Impact of sulfate attack on mechanical properties and hydraulic conductivity of a cement-admixed clay

Context and purpose Treatment of clay with cement has been used for various ground improvement and geoenvironmental applications including vertical barriers to isolate contaminated areas. An important issue with cement-treated clays is their durability especially when applied in chemically aggressive environments. The purpose of this study is to evaluate the impact of chemical degradation on engineering properties of cement-treated clay. Methodology The mechanical and hydraulic behaviors of a cement-treated clay in contact with water and an aggressive sodium sulfate solution were investigated. Bender elements were installed in a flexible-wall hydraulic conductivity cell to simultaneously monitor the small-strain shear modulus (G0) and the hydraulic conductivity (k) of the cement-admixed clay. Results During permeation with clean water, an increase of G0 and a gradual decrease of k with time were observed due to cement hydration. Conversely, after permeation with the sulfate solution, a sudden decrease of G0 and a gradual increase of k were recorded. Conclusions G0 measurements provided evidence of immediate deterioration of the sample as it comes in contact with sulfates. However, in order to have significant impact on the permeability, a network of interconnected preferential flow paths had to first develop through the whole sample. Monitoring of G0 was shown to provide valuable additional information to study the impact of chemical degradation of cement-treated clays.