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The impact of novel supplementary cementitious materials (SCMs) on the phase assemblage and the pore structure in cement pastes was studied and linked to their impact on the compressive strength in mortar. The composite cements analysed had a composition of 78 wt.% Portland cement, 18 wt.% SCM and 4 wt.% limestone filler, and the samples were cured sealed for 91 days at 20°C. The investigated SCMs comprise natural materials such as clays and volcanic rocks (rhyolite and hyaloclastite), and industrial products such as fly ash, slag, oil shale ash, bio-fuel ash or bio-coal fly ash. The results revealed that all the SCMs except oil shale ash contribute to the phase assemblage in a similar way, when clinker is replaced with 18 wt.% SCM. The pore structure of the different cement pastes was similar. Even when the composite cement pastes showed a higher total intruded pore volume compared to the Portland cement paste sample, these samples showed higher compressive strength. This indicates that total intruded porosity is not the only contribution to strength. [ABSTRACT FROM AUTHOR]

The reactivity of synthetic glasses depends on their chemical compositions. In far from equilibrium dissolution experiments, the reactivity of Ca-rich glasses with compositions similar to blast-furnace slag is found to be much higher (up to ~60 wt.% after 7 days) compared to Si-rich glasses with compositions similar to type F fly ash (up to ~20 wt.% after 7 days). Isothermal calorimetry and TGA experiments conducted on model systems containing portlandite and calcite and on glass-blended Portland cement confirmed the higher reactivity of the Ca-rich glasses. The degree of glass reaction after 91 days ranged from 7 to 20 wt.%. The results showed also a higher reactivity of the glasses containing more aluminum (both for Ca-rich and Si-rich glasses) indicating that not only calcium but also aluminum acted rather as network modifier than as network former. The results confirm a strong dependence of the glass reactivity on the degree of polymerization of the glass network. [ABSTRACT FROM AUTHOR]

In this study the hydration kinetics and the development of concentrations in the pore solution of cement pastes containing different supplementary cementitious materials (blast-furnace slag, Si-rich fly ash, limestone, quartz) at a cement replacement of 50 wt.% were investigated during the first 6 h of hydration. The results indicate that the degree of undersaturation with respect to alite is the primary factor driving the early hydration kinetics. The accelerating effect of the limestone is related to a higher undersaturation. The data reveal also that high aluminium and sulfate concentrations, which depend on the type and chemical composition of the used mineral addition, retard the reaction. High calcium concentrations had no adverse effect on hydration kinetics. The investigations underpin that the mechanisms controlling the early hydration are a complex combination of the filler effect, the pore solution chemistry as well as intrinsic reactivity of the mineral additions and their surface characteristics. [ABSTRACT FROM AUTHOR]

Model Ca–Mg–Na-aluminosilicate glasses based on compositions found in a calcareous fly ash were synthesised and their reactivity assessed in NaOH solution and in Portland cement paste. It was found that the reactivity followed the same trend in both systems and that the reaction of the glasses in pastes was very similar to that of the components of similar composition in the real fly ash. This finding indicates that the reactivity of glass in cement can be directly linked to the chemical composition of the glass. Further, when the reactivity of the glasses was normalized to their surface area, it was found that there exists a strong correlation with the NBO/T, the ratio of non-bridging oxygens and tetrahedral ions in the glass. [ABSTRACT FROM AUTHOR]