Effect of Locust Bean Pod Ash on Strength Properties of Weak Soils

Abstract

Chemical stabilization of weak subgrade soils using locust bean pod ash (LBPA) produced from incinerator burnt locust bean pod waste was studied and reported in this paper. The LBPA was considered as a Class C group of the ASTM (American Society for Testing and Materials) pozzolan. The soils used in the study were obtained from depth of exhausted good quality materials of old borrow pits along the Minna-Kataeregi-Bida road in north-central Nigeria. The materials were analyzed for main geotechnical index properties and compaction characteristics. The LBPA pozzolan stabilizer was administered to the raw soil up to 12% and at a rate of 2%. The LBPA-treated samples were cured under moist conditions for a period of seven days before strength tests were carried out. The experimental results comparing the strength of the natural soil samples with the LBPA-stabilized samples revealed that LBPA increases the California Bearing Ratio (CBR) and unconfined compressive strength of the weak AASHTO (American Association of State Highway and Transportation Officials) classified A-7-6 and A-6 subgrade soils. An optimum stabilizer content of 8% was determined with about 50% advantages in the CBR (increase in CBR of stabilized soil / CBR of raw soil × 100) for both soaked and unsoaked conditions. At the established optimum stabilizer content, the weak hitherto unsuitable soils have been improved to meet the requirements for Type 2 subbase road development soils.