Evaluation of the potential for delayed ettringite formation in concrete

Abstract

Delayed ettringite formation (DEF) is commonly referred to as heat-induced internal sulfate attack, which affects the durability and strength of the concrete like in alkali–silica reaction (ASR). Several researches have been done to identify the factors governing DEF and to quantify the effect and also to provide necessary prevention methods. However, most of the factors are yet to be investigated and quantified. It is evident that when fly ash is present, the risk of formation of delayed ettringite is low but its behavior with different types of cement have not been found out yet. DEF is long term deterioration in concrete and for effects of DEF to appear in actual structures may take 2 - 20 years. There is no standardized accelerated method of testing cement- aggregate combinations for premature deterioration due to DEF but there are test methods proposed by several researchers. This paper presents an evaluation of potential of DEF for different cement types available in the local market based on FU’s Method. In this method, expansion of mortar bar specimens (25mm × 25mm × 285mm) is monitored after specimens are subjected to specified heating and drying cycles. Evaluation of DEF was carried out for Ordinary Portland Cement, Portland Limestone Cement, Fly Ash Blended Cement and Triple Blended Cement. It was found that there is a significant effect of cement type on DEF. Further it was found that the potential for formation of delayed ettringite is less with partial replacement of OPC with supplementary cementitious materials such as fly ash. Furthermore it has been revealed that the risk of formation of DEF in fly ash blended cements is less than in Ordinary Portland cement and Portland limestone cement. It was also found that the influence of coarse aggregate phase on expansion due to DEF is significant.