Abstract

     The corrosion of chloride-induced on concrete is affected by many factors. In this research, an innovative empirical model was developed to predict the long-term chloride migration behavior in concrete, considering the effects of water-cement ratio, time, bonding effect, temperature, relative humidity, and concrete deterioration. The reliability and validity of the results evaluated by the empirical prediction model were verified by the chloride concentration data in concrete specimens exposed to the marine environment for 3, 5, and 10 years reported in the literature. Combined with the established empirical prediction model, the concrete model was regarded as a three-phase composite material composed of mortar, coarse aggregate, and interfacial transition zone. The effects of key factors on chloride migration were further analyzed by using the mesoscopic finite element numerical simulation method. It was observed that when temperature increases from 5 ℃ to 65 ℃, chloride diffusion depth rises by 3.3 times. When relative humidity increases from 20% to 100%, chloride diffusion depth rises by 4.3 times. Also, the water-cement ratio, concrete deterioration, and chloride binding effect have a non-negligible impact on chloride migration.

Introduction

     The steel bar corrosion caused by chloride plays a crucial role in reducing concrete durability [1], [2], [3], [4]. In the marine and de-icing salt environment, chloride aggression causes non-uniform corrosion of rebar in concrete, which leads to cracking of concrete structures [5], [6]. The chloride permeability directly impacts the durability of concrete structures [7], [8].

     The chloride migration is impacted by many factors such as time, binding effect and water-cement ratio temperature, etc. Considering these factors, various chloride migration models have been proposed. A modified formula considering the variation of chloride diffusion coefficient with time in concrete was proposed [9]. Weyers et al. [10] revised the chloride ion diffusion model by comprehensively considering the impact of erosion time on chloride migration. It was found that chloride diffusivity is significantly affected by temperature change [11]. Considering the multi-factor coupling conditions of concrete structure micro-defects, bonding effect, and chloride diffusivity varying with time, the chloride transport model of concrete was established [12]. Lu et al. [13] demonstrated the regression formula of crack on chloride diffusivity. Many studies have shown that the admixing of supplementary cementitious materials can significantly improve the working performance of concrete [14], [15]. A chloride migration model in concrete mixed with fly ash was developed, considering the time dependence of diffusivity and chloride of external [16].

Conclusions

     In this paper, through an in-depth analysis of influencing factors of chloride transmission, a chloride migration model considering key factors was developed. The proposed model was validated by the test data of marine concrete. On a mesoscale, the impact of key factors on chloride transmission was analyzed by numerical simulation. Combined with the above results, the following observations can be reached:

(۱) For optimum analysis of the influencing factors of chloride migration, a novel and reliable chloride migration model is established to generally consider the influences of water-cement ratio, time, chloride ion binding effect, temperature, relative humidity, and concrete deterioration in concrete.

(۲) Temperature increase will accelerate chloride transmission. When the temperature rises from 5 ℃ to 65 ℃, the chloride diffusion depth increases by 3.3 times.

(۳) Relative humidity augment can significantly promote chloride migration behavior. When relative humidity increases from 20% to 100%, the chloride diffusion depth increases 4.3 times.

(۴) The chloride diffusion performance in concrete enhance with the rise of water-cement ratio and concrete deterioration.

(۵) The greater the binding effect, the lower the content of free chloride in concrete.