STUDY ON THE COMBINED ALKALI SILICA REACTION AND DELAYED ETTRINGITE FORMATION

Abstract

While expansive reaction due to the Alkali-Silica Reaction (ASR) and Delayed Ettringite
Formation (DEF) have been found to be correlated and the appearances of their cracking patterns are similar,
the dominance of DEF or ASR on the expansion is still unknown. However, it is generally believed that ASR
and DEF cause crack formation leading to a deleterious effect on concrete. This study investigated the
expansion due to ASR, DEF and their combination coupled with the dynamic Young’s modulus (ED) and water
absorption in concrete test specimens, some of which contained reactive aggregates through a replacement of
30 wt% of the coarse aggregate. K2SO4 and CaSO4 were further added (2.5 wt% SO3 addition) to study the
effect of reactive metal ions with sulphate ion on ASR and DEF. Some specimens were cured at an elevated
temperature of 90 C at the early age to accelerate the DEF expansion. The specimens with the addition of SO3
showed higher expansion and lower ED as compared to those without SO3, regardless of the curing temperature.
The expansion was significant and rapid with the reduction of ED when reactive aggregate and K2SO4 were
used. According to the expansion with ED and moisture absorption, it is indicated that ASR may promote DEF
to cause the expansion and subsequent damage after hardening when adequate sulphate and a high temperature
are concurrently present.