Experimental determination of crack softening characteristics of normalweight and lightweight concrete

For modelling fracture behaviour of concrete various types of deformation controlled uniaxial tests were performed on normal weight and on lightweight concrete. These two types of concrete were compared with respect to their envelope curves, material stiffness and degradation during post-peak cycles, and residual compressive deformation on crack closure. Differences in behaviour were explained on the basis of the properties of the aggregates which result in specific fracture surfaces. Based on narrow specimens with uniform stress distribution, unique stress deformation curves were determined and the descending branches were modelled. These models were applied to calculate the stress distribution in wide specimens with a sawcut. The total force was in good agreement with the experiment. Probable reasons for the different behaviour of lightweight and normalweight concrete are discussed.