Geopolymer and Portland cement concretes in simulated fire

High-strength Portland cement concrete has a high risk of spalling in fire. Geopolymer, an environmentally friendly alternative to Portland cement, is purported to possess superior fire-resistant properties. However, the spalling behaviour of geopolymer concrete in fire is unreported. In this paper, geopolymer and Portland cement concretes of strengths from 40 to 100 MPa were exposed to rapid temperature rises, simulating fire exposures. Two simulated fire tests, namely rapid surface temperature rise exposure test and standard curve fire test, were conducted. In both types of test, no spalling was found in geopolymer concretes, whereas the companion Portland cement concrete exhibited spalling. This can be attributed to different pore structures of the two concretes. The sorptivity test found that geopolymer concrete had a significantly higher sorption, therefore more connected pores, than Portland cement concrete when compared at the same strength level. Hence, it is suggested that the water vapour can escape from the geopolymer matrix quicker than in Portland cement concrete, resulting in lower internal pore pressure. The paper concludes that, when compared at the same strength level, the geopolymer concrete possesses higher spalling resistance in a fire than Portland cement concrete due to its increased porosity.