Microstructure & properties of steel-reinforced concrete incorporating Portland cement and ground granulated blast furnace slag hydrated at 20 °C

The results of a backscattered electron imaging study of the microstructure of the steel- and aggregate-cement paste interfaces of reinforced concrete systems hydrated at 20 °C temperature are reported. The mix using neat OPC showed increasing calcium hydroxide (CH), and decreasing porosity and anhydrous cement levels with respect to age. Higher CH and porosity, and lower anhydrous cement levels at the interfaces compared to the bulk cement were also shown. Mixes incorporating ground granulated blast furnace slag (GGBS) at various cement replacement levels showed consistently low CH, and decreasing porosity, anhydrous cement and unreacted slag levels with respect to age. Higher CH and porosity, and lower anhydrous cement and unreacted slag at the interfaces compared to the bulk were also shown. The slope profiles of unreacted slag at the interfaces were steeper suggesting a narrower interfacial transition zone and thus tighter packing for the GGBS incorporated mixes.