The Role of Microstructure in Alkali-Silica Reaction Tests

Alkali-silica reactions were set off in cementitious mortars in different curing conditions, simulating short-term tests on reactivity. The investigated composites differed in some of their microstructural features. The total open porosity was modulated by changing the water/cement ratio and also by adding an air-entraining additive. By keeping the mortars' porosity as the only variable, the effect on the measured expansion was evaluated. The dependence on porosity, specifically on the microstructure, of the macroscopic expansion that was used to assess the reactivity of the aggregates was studied. In particular, the connectivity of the porous network in the material, which is the dimension of the most frequent capillary porosity, exerts an influence on the expansion rate and extent. The results obtained under different conditions underline that the microstructure, that is the porosity of a composite and its size, always plays an important role in influencing the extent of expansion, a role that should be investigated and analyzed more deeply in accelerated procedures.