GEOTECHNICAL AND LEACHING EVALUATION OF ORDINARY PORTLAND CEMENT STABILIZED CONTAMINATED LATERITIC SOILS

Abstract

This research work was focused on the use of Ordinary Portland Cement (OPC) to enhance the engineering properties of lateritic soil and the beneficial reuse of contaminated soils for environmental sustainability in developing countries especially Nigeria. This was done by the stabilization of lateritic soil contaminated with inorganic (Lead) and organic (Naphthalene) contaminants with the binder (OPC). The lateritic soil samples were contaminated with Lead and Naphthalene at varying degrees of contamination of 500; 1,000; 1500 and 2,000 ppm (parts per million) for lead and 0.5 %, 1.0 %, 1.5 %, 2.0 %, 2.5 % and 3.0 % by weight of the sample for Naphthalene. X-ray diffraction (XRD) was carried out on the uncontaminated lateritic soil samples which showed that predominant minerals present in the lateritic soil sample without contaminant and binder were Quartz, Kaolinite and Illite. Strength and environmental performance evaluation were performed on the stabilized samples to evaluate their strength characteristics and environmental suitability. The strength evaluation tests were Unconfined Compression and Direct Shear Tests. The results of the Unconfined Compressive Strength Tests show an increase in strength as the binder was increased from 0 % to 5 % to 10 %. At 0% OPC content, the strength was in the range of 335– 460 kN/m2 (500 ppm – 2000 ppm of Lead), in the range of 495 – 545 kN/m2 (500 ppm – 2000 ppm of Lead) at 5%, and in the range of 720 – 1022 kN/m2 (500 ppm – 2000 ppm of Lead) at 10% OPC content. The same trend was observed in naphthalene contaminated soil samples. Strength increased from the range of 330 – 500 kN/m2 (0.5 % - 3.0 % of naphthalene) at 0% OPC content to the range of 680 – 940 kN/m2 (0.5 % - 3.0 % of naphthalene) at 5% binder content, to the range of 1080 – 1295kN/m2 (0.5 % - 3.0 % of naphthalene) at 10% binder content respectively. The strength also increases as the binder was increased from the range of 173.5 – 164.4 kN/m2 (5 – 10% OPC addition after 7 days) at 0 % OPC, to the range of 223.9 – 241.9 kN/m2 (5 – 10% OPC addition after 14 days) at 5% OPC to the range of 163.3 – 223.2 kN/m2 (5 – 10 % OPC addition after 28 days) at 10 % OPC content. The Direct Shear tests results shows that cohesion (c) and angle of internal friction (ϕ) values ranges between 130-225 kN/m2 and 10.5°-20.07° as lead contaminant concentration increased and 60.5-135 kN/m2 and 31.61°-14.42° as naphthalene contaminant concentration increased. Meanwhile there was an increase in the cohesion (c) values and a decrease in the range of internal friction. The values are 27.02, 54.85 and 6.28 kN/m2 after 7, 14 and 28 days respectively for 10 % OPC addition and 15, 26 and 500 after 7, 14 and 28 days respectively for 10 % binder addition. The leaching test was run for 90 days for both Lead and Naphthalene. The effect of lead concentrations varied between 0.9-1.0 mg/l, 0.7-0.8 mg/l and 0.3-0.1 mg/l, after 30 days and 0.12-0.07 mg/l to 0.07-0.05 mg/l to 0.02 to 0.02 mg/l after 60 days as the OPC increased from 0 % to 5 % to 10 % by weight of sample and as contaminant concentration increased. While the effect of the binder (OPC) on naphthalene concentrations varied from 0.50-0.63 mg/l to 0.55-0.57 mg/l to 0.67-0.63 mg/l, after 30 days, 0.52-0.54 mg/l to 0.65-0.64 mg/l to 0.69-0.67 mg/l, after 60 days and 0.52-0.53 mg/l to 0.66-0.65 mg/l to 0.69-0.69 mg/l, after 90 days as the OPC increased from 0 % to 5 % to 10 % by weight of sample and as contaminant concentration increased respectively. The leaching potential of the natural contaminant in the lateritic soil decreases with an increase in the binder (OPC) addition except for Nickel which increased 0.1 mg/l to 0.22 mg/l to 0.24 mg/l as the binder addition was increased from 0% to 5 % to 10 % by weight of sample and as contaminant concentration increased. Also, as binder content and contaminant concentration increased, a varying trend was noticed with the lead concentration levels at 0.55 mg/l for 0 % binder, at 0.06 mg/l for 5 % and at 0.05 mg/l for 10 % binder, after 30 days. The batch equilibrium adsorption test exhibit a positive linear trend for both Lead ions and Naphthalene solution. The Total Petroleum Hydrocarbon (TPH) and Polynuclear Aromatic Hydrocarbon (PAH) concentration in the leachate are given as 1.250 mg/l which is above DPR intervention level of 0.6 mg/l and 0.0015 mg/l which is below EPA/GAHP standard of 0.015 mg/l after 30 days leaching with 10 % OPC additions. It can therefore be recommended that the 10 % of the OPC is the most environmentally suitable (of the two binder addition variation of 5 % and 10 % used) to stabilize the artificial and naturally contaminated soils.