Performance of volcanic ash and pumice-based blended cements in sulphate and sulphate–chloride environments

Abstract

The deterioration of concrete structures due to sulphate and mixed sulphate—chloride in soils, groundwater and marine environments is a well-known phenomenon. The use of blended cements incorporating supplementary cementing materials and cements with low C3A content is becoming common in such aggressive environments. This paper presents the results of an investigation on the performance of volcanic ash (VA)- and finely ground volcanic pumice (VP)-based ASTM Type I and Type V (low C3A) blended cements (using 20% VA or VP as cement replacement) with varying immersion periods of up to 80 weeks in environments characterised by the conjoint presence of chlorides and sulphates. The effect of sulphate and sulphate—chloride environments on the strength and expansion characteristics of mortar specimens was evaluated. X-ray diffraction analysis and differential scanning calorimetry tests were also conducted to determine phase composition, pozzolanic activity and chloride binding of plain and blended cements. The performance of blended cements was found to be better in comparison with plain cements in terms of strength reduction and expansion characteristics and the performance was also found to depend on the type of cement (Type I or Type V). Results also indicate that the presence of chloride ions in the sulphate environment mitigates the sulphate attack in both plain and blended cements.