ABSTRACT
The precursors used in this study are commercially available products used for crack injection of concrete. These are polyurethane-based products that cure upon contact with moisture. Products with low viscosity were chosen, as this is a critical property to guarantee a large crack coverage and good healing performance. Good adhesion to concrete was also considered essential, otherwise detachment of the polymer from the crack walls would occur before considerable crack widening. The precursor here designated by SLV (super low viscosity) has a viscosity of 200 mPa⋅s and a maximum elongation of 100% according to its
1 INTRODUCTION
Within the European FP7 project HEALCON, different self-healing techniques are developed and optimized. For the evaluation of the performance, it is essential to study the efficiency of the different self-healing methods. The efficiency is mostly investigated through performance of permeability tests or by reloading and investigating the regain in mechanical properties. However, these techniques have several disadvantages i.e. that the specimen are not available for further investigations after destruction and that the techniques are of limited use in practice. Therefore, project partners are developing non-destructive testing and monitoring techniques and are combining existing techniques in order to characterize the effects of different self-healing mechanisms in small and full size specimens. In the first stage of the project, healing mechanisms were observed at lab-scale. Techniques as acoustic emission analysis (Van Tittelboom et al. 2012, Malm & Grosse 2014), vibration analysis (Neild et al. 2003)
technical sheet. The precursor designated by CUT has a viscosity of 350 mPa⋅s and was chosen for comparison purposes due to its considerably lower maximum elongation (not available), according to the manufacturer. For the tests on mortar specimens, the precursors were mixed with 2 wt% of an accelerator, to reduce the time for full curing. Additionally, the accelerator also induces a foaming effect upon contact with moisture.
