Characterization of cement stabilized pond ash using FTIR spectroscopy

Pond ash is a mixture of fly ash and bottom ash obtained from thermal power plants. It has pozzolanic properties and is commonly treated with cement to impart cohesion and improve strength. The increase in strength gain in cemented pond ash is attributed to the hydration of cement and pozzolanic reactions due to silica present in the pond ash. Unconfined Compressive Strength (UCS) test is commonly used to determine the dosage of cement. While the strength gain is addressed by this test, the interaction mechanisms and the resulting compounds that are responsible for strength gain in such systems have not been identified at this point in time. In this study, an attempt is made to understand the interaction mechanisms between cement and pond ash by quantifying the influence of the dosage of cement, curing period, and curing temperature. FTIR spectroscopy is used for this purpose. Five dosages of cement (2, 4, 6, 8, and 24%), three variations in curing period (7, 14, and 28 days) and two different curing temperatures (27 °C and 50 °C) were adopted. Results showed that pond ash, used in this study, did not undergo any hydration reaction due to its low calcium content. In cemented pond ash, the hydration products formed in cement (Ca(OH)2) triggered pozzolanic reactions with silica present in pond ash to further form C-S-H, which is responsible for increased strength gain. The C-S-H formation did not vary linearly with cement content/curing period/curing temperature due to the pozzolanic reactions and the magnitude of influence exerted by each of these parameters depended on the other two parameters.