Predicting cracks in hardening concrete using a stress-based cracking criterion

A traditional way to assess the risk of cracking at early ages consists of minimising temperature differentials between warm and cold concrete. When using modern low waterbinder ratio concretes, which concretes are susceptible to cracking due to autogenous shrinkage, the reliability of temperature-based criteria becomes questionable. In this contribution, the results of a recently finished four-year study on the risk of cracking and crack criteria for hardening concrete will be presented. The stress development and the tensile stress at the moment of cracking have been measured in a Temperature Stress Testing Machine. Based on the test results, a criterion for cracking at early ages was developed. A procedure for determination of stresses in hardening concrete is briefly described. In that procedure, allowance is made for the effect of the hydration process and the associated evolution of the microstructure on relaxation of stresses in hardening concrete.