Evaluation of Corrosion Degradation Law of Recycled Reinforced Concrete in Saline Soil Under Electrifeid Environment

LI Qiong, QIAO Hongxia, LI Aoyang

(School of Civil Engineering, Lanzhou University of Technology, Lanzhou 730050,China)

Abstract: In order to investigate the corrosion mechanism of recycled reinforced concrete (RRC) under harsh environments, four recycled coarse aggregate (RCA) contents were selected, and saline soil was used as an electrolyte to perform electrified accelerated corrosion experiments. The relative dynamic elastic modulus and relative corrosion current density were considered to describe the deterioration law of the RRC in saline soil.The results indicated that as the energization time increased, the corrosion current density, corrosion potential,and polarization resistance of the steel bar decreased gradually. Compared with ordinary reinforced concrete,when the RCA content was 30%, the ability of the RRC to resist corrosion was improved slightly; however,when the RCA content exceeded 30%, the corrosion resistance of the RRC deteriorated rapidly. Scanning electron microscopy revealed that for a dense RRC, less corrosion products were generated in the pores inside the concrete and on the surface of the steel bar. X-ray diffraction results indicated that SO42- can generate ettringite and other corrosion products, along with volume expansion. The main corrosion products generated on the surface of the steel bars included Fe2O3, Fe3O4 and FeO(OH), which were the corrosion products generated by steel bars under natural environments. Therefore, using saline soil as an electrolyte is more consistent with the actual service environments of RRC. Both the relative dynamic mode and relative corrosion current density of the degradation parameters conform to the Weibull distribution; furthermore, the relative dynamic mode is more sensitive and the corresponding reliability curve can better describe the degradation law of RRC under saline soil environments.

Key words: recycled aggregate concrete; corrosion mechanism; saline soil; accelerated corrosion;durability evaluation parameters

1 Introduction

Recycled aggregate concrete (RAC) is an ecofriendly construction material that is composed of recycled coarse aggregates (RCAs), which are obtained from abandoned concrete. Using RAC as an alternative to natural aggregate concrete (NAC) can produce significant environmental and economic benefits,including the conservation of natural resources, a reduction in the amount of land used for waste disposal,and the reuse of construction and demolition waste[1-3].

Durability is one of the main factors affecting the long-term performance of recycled reinforced concrete (RRC) structures, particularly in harsh environments, such as those of Qinghai in western China. The soil in these areas contains a significant amount of crystalline salts, primarily chloride,sulfate, and magnesium salts[4]. In these regions, the corrosion damage of reinforced concrete structures is considerably higher than that in other parts of China;this significantly hinders the promotion and application of RRC. Therefore, systematic research focusing on the corrosion degradation law of RRC in saline soil environments must be conducted.

Chloride ion permeability and sulfate attacks are the primary factors influencing the corrosion of RAC in harsh environments, as reported extensively[5,6]. Vazquezet al[7]investigated the law of chloride penetration and diffusion using four RCA contents; these were subjected to saline attacks as the water-binder ratio(w/c) changing from 0.45 to 0.6. The results showed that a high RCA content resulted in an improvement in the durability of the RAC, and thew/cratio was sufficiently low. Maet al[8]performed investigations involving freeze-thaw cycles, elevated temperatures,and mechanical damage; the results showed that the chloride permeability of the RAC increased with the RCA content and that the incorporation of RCAs increased the chloride permeability sensitivity of the RAC. Several researchers have reported that RAC has a higher chloride ion permeability than NAC, and as the content of RCA increases, the diffusion coefficient of chloride increases[9,10]. The presence of RCA surface old adhesion mortar results in an increase in the total porosity of concrete, and RCAs result in additional microcracks owing to the crushing process; this provides more paths for the chloride ions to penetrate the RAC. RAC includes additional types of interfaces,and the old and new ITZs between the aggregate and mortar is looser, thereby further reducing the resistance to chloride permeability[11-13].

The effects of sulfate attacks on the RAC properties should be considered for RRC structures employed in sulfate-rich environments, such as salinealkali lands, salty lakes, or marine environments[14].Sulfate ions from the external environment can react with the cement hydration products and yield corrosion products with volume expansion; this generates an expansion stress inside the concrete and cause cracks[15]. Zhanget al[16]experimentally investigated the performance evolution of different types of ITZs in RAC using a 5% Na2SO4solution immersion and dry-wetting cycles; the results showed that sulfate ions accumulated faster in RAC than in NAC, whereas the erosion products remained the same. Leiet al[17]demonstrated that after freeze-thaw cycles in a salt solution and cyclic mechanical loading, the durability of RAC was superior to that of NAC and the interfacial transition zone (ITZ) in NAC deteriorated faster than that in RAC. Yanet al[18]and Higueraet al[19]reported that reducing thew/cand increasing the fly ash content can improve the ITZs of RAC; this enhances the sulfate corrosion resistance of RAC.

In the above-discussed studies, most achievements were based on the durability of RAC. However,to improve the utilization rate of RCAs, they need to be used for preparing plain concrete for nonbearing structures as well as for bearing structures[20];nevertheless, research pertaining to the performance of RRC in saline soil environments remains limited.

The corrosion of a steel bar is an electrochemical reaction[21]. Hence, scholars have proposed an electrochemical corrosion method to accelerate the corrosion of reinforced concrete[22]. Compared to natural exposure and solution immersion accelerated method, this method requires less time, and the corrosion efficiency of steel bars can be controlled by changing the temperature, humidity, and oxygen content of the concrete surface[23]. Wanget al[24]adopted full-immersion, half-immersion, and dry-wet cycling methods based on impressed current densities to accelerate corrosion; the results showed that full immersion resulted in poor non-uniformity, whereas semi-immersion yielded a low expansion rate. Hence,the dry-wet method was recommended. However,Fenet al[25]reported that using a salt solution as the electrolyte for constant-current accelerated corrosion experiments is inconsistent with the actual environment and that the corrosion products when using salt solution flow easily, thereby reducing the corrosion products on the concrete and decreasing the crack development rate of concrete surfaces.

This study aimed to investigate the degradation law of concrete and steel bars inside RRC with different RCA contents under saline soil environments,by using the electrified accelerated corrosion method.To better simulate the actual saline soil environment,saline soil was obtained from Qinghai Province,instead of using a salt solution as the electrolyte.A dynamic elastic modulus experiment and an electrochemical experiment were conducted to analyze the durability degradation mechanism of the RRC in the saline soil. Scanning electron microscopy (SEM)and X-ray diffraction (XRD) were used to reveal the internal micromorphology and corrosion products after RRC corrosion. Finally, the deterioration law for RRC durability was analyzed based on the Weibull theory. The results presented herein are expected to be beneficial for the application of RRC in saline soil environments.

2 Experimental

2.1 Materials

2.1.1 Cement, fly ash

In this study, ordinary Portland cement with a grade of 42.5 according to Chinese standard GB175-2007[26], was used and the properties are shown in Table 1. The fly ash is classified as class II based on the Chinese standard GB/T1596-2017[27]. The chemical compositions of these two cementitious materials are listed in Table 2.

Table 1 Properties of cement

Table 2 Chemical compositions of cementitious materials/%

2.1.2 Aggregates

According to the Chinese standard GB/T14684-2011[28], natural fine aggregates are considered as medium sand, and their fineness modulus is 2.78.Crushed stone with a gradation range of 5-25 mm was used as the natural aggregates (NCAs). Furthermore,RCAs were obtained from waste concrete at a 10-yearold shopping mall in Lanzhou City, China; the concrete was crushed with a jaw crusher and then screened and cleaned. The parent concrete, which may be considered as originating from a single source, featured a cubic compressive strength of 35-40 MPa. The properties of the three aggregates are shown in Table 3. The size grading of RCA and NCA are shown in Fig.1.

Fig.1 Grading curves of RCA and NCA

Table 3 Physical properties of the aggregates

2.1.3 Steel bar

The steel bar was HRB400 according to the Chinese standard GB/T1499.2-2018[29]. The chemical composition of steel bar is shown in Table 4.

Table 4 Chemical composition of steel bar/%

2.1.4 Superplasticizer

A powder-superplasticizer provided by Jiangsu Subote Co. Ltd. was used and the water reducing rate was 20% (Provided by the manufacturer).

2.2 Specimen preparation

In order to study the effect of RCAs content on the durability of RRC, four different RCA contents of 0%, 30%, 50%, 70% were designed (replace NCAs with the same quality).

Owing to the high water absorption capacity of RCAs (as listed in Table 3), RAC requires more water than NAC in order to achieve the same workability during the mixing process. To obtain the same workability, Poonet al[30]and Matiaset al[31]suggested presoaking the RCAs and adding an appropriate amount of high-performance superplasticizer. Accordingly,in this study, the desired workability of the RAC was obtained by adding a superplasticizer. The RAC mixtures and the slumps of each group are detailed in Table 5.

Table 5 Mixture design and slump of RAC

RAC specimens with dimensions of 100 mm× 100 mm × 100 mm were prepared; each group contained three specimens. A steel bar with a diameter(d) of 8 mm was placed vertically at the center of the specimen, and a steel bar extended to 25 mm (from the specimen surface) was used to wind the copper wire.The specimen is shown in Fig.2. After 24 h of molding,the specimen was removed from the mold. The exposed steel bar was wound with copper wire, and the exposed steel bar and copper wire were coated with epoxy resin to prevent corrosion. The specimens were placed in a standard curing room at a temperature of 20±2 °C and relative humidity of 95% for 28 d of curing.

Fig.2 Reinforced recycled concrete specimen

2.3 Methods

2.3.1 Constant current acceleration experiment

Saline soil from Golmud, Qinghai Province,was used as the electrolyte. The composition of the corrosive ions in the saline soil is shown in Table 6. To ensure a constant content of corrosive ions in the saline soil throughout the experiment, a composite solution of Na2SO4(25g/L) and NaCl (140g/L) was prepared and sprayed on the soil once a week. After curing under standard conditions for 28 d, the RRC specimens were immersed in water for 72 h to allow them to attain the water-retaining state. Subsequently, the specimen was vertically buried in the saline soil, the steel bar was connected to the positive electrode (anode), the carbon bar was connected to the negative electrode (cathode),and the PS3002D-II direct-current power supply was used for constant-current energization. The corrosion current density was set to 150 μA/cm2[32], which is similar to the natural corrosion current density of a steel bar.

Table 6 Content of corrosive ions in soil /(mg·kg-1)

2.3.2 Electrochemical experiment

After each energized acceleration period, the electrochemical parameters of the steel bars were measured using an electrochemical workstation. The experimental system was a three-electrode test system,as shown in Fig.3. A steel bar was used as the working electrode. A thin stainless-steel plate with an area of 30 cm2,i e, greater than that of the working electrode,served as an auxiliary electrode, whereas a saturated KCl electrode served as the reference electrode. The electrochemical impedance spectrum (EIS) frequency ranged from 10 μHz to 4 MHz, and the impedance test accuracy ranged from 1 mΩ to 1 GΩ/±2%. The scanning rate for the polarization curve was 334 μV/s,under the voltage range of ±10 V and current resolution of 25 fA.

Fig.3 Electrochemical experimenting system

According to Faraday’s theorem (Eq.(1)), when the theoretical mass loss rate of the steel bar increased by 0.5%, the corresponding electrification time was 72 h, which was assumed as one period. Seven cycles were selected as the standard, and the experiment was terminated after 504 h.

where Δmis the theoretical steel bar quality loss, g;Zis the chemical valence of the reaction electrode, +2;Fis the Faraday constant, 96 500 A;Mis the atomic mass number of iron, 56;Iis the current intensity.

When the open circuit potential is ±0.01V,the metal is micro polarized. According to Stern-Geary Equation, the corrosion current density (icorr)of steel bars can be obtained by Eqs.(2) and (3)[33].

The relationship between theicorrand the steel bar’s corrosion is shown in Table 7[34].

Table 7 Relationship between corrosion current density and corrosion degree of steel bar

whereicorris the corrosion current density, μA·cm-2; ΔEis the open circuit potential, mV;Rpis the polarization resistance, Ω·cm2; γmis the Tafel slope of the anode; γnis the Tafel slope of the cathode.

2.3.3 Ultrasonic experiment

After each electrochemical experiment, the specimens were dried in air for 24 h; subsequently,an ultrasonic wave experiment was performed. In this ultrasonic experiment, the HC-U83 ultrasonic detector, which has a sampling period of 0.05-2.0 μs and a precision of 0.05 μs, was adopted. Four points on each of the two faces were tested, and the average value of the four points was regarded as the final value.The ultrasonic instrument and the test points of the specimen are illustrated in Fig.4.

Fig.4 Distribution of test points

Fig.5 RRC-0 group

Fig.6 RRC-30 group

Fig.7 RRC-50 group

Fig.8 RRC-70 group

Fig.10 COV of corrosion current density

Fig. 11 Nyquist plot

2.3.4 Microscopic experiment

After performing the electrically accelerated corrosion experiment, the concrete and steel bars for each group were scanned using the JSM-6701F cold field emission electron microscope and the JSM-5610LV low-vacuum SEM, respectively. A magnification of 5 000× was used for concrete, whereas a magnification of 500× was used for the steel bar. D8 ADVANCE XRD was used to analyze the changes in the images of the concrete and steel bars during degradation. The scanning angles were 10°-50° and 10°-90°, respectively.

2.4 Durability evaluation parameters

RRC durability is evaluated by the relative corrosion of steel bar ω1and the relative dynamic elastic modulus ω2, which are calculated according to the reference[35,36], as shown in Eqs.(4)-(5).

whereimc=1 μA·cm-2, the threshold value oficorrfor serious corrosion of steel bars:

wherevtis the ultrasonic sound velocity att, km/s;v0is the initial ultrasonic sound velocity, km/s.

3 Results and analysis

3.1 Analysis of RRC electrochemical experiment results

3.1.1 Polarization curve

The polarization curves of the three specimens in each group exhibited similar change rules.Subsequently, the polarization curves of one sample from each group were analyzed. The polarization curves,icorrand corrosion potential (Ecorr) of each group are shown in Figs.5-8. The coefficient of variation(COV) ofEcorrandicorrof three specimens in each group are shown in Figs.9 and 10.

3.1.2 Alternating-current impedance spectroscopy analysis

The electrochemical impedance diagrams(Nyquist diagrams) of the three specimens in each group exhibited similar variations. We analyzed one sample from each group, as presented in Fig.11.As shown, during the initial stage of the electrified accelerated corrosion, capacitive arcs were formed, and their radii were small and large in the high and lowfrequency regions, respectively. The radius in the highfrequency region was smaller and almost resembled a straight line, which indicates the high corrosion resistance of the concrete protective layer[44]. The radius in the low-frequency region was larger, indicating that the steel bar was in a stable protection state. With the continuous application of a constant current to the steel bars, the two-stage capacitive arc radius in the highfrequency region decreased gradually. At this time, the internal steel bars changed from the passive state to the active state, and the effect of the concrete protective layer weakened gradually.

The Nyquist diagrams of each group were fitted according to the equivalent circuit of Fig.12, and the polarization resistance of the steel bars (Rp) were obtained, as shown in Fig.13.

Fig.12 Equivalent circuit(Rs is solution resistance, Rc and Cc are the resistance and capacitance of concrete protective layer,respectively, Rp is steel bar surface charge transfer resistance(polarization resistance), and Ce is double layer capacitance)

Fig.13 Polarization impedance of each period

Fig.13 shows that the value ofRpfor the steel bar increased and decreased during the degradation,with an overall decrease. The value ofRpfor each group decreased gradually during the early stages and decreased slowly in the later stage, and maintained a higher corrosion level subsequently, which is consistent with the findings of Rengarajuet al[45]regarding the corrosion behavior of the steel bars in ordinary concrete. At 504 h, the values ofRpfor RRC-0 and RRC-30 were 375 and 521 Ω, respectively. The corrosion development rate of RRC-30 was slightly lower than that of RRC-0. However, the corrosion developed further in RRC-50 and RRC-70, and these underwent rapid deterioration. At 504 h, the values ofRpfor RRC-50 and RRC-70 were 343 and 312 Ω, respectively. This indicates that when the RCA content is low, the RCAs do not significantly affect the corrosion resistance of the RRC in the saline soil environment. This is in agreement with the effect of the RCA content on the polarization curve. Fig.14 shows that the COV ofRpfor each group increased with the energizing time but did not exceed 0.1, thereby indicating weak variations. Thus, the effect of the RCA content on the COV ofRpwas insignificant.

Fig.16 SEM of RRC-30

Fig.17 SEM of RRC-30

Fig.18 SEM of RRC-70

Fig.19 XRD pattern

Fig.20 Trend of durability evaluation parameters of RRC

3.2 SEM morphology analysis

After the completion of the electrified accelerated corrosion tests on the four groups of RRC specimens under the saline soil environment, the micromorphologies of the concrete and the steel bar were obtained, as shown in Figs.15-18.

Layered corrosion products were observed on the surface of the RRC-0 steel bar, and the bond between the layers was weak. The concrete pores contained sparse rod-shaped crystals that were interlaced with each other, forming a loose spatial structure. Relatively few corrosion products were observed on the surface of the RRC-30 steel bars. The concrete featured a few internal pores; its surface was relatively dense, and its degree of corrosion was the lowest. The corrosion products on the surface of the RRC-50 steel bars formed a loose cloud-like structure, and extensive cracks were noted. The internal structure of the concrete featured many pores, and needle-like crystals were developed inside these pores. The surface of the RRC-70 steel bars was covered with flower-like corrosion products, and its structure was loose and porous. The pores in RRC-70 were scattered, containing short columnar crystals that developed outward along the direction of the pores.

The analysis revealed that the compactness of the internal structure of the concrete significantly affected the corrosion resistance of the RRC. A denser internal structure resulted in the generation of fewer corrosion products inside the concrete and accordingly, fewer corrosion products on the surface of the steel bars. It is evident from Figs. 15-18 that the RRC corrosion degree was RRC-30 > RRC-0 > RRC-50>RRC-70, which is consistent with the polarization curves and Nyquist plots.

3.3 Corrosion mechanism and XRD result analysis

Under a saline soil environment, the corrosion mechanism of RRC when accelerated by electricity is analyzed as follows:

(1) Corrosion mechanism of steel bars[46]:

Under sufficient O2, Fe(OH)2can generate loose Fe2O3:

Under sufficient O2and H2O, Fe2+can generate FeO(OH):

As shown in Figs.19(a) and 19(b), the compositions of Fe2O3, Fe3O4, and FeO(OH) were identified qualitatively from the corroded samples of the two groups. The peak area of the corrosion products of RRC-0 was larger than that of RRC-30, indicating the low corrosion degree of RRC-30; this is also consistent with the SEM results. The composition of these corrosion products on the steel bar surface was the same as that in a natural environment. The corrosion was caused by Cl-ions[47], indicating that the electrified accelerated corrosion experiments using saline soil as the electrolyte could effectively simulate the corrosion effect in a natural environment.

(2) Corrosion mechanism of concrete:

The SO42-in saline soil reacts with the hydration products of concrete to form gypsum, ettringite (Aft),and monosulfide-hydrated aluminum sulfate (Afm):

As shown in Figs.19(c) and (d), the peak area of Ca(OH)2in RRC-0 was less than that in RRC-30,whereas the peak area of Aft increased; this indicates that the alkalinity of RRC-0 decreased and the corrosion products increased, which is consistent with the SEM results.

3.4 Reliability analysis based on Weibull theory

3.4.1 Degradation parameters

The degradation parameters of each group were obtained using Eqs.(4) and (5), as shown in Fig. 20,where ω1and ω2are the average values of the three specimens in each group. ω1<0 indicates that the steel bar has reached the threshold corrosion state, whereas ω2<0 indicates RRC damage. The two parameters were compared over the same period; ω1of each group decreased faster during the early stage and slowly during the later stage. Meanwhile, the decrease in the amplitude of ω2was slower during the early stage and faster during the late stage. This is attributed to the significant volume expansion caused by the corrosion products in the pores. When the internal expansion force in the pores exceeded the tensile strength, the bond between the aggregate and the cement stone was destroyed, resulting in the generation of cracks. Under the combined action of the applied electric current and the corrosive ions, the cracks develop rapidly[48].

3.4.2 Weibull theory

The Weibull function was proposed by Weibull in 1939. It is widely used for solving reliability problems,because it can yield more accurate reliability analyses based on a small sample dataset[49-50]. In this study, the durability modeling of steel corrosion in RRC was performed using the two-parameter Weibull function.

The distribution function of two-parameter Weibull:

where β>0, η>0, β is the shape parameter, η is the scale parameter, defineT-wei(η, β).

The density function:

Reliability function:

Failure density function:

Take the logarithm of both sides of Eq.(8) to simplify the reliability function:

Define,y=ln(-ln(R(t)),x=ln(t), a=β,b=-βln(η),Eq.10 can be simplified as:

3.4.3 Weibull function distribution check

The damage parameters ω1and ω2for different corrosion stages during the electrification process in a saline soil environment were adopted in Minitab software to verify the Weibull distribution hypothesis;the significance level a was set as 0.05. As the modeling process for each group was identical, RRC-0 and RRC-30 were used as the examples for analyses.As can be seen from Fig.21, ω1, ω2of RCR-0 and RCR-30 obey Weibull function distribution.

Fig.21 Weibull distribution check for ω1 and ω2

3.4.4 Deterioration model based on Weibull distribution

In this study, the least-squares method[50,51]was used to calculate β and η of the Weibull function (the specific calculation steps are the same as those in literature[52], therefore, not repeated in this paper),which were then substituted in Eq.(3) to obtain the Weibull distribution reliability function; the distribution reliability function curves corresponding to ω1and ω2are presented in Fig.22.

Fig.22 Weibull distribution reliability function curve

Fig. 22 shows the parameters ω1, ω2of RRC-0 and RRC-30 and the corresponding reliabilityR(t) = 1 at 0 h. Under the combined action of the applied current and the corrosive ions, the reliabilityR(t) decreased continuously and finally reached 0. Att= 220 h for RRC-0 andt= 300 h for RRC-30, the reliability curves corresponding to ω1and ω2intersected. The degradation degree oficorrbefore this intersection point was greater than the dynamic elastic modulus, whereas the degradation degree of the dynamic elastic modulus beyond this intersection point was greater than the corrosion current density. The values of ω1and ω2for RRC-0 corresponded to the failure time of 460 and 340 h, respectively. Meanwhile, the values of ω1and ω2for RRC-30 correspond to the failure time of 510 and 393 h,respectively. Thus, using a single factor to evaluate the degradation law of RRC in a saline soil environment is expected to introduce errors; therefore, additional factors should be considered for a more comprehensive evaluation. Notably, ω2is more sensitive, and its reliability curve can reflect the deterioration trend of the RRC in a more comprehensive manner.

4 Conclusions

a) In a saline soil environment, as the energization time increases, the ability of the concrete protective layer to resist corrosion weakens gradually; moreover,the steel bar changes from the passivated state to the activated state in the early stage, while also gradually reaching a high corrosion state.Ecorrandicorrcan qualitatively and quantitatively describe the corrosion tendency of RRC, respectively, whereasRpof the steel bars can quantitatively describe their ability to resist external corrosion.

b) The physical properties of the RCAs exerted positive and negative effects on the ability of the RRC to resist corrosion in a saline soil environment.Compared with RRC-0, RRC-30 exhibited slower corrosion development and a lower degree of corrosion. When the RCA content exceeded 30%, the corrosion commenced earlier and also developed faster.Therefore, an optimal RCA content exists, at which the RCAs do not significantly affect or slightly improve the corrosion resistance of the RRC.

c) The COV ofEcorrandRpof the steel bars in each group were less than 0.1, indicating weak variations.The COV oficorrwas sensitive to the increase in the energization time and medium variations. The RCA content did not significantly affect the COV of various electrochemical parameters. A unique source and appropriate classification, cleaning, and preparation processes for the RCAs were essential for ensuring the homogeneity of the RRC.

d) SEM and XRD were used to reveal the microstructure of the RRC. A denser internal structure resulted in fewer corrosion products inside the concrete and also on the surface of the steel bars. Corrosive SO42-ions reduced the alkalinity of the concrete and generated the corrosion products Aft and Afm,resulting in volume expansion. Fe2O3, Fe3O4, and FeO(OH) were the main chemical components in the corrosion products of the steel bars, and their chemical compositions were the same as those generated by steel bars in a natural environment. The order of the RRC corrosion degree was obtained based on the micromorphologies, as follows: RRC-30 > RRC-0> RRC-50>RRC-70. Furthermore, the conclusions obtained based on the electrochemical indicators were re-verified.

e) The degradation law of the corrosion current density and dynamic elastic modulus with an increase in the energization time was consistent with the Weibull distribution function. ω1and ω2of RRC-0 corresponded to the failure time of 460 and 340 h, respectively.Meanwhile, ω1and ω2of RRC-30 corresponded to the failure time of 510 and 393 h, respectively.Furthermore, ω2was more sensitive, and its reliability reflected the deterioration trend of the RRC in a more comprehensive manner.

f) Based on a comprehensive analysis, it was confirmed that electrified accelerated corrosion experiments using saline soil as the electrolyte can reflect the corrosion of steel bars in a natural environment more accurately, while also yielding more reliable results.

Conflict of interest

All authors declare that there are no competing interests.