Ceramics-Silikáty 68, (1) 67 - 79 (2024)

Compositional and microstructural changes with respect to the progressive alkali-carbonate reaction (ACR) during two years of accelerated ageing in concretes with silica-free dolomite aggregates and blast furnace cement CEM III were monitored. It was observed that the addition of slag substantially reduces the kinetics of the reactions involved in the ACR mechanism. CO₃^2- ions are released during the dedolomitisation to catalyse slag hydration, producing an Mg-Si-Al-gel phase, which encloses unreacted slag particles. Additionally, slag hydration is a source of soluble Ca- and Si-involving species helping in CSH or CSAH formation in the vicinity of the decaying slag particles. Strength development in BSF-containing concretes during ageing is strongly related to the progress of slag hydration. While CSH and CSAH contribute to strength increase, the Mg-Si-Al-gel phase development reduces the mechanical strength of the monitored concrete systems.