Rob van der PLUIJM Eindhoven University of Technology and TNO Building and Construction Research
and Ad VERMELTFOOT Eindhoven University of Technology

Very limited experience exists with bond wrench testing in the Netherlands. The research described in this paper had two main goals: to gain experience with bond wrench testing and validating this method; to explore the possibilities for quality control of bond at an early stage. The bond wrench is useful to establish bond strength in the laboratory. When loaded manually the influence of unintended horizontal forces is negligible, so that it can also be used on building sites. The results of the bond wrench tests were equal to those of the four point bending tests. Therefore, they can be regarded as the flexural bond strength. A strength versus time relationship in the shape of a photosynthesis curve was established. When specimens of an age of 24h or more are used the bond strength prediction curve gives a good indication of the final bond strength. However, the prediction curve does not apply to the results found in the literature. Research has to be done to find a more general description for the strength development to make quality control possible at an early stage.