Performance of Geopolymer Concrete at Elevated Temperatures

Currently there is sufficient evidence that Geopolymer Cement (GPC) concrete has a better resistance to fire than Ordinary Portland Cement (OPC) concrete, however not all of its behavioural aspects at high temperatures have been investigated. The aim of this research therefore is to investigate the deformational behaviour of GPC concrete under varying stress-temperature histories as well as at-temperature and residual strength properties. Additionally, given the lack of mix design methods for GPC concrete, a framework and design aids are developed to apportion mixes for low calcium alkali activated class F fly ash GPC concretes, which allow for a wide range of strength and workability values for engineering applications.At elevated temperatures, it was found that not only GPC undergoes transient creep, but also exhibits both expansive and contractive volume changes during heating, while maintaining its structural integrity up to 1000oC. The residual strength properties were found to be lower than at ambient, but significantly higher than those of OPC concrete. The loss in residual properties can be due to several phenomena such as damage caused by escaping water, damage to the matrix due to the disintegration of the geopolymer gel, the formation of new phases within the system, damage to the molecular structure of the aggregates, and thermal incompatibilities between the matrix and the aggregates. Replacing the natural aggregates with non-pelletized fly ash aggregates improved the residual properties of GPC concrete because of the better thermal compatibility between the matrix and the aggregates. Finally, experimental data on the evolution of strength properties and stress-strain behaviour of GPC concrete with temperatures are presented, as well as a uniaxial stress strain law