Crack provokes to lose a main performance of watertightness of concrete and leads to accelerate the deterioration of concrete. This brings about reduction of service life of concrete eventually. The background is a good motivation to define a critical crack width to prevent chloride from penetrating through crack in concrete. Since concrete structures have to be proven for a minimum service life, the critical crack width can be regarded as a crucial factor for estimating durability performance and integrity of concrete structures. This study is focused on examining the effect of micro-crack on chloride penetration in concrete and identifying the critical crack width experimentally. Because concrete structures have to meet a minimum service life, crack width must be smaller than the critical crack width. Specimens with different crack width have been subjected to Rapid Chloride Migration testing (RCM). The results of this study show the critical crack width of about 0.013 mm. Cracks smaller than the critical crack width are considered not to have a significant influence on the rate of chloride penetration inwards, while chloride penetration does proceed faster above this critical crack width. Meanwhile, cracked specimens were immersed in artificial seawater for 472 days. The result of this long term experiment indicates critical crack width of 0.04 mm. It is thought that crack healing leads the difference between short and long tem experiment.

Carbonation of cementitious materials is one of main causes of reinforcement corrosion and CO₂ diffusivity influenced by microstructural characteristics of the cementitious materials is a decisive parameter for the carbonation rate. This study focused on establishing a multifactor functional model to calculate the CO₂ diffusivity of carbonated cementitious materials. Because CO₂ gas flows through carbonated zone, it is necessary to estimate CO₂ diffusivity of carbonated concrete. Many factors on the CO₂ diffusivity, such as the diffusivity in vapor, tortuosity, microstructural characteristics of cement paste, contribution of aggregate, and reduction of porosity due to carbonation, were considered. Apparent and effective CO₂ diffusivity were calculated according to the absence or presence of moisture in the pore system of concrete, and the results were compared with previous research.

The resistivity of a concrete structure exposed to chloride ions indicates the risk of early corrosion damage, because a low resistivity is related to rapid chloride penetration and to a high corrosion rate. Concrete resistivity is a geometry-independent material property that describes the electrical resistance, which is the ratio between the applied voltage and resulting current in a unit cell. The current is carried by ions dissolved in the pore liquid. While some data exist on the relationship between the moisture content and electrical resistivity of concrete, very little research has been conducted to evaluate the effect of chloride on the conduction of electricity through carbonated and non-carbonated concrete. The purpose of this study is to examine the effect of chloride concentration on the surface electrical resistivity measurement of carbonated and non-carbonated concrete. Chloride concentration had influenced the resistivity of concrete and the relationship showed a linear function. However, for concrete under the combined deterioration of carbonation and chlorides, a reduction in porosity due to the carbonation had a greater effect on the electrical resistivity than the increase in conductivity due to the chloride ions. Conclusively, this paper suggested the quantitative solution to depict the electrical resistivity of concrete with various chloride concentrations.

Oxygen diffusion would not be important for healthy concrete. Once concrete is carbonated, however, oxygen diffusion is very crucial to lead reinforcement corrosion. Therefore, oxygen is always a...

For enhancing the service life of concrete structures, it is very important to minimize crack at surface. Even if these cracks are very small, the problem is to which extend these cracks may jeopardize the durability of these decks. It was proposed that crack depth corresponding with critical crack width from the surface is a crucial factor in view of durability design of concrete structures. It was necessary to deal with chloride penetration through microcracks characterized with the mixing features of concrete. This study is devoted to examine the effect of high strength concrete and reinforcement of steel fiber on chloride penetration through cracks. High strength concrete is regarded as an excellent barrier to resist chloride penetration. However, durability performance of cracked high strength concrete was reduced seriously up to that of ordinary cracked concrete. Steel fiber reinforcement is effective to reduce chloride penetration through cracks because steel fiber reinforcement can lead to reduce crack depth significantly. Meanwhile, surface treatment systems are put on the surface of the concrete in order to seal the concrete. The key-issue is to which extend a sealing is able to ensure that chloride-induced corrosion can be prevented. As a result, penetrant cannot cure cracks, however, coating and combined treatment can prevent chloride from flowing in concrete with maximum crack width of 0.06 mm and 0.08 mm, respectively.

Many studies have only studied carbonation and chloride penetration separately, and study dealt with synergy interaction between these is very rare. This study is devoted to examining the chloride penetration parameters of carbonated cementitious materials, i.e. (a) surface chloride content, (b) chloride diffusivity, (c) chloride adsorption capacity and (d) critical chloride content linked with reinforcement corrosion directly. These chloride transportation parameters were expressed as a function of time in each condition because these depend on the mixing proportional properties and the degree of cement hydration. This study is expected to be useful to develop a chloride penetration model of carbonated concrete in the future.