Experimental investigations on the durability of fibre–matrix interfaces in textile-reinforced concrete

Changes in the strength and toughness of textile-reinforced concrete with increasing age are determined essentially by the durability of the armouring fibres, the matrix itself, and the bond between the matrix and the fibres. Based on new experimental results, important mechanisms influencing the durability of the fibre–matrix bond are treated in this article and discussed as to their significance. The investigations were conducted on multi-filament yarns of AR-glass which were imbedded in matrices of varying alkalinity and hydration kinetics. The loading capacity of the fibre–matrix bonds was determined in direct tension tests on under-reinforced specimens after they had undergone accelerated aging. Further, the condition of the microstructure between fibre and matrix was ascertained with both image analysis and analytical procedures. It was concluded that measured reductions in the toughness of the composite material could be attributed to the diminishing protective effect of organic polymer sizing on the surface of the filaments as well as to the disadvantageous new formation of solid hydration phases (mainly Portlandite) in the fibre–matrix interface.