Assessment of Concrete Properties by Partial Replacement of Fly Ash and Rice Husk Ash with Cement and Recycled Aggregate with Natural Coarse Aggregate

Shivangi Bundela, Chaitali Gangwal, Chaitanya Mishra

Abstract: Concrete production consumes substantial quantities of Portland cement and natural aggregates, resulting in the depletion of natural resources and significant greenhouse gas emissions. At the same time, coal-based power generation, rice processing, and construction and demolition activities generate substantial volumes of fly ash (FA), rice husk ash (RHA), and waste concrete, which present major disposal and environmental challenge concrete technology, therefore, focuses on incorporating such industrial and agricultural by-products as supplementary cementitious materials and recycled aggregates to reduce environmental impact while maintaining or improving mechanical and durability performance. This paper reviews and extends existing research on the combined use of FA, RHA, and recycled concrete aggregate (RCA) in structural concrete, with emphasis on compressive and flexural strength development for M25 grade concrete. A two-stage experimental program was conducted: in Stage 1, cement was partially replaced by FA and RHA at an overall binder replacement level of 25%, distributed across seven mixes varying from 25% FA to 25% RHA; in Stage 2, the optimum FA-based mix from Stage 1 was used as the base binder while natural coarse aggregate (NCA) was partially replaced by RCA at 10-40% by weight. For all mixes, cubes (150 mm) and beams (100?100?500 mm) were cast and tested for compressive and flexural strength at 7, 14, and 28 days in accordance with IS 516:1959. Stage 1 results showed that replacing 25% of cement by FA alone (75% cement + 25% FA) increased compressive strength by about 25-27% and flexural strength by about 25% at all ages relative to conventional M25 concrete. Progressive substitution of FA by RHA within the 25% replacement (up to 25% RHA) reduced both compressive and flexural strengths, indicating that for the RHA used in this study, fineness and reactivity were not sufficient to match the performance of FA at the same dosage. In Stage 2, using the optimum binder (75% cement + 25% FA), partial replacement of NCA with RCA at 10% further increased compressive strength by roughly 29% and flexural strength by about 34% compared to conventional concrete without FA or RCA, whereas higher RCA contents (20-40%) led to gradual strength reductions, though many mixes still performed competitively. The experimental findings align with previous studies showing that FA and RHA can act as effective pozzolanic materials, and that RCA can be used to partially replace NCA without compromising strength, provided its higher absorption and lower density are properly accommodated in the mix design. The results suggest that for M25 concrete under Indian conditions, an optimum sustainable mix can be obtained by replacing about 25% of cement with FA and about 10% of NCA with RCA, while RHA requires careful control of production and fineness to avoid strength penalties. The study contributes to the growing body of evidence supporting the integrated use of industrial and agricultural by-products and recycled aggregates in structural concrete, and provides data that can inform future code provisions and practical guidelines for sustainable construction.

Keywords: fly ash, rice husk ash, recycled concrete aggregate, sustainable concrete, M25 concrete, compressive and flexural strength

How to Cite?: Shivangi Bundela, Chaitali Gangwal, Chaitanya Mishra, "Assessment of Concrete Properties by Partial Replacement of Fly Ash and Rice Husk Ash with Cement and Recycled Aggregate with Natural Coarse Aggregate", Volume 15 Issue 1, January 2026, International Journal of Science and Research (IJSR), Pages: 585-589, https://www.ijsr.net/getabstract.php?paperid=SR26108123945, DOI: https://dx.doi.org/10.21275/SR26108123945