Investigation of internal frost damage in cementitious materials with micromechanics analysis, SEM imaging and ultrasonic wave scattering techniques

• We conducted SEM characterization of freeze–thaw damaged samples.
• XFEM was applied for fracture simulation with digital samples.
• Ultrasonic wave scattering techniques were developed to measure pore size distribution and volume fraction in concrete.

This study investigates the internal-frost damage due to the development of ice crystallization pressure in the capillary pores of concrete. The SEM imaging analysis, microdamage modeling and ultrasonic wave scattering techniques were developed and integrated to study the internal-frost damage in cementitious material samples. The pore structures have significant impacts on the freeze–thaw durability of cement/concrete specimens. The scanning electron microscope (SEM) techniques were applied to characterize the microstructure of concrete as well as the patterns of freeze–thaw damage within the pore structure. The digital sample was generated by processing the SEM images. In the microscale pore system, the development of crystallization pressures at subcooling temperatures were calculated using the interface energy balance with the principles of thermodynamics. The largest crystallization pressure on the pore wall was used for the fracture simulation with the developed Extended Finite Element Model (XFEM). The comparison study between model simulation and test results indicates that the internal-frost damage model can reasonably predict the crack nucleation and propagation within multiphase cement microstructure. In addition, the ultrasonic wave scattering technique was developed for rapid measurement of the pore size distribution and volume fraction of the air in cementitious concrete, which provided important inputs to simplify the computational model for materials damages simulations. The inverse analysis results show the promising measurements of size distribution of pores in concrete samples. Future study can link the micromechanics analysis and the ultrasonic wave scattering techniques to provide a full-blown study on the internal-frost damage evolution mechanisms.