Expansion Behavior of Portland Cement Mortars under Sulfate Attack

摘要

The expansion behaviors are studied on mortars at water-cement ratio (w/c)=0.4, 0.6, and 0.8, stored in sodium sulfate solutions with sulfate concentration of 0 ppm, 20,250 ppm, and 54,000 ppm, respectively. The mortars stored in control solution show no expansion, whereas the expansion of the ones exposed to sodium sulfate solutions occurs in two stages (i.e., "dormant" and "speedup" Stages). The high concentration of sulfate accelerates the expansion, but control of water-cement ratio (0.60 in this case) can put up higher resistance to sulfate attack. The XRD analysis shown that the macro-expansion depends on the formation and growth of both ettringite and gypsum. The analysis obtained by means of Sigmoidal Fit Method indicates that the microdamage evolution depends strongly on the average size of microvoids in the material.