Crack propagation and coalescence in quasi-brittle materials at high temperatures

• A thermo-mechanical-damage model is proposed for heterogeneous quasi-brittle material.
• The thermal cracking significantly depredates the residual strength of material.
• Shear fracture formed through the interaction and coalescence of tensile microcracks.
• The brittle–plastic damage model can study the mechanical behavior of material.
• The transient creep strain plays an important role in decreasing the axial stress.

A numerical model allowing for the thermo-mechanical analysis of quasi-brittle materials (concrete structures) at high temperatures via the finite element method and damage mechanics is presented. It incorporates a damage constitutive law to capture the initiation, propagation, coalescence and the interaction of cracks as a natural outcome of the calculated material response. Furthermore, the degradation of the mechanical properties due to temperature is estimated using a transient thermo-damage model. The numerical results obtained from the proposed model correspond well with those obtained in experimental tests performed by other authors on concrete specimens at high temperatures.