Elemental Assessment of Pond Ash for Evaluating Its Application as a Subbase Material for Hardstand Construction

Abstract

Utilizing pond ash (PA) deposited in ash lagoons generated from thermal power plants (TPPs) as subbase material for hardstand foundation not only helps the cause of residual waste disposal problem but also solves associated shortcomings like, lower utility and degrading environmental impact for prolonged deposition. However, the property of the PA varies not only among various TPP but also within a single ash lagoon, depending on the point of deposition and subsequent settlement. This study presents detailed analysis of chemical, physical, morphological, and mineralogical properties of inflow and outflow PA within the same ash lagoon. Local sand (LS) has been used as conventional granular subbase material. A comparative analysis of the respective material properties has been drawn to access the feasibility of PA as subbase material, substituting sand. The results showed CBR ranging from 16.63 to 17.19% for standard compacted unsoaked samples, 23.55–24.17% for modified compacted-soaked samples of PA, compared to 25.08 and 32.96% of LS. Consolidated drained triaxial tests showed cohesiveness and φ value 32° for PA samples compared to 40° for LS. FESEM explained distinguished morphological forms of the mineral and showed the presence of microspheres in PA. XRD detected alumina-silicates, cristobalite, anorthite and showed PA particle size is directly proportional to its pozzolanic reactivity. FTIR detected presence of hydroxyl (–OH) stretches and (H–O–H) vibrations along with bond water molecule bending, revealing its pozzolanic nature. Finally, LFWD test provides 1.7% less peak surface deflection than LS predicting PA’s favorably as supplementary granular material for hardstand subbase layer.