Rice husk-derived biosilica aerogel as a lightweight additive for heat-gain mitigation in cementitious blocks

The development of heat-gain mitigating construction materials from agro-industrial residues is relevant for improving building-envelope performance while promoting circular material use. This study evaluated a rice husk-derived biosilica aerogel as a lightweight additive for scaled cementitious blocks. Rice husk was converted into amorphous biosilica through acid leaching, washing, drying, and calcination at 550 °C. The obtained precursor was transformed into a biosilica aerogel by alkaline dissolution, acid neutralization, aging, washing, ethanol exchange, freezing, and freeze-drying. The biosilica precursor showed characteristic Si-O-Si and Si-OH bands, an amorphous XRD halo between 22° and 26° 2θ, Si- and O-rich surface composition, a BET surface area of 256 m 2 g -1 , a mean pore width of 3.79 nm, and a total pore volume of 0.32 cm 3 g -1. Among the tested formulations, the additive-free AG-SiO 2 aerogel showed the lowest apparent density, approximately 0.26-0.33 g cm -3 , and was selected for block-scale evaluation. Under outdoor exposure, aerogel-modified blocks showed lower internal temperatures than the reference block. The AG-1.00 formulation achieved the highest thermal-response improvement, with a maximum temperature reduction of 7 °C and an average ΔT of 2.71 °C during the 14 h test. These results support the potential of the proposed rice husk-derived biosilica aerogel as a lightweight additive for heat-gain mitigation. However, direct thermal conductivity, compressive strength, moisture resistance, and durability tests are still required before construction-scale application.