Bond of post-tensioning strands in case of grouting defects

This paper investigates the problem of bond in post-tensioning strands in the presence of grout injection defects. In particular, the paper describes a campaign of experimental pull -out tests with a single 7-wire steel strand in the centre of a galvanised sheet metal duct with no grouting defects and with 25% and 50% defects, i.e. voids in the cross -section area of the grout. The grouted length is short in order to obtain a local bond-slip relationship. This relationship has an initial branch followed by a jump descent and a subsequent growing branch in the form of a sawtooth. The experimental data are used to define a specific bond-slip relationship that takes into account the presence of defects. The results show that the obtained bond-slip law is very different from those proposed in the literature for the case of ribbed steel bars. Furthermore, the defects cause a decrease in bond stresses and a flattening of the shape of bond-slip curves.