Analysis On Entire Period Of Corrosion-induced Crack Of Reinforced Concrete Based On Digital Image Correlation Method

Durability Problem of reinforced concrete structures is increasingly serious. One of the main cause of deterioration of structural durability is chloride erosion. Invasion of chloride ions into the internal structure causes reinforcement corrosion and corrosion products. And the volume expansion of corrosion products leads to cracking of concrete cover. Research on the whole cracking process of concrete which is induced by the corrosion of reinforced concrete structure is of great importance to the analysis of service life and service performance. Therefore, focus on the study of whole cracking process of concrete, the main research works of this paper are as follows.(1) With the application of Digital Image Correlation (DIC) method through matching and tracking on the digital speckle image, the whole corrosion-induced crack process of the concrete cover of reinforced concrete specimen under accelerated corrosion using impressed current in half-immersed chlorides environment was investigated. The spatial and temporal evolution law of relative deformation field on surface of corroded reinforced concrete specimen was analyzed. The impact of stirrups and thickness of concrete cover on the relative deformation field of corroded reinforced concrete surface was interpreted. The time, position and trend of surface cracking of concrete cover were precisely determined. The affect range of relative deformation on concrete surface caused by tensile expansive force was identified. The standard for initial cracking on concrete surface was established based on the measurement of DIC method, quantitatively providing the basis to characterize the whole process of corrosion-induced crack of reinforced concrete structure.(2) The evolution of the longitudinal length of the corrosion-induced crack with time on the surface of specimens was studied by DIC method. The impact of thickness of concrete cover and stirrups on longitudinal crack length of corroded reinforced concrete surface was analyzed. Adopting the Digital Image Technology to calculate the internal corrosion-induced crack length of reinforced concrete specimens, and scanning electron microscope (SEM) and CMS-200microscope to observe the thickness of rust layer in corrosion-induced cracks, a considerably accurate method to calculate the quantity of overflow rust into cracks was presented. The relationship among corrosion time, thickness of internal effective rust layer, and corrosion-induced crack width on the surface of specimens was quantitatively analyzed. A new model to predict the corrosion-induced crack width on specimen surface was established by an improved Li’s model considering the distribution of overflow rust in cracks. (3) Characteristics of the internal corrosion-induced cracks of reinforced concrete cover were studied. Three types of cracking model caused by longitudinal steel corrosion, namely, type ’1", type "L" and type "(?)" were defined. Four possible forms of internal corrosion-induced cracks and internal distribution area of corrosion-induced cracks were proposed. Ingredient and morphology of corrosion products at the interface of steel and concrete as well as the overflow rust were comprehensively analyzed from micro scale by SEM. Fractal characteristics of the internal corrosion-induced cracks in reinforced concrete were verified. Quantitative parameters D, C, r*, were proposed to describe the degree of development of internal corrosion cracks, which provides a new method for assessing corrosion-induced cracks of reinforced concrete structures.