Abstract
As a promising alternative to alkali-activated fly ash (AAF) for high temperature application, the degradation mechanism of alkali-activated fly ash/GGBS (AAFS) under high temperature is not clear. This work investigates physicochemical properties of AAFS up to 800 °C and presents their synergetic influence on the thermal behavior. A quantitative assessment of the crack is developed to learn the cracking behavior. Results reveal that the crack density exhibits a linear relationship with ultrasonic pulse velocity. The crack density and compressive strength exhibit a positive correlation before 100 °C, but a negative relationship beyond 100 °C. The addition of slag into geopolymers lessons the geopolymeric behaviors such as further geopolymerization and viscous sintering, but further aggravates the thermal damage owing to the compact structure and unstable hybrid gel. The conceptual models of AAF and AAFS are proposed to explain the degradation mechanism of low slag contained geopolymers under elevated temperatures.
Highlights
Alkali-activated fly ash (AAF), named geopolymer, exhibits significant mechanical property and structural integrity under hightemperature exposure compared to Portland cement (PC) binders [1,2,3]
Comparable features are iden tified in AAF and activated fly ash/ground granulated blast furnace slag (GGBS) (AAFS), with the main crystalline phases are quartz, mullite, hematite and magnetite, which are similar to raw fly ash (FA)
This in dicates that the crystalline phase of AAFS is mainly determined by FA
Summary
Alkali-activated fly ash (AAF), named geopolymer, exhibits significant mechanical property and structural integrity under hightemperature exposure compared to Portland cement (PC) binders [1,2,3]. For AAF, the energy-consuming high-temperature curing process, as well as the un satisfied initial strength, largely hinder the further development of its insitu applications [11]. To counterbalance these limitations, growing attention has been paid to blended alkali-activated fly ash/GGBS binders (AAFS), which combine aluminosilicate source (fly ash or metakaolin) with calcium additives [12,13,14]. Up to now, it remains largely un explored regarding the thermal degradation of AAFS in comparison to that of AAF
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