Bagasse ash–fly ash-geopolymer-treated soft Bangkok clay as subgrade material

Abstract

A geopolymer was investigated as a low-carbon dioxide emission binder for soft Bangkok clay improvement. Bagasse ash (BA), an industrial by-product, was used as the main precursor, while fly ash (FA) was used as a supplementary to develop a geopolymer. A mixture of sodium hydroxide (NaOH) and sodium silicate (Na2SiO3) was used as a liquid alkaline activator. The unconfined compressive strength, q u, of the geopolymers was found to be directly dependent on the precursor (BA and FA) to liquid alkaline solution (P:L) ratio, sodium hydroxide concentration, FA:BA ratio and curing time. The geopolymer binder with P:L = 55:45, BA:FA = 70:30, sodium silicate:sodium hydroxide = 2:1 and sodium hydroxide concentration = 16 M was selected to treat Bangkok clay based on engineering and economic perspectives. The q u improvement with geopolymer content was divided into active and inert zones. The 10% geopolymer content was found to be the threshold limit. Beyond this limit, the q u improvement was insignificant. The 5% geopolymer content could improve the q u of soft Bangkok clay to meet the minimum requirement for subgrade according to the local road authority. The outcome from this research will promote the BA–FA geopolymer as a cleaner binder by using recycled waste materials in ground improvement applications.