DEVELOPMENT OF ECO-FRIENDLY CONCRETE USING BINARY BLENDS AND RECYCLED CONSTRUCTION WASTE

The experimental study focused on assessing the behavior of binary blended concrete in which Fly Ash (FA) and Rice Husk Ash (RHA) were used as partial substitutes for cement. The performance of the mixes was examined by analyzing their compressive strength and split tensile strength at curing periods of 7 and 28 days. 1.                Compressive Strength Analysis Ø    The compressive strength results clearly show that both fly ash (FA) and rice husk ash (RHA) have a noticeable impact on the mechanical behavior of concrete. In the case of fly ash–based mixes, strength improves as the replacement level increases up to 10%, after which a decline is observed. The mix with 90% cement and 10% fly ash (90C+10FA) recorded the highest 28-day compressive strength of 43.93 N/mm², which is significantly higher than that of the control mix (39.28 N/mm²). This improvement is mainly due to the pozzolanic action of fly ash, which leads to the formation of additional calcium silicate hydrate (C–S–H) gel and results in a denser and stronger microstructure. Ø    On the other hand, mixes containing rice husk ash showed only a moderate increase in compressive strength. The highest value for RHA-based concrete was obtained for the 85C+15RHA mix, reaching 39.80 N/mm², which is only slightly higher than the reference mix. The comparatively lower improvement may be attributed to variations in particle size, surface characteristics, and reactivity of RHA. At higher replacement levels, such as 20%, both FA and RHA mixes exhibited a reduction in strength, likely due to the decreased cement content, which affects the overall binding capacity of the concrete. 2.                Split Tensile Strength Analysis Ø    The split tensile strength results show a trend similar to that observed in compressive strength. Concrete mixes containing fly ash exhibited better tensile performance compared to those with rice husk ash. The highest tensile strength was achieved by the 90C+10FA mix, recording 2.95 N/mm² at 28 days, which is a clear improvement over the reference mix value of 1.97 N/mm². This enhancement can be linked to improved bonding between the aggregates and the cement paste, supported by the fine particles of fly ash that contribute to a denser and more compact matrix. Ø    In the case of rice husk ash, the mixes showed an increase in tensile strength up to a replacement level of 15%. The 85C+15RHA mix reached a tensile strength of 2.64 N/mm² at 28 days. The high silica content in RHA helps improve the interfacial transition zone (ITZ), leading to better bonding, although the overall improvement is not as significant as that observed with fly ash. Ø    Overall, concrete mixes with fly ash perform better than those with rice husk ash in terms of both compressive and split tensile strength. This can be attributed to improved particle packing, higher pozzolanic reactivity, and better microstructural development. However, rice husk ash still shows stable and consistent performance, making it a suitable option when the focus is on sustainability and effective utilization of agricultural waste.

[1].            Al-Naghi, A. A. A., Ali, T., Inam, I., et al. (2025). An innovative approach to enhancing the strength and durability of recycled aggregate concrete through fly ash-silica fume coating and rice husk ash supplementation. Scientific Reports, 15, 32780. [2].            Barragán-Ramírez, R., González-Hernández, A., Bautista-Ruiz, J., et al. (2024). Enhancing concrete durability and strength with fly ash, steel slag, and rice husk ash for marine environments. Materials, 17(12), 3001. [3].            Ganesan, K., Rajagopal, K., & Thangavel, K. (2008). Rice husk ash blended cement: Assessment of optimal level of replacement. Construction and Building Materials, 22(8), 1675–1683. [4].            Indumathi, M., Nakkeeran, G., Roy, D., et al. (2024). Innovative approaches to sustainable construction: A detailed study of rice husk ash as an eco-friendly substitute in cement production. Discover Applied Sciences, 6, 597. [5].            Malhotra, V. M. (2002). Introduction: Sustainable development and concrete technology. ACI Concrete International, 24(7), 22–23. [6].            Mehta, P. K., & Monteiro, P. J. M. (2014). Concrete: Microstructure, properties, and materials (4th ed.). McGraw-Hill Education. [7].            Naik, T. R. (2008). Sustainability of concrete construction. Practice Periodical on Structural Design and Construction, 13(2), 98–103. [8].            Neville, A. M. (2011). Properties of concrete (5th ed.). Pearson Education. [9].            Onyelowe, K. C., Ebid, A. M., & Mahdi, H. A. (2022). Optimization of green concrete containing fly ash and rice husk ash based on hydro-mechanical properties and life cycle assessment. Civil Engineering Journal, 8(12). [10].         Ordoñez, L. M., Borrachero, M. V., Monzó, J., et al. (2024). Binary and ternary blended Portland cements containing different types of rice husk ash. Materials, 17(12), 2923.