Abstract
This paper presents a comparative study of the characteristic of unfoamed and foamed geopolymers after exposure to elevated temperatures (200–800 °C). Unfoamed geopolymers were produced with Class F fly ash and sodium hydroxide and liquid sodium silicate. Porous geopolymers were prepared by foaming with hydrogen peroxide. Unfoamed geopolymers possessed excellent strength of 44.2 MPa and degraded 34% to 15 MPa in foamed geopolymers. The strength of unfoamed geopolymers decreased to 5 MPa with increasing temperature up to 800 °C. Foamed geopolymers behaved differently whereby they deteriorated to 3 MPa at 400 °C and increased up to 11 MPa at 800 °C. Even so, the geopolymers could withstand high temperature without any disintegration and spalling up to 800 °C. The formation of crystalline phases at higher temperature was observed deteriorating the strength of unfoamed geopolymers but enhance the strength of foamed geopolymers. In comparison, foamed geopolymer had better thermal resistance than unfoamed geopolymers as pores provide rooms to counteract the internal damage.
Highlights
OPEN Thermal Resistance Variations ofResponses received: 17 November 2016 accepted: 22 February 2017 Published: 27 March 2017
From the past decades, the concern on the thermal performance and fire resistance of building materials has become one of the research interests
At high temperature (600 °C), geopolymer mortars with high slag content exhibited greater strength loss, which is mainly due to the dehydration of calcium silicate hydrate (CSH) phases
Summary
Responses received: 17 November 2016 accepted: 22 February 2017 Published: 27 March 2017. The formation of crystalline phases at higher temperature was observed deteriorating the strength of unfoamed geopolymers but enhance the strength of foamed geopolymers. It is because there is lower binder content in concretes to counteract the shrinkage of paste and due to the difference in the thermal expansion between coarse aggregates and binder that contributed to significant microcracking. The porous geopolymer foam is usually assumed to have the same thermal behaviour as the dense geopolymers when exposed to elevated temperature and fire. In this study, a comparative study is carried out to investigate the thermal behaviour of unfoamed and foamed geopolymers based on the fly ash from a local coal combustion power plant. In order to synthesize porous geopolymer foam, the hydrogen peroxide (0.75 wt.%) was added and stirred followed by moulding and curing process at room temperature
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