Softening reversal and other effects of a change in loading rate on fracture of concrete

Time dependence of concrete fracture, in particular the effect of loading rate has been studied mainly in the dynamic range. In the present work, a previous investigation of the rate effect in the static range that covered times to peak from 1 to 300,000 seconds is extended. For this purpose, three-point-bend specimens of three different sizes are subjected to either a sudden 1000-fold increase of the loading rate or a 10-fold sudden decrease of the loading rate. Results obtained including those of a previous study indicate that there exists a significant difference in fracture behaviour for short-time and long-time loads.