Investigation On Chloride Ions Transport In Crumb Rubber Concrete

Crumb rubber concrete must meet the requirement of durability before it can be applied to engineering,while the intrusion of chloride ions is an important factor affecting the durability.The floating of rubber particles produced during the construction process will result in its uneven distribution due to that the apparent density of rubber is far smaller than the densities of cement mortar.Therefore,it is of great significance to propose an effective strategy for improving distribution of rubber particles in concrete,and to describe the transmission behavior of chloride ions in rubber concrete,which is a key element in the durability design and performance evaluation of rubber concrete.Based on the motion equation of solid particles and the multi-mechanism transport theory of ions in concrete,the thesis studied the transport behavior of chloride ions in rubber concrete by macro experiment,theoretical analysis and numerical simulation,proposed an rubber particle floating controlling method base on the layer index of mortar,built a multi-mechanism transport model of chloride in crumb rubber concrete considering diffusion,convection,and electromigration,and then clarified influence law of water-cement ratio,rubber replacement rate,and environment temperature on chloride ions transport in crumb rubber concrete.The main results can be summarized as follows:(1)Research on the rubber particle distribution uniformity in concreteAccording to the motion equation of solid particles in the mixture,increasing the consistency and viscosity of the mixture can reduce the relative speed of aggregate particles in the vibrating process and the floating of rubber particles,so as to improve the uniformity of rubber concrete.Thus,the mechanism of rubber particles’ movement and the control method for the floating of rubber particles in concrete are studied systematically in the thesis.The results show that the incorporation of cellulose ether can significantly improve the consistency and stratification of the mixture,then inhibit the floating of rubber particles,and finally improve the distribution uniformity of rubber particles.The uniformity shows an increasing trend,from 0.86 to 1.20,with the incorporation of cellulose ether when the rubber replacement rate is 0.25.The distribution uniformity of rubber particles can be improved by decreasing the delamination degree of mortar mixture,which indicates a linear correlation with rubber replacement sand ratio.(2)Experimental analysis and calculation model of chloride ions transport in crumb rubber concreteThe accelerated corrosion tests were carried out to comparatively study the resistance performances of chloride ions erosion for common concrete and crumb rubber concrete in different environmental temperatures,so as to develop the transport model of chloride ions in crumb rubber concrete.The results show that the influence of ambient temperature on crumb rubber concrete is larger than that of common concrete.In other words,the lower the temperature is,the higher penetration resistance of chloride for crumb rubber concrete is.With the increase of water-cement ratio and rubber replacement sand ratio,the total porosity of slurry and the pore size increases at the same time,which will enlarge the permeability coefficient of water and the convective effect of chloride ions with pore fluid in concrete.However,the addition of rubber particles increases the effects of dilution,zigzag,and ITZ,and obviously reduces the hydraulic diffusivity of concrete.The permeability coefficient of chloride ions at 303.15 K temperature is 8.8 times that at 273.15 K,indicating that temperature has a significant effect on the permeability coefficient.(3)Experimental study on the influencing factor of chloride ions transport in crumb rubber concreteThe test device of concrete chloride ions is developed to monitor and analyze the influencing factors of chloride ions transmission in crumb rubber concrete,and the influence factors on the resistance performance of chloride ions erosion are evaluated from the monitoring data and evaluation indicators.The influences of water-cement ratio,rubber replacement sand ration,and environmental temperature on the performance of crumb rubber concrete by chloride ions erosion are systematically studied here.The results show that the reinforcement potential tends to be stable with the increase of monitoring time within 30 minutes.The steel corrosion in concrete can be reduced by decreasing the current and increasing the potential with the increase of rubber replacement ratio,the decrease of water-cement ratio,and the decrease of environmental temperature.The weight loss of reinforcement decreases by 1.54 g when the rubber replacement ratio is 0.4 compared with 0;the weight loss of reinforcement increases by 2.47 g,when the water-cement ratio increases from 0.37 to0.43;the weight loss increases by 3.45 g,when the environmental temperature increases from 0℃ to 45℃.(4)Simulation study on the influencing factor of chloride ions transport in crumb rubber concreteBased on the multi-mechanism transport theory of chloride ions in crumb rubber concrete,a two-dimensional finite element model is established with COMSOL to simulate the influencing factors of chloride ions transport in crumb rubber concrete.The results show that the transport of chloride ions is mainly convection and diffusion in the natural diffusion state.Concrete with different water-cement ratio,different rubber replacement ratio,and different environmental temperature have consistent trends but different transmission law of chloride ions under natural diffusion and electric migration conditions.Thus,it is feasible to study the durability of concrete structure by using accelerated corrosion test under electric field.In the electric migration state,the initial saturation significantly affects the migration of chloride ions.The smaller the initial saturation is,the more chloride ions accumulate at the saturation edge.In the natural diffusion state,the initial saturation has a little effect on the migration of chloride ions,while concrete tends to be saturated due to the long diffusion time.