Application of rice-husk derived zeolites for green roadway production for enhanced resource sustainability & reduced environmental impact

The major objective of this research was to synthesize and assess (mechanical and environmental perspectives) a set of six zeolites from agricultural waste byproducts: rice husk (RH) and rice husk ash (RHA), which could hold a sizeable water content in the crystal structure and serve as foaming warm-mix asphalt (WMA) additives aiding in the reduction of production and placement temperatures of hot mix asphalt mixtures. The major steps involved extraction of silica from RH to obtain rice husk silica (RHS) and synthesis of RHS- and RHA-derived zeolites followed by the selection of the best suitable foaming WMA additive: RHA-derived zeolite, which was subjected to environmental impact assessment for it to be recommended as a green roadway material. The RHA-derived zeolite synthesized at 100 °C displayed 22 % water content similar to the commercially available WMA additives. Furthermore, 0.75 % RHA-derived zeolite by weight of the total asphalt mix was found as the optimum dosage that achieved a reduction of 15 °C mixing and compaction temperatures compared to the control mix, which potentially decreased the fuel consumption and greenhouse gas emissions by about 11 and 9.8 % respectively. The leaching procedure test results revealed an exceptional ability of RHA-derived zeolite in mitigating leaching of heavy metals, thus establishing the transformation of RHA into RHA-derived WMA additive as an enhancement to the environmental performance of green paving product, thus, fostering the principles of circular economy and practices of innovative waste management techniques, specifically, promoting the waste-to-wealth concept.