Alteration in the Microstructure of Fly Ash Geopolymers upon Exposure to Elevated Temperatures

Abstract

This paper represents the mechanical and microstructure changes in geopolymeric material synthesized by the alkali activation of locally source fly ash at high temperatures of 400, 600 and 800 °C. The high compressive strength of geopolymer cured at 70 °C underwent thermal shrinkage and substantial strength losing at temperatures of 400, 600 °C caused by the high dehydration of the structural water. Exposure to temperature of 800 °C, the geopolymer lost its strength due to extremely densification and expansion processes of the high unreacted silicate phase in the structure. The SEM results showed that the high activator content generated large quantities of unreacted silicate crystals at high temperatures which sintered at range of temperatures of 700-800 °C causing system failure.

Durability of mortar and concrete containing alkali-activated binder with pozzolans: A review

“…In general, AA mortar has an excellent acid resistance due to the absence of Ca(OH) 2 . On acid exposure, activated mortars have shown a weight gain of up to 2.5% after a 28-day exposure, which is due to scale formation in acid as reported by researchers [90,91]. Based on acid immersion studies, AA mortars turned out to be better in terms of acid resistance property (Figs.…”

Strength and Durability Performance of Alkali-Activated Rice Husk Ash Geopolymer Mortar

“…In general geopolymer mortar has excellent acid and sulfate resistance due to the absence of cement (Ca(OH) 2 ). In acid and sulfate exposure, geopolymer mortars have shown weight gain of up to 2.5% after 28 days of exposure, which is due to scale formation in acid and deposition of white powder formation in sulphate exposure on the surface of the specimens [ 22 , 23 ].…”

Mechanical and Microstructural Evaluations of Lightweight Aggregate Geopolymer Concrete before and after Exposed to Elevated Temperatures

“…It is likely that a portion of the activating solution remained unreached, or partially reacted, in the geopolymeric matrix during the geopolymer formation [ 19 ]. These unreached, or partially reacted, residual species are composed mainly from silicate [ 20 ], which experienced extensive thermal expansion at temperature ranges of 700–800 °C, due to the swelling of the high silicate secondary phases as described in references [ 19 , 21 ].…”