PHYSICAL, MECHANICAL PROPERTIES AND INTERNAL STRUCTURE CHARACTERISTICS OF CEMENT-LOCUST BEAN POD WASTE ASH MORTARS

Abstract

The need to reduce the environmental pollution resulting from agro-wastes and to source a material that can be used to replace cement in order to reduce the pressure on its consumption necessitated this research. This study was designed to investigate the effect of cement replacement with locust bean pod ash (LBPA) as a supplementary cementitious material on compressive strength of mortars. The fresh properties (workability, initial and final setting times), compressive strength at 7, 14, 21 and 28 days and microstructural analysis Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS), and X ray diffraction analysis (XRD) were evaluated. LBPA were considered at replacement levels of 0, 10, 15, 20 and 30% of cement mass for preparation of the mortar samples. Workability of the cement mortars reduced as the content of LBPA increases while initial and final setting times increased in relation to increase in LBPA content in the matrix. A decrease of about 98% in compressive strength occurred at 30% LBPA and after 14 days of curing and the highest increase in compressive strength was recorded at 15% LBPA after 28 days of curing. Maximum compressive strength ranged 38.3 and 65 MPa after 7 to 28 days curing. Microstructural analysis revealed less voids and pores, and the presence of dense Calcium- Silicate-Hydrate (CSH) gels which helped to maintain the optimum compressive strength at 15% LBPA cement replacement level of the mortar. The results indicated that LBPA is a reactive pozzolanic material and can be used as a supplementary cementitious material for producing medium-strength concrete.