Evaluation of the thermal and shrinkage stresses in restrained concrete: New method of investigation

The leading cause of concrete cracking is the generation of internal stress generated by the volume change under restrained conditions, which exceed the ultimate value of strength. In particular, the restrained stress generated by temperature change is significant, particularly for large-volume concrete. This study proposed a new restrained method to separate the thermal stress, autogenous shrinkage stress, and drying shrinkage stress from total restrained stress. Unlike traditional restrained methods, Invar steel's characteristic low coefficient of linear expansion was used to generate the thermal stress in this method. To investigate the feasibility of this method, two ordinary cement concrete with 0.30 and 0.40 water-to-binder (w/b) ratios and a ultra high performance concrete (UHPC) with 0.21 w/b ratio were tested. The total stress obtained by the accumulation of the three separated stresses were compared with the experimental total stress. The discrepancy between the direct value and the accumulated value of total stress was within 20 %, indicating that the restrained stress separation method proposed in this study produced viable results. Overall, the new restrained method proposed in this study enabled to test and separate the concrete restrained stresses easily and accurately, which was meaningful for evaluating the risk of concrete cracking in practical engineering.