Use of Rice Husk Ash in Concrete Blocks

Abstract

With an ever increasing concern over environmental issues associated with the production of Ordinary Portland Cement (OPC) and also the need for managing wastes, researchers are looking into supplementary cementitious materials (SCMs).Rice Husk Ash (RHA), a agricultural byproduct obtained from burning of millinghusks under controlled temperatures is known for it\'s high amorphous silica content and therefore it is a high reactive pozzolanic .This study was to determine the possibility and the effects of using RHA as a partial substitute of cement in manufacturing standard concrete blocks. The study examines effect of RHA on workability, compressive strength, unit weight and durability and came to the conclusion that optimum replacement level could be used to produce structural concrete blocks which will be economical and ecologically safe.

Introduction

This study examines the use of Rice Husk Ash (RHA) as a sustainable supplementary cementitious material in concrete block production. With growing concerns over the environmental impact of cement manufacturing, which contributes approximately 7–8% of global man-made CO? emissions, agricultural waste materials such as RHA offer an eco-friendly alternative. Rice husk, a by-product of rice milling, is abundantly available in rice-producing countries, and its controlled combustion produces RHA, which contains 80–95% amorphous silica and exhibits strong pozzolanic properties.

RHA reacts with calcium hydroxide in the presence of water to form additional calcium silicate hydrate (C-S-H) gel, which enhances the strength and durability of concrete. Previous research has shown that replacing cement with RHA at optimal levels (generally between 5% and 10%) improves compressive strength, reduces permeability, and increases resistance to sulfate and chloride attacks. However, excessive replacement levels can reduce strength due to lower cement content and increased water demand.

The literature review highlights several studies demonstrating that RHA improves concrete performance through its pozzolanic activity and micro-filling effect. Researchers found that properly burnt and finely ground RHA can enhance compressive strength, durability, chemical resistance, and long-term performance while reducing cement consumption and environmental impact. Most studies identified an optimum replacement range of 5–10%, although some reported benefits up to 20% replacement under controlled conditions.

The experimental program used M30 grade concrete with cement partially replaced by RHA at 0%, 5%, 10%, and 15% levels. Concrete blocks were cast and cured for 3, 7, 14, and 28 days, and compressive strength tests were conducted. Materials included OPC 53-grade cement, manufactured sand, coarse aggregates, potable water, RHA, and a superplasticizer to maintain workability.

The results showed that compressive strength increased with curing age for all mixes due to continued cement hydration. The control mix (0% RHA) achieved the highest strength of 17.81 MPa at 28 days. Concrete containing 5% RHA reached 16.14 MPa, while 10% RHA achieved 14.44 MPa, indicating satisfactory performance because of the pozzolanic and filler effects of RHA. However, 15% RHA resulted in a significant reduction in strength (13.93 MPa) due to reduced cementitious content and increased porosity.

The study concluded that the optimal replacement level is between 5% and 10%, where concrete blocks retain 81–91% of the strength of conventional concrete while benefiting from improved sustainability. At later curing stages, the amorphous silica in RHA reacts with calcium hydroxide to produce secondary C-S-H gel, refining the pore structure and improving durability.

Economic analysis revealed that RHA also reduces production costs. The cost of producing 100 conventional concrete blocks was estimated at ?1560, whereas blocks containing 5%, 10%, and 15% RHA cost ?1524, ?1488, and ?1452 respectively. This represents a saving of up to ?108 per 100 blocks at 15% replacement.

Conclusion

1) The increase in compressive strength with curing age in all the mixes represents continuous hydration and cementitious matrix development from 3 days to 28 days. 2) The compressive strength of the control mix (0% RHA) was found to be 17.81MPa at 28 days which was taken as the reference for measuring RHA mixed concrete. 3) As the replacement level increases the compressive strength of the RHA mixed concrete was found to decrease, this happens due to the decrease in cement quantity and very slow pozzolanic reaction of RHA at earlier ages. 4) Strength of the all RHA mixed concrete was found to be developing with age (although slow) indicating that pozzolanic reactivity of RHA contributes to long-term strength gain. 5) Strength of 5% RHA mixed concrete was found to be 16.14 MPa at 28 days representing a loss of mechanical properties of only about 90.6% compared to control mix. 6) Strength of 10% RHA mixed concrete was found to be 14.44 MPa at 28 days which falls under a reasonable limit for structural and masonry blocks as well and cement substitution is significant. 7) At 15% replacement level, concrete block had the lowest strength of 13.93 MPa at 28 days indicating high percentage of RHA has detrimental effect on load carrying capacity. 8) 5-10% RHA substitution range is considered as an optimum range considering strength performance, durability, sustainability and material economy. 9) A combination of strength retention and cost reduction due to substitution in this range makes it a technically sound and sustainable option. 10) Economic evaluation of 5-10% RHA replacement provides reduced cement substitution, reduced cost of cement production and usage of agricultural waste products..

References

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Copyright

Copyright © 2026 Manas Suryawanshi, Mahesh Tatikonda, Aryan Pawar, Dhruv Babar, Pankaj Waghmare. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.