## 3 Durability Coefficients of Constructed Reinforced Concrete
### Chloride Diffusion Coefficient  
The rapid chloride migration (RCM) test was conducted to determine the apparent chloride diffusion coefficient of the concrete according to Chinese design code for marine concrete (GB/T  
Figure 6: Concrete surface defects. (**a**) Concrete surface; (**b**) Gray level processing; (**c**) Bubble area calculation; (**d**) Relationship between bubble area and bubble number; (**e**) Percentage of bubbles area occupied; (**f**) Percentage of bubble number occupied.  
50476-2008) [28]. For the concrete used in the marine and land sections, after curing in situ for 28 days, the mean chloride diffusion coefficients were 2.32\(\times\)10\({}^{-12}\) m\({}^{2}\)/s and 4.38\(\times\)10\({}^{-12}\) m\({}^{2}\)/s, respectively. [PERSON] [29] reported that the relationship between the chloride diffusion coefficient and the compressive strength can be expressed by the exponential function. Figure 5 shows that the compressive strengths of concrete follow a normal distribution. Therefore, the mean chloride diffusion coefficients of concrete in the marine section and the land section are 2.32\(\times\)10\({}^{-12}\) m\({}^{2}\)/s and 4.38\(\times\)10\({}^{-12}\) m\({}^{2}\)/s, and their corresponding standard deviations are 0.10 m\({}^{2}\)/s and 0.23 m\({}^{2}\)/s, respectively.  
For the reinforced concrete structure subjected to loading, the loading affects the chloride ions' penetration, and sulfate and frost damage to the concrete. Based on the assumption of uniaxial compression load, the influence of load level (the ratio of uniaxial load to the prismatic compressive strength of the concrete specimen) on the chloride ion diffusion coefficient can be ignored due to the excellent compressive strength of high-performance concrete when the stress level does not exceed 0.3 [30]. However, if the stress level is higher than 0.3, the diffusion coefficient of chloride ions will be increased because of the formation of micro-cracks inside the concrete. Hence, if the sustained loading effect is not taken into account in the assessment of the durability of the structure, this will give an inaccurate prediction of the service life of the structure [31]. In order to evaluate the stress applied on the concrete, six reinforced stress gauges were installed inside the concrete. Figure 7 shows the arrangement of the reinforced stress gauges. Due to the self-calibration process, the strain of the reinforced concrete can be calculated using the following equation:  
\[\sigma=K[\varepsilon_{0}-\varepsilon_{i}-K_{T}(T-T_{0})] \tag{1}\]  
where \(\sigma\) is the strain of the reinforced concrete, \(K\) is the coefficient of the monitoring sensor, \(\varepsilon_{0}\) is the initial strain, \(\varepsilon_{i}\) is the final strain, \(K_{T}\) is the temperature coefficient, \(T\) is the final temperature, and \(T_{0}\) is the initial temperature.  
Figure 8 shows that the stress applied onto the vertical bar decreases with time, and the stress applied onto the horizontal bar increases with time. [PERSON] [32] developed a relationship between the axial load and the chloride ion diffusion coefficient of concrete, as shown in Table 3. Considering the effect of the loading and because of the measured stress applied onto the reinforced concrete, the enlargement coefficient \(k_{s}\) of 1.02 was selected.  
Figure 7: Schematic diagram of the arrangement of reinforced stress gauges in concrete piers.