Editing Bitumen (section)

=== Bitumen emulsion ===
[[File:Bitumenemulsion.jpg|thumb|Volume-weighted particle size distribution of 2 different asphalt emulsions determined by laser diffraction]]
Bitumen emulsions are colloidal mixtures of bitumen and water. Due to the different surface tensions of the two liquids, stable emulsions cannot be created simply by mixing. Therefore, various emulsifiers and stabilizers are added. Emulsifiers are amphiphilic molecules that differ in the charge of their polar head group. They reduce the surface tension of the emulsion and thus prevent bitumen particles from fusing. The emulsifier charge defines the type of emulsion: anionic (negatively charged) and cationic (positively charged).<ref name="Al-Mohammedawi-2022">{{Cite journal |last1=Al-Mohammedawi |first1=Ahmed |last2=Mollenhauer |first2=Konrad |date=9 March 2022 |title=Current Research and Challenges in Bitumen Emulsion Manufacturing and Its Properties |journal=Materials |language=en |volume=15 |issue=6 |page=2026 |doi=10.3390/ma15062026 |issn=1996-1944 |pmc=8952829 |pmid=35329476|bibcode=2022Mate...15.2026A |doi-access=free }}</ref> The concentration of an emulsifier is a critical parameter affecting the size of the bitumen particles—higher concentrations lead to smaller bitumen particles.<ref name="Al-Mohammedawi-2022" /> Thus, emulsifiers have a great impact on the stability, viscosity, breaking strength, and adhesion of the bitumen emulsion.<ref name="Al-Mohammedawi-2022" /> The size of bitumen particles is usually between 0.1 and 50{{nbs}}μm with a main fraction between 1{{nbs}}μm and 10{{nbs}}μm. Laser diffraction techniques can be used to determine the particle size distribution quickly and easily.<ref name="Al-Mohammedawi-2022" /><ref>{{Cite web|url=https://wiki.anton-paar.com/at-de/particle-size-in-building-materials-from-cement-to-bitumen/|title=Particle Size in Building Materials: From Cement to Bitumen |website=Anton Paar}}</ref> Cationic emulsifiers primarily include long-chain amines such as imidazolines, amido-amines, and diamines, which acquire a positive charge when an acid is added.<ref name="Al-Mohammedawi-2022" /> Anionic emulsifiers are often fatty acids extracted from lignin, tall oil, or tree resin saponified with bases such as NaOH, which creates a negative charge.<ref name="Al-Mohammedawi-2022" />

During the storage of bitumen emulsions, bitumen particles sediment, agglomerate (flocculation), or fuse (coagulation), which leads to a certain instability of the bitumen emulsion. How fast this process occurs depends on the formulation of the bitumen emulsion but also storage conditions such as temperature and humidity. When emulsified bitumen gets into contact with aggregates, emulsifiers lose their effectiveness, the emulsion breaks down, and an adhering bitumen film is formed referred to as 'breaking'. Bitumen particles almost instantly create a continuous bitumen film by coagulating and separating from water which evaporates. Not each asphalt emulsion reacts as fast as the other when it gets into contact with aggregates. That enables a classification into Rapid-setting (R), Slow-setting (SS), and Medium-setting (MS) emulsions, but also an individual, application-specific optimization of the formulation and a wide field of application<ref name="Al-Mohammedawi-2022" /> (1). For example, Slow-breaking emulsions ensure a longer processing time which is particularly advantageous for fine aggregates<ref name="Al-Mohammedawi-2022" /> (1).

Adhesion problems are reported for anionic emulsions in contact with quartz-rich aggregates. They are substituted by cationic emulsions achieving better adhesion. The extensive range of bitumen emulsions is covered insufficiently by standardization. DIN EN 13808 for cationic asphalt emulsions has been existing since July 2005. Here, a classification of bitumen emulsions based on letters and numbers is described, considering charges, viscosities, and the type of bitumen.<ref name="Al-Mohammedawi-2022" /> The production process of bitumen emulsions is very complex. Two methods are commonly used, the "Colloid mill" method and the "High Internal Phase Ratio (HIPR)" method.<ref name="Al-Mohammedawi-2022" /> In the "Colloid mill" method, a rotor moves at high speed within a stator by adding bitumen and a water-emulsifier mixture. The resulting shear forces generate bitumen particles between 5{{nbs}}μm and 10{{nbs}}μm coated with emulsifiers.<ref name="Al-Mohammedawi-2022" /> The "High Internal Phase Ratio (HIPR)" method is used for creating smaller bitumen particles, monomodal, narrow particle size distributions, and very high bitumen concentrations. Here, a highly concentrated bitumen emulsion is produced first by moderate stirring and diluted afterward. In contrast to the "Colloid-Mill" method, the aqueous phase is introduced into hot bitumen, enabling very high bitumen concentrations.<ref name="Al-Mohammedawi-2022" />

T The "High Internal Phase Ratio (HIPR)" method is used for creating smaller bitumen particles, monomodal, narrow particle size distributions, and very high bitumen concentrations. Here, a highly concentrated bitumen emulsion is produced first by moderate stirring and diluted afterward. In contrast to the "Colloid-Mill" method, the aqueous phase is introduced into hot bitumen, enabling very high bitumen concentrations (1).he "High Internal Phase Ratio (HIPR)" method is used for creating smaller bitumen particles, monomodal, narrow particle size distributions, and very high bitumen concentrations. Here, a highly concentrated bitumen emulsion is produced first by moderate stirring and diluted afterward. In contrast to the "Colloid-Mill" method, the aqueous phase is introduced into hot bitumen, enabling very high bitumen concentrations (1).

Bitumen emulsions are used in a wide variety of applications. They are used in road construction and building protection and primarily include the application in cold recycling mixtures, adhesive coating, and surface treatment (1). Due to the lower viscosity in comparison to hot bitumen, processing requires less energy and is associated with significantly less risk of fire and burns.<ref name="Al-Mohammedawi-2022" /> [[Chipseal]] involves spraying the road surface with bitumen emulsion followed by a layer of crushed rock, gravel or crushed slag. Slurry seal is a mixture of bitumen emulsion and fine crushed aggregate that is spread on the surface of a road. Cold-mixed asphalt can also be made from bitumen emulsion to create pavements similar to hot-mixed asphalt, several inches in depth, and bitumen emulsions are also blended into recycled hot-mix asphalt to create low-cost pavements. Bitumen emulsion based techniques are known to be useful for all classes of roads, their use may also be possible in the following applications: 1. Asphalts for heavily trafficked roads (based on the use of polymer modified emulsions) 2. Warm emulsion based mixtures, to improve both their maturation time and mechanical properties 3. Half-warm technology, in which aggregates are heated up to 100 degrees, producing mixtures with similar properties to those of hot asphalts 4. High performance surface dressing.<ref>Read, J. and Whiteoak, D., 2003. ''The Shell Bitumen Handbook''. Thomas Telford.</ref>