COMPRESSIVE STRENGTH RESPONSE OF SDA–SGA BLENDED CONCRETE FOOTINGS UNDER VARYING SOIL BEARING CONDITIONS

Abstract

This research examines the structural response of concrete pad footings produced with ternary cementitious blends comprising Ordinary Portland Cement (OPC), Sawdust Ash (SDA), and Sponge Gourd Ash (SGA) when founded on five different soil types—clayey, silty, sandy, lateritic, and gravelly—whose bearing capacities range from 150?kN/m² to 250?kN/m². The concrete mixes were designed using an 85:15 cementitious blend ratio (OPC: [SDA?+?SGA]) and a constant mix proportion of 1:2:4, consistent with general practice for footings. A total of five mix variants (M1–M5) were cast, cured for 28 days, and tested for compressive strength using standard procedures. The test results reveal a progressive increase in 28-day compressive strength corresponding with the increasing soil bearing capacity. The lowest strength was recorded by mix M1 on weak, cohesive clayey soil (24.1?MPa), while the highest strength was attained by mix M4 on lateritic soil (27.2?MPa), marking a significant 12.86% improvement over the baseline. This strength enhancement is attributed to the synergistic pozzolanic reactivity of SDA and SGA, which improved the microstructure and densification of the concrete matrix, particularly under supportive soil conditions that minimized differential settlement and stress concentration. These findings confirm the mechanical viability and soil sensitivity of SDA–SGA blended concrete for shallow foundations, especially in structurally favorable soils such as lateritic and gravelly profiles. The environmental and technical advantages observed also highlight the potential of using agro-waste-based cementitious materials to enhance the sustainability and performance of concrete in structural applications.

Keywords: Sawdust ash (SDA), sponge gourd ash (SGA), blended concrete, soil bearing capacity, sustainable foundations