The hydration properties of ultra-fine ground granulated blast-furnace slag cement with a low water-to-binder ratio

Based on the fundamental principles of preparing reactive powder concrete (RPC), a new type of RPC was composed by replacing cement with the active powder component ultra-fine ground granulated blast-furnace slag (GGBS). GGBS is proposed as a potential alternative to silica fume (SF), which is currently the most commonly used RPC mineral admixture. In order to improve the brittleness of RPC, a steel fibre with appropriate length/diameter ratio was added. The ultra-fine GGBS (UFS) or SF replacement level was 20% by mass, with a water-to-binder (w/b) ratio of 0.18. The concrete specimens were pre-cured for 6 h at 20 °C and then exposed to steam curing conditions for 3 days. This study investigates the effects of the UFS and the SF on the durability of the RPC by examining the hydration properties, mechanical properties and permeability of RPC. Test results reveal that replacing the cement with UFS or SF does have a significant effect on the hydration properties, our results indicate that the inclusion of SF or UFS can accelerate the early hydration of cement and increase the consumption of Ca(OH)2. The mercury porosimetry and chloride ion penetration tests results revealed that RPC has a very low porosity and very dense structure. RPC with the addition of steel fibre exhibited a higher compressive strength than the RPC without steel fibre. Incorporating UFS into RPC had similar advantages to incorporating SF, but UFS proved to be the more economical admixture.