Flexural strength of concrete containing rice husk ash with a constant 2% palm kernel shell ash as partial cement replacement
Department of Civil Engineering, Faculty of Engineering and Technology, Nigerian Army University Biu, Borno State.
* Corresponding Author
ORCID Details
Yahaya Watafua: https://orcid.org/0009-0006-8497-7901
Research Article
Open Access Research Journal of Engineering and Technology, 2026, 11(02), 015–023.
Article DOI: 10.53022/oarjet.2026.11.2.0071
Publication history:
Received on 29 August 2026; revised on 10 October 2026; accepted on 12 October 2026
Abstract:
Flexural strength governs the performance of concrete pavements and slabs, yet the combined effect of rice husk ash (RHA) and palm kernel shell ash (PKSA) on it has received little attention. This study evaluated the workability and flexural strength of concrete in which Ordinary Portland Cement (OPC) was partially replaced by 5%, 10%, 15% and 20% RHA with a constant 2% PKSA, relative to a plain OPC control. Thirty 100 mm × 100 mm × 500 mm beams (nominal 1:2:4 mix, water–binder ratio 0.50) were water-cured and tested in centre-point flexure to BS EN 12390-5 at 7, 14 and 28 days. Slump decreased from 70 mm for the control to 60 mm at 20% RHA, but all mixes remained within the S2 consistence class. At 7 days, all blended mixes were weaker than the control. At 28 days, the mix with 5% RHA and 2% PKSA gave the highest flexural strength, 43.3% above the control; 15% and 20% RHA gave increases of 0.6% and 14.0%, whereas 10% RHA reduced the strength by 18.5%. The measured 28-day strengths (6.1–10.8 N/mm²) were 1.7–3.9 times the Eurocode 2 estimates derived from companion cubes from the same batches, so their absolute values need confirmation; the conclusions therefore rest on changes relative to the control, which depend only on failure-load ratios. A blend of 5% RHA and 2% PKSA was the most favourable of the levels studied, subject to confirmation by a larger test programme.
Keywords:
Flexural strength; Modulus of rupture; Palm kernel shell ash; Rice husk ash; Workability
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