On the mechanism of plastic shrinkage cracking in fresh cementitious materials

In this study, a continuum poromechanics approach is presented to model the plastic shrinkage cracking of fresh cementitious materials. The boundary conditions are according to the modified ASTM C1579-13 standard for mortars. The restrained deformations are linked to the restraint stresses according to the Cauchy-Navier equations of elasticity, assuming an incremental stress-strain relationship. The Bresler-Pister and Rankine failure criteria are utilized to model failure. The material parameters are adapted according to the Drucker-Prager and Griffith criteria. The crack initiation and propagation is verified experimentally by X-ray radiography. Eventually, the cracking mechanism is discussed and a safe capillary pressure limit is proposed. It is found that capillary pressure stiffening occurring before air entry, when deformations take place in the saturated state, is the predominant cause of plastic shrinkage cracking in the drying state.