Micromechanics Models and Innovative Sensor Technologies to Evaluate Internal-Frost Damage of Concrete

摘要

Intemal-frost damage is one of the major problems affecting the durability of concrete in cold regions. This paper presents micromechanics models and innovative sensor technologies to study the fundamental mechanisms of frost damage in concrete. The crystallization pressure due to ice nucleation with capillary pores is the primary cause of internal-frost damage of concrete. The crystallization pressure of a cylinder pore was formulated using interface energy balance with thermodynamics equations. The obtained crystallization pressure on the pore wall was input for the fracture simulation with the developed Extended Finite Element Model (XFEM). The XFEM fracture simulation on a homogeneous beam sample with a vertical cylinder pore leads to a straight line. The XFEM simulation was also conducted on the generated digital sample. The simulation results were favorable compared with the middle-notched single edge beam bending specimen due to the open-mode fracture behavior in both cases. An innovative Time-Domain Reflectometry (TDR) sensor was developed to nondestructively monitor the freezing process. The experimental data shows that the TDR sensor signals can detect the freezing degree, an important input parameter to micromechanics models. These studies indicate that the developed micromechanics models and TDR sensor techniques can be used by the practitioners to evaluate internal-frost damage of concrete. Future work will incorporate the TDR sensor measurements into micromechanics models to real-time predict the internal-frost damage process in concrete specimens. The predicted freeze-thaw damage process will be verified with acoustic emission detection.