Moving beyond cement replacement: High-volume utilization of rice husk ash through artificial aggregates

The sustainable management of rice husk ash (RHA), a silica-rich agricultural residue generated after biomass-based energy production, remains a significant environmental challenge because its utilisation as a cement substitute is generally limited to replacement levels of only 10–20%, restricting its large-scale valorisation. This study investigates an alternative utilisation pathway by developing cold-bonded RHA aggregates (RHAA) and evaluating their mechanical, durability, environmental, and large-scale utilisation potential as replacements for natural coarse aggregates in concrete. Concrete mixtures containing 25%, 50%, 75%, and 100% volumetric RHAA replacement were produced using a binary binder comprising 40% ground granulated blast furnace slag (GGBFS). Environmental performance was quantified through embodied energy (EE) and embodied carbon (EC). Increasing RHAA replacement progressively reduced concrete density, with the 100% replacement mixture exhibiting a 25.5% reduction and satisfying lightweight concrete requirements. Although mechanical properties and durability decreased because of the higher porosity of RHAA, the 25% replacement maintained structural-grade performance, water absorption below 10%, and chloride migration comparable to the binary binder concrete. Replacing ordinary Portland cement with GGBFS reduced EE and EC by 604.49 MJ/m 3 and 124.94 kgCO 2 /m 3 , respectively. Finally, 25% RHAA replacement was identified as the optimum level for structural concrete, whereas 100% replacement is suitable for lightweight non-structural applications such as hollow masonry blocks. An Indian case study further demonstrated that RHAA-based hollow masonry blocks could support the annual construction of approximately 2.54 million 1BHK houses, highlighting the considerable circular economy potential of this approach.