The Mechanistic differences between alkali silica and alkali carbonate reactions as studied by X-ray diffraction

The differences in the expansive mechanisms of both Alkali Silica (ASR) and Alkali Carbonate Reactive (ACR) rock samples were examined using X-ray diffraction techniques. Reactive aggregates were ground and placed in 1 molar NaOH solution at both 80 and 20°C. Multiple measurements were taken over a 150 day time period. Volume and composition changes were noted. Composition changes were tracked using quantitative Rietveld analysis methods. The observation of a new semi-crystalline tobermorite-like phase common to both ASR and ACR samples raises the possibility of similar mechanisms at work in both processes. However the tobermorite-like phase is less abundant in the alkali silica samples. This new phase only occurred at 80°C, hence the possibility of a temperature induced mechanistic changes is debated.
The 12th International Conference on Alkali-Aggregate Reaction in Concrete: 15 October 2004, Beijing, China