In Ultra High Performance Matrices (UHPM) mix design focuses on improving homogeneity, compactness, reactivity of the fine powders, and the microstructure of the cementitious matrix. Therefore, UHPM do not contain any coarse aggregate. Finely crushed quartz is also added to correct the granular distribution as well as to decrease the potential Ca/Si ratio of the C-S-H when the matrix is cured at high temperature. The main purpose of this study was to see if UHPM could be made using less Portland cement and materials more reactive than crushed quartz such as fly ashes or blast-furnace slag. The consequences of these substitutions on the characteristics of fresh and hardened mortars were studied. Compressive strength was measured before and after hot-water curing at 90C. For example, with slag, it was possible to reach a compressive strength of about 180 MPa with a replacement rate of 60 percent of Portland cement. Slag matrices samples were also analysed using Nuclear Magnetic Resonance (NMR). 29Si probe was used to identify and quantify all the phases produced during the hydration process. It was found that the Q2/Q1 ratio increased with the slag content, which means an increase of the average length of the C-S-H chain.
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