Stabilization Techniques for Reactive Aggregate in Soil-Cement Base Course

Anhydrite (CaSO4) beds occur as a cap rock on a salt dome in Winn Parish in north Louisiana. Locally known as Winn Rock, it has been quarried for gravel for road building. It has been used as a surface course for local parish and logging roads. Stabilization of these roads with Type I portland cement followed by an overlay of asphaltic concrete sometimes resulted in heaving. The causes of heaving and possible solutions were investigated. In the laboratory, 2 in. x 4 in. molds of Winn Rock containing soil were stabilized with various cementitious mixes and cured in a 40 deg C water bath, in a 100% relative humidity room, in a sealed plastic bag at room temperature, and in air. The mixes contained 5% to 20% cementitious material. The cementitious materials were Type I portland cement, lime, and supplementary cementitious materials (SCM) such as granulated blast furnace slag (BFS), Class C fly ash, silica fume and amorphous silica. The expansion of the specimens over time was monitored. Mineralogical and microstructural analyses of the specimens were also performed over time and correlated to expansion. The Winn Rock gravel was partially weathered in the soil to gypsum, which was detected in all size fractions. The highest amount of expansion occurred in Winn Rock soil stabilized by lime cured at 40 deg C in a water bath. The magnitude of the expansion is 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 reduced the expansion by almost an order of magnitude even at the highest moisture content. No expansion was detected when a mixture of Class C fly ash and amorphous silica was used as a partial replacement. The costs of portland cement and blast furnace slag mixtures are less than the cost of portland cement only. The addition of amorphous silica or silica fume to the cementitious mix will increase the cost significantly.