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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.

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]

The effect of additions of limestone and dolomite powder on the properties of blended cements cured at 40 and 60°C was investigated using a multi-method approach. The presence of limestone leads to the formation of hemi- and mono-carbonate and to the stabilization of ettringite at 40°C. An increase of temperature to 60°C results in the destabilization of ettringite and formation of monosulfate in the limestone cement. The dolomite is almost depleted in the cementitious matrix over the hydration time at the studied temperatures. As a result, the formation of hydrotalcite is observed which binds part of the alumina from clinker dissolution. At 60°C, no monosulfate is found and the CSH contains less alumina in the presence of dolomite in comparison to when limestone is present. The dolomite dissolution increases the strength at higher temperatures as a result of the additional hydrotalcite formation. [ABSTRACT FROM AUTHOR]