Influence of EICP on Strength Properties of Compacted Pond Ash

Abstract

Pond ash (PA) is a mix of bottom ash and fly ash that is deposited in ash ponds/lagoons. It is conventionally stabilized with cement/lime and used as a geo-material. In recent times, the use of these stabilizers has been discouraged due to their higher energy consumption and emission of greenhouse gases, leading to unsustainable geotechnical applications. Hence, in this study, PA is stabilized with enzyme-induced calcium carbonate precipitation (EICP) using urea (CO(NH2)2), calcium chloride dihydrate (CaCl2.2H2O), and soybean flour as a source of urease enzyme. The strength characteristics of PA at different calcium-to-urea (CU) ratios (1.5:1, 1.5:2, and 1.5:3) and soybean flour (SF) concentrations (20, 30, and 40 g/L) and curing periods (7 and 28 days) are explored. The results show an enhancement in the unconfined compressive strength (UCS) and split tensile strength (STS) of stabilized PA with increased CU ratios and curing durations. However, strength properties are reduced with an increase in the SF concentrations. At 20 g/L SF concentration, the 28-day UCS of stabilized material enhanced from 273 kPa to 1332 kPa when the CU ratio increased from 1.5:1 to 1.5:3, respectively, and the 28-day STS increased from 17 kPa to 26 kPa, respectively. The mineralogical studies show that the precipitation of calcium carbonate in the compacted specimen mainly contributes to strength gain.