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Proctor Testing

Maximum Dry Density (Standard/Moderate) – The Proctor test is used to determine the optimum moisture content for compacting a given soil, and to also determine the target density for contractors to use when compacting soil on the site. The soil sample is split into three to five samples, each with moisture contents that vary by roughly 2%. Each of the samples is compacted into a 1/30 cubic foot steel mold, using a standard number of blows from a calibrated hammer, with the sampler placed on a concrete slab or block. The dry density and moisture content of each sample are tested, and a roughly parabolic curve is plotted showing how density varies with moisture content. The peak of the curve is the maximum dry density and the optimum moisture content. Target densities in the field usually are 90% or 95% of the maximum dry density.