The Research On The Effect Of Uniaxial Compressive Load And Mineral Admixtures On Chloride Permeability Of Concrete

Previous study on the durability of concrete structures tended to focus on concrete structures under non-stress state, with little considering the combined effect of many complex factors on the durability of concrete structures under actual service conditions, especially the effect of the load on the permeability of concrete structures. The concrete structures in practical engineering applications are generally required to bear a variety of different types of complex loads. Obviously, the concrete structures under non-stress situations often do not represent the structures under actual state in complex environment. Without considering the load conditions, the obtained static indicators about permeability and durability of concrete structures do not correspond to the actual service conditions, and even there is a big deviation.In response to this situation, the loads withstanded by concrete structures under actual state were considered and the effect of sustained loads on the permeability and durability of concrete structures was studied. In this paper, the coastal highway bridge over Liao river in Liaoning Province is the engineering background. In accordance with the requirements of durability design of concrete structures, the mix proportions design of concrete at C30 was made by separate addition of different mineral admixtures (fly ash, slag, silica fume) into concrete, so that the concrete project in the northern cold regions in the marine environment could meet the structural durability requirements. On this base, by using a self-designed loading device, the chloride permeability of plain concrete mixed with different mineral admixtures under sustained uniaxial compressive load at different stress ratios was studied, the variation of chloride ion permeability as mineral admixture content and stress level was tested, the differences between the influence of different mineral admixtures on the permeability of concrete were found, the mechanisms of the influence of sustained uniaxial compressive load and mineral admixtures on the the permeability of concrete were analyzed, the relationship between the chloride ion permeability coefficient and load level and the mineral admixtures content was explored, and the corresponding mathematical models were proposed as well.Through the analysis of the results of this experiment, the main conclusions can be obtained as follows:1. The sustained uniaxial compressive load has a significant impact on the permeability of concrete. When the stress ratio is less than 50%, the changes in diffusion coefficient is relatively slow; when the stress ratio is more than 50%, the diffusion coefficient increases significantly. The relationship between chloride ion diffusion coefficient and stress ratio approximately meets the mathematic model of parabola.2. Separate addition of different mineral admixtures into concrete can improve its resistance to chloride ion penetration, and the effect of silica fume is the best, followed by slag, fly ash is the worst. The chloride ion diffusion coefficient decreases with increasing mineral admixture content by the negative exponential function.3. For concrete incorporation of mineral admixtures, the permeability and compressive strength do not have good correlation.