Alkali-resistant glass composition and glass fibers made therefrom

Alkali resistant glass fibers composed of a glass composition consisting essentially of

• ______________________________________ SiO.sub.2 61 - 69 mole%, ZrO.sub.2 11.5 - 12.5 mole%, CaO 2 - 5 mole%, R.sub.2 O 16 - 20 mole%, K.sub.2 O 2 - 5 mole%, B.sub.2 O.sub.3 1 - 4 mole%, P.sub.2 O.sub.5 substantially O TiO.sub.2 0 - 0.3 mole%, and M.sub.x O.sub.y 0 - 1 mole% ______________________________________
• wherein R.sub.2 O represents the total amount of Na.sub.2 O and K.sub.2 O;
• M is at least one metal selected from the group consisting of V, Cr, Mn, Fe, Co, Cu, Zn, As, Y, Mo, Cd, Sn, Sb, Hf and Ce;
• x and y are positive integers with the proviso that the valence of M multiplied by x equals 2y;
• and the content of fluorides, calculated as F.sub.2, is 0 to 1 mole%, and meeting the following conditions,
• A. r.sub.2 o + caO .gtoreq. 19 mole%,
• B. zrO.sub.2 + CaO + B.sub.2 O.sub.3 .ltoreq. 18.5 mole %, and
• C. the molar ratio of K.sub.2 O/CaO .gtoreq. 0.5.

A cementitious product reinforced with alkali resistant fibers composed of a glass composition, aid glass composition consisting essentially of

• ______________________________________ SiO.sub.2 61 - 69 mole%, ZrO.sub.2 11.5 - 12.5 mole%, CaO 2 - 5 mole%, R.sub.2 O 16 - 20 mole%, K.sub.2 O 2 - 5 mole%, B.sub.2 O.sub.3 1 - 4 mole%, P.sub.2 O.sub.5 substantially O TiO.sub.2 0 - 0.3 mole%, and M.sub.x O.sub.y 0 - 1 mole% ______________________________________
• wherein R.sub.2 O represents the total amount of Na.sub.2 O and K.sub.2 O;
• M is at least one metal selected from the group consisting of V, Cr, Mn, Fe, Co, Cu, Zn, As, Y, Mo, Cd, Sn, Sb, Hf and Ce;
• x and y are positive integers with the proviso that the valence of M multiplied by x equals 2y;
• and the content of fluorides, calculated as F.sub.2, is 0 to 1 mole%, and meeting the following conditions,
• A. r.sub.2 o + caO .gtoreq. 19 mole%,
• B. zrO.sub.2 + CaO + B.sub.2 O.sub.3 .ltoreq. 18.5 mole%, and
• C. the molar ratio of K.sub.2 O/CaO .gtoreq. 0.5.