Concrete specimens with unidirectional embedded AR-glass rovings were stored in a climatic test chamber at 40 °C (104 °F) and 99 % r.h. After this storage, the bending strengths of the specimens were tested. The uncovered fibers were observed with an Environmental Scanning Electron Microscope (ESEM). The specimens made of the low alkaline matrix and AR-glass rovings showed no strength losses. Whereas, the specimens reinforced with E-glass showed dramatic losses of strength and corrosion of glass fibers. Also, the specimens made of the high alkaline matrix and AR-glass reinforcement showed losses of strength. A corrosion of the fibers could not be detected. Causes for the measured losses of load capacity when using AR-glass reinforcement and Portland cement matrix are the weak points inside the interface fiber-matrix, caused by portlandit crystals. Storage tests in simulated pore solution of 80 °C (176 °F) and pH 13 showed clearly, that glass corrosion cannot start before the protective fiber size is at least partially dissolved. In this case, the VET-AR-glass fibers are of advantage. During the alkaline attack on the unprotected AR-glass surface, the content of zirconium dioxide determines the corrosion resistance for the respective glass. In this case, the NEG-AR fibers are of advantage. The investigations show, that durable fiber concretes and textile reinforced concretes with AR-glass respectively can be produced by optimizing the mixtures. In this respect, the climatic test chamber storage proved to be an accelerated aging test.
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