Density of CaO-Al2O3-SiO2 glasses with (CaO/Al2O3) ≥ 1; the hidden factors

•Density of CaO-Al2O3-SiO2 glasses (SiO2 ≥ 50 mol%, CaO/Al2O3 ≥ 1) has been studied.•Volumes and densities of structural units could be determined.•Density of structural units decreases in the sequence AlO4 > Q3 > Q4.•For constant SiO2 content, the density decreases with replacing CaO by Al2O3.•This trend is related to contribution of structural units to the glass density.

Density of CaO-Al2O3-SiO2 glasses with SiO2 ≥ 50 mol% and CaO/Al2O3 ≥ 1 has been analyzed. The basis of analysis is that the entire Al2O3 content forms AlO4 tetrahedra by association with an equivalent amount of CaO. The rest of CaO forms Q3 and Q2 units in the silicate network. The results indicate that the density of structural units decreases in the sequence DAlO4 > DQ3 > DQ4. Nevertheless, at a constant content of SiO2, the density decreases with replacing CaO by Al2O3. This unexpected trend has been explained by taking in account the contribution of various structural units to the glass density.