Upcycling rice husk biowaste to improve cement-based peat soil stabilization

• A three-stage experimental strategy confirmed that RHA and RHF improved cement-based peat soil stabilization. • RHA played a major role as a pozzolanic material, while RHF is secondary as reinforcement. • UCS increased by 146.6 % with RHA alone and by 202.1 % with both RHA and RHF compared to cement only. • Cementitious products (C-S-H) resulted from RHA and Ca(OH) 2 -treated RHF filled pores and bonded soil particles. • Upcycling biowaste significantly reduces CO 2 emissions and cost by 61.9 % and 25.8 % compared with using cement only. Traditional stabilizers, such as kaolin and sodium bentonite, introduce complications when applied to cement-based peat soil stabilization. This study explores biowaste stabilizers – rice husk ash (RHA) as a pozzolan material and rice husk fiber (RHF) as reinforcing – as a sustainable and practical alternative. A three-stage experimental strategy was designed to identify the optimal stabilization method. Stage 1 determined the ideal RHA particle size and content without RHF. Stage 2 incorporated RHF to assess its best pretreatment method and optimal dosage; Stage 3 investigated the stabilization mechanisms. A series of physical and mechanical experiments confirmed that RHA and RHF improved cement-based peat soil stabilization. RHA played a primary role as a pozzolanic material, while RHF is secondary as reinforcement. Unconfined compressive strength (UCS) increased by 146.6 % with RHA alone and by 202.1 % with both RHA and RHF compared to cement only. This is achieved by using fine RHA particles and Ca(OH) 2 -treated RHF. The content for both RHA and RHF is critical, especially noting that the optimal content of RHA varies as the cement content varies. Microscopic analysis confirmed that RHA enhanced pozzolanic reaction, producing more cementitious products (C-S-H) that filled pores and bonded soil particles. Additionally, a significant quantity of cementitious products formed on the coarse surface of pre-treated RHF, reinforcing soil-fiber bonding. Stabilizing 1 m 3 of peat soil by upcycling biowaste reduces carbon emissions by 61.9 % and costs by 25.8 % compared to using cement only. This study demonstrates that upcycling biowaste provides an effective, sustainable, economical, and easy-to-implement solution for improving cement-based peat soil stabilization.