Steel fibre reinforced geopolymer concrete (SFRGC) with improved microstructure and enhanced fibre-matrix interfacial properties

Geopolymers are aluminosilicate materials formed by mixing by-product materials with alkaline solutions, and which have several desirable properties compared to Portland cement concrete in terms of strength and durability. Most of the previous research on steel fibre reinforced geopolymer concrete (SFRGC) has focused on the properties of single or binary mixes hardened under heat curing conditions, which is a severe limitation for on-site, cast-in-place applications. In the current study, a novel plain and steel fibre reinforced geopolymer concrete (SFRGC), containing various types of commercial Silica Fume (SF) (densified, undensified and slurry silica fume) and varying Ground Granulated Blast Furnace Slag (GGBS) content in a ternary binder mixture, cured under ambient (room) temperature has been examined. An extensive experimental investigation was conducted to evaluate the fresh properties, mechanical characteristics and microstructure of the examined material. The experimental results indicate that the mechanical characteristics of all the examined mixes are enhanced by increasing the GGBS content, in both plain and steel fibre reinforced geopolymer concrete. Geopolymer concrete with undensified silica fume showed better mechanical strength compared to that with densified and slurry SF, due to the agglomeration and ineffective dispersion of the latter fume types. SEM microstructural observations and porosity measurements were also conducted. The results indicate that the inclusion of silica fume and increasing GGBS content leads to higher pozzolanic activity and pore infilling, providing relatively homogeneous, compact and dense microstructures and subsequently improved mechanical properties.