Leachate testing for delayed ettringite formation potential in cementitious systems

Abstract

The aim of this research was to investigate the relation between leachate data and expansion due to delayed ettringite formation (DEF). These correlations have the potential for identifying the probability of delayed ettringite formation in a shorter time than the traditional method of monitoring expansion over time. Ions leached from the samples after heat curing of the cement paste were measured and the resultant data were used to calculate relative quasi-crystallization pressures within the cement microstructure. Potential relationships exist between these pressures, time to expansion initiation, and overall percent expansion of samples. The results indicate that sulfates and alkalis affect the onset and overall percent expansion observed. The calculated quasi-crystallization pressures strongly correlate with the observed overall percent expansion of mortar bars. Time to expansion initiation was negatively correlated with alkali content, indicating that cement with higher amounts of alkalis tends to expand at earlier ages. Overall, the leachate test corroborates earlier findings in the determination of DEF potential in cementitious materials and allows for the possible prediction of expansive behavior in 28 days or less using experimental results as opposed to cement composition.