Production, composition and aftertreatment of mineral fibers for the micro-reinforcement of binders of building materials

Method for the production of mineral fibers resistant to alkaline media which are to be used for the micro-reinforcement of cement-, lime- and/or plaster-bound or bituminous binders of building materials, which comprises the steps of preparing a starting material which is a mixture of extrusive rocks with an addition of 4 to 6 weight percent ZrO.sub.2, related to the resultant mineral fibers, the composition of the mixture used as the starting material, related to the purely oxidic constituents, being as follows:

• ______________________________________ SiO.sub.2 between 48 and 51 weight percent Al.sub.2 O.sub.3 between 12 and 14 weight percent Fe.sub.2 O.sub.3 between 8 and 10 weight percent CaO between 6 and 8 weight percent MgO between 10 and 12 weight percent TiO.sub.2 between 2 and 6 weight percent ZrO.sub.2 between 4 and 6 weight percent K.sub.2 O + Na.sub.2 O up to 5 weight percent maximum ______________________________________
• the mixture being readily fusible and easy to process into fibers, fusing said mixture at a temperature between 1350.degree. C. and 1500.degree. C., processing said fused mixture into fibers having a diameter of 10 to 20 .mu.m, and subjecting the fibers to a two stage heat treatment to achieve recrystallization, the temperature during the first stage being between 650.degree. and 750.degree. C. and during the second stage being between 800.degree. and 900.degree. C., and the treatment time in the first and second stages of the two stage being less than one minute, the resultant fibers being resistant to alkaline media and having high mechanical strength.