In situ Raman studies on cement paste prepared with natural pozzolanic volcanic ash and Ordinary Portland Cement

Raman Spectroscopy was used to track the free water and the cementitious gel phases when Ordinary Portland Cement (OPC) and tricalcium silicate (C₃S) were partially substituted by natural pozzolanic volcanic ash. Two different particle sizes of volcanic ash (VA), (namely 17 and 6 μm) were each used to substitute 10%, 30% and 50% of OPC and C₃S by weight. Particle size and concentration of VA significantly affected the hydration behavior of cement paste by influencing the water dynamics during the course of hydration. Increase in concentration of VA also led to an increase in “free water” during the course of hydration. Calcium silicate hydrate (C-S-H) phases along with calcium/magnesium based zeolites were detected as the concentration of volcanic ash increased in the mix. This work shows that Raman spectroscopy is a powerful tool to examine the hydration process when Portland cements are substituted by volcanic ashes of different sizes.