Experimental Analysis of Early Compressive Strength of Sandcrete Block Blended with Rice Husk Ash and Activated with Soda Ash

• John O. NWODO

  Author

• Toyin Y. AKANBI

  Author

• Hassan K. ABDULRASHEED

  Author

Sandcrete blocks are widely used masonry units in construction, and partial cement replacement with agricultural waste materials has been investigated as a means of reducing cement consumption, production cost, and environmental impact. Rice husk ash (RHA), a silica-rich pozzolanic material, and soda ash (Na₂CO₃), an alkaline activator, have potential to modify the hydration and strength development of cementitious materials. This study experimentally analysed the early compressive strength and water absorption of 150 mm (6-inch) hollow sandcrete blocks produced by partially replacing ordinary Portland cement (OPC) with RHA at 10–50% and activating the blends with soda ash at 0.5–3.0%. The physical properties of the fine aggregate were determined in accordance with BS EN 933-1 and BS EN 1097-6, while the chemical composition of RHA was determined using X-ray fluorescence (XRF) analysis. A total of 54 sandcrete-block specimens were produced from the experimental programme and cured for 7 days before testing for wet mass, dry mass, water absorption, and compressive strength in accordance with BS EN 772-1 and NIS 87. The sand had a fineness modulus of 1.93 and a specific gravity of 2.56. XRF analysis showed that the combined SiO₂ + Al₂O₃ + Fe₂O₃ content of the RHA was 85.84%, indicating strong pozzolanic potential. Compressive strength increased at low RHA and soda ash contents but declined at higher replacement levels. Water absorption increased with RHA content but remained below the 12% limit reported in NIS 87. The optimum combination within the tested range was 10% RHA with 1.0% soda ash, which achieved 1.76 N/mm² at 7 days, compared with 1.23 N/mm² for the control. The novelty of the study is the experimental evaluation of combined RHA replacement and low-dose soda ash activation for improving early-age performance of 150 mm hollow sandcrete blocks. The findings identify a practical blend that meets the stated 1.50 N/mm² minimum for non-load-bearing blocks and provides a basis for further optimisation at lower RHA replacement levels.

• 60_Nwodo et al. (2026)

Copyright (c) 2026 John O. NWODO, Toyin Y. AKANBI, Hassan K. ABDULRASHEED (Author)

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