Predicting the Hydration of Ground Granulated Blast Furnace Slag and Recycled Glass Blended Cements

The use of recycled glass powder (RCGP) is investigated as a partial replacement for ground granulated blast furnace slag in blended CEM II/A-LL cements using thermodynamic modelling to simulate cement paste hydration at a water-to-cement (w/c) ratio of 0.5. This study allows a rapid means of examining the likely evolution of these materials over the first two to three years, allowing experimental work to focus on promising formulations. A comparison is made between the evolving solid phase and solution chemistries of four materials: a standard Portland-limestone (CEM II/A-LL), a ‘control’ blend, comprising equal quantities of CEM II/A-LL with GGBS and two novel blended cements containing RCGP. These represent 15% replacement (by mass) of GGBS by RCGP blended with either 40% or 60% CEM II/A-LL. The simulations were performed using the code HYDCEM, a cement hydration simulator, which calls on the thermodynamic model PHREEQC to sequentially simulate the evolution of the four cements. The results suggest that partial replacement of GGBS by 15% RCGP results in no significant change in system chemistry. The partial replacement of cementitious slag by waste container glass provides a route by which this material can be diverted from the landfill inventory, and the mass-balance and energy balance implications will be reported elsewhere.