Physicochemical Characterisation and Strength-Based Screening of The Calcination Temperature for Locust Bean Pod Ash
DOI:
https://doi.org/10.33003/fjs-2026-1021-6215Keywords:
Locust bean pod ash, calcination temperature, agro-waste ash, supplementary cementitious materialAbstract
Locust bean pod ash (LBPA) is an abundant West African agricultural residue with potential as a supplementary cementitious material, but the effect of calcination temperature on its composition and performance is poorly documented. Pods were pre-burnt in open air and then calcined in a muffle furnace for 2 hours at 400, 500, 600 and 700 °C. The ashes were characterised by X-ray fluorescence (XRF), X-ray diffraction (XRD) and nitrogen physisorption, and each ash replaced 5% of the cement by mass in concrete with a water-to-binder ratio of 0.58. Calcination raised the SiO2 + Al2O3 + Fe2O3 sum from 66.99% at 400 °C to 78.30–81.84% at 500–700 °C and lowered the loss on ignition from 5.67 to 3.02%. Carbonate phases matched by XRD at 400–500 °C were no longer leading matches at 600–700 °C, where potassium and calcium-bearing phases were the main matches. The BET surface area was highest at 400 °C (13.38 m²/g) and did not follow the strength ranking, so surface area alone is a poor guide to performance for this ash. The 600 °C ash gave the highest 28-day strength (24.58 N/mm², a relative strength index of 90.67%) and was significantly stronger than the other blends (p ≤ 0.008). It was 1.68% below the 25 N/mm² design strength and 9.33% below the control, whereas the other blends ranged from 20.03 to 21.49 N/mm². Calcination at 600 °C is therefore recommended as the best of the tested temperatures for preparing LBPA.
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