ASR Expansion in Alkali-Free Cement Samples

ASR expansion is caused by the confined precipitation of an alkali gel, formed from the reaction of Alkalies in the cement paste pore solution and reactive silica in the aggregates. The role of alkali concentration on the development of the reaction has led to the formulation of guidelines imposing alkali thresholds when using potentially reactive aggregates. However, it is difficult, experimentally to verify the effect of very low alkali concentrations, due to alkalies being systematically present in cement paste. Even low-alkali cements can provide sufficient alkalies for the reaction of highly reactive aggregates. Further, some aggregates are suspected of releasing their own alkalies, and testing methods to evaluate this potential are still in development. Here, a clinker has been specially produced at a high temperature (above 1700 ℃) to almost eliminate all alkalies through volatilisation. Ground and sulphated, we obtain an alkali-free cement from this clinker. We test the expansion of samples prepared with this cement and known reactive and unreactive aggregates. We use the results from these experiments to evaluate the effect of very low alkali concentrations and aggregate alkali leaching in mortars.