Effect of sulfate resistance cement treatment on saline soil (Sebkha) subgrades

Sebkha soil, a type of saline soil, is considered a challenging foundation material for pavement design due to its unfavorable behavior upon exposure to moisture. To overcome this problem, sulfate resistance cement (SRC) is often used instead of Portland cement since the chosen SRC has proved its ability to minimize expansion phase formation. This study examines the potential stabilization of Sebkha soil from the Ain M'lila region in Algeria using SRC. Four trial percentages of SRC were used (0, 2, 5, and 8% by dry mass) while preparing samples and different tests were conducted to determine mechanical strength, X-ray diffraction(XRD), thermogravimetric analysis(TGA), Fourier transform infrared spectroscopy (FTIR), pH, and electrical conductivity (EC) properties. After 14 days, treated specimens showed an increase in unconfined compressive strength (UCS) varying from 4.18 to 11.56-fold compared to untreated soil, correlating with an increase of SRC dosages from 2 to 8%. After 28 days of curing, the 8% SRC mixture showed minimal strength loss. The strength enhancement is attributed to hydration gels (such as C-S-H) and Friedel's salt (Fs) formation. This conclusion was confirmed by the results of XRD, TGA, and FTIR analyses. A decrease in the halite (NaCl) phase corresponded to Fs appearance, indicating the role of NaCl in Fs formation. Slight increases in pH and EC after 14 days suggested hydroxide (OH-) increase, confirming Fs precipitation. Initially, Fs acts as a void filler, but since C-S-H formation reduces available space, additional Fs precipitation increases pressure, which leads to a minor strength loss prior to 28 days of curing. The modified subgrade resulted in a 30% reduction in total pavement thickness and the cost of the raw material (SRC-Sebkha soil mixture) used in the treated subgrade is 5.7 times lower than that of the raw material used in the untreated subgrade, demonstrating the economic viability of SRC stabilization for Sebkha soils in pavement construction.