Auswirkungen der Matrixzusammensetzung auf die Dauerhaftigkeit von Betonen mit textilen Bewehrungen aus AR-Glas

Effect of Matrix Composition on the Durability of Concretes Reinforced with Glass Fibre Fabric

The mechanical performance of composites made of finegrained concrete and textile reinforcement can worsen markedly with increasing age if alkali-resistant glass (AR-glass) is used as the reinforcing material. For reliable practical applications of textile-reinforced concrete, precise knowledge as to the extent and causes of such degradation is indispensable.
This paper discusses important aging mechanisms resulting from the composition of fine-grained concrete. Tensile tests on composites made of different concrete compositions distinguished from one another by their hydration kinetics and alkalinity were performed before and after accelerated aging. Composites made of concrete with high alkalinity showed dramatic losses of tensile strength and strain capacity. In contrast the mechanical performance of composites whose binders had reduced Portland cement clinker content plus added puzzolana was hardly affected by the accelerated aging.
To clarify the mechanisms of degradation, yarn pullout tests were performed on specimens of equal matrix composition and age. Additionally, the morphology of the interphase between matrix and fibre was characterised using direct microscopic examination and analytical methods. The new formation of unfavourably structured products of hydration in the filament-matrix interphase and/or in the empty spaces between filaments was found to be the main reason for the performance losses observed. The morphology of these hydration products is determined to a great extent by the binder composition.
Under unfavourable conditions corrosion of AR-glass can occur as well and lead to distinct composite damage. However, if the formulation of the binder is proper, bulk glass corrosion is of minor importance.