Using Natural Pozzolans to Improve the Sulfate Resistance of Cement Mortars

Abstract

Concrete in contact with a sulfate environment can severely degrade due to expansion accompanying the formation reaction products such as ettringite. The use of portland-pozzolan cement has been successful in mitigating this expansion. However, it is important to study the effectiveness of natural pozzolans to improve the resistance to attack by sulfates. This paper reports results of different portland-pozzolan cements containing different natural pozzolans and ASTM Types I, II, and V portland cements. The pozzolanic activity and composition of each pozzolan was evaluated. The susceptibility to sulfate attack was studied by measuring the expansion in mortar bars at different ages according to ASTM Method 1012 for 78 weeks. It was found that cements containing pozzolans with high activity or low alumina content improved the sulfate resistance. Also, the pozzolan content in the cement was found to be important.