insulation reduces energy loss through the building envelope, thermal mass uses walls to store and release energy. Modern concrete wall systems use both external insulation and thermal mass to create an energy-efficient building. Insulating concrete forms (ICFs) are hollow blocks or panels made of either insulating foam or [[rastra]] that are stacked to form the shape of the walls of a building and then filled with reinforced concrete to create the structure.

===Fire safety===
[[File:Boston City Hall - Boston, MA - DSC04704 (cropped).JPG|thumb|[[Boston City Hall]] (1968) is a [[Brutalist]] design constructed largely of precast and poured in place concrete.]]

Concrete buildings are more resistant to fire than those constructed using steel frames, since concrete has lower heat conductivity than steel and can thus last longer under the same fire conditions. Concrete is sometimes used as a fire protection for steel frames, for the same effect as above. Concrete as a fire shield, for example [[Fondu fyre]], can also be used in extreme environments like a missile launch pad.

Options for non-combustible construction include floors, ceilings and roofs made of cast-in-place and hollow-core precast concrete. For walls, concrete masonry technology and [[Insulating concrete forms|Insulating Concrete Forms]] (ICFs) are additional options. ICFs are hollow blocks or panels made of fireproof insulating foam that are stacked to form the shape of the walls of a building and then filled with reinforced concrete to create the structure.

Concrete also provides good resistance against externally applied forces such as high winds, hurricanes, and tornadoes owing to its lateral stiffness, which results in minimal horizontal movement. However, this stiffness can work against certain types of concrete structures, particularly where a relatively higher flexing structure is required to resist more extreme forces.

===Earthquake safety===
As discussed above, concrete is very strong in compression, but weak in tension. Larger earthquakes can generate very large shear loads on structures. These shear loads subject the structure to both tensile and compressional loads. Concrete structures without reinforcement, like other unreinforced masonry structures, can fail during severe earthquake shaking. Unreinforced masonry structures constitute one of the largest earthquake risks globally.<ref>{{cite web|url=http://www.fema.gov/library/viewRecord.do?id=4067 |title=Unreinforced Masonry Buildings and Earthquakes: Developing Successful Risk Reduction Programs FEMA P-774 |archive-url=https://web.archive.org/web/20110912163041/http://www.fema.gov/library/viewRecord.do?id=4067|archive-date=12 September 2011 }}</ref> These risks can be reduced through seismic retrofitting of at-risk buildings, (e.g. school buildings in Istanbul, Turkey).<ref>{{cite conference|url=http://www.curee.org/architecture/docs/S08-034.pdf |title=Seismic Retrofit Design Of Historic Century-Old School Buildings In Istanbul, Turkey |archive-url=https://web.archive.org/web/20120111151034/http://www.curee.org/architecture/docs/S08-034.pdf|archive-date=11 January 2012|first1=C.C. |last1=Simsir |first2=A. |last2=Jain |first3=G.C. |last3=Hart |first4=M.P. |last4=Levy |conference=14th World Conference on Earthquake Engineering|date=12–17 October 2008}}</ref>

==Construction ==
[[File:Buffalo City Court Building, 1971-74, Pfohl, Roberts and Biggie (8448022295).jpg|thumb|upright|The [[Buffalo City Court Building|City Court Building]] in [[Buffalo, New York]]]]

Concrete is one of the most durable building materials. It provides superior fire resistance compared with wooden construction and gains strength over time. Structures made of concrete can have a long service life.<ref>{{Cite book|last=Nawy|first=Edward G.|url={{google books|plainurl=y|id=1OwkUrXuhjQC}}|title=Concrete Construction Engineering Handbook|year=2008|publisher=CRC Press|isbn=978-1-4200-0765-7|language=en}}</ref> Concrete is used more than any other artificial material in the world.<ref name=Lomborg>{{cite book|title=The Skeptical Environmentalist: Measuring the Real State of the World|author-link=Bjørn Lomborg|last=Lomborg|first=Bjørn|date=2001|isbn=978-0-521-80447-9|page=[https://archive.org/details/skepticalenviron00lomb_0/page/138 138]|url=https://archive.org/details/skepticalenviron00lomb_0/page/138|publisher=Cambridge University Press}}</ref> As of 2006, about 7.5 billion cubic meters of concrete are made each year, more than one cubic meter for every person on Earth.<ref>{{cite web|title=Minerals commodity summary – cement – 2007|publisher=US [[United States Geological Survey]]|date=1 June 2007 |url=http://minerals.usgs.gov/minerals/pubs/commodity/cement/index.html|access-date=16 January 2008 |url-status=live |archive-url=https://web.archive.org/web/20071213052530/http://minerals.usgs.gov/minerals/pubs/commodity/cement/index.html|archive-date=13 December 2007}}<!--Computed by taking 2007 figure for world concrete production and the mix at http://en.wikipedia.org/wiki/Concrete#Regular_concrete and computing the volume--></ref>

=== Reinforced ===
{{Main|Reinforced concrete}}
[[File:O Cristo Redentor.JPG|thumb|upright|''[[Christ the Redeemer (statue)|Christ the Redeemer]]'' statue in [[Rio de Janeiro]], Brazil. It is made of reinforced concrete clad in a mosaic of thousands of triangular [[soapstone]] tiles.<ref name="brit">{{Cite encyclopedia |title=Christ the Redeemer (last updated 13 January 2014) |encyclopedia=[[Encyclopædia Britannica]] |url=http://www.britannica.com/EBchecked/topic/1435544/Christ-the-Redeemer |access-date=November 5, 2022 |last1=Murray |first1=Lorraine}}</ref>]]

The use of reinforcement, in the form of iron was introduced in the 1850s by French industrialist François Coignet, and it was not until the 1880s that German civil engineer G. A. Wayss used steel as reinforcement. Concrete is a relatively brittle material that is strong under compression but less in tension. Plain, unreinforced concrete is unsuitable for many structures as it is relatively poor at withstanding stresses induced by vibrations, wind loading, and so on. Hence, to increase its overall strength, steel rods, wires, mesh or cables can be embedded in concrete before it is set. This reinforcement, often known as rebar, resists tensile forces.<ref name="designingbuildings">{{Cite web|url=https://www.designingbuildings.co.uk/wiki/Reinforced_concrete|title=Reinforced concrete|website=www.designingbuildings.co.uk}}</ref>

[[Reinforced concrete|Reinforced concrete (RC)]] is a versatile composite and one of the most widely used materials in modern construction. It is made up of different constituent materials with very different properties that complement each other. In the case of reinforced concrete, the component materials are almost always concrete and steel. These two materials form a strong bond together and are able to resist a variety of applied forces, effectively acting as a single structural element.<ref name="Claisse-2016">{{Citation|last=Claisse|first=Peter A.|title=Composites|date=2016|url=https://linkinghub.elsevier.com/retrieve/pii/B9780081002759000383|work=Civil Engineering Materials|pages=431–435|publisher=Elsevier|language=en|doi=10.1016/b978-0-08-100275-9.00038-3|isbn=978-0-08-100275-9|access-date=2021-10-05}}</ref>

Reinforced concrete can be precast or cast-in-place (in situ) concrete, and is used in a wide range of applications such as; slab, wall, beam, column, foundation, and frame construction. Reinforcement is generally placed in areas of the concrete that are likely to be subject to tension, such as the lower portion of beams. Usually, there is a minimum of 50&nbsp;mm cover, both above and below the steel reinforcement, to resist spalling and corrosion which can lead to structural instability.<ref name="designingbuildings" /> Other types of non-steel reinforcement, such as [[Fiber-reinforced concrete|Fibre-reinforced concretes]] are used for specialized applications, predominately as a means of controlling cracking.<ref name="Claisse-2016" />

=== Precast ===
{{main|Precast concrete}}

Precast concrete is concrete which is cast in one place for use elsewhere and is a mobile material. The largest part of precast production is carried out in the works of specialist suppliers, although in some instances, due to economic and geographical factors, scale of product or difficulty of access, the elements are cast on or adjacent to the construction site.<ref name="Richardson-2003">{{cite book |doi=10.1016/B978-075065686-3/50307-4 |chapter=Precast concrete structural elements |title=Advanced Concrete Technology |date=2003 |last1=Richardson |first1=John |pages=3–46 |isbn=978-0-7506-5686-3 }}</ref> Precasting offers considerable advantages because it is carried out in a controlled environment, protected from the elements, but the downside of this is the contribution to greenhouse gas emission from transportation to the construction site.<ref name="Claisse-2016" />

Advantages to be achieved by employing precast concrete:<ref name="Richardson-2003" />

* Preferred dimension schemes exist, with elements of tried and tested designs available from a catalogue.
* Major savings in time result from manufacture of structural elements apart from the series of events which determine overall duration of the construction, known by planning engineers as the 'critical path'.
* Availability of Laboratory facilities capable of the required control tests, many being certified for specific testing in accordance with National Standards.
* Equipment with capability suited to specific types of production such as stressing beds with appropriate capacity, moulds and machinery dedicated to particular products.
* High-quality finishes achieved direct from the mould eliminate the need for interior decoration and ensure low maintenance costs.

===Mass structures===
{{main|Mass concrete}}
[[File:UserKTrimble-AP Taum Sauk Reservoir UnderConstruction Nov 22 2009 crop1.jpg|thumb|Aerial photo of reconstruction at [[Taum Sauk Hydroelectric Power Station|Taum Sauk]] (Missouri) pumped storage facility in late November 2009. After the original reservoir failed, the new reservoir was made of roller-compacted concrete.]]

Due to cement's [[exothermic]] chemical reaction while setting up, large concrete structures such as [[dam]]s, [[navigation lock]]s, large mat foundations, and large [[breakwater (structure)|breakwaters]] generate excessive heat during hydration and associated expansion. To mitigate these effects, ''post-cooling''<ref name="BerkCE">{{cite web|url=http://www.ce.berkeley.edu/~paulmont/165/Mass_concrete2.pdf |title=Mass Concret |archive-url=https://web.archive.org/web/20110927073606/http://www.ce.berkeley.edu/~paulmont/165/Mass_concrete2.pdf |archive-date=27 September 2011 }}</ref> is commonly applied during construction. An early example at Hoover Dam used a network of pipes between vertical concrete placements to circulate cooling water during the curing process to avoid damaging overheating. Similar systems are still used; depending on volume of the pour, the concrete mix used, and ambient air temperature, the cooling process may last for many months after the concrete is placed. Various methods also are used to pre-cool the concrete mix in mass concrete structures.<ref name="BerkCE"/>

Another approach to mass concrete structures that minimizes cement's thermal by-product is the use of [[roller-compacted concrete]], which uses a dry mix which has a much lower cooling requirement than conventional wet placement. It is deposited in thick layers as a semi-dry material then roller [[compactor|compacted]] into a dense, strong mass.

===Surface finishes===
{{main|Decorative concrete}}
[[File:Smpolishedconcrete2.jpg|thumb|Black basalt polished concrete floor]]

Raw concrete surfaces tend to be porous and have a relatively uninteresting appearance. Many finishes can be applied to improve the appearance and preserve the surface against staining, water penetration, and freezing.

Examples of improved appearance include [[stamped concrete]] where the wet concrete has a pattern impressed on the surface, to give a paved, cobbled or brick-like effect, and may be accompanied with coloration. Another popular effect for flooring and table tops is [[polished concrete]] where the concrete is polished optically flat with diamond abrasives and sealed with polymers or other sealants.

Other finishes can be achieved with chiseling, or more conventional techniques such as painting or covering it with other materials.

The proper treatment of the surface of concrete, and therefore its characteristics, is an important stage in the construction and renovation of architectural structures.<ref>{{cite journal | last1 = Sadowski | first1 = Łukasz | last2 = Mathia | first2 = Thomas | year = 2016| title = Multi-scale Metrology of Concrete Surface Morphology: Fundamentals and specificity | journal = Construction and Building Materials | volume = 113 | pages = 613–621 | doi = 10.1016/j.conbuildmat.2016.03.099 }}</ref>

===Prestressed ===
{{Main|Prestressed concrete}}
[[File:Scott System cacti.jpg|thumb|Stylized cacti decorate a sound/retaining wall in [[Scottsdale, Arizona]]]]

[[Prestressed concrete]] is a form of reinforced concrete that builds in [[compressive stress]]es during construction to oppose tensile stresses experienced in use. This can greatly reduce the weight of beams or slabs, by
better distributing the stresses in the structure to make optimal use of the reinforcement. For example, a horizontal beam tends to sag. Prestressed reinforcement along the bottom of the beam counteracts this.
In pre-tensioned concrete, the prestressing is achieved by using steel or polymer tendons or bars that are subjected to a tensile force prior to casting, or for post-tensioned concrete, after casting.

There are two different systems being used:<ref name="Claisse-2016" />

* [[Prestressed concrete|Pretensioned concrete]] is almost always precast, and contains steel wires (tendons) that are held in tension while the concrete is placed and sets around them.
* [[Prestressed concrete|Post-tensioned concrete]] has ducts through it. After the concrete has gained strength, tendons are pulled through the ducts and stressed. The ducts are then filled with grout. Bridges built in this way have experienced considerable corrosion of the tendons, so external post-tensioning may now be used in which the tendons run along the outer surface of the concrete.

More than {{convert|55000|mi|km}} of highways in the United States are paved with this material. [[Reinforced concrete]], [[prestressed concrete]] and [[precast concrete]] are the most widely used [[types of concrete]] functional extensions in modern days. For more information see [[Brutalist architecture]].

===Placement===
Once mixed, concrete is typically transported to the place where it is intended to become a structural item. Various methods of transportation and placement are used depending on the distances involve, quantity needed, and other details of application. Large amounts are often transported by truck, poured free under gravity or through a [[tremie]], or [[Concrete pump|pumped]] through a pipe. Smaller amounts may be carried in a skip (a metal container which can be tilted or opened to release the contents, usually transported by crane or hoist), or wheelbarrow, or carried in toggle bags for manual placement underwater.

====Cold weather placement====
[[File:Pohjolatalo Kouvola 001.jpg|thumb|''Pohjolatalo'', an office building made of concrete in the city center of [[Kouvola]] in [[Kymenlaakso]], Finland]]

[[Extreme weather]] conditions (extreme heat or cold; windy conditions, and humidity variations) can significantly alter the quality of concrete. Many precautions are observed in cold weather placement.<ref name="FPrimeC">{{cite news|url=http://www.fprimec.com/cold-weather-concreting|title=Winter is Coming! Precautions for Cold Weather Concreting |date=14 November 2016|newspaper=FPrimeC Solutions|language=en-US|access-date=11 January 2017|url-status=live|archive-url=https://web.archive.org/web/20170113155033/http://www.fprimec.com/cold-weather-concreting|archive-date=13 January 2017}}</ref> Low temperatures significantly slow the chemical reactions involved in hydration of cement, thus affecting the strength development. Preventing freezing is the most important precaution, as formation of ice crystals can cause damage to the crystalline structure of the hydrated cement paste. If the surface of the concrete pour is insulated from the outside temperatures, the heat of hydration will prevent freezing.

The [[American Concrete Institute]] (ACI) definition of cold weather placement, ACI 306,<ref>{{cite web|title=306R-16 Guide to Cold Weather Concreting|url=https://www.concrete.org/store/productdetail.aspx?ItemID=30616|url-status=live|archive-url=https://web.archive.org/web/20170915204757/https://www.concrete.org/store/productdetail.aspx?ItemID=30616|archive-date=15 September 2017}}</ref> is:

* A period when for more than three successive days the average daily air temperature drops below 40&nbsp;°F (~ 4.5&nbsp;°C), and
* Temperature stays below {{convert|50|°F|°C|abbr=on}} for more than one-half of any 24-hour period.

In [[Canada]], where temperatures tend to be much lower during the cold season, the following criteria are used by [[Canadian Standards Agency|CSA]] A23.1:

* When the air temperature is ≤ 5&nbsp;°C, and
* When there is a probability that the temperature may fall below 5&nbsp;°C within 24 hours of placing the concrete.

The minimum strength before exposing concrete to extreme cold is {{convert|500|psi|MPa|abbr=on}}. CSA A 23.1 specified a compressive strength of 7.0&nbsp;MPa to be considered safe for exposure to freezing.

==== Underwater placement ====
{{see also|Underwater construction}}
[[File:Tremie operation.png|thumb|upright|Assembled tremie placing concrete underwater]]

Concrete may be placed and cured underwater. Care must be taken in the placement method to prevent washing out the cement. Underwater placement methods include the [[tremie]], pumping, skip placement, manual placement using toggle bags, and bagwork.<ref name="Larn and Whistler 1993">{{cite book|last1=Larn|first1=Richard|last2=Whistler|first2=Rex|title=Commercial Diving Manual|edition=3rd|year=1993|publisher=David and Charles|location=Newton Abbott, UK|isbn=0-7153-0100-4 |chapter=17 – Underwater concreting |pages=297–308}}</ref>

A tremie is a vertical, or near-vertical, pipe with a hopper at the top used to pour concrete underwater in a way that avoids washout of cement from the mix due to turbulent water contact with the concrete while it is flowing. This produces a more reliable strength of the product. The {{visible anchor|toggle bag}} method is generally used for placing small quantities and for repairs. Wet concrete is loaded into a reusable canvas bag and squeezed out at the required place by the diver. Care must be taken to avoid washout of the cement and fines.

{{visible anchor|Underwater bagwork}} is the manual placement by divers of woven cloth bags containing dry mix, followed by piercing the bags with steel rebar pins to tie the bags together after every two or three layers, and create a path for hydration to induce curing, which can typically take about 6 to 12 hours for initial hardening and full hardening by the next day. Bagwork concrete will generally reach full strength within 28 days. Each bag must be pierced by at least one, and preferably up to four pins. Bagwork is a simple and convenient method of underwater concrete placement which does not require pumps, plant, or formwork, and which can minimise environmental effects from dispersing cement in the water. Prefilled bags are available, which are sealed to prevent premature hydration if stored in suitable dry conditions. The bags may be biodegradable.<ref>{{cite report |url=https://www.soluform.co.uk/wp-content/uploads/2020/11/Underwater-Bagwork-Datasheet.pdf |title=Prefilled lined underwater hand-placed bagwork product datasheet |publisher=Soluform |website=www.soluform.co.uk |access-date=8 September 2024 }}</ref>

{{visible anchor|Grouted aggregate}} is an alternative method of forming a concrete mass underwater, where the forms are filled with coarse aggregate and the voids then completely filled from the bottom by displacing the water with pumped [[grout]].<ref name="Larn and Whistler 1993" />

===Roads===
[[Road surface#Concrete|Concrete roads]] are more fuel efficient to drive on,<ref>{{cite web|title=Mapping of Excess Fuel Consumption|url=https://cshub.mit.edu/news/lca-research-brief-mapping-excess-fuel-consumption|url-status=live|archive-url=https://web.archive.org/web/20150102190351/https://cshub.mit.edu/news/lca-research-brief-mapping-excess-fuel-consumption|archive-date=2 January 2015}}</ref> more reflective and last significantly longer than other paving surfaces, yet have a much smaller market share than other paving solutions. Modern-paving methods and design practices have changed the economics of concrete paving, so that a well-designed and placed concrete pavement will be less expensive on initial costs and significantly less expensive over the life cycle. Another major benefit is that [[pervious concrete]] can be used, which eliminates the need to place [[storm drain]]s near the road, and reducing the need for slightly sloped roadway to help rainwater to run off. No longer requiring discarding rainwater through use of drains also means that less electricity is needed (more pumping is otherwise needed in the water-distribution system), and no rainwater gets polluted as it no longer mixes with polluted water. Rather, it is immediately absorbed by the ground.{{citation needed|date=August 2020}}

=== Tube forest ===
Cement molded into a forest of tubular structures can be 5.6 times more resistant to cracking/failure than standard concrete. The approach mimics mammalian [[Bone|cortical bone]] that features elliptical, hollow [[osteons]] suspended in an organic matrix, connected by relatively weak "cement lines". Cement lines provide a preferable in-plane crack path. This design fails via a "stepwise toughening mechanism". Cracks are contained within the tube, reducing spreading, by dissipating energy at each tube/step.<ref>{{Cite web |last=Paul |first=Andrew |date=2024-09-17 |title=Bone-like, hollow concrete design makes it 5.6 times stronger |url=https://www.popsci.com/technology/hollow-concrete/ |access-date=2024-10-11 |website=Popular Science |language=en-US}}</ref>

==Environment, health and safety==
{{main|Environmental impact of concrete}}
{{unbalanced section|date=January 2024}}

The manufacture and use of concrete produce a wide range of environmental, economic and social impacts.

===Health and safety===
{{see also|Occupational dust exposure#Construction}}
[[File:Dust emission when using electrical power tools.webm|thumb|upright=0.83|[[Concrete dust]] emission from the use of power tool]]
[[File:Crushed Concrete Granular Fill.jpg|thumb|Recycled crushed concrete, to be reused as granular fill, is loaded into a semi-dump truck]]

Grinding of concrete can produce [[hazardous dust]]. Exposure to cement dust can lead to issues such as [[silicosis]], kidney disease, skin irritation and similar effects. The U.S. [[National Institute for Occupational Safety and Health]] in the United States recommends attaching local exhaust ventilation shrouds to electric concrete grinders to control the spread of this dust. In addition, the [[Occupational Safety and Health Administration]] (OSHA) has placed more stringent regulations on companies whose workers regularly come into contact with silica dust. An updated silica rule, which OSHA put into effect 23 September 2017 for construction companies, restricted the amount of breathable crystalline silica workers could legally come into contact with to 50 micro grams per cubic meter of air per 8-hour workday. That same rule went into effect 23 June 2018 for general industry, [[hydraulic fracturing]] and maritime. That deadline was extended to 23 June 2021 for engineering controls in the hydraulic fracturing industry. Companies which fail to meet the tightened safety regulations can face financial charges and extensive penalties. The presence of some substances in concrete, including useful and unwanted additives, can cause health concerns due to toxicity and radioactivity. Fresh concrete (before curing is complete) is highly alkaline and must be handled with proper protective equipment.

===Cement ===
A major component of concrete is [[cement]], a fine powder used mainly to bind sand and coarser aggregates together in concrete. Although a variety of cement types exist, the most common is "[[Portland cement]]", which is produced by mixing clinker with smaller quantities of other additives such as gypsum and ground limestone. The production of clinker, the main constituent of cement, is responsible for the bulk of the sector's greenhouse gas emissions, including both energy intensity and process emissions.<ref>{{cite web |last1=Akerman |first1=Patrick |last2=Cazzola |first2=Pierpaolo |last3=Christiansen |first3=Emma Skov |last4=Heusden |first4=Renée Van |last5=Iperen |first5=Joanna Kolomanska-van |last6=Christensen |first6=Johannah |last7=Crone |first7=Kilian |last8=Dawe |first8=Keith |last9=Smedt |first9=Guillaume De |last10=Keynes |first10=Alex |last11=Laporte |first11=Anaïs |last12=Gonsolin |first12=Florie |last13=Mensink |first13=Marko |last14=Hebebrand |first14=Charlotte |last15=Hoenig |first15=Volker |last16=Malins |first16=Chris |last17=Neuenhahn |first17=Thomas |last18=Pyc |first18=Ireneusz |last19=Purvis |first19=Andrew |last20=Saygin |first20=Deger |last21=Xiao |first21=Carol |last22=Yang |first22=Yufeng |title=Reaching Zero with Renewables |date=1 September 2020 |url=https://www.h2knowledgecentre.com/content/researchpaper1611 }}</ref>

The cement industry is one of the three primary producers of carbon dioxide, a major greenhouse gas – the other two being energy production and transportation industries. On average, every tonne of cement produced releases one tonne of CO<sub>2</sub> into the atmosphere. Pioneer cement manufacturers have claimed to reach lower carbon intensities, with 590&nbsp;kg of CO<sub>2</sub>eq per tonne of cement produced.<ref>{{cite web |title=Leading the way to carbon neutrality |publisher=HeidelbergCement |date=24 September 2020 |url=https://www.heidelbergcement.com/en/system/files_force/assets/document/7e/8c/co2-strategie_factsheets_en.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://www.heidelbergcement.com/en/system/files_force/assets/document/7e/8c/co2-strategie_factsheets_en.pdf |archive-date=2022-10-09 |url-status=live }}</ref> The emissions are due to combustion and calcination processes,<ref>{{cite web |title=Cement Clinker Calcination in Cement Production Process |url=http://www.cementplantequipment.com/all-the-things-about-cement-clinker-calcination-in-cement-production-process/ |website=AGICO Cement Plant Supplier |date=4 April 2019 }}</ref> which roughly account for 40% and 60% of the greenhouse gases, respectively. Considering that cement is only a fraction of the constituents of concrete, it is estimated that a tonne of concrete is responsible for emitting about 100–200&nbsp;kg of CO<sub>2</sub>.<ref>{{cite web |publisher=Portland Cement Association |title=Carbon footprint |url=https://www.cement.org/docs/default-source/th-paving-pdfs/sustainability/carbon-foot-print.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://www.cement.org/docs/default-source/th-paving-pdfs/sustainability/carbon-foot-print.pdf |archive-date=2022-10-09 |url-status=live }}</ref><ref name="Lehne-2018">{{cite web |last1=Lehne |first1=Johanna |last2=Preston |first2=Felix |title=Making Concrete Change: Innovation in Low-carbon Cement and Concrete |date=13 June 2018 |url=https://www.chathamhouse.org/2018/06/making-concrete-change-innovation-low-carbon-cement-and-concrete }}</ref> Every year more than 10 billion tonnes of concrete are used worldwide.<ref name="Lehne-2018" /> In the coming years, large quantities of concrete will continue to be used, and the mitigation of CO<sub>2</sub> emissions from the sector will be even more critical.

Concrete is used to create hard surfaces that contribute to [[surface runoff]], which can cause heavy soil erosion, water pollution, and flooding, but conversely can be used to divert, dam, and control flooding. [[Concrete dust]] released by building [[demolition]] and natural disasters can be a major source of dangerous [[air pollution]]. Concrete is a contributor to the [[urban heat island]] effect, though less so than [[Asphalt concrete|asphalt]].

===Climate change mitigation===
Reducing the cement clinker content might have positive effects on the environmental life-cycle assessment of concrete. Some research work on reducing the cement clinker content in concrete has already been carried out. However, there exist different research strategies. Often replacement of some clinker for large amounts of slag or fly ash was investigated based on conventional concrete technology. This could lead to a waste of scarce raw materials such as slag and fly ash. The aim of other research activities is the efficient use of cement and reactive materials like slag and fly ash in concrete based on a modified mix design approach.<ref>{{cite journal |last1=Proske |first1=Tilo |last2=Hainer |first2=Stefan |last3=Rezvani |first3=Moien |last4=Graubner |first4=Carl-Alexander |title=Eco-friendly concretes with reduced water and cement contents – Mix design principles and laboratory tests |journal=Cement and Concrete Research |date=September 2013 |volume=51 |pages=38–46 |doi=10.1016/j.cemconres.2013.04.011 }}</ref>

The embodied carbon of a precast concrete facade can be reduced by 50% when using the presented fiber reinforced high performance concrete in place of typical reinforced concrete cladding.<ref>{{cite journal |last1=O'Hegarty |first1=Richard |last2=Kinnane |first2=Oliver |last3=Newell |first3=John |last4=West |first4=Roger |title=High performance, low carbon concrete for building cladding applications |journal=Journal of Building Engineering |date=November 2021 |volume=43 |page=102566 |doi=10.1016/j.jobe.2021.102566 }}</ref> Studies have been conducted about commercialization of low-carbon concretes. [[Life-cycle assessment|Life cycle assessment]] (LCA) of low-carbon concrete was investigated according to the ground granulated blast-furnace slag (GGBS) and fly ash (FA) replacement ratios. Global warming potential (GWP) of GGBS decreased by 1.1&nbsp;kg CO<sub>2</sub> eq/m<sup>3</sup>, while FA decreased by 17.3&nbsp;kg CO<sub>2</sub> eq/m<sup>3</sup> when the mineral admixture replacement ratio was increased by 10%. This study also compared the compressive strength properties of binary blended low-carbon concrete according to the replacement ratios, and the applicable range of mixing proportions was derived.<ref>{{cite journal |last1=Lee |first1=Jaehyun |last2=Lee |first2=Taegyu |last3=Jeong |first3=Jaewook |last4=Jeong |first4=Jaemin |title=Sustainability and performance assessment of binary blended low-carbon concrete using supplementary cementitious materials |journal=Journal of Cleaner Production |date=January 2021 |volume=280 |page=124373 |doi=10.1016/j.jclepro.2020.124373 |bibcode=2021JCPro.28024373L |s2cid=224849505 }}</ref>

===Climate change adaptation===
High-performance building materials will be particularly important for enhancing resilience, including for flood defenses and critical-infrastructure protection.<ref>{{Cite book |last=Sabry |first=Fouad |url=https://books.google.com/books?id=udiTEAAAQBAJ&dq=High-performance+building+materials+will+be+particularly+important+for+enhancing+resilience,+including+for+flood+defenses+and+critical-infrastructure+protection.&pg=PT145 |title=Translucent Concrete: How-to see-through walls? Using nano optics and mixing fine concrete and optical fibers for illumination during day and night time |date=2022-01-17 |publisher=One Billion Knowledgeable |language=en}}</ref> Risks to infrastructure and cities posed by extreme weather events are especially serious for those places exposed to flood and hurricane damage, but also where residents need protection from extreme summer temperatures. Traditional concrete can come under strain when exposed to humidity and higher concentrations of atmospheric CO<sub>2</sub>. While concrete is likely to remain important in applications where the environment is challenging, novel, smarter and more adaptable materials are also needed.<ref name="Lehne-2018" /><ref>{{Cite journal|last=Mehta|first=P. Kumar|date=2009-02-01|title=Global Concrete Industry Sustainability |url=https://www.concrete.org/publications/internationalconcreteabstractsportal/m/details/id/56323|journal=Concrete International|language=en|volume=31|issue=2|pages=45–48}}</ref>

=== End-of-life: degradation and waste ===
[[File:Tunkhannock Viaduct, NE Pennsylvania USA.jpg|thumb|The [[Tunkhannock Viaduct]] in northeastern Pennsylvania opened in 1915 and is still in regular use today]]{{Excerpt|Concrete degradation|only=paragraph}}

===Recycling ===
{{Excerpt|Concrete recycling|only=paragraph|paragraphs=2}}There have been concerns about the recycling of painted concrete due to possible lead content. Studies have indicated that recycled concrete exhibits lower strength and durability compared to concrete produced using natural aggregates.<ref>{{Cite journal |last1=Abdo |first1=Ayman |last2=El-Zohairy |first2=Ayman |last3=Alashker |first3=Yasser |last4=Badran |first4=Mohamed Abd El-Aziz |last5=Ahmed |first5=Sayed |date=2024-01-01 |title=Effect of Treated/Untreated Recycled Aggregate Concrete: Structural Behavior of RC Beams |journal=Sustainability |language=en |volume=16 |issue=10 |pages=4039 |doi=10.3390/su16104039 |doi-access=free |bibcode=2024Sust...16.4039A |issn=2071-1050}}</ref><ref>{{Cite web |title=Khoan Cắt Bê Tông |url=https://khoanphabetong365.net/ |access-date=2024-10-25 |website= |language=}}</ref><ref>{{Cite journal |last1=Abdelfatah |first1=Akmal S. |last2=Tabsh |first2=Sami W. |date=2011 |title=Review of Research on and Implementation of Recycled Concrete Aggregate in the GCC |journal=Advances in Civil Engineering |language=en |volume=2011 |pages=1–6 |doi=10.1155/2011/567924 |doi-access=free |issn=1687-8086}}</ref><ref>{{Cite journal |last=Lu |first=Linfeng |date=July 2024 |title=Optimal Replacement Ratio of Recycled Concrete Aggregate Balancing Mechanical Performance with Sustainability: A Review |journal=Buildings |language=en |volume=14 |issue=7 |pages=2204 |doi=10.3390/buildings14072204 |doi-access=free |issn=2075-5309}}</ref> This deficiency can be addressed by incorporating supplementary materials such as fly ash into the mixture.<ref>{{Cite journal |last1=Rao |first1=Akash |last2=Jha |first2=Kumar N. |last3=Misra |first3=Sudhir |date=2007-03-01 |title=Use of aggregates from recycled construction and demolition waste in concrete |url=https://linkinghub.elsevier.com/retrieve/pii/S0921344906001315 |journal=Resources, Conservation and Recycling |volume=50 |issue=1 |pages=71–81 |doi=10.1016/j.resconrec.2006.05.010 |bibcode=2007RCR....50...71R |issn=0921-3449}}</ref>

==World records==
The world record for the largest concrete pour in a single project is the [[Three Gorges Dam]] in Hubei Province, China by the Three Gorges Corporation. The amount of concrete used in the construction of the dam is estimated at 16 million cubic meters over 17 years. The previous record was 12.3 million cubic meters held by [[Itaipu Dam|Itaipu hydropower station]] in Brazil.<ref>{{cite web
 |title       = Itaipu Web-site
 |date        = 2 January 2012
 |url         = http://www.itaipu.gov.br/en/energy/concrete-pouring
 |access-date  = 2 January 2012
 |url-status     = live
 |archive-url  = https://web.archive.org/web/20120209223146/http://www.itaipu.gov.br/en/energy/concrete-pouring
 |archive-date = 9 February 2012
 |df          = dmy-all
}}
</ref><ref name="probeinternational.org">{{Cite web |last=Sources |first=Other News |date=2009-07-14 |title=China's Three Gorges Dam, by the Numbers |url=https://journal.probeinternational.org/2009/07/14/chinas-three-gorges-dam-numbers-2/ |access-date=2022-08-13 |language=en|archive-url=https://web.archive.org/web/20170329045941/https://journal.probeinternational.org/2009/07/14/chinas-three-gorges-dam-numbers-2/ |archive-date=29 March 2017 |website=Probe International}}</ref><ref>{{cite web
 |title       = Concrete Pouring of Three Gorges Project Sets World Record
 |work        = People's Daily
 |date        = 4 January 2001
 |url         = http://english.peopledaily.com.cn/200101/02/eng20010102_59432.html
 |access-date  = 24 August 2009
 |url-status     = live
 |archive-url  = https://web.archive.org/web/20100527044056/http://english.peopledaily.com.cn/200101/02/eng20010102_59432.html
 |archive-date = 27 May 2010
 |df          = dmy-all
}}
</ref>

The world record for concrete pumping was set on 7 August 2009 during the construction of the [[Parbati River (Himachal Pradesh)|Parbati]] Hydroelectric Project, near the village of Suind, [[Himachal Pradesh]], India, when the concrete mix was pumped through a vertical height of {{convert|715|m|ft|abbr=on}}.<ref>{{cite web|url=http://www.masterbuilder.co.in/ci/293/Concrete-Pumping/ |title=Concrete Pumping to 715&nbsp;m Vertical – A New World Record Parbati Hydroelectric Project Inclined Pressure Shaft Himachal Pradesh – A case Study |publisher=The Masterbuilder |access-date=21 October 2010 |archive-url=https://archive.today/20110721155834/http://www.masterbuilder.co.in/ci/293/Concrete-Pumping/ |archive-date=21 July 2011}}</ref><ref>{{cite web |url=http://www.nbmcw.com/articles/equipment-a-machinery/5470-schwing-stetter-launches-new-truck-mounted-concrete-pump-s-36.html |title=SCHWING Stetter Launches New Truck mounted Concrete Pump S-36 |date=October 2009 |publisher=NBM&CW (New Building Materials and Construction World) |access-date=21 October 2010 |url-status=live |archive-url=https://web.archive.org/web/20110714161027/http://www.nbmcw.com/articles/equipment-a-machinery/5470-schwing-stetter-launches-new-truck-mounted-concrete-pump-s-36.html |archive-date=14 July 2011  }}</ref>

The [[Polavaram Project|Polavaram dam]] works in [[Andhra Pradesh]] on 6 January 2019 entered the [[Guinness World Records]] by pouring 32,100 cubic metres of concrete in 24 hours.<ref>{{cite web|url=https://indianexpress.com/article/india/andhra-pradesh-polavaram-project-enters-guinness-book-of-world-record-for-concrete-pouring-5526168/|title=Andhra Pradesh: Polavaram project enters Guinness Book of World Record for concrete pouring|last=Janyala|first=Sreenivas|date=January 7, 2019|website=The India Express|access-date=7 January 2020}}</ref> The world record for the largest continuously poured concrete raft was achieved in August 2007 in Abu Dhabi by contracting firm Al Habtoor-CCC Joint Venture and the concrete supplier is Unibeton Ready Mix.<ref name="Concrete Supplier for Landmark Tower">{{cite news|title=Concrete Supplier for Landmark Tower|newspaper=Construction Week Online |date=19 April 2011 |url=http://www.constructionweekonline.com/article-11966-unibeton-aims-for-93-co2-reduction/|url-status=live|archive-url=https://web.archive.org/web/20130515025317/http://www.constructionweekonline.com/article-11966-unibeton-aims-for-93-co2-reduction/|archive-date=15 May 2013}}</ref><ref name="The world record Concrete Supplier for Landmark Tower Unibeton Ready Mix">{{cite web|title=The world record Concrete Supplier for Landmark Tower Unibeton Ready Mix|url=http://www.aeconline.ae/leading-uae-construction-supplier-to-reduce-co2-emissions-in-concrete-product-27039/news.html|url-status=live|archive-url=https://web.archive.org/web/20121124093945/http://www.aeconline.ae/leading-uae-construction-supplier-to-reduce-co2-emissions-in-concrete-product-27039/news.html|archive-date=24 November 2012}}</ref> The pour (a part of the foundation for the Abu Dhabi's [[The Landmark (Abu Dhabi)|Landmark Tower]]) was 16,000 cubic meters of concrete poured within a two-day period.<ref>{{cite web|url=http://www.leighton.com.au/verve/_resources/AlHabtoorIssue24.pdf |publisher=Al Habtoor Engineering |archive-url=https://web.archive.org/web/20110308031844/http://www.leighton.com.au/verve/_resources/AlHabtoorIssue24.pdf |archive-date=8 March 2011
|title=Abu Dhabi – Landmark Tower has a record-breaking pour |date=September–October 2007| page= 7}}</ref> The previous record, 13,200 cubic meters poured in 54 hours despite a severe tropical storm requiring the site to be covered with [[tarpaulin]]s to allow work to continue, was achieved in 1992 by joint Japanese and South Korean consortiums [[Hazama Corporation]] and the [[Samsung C&T Corporation]] for the construction of the [[Petronas Towers]] in [[Kuala Lumpur]], Malaysia.<ref>National Geographic Channel International / Caroline Anstey (2005), Megastructures: Petronas Twin Towers</ref>

The world record for largest continuously poured concrete floor was completed 8 November 1997, in [[Louisville, Kentucky|Louisville]], Kentucky by design-build firm EXXCEL Project Management. The monolithic placement consisted of {{convert|225000|sqft|m2}} of concrete placed in 30 hours, finished to a flatness tolerance of F<sub>F</sub> 54.60 and a levelness tolerance of F<sub>L</sub> 43.83. This surpassed the previous record by 50% in total volume and 7.5% in total area.<ref>{{cite web
 |title       = Continuous cast: Exxcel Contract Management oversees record concrete pour
 |website     = concreteproducts.com
 |date        = 1 March 1998
 |url         = http://concreteproducts.com/mag/concrete_continuous_cast_exxcel/?smte=wr
 |access-date  = 25 August 2009
 |archive-url  = https://web.archive.org/web/20100526044112/http://concreteproducts.com/mag/concrete_continuous_cast_exxcel/?smte=wr
 |archive-date = 26 May 2010
 |df          = dmy-all
}}
</ref><ref>[http://www.exxcel.com/ Exxcel Project Management – Design Build, General Contractors] {{webarchive|url=https://web.archive.org/web/20090828125821/http://www.exxcel.com/ |date=28 August 2009}}. Exxcel.com. Retrieved 19 February 2013.</ref>

The record for the largest continuously placed underwater concrete pour was completed 18 October 2010, in New Orleans, Louisiana by contractor C. J. Mahan Construction Company, LLC of Grove City, Ohio. The placement consisted of 10,251 cubic yards of concrete placed in 58.5 hours using two concrete pumps and two dedicated concrete batch plants. Upon curing, this placement allows the {{convert|50180|sqft|m2|adj=on}} cofferdam to be dewatered approximately {{convert|26|ft|m}} below sea level to allow the construction of the [[Industrial Canal|Inner Harbor Navigation Canal]] Sill & Monolith Project to be completed in the dry.<ref>{{Cite web |url=https://www.construction.com/toolkit/reports |access-date=2022-08-13 |website=www.construction.com|title=Contractors Prepare to Set Gates to Close New Orleans Storm Surge Barrier |archive-url=https://web.archive.org/web/20130113043115/http://texas.construction.com/texas_construction_news/2011/0512_orleansstormsurgebarrier.asp|archive-date=13 January 2013|date=12 May 2011}}</ref>

== Art ==
Concrete is used as an artistic medium.<ref>{{Cite journal |last=Rider |first=Alistair |date=2015-07-03 |title=The Concreteness of Concrete Art |url=https://www.tandfonline.com/doi/full/10.1080/13534645.2015.1058887 |journal=Parallax |volume=21 |issue=3 |pages=340–352 |doi=10.1080/13534645.2015.1058887 |issn=1353-4645|hdl=10023/10329 |hdl-access=free }}</ref> Its appearance is also imitated in other media: for example Congolese artist [[Sardoine Mia]] creates canvases that look like concrete surfaces.<ref name=":2">{{Cite web |title=Distinction : Sardoine Mia, lauréate du prix " Faces of peace and art " {{!}} Le Courrier de Kinshasa |url=https://www.lecourrierdekinshasa.com/node/142647 |access-date=2025-02-16 |website=www.lecourrierdekinshasa.com}}</ref>

==See also==
<!---This list has been trimmed to articles that pertain directly to concrete as a material or product.--->
* {{annotated link|Concrete leveling}}
* {{annotated link|Concrete mixer}}
* {{annotated link|Concrete masonry unit}}
* {{annotated link|Concrete plant}}
* [[Eurocode 2: Design of concrete structures]]
* {{annotated link|Heavy metals}}
* {{annotated link|Hempcrete}}
* {{annotated link|Particulates}}
* {{annotated link|Schmidt hammer}}
* {{annotated link|Syncrete}}
* {{annotated link|Thermal integrity profiling}}

==References==
{{Reflist}}

==Further reading==
* {{cite web |title=The world's growing problem with concrete, the world's most destructive material |date=6 Mar 2023 |publisher=BBC Reel |format=Video |url=https://www.bbc.com/reel/video/p0f6jmwc/the-world-s-growing-problem-with-concrete}}

== External links ==
{{Commons category|Concrete}}
* [https://web.archive.org/web/20190504100410/https://www.constructiontest.org/concrete-meaning-properties-strength-advantages-construction/ Advantage and Disadvantage of Concrete]
* {{Skeptoid | id=4813 | number=813 | date=4 January 2022 | title=Why You Need to Care About Concrete | access-date=14 May 2022}}
* {{YouTube|rWVAzS5duAs|Getting Buried in Concrete to Explain How It Works}}
* [https://openresearch.surrey.ac.uk/view/pdfCoverPage?instCode=44SUR_INST&filePid=13140253340002346&download=true Release of ultrafine particles from three simulated building processes]
* Concrete: [https://sustainabilitydocs.com/concrete-the-quest-for-greener-alternatives/ The Quest for Greener Alternatives]
 
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