Abstract

Soft Bangkok clay (SC) is recognized as a problematic soil in Thailand. This research investigates the possibility of using polyvinyl alcohol (PVA) and high calcium fly ash (FA) geopolymers to improve the strength of SC in deep soil mixing applications. The liquid alkaline activator (L) was composed of sodium silicate (Na2SiO3) and sodium hydroxide (NaOH). The studied influence factors included FA content, water content, L content, Na2SiO3/NaOH ratio, PVA concentration, PVA content, and curing time. Strength development and microstructure in the PVA-FA geopolymer stabilized SC were evaluated via the unconfined compressive strength (UCS) test and scanning electron microscope (SEM) test. The optimum ingredient considering workability and cost of FA geopolymer stabilized SC was found to be at a mix design of 1.0LL, Na2SiO3/NaOH = 1, FA = 40% and L/FA = 0.6, whereby a 28-day UCS of 1026 kPa was attained. The optimum PVA content and PVA concentrations were found at 15% and 4%. The 7-day and 28-day UCS values were improved by PVA up to 40% and 42% compared to those of the specimen without PVA, respectively. The outcome of this research will promote the usage of PVA-FA geopolymer as an alternative green soil stabilizer alternative to Portland cement for a DM improved soft Bangkok clay.

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