Inhibition of internal expansive reactions in cement based materials with mineral additions

Abstract

The degradation of concrete structures caused by internal sulphate reaction, with delayed etringite formation (DEF) and alkali-silica reaction (ASR) is a problem that affects many concrete structures worldwide (Divet et al., 2004). When these reactions occur their effects are particularly dangerous since their reaction products are extremely expansive causing the cracking of the concrete, contributing for a large reduction in the lifetime of the structure and in some extreme cases forcing its demolition. Hence, there is an urgent need to find preventive methods that may inhibit such reactions in new concrete structures. Today, it’s well known that the use of supplementary cementicious materials, e.g. type II mineral additions, could sustain this degradation form. Moreover, their effect depends on the chemical and mineralogical composition and also the cement content replacement. This paper presents the findings of a long-term study (Santos Silva et al., 2006; Divet et al., 2006) on the expansion rate and microstructure of concretes with different amounts of mineral additions, like fly ash, metakaolin, ground granulated blast-furnace slag, silica fume and limestone filler. For this purpose different concrete compositions were produced by using the same cement type (CEM I 42.5R) and water/cement (w/c) ratio. The results of the blended-concrete compositions were compared with those of control compositions, and the conclusions were extracted