Influence of Water Content on Hydration Products in Cement-Stabilized Pond Ash Using FTIR Spectroscopy

Pond ash is a mixture of fly ash and bottom ash obtained from thermal power plants. The cement treatment of pond ash results in improved cohesion and strength gain due to cement hydration and pozzolanic reactions. The optimum moisture content (OMC) obtained from standard Proctor compaction tests on untreated and cemented pond ash is about 25%. This study investigates the sufficiency of this OMC for complete hydration of cement, especially for higher dosages, in cement stabilized pond ash systems. The degree of hydration is quantified using Fourier transform infrared (FTIR) spectroscopy, and the corresponding improvement in strength is evaluated using unconfined compressive strength (UCS) tests. The corresponding porosity is not measured directly, but calculated from the dry unit weight and specific gravity of the material. Three water contents ($\mathrm{OMC}\text{-}2\%$, OMC, and $\mathrm{OMC}+2\%$), five cement dosages (2%, 4%, 6%, 8%, and 24%) and three curing periods (7, 14, and 28 days) are adopted. The results show that the untreated pond ash did not undergo hydration reactions upon adding water due to its lower calcium content. For cement-treated pond ash, the formation of calcium silicate hydrates (C-S-H) increases with cement dosage, curing period, and water content. At intermittent curing conditions of 7 and 14 days, the C-S-H formation reached a saturation point for lower cement dosages at OMC but continued to increase with the increase in water content for 24% cemented pond ash system. For 28 days curing, the C-S-H formation reached a maximum at OMC, and a further increase in water content did not increase the C-S-H content. Here, further addition of water does not contribute to hydration and pozzolanic reactions, but water acts as a pore-filling fluid. This is reflected through a corresponding variation in porosity and the UCS value.