Optimizing rice husk ash for ultra-high-performance concrete: A comprehensive review of mechanical properties, durability, and environmental benefits

Abstract

This review critically examines the potential of rice husk ash (RHA) as a supplementary cementitious material (SCM) in ultra-high-performance concrete (UHPC), focusing on its impact on mechanical properties, microstructure, and sustainability. Literature for this review was selected through a systematic search of Scopus, Web of Science, and Google Scholar, focusing on studies from the last two decades that provide empirical data on RHA-enhanced UHPC performance and microstructure. With a silica content ranging from 85% to 95%, RHA enhances pozzolanic reactions, leading to improved UHPC performance. Maximizing RHA's efficacy in UHPC requires optimization techniques, such as utilizing superplasticizers and fibers, maintaining low water-to-binder ratios (0.18-0.22), and regulating replacement amounts (10-20%). At optimal replacement levels of 10-15%, RHA increases compressive strength by up to 9.78%, tensile strength by 25.09%, and flexural strength by 10.9%, compared to control mixes. Additionally, its use reduces carbon dioxide emissions by approximately 10-15% and energy consumption by up to 20%, contributing to more sustainable concrete production. The review also highlights a reduction in chloride penetration and improved resistance to sulfate attack and freeze-thaw cycles, due to microstructural densification and reduced porosity. However, performance is sensitive to RHA quality, processing methods, and mix design parameters. This review identifies current limitations and recommends future research in standardization, long-term durability, and optimization strategies, underscoring the role of RHA in advancing eco-efficient, high-performance concrete technologies.