Investigation of Internal Frost Damage in Concrete with Thermodynamic Analysis, Microdamage Modeling, and Time-Domain Reflectometry Sensor Measurements

摘要

This study investigates the internal-frost damage due to ice-crystallization pressure in the concrete pore system. The methodology integrates thermodynamic analysis and a microdamage model as well as a unique time-domain reflectometry (TDR) sensor. The crystallization pressure in the microscale pore system of concrete at subcooling temperatures was calculated based upon thermodynamic analysis. An extended finite-element method (XFEM) was applied to simulate the fracture development induced by internal frost, with the estimated internal crystallization pressure as the input. The XFEM fracture simulation was conducted on a digitized concrete sample obtained with imaging processing and ellipse-fitting techniques. The simulated crack development under the crystallization pressure was found to match the observed fracture patterns of the tested single-edge notched specimen. The XFEM simulation results were verified by the open-mode fracture behavior in both middle-notched single-edge notched beam bending test and freezing-damage tests. Furthermore, the crystallization-pressure analysis and freezing-damage simulation were conducted to demonstrate the freezing-damage process using cement samples with idealized pore structures. To provide direct estimation of the crystallization pressure, an innovative TDR tube sensor was developed to nondestructively monitor the extent of freezing in concrete specimens. The results show that this new sensor provides noninvasive measurement of freezing degree, which can be used to directly estimate the internal crystallization pressure for XFEM analyses. A volume-based damage criterion was also proposed based on the new TDR sensor. This work established a framework to integrate sensor and simulations to holistically predict the internal-frost damage process in concrete specimens.