HPCs and Alkali Silica Reactions. The Double Role of Pozzolanic Materials
The quality of a high performance concrete (HPC) formulation must guarantee long-term physico-chemical resistance of the material to its environment. Effective preventive solutions against Alkali-Silica/Silicate Reactions (ASR) exist and are particularly compatible with the notion of HPCs. There are few references from real-life applications as far as durability in relation to ASR is concerned. In the absence of pozzolanic materials, low water/binder ratios of high performance concretes should lead to increases in alkalinity of the interstitial solution and hence favor alkali-silica reaction. Pozzolanic materials act both on the chemical nature of concrete and on its microstructure. This double role is fulfilled to an even greater degree if there is a homogeneous distribution of constituents in the mixture. Use of pozzolanic additions, the quest for optimum compactness and reduced quantities of water contribute overall to obtaining a durable HPC as far as alkali aggregate reactions are concerned. The reaction products have very variable morphologies and compositions.