Stabilization of Sulfate-Containing Soil by Cementitious Mixtures Mechanical Properties

Winn Rock (CaSO ) gravel from a quarry in Winn Parish in north Louisiana was used extensively as a surface course for local parish roads. Stabilization of these roads with Type I portland cement followed by an overlay of asphaltic concrete resulted in heaving. A study was undertaken to investigate the cause or causes of the expansion as well as to identify an alternate means of stabilization. Specimens of representative soil from the affected area were stabilized in the laboratory using various cementitious materials and were cured using a variety of methods. The mix contained 5% to 20% cementitious material. The cementitious materials were Type I portland cement, lime, and supplementary cementing materials such as granulated blast furnace slag (BFS), Class C fly ash (CFA), silica fume, and an amorphous silica (AS). The unconfined compressive strength of the stabilized soil was determined. The effect of size fractions other than the gravel on the expansion was assessed, and the expansion of the specimens over time was monitored. The cement and BFS mixtures almost doubled the compressive strength of the specimens compared with portland cement alone. The finer size fractions were responsible for expansion. The magnitude of expansion was directly proportional to the amount of Type I portland cement, the amount of available moisture, and the curing temperature. Replacement of a part of the portland cement by BFS significantly reduced the amount of expansion even at the highest moisture content. No expansion was detected when CFA and AS partially replaced the cement.