Durability properties of low-carbon concrete

Abstract

In recent years, the partial replacement of cement in concrete with ground granulated blast furnace slag (GGBFS) has received significant attention in order to reduce the environmental impact of concrete. Cement being a major binding constituent of concrete, it’s production releases enormous amount of carbon dioxide into the atmosphere.

This research focuses on performing and analyzing the experimental study on the durability properties of concrete containing different binders with varying content of GGBFS. The tested cement types are CEM II/B, CEM III/B, CEM III/A, CEM II/A, and CEM I. A total of 9 binders (cement + slag) with replacement increments of GGBFS content between 17% - 79% were casted and tested. As one of the aims is to lower the CO2 emissions, the CO2 produced by the binders used in this research is also calculated.

Experimental tests were conducted to establish the workability, air content, compressive strength, freeze – thaw resistance of non-carbonated and accelerated carbonated specimens, carbonation depth, pore structure through capillary suction test and thin-section analysis. Test specimens were prepared according to respective test standards.

Results conclude that slag content have clear effect on almost all properties of concrete. Concrete with high slag content have lower compressive strength at 7 days age, as hydration process becomes slower in the presence of slag, but at later ages, compressive strength can be higher than OPC concrete. Moreover, slag has a dominant effect on freeze-thaw resistance, especially when subject to saline water, so 50% slag replacement is critical or recommended and provides promising results. P-factor calculations suggests that, lower the slag content, higher will be the p-factor, which concludes that with increasing slag the service life of concrete infrastructures may reduce.

Furthermore, increase in slag content makes concrete pore structure denser, that in turn slows down the capillary rise through pores. Also, thin-section analysis gave very low spacing factors for all concrete types and confirms that this method is not useful for evaluating the salt freeze-thaw resistance, in cases when using high slag content. All the test specimens were cast with same water/binder ratio of 0,45 because the binders were different in all the castings.