Effect of metakaolin on alkali-silica reaction in concrete: Fid-Bau Portal

Effect of metakaolin on alkali-silica reaction in concrete

Ramlochan, T. / Thomas, M. / Gruber, K.A.

This article reports on a study to evaluate the efficacy of high-reactivity metakaolin (HRM) in controlling expansion due to alkali-silica reaction (ASR). The expansion of concretes and mortars containing 0-20% HRM as a partial replacement for OPC was studied. Concrete prisms were prepared according to the CAN/CSA A23.2-14A concrete prism method with alkali-silica reactive aggregates: a siliceous limestone (Spratt) and a greywacke-argillite gravel (Sudbury). The amount of HRM required to control the expansion to <0.04% at 2 years was found to be between 10% and 15% depending on the aggregate. A modified version of the accelerated mortar bar method (CAN/CSA A23.2-25A) was also conducted with HRM and both reactive aggregates. In addition to expansion testing, the chemistry of expressed pore solutions from cement pastes containing 0%, 10%, and 20% metakaolin was determined over a 2-year period. Incorporation of 20% metakaolin was found to significantly reduce the long-term OH^-, Na^PLU, and K⁺ ion concentrations in pore solutions. The reduction in the pH and the alkalinity of pore solutions correlate well with the observed reduction in expansion of the concrete prisms and mortar bars.