Impact Of Expanding Agent On Delayed Ettringite Formation In Concrete

Delayed ettringite formation (DEF) is a kind of initial sulfate attack, whichnormally occurs in concrete experienced high curing temperature (generallyconsidered to be above about70℃). The destruction mechanism of DEF is usuallyconsidered to be the formation of ettringite in hardened concrete, as ettringiteexpands, the concrete results in durability damage. The source of DEF is meanlybelieved to be the decomposition of early formed ettringite caused by hightemperature. In China, some large concrete structures and long concrete structuressuch as concrete slab, waterproof wall are usually mixed with expanding agent, withettringite as expansion source. In these concrete DEF is likely to occur. Therefore,this paper researches the impact of temperature and expansive on DEF, as well asthe mitigation effect of fly ash, silica fume on DEF with the LCPC methodcombining SEM and EDXA.The research shows that there are two modules of ettringite crystal growing inconcrete as this paper calls: Clusters-like ettringite crystals and dense ettringiteballs. It is found that expanding agent can significantly increase the ettringitecrystals formed in sample holes, and improve the expansion of the samples, as10%of the expanding agent mixed in concrete can increase the maximum expansion rateby about40%. And high curing temperature can also increase the maximumexpansion rate of the sample, by45%and80%for concrete without and with10%of expanding agent. Until the sample soaked in water for20weeks, sample cured at80℃expands the most. Fly ash and silica fume can significantly reduce theexpansion of the sample cured at each temperature, reducing delayed ettringiteformation in holes. Fly ash also changes the crystal morphology of ettringite.