Stabilization of Local Alluvial (Kankar-Bearing) Soil of Jaipur Using Wollastonite and SoilTech Polymer, and Utilisation of Coal Bottom Ash as Coarse Aggregate Replacement in Wollastonite-Blended Concrete

Abstract

Jaipur district is predominantly covered by New Alluvial, kankar-bearing soil, which shows considerable site-to-site variability in bearing capacity due to the irregular distribution of calcium-carbonate (kankar) nodules. This study investigates soil stabilization using two additives—Wollastonite, a natural calcium-silicate mineral, and SoilTech, a nano-polymer stabilizer—and evaluates coal Bottom Ash as a partial replacement of natural coarse aggregate in M30 concrete containing 10% Wollastonite as cement replacement. Standard Proctor, soaked CBR and Atterberg-limit tests were conducted for soil, while compressive, flexural and split-tensile strength tests at 7 and 28 days were performed for concrete. Wollastonite showed optimum performance at 15% by dry soil weight, increasing MDD from 1.68 to 1.82 g/cc (+8.33%) and soaked CBR at 5.0 mm from 4.5% to 7.4% (+64.44%), while reducing plasticity index from 12.7% to 9.1%. SoilTech performed best at 0.50% of OMC, increasing MDD to 1.80 g/cc and soaked CBR to 8.2% (+82.22%), the highest CBR improvement among the single additives. Both stabilizers exhibited an optimum dosage followed by reduced performance at higher contents. In concrete, 10% Wollastonite increased 28-day strength from 34.20 to 35.80 N/mm², whereas increasing Bottom Ash replacement reduced strength. A 5% Bottom Ash replacement retained approximately 97.5% of the Wollastonite-baseline strength, compared with 77.7% at 20% replacement. Although stabilized materials had higher unit costs, the soil treatments offered potential economic benefit through reduced pavement-layer thickness due to improved CBR. The study identifies 15% Wollastonite and 0.50% SoilTech as effective stabilizers for Jaipur's alluvial subgrade, while 5% coarse Bottom Ash replacement with 10% Wollastonite cement substitution provides a technically viable and sustainable option for low-volume concrete applications.

Keywords: Alluvial soil; kankar; Wollastonite; SoilTech polymer; soil stabilization; CBR; coal Bottom Ash; coarse aggregate replacement; concrete; sustainability