Performance and Durability Assessment of Sustainable Green Concrete Incorporating Fly Ash and Rice Husk Ash
The global demand for concrete has escalated rapidly due to the swift expansion of residential and commercial infrastructure. This phenomenon has consequently intensified cement manufacturing and aggravated anthropogenic carbon dioxide (CO2) emissions. To tackle these environmental issues and restrict fluid-induced microcracking in concrete elements, this experimental work evaluates the engineering properties of modified M20 concrete utilizing agro-industrial byproducts as alternative cementitious binders. In this study, Ordinary Portland Cement (OPC) was partially substituted with Class F fly ash at replacement levels of 30%, 35%, and 40%, alongside rice husk ash (RHA) at 5% and 10% by weight, establishing six distinct replacement categories. A total of seventy-seven cube specimens (150 mm × 150 mm × 150 mm) were fabricated to investigate workability, water absorption, compressive strength development, and water permeability resistance. The laboratory outcomes demonstrate that high cement substitution rates significantly alter the internal pore network, thereby governing both the strength gain and long-term durability behavior. Slump values across all formulated design mixes exceeded 100 mm, classifying the fresh concrete as collapsed slumps with high fluid consistency. Although the unblended control mixture displayed the highest 28-day compressive strength (19.53 N/mm²) and superior fluid penetration resistance (80.44 mm depth), the ternary blend containing 5% RHA and 40% fly ash was identified as the optimal eco-friendly formulation. This specific matrix yielded a 28-day compressive strength of 17.79 N/mm² and recorded the highest resistance to water penetration among all modified cohorts (141.00 mm). Even though the high volume of fly ash prevented the blended mixes from satisfying the empirical threshold of standard M20 concrete, the formulated green concrete exhibits promising technical viability for structural applications under the M15 classification. Ultimately, this research validates viable pathways for recycling natural waste products to minimize infrastructure deterioration and promote circular economy strategies within the construction sector.