Thursday, 12 October 2017
Austroads has published the results of an experimental phase of a project to review the specifications and use of geopolymer concrete.
The results indicate that acceptable grades of structural and non-structural geopolymer concrete can be made for field applications.
This phase of the project involved formulating and testing geopolymer recipes for their workability, setting time, strength development, mechanical behaviour, durability properties and abrasion resistance.
The flexural and ductility behaviours of large reinforced geopolymer concrete beams were also compared to those of equivalent ordinary Portland cement (OPC) concrete.
The results show that commercially available Australian fly ash and blast furnace slag materials are suitable for the manufacture of geopolymer concrete, using solid sodium metasilicate alkali activators.
Geopolymer concrete formulations were developed for casting under ambient conditions; they performed satisfactorily with respect to workability, setting time, drying shrinkage, strength development, mechanical properties, and durability properties.
Fly ash/slag blends in the range of 60/40 and 40/60, including 50/50 fly ash/slag, performed particularly well, and exhibited superior performance with respect to drying shrinkage, sulfate resistance, chloride penetration and alkali-aggregate reaction (AAR) compared to OPC‑based concretes. However, 100% slag‑based geopolymers may be prone to AAR, at high alkali contents, and exhibited much larger volume of permeable voids (VPV) values than equivalent OPC concretes, although the high VPV values do not necessarily indicate high porosity, but are relate to hydrated phases in the geopolymer concrete.
The research found that the abrasion resistance of geopolymer concrete is slightly lower than the equivalent OPC concrete, but formulations can be improved by lowering the water content.
The ultimate load capacity of large beams made with OPC and geopolymer concretes are very similar, but the ductility of geopolymer beams was lower than that of OPC concrete, arising from the higher bond strength between the geopolymer concrete and steel than between OPC concrete and steel.
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