Investigation On Damage And Failure Of Reinforced Concrete Under Synergistic Effects Of Environmental Corrosion And Bending Load

The damage evolution and failure of reinforced concrete samples under synergistic effects of cyclic freeze-thaw, deicing-salt attack, rebar corrosion and bending load were investigated using a comprehensive testing method. The resistance of four kinds of concrete (C70, C60A, C60B, C45) against the synergistic effects of freeze-thaw, deicing-salt attack, rebar correction and bending stress were evaluated through measuring the dynamic modulus and the strain, using four-point bending load in salt solution at cyclically alternate temperature.Under the impact of HC1, damage induced by surface denudation, neutralization and intensive dissolution of cement stone would occur in the concrete structure. The permeability of concrete was mainly attributed to the diffusivities of aggressive ions into concrete, which depended on material microstructure and fluid properties. However, in general, chemical reactions were much faster than the diffusion rate, and thus, the overall rate of the degradation processes would be governed by the slower diffusion of one of the species (reactant or product). The diffusivities of chloride ion had significant effect on the corrosion resistance of concrete to HC1.Three important features were revealed from this study as below (1) Damage rate increased with increasing effecting factors, and the applied bending stress accelerated obviously the damage rate, (2) High-strength fly ash concrete with 30% I grade fly ash had good corrosion resistance, because the chloride permeability decreased with increasing fly ash content, (3) At the fixed temperature difference(-17C-8C), the amplitude of cyclic strains increased with the numbers of freeze-thaw cycles, which discovered the effects of thermal fatigue and corrosion on the thermal expansion coefficient.Stresses in reinforced concrete beam under synergistic effects of cyclic freeze-thaw and four-point bending were analyzed based on thermomechanics and mechanics of materials, and the variations of these stresses with damage evolution of concrete were also investigated. As a result, a series of formula for calculating thermal and mechanical stresses in the concrete were presented. It was found that the thermal stresses distributed nonlinearly along the length of the beam sample and that the bending stresses depended on the ratio of steel modulus to the concrete modulus. Thedamage mechanism of the concrete under the synergistic loads was demonstrated to be a combination of thermal fatigue and corrosion penetration.Examination of SEM/EDXA and stress analysis was performed to explore the deterioration mechanism of reinforced concrete, and the damage evolution is highlighted briefly as follows (1) concrete's damage such as microcracks were caused by thermal fatigue stress and applied stress, (2) since the corrosion solution and Cl" irons penetrated into concrete and the interface of rebar-concrete, rebar corrosion is accelerated, the existence of Fe(OH)? is proved by XRD analysis, (3) the concrete failed due to the vicious circles in expediting each other between the corrosion and damage. An interesting phenomenon was found that the micro-structural features of corrosion layers of lognitudinal tensile rebar, lognitudinal compressive rebar and stirrups in reinforced concrete beam under synergistic effects of cyclic freeze-thaw, deicing-salt attack, rebar corrosion and bending load, were obviously different. In detail, corrosion layers of lognitudinal tensile rebars were like floccule, while those of lognitudinal compressive rebars were like honeycomb, and those of stirrups were like claw. The difference may be caused by the influence of the different stress state, which need further study in the future.The life of reinforced concrete beam under synergistic effects of cyclic freeze-thaw, deicing-salt attack, rebar corrosion and bending load was investigated, and the failure process was divided into two stages, i.e. steady deterioration stage and accelerating deterioration stage. The steady deterioration stage was in the highest flight. While accel...