STATISTICAL ANALYSIS OF CONCRETE INCORPORATING AGRO-WASTE ASH UNDER SULPHATE EXPOSURE

Abstract

This study presents a multifactorial statistical analysis of concrete and mortar incorporating two agricultural-waste ashes — soybean husk ash (SHA) and sugarcane bagasse ash (SBA) as partial cement replacements, under magnesium-sulphate exposure. Water absorption, compressive strength, and sulphate-induced length change (expansion) were measured for 10 cement:SHA:SBA proportions at three water-to-cement (w/c) ratios (0.30, 0.40, 0.45). Specimens were water-cured for 28 days and then immersed in a magnesium sulphate solution following a modified ASTM C1012 procedure, with properties tracked over a 1–365-day exposure period. Factorial analysis of variance (ANOVA), homogeneous-subset grouping with 95% confidence intervals from the pooled error term, correlation analysis linking the three responses, and Design-Expert® desirability optimisation were used. All three factors significantly affected both responses (p < 0.001), with exposure age and the proportion of mix as the dominant terms. Compressive strength declined progressively with sulphate exposure, from a mean of 26.8 MPa at day 1 to 17.3 MPa at day 365. Sulphate expansion was lowest for moderate ternary blends: averaged across all exposure ages, the 80-10-10 mix expanded least (mean 0.134%) versus 0.389% for the control, and at 180 days the best blend (75-15-10 at 0.40 w/c) reached only 0.424% against 0.935% for the control at the same w/c — a 55% reduction. Strength retention and expansion were significantly correlated (r = ?0.68), confirming that mixes that resisted expansion retained more strength. Durability-prioritised desirability optimisation identified moderate ternary blends (10–20% total ash, 80-10-10 / 75-15-10) at low w/c (? 0.40) as the best compromise between retained strength and low expansion. The findings support moderate ternary SHA/SBA replacement as a durable, lower-carbon supplementary cementitious strategy for sulphate-rich environments.

Keywords: soybean husk ash; sugarcane bagasse ash; sulphate resistance; agro-waste concrete; compressive strength; ANOVA; desirability optimisation