Title: Strength Increase of Geopolymer at Elevated Temperatures and subsequent Glass Transition Behaviour

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Publication: CIA

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Date: 2/28/2011

Abstract:
Superior fire resistant properties geopolymers synthesized with fly ash are previously reported. However, the reported results are residual properties obtained after cooling to room temperature. This paper reports stress versus strain curves of geopolymers tested while the specimens were kept at the elevated temperatures. Tests were performed at temperatures from 23 to 680°C and after cooling. Hot strengths of geopolymers increased when the temperature increased from 290 to 520°C, reaching the highest strength at 520oC, which is almost double of its initial strength at room temperature. However, an abrupt change of material behaviour from solid to rubbery nature was observed between 520 and 600°C. This abrupt change emulates glass transition behaviour. The glass transition temperature is determined to be 560oC. Further, the increased hot strengths were not maintained after cooling to room temperature. This is attributed to the damage due to brittle nature of the material making it difficult to accommodate thermal strain differentials during cooling phase.