Material Characterization of Geopolymer Concrete for Its Beneficial Use in Composite Construction

Geopolymer concrete (GPC) is an inorganic, mineral-based construction material with high resistance to chemical attack and further excellent properties such as rapid strength development and relatively low CO₂ emissions in comparison to ordinary Portland cement based normal concrete (PCC). However, production technologies, corresponding to the workability and time-dependent properties during the hardening of GPC are not known in detail. The aim of an ongoing research project is to combine GPC with PCC to form composite structures for applications in chemically aggressive environments such as sewers. This paper deals with material properties of GPC, which have significant impact on the composite action. GPC formulations with different workability (soft and stiff-plastic consistencies) were developed and investigated with regard to their compressive and tensile strength development over time, as well as shrinkage during hardening under different ambient conditions (autogenous shrinkage, drying shrinkage, early shrinkage). The GPCs investigated show significant autogenous shrinkage and drying shrinkage. Under dry conditions, additionally very high early shrinkage occurs immediately after the beginning of hardening, which was tested using the image correlation method. The extent of this early shrinkage depends strongly on the thickness of the specimen. As another result of this experimental study, equations for the prediction of the strength development over time are given in this paper.