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The structural arrangement of alkali-modified calcium aluminosilicate glasses has implications for important properties of these glasses in a wide range of industrial applications. The roles of sodium and potassium and their competition with calcium as network modifiers in peralkaline aluminosilicate glasses have been investigated by Al andSi MAS NMR spectroscopy. The Si MAS NMR spectra are simulated using two models for distributing Al in the silicate glass network. One model assumes a hierarchical, quasi-heterogeneous aluminosilicate network, whereas the other is based on differences in relative lattice energies between Si-O-Si, Al-O-Al, and Si-O-Al linkages. A systematic divergence between these simulations and the experimentalSi NMR spectra is observed as a function of the sodium content exceeding that required for stoichiometric charge-balancing of the negatively charged AlO tetrahedra. Similar correlations between simulations and experimental Si NMR spectra cannot be made for the excess calcium content. Moreover, systematic variations in theAl isotropic chemical shifts and the second-order quadrupole effect parameters, derived from the Al MAS NMR spectra, are reported as a function of the SiO content. These observations strongly suggest that alkali ions preferentially charge-balance AlO as compared to alkaline earth (calcium) ions. In contrast, calcium dominates over the alkali ions in the formation of nonbridging oxygens associated with the SiO tetrahedra.

The potential of calcium aluminosilicate (CAS) glasses as supplementary cementitious materials is studied in terms of the development of compressive strength for mortars containing a mixture of portland cement, CAS glass, and limestone. In addition, the impact of internal and external alkali activation of the cementitious systems on the mortar performances is investigated. Internal alkali activation is obtained by adding alkali oxides to the CAS glass system, whereas external alkali activation is realized by hydration of the blended cements containing alkali‐free CAS glasses using alkaline solutions. For the internally alkali‐activated systems and the alkali‐free mortars, higher strengths are achieved in comparison to the reference mortar prepared from plain ordinary portland cement. In contrast, the externally alkali‐activated mortars exhibit lower compressive strengths, implying the importance of both the immediate availability of alkali ions in the cementitious system and the increased dissolution rate of the glass particles caused by the network depolymerization. The glasses are also studied by thermal analysis and the results are used to calculate the theoretical CO2 emissions. The lowest embodied CO2 emission is estimated for the blends containing alkali‐activated CAS glasses.