Bewertung des Einflusses einer mechanisch induzierten Rissbildung auf den Verlauf der schädigenden AKR mit innovativen Prüftechniken

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The aim of part 4 of the project is to complete the basis for numerical models on meso and micro scale by fundamental tests. The focus is on the quantitative description of the cracking and transport processes by means of innovative measurement techniques. The research spectrum includes the de-scription of the mechanically induced cracking prior to ASR damage, the analyses of the mass transport processes and the characterization of the resulting ASR-induced cracking. During the first funding period, cyclic four-point bending tests with test solution on top showed that concrete degradation in the tensile zone of the cyclic loaded beam significantly decreased. This is a result of the hygric induced residual stress. For this reason an additional test regime will be considered. The influence of the intermittent opening and closing of fatigue induced cracks on the mass transport processes will be investigated in more detail. X-Ray-3D-CT techniques, which were optimized during the first funding period, will be used for three dimensional characterization of the road surface concrete after various damage inducing procedures. Additionally, sodium and chloride ingress into the concrete after cyclic loading with test solution on top or after rolling wheel test will be compared, analyzed and assessed. During the first funding period only the cyclic climate storage test revealed that fatigue induced cracking concrete degradation, and the resulting increased sodium and chloride ingression, led to greater ASR damage. The effect of the freeze thaw period on ASR was still unclear. The effect of the alkalis, introduced during the damage inducing procedures, was not detectable in the fog chamber. Alternative aggregates will be used to clarify this effect. Additional tests on a modified road surface concrete (substitution of road cement by special test cement (Na2Oequivalent: 1,30 M.-%)) shall clarify the role of the fatigue induced cracking on ASR and will be the basis for the validation of the ASR damage model (TP3). Additional suction tests using various test solutions on different hygric preconditioned road surface concretes (damaged and undamaged) will complete the test program for a comprehensive validation of the numerical model. The spatial moisture and ion transport will be analyzed simultaneously and correlated to the associated crack system. Large concrete beams with different sodium distributions over the depth will be stored in an ASR provoking climate. These tests will elucidate the influence of a heterogeneous ASR severity that varies with depth on the deformation. The deformation and the moisture distribution, measured vertically, will form the basis for the development and validation of a macroscopic model (TP6).