Effect of binder content and recycled concrete aggregate on freeze-thaw and sulfate resistance of GGBFS based geopolymer concretes

The use of waste materials in concrete production is important because of the recycling of these materials. In this context, the use of both geopolymer binder and recycled concrete aggregate (RCA) becomes important. For this purpose, in this study, ground granulated blast furnace slag (GGBFS) based geopolymer concrete containing RCA was designed and freeze-thaw (F-T) and sulfate resistance of these samples were determined. In the production of geopolymer concrete, three different binder contents (300, 400 and 500 kg/m3) and five different ratios of RCA (0, 25, 50, 75 and 100%) were used. Samples that completed curing period were exposed to 100F-T cycles and two sulfate solutions (3% MgSO4 and 1.5% Na2SO4 + 1.5% MgSO4). Compressive strength, ultrasonic pulse velocity (UPV), weight change and sorptivity values of these samples were determined. At the same time, these results were interpreted together with microstructure analysis (SEM and EDS). An exponential relationship was found between Ca/Si and Si/Al ratios of the samples and their compressive strength. Increasing in Ca/Si ratio and decreasing in Si/Al ratio caused an increase in compressive strength. As the binder content amount increased, the resistance of the samples against F-T cycles and sulfate solutions increased. With the increasing RCA ratio in the samples, there were increases in strength losses, but these losses were low and indicated that RCA was suitable for use in geopolymer concrete production.

Automated summary

In this study, GGBFS-based geopolymer concrete containing RCA was designed and tested for freeze-thaw and sulfate resistance. Results showed that increasing binder content led to improved resistance against freezing-thawing cycles and sulfate solutions. Additionally, the use of RCA in geopolymer concrete production showed potential as it resulted in minimal strength losses.