Transmission X-Ray Microscope Nanoscale Characterization and 3D Micromechanical Modeling of Internal Frost Damage in Cement Paste

This study employed the transmission X-ray microscope (TXM) characterization and three-dimensional (3D) cohesive zone modeling (CZM) techniques to investigate the internal-frost damage in cement paste samples. The microscale cement samples were tested under controlled freeze-thaw cycles. The TXM technique was applied to perform fast-image acquisition of capillary pores and micro-damage evolution at 30 nm resolutions. The constructed 3D nanostructures of tested specimens were used in two ways: digital sample generation for model simulation and model prediction on crack propagation. The thermodynamics principles were applied to calculate the ice crystallization pressure within saturated pores under subcooling temperatures. The 3D bilinear CZM techniques were applied to predict the internal-frost damage evolution under the calculated crystallization pressure exerted on pore walls. The CZM predicted crack propagation was favorably compared with the TXM captured micro-damage. The micromechanical modeling and the TXM characterized nanostructure demonstrate that the ice crystallization pressures generated within nanoscale pores are sufficient to cause internal-frost damage in cement paste samples. (C) 2013 American Society of Civil Engineers.