The influence of mix composition, w/b ratio and curing on restrained shrinkage cracking of cementitious mortars

Cracking due to restrained shrinkage deformations affects the durability and structural performance of concrete structures negatively. This paper initially reviews the outcome of previous studies, in which several crack-influencing parameters were investigated. A simplified analytical model for predicting the age at cracking based on elastic modulus, tensile relaxation, shrinkage strain and tensile strength is also presented. The experimental investigations confirm that the analytical model can predict the age at cracking with good accuracy. Results from the studies presented indicate that, against common belief, an increase in overlay strength decreases the age at cracking. To investigate this phenomenon further, many mortar mixes with different strength and mix characteristics were tested against cracking performance. An inverse relationship between mortar strength and age at cracking was identified. For the particular application of patch repair mortars, the outcome of this study is used to critique common performance requirements in the European Standards.