Influence of specific surface area on sulfate attack-induced expansion of cement-treated aggregates

Sulfate attack-induced expansion of cement-treated aggregates is a well-known problem to be addressed causing remarkable heave in road and railway subgrades. The specific surface area (SSA) of the materials influences chemical reactions significantly. In this study, cement, sodium sulfate, and basalt powder were ground in a ball mill for 0 (without grinding), 5, 10, 30, and 60 min respectively to achieve different SSA gradients. Under the curing condition of a constant temperature of 10 degrees C and humidity of 70%, with 5% cement, the effects of sodium sulfate contents and SSA gradients on the expansion of sulfate attack in cement-treated aggregate (SACA) were investigated during 60 days in laboratory. Based on nitrogen absorption methods, microscopic tests, and swelling tests, the results show that, grinding within 60 min, the respective peak value of SSAs of cement, mixture of 3% (or 8%) sodium sulfate and basalt powder, and mixture of 3% (or 8%) sodium sulfate, cement, and basalt powder was 1.867 m(2)/g, 1.109 m(2)/g (or 1.393 m(2)/g), and 1.128 m(2)/g (or 1.404 m(2)/g), respectively. The SSAs increase as the aggregates refined, then decrease as the aggregates gathered. The strain variation can be generally divided into four stages with 3% sodium sulfate attack in cement-treated aggregate (3% SACA): rapid strain increase, short stagnation, continuous heave, and constant strain. Two stages of strain variation have been observed with 8% sodium sulfate attack in cement-treated aggregate (8% SACA): rapid strain increase, and a constant strain. Finer needle-like ettringite crystals (average length: 0.5-1 mu m) filling in the smaller holes produce the greater expansion induced by SACA. Based on grey incidence analysis, the SSAs of cement, mixture of sodium sulfate and basalt powder (S+B), and the whole mixture of cement, sodium sulfate, and basalt powder (C+S+B) have a significant effect on strain. This work provides theoretical support for amending SACA at the SSA level.