Synergistic Effects of Silica and Calcium‐Based Dual Admixtures on the Flowability, Microstructure, and Strength Development in Low‐Carbon Concrete

ABSTRACT

Eco‐friendly construction practices have emerged as a cornerstone of modern development. Due to the substantial carbon emissions from cement production, there is a growing demand for supplementary cementitious materials. This study investigated the synergistic effects of two different wastes, silica‐rich rice husk ash (RHA) and calcium‐rich seashell powder (SSP), on the flowability, microstructure, strength development, and reduction in carbon emissions. RHA (0%–12.5%) and SSP (0%–12.5%) were incorporated in equal proportions, replacing cement at levels ranging from 0% to 25%. The fresh and hardened properties of the concrete were evaluated through slump, compressive strength, and split tensile strength tests. Microstructural characteristics were analyzed using scanning electron microscopy (SEM) and energy‐dispersive X‐ray spectroscopy (EDS). In addition, the environmental performance was assessed based on global warming potential (GWP) and eco‐strength efficiency (ESE). The results revealed that incorporating RHA and SSP reduced both the workability and the unit weight of the hardened concrete. Replacing 5%–10% of the cement with these ash powders initially had a negative impact on mechanical performance. However, beyond 10% replacement, gradual improvements were observed. At 25% replacement, the modified concrete achieved superior compressive strength, along with enhanced split tensile strength, modulus of elasticity, and cement efficiency. Moreover, the blended concrete demonstrated notable environmental benefits by reducing carbon emissions. Overall, the combined use of RHA and SSP offers a promising approach for sustainable waste management and eco‐efficient construction practices.