Research On Chloride Binding Capacity Of Concrete And Its Test Method

Cloride binding is significant to the study of the service life of concrete structures. In this paper,9series mix proportion concretes were prepared through optimum choosing cementitious material andcomprehensively using mineral admixtures. In the experimental process, according to two testingmethods, namely natural diffusion method and isothermal adsorption method, the chloride bindingcapacities of different concretes were determined, its nonlinear problem were analyzed. Eventually,the influences of curing age, content of mineral admixtures on chloride binding capacity disciplinewere discussed. Comparison of two methods, an alternative method was proposed to replace thelong-term diffusion method. Main results achieved are as follows:（1）Chloride total binding isotherm and physical adsorption of concrete accord with Freundlichisotherm, while chemical binding can be described by Langmuir isotherm. For Ordinary Portlandconcrete(OPC), chloride chemical binding is dominant.The ratios of chloride physical adsorptionconcentration continue to increase, while the ratio of chemical binding concentration tends to limit.（2）Binding capacity of concrete reduced with the increasing of free chloride concentration. Thebinding capacity of concrete with fly ash or slag reduced with the increasing of mineral additivescontent at low equilibrium concentration, physical adsorption is dominant. At high equilibriumconcentration, the binding capacity increases as the content of mineral additives increases.（3）The experimental results of natural diffusion method show that, it has no relationship ofexposed time with chloride binding capacity of concrete. Within a certain range, the binding capacityincreased with prolongation of standard curing age, and has great relationship with contents of fly ashor slag, accords with the quadratic equation. The best dosage of fly ash is28.2%, and slag is31.3%.Slag concrete binding capacity is higher than ordinary concrete and fly ash concrete.(4) Comparing chloride binding capacity of concrete based on two test method, the results ofOPC was similar, which of concrete with fly ash and slag were quite different. Adsorption isothermsmethod only can be used to study the chloride binding mechanism. However, adsorption isothermmethod selected specific equilibrium concentration was proposed as a rapid testing method to replacethe long-term diffusion method.