Study on the utilization of byproducts for geopolymer synthesis

Abstract

Geopolymer is a material that is hardened using alkaline solution and active fillers such as coal fly ash. One advantage of geopolymer is that it allows for the utilization of by-products in the material. This study aimed to effectively utilize by-products in civil engineering materials and investigated the relationship between uniaxial compressive strength of geopolymer and the concentration of sodium hydroxide using various by-products: municipal solid waste incineration ash, municipal solid waste incineration fly ash, coal fly ash, and steel slag. Leaching tests were also conducted using each filler and alkaline solution to examine the dissolution concentration and ratio (Si/Al) of silicon (Si) and aluminum (Al), which are believed to be related to the solidification process. As a result, coal fly ash exhibited a significant increase in strength. When focusing on the Si/Al ratio, it was found to be around 1, suggesting that the balance of dissolved Si and Al played a crucial role in the strength enhancement. Furthermore, for almost all fillers, higher NaOH concentrations resulted in increased strength and higher concentrations of dissolved Si and Al. This indicates that not only the balance of dissolved Si and Al, but also their absolute concentrations, are important for strength enhancement.