Non-expansive delayed ettringite formation in low sulphate and low alkali cement mortars

This paper identifies the critical cement parameters that cause expansive delayed ettringite formation (DEF) and compares them with Australian cement standards and specifications. The comparison shows that general-purpose (GP) cements adhering to Standards Australia and specifications stipulating low sulphate, alkali contents may not be prone to expansive DEF. However, there is a lack of experimental evidence supporting the low risk of Australian cements for expansive DEF. Hence, in this study, the susceptibility of Australian GP cements to expansive DEF under different heat curing temperatures up to 90 degrees C have been studied. Further, these cements have been chemically modified to simulate the characteristics of cements used where deleterious DEF is observed in field cases. The testing protocol included long-term mortar expansion studies supported by phase and microstructural analyses. The results indicate that mortars containing Australian GP cements do not exhibit DEF expansion. Furthermore, increasing the cement sulphate content to 4% or alkali content to 1% did not result in DEF expansion. However, for cements where both the sulphate and alkali contents were increased to 4% and 1%, respectively, mortars generated significant expansion associated with ettringite precipitation. Overall, the results obtained from this study indicate that GP cements complying with Standards Australia and specifications for sulphate and alkali limits are not susceptible to expansive DEF.