Durable and Low-Carbon Concrete: Engineering Properties of Cement Blended with Soybean Husk Ash and Sugarcane Bagasse Ash

Abstract

The growing demand for sustainable, low-carbon construction materials has sparked interest in using crop residues in replacing supplementary cementitious materials (SCMs). This study evaluated the Engineering performance and durability under Sulphate attack using a ternary blend of cement, with SHA and SBA fully and partially replaced. Four agricultural residues, soybean husk, Bambara nut shell, melon husk, and sugarcane bagasse, were screened using the modified Chapelle test at calcination temperatures of 500, 600, 700, and 800°C. Soybean husk and sugarcane bagasse were the most reactive when calcined at 700°C, fixing 1620.19 and 879.99 mg Ca(OH)2 per gram, respectively, and were consequently selected and processed into SHA and SBA for physical and chemical characterization, including oxide composition, particle-size distribution and specific gravity. Concrete was proportioned as one OPC control and nine ternary OPC SHA SBA blends spanning 5-35% total ash replacement, mixed at three water-cement ratios (0.30, 0.40 and 0.45). Each mix was evaluated for fresh-state performance (initial and final setting time, slump) and for hardened compressive strength after 28 days of water curing followed by prolonged exposure to magnesium sulphate. The inclusion of SHA and SBA progressively retarded both the initial and final setting and reduced the slump from 58 mm (control) to 45 mm at the highest replacement level, indicating reduced workability at high ash contents. Cubes were monitored for compressive strength at nine ages up to 360 days. Under sulphate exposure, all mixes lost strength over time; the control (100-0-0) at 0.30 w/c fell from 33.86 MPa (1 day) to 19.82 MPa (360 days). The ternary 75-15-10 blend (75% OPC, 15% SHA, 10% SBA) showed the best long-term sulphate resistance, retaining 20.52 MPa at 360 days and exceeding the control's 360-day strength by about 12% (0.45 w/c). The combined SiO2 + Al2O3 + Fe2O3 content was 85.42% for SHA and 91.26% for SBA, both exceeding the 70% threshold specified in ASTM C618-19. The findings demonstrate the viability of soybean husk ash and sugarcane bagasse ash as eco-friendly cement replacements, with moderate replacement levels (≤15% of total) offering the best balance of strength and sulphate resistance.