Abstract
Natural resources can be conserved if we carefully maintain the building stock and indeed extend the useful economic life of buildings. One way to achieve this is to enhance load-bearing structures by repair, restoration, or strengthening. Such upgrading often involves applying a strengthening to existing concrete elements. Over the past decade, textile-reinforced concrete (TRC), encompassing a combination of fine-grained concrete and noncorrosive multiaxial textile fabrics, has emerged as a promising novel alternative for strengthening of conventional steel-reinforced concrete (RC) structures, offering enhanced load-bearing capacity with minimal weight and stiffness change. Although TRC has been extensively researched during the last two decades, the formalization of experimental methods and design standards is still in progress. Attempts to design for good load transfer are often hindered by lack of knowledge regarding bond behaviour. For instance, there are neither standard recommendations nor proofs regarding the required development length of textile fibres in TRC for practical applications up to now. The aim of this work was to provide a test specification, which gives a direct result for the development length (required for the anchorage of a reinforcement, also referred to as “anchorage length”) of textile reinforcements in fine-grained concrete—quickly and easily. The aim of this paper was to present the test specification developed in a way that it is useful for the future work of other researchers as well as for construction engineers. Some selected experimental investigations with different textile reinforcements and different bonding properties were performed with the aim of showing the applicability of the proposed adaptive test specification. The results of these tests indicated that conventional AR glass and carbon fabrics without coating required large anchoring lengths. The tests further showed that an additional application of different kinds of coating to textile fabrics greatly increased the reinforcement’s resistance to pullout. This is of special interest for carbon fibres, which have a substantially higher strength than AR glass fibres and different bond behaviour; that is, carbon fibres have, by nature, larger development lengths.
Highlights
Butler et al [36] performed experimental investigations on important mechanisms influencing the durability of the fibre-matrix bond in textile-reinforced concrete (TRC) using double-sided pullout test on slender notched specimens reinforced with a few multifilament AR glass yarns. e yarns were imbedded in matrices of varying alkalinity and hydration kinetics. ey found out that the extent of the performance losses with increasing duration of aging depends primarily on the alkalinity of the pore solution in the matrix. ese tests do, provide some information on the bond behaviour of fibres being processed in textile manufacturing
E column pullout length describes the measured length of the longest protruding fibres. e value given in this column indicates the development length for those specimen which failed by mixed failure
Cross fibre distance suspension (e.g., 15% of polymer content instead of 30%). e pullout tests on these textiles showed that even this reduced coating leads to a substantial reduction of the development length of the textile fabric, this effect is less than using larger polymer content (Figure 10)
Summary
As long as the majority of TRC materials do not follow standardization, an alternative method is needed for proving the bond capacity (initially focussed on static loading), that is, how to eliminate the possibility of failure due to fabric pullout from the matrix, in research as well as in practical applications. De Andrade Silva et al [8] investigated the influence of elevated temperatures on the bond behaviour of uncoated and polymer-coated carbon yarns embedded in a concrete matrix using double-sided pullout tests. Butler et al [36] performed experimental investigations on important mechanisms influencing the durability of the fibre-matrix bond in TRC using double-sided pullout test on slender notched specimens reinforced with a few multifilament AR glass yarns. An applicable testing method for quick direct obtaining of the development length of textile fabrics embedded in fine-grained concrete matrix of TRC is urgently needed. In order to present the results of the investigations from the first phase in a transparent and reproducible manner, the first test method will be described in addition to the final test method
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