| As one of the most widely used engineering materials, the strength and durability of concrete material are of great concern of engineers and scientists. Concrete is an porous anisotropic composite material.The microstructure of concrete has a significant impact on its macroeconomic performance. In this paper, a conventional water/cement ratio concrete microstructure and it’s interfacial transition zone was characterized, the components and mechanical properties of the interfacial microstructure was analyzed, and the freezing/thawing effect was studied. The application of nanoscratch test method for the study of the macro-micro mechanical properties of concrete was discussed. Providing a new method for the study of the microscopic mechanical properties of concrete, thus offering some guidance for the design and analysis of the macro-structure.Based on the nanoscratch test method as well as scanning electronic microscope and scanning probe microscope techniques, this paper focused on the characterization of the microscopic aggregate-cement paste interface. The test results were analyzed using statistical methods and the variation of scratch hardness according to the distance from the interface was obtained by Gaussian Mixture Model. The interfacial transition zone between aggregate and cement paste was defined and the changes in mechanical properties of the transition zone under freezing-thawing cycles were furtherly studied. These presented the interfacial transition zone to be an area with higher porosity and more micro-cracks. The scratch hardness of the interfacial transition zone is about 75% of that of the cement paste. And the thickness of the zone is about 25 ~ 40μm. Under the effect of freeze-thaw cycles, the cement paste, especially the interface transition zone, was most effected of the three-phase structure of the concrete, leading to the degradation of the microstructure mechanical properties with a 40% loss in scratch hardness for 1500 F/T cycles. These studies showed that the interfacial transition zone to be the most vulnerable part of the three-phase structure of concrete though accounted for a relatively small volumn fraction. The deterioration of the microstructure in cement paste and the interfacial transition zone is the key factor for the degradation in concrete structure under freezing/thawing effect. The performance of the interfacial transition zone played a crucial role in the overall performance of concrete. |
