ABSTRACT
A black cotton soil collected from Deba Local Government Area of Gombe state classified as A-7-6 (25) or CH in AASHTO and Unified Soil Classification System (USCS), respectively. It was treated with lime - iron ore tailing (IOT) blend in stepped concentration of 0, 2, 4, 6 and 8 % lime as well as 0, 2, 4, 6, 8, and 10 % IOT by dry weight of soil. Compaction was carried out using three energy levels namely, the British Standard light (BSL), West African Standard (WAS) and the British Standard heavy (BSH). Index, compaction, strength and durability tests as well as microanalysis of the natural and optimally stabilized specimens cured for 7 and 28 days were carried out. Liquid limit and plastic limit values decreased from 56.8 and 29.2 % for the natural black cotton soil to minimum values of 43.8 % at 8 % lime / 6 % IOT and 18 % at 8 % lime / 8 % IOT treatments, respectively. Plasticity index value decreased from 27.6 % for the natural soil to 24.3 % at 6 % lime / 10 % IOT treatment. The 7-day unconfined compressive strength (UCS) of the natural soil increased from 107.24, 326.25 and 408.35 kN/m2 for BSL, WAS and BSH compactions to 1074.54, 1569.02 and 1688.76 kN/m2 , respectively, for 8 % lime/ 8 % IOT treatment. The recorded UCS values of the treated specimens met the 1034.25 kN/m2 criterion normally utilized/specified for adequate lime stabilization. The California bearing ratio (CBR) values (unsoaked condition) increased from 3, 4 and 8 % for the natural soil compacted with BSL, WAS and BSH energies, respectively, to 52, 79 and 88 %, respectively, when treated with 8 % lime/8 % IOT blend. For the 24-hour soaked condition the CBR values for BSL, WAS and BSH compactive effort recorded peak values of 41, 61 and 69 %, respectively, for 8 % lime/8 % IOT treatment. Only 67 % resistance to loss in strength (33 % loss in strength) at 8 % lime/6 % viii IOT with BSH is close to the limiting value of 80 % resistance to loss in strength based on 4 days soaking. The 8 % lime/6 % IOT treatment of the soil can be used, at BSH compaction, for sub-base material because the soil was subjected to a harsher condition (of 7 days soaking).The scanning electron microscopy revealed that crystalline hydration products presumed to majorly contribute to strength gain were present in the optimally treated soil-lime-IOT mixture. The two-way statistical analysis of variance (ANOVA) without replication showed that the lime-IOT blend significantly improved properties of the soil.