Utilization of Alkali-Activated Rice Husk Ash for Sustainable Peat Stabilization

Abstract

Abstract Peat is formed from organic matter (OM) in wetlands under an anaerobic environment. Peat is considered weak and problematic soil because of high-water retaining capability, high compressibility, and low shear strength. The cement is generally used to stabilize peat, but cement production is energy intensive and contributes 7–8 % of total carbon dioxide to the atmosphere. Nowadays, there is a need to use a potential “greener” alternative that is sustainable in the long term. Therefore, this research assesses the feasibility of rice husk ash (RHA)–based alkali-activated binder (AAB)–stabilized peat with varying fiber content (6–73 %) and OM (21–79 %). The RHA-based AAB was prepared by adding bauxite powder (as alumina source) to RHA in proportion to keep constant silica to alumina ratio (silica/alumina = 3). The samples were prepared using sodium hydroxide (NaOH) of molarities 3, 6, and 9 to activate the binder with percentages 10, 20, and 30 % by weight of dry peat and alkali (A) to binder (B) ratio chosen as 0.5, 0.7, and 0.9. The results illustrate that the factors like pH of pore solution, the molarity of NaOH, binder content, A/B ratio, OM, and curing affect the unconfined compressive strength (UCS) of treated peat. The maximum UCS of 962, 873, and 668 kPa was found at an optimum combination of molarity (6M), binder content (20 %), and A/B ratio (0.7) for sapric, fibric, and hemic peat. It was seen that OM has a negative impact, whereas the curing period positively impacts the UCS of treated peat. Furthermore, the cumulative mass loss of fibric peat (13.6 %) is more than hemic (11.4 %) and sapric (10.6 %) peat. The X-ray diffraction patterns and field emission scanning electron microscopy micrographs confirm the cementitious minerals that fill pore spaces or cavities to form a smooth and dense gel responsible for strength gain.