Effects of Ultrafine Blast Furnace Slag on the Microstructure and Chloride Transport in Cementitious Systems under Cyclic Drying–Wetting Conditions

Abstract

This paper presents experimental investigations into the effects of ultrafine blast furnace slag on microstructure improvements against chloride penetration in saturated and unsaturated cementitious systems exposed to cyclic drying–wetting conditions. The hydration kinetics of ultrafine slag powders and pore solution chemistry in slag-blended cementitious systems at different ages, together with the main hydration products and pore structure characteristics, were determined. The chloride profiles accounting for different slag contents and drying–wetting cycles were measured. The results reveal that the reactivity of ultrafine slag can be well described with Avrami’s equation. The dilution effect of the slag predominated the pore solution chemistry, and the pH value decreased with a higher inclusion of slag. An optimal inclusion of 65% slag by mass of the binder corresponding to the finest pore structure and highest hydrotalcite content was found, which provides a reasonable basis for the slow chloride diffusion and high chloride binding. Under drying–wetting exposure, the specimen with a lower saturation exhibited a higher chloride transport caused by capillary absorption in the skin layer. The chloride transport tended to be diffusion controlled after sufficient drying–wetting cycles.

Effect of Ultrafine Slag Powder on the Rheological Behaviour, Compressive Strength, and Microstructure of Ultra-High Performance Concrete

“…Figure 9b further illustrated the filling effect of the USL promoted the homogenisation of the paste and improved the uniform distribution of the USL particles in the UHPC. Further magnification of the BSE microscopy image of the pastes revealed that the USL particles were covered by the hydration products in Figure 9b, indicating that secondary hydration of the USL particles occurred and organically combined with the surrounding hydration products [28]. This is further evidence that the addition of 20% USL improved the homogeneity of the microstructure of the hydration products and increased the denseness of the cement paste, which is consistent with the results presented by the MIP and SEM analyses.…”