Effect of Tannery Sludge Ash Additions on the Properties of Subgrade Soil Stabilized by Cement

The present study used hazardous tannery sludge (TS) ash and cement in subgrade soil stabilization. TS ash in increasing weight percentages (5, 10, and 15) was added to the soil mix (soil + 8% cement by weight of soil). The properties of subgrade soil were evaluated by studying the liquid limit, plastic limit, plasticity index, optimum moisture content, maximum dry density, California bearing ratio (CBR), and Toxicity Characteristics Leaching Procedure (TCLP) test. TS ash was nonplastic in nature; hence, the increased weight percentage of TS ash in the soil mix resulted in a reduction of the liquid limit, plastic limit, plasticity index, and optimum moisture content, making the soil mix more workable. TS ash is a material of lower specific gravity, so the increased additions of the TS ash in the soil mix decreased the maximum dry density. The addition of TS ash interfered with the hydration process of cement and reduced the pozzolanic activity, resulting in reduced calcium silicate hydrate (CSH) gel and CBR of the soil mix. CBR of the soil mix containing five and ten weight percentages of TS ash satisfied the minimum CBR requirements of Indian Road Congress (IRC) 37–2012. Most of the heavy metals of TS ash were bound in the CSH gel in all the samples, and the leaching of heavy metals was well below the permissible limits according to the United States Environmental Protection Agency, indicating the possibility of using TS ash in subgrade soil without affecting the environment.