Influence of Slag Composition and Temperature on the Hydration and Performance of Slag Blends in Chloride Environments

The use of GGBS as supplement for cements has been shown to improve the long-term strength and durability properties of concrete. In practice, while the chemical composition of GGBS from a single plant may be constant, due to the varying sources from which GGBS is obtained the chemical composition from plant to plant may vary. The wide variability in the use of GGBS as a SCM in different climates, coupled with differences in chemical composition, is bound to have impact on the performance of slag blends.
This study investigated the combined influence of difference in slag composition and temperature on the performance of slag blends. Performance was evaluated in terms of strength and transport properties. Paste samples were characterised by calorimetry, TGA, XRD and SEM to follow hydration and microstructural development. Mortar samples were used to follow strength development and transport properties. All tests were carried out at temperatures of 20 and 38°C.
Curing at 38°C accelerated the early hydration, but not the later hydration. This led to higher early strengths and lower later strengths, and was attributed to the coarsening of the pore structure caused by the high temperature curing. Except at the early ages at 20°C, both slag blends showed better strength performance than the reference cement. The slag blends also showed better transport properties than the reference cement, especially at 38°C, and this was attributed to their finer pore structure and higher chloride binding capacity.
Of the two slags studied, the more reactive slag (slag 1) had better performance, especially at 38°C. Performance of the slag blends at 20°C was influenced mainly by the length of curing, and by the difference in chemical composition at 38°C.