Sustainability of cement-stabilised clay: sulfate resistance

Sulfate attack on cement-stabilised soil is a durability problem which is directly related to the sustainability of the foundations. In this study, an experimental framework was established to evaluate the effects of sulfate attack on the strength and penetrability properties of cement-stabilised kaolin clay. Specimens incorporating ordinary Portland, pozzolanic and sulfate-resistant cements were compacted by standard Proctor effort, later cured for 1, 7, 28 and 90 d. Sodium and magnesium sulfates were used at concentrations of 0.3, 0.5 and 1%. At the end of the curing periods, the strength and penetrability characteristics of specimens were determined by conducting unconfined compressive strength and chloride-ion penetration tests. The results revealed that increase in cement content and curing time led to evident increase in strength and decrease in penetrability. Moreover, magnesium sulfate salt adversely affected hydration bonding between soil and cement in stabilised specimens. Increase in cement content caused increases in unconfined compressive strength; however, the rate of strength gain decreased in specimens exposed to sulfate attack. After 7 d of curing, the penetrability of specimens incorporating normal Portland cement is lower compared with that of other specimens including other types of cements; nevertheless, the reverse situation is valid after 28-d curing.