Sulfate attack on hardened cement paste

Hardened cement paste specimens made with fifferent cement types and varying water-cement ratios (w/c) were immersed in 5% sodium sulfate solution maintained at constant pH value of 6. The distribution curves for ettringite, gypsum, and portlandite phases were obtained by using layer by layer XRD analysis and interpreted in terms of material damage due to sulfate attack. The mechanism of sulfate attack is evaluated in regard to the leaching of Ca(OH)2 and formation of gypsum and ettringite.