ABSTRACT
The black cotton soil (BCS) used in the study was classified as A-7-6(22) soil group of the AASHTO soil classification system and CH group in the Unified Soil Classification System (USCS). The effect of iron ore tailing (IOT) on ordinary Portland cement (OPC) modified soil was studied with respect to specific gravity, particle size distribution, Atterberg limits, cation exchange capacity, compaction characteristics and shear strength parameters, (cohesion and angle of internal friction using three (3) compactive efforts (i.e., British Standard light, BSL, West African Standard, WAS or ?Intermediate' and British Standard heavy, BSH). Microanalysis was carried out on specimens cured for 7 and 28 days and batch equilibrium tests results were evaluated to determine the effects of pozzolanic and particle inter-surface activities on the properties listed above as well as determine the leachability of IOT into the soil. Generally, treatment of BCS with OPC /IOT blend improved the soil properties and workability. BSL, WAS and BSH compaction energies effectively altered the shear strength parameters of BCS at 4 % cement 6 % IOT treatment. Tests results show that specific gravity of the soil increased while fine fraction and cation exchange capacity (CEC) decreased; liquid limit and plastic limit decreased; MDD increased while OMC decreased; cohesion decreased while angle of internal friction increased for all cement contents considered when admixed with up to 6 % IOT content by dry weight of soil. The Microsoft Excel Analysis Tool Pak Software Package was used to carry out statistical analysis tests results. A two-way analysis of variance (ANOVA) without replication was carried out to determine the levels of contributions of cement and IOT to the improvements recorded. Study of leaching potential of iron into the environment using batch equilibrium test showed that the desorbed values of iron and pH for the optimally modified soil falls within the permissible value recommended by the World Health Organisation (WHO) and the Nigeria Industrial Standard (NIS). The modified soil did not meet the Nigerian General Specifications requirements when used as a subgrade material in road construction. However, an optimal blend of 4 % cement 6% IOT treated black cotton soil compacted with BSH) energy is recommended for use as subgrade material for lightly trafficked road.