ABSTRACT
This research was carried out to investigate the effect of elapse time after mixing on the geotechnical properties of soil-lime-bagasse ash mixture. Preliminary investigation on the black cotton soil used showed that the soil belongs to A-7-6 and CH in the AASHTO and Unified Soil Classification System (USCS), respectively. Soils in these groups are unsuitable for engineering purposes. Evaluation of the effect of elapse time on the Atterberg limit, moisture - density relationship, unconfined compressive strength, durability and California bearing ratio (CBR) of the soil-lime-bagasse ash mixes showed that the consistency, compaction and strength properties of the soil decreased with increase in elapse time. The liquid limit, plastic limit and plasticity index of the soil reduced from 60 to 37 %, 22 to 11 % and 38 to 23 % at 8 % lime/6 %, 8 %lime/6 % bagasse ash and 8 % lime/4 % bagasse ash treatment respectively after 3 hours elapse time. The maximum dry density (MDD) of soil treated with 6 % lime/8 % bagasse ash reduced from 1.42 to 1.31 Mg/m3, 1.55 to 1.29 Mg/m3 and from 1.83 to 1.42 Mg/m3 after 3 hours delays for British Standard light (BSL), West African Standard (WAS) and British Standard heavy (BSH) compactive efforts, respectively. The unconfined compressive strength (UCS) values decreased for all compactive efforts and curing periods with elapse time. At the peak curing period of 28 days considered in this study, the UCS decreased from 540 to 380 kN/m2, 850 to 620 kN/m2, and 1330 kN/m2 reduced to 1020 kN/m2 for soil treated with 6% lime/ 8% bagasse ash at BSL, WAS and BSH energy levels. Durability assessment of the soil-lime-bagasse ash mix showed a decrease in the resistance to loss in strength of the mixes with elapse time for all compactive efforts. A peak value of 50 kN/m2 was attained at 6 % lime/8 % bagasse ash for BSL, 120 kN/m2 for WAS and 200 kN/m2 for BSH compactive efforts. This decrease to 20, 58 and 60 kN/m2 after three hours respectivly. The CBR values also showed a decrease in value with elapse time. A decrease from 14 % to 5 %, 24 to 11 % and 34 to 20 % after three hours elapse time was observed at 6 % lime/8 % bagasse ash treatment for BSL, WAS and BSH energy level. The strength properties of the soil-lime-bagasse ash obtained in this work at no compaction delay and at compaction delay of three hours established the maximum and minimum that can be achieved. An optimal mix of 6 %lime/8 % bagasse ash is recommended at the BSH compactive effort and elapse time not exceeding one hour.