Research On Corrosion Cracking Performance And Erosion Regularity Of Concrete Member Under The Action Of Sustained Load Effect

Reinforced concrete structures are widely used in all kinds of projects including water conservancy, industry, civil construction, transportation and port engineering. Study on durability of reinforced concrete has become one of the key problems. Suffered a double effect with load and the chlorine salt erosion for a long time period, appearance of crack in part of the engineering buildings’ structure is inevitable.Relied on National Natural Science Foundation of China project "The research of whole-life time-varying properties and performance reliability based on the reinforced concrete structure under chlorine salt environment"(No.51278444), the following contents are studied based on theoretical analysis and related durability tests:(1) Four kinds of experimental schemes which included without adding admixture, only mixed fly ash or mineral powder, double mixed fly ash and mineral powder were carried out in order to analyze the effect of mineral admixtures on compressive strength and chloride ion permeability of concrete. The result showed that the early compressive strength of concrete decreased with the increase of mineral admixture, while the ability to resist chloride ion penetration was gradually strengthened. Additionally, concrete with 15% fly ash has a better comprehensive performance for both strength and resistance to chloride ion penetration.(2) In order to analysis the relationship between corrosive crack width and the corresponding corrosion rate, by applying continuous load to designed elements, and accelerating their corrosion with the method of electro-constant current-dry cycle, the influence law of corrosive crack time and the expansion rate influenced by steel bar diameter and concrete protection layer was studied. The results showed that the corrosive crack time of concrete member is inversely proportional to the diameter of the steel bar, and is proportional to the thickness of the concrete. In the meantime, the crack longitudinal velocity develops faster when the members are in the area of alternating wet and dry than the ones in the long-term humid area. Besides, the corrosions near the protection layer, or parts in the area of alternating wet and dry are obviously serious, which shows that the distribution of steel corrosions in the test component is not uniform. The corrosion expansion crack width has a linear relationship with the steel bar corrosion ratio.(3) Under coupling effects of long-term load and multidimensional corrosion of chloride, the concrete member produces multiple cracks. By means of studying on the distribution of chloride ions in different locations of the concrete members, the influence law of the cracks on chloride ion erosion was analyzed. The conclusions are obtained as follows:Due to influence of multidimensional penetrations, the concentration of chloride ion of the corrosion cracking decreased in the 0-25mm area along depth direction, while the concentration of chloride ion of the corrosion cracking increased in the 25-60mm area.Except for that the change of chloride ion content at the intersection of the crack is unclear, the component has a most content of chloride ion in the location without cracks, and has a second most content of chloride ion in the location with corrosion cracks, and has a least content of chloride ion in the location with load cracks. Around the cracks area, the content of chloride ion is in the direction of wave shape along the length direction of corrosion expansion crack. Additionally, the wider the fracture is, the greater the concentration of chloride ion in the fracture is.