A Study of the Residual Strength of Reactive Powder-Based Geopolymer Concrete under Elevated Temperatures

This paper reports on studies relating to the unstressed residual compressive strengths of geopolymer pastes that are heated up to 800 °C, behavior of reactive powder concrete before and after exposure to elevated temperatures and thermal behavior of novel reactive powder geopolymer-based concretes. For this purpose, 10 geopolymer pastes and three reactive powder concrete mixtures were tested for residual strengths. Gladstone fly ash was used as the primary binder for both geopolymer pastes and reactive powder geopolymer concretes. In addition, four novel reactive powder geopolymer concrete mixes were prepared with zero cement utilization. While reactive powder concretes achieved the highest seven-day compressive strengths of approximately 140 MPa, very poor thermal behavior was observed, with explosive spalling occurring at a temperature of ca. 360 °C. The reactive powder geopolymer concretes, on the other hand, displayed relatively high thermal properties with no thermal cracking at 400 °C, or visible signs of spalling and very mild cracking in one case at 800 °C. In terms of the strength of reactive powder geopolymer concrete, a maximum compressive strength of approximately 76 MPa and residual strengths of approximately 61 MPa and 51 MPa at 400 °C and 800 °C, respectively, were observed.