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.