Jian-kang Chen a,*, Min-qiang Jiang b
 a Department of Mechanics and Engineering Science, Ningbo University, Ningbo 315211, China
 b State Key Laboratory of Non-linear Mechanics (LNM), Institute of Mechanics, Chinese Academy of Sciences, Beijing 100871, China

ABSTRACT:

The magnitude evolution of ettringite and gypsum in hydrated Portland cement mortars due to sulfate attack was detected by X-ray powder diffraction. The influences of sulfate concentration and water-to-cement ratio on the evolution of ettringite and gypsum were investigated. Experimental results show that the magnitude of ettringite formation in sodium sulfate solution follows a three-stage process, namely, the ‘penetration period’, ‘enhance period of strength’, and ‘macro-crack period’. The cracking of concrete materials is mainly attributed to the effect of ettringite. The gypsum formations  occurred
in two stages, the ‘latent period’ and the ‘accelerated period’. The gypsum formation including ettringite formation was relative to the linear expansion of mortars to some extend. Both water-to-cement ratio and sulfate concentration play important roles in the evolution of ettringite and gypsum.