R717 glass alteration was investigated in the presence of four mortars prepared from four different cement grades: “CPA” Portland cement (mortar M1), CPA with pozzolana additive (M2), CPA with amorphous silica additive (M3) and “CLK” blast furnace slag cement (M4). Glass specimens were also altered in Volvic mineral water and in a cement effluent. Glass corrosion in the cement media was greater than in Volvic water, but well below what could be expected from the high pH (approx 12.5). The relatively low alteration was probably related to the protective action of the calcium-enriched gel layer that formed at the glass surface. The glass corrosion rate was 2 to 3 times lower with cement containing pozzolana or silica gel additives or with CLK cement than with CPA cement alone.