Investigation of sulphate attack on limestone-calcined clay cement mortars

Calcined clay, especially in combination with limestone powder, is emerging as an excellent supplementary cementitious material. While a number of studies have reported on the pozzolanic performance of calcined clay blended cements, a detailed investigation on the durability characteristics is not available in the existing literature. In this context, the resistance of calcined clay blended cements against sulphate attack needs to be comprehensively studied to understand its potential for use in sulphate rich environments. This paper reports an experimental investigation on cementitious mortars that are subjected to (i) continuous immersion and (ii) alternate wetting and drying, in highly concentrated sodium sulphate solutions, with a methodology based loosely on ASTM C1012. The length change and flexural strengths are monitored periodically to get an assessment of the degree of damage. The cementitious systems considered in the study are: (i) OPC, (ii) OPC with 30% fly ash, and (iii) Limestone calcined clay cement (LC3). The alterations in microstructure are studied using X-ray diffraction and thermal analysis. The work reported in this paper is part of a larger project that investigates the potential for limestone—calcined clay based cementitious binders in concrete.