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Macadam
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===McAdam's methods=== [[File:macadam road 1850s.jpg|thumb|A macadam road in [[Nicolaus, California]], {{circa|1850s}}]] McAdam's method was simpler yet more effective at protecting roadways: he discovered that massive foundations of rock upon rock were unnecessary and asserted that native soil alone would support the road and traffic upon it, as long as it was covered by a road crust that would protect the soil underneath from water and wear.<ref name=ColossusofRoads>{{citation |author=Craig, David|title=The Colossus of Roads |work=Palimpsest |publisher=Strum.co.uk |url=http://www.strum.co.uk/palimps/macadam.htm |access-date=18 June 2010}}</ref> An under-layer of small angular broken stones would act as a solid mass. Keeping the surface stones smaller than the width of a wheel made for a good running surface. The small surface stones also provided low stress on the road, so long as it could be kept reasonably dry.<ref name=Lay1992pp76-77>Lay (1992), pp. 76β77</ref> Unlike Telford and other road builders of the time, McAdam laid his roads almost level. His {{convert|30|ft|m|adj=mid|-wide}} road required a rise of only {{convert|3|in|cm}} from the edges to the centre. Cambering and elevation of the road above the [[water table]] enabled rain water to run off into ditches on either side.<ref name=McAdam1824p38>McAdam (1824), p. 38</ref> Size of stones was central to McAdam's road building theory. The lower {{cvt|20|cm|in|0|adj=on|order=flip}} road thickness was restricted to stones no larger than {{convert|7.5|cm|in|0|order=flip}}. The upper {{convert|5|cm|in|adj=mid|0|-thick|order=flip}} layer of stones was limited to stones {{convert|2|cm|in|frac=8}} in diameter; these were checked by supervisors who carried scales. A workman could check the stone size himself by seeing if the stone would fit into his mouth. The importance of the 2 cm stone size was that the stones needed to be much smaller than the {{convert|4|in|cm|0|spell=in|adj=on}} width of the iron [[carriage]] wheels that travelled on the road.<ref name=Lay1992p75/> McAdam believed that the "proper method" of breaking stones for utility and rapidity was accomplished by people sitting down and using small hammers, breaking the stones so that none of them was larger than {{convert|6|oz|g|-1|spell=in}} in weight. He also wrote that the quality of the road would depend on how carefully the stones were spread on the surface over a sizeable space, one shovelful at a time.<ref name=McAdam1824pp39-40>McAdam (1824), pp. 39β40</ref> McAdam directed that no substance that would absorb water and affect the road by frost should be incorporated into the road. Neither was anything to be laid on the clean stone to bind the road. The action of the road traffic would cause the broken stone to combine with its own angles, merging into a level, solid surface that would withstand weather or traffic.<ref name=McAdam1824p41>McAdam (1824), p. 41</ref>
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