Effect of environmental exposure on the microstructure of textile concrete.

Abstract

This paper presents the results of recent experimentation performed to study time-dependent changes in the mechanical performance of textile reinforced concrete (TRC) made with AR glass fibre and to specify the decisive mechanisms influencing the durability of this composite material. The effect of the matrix composition was investigated by varying hydration kinetics and alkalinity of the binder mix. At first, tensile tests on (accelerated) aged specimens made of TRC were performed. The results showed a pronounced decrease in the tensile strength and strain capacity for TRC whose matrix was most alkaline (Portland cement was used exclusively as binder in this composition). The performance of TRC made with modified, alkali reduced matrix composition was to a great extent unaffected by exposure to accelerated ageing. In order to investigate the mechanisms leading to such different behaviours, changes in the mechanical performance of the fibre–matrix bond were studied using double-sided pullout test specimens with under-critical fibre reinforcement after they had undergone accelerated ageing. Furthermore, the appearance of the microstructure in the interface between fibre and matrix was described by images obtained from SEM-investigations. Measured reductions in the toughness of the composite materials could be attributed mainly to the visual observed disadvantageous new formation of solid phases in the fibre–matrix interface, while the deterioration of the AR glass fibre seemed to play only a secondary role. It could be shown that the morphology of the formed solid hydration phases depends to a large extent on the matrix composition.