Micro-mechanical Property Characterization Of Concrete And Freezing/Thawing Effects

Extreme climate brings the structural durability of concrete to the spotlight, and research into the durability of concrete, especially under freezing/thawing(F/T) cycles will have great impact on engineering aspects. The macromechanical properties of concrete which is a multiscale and multiphase material depend on the microscale structure and constituent properties. This study utilizes the nanoindentation technique to characterize the micromechanical properties of concrete including the indentation modulus, hardness and creep ratio. Statistical analysis is used to analyze the experimental data, and it finds that the difference between the aggregate and cement paste is quite large, providing the basis for determining the interfacial transition zone(ITZ). The correlation coefficient between the indentation modulus and hardness is 0.75, and both of them do not comply with the normal distribution. The creep experiment demonstrates that the cement paste contributes more to the creep phenomenon of concrete.The F/T cycling effects on concrete are explored in the same manner with the help of nanoindentation and scanning electron microscopy(SEM). A new statistical method so called the kernel density estimation plays an important role in estimating the probability density function. The results shows that the F/T cycling conditioning promotes the formation of high density calcium-silicate-hydrate at the 500 nm scale while more microcracks are present at the 10 ?m scale. This study provides a thorough experimental characterization of concrete at microscale using the nanoindentation technique, and it sheds some light on the material property changes due to the F/T cyclic conditioning.