Residual mechanical properties of GGBS-FA-SF blended geopolymer concrete after exposed to elevated temperatures

Geopolymer concrete has been increasingly used in industry. However, if the geopolymer concrete is blended using a single percussor its performance is often very limited by the properties of the percussor. Thus, it is preferable to use multiple percussors to produce geopolymer concrete. In this paper an experimental study is reported on the residual micro- and macro-mechanical properties of the steel-fibre reinforced geopolymer concrete blended by using combined percussors of ground granulated blast-furnace slag, fly ash, and salic fume. The experimental work included the examination of the effects of exposure temperature, the volume fractions of coarse aggregate and steel fibre on the compressive strength, elastic modulus, peak strain, toughness, and stressstrain constitutive relationship of the mixed geopolymer concrete, and the characterisation of the micro-structure of the materials after they were exposed to various elevated temperatures by using X-ray diffraction, scanning electron microscopy, thermal gravimetric analysis, and mercury intrusion porosimetry techniques. The experimental results showed that the residual compressive strength and residual elastic modulus decrease with the increase of exposure temperature regardless of the mix designs. The residual compressive strength of the geopolymer concrete is higher than that of the geopolymer mortar when they both are not reinforced with steel fibre. However, when they are reinforced with steel fibre the residual compressive strength of the geopolymer concrete is lower than that of the geopolymer mortar. Based on the experimentally obtained results, a temperaturedependent uniaxial stress-strain empirical equation is also proposed for the purpose of practical use.