Features of mechanics of quasi-brittle crack propagation in concrete

Physical observations of crack propagation in concrete are discussed in the present paper. Based on these physical observations, different models proposed for mode I fracture of concrete are examined. In the past, verification of validity of fracture models has always been difficult. It is proposed that notch sensitivity and size effect be used as criteria to evaluate the validity of fracture models. In addition, a successful model should also satisfy a 'portability' condition, namely the model should be applicable to structures of an arbitrary geometry. Discussion on the effects of different loading conditions, i.e. mixed-mode loading conditions and different loading rates, on the fracture process in concrete is also presented.