Experimental study on bond of prestressing strand in high-strength concrete (Spanish text)

The bond between strand and concrete is essential to guarantee, on one hand, the appropriate prestressing transfer and, on the other, to allow the anchoring of the strand throughout the useful life of the structural element. However, nowadays there is some uncertainty on the knowledge of the bond behaviour of prestressing strands to concrete, even more in concretes with high initial performance.; We have conducted a revision of the scientific literature from three different perspectives: (1) compilation of existing types of tests in order to classify the bond properties; (2) analysis of the influence on bond of the main parameters studied in experimental research; and (3) analysis of the calculation expressions for the determination of transfer and development lengths suggested by researchers and standards.; We have designed a test to determine the bond characteristics of prestressing strands to concrete using transfer and development lengths. The most remarkable innovation is that it allows to determine the strand development length after the prestressed force transfer. With this test method, the operations of release and removal are performed on the same piece of concrete, and this situation displays with a higher degree of reliability the actual state of the pretensioned prestressed concrete elements, as the transfer operations of prestressing and start are sequentially reproduced.; We have developed an experimental program to assess the bond of steel strands upon prestressing 7 wires in initial high performance concrete, and we have analysed the influence on bond of variables such as the dosification of concrete, the age of release, the transversal section of the element, the level of stress, the level of concrete tensions, the energy of concrete compaction and the speeds of load applications during release and removal operations.; Finally, we have checked the feasibility of the application of the test previously designed and the transfer and development lengths for the materials tested. The designed test method is a considerable contribution that will allow an in-depth study of the bond behaviour of concrete prestressing strands.