Enhancing the Geotechnical Properties of Pond Ash via EICP Technique- A Sustainable Approach

Abstract

Pond ash, a byproduct of coal combustion in thermal power plants, poses significant environmental challenges due to its bulk disposal requirements. Its sustainable utilisation in geotechnical applications presents an opportunity to reduce environmental impact and conserve natural resources. This study explores a sustainable approach to improve the strength properties of pond ash (PA) by incorporating demolished cement mortar (DCM) through the Enzyme-Induced Calcium Carbonate Precipitation (EICP) process. PA was mixed with 10%, 20%, and 30% finely sieved DCM (sieved to pass through a 75-micron mesh). The EICP treatment solution was prepared using calcium chloride (CaCl2), urea [CO(NH2)2], and soybean flour (SF), with SF acting as a source of natural urease enzyme. Test tube experiments were conducted with calcium-to-urea (CU) molar ratios of 1:1, 1:1.25, 1:1.5, and 1:1.75 by keeping the urea concentration constant (1 M) to optimise the CU molar ratio. SF was varied from 10 g/L to 30 g/L. The highest calcium carbonate precipitation (CaCO3) was recorded at a CU ratio of 1:1.25 with 1 M urea and 25 g/L SF. Unconfined compressive strength (UCS) and split tensile strength (STS) tests were conducted on specimens compacted at their respective optimum moisture content (OMC) and maximum dry density (MDD), and then cured at 40°C for 0, 7, and 28 days. The results show an improvement in the unconfined compressive strength (UCS) and split tensile strength (STS) of EICP-treated pond ash (PA) with increased demolished cement mortar (DCM) content and curing durations. The 28-day UCS of EICP-treated pond ash increased from 343 kPa to 2190.03 kPa, and the 28-day STS increased from 35.7 kPa to 144.2 kPa, respectively, with the addition of 30% demolished cement mortar (DCM). Furthermore, SEM and XRD analysis were carried out to gain deeper insights into the material’s microstructural Properties. This study presents an environmentally sustainable approach for improving the engineering properties of PA, promoting its beneficial reuse in geotechnical and construction applications.