Fuyuan Gong

Modeling and Mesoscale Simulation of Ice-Strengthened Mechanical Properties of Concrete at Low Temperatures

AbstractFormation of ice plays a key role in the behavior of concrete materials at low temperatures in cold and wet regions. The internal stresses generated during the freeze-thaw process could cau...

Electrical Response of Mortar Saturated with NaCl Solutions under Freeze–Thaw Cycles

This paper presents the test results of electrical response of mortar saturated with sodium chloride (NaCl) solutions under freeze–thaw cycles (FTCs). To quantitatively evaluate the salt frost damage of mortar based on its electrical response, mesoscale samples are prepared to assure the uniform pore solution concentration. The reduction of electrical resistivity shows the same tendency with elastic modulus, but with less degree. The investigation shows that electrical resistivity of mortar decreases with temperature and the phase changes can be observed based on their relationship. The freezing and thawing points decreasing with increment of solution concentration can be found, but their variations with FTCs are not significant. Basically, along with frost damage development, the electrical resistivity of mortar at 23 and -28°C is decreasing with FTCs. However, for lower water-to-cement ratio and higher NaCl concentration solution exposed samples, contrary tendency are observed. In addition, with FTCs, there is no clear change for the activation energy of DI water case, whereas the decreasing tendency is observed in the cases of 5 and 15% NaCl solution. Therefore, the electrical properties are important for understanding the salt frost damage, but a comprehensive parameter to quantify the damage is still in need.

Physical Model and Mesoscale Simulation of Mortar and Concrete Deformations under Freeze–Thaw Cycles

The degradation of concrete material under multiple freeze–thaw cycles is an important issue for structures in cold and wet regions. This paper proposed a physical and mechanical model to explain the deformation behavior observed in previous experiments, from internal pressure calculation to mesoscale simulation, and for both closed and open freeze–thaw tests. Three kinds of internal pressures are considered in this study: hydraulic pressure due to ice volume expansion, crystallization pressure, and cryosuction pressure due to liquid–ice interface. The hydraulic pressure model combines Power’s model with poromechanical theories, which can well explain the reverse phenomenon (from expansion to contraction) observed in the closed test. The total internal pressure will be applied in a discrete numerical method (Rigid Body Spring Model) to simulate the deformation during each cycle, as well as the unrecoverable cracking (residual strain) at the end of each cycle. The constitutive laws are also modified considering the features of those internal pressures. Finally, the deformation behaviors of mortar, mortar–aggregate interface (closed test, 30 cycles), and the concrete (open test, 300 cycles) are simulated and compared with experiment measurements, which are found in a satisfactory agreement.