Abstract
In this study, an alkaline activator was synthesized by dissolving waste glass powder (WGP) in NaOH-4M solution to explore its effects on the formation of alkali-activated material (AAM) generated by Class-C fly ash (FA) and ground granulated blast furnace slag (GGBS). The compressive strength, flexure strength, porosity and water absorption were measured, and X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive X-ray (SEM-EDX) were used to study the crystalline phases, hydration mechanism and microstructure of the resulting composites. Results indicated that the composition of alkali solutions and the ratios of FA/GGBS were significant in enhancing the properties of the obtained AAM. As the amount of dissolved WGP increased in alkaline solution, the silicon concentration increased, causing the accelerated reactivity of FA/GGBS to develop Ca-based hydrate gel as the main reaction product in the system, thereby increasing the strength and lowering the porosity. Further increase in WGP dissolution led to strength loss and increased porosity, which were believed to be due to the excessive water demand of FA/GGBS composites to achieve optimum mixing consistency. Increasing the GGBS proportion in a composite appeared to improve the strength and lower the porosity owing to the reactivity of GGBS being higher than that of FA, which contributed to develop C-S-H-type hydration.
Highlights
To combat the high CO2 emissions emitted by the production of cement-based construction materials, there is an increased focus on research into “alkali-activated binders”. The production of such binders consists of alkaline activation of aluminosilicate material, such as fly ash (FA), ground granulated blast furnace slag (GGBS), metakaolin, bagasse or ashes of wood or paper [1]
Non-congruent dissolution of Mg was observed in WGA-30 solution, the more dissolution occurred, the releasing most of the Mg from the glasses
AndWGA-30WGA30 activated samples have greater open porosity and greater water absorption due to these solutions. This dramatic decrease in porosity again highlights the benefit of using GGBS over samples demanding more water during mixing
Summary
To combat the high CO2 emissions emitted by the production of cement-based construction materials, there is an increased focus on research into “alkali-activated binders”. The production of such binders consists of alkaline activation of aluminosilicate material, such as fly ash (FA), ground granulated blast furnace slag (GGBS), metakaolin, bagasse or ashes of wood or paper [1]. This energy doubles when Na2 SiO3 is used together with NaOH, as the production of NaOH pellets requires 20.50 MJ per kg [12] Based on these figures, it is clear that alternative alkaline solutions need to be identified to enable manufacture of alkali-activated material (AAM) with lower environmental impact
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