Deterioration Behavior of Interfacial Transition Zone and Its Correlation with Strength of a Concrete Pavement in Seasonal Frost Region

To obtain the deterioration behavior of the interfacial transition zone (ITZ) and its effect on the durability of concrete pavement suffering from a combination of an environment attack and mechanical fatigue load (in a seasonal frost region), coupled loading condition of fatigue load (normal traffic and overload), freeze-thaw cycles (FTC) and dry-wet cycles (DWC) was conducted to simulate this interactive effect on concrete during service. The single fatigue load condition and the coupled loading condition of fatigue load and FTC were designed under normal traffic to discover the critical factor that influences the deterioration behavior of ITZ. Studies on the microstructure and Ca/Si ratio of the ITZ at different loading stages have been conducted by means of scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDXA). The mechanical properties of pavement concrete under coupled condition of load, FTC, and DWC were measured through a static flexural tensile strength test. Furthermore, the correlation between strength and ITZ deterioration were studied using multiple regression analysis. The results demonstrate that during concrete pavement service in seasonal frost region, the mechanical load leads to localized damage around the principle intrinsic cracks while the environment attack of FTC and DWC contribute to crack propagation in all directions to form large defects, during which the ITZ deterioration is observed to be a physico-chemical process. As the flexural tensile strength of concrete keeps decreasing, many cracks intersect and breakthrough in ITZ, the density C decreases, and calcium hydroxide crystallizes; during overload, the fatigue life of concrete is much shorter and the micro-cracks in ITZ widens. When concrete ruptures, the ITZ width is 70 μm, density C is 50.96%-54.25%, maximum length and width of micro-cracks are 24.48-26.04 μm and 11.73-15.72 μm, respectively. The multiple linear regression equation could be used to quantitatively analyze the relationship between the strength of concrete and ITZ structural defects. Their extents of effect on strength are density C > crack width > crack length. © 2019, Editorial Department of China Journal of Highway and Transport. All right reserved.