1 Introduction

The most significant factor that affects the longevity and failure of concrete structures in the Persian Gulf is steel corrosion in reinforced concrete buildings [1]. A substantial amount of money is spent each year on repairing and rebuilding buildings damaged by this issue [2]. One contributing factor to the creation and acceleration of the corrosion process is the usage of rebars with varying degrees of rust due to improper storage. While research has been conducted on the corrosion process caused by such rebars, specific issues still require further investigation. One crucial aspect that needs to be studied is the role of concrete type and quality in preventing corrosion of reinforced concrete when pre-rusted rebars are used.

Chloride emissions and carbonation are the two primary causes of steel corrosion in reinforced concrete structures [3]. Due to the high levels of airborne chlorine in the Persian Gulf, along with the high temperatures and humidity, corrosion of steel in reinforced concrete is predominantly of the chloride type [4]. The required chloride ions to initiate the corrosion process can be obtained from internal sources, such as chloride ion-contaminated materials, and external sources, such as air and water [5]. The risk of using contaminated materials can be reduced by implementing proper storage procedures and conducting relevant testing before applying the concrete. However, mitigating the risk of chloride penetration into the concrete from external sources can be achieved by improving the quality of the concrete.

Modifications in the design of concrete mixes can significantly impact chloride entry [6]. The resistance to chloride penetration in concrete is primarily determined by its transfer properties, which include permeability, diffusion, and adsorption. In the early stage, the pore structure of the cement paste in concrete hardens when exposed to external chlorides. Furthermore, the chemistry of hydrated cement paste affects the concrete’s ability to chemically bind chlorides, preventing them from bonding with the steel in reinforced concrete.

Numerous studies have examined self-compacting and ordinary concrete’s mechanical properties and durability. The research conducted by [7] investigated the impact of various environmental conditions from the Oman Sea on the mechanical characteristics of self-compacting concrete (SCC) and regular concrete. The results indicated that the diffusion coefficient of SCC was 10% and 15% lower than regular concrete at 28 and 150 days, respectively. Moreover, the surface chloride concentration of self-compacting concrete was 18% and 52% lower than that of regular concrete. Another study [8] compared self-compacting concrete’s and conventional concrete’s durability with varying water-to-cement ratios in a coastal environment. The findings revealed that SCC exhibited 11.4% higher electrical resistance than ordinary concrete. Several researchers [9, 10] concluded that SCCs demonstrated lower porosity, chloride absorption, and release than conventional concrete. However, it is essential to note that contrary findings were also reported in several studies [11, 12].

The effect of using self-compacting concrete exposed to external sources of chloride ions on steel corrosion in reinforced concrete has received limited attention. However, a few research studies have addressed this subject. Studies [13, 14] noted that the likelihood of corrosion in self-compacting concrete mixtures is low until the age of 360 days. Another study [15] found that the corrosion rate for self-compacting concrete was approximately 2–12 times lower than ordinary concrete. Furthermore, research [16] evaluated the performance of four self-compacting concrete mixtures with different combinations of additives, such as silica fume, metakaolin, and limestone powder, against corrosion. Electrochemical tests in [17] compared the onset of steel corrosion in self-compacting concrete and conventional concrete, revealing that self-compacting concrete samples demonstrated superior corrosion control. Additionally, paper [18] investigated the long-term corrosion of rebars in various types of concrete commonly used in construction, demonstrating that rebars in self-compacting concrete exhibited higher resistance than those in ordinary concrete. In a study on reinforced concrete beams [19], corrosion in self-compacting concrete samples outperformed normal concrete samples in terms of intensity and corrosion potential.

In addition to the type of concrete (ordinary or SCC), the use of Supplementary Cementitious Materials (SCMs) can influence the performance of concrete. Studies [20,21,22] have shown that the use of cementitious additives affects the chloride permeability performance of high-strength concrete and significantly reduces the rate of chloride penetration and migration. Furthermore, in the research [23], it was observed that using natural pozzolans reduces water absorption, increases porosity, and generally improves the transport properties of concrete. Based on the findings of the study [24], the use of cementitious materials in self-compacting concrete also improves the properties of both fresh and hardened concrete. Moreover, in research [25], it was reported that using cementitious additives in high-strength self-compacting concrete improves transport properties and reduces chloride permeability.

Therefore, based on the instances above, it can be concluded that improving the functionality and quality of concrete is crucial in reducing steel corrosion in reinforced concrete in chloride-contaminated areas. This can be achieved mainly by utilizing self-compacting concrete incorporating supplementary cementitious materials (SCMs) and a lower water-to-cement ratio. However, it is essential to note that most studies focused on the impact of concrete type and quality when used with rebar that had suitable surface conditions and no rust. In reality, in many construction projects in the Persian Gulf, steel rebars often have a rusty surface and are contaminated with chloride due to inadequate attention to proper storage. Although a few studies [26,27,28,29,30,31] have examined the effect of rusted rebar on reinforced concrete corrosion, most researchers [26,27,28, 30] reported increased corrosion intensity and potential when such rebar was used. Therefore, there is a significant need to investigate the effect of enhancing concrete quality on corrosion when utilizing such rebars.

Hence, the primary objective of this study is to determine the influence of self-compacting concrete quality on steel corrosion in reinforced concrete when pre-rusted rebar is employed. Two types of concrete were used to assess the impact of quality: ordinary concrete and self-compacting concrete with SCMs, using water-to-cementitious materials ratios of 0.4 and 0.5. Additionally, pre-rusted rebar samples with varying degrees of corrosion, subjected to real-world conditions of the project, were used for reinforcing the concrete.

2 Laboratory Program

2.1 Materials

Table 1 presents the chemical properties of the powder materials used in this research. The type II cement, zeolite, and silica fume utilized in this investigation have densities of 3150, 2140, and 2200 kg/m3, respectively, and conform to ASTM C150 and ASTM C1240 standards. Stone powder, sand, and gravel used in concrete mix ratios have a maximum size of 0.175, 4.75, and 19 mm, and a density of 2610, 2580, and 2500 kg/m3, respectively. The ASTM C33 standard was used to granulate stone materials. The workability and performance of concrete mixes are enhanced by using a polycarboxylate-based lubricant with a density of 1100 kg/m3 according to with ASTM C494 standard. Rebars with a diameter of φ 12 mm were used to reinforce concrete.

Table 1 Chemical properties of powder materials
Full size table

2.2 Preparation and Storage of Rebar

To simulate the rusted rebar condition, 1-m samples were placed in two different locations and at two distances within the project environment in the Persian Gulf. The first approach involved placing the samples directly on a wooden spacer without any protection, while in the second approach, the samples were thoroughly enclosed with a plastic cover. Additionally, the samples were positioned at two distances from the sea: 70 m (close) and 300 m (far). These specific distances were chosen to reflect the actual conditions of the project closely. The decision to use these distinctions was based on the findings of a study conducted by [32], which demonstrated that the corrosion of chloride-type steel decreases with increasing distance from the sea across various beaches, accompanied by a decrease in the amount of suspended chlorine in the air. Furthermore, for comparative purposes, a reference sample of rebar in its normal condition (as received from the factory) and rebar exposed to accelerated corrosion through the constant current method were also included in the study.

For a detailed explanation of this method, please refer to the research conducted by [33]. The weight loss resulting from corrosion (measured through gravimetry) was utilized to assess the rust condition of the rebar surface. The weight loss caused by corrosion was determined using brushing following the standard ASTM G1 method. The weight reduction and rebar ranking results are presented in Table 2.

Table 2 The condition of the surface of the rebars
Full size table

By implementing these specific methodologies, we can effectively replicate and evaluate the effects of environmental factors and corrosion methods on the condition of the rebars. This comprehensive analysis provides valuable insights into the behavior and performance of the materials, thereby contributing to the development of effective corrosion prevention strategies for reinforced concrete structures in chloride-contaminated areas.

2.3 Mixture Proportions

Six different mixing ratios were utilized to examine the impact of the self-compacting concrete’s performance on the corrosion of pre-rusted steel in concrete. Based on the findings of earlier studies [34, 35], the optimum ratio of SCMs for silica fume 8% and zeolite 15% of cement weight has been chosen. Additionally, six proportions of ordinary concrete mix with the same composition as the self-compacting concrete samples have been employed for more precise comparison. The quantities of the concrete mix used in this study are shown in Table 3.

Table 3 Mixture proportions of concrete
Full size table

Viscosity, yield stress, water volume absorption, total porosity, compressive strength, electrical resistance, electrical conductivity, rapid chloride permeability, rapid chloride migration, chloride diffusion coefficient, half-cell corrosion potential, and corrosion current intensity are among the tests that were performed. The samples were cured till the test age in accordance with ASTM C156 standard procedure, in a saturated lime water solution. Additionally, after being cured for 7 days in saturated lime water until the test age, the samples related to determining the potential and intensity of the corrosion current were put in a 5% NaCl solution. This was done to speed up the corrosion process in accordance with the technique described in the study by [36].

2.4 Experiments

2.4.1 Fresh and Hardened Concrete Tests

A coaxial rheometer with controllable speed was used to measure the yield stress of plastic viscosity as the rheological properties of self-compacting concrete. According to study [37], this device measures the torque applied to the blades when immersed in concrete. Also, to determine the volumetric absorption of water and the volume of permeable pores of concrete samples, the instructions expressed in ASTM C642 standard were used. A compressive strength test evaluated the mechanical properties of concrete. Cubic specimens (100 × 100 × 100 mm) were loaded at 28 days of age according to BS1881-PART116 to perform the compressive strength test.

Electrical resistivity test is applied to evaluate the electrochemical properties of concrete at 28 days of age according to the presented method by [38]. In addition, according to ASTM C1202, concrete samples’ rapid chloride permeability test (RCPT) was measured at 28 days of age. Also, an electrical conductivity test according to ASTM C1760 standard and a chloride ion migration test (RCMT) according to NT BUILD 492 standard were performed to determine the resistance of concrete against chloride ion penetration at the age of 28 days on concrete samples.

The standard method of ASTM C1556 was used to determine the apparent diffusion coefficient of chloride ions in concrete. Fick’s second law [39] was used to obtain the chloride ion diffusion coefficient from Eq. 1:

$$\frac{{C{(}x{, }t{)}}}{{C_{0} }} = 1 - {\text{erf}}\left( {\frac{x}{{\sqrt {4D_{{\text{c}}} t} }}} \right),$$
(1)
$${\text{erf}}_{{{(}x{)}}} = \frac{2}{\sqrt \pi }\int\limits_{0}^{x} {e^{{ - t^{2} }} } {\text{dt}}{.}$$
(2)

In this equation, x is the distance from the surface (mm), t the duration of chloride exposure (days), Dc the effective chloride diffusion coefficient (m2/s), C0 the weight percentage of chloride ions on the concrete surface, and C(x, t) the weight percentage of chloride ion at depth x relative to the surface at time t. erf is also an error function expressed according to Eq. 2 [40].

2.4.2 Corrosion Tests of Steel in Reinforced Concrete

Half-cell potential corrosion test was performed according to the ASTM C876 standard guidelines using a voltmeter and a reference electrode at different ages on the samples. The cylindrical specimens used to test half-cell potential and corrosion intensity in this study had a height of 200 mm and a diameter of 60 mm.

In this research, the corrosion intensity test was performed on the samples made for the half-cell test (cylindrical samples 200 × 60 mm) using a potentiostat device according to the ASTM G102 standard.

To increase the accuracy and reduce inadvertent laboratory error, the average results of three tests in each experiment were recorded as the final result.

3 Results and Discussion

3.1 Fresh Concrete Tests and Special Weight

According to the slump test results presented in Table 4, the inclusion of silica fume in fresh concrete leads to a reduction in flow and workability, and this influence is further amplified by the addition of zeolite alongside silica fume. The diminished workability observed in concrete with supplementary cementitious materials (SCMs) can be attributed to their high specific surface area within the internal structure. Additionally, a decrease in a slump was observed as the ratio of water to cementitious material decreased. To compensate for the decrease in workability and achieve the desired slump, an additional superplasticizer was added. In the case of self-compacting concrete, the workability is typically lower compared to ordinary concrete, especially when SCMs are employed and the ratio of water to cementitious material is reduced. Consequently, higher consumption of superplasticizers is necessary. It was found that the maximum slump values for both regular and self-compacting concrete were obtained when the water-to-cement ratio was set at 0.5.

Table 4 Fresh and hardened concrete tests
Full size table

Also, samples with a ratio of 0.4 water to cementitious materials used the most superplasticizer. These samples contained silica fume and zeolite. In comparison to the lowest superplasticizer usage, which corresponds to sample C0.5 with 0.2% cementitious materials by weight, the SSZ0.4 and CSZ0.4 samples required 89% and 84% more superplasticizer, respectively. Studies [41, 42] have also reported a reduction in slump and workability when zeolite is utilized in fresh concrete.

The T50 test measures concrete viscosity. The results of the slump flow tests on self-compacting concrete indicate that the samples containing silica fume and zeolite with water-to-cementitious material ratios of 0.4 and 0.5 exhibit the highest values. As shown in Table 4, achieving the target slump in samples containing both zeolite and silica fume requires a higher amount of superplasticizer compared to other mixtures. Consequently, the viscosity of these samples is higher, resulting in a more significant T50 value and a smaller slump flow diameter. These findings hold for both regular and self-compacting concrete and align with the results of previous research [43, 44].

In terms of density, an increase in the ratio of water to cementitious material leads to a decrease in density. This trend is also observed in concrete containing silica fume and zeolite SCMs due to their lower specific gravity compared to cement. On the other hand, self-compacting concrete, which incorporates limestone powder with a higher specific gravity than aggregates, exhibits a higher density compared to ordinary concrete due to its greater compressibility. Similar findings have been reported in other studies [35].

Yield stress and plastic viscosity are crucial indicators of the rheological properties of self-compacting concrete, which affect its mechanical properties and durability. The experimental results in Fig. 1 indicate that increasing the water-to-cementitious materials ratio from 0.4 to 0.5 reduces the yield stress. The addition of silica fume and zeolite to the concrete mix also increases the yield stress, which is attributed to the finer particle size of SCMs compared to cement. The percentage of superplasticizers used effectively determines the yield stress. Our work aimed to minimize the use of superplasticizers while achieving the desired slump and mitigating the negative effects of excessive usage.

Fig. 1
figure 1

Yield stress

Full size image

In addition, plastic viscosity tests (Fig. 2) showed a decrease in the amount of SCMs in the mixture with their addition, especially when silica fume and zeolite were combined. Increasing the ratio of the water to cementitious material leads to a decrease in plastic viscosity. These findings align with the report [40].

Fig. 2
figure 2

Viscosity plastic

Full size image

3.2 Volumetric Absorption of Water

Water absorption is a test used to assess the permeability of concrete, and the corresponding results are presented in Fig. 3. Generally, self-compacting concrete exhibits lower water absorption compared to ordinary concrete samples due to its dense microstructure. This indicates that self-compacting concrete possesses a lower density and fewer large cavities than ordinary concrete. Among the samples, the lowest water absorption is observed in the SSZ0.4 sample, while the highest is recorded in the C0.5 sample. The results demonstrate that reducing the water-to-cement ratio leads to a decrease in water absorption, particularly evident in self-compacting concrete.

Fig. 3
figure 3

Water absorption

Full size image

The inclusion of silica fume as a supplementary cementitious material (SCM) in the SSF0.4 sample results in a 20% reduction in water absorption compared to the CSF0.4 sample of ordinary concrete. Similarly, in the SSF0.5 sample compared to the CSF0.5 sample, a significant decrease of 38% in water absorption is observed. The combined use of two SCMs, zeolite and silica fume, further improves the reduction in water absorption. The SSZ0.4 and SSZ0.5 samples exhibit a decrease in water absorption of 25% and 27%, respectively, compared to the corresponding samples of CSZ0.4 and CSZ0.5 ordinary concrete. This improvement can be attributed to the fine structure of SCMs, which act as fillers for voids between cement and aggregates, resulting in a larger volume of C–S–H gel through interaction with calcium hydroxide (CH). Consequently, water absorption and porosity are reduced [45]. The volumetric water absorption test confirms the superior quality of the self-compacting concrete samples. Similar findings have been reported in previous research [9].

3.3 Total Porosity

The results of the total porosity test are shown in Fig. 4. The primary reason for using supplementary cementitious materials (SCMs) is to create a mixture with a homogeneous microstructure. Furthermore, reducing the ratio of water to cementitious materials effectively decreases the total porosity. In the case of self-compacting concrete (SCC) samples, the total porosity is consistently lower than that of the corresponding ordinary concrete samples across all mixture ratios. This improvement can be attributed to the incorporation of stone powder and finer aggregate in this particular type of concrete. The obtained results indicate that, at a water-to-cementitious materials ratio of 0.4, the total porosity of S, SSF, and SSZ samples is, respectively, 60%, 63%, and 73% lower than that of C, CSF, and CSZ samples. When the water-to-cementitious materials ratio is 0.5, the improvement values for self-compacting concrete compared to ordinary concrete range between 56 and 64%. These findings align with the results of the aforementioned research [45].

Fig. 4
figure 4

Total porosity

Full size image

3.4 Compressive Strength

The compressive strength test results for both self-compacting concrete and ordinary concrete samples are illustrated in Fig. 5. Previous research [46] has demonstrated that reducing the water-to-cement ratio and incorporating supplementary cementitious materials (SCMs) enhances the quality of concrete and increases its compressive strength. Silica fume, for instance, reacts with hydrated calcium hydroxide, limiting the pore size of cement particles and reducing cracking. By utilizing SCMs and their filler effect, the strength of the boundary layer is augmented while significantly reducing porosity. Notably, the SSZ0.4 sample exhibited the highest resistance with a strength of 68 MPa, whereas the lowest resistance was observed in the C0.5 sample, reaching only 37 MPa. A clear comparison between ordinary and self-compacting concrete samples reveals that self-compacting concrete exhibits superior strength compared to similar ordinary concrete samples. The ability of SCC concrete to flow effortlessly and resist segregation fills the entire concrete formwork without requiring vibration. This characteristic, combined with the compactness and uniformity of self-compacting concrete, significantly contributes to its enhanced compressive strength. In line with research findings [18], self-compacting concrete consistently exhibits higher compressive strength compared to ordinary concrete. The improvement in compressive strength for S, SSF, and SSZ samples, compared to C, CSF, and CSZ samples, at a water-to-cement ratio of 0.4, is 8%, 10%, and 7%, respectively. Similarly, at a water-to-cement ratio of 0.5, the improvement percentages are 15%, 18%, and 8%, respectively. Thus, based on the results of this test, it can be concluded that self-compacting samples outperform ordinary concrete samples.

Fig. 5
figure 5

Compressive strength

Full size image

3.5 Electrical Resistivity

The electrical resistivity of concrete serves as a valuable parameter for assessing its resistance to ions that affect its microstructure. A comparison between the S0.4 and C0.4 samples revealed a 10% improvement in electrical resistance for the former, while the S0.5 sample exhibited a 15% improvement compared to the C0.5 sample. Research [14] supports the notion that self-compacting concrete outperforms ordinary concrete with its dense and homogeneous microstructure. Incorporating silica fume further enhances the electrical resistance of self-compacting concrete samples in the water-to-cementitious materials ratios of 0.4 and 0.5, resulting in improvements of 11% and 18%, respectively. Including supplementary cementitious materials (SCMs) amplifies the degree of enhancement in electrical resistance. Alkaline ion concentrations in concrete represent the primary source of ion transfer. By incorporating SCMs, the content of sodium and potassium, which contribute to high conductivity, is reduced in the pore solution, thereby lowering electrical resistance [47, 48]. SSZ0.4 demonstrated the highest electrical resistance among the samples at 189 Ω.m [43]. Additionally, the study indicates that reducing the water-to-cementitious materials ratio increases electrical resistance. Electrical resistance levels are categorized into five ranges, as suggested by [49], ranging from negligible to high. Except for the C0.5 sample, most of the samples in this research exhibited moderate levels of electrical resistance, as depicted in Fig. 6. Overall, self-compacting concrete exhibits superior electrical resistance compared to regular concrete. Please refer to Fig. 6 for the results of the electrical resistance test.

Fig. 6
figure 6

Electrical resistivity

Full size image

3.6 Electrical Conductivity

The electrical conductivity test of concrete is a crucial assessment that measures the volumetric electrical conductivity of a saturated concrete sample, providing insights into its resistance to chloride ion penetration. Figure 7 illustrates the electrical conductivity values of ordinary and self-compacting concrete samples. The results demonstrate that an increase in the ratio of the water to cementitious material leads to higher electrical conductivity, while the use of supplementary cementitious materials (SCMs) reduces it. Notably, the self-compacting concrete samples exhibit lower electrical conductivity than ordinary concrete. In the case of self-compacting concrete, the S0.4, SSF0.4, and SSZ0.4 samples exhibit reduced electrical conductivity by 30%, 58%, and 35%, respectively, compared to their corresponding ordinary concrete samples.

Fig. 7
figure 7

Electrical conductivity

Full size image

Similarly, the improvement values for the S0.5, SSF0.5, and SSZ0.5 samples amount to 48%, 43%, and 39%, respectively. Incorporating SCMs in ordinary and self-compacting concrete samples effectively reduces conductivity, a finding also supported by Research [50]. For instance, the decrease in electrical conductivity observed in the SSF0.4 sample is one-third compared to the S0.4 sample and 1.1 times in the CSF0.4 sample compared to the C0.4 sample. In the water-to-cementitious materials ratio of 0.5, these values amount to 1.5 and 1.4 times, respectively. Moreover, when combining SCMs such as silica fume and zeolite with self-compacting and ordinary concrete, a significant improvement of approximately two times is achieved compared to the reference sample for each ratio. The assessment of water content has been performed for cementitious materials as well.

3.7 Rapid Chloride Permeability Test (RCPT)

The RCPT test is widely utilized for assessing the permeability of concrete. By reducing the ratio of the water–cementitious material and incorporating supplementary cementitious materials (SCMs), notably when zeolite and silica fume are combined, the RCPT value of concrete is effectively reduced. Using SCMs in concrete serves two purposes: filling the empty spaces between cement paste particles and facilitating the pozzolanic reaction, forming C–S–H. These physical and chemical functions contribute to a reduction in permeability and chloride release [51]. A comparison between ordinary concrete and self-compacting concrete samples reveals that the latter demonstrates lower RCPT values. This can be attributed to self-compacting concrete’s homogeneous mixing and cohesion properties [52]. Specifically, the reduction in RCPT values for the S0.4 and S0.5 samples amounts to 39% and 34%, respectively, compared to the C0.4 and C0.5 samples. The addition of silica fume results in a significant improvement of 54% and 60% in the SSF0.4 and SSF0.5 samples, respectively, compared to the corresponding control samples of ordinary concrete. Notably, the combination of silica fume and zeolite samples, leveraging the synergistic effect of SCMs, yields remarkable RCPT reductions of 65% and 60% in the SSZ0.4 and SSZ0.5 samples, respectively, compared to their ordinary concrete counterparts. The results of the RCPT test are illustrated in Fig. 8. According to the ASTM C1202 standard, only the C0.5 sample falls within the high range of the chart. Most self-compacting concrete specimens exhibit very low RCPT values, indicating their excellent resistance to chloride penetration. This classification further confirms the superior performance of self-compacting samples compared to ordinary concrete, which aligns with the findings of a previous report [53].

Fig. 8
figure 8

RCPT

Full size image

3.8 Rapid Chloride Migration Test (RCMT)

Figure 9 displays the findings of the chloride ion migration coefficient for the concrete samples. The results indicate that increasing the water-to-cementitious materials ratio enhances the samples’ RCMT (Resistance to Chloride Ion Migration), while substituting cement with SCMs increases the resistance of concrete to chloride ion transit. A similar trend is observed in self-compacting concrete, albeit with lower RCMT than ordinary concrete. The sample from SSZ0.4 exhibits the lowest chloride migration coefficient, while sample C0.5 shows the highest.

Fig. 9
figure 9

RCMT

Full size image

By reducing the water-to-cementitious materials ratio from 0.5 to 0.4 in samples without SCMs, the chloride migration coefficient decreases by approximately 65%. In samples containing silica fume, this reduction is 1.4 times, and in samples containing a combination of silica fume and zeolite, it reaches 2.3 times. In self-compacting concrete, these reductions amount to 90%, 22%, and 1.25 for S0.4, SSF0.4, and SSZ0.4, respectively. Compared to ordinary concrete, a 49% reduction in chloride migration coefficient is observed in self-compacting concrete at a water-to-cementitious materials ratio of 0.4. This reduction increases to 64% in samples containing silica fume, and in samples with a combination of silica fume and zeolite, it reaches 1.65 times compared to ordinary concrete samples. At a water-to-cementitious materials ratio 0.5, these reductions are calculated as 71%, 2.2 times, and 2.86 times, respectively.

What draws more attention to these results is the significant effect of using SCMs in reducing the chloride ion migration coefficient in different types of concrete. Specifically, in ordinary concrete, the migration coefficient is reduced by 2 times at a water-to-cementitious materials ratio of 0.4, and in self-compacting concrete, this reduction reaches 2.6 times. At a water-to-cementitious materials ratio of 0.5, these values increase to 1.5 and 3.6 times, respectively. The reduction is even more substantial when employing a combination of silica fume and zeolite. In ordinary concrete, it measures 5.5 times at a water-to-cementitious materials ratio of 0.4; in self-compacting concrete, it reaches 7.83 times lower. The reduction of the chloride migration coefficient at a water-to-cementitious materials ratio of 0.5 is 2.3 times for ordinary concrete and 6.5 times for self-compacting concrete.

According to the classification provided in [54], the resistance of concrete to chloride penetration is divided into four categories based on the chloride ion migration test conducted at 28 days of age. In this classification, an RCMT value [in terms of (m2/s × 10–12)] below 2 falls into the very good range, between 2 and 8 is categorized as good, between 8 and 16 is considered acceptable, and above 16 is classified as unacceptable in terms of resistance to chloride penetration. Applying this classification, sample C0.5 is the only one in the unacceptable range, while samples CSZ0.4, SSF0.4, SSZ0.4, and SSF0.5 fall within the very good range. Samples CSF0.4, CSF0.5, CSZ0.5, S0.4, and SSF0.5 are in the good range, and samples C0.4 and S0.5 are categorized as acceptable.

3.9 Apparent Chloride Diffusion Coefficient

Chloride diffusion in concrete is controlled through diffusion tests. Consistent with the excellent performance observed in other tests conducted in this study, self-compacting samples also exhibited better conditions in this test. The results of this experiment are depicted in Fig. 10. Including SCMs reduced the diffusion coefficient in all samples due to their filling properties, pore reduction, and ion transfer capabilities. Decreasing the ratio of the water to cementitious material reduced the diffusion coefficient through a denser microstructure and relative porosity reduction. However, the improvements from decreasing the ratio of the water to cementitious material were less significant than the changes induced by adding SCMs. The sample with the lowest diffusion coefficient was SSZ0.4, with a value of 1.1 (m2/s × 10–12), while the highest emission coefficient was observed in sample C0.5, with a value of 12.1 (m2/s × 10–12). Similar findings were reported in the study [55]. The reduction coefficient of the S0.4 sample compared to the C0.4 sample was 14%, and for the S0.5 sample compared to the C0.5 sample, it was 22%. Moreover, samples incorporating silica fume in self-compacting concrete exhibited diffusion coefficients of 24% and 13% lower than those of ordinary concrete at water-to-cementitious materials ratios of 0.4 and 0.5, respectively, while in samples containing silica fume and zeolite, the chloride diffusion coefficient for SSZ0.4 and SSZ0.5 self-compacting samples improved by 18% and 19%, respectively, compared to ordinary concrete samples CSZ0.4 and CSZ0.5.

Fig. 10
figure 10

Chloride ion diffusion

Full size image

According to the classification proposed by NT BUILD 492, chloride diffusion coefficient values are categorized into five parts: less than 2, between 2 and 5, between 5 and 10, between 10 and 15, and more than 15, corresponding to the negligible to high range. Based on this ranking, only sample C0.5 falls into the high range, while samples CFZ0.4, SSF0.4, and CSZ0.4 fall into the negligible range, exhibiting the lowest chloride emissions.

3.10 Electric Potential

Figure 11 displays the electrical potential difference between self-compacting and ordinary concrete samples aged between 7 and 91 days for samples S1, S4, and S6. Due to the similarity and proximity of these samples and to avoid repetition, the findings of other samples are not presented. By comparing the corrosion results of the rusted rebar samples with the normal rebar obtained from the factory, it was observed that an increase in the rust condition of the pre-rusted rebar surface led to an increase in corrosion potential. This finding indicates the influence of pre-rusting on steel corrosion when used in concrete, as also mentioned in the research by [28].

Fig. 11
figure 11

The electrical potential of rebars in concrete samples. a Rebar S1, b rebar S4, and c rebar S6

Full size image

When using S1 as reinforcement in concrete, the corrosion rate of the steel is low. Moreover, corrosion is further reduced in self-compacting concrete compared to ordinary concrete, consistent with the research findings [13]. The corrosion reduction in S0.4 and S0.5 samples compared to C0.4 and C0.5 samples at 91 days is 12% and 15%, respectively. An important observation in this graph is the use of SCMs in concrete. When SCMs are incorporated, the potential for corrosion is significantly decreased, and the potential half-cell trend in samples with SCMs differs significantly from those without SCMs. Compared to ordinary concrete, including SCMs in self-compacting concrete improved by 31% and 33% in samples with a water-to-cementitious materials ratio of 0.4 and 0.5, respectively. The findings in [46] support these results. Additionally, the results indicate that the age of corrosion initiation for S1 rebar, when utilized in concrete sample C0.5 (reaching the potential difference value of −270 mV), is 72 days.

When rebars S2 and S3 are used as reinforcement in concrete, the corrosion potential trend is similar to S1. However, the magnitude of corrosion potential in these samples is higher in the S1 sample, and the age of corrosion initiation for the S2 sample in C0.5 concrete is reduced to 66 days, while for the S3 sample in the C0.5 concrete sample, it is lowered to 56 days. Self-compacting concrete samples reduce the amount of corrosion compared to ordinary concrete samples. The lowest corrosion value is observed in the SSZ0.4 sample. Using SCMs in self-compacting concrete improves its performance and reduces the ratio of the water to cementitious material to mitigate corrosion of pre-rusted steel. When using S4 and S5 rebars, the potential corrosion in all concrete specimens increases. As the corrosion of the pre-rusted rebar intensifies, steel corrosion in reinforced concrete also increases. The age of corrosion initiation is lower in these samples, with the quickest corrosion initiation occurring in concrete sample C0.5. The initiation time is 49 days for the S4 sample and 35 days for the S5 sample. Self-compacting concrete and SCMs reduce the corrosion potential of the rebar in these samples.

Furthermore, according to [31], increasing the distance from the sea and storing rebar with plastic covering reduce surface rust on the rebar and, consequently, steel corrosion in reinforced concrete. The most significant change in corrosion potential was observed in the samples containing rebar with artificial rust S6 (Fig. 7c). The age of corrosion initiation in this sample is reduced to 28 days. Due to this rebar’s high surface rust level, steel corrosion in reinforced concrete is more pronounced than in other samples. The reduction in corrosion potential is more substantial in samples with SCMs, and the ratio of the water to cementitious material is lower.

When comparing rebar samples embedded in self-compacting concrete to those in ordinary concrete, it is evident that they exhibit reduced corrosion potential regardless of the surface condition. However, it should be emphasized that the impact of self-compacting concrete quality, with the addition of SCMs and a lower water-to-cementitious materials (W/C) ratio, on steel corrosion in reinforced concrete diminishes as the pre-rusting of the rebar surface increases.

3.11 Intensity of Corrosion

Similar results were obtained in the corrosion intensity test following the potential half-cell test. Figure 12 shows the corrosion intensity of different rebars in ordinary and self-compacting concrete samples at 91 days. The corrosion current intensity in sample C0.5, when utilizing rebar S1, falls within the medium range, while sample S0.5 falls within the low corrosion intensity range. Apart from these two concrete samples, the corrosion intensity in other concrete samples is considered negligible based on the classification by [56]. Nonetheless, in self-compacting samples, the extent of steel corrosion in concrete is lower than that in ordinary concrete samples. By comparing the results of different rebars, it is evident that increased surface rust on the pre-rusted rebar also heightens the intensity of steel corrosion in concrete.

Fig. 12
figure 12

Corrosion intensity, a ordinary concrete samples, b SCC samples

Full size image

Furthermore, when comparing the influence of concrete quality on corrosion, it is clear that employing higher-quality concrete (self-compacting, low W/C ratio, and SCMs) minimizes corrosion. The behavior of rebars S2 and S3 is nearly identical to that of rebar S1. However, due to the greater amount of rust on the surfaces of these rebars compared to the ordinary rebars supplied by the factory, a higher degree of steel corrosion is observed in the superior concrete. When these rebars are used in self-compacting concrete, the corrosion intensity is lower in ordinary concrete. Among these samples, the C0.5 concrete sample exhibits the highest corrosion intensity. In self-compacting concrete with water-to-cement ratios of 0.5 and 0.4, respectively, a 21% and 36% improvement in corrosion resistance is observed compared to the corresponding concrete samples when utilizing S2 rebar, and a 34% and 12% improvement is observed when using S3 rebar. The SSZ0.4 sample demonstrates the best corrosion resistance when employing these rebars, with corrosion intensities of 0.046 (A/cm2) in S2 and 0.057 (A/cm2) in S3. Samples incorporating silica fume SCMs exhibit lower corrosion levels than samples without silica fume at water-to-cementitious materials ratios of 0.4 and 0.5. The integration of SCMs further enhances corrosion resistance.

In the S4 and S5 samples, there is a significant change in corrosion intensity. Consequently, the corrosion intensity of these samples in concrete sample C0.5 increases by 21% and 37%, respectively, compared to rebar S1. Among these rebars, SSZ0.4 exhibits the best performance when used in concrete. When S4 is embedded in concrete, it demonstrates lower corrosion than S5 due to its better surface rust condition. Using the S5 rebar, the maximum and minimum corrosion intensities are 1.21 (µA/cm2) and 0.54 (µA/cm2), respectively, whereas, with the S4 rebar, the maximum and minimum corrosion current intensities are 0.96 (µA/cm2) and 0.028 (µA/cm2). In these samples, self-compacting concrete outperforms ordinary concrete. Compared to ordinary concrete, the corrosion intensity value in self-compacting concrete samples with water-to-cementitious materials ratios of 0.4 and 0.5 is reduced by 15% to 23% when utilizing the S4 rebar and 10% to 18% when utilizing the S5 rebar, respectively.

The rebar sample S6 exhibits the highest intensity of corrosion. When used in C0.5 concrete, the corrosion current intensity of this sample reaches 1.28 (µA/cm2) at 91 days, which is the upper limit of the corrosion intensity diagram. In the best-case scenario, when this sample is used in SSZ0.4 concrete, the corrosion intensity is 0.58 (µA/cm2), falling within the moderate range. In all ordinary concrete specimens except CSZ0.4, the corrosion intensity of this rebar falls within the high range. However, the situation improves in self-compacting concrete, and the corrosion intensity decreases. Based on the results, the influence of self-compacting concrete performance in mitigating steel corrosion in reinforced concrete is evident in all rebar samples.

3.12 Relation of Different Parameters of Concrete Quality With the Intensity of Corrosion

The relationship between different concrete performance tests and the corrosion intensity of normal rebar received from the factory was investigated. Since factors other than concrete quality, such as the condition of the rebar surface, can also influence the corrosion intensity in other rebars, the results of ordinary rebar S1 were used to minimize side effects and solely focus on comparing the effect of concrete type on the intensity of steel corrosion. The evaluation indicates that the results of electrical resistance, electrical conductivity, RCPT, RCMT, and diffusion tests are closely related to the corrosion current intensity. These tests are associated with the penetration and diffusion properties of chloride ions in concrete. Since corrosion in the Persian Gulf region is mainly chloride induced, it is predictable that there would be a relationship between the results of these tests and the corrosion intensity rate. Figure 13 shows the relationship between electrical resistance tests, RCPT, and diffusion with the rate of corrosion intensity of steel in reinforced concrete when using S1 rebar, measured based on the type of self-compacting concrete. Table 5 presents the data from correlating other tests with the current intensity of corrosion. The lack of a significant correlation between mechanical parameters (compressive strength, water absorption volume, and total porosity) and corrosion rate may suggest that the free chloride required to initiate corrosion is supplied from within the structure (pre-rusted rebar). Therefore, steel corrosion in reinforced concrete is primarily influenced by the electrochemical properties of concrete.

Fig. 13
figure 13

Relationship between corrosion intensity and a electrical resistivity, b RCPT, c diffusion

Full size image
Table 5 Relationship between concrete quality tests and corrosion intensity in OC and SCC samples
Full size table

The relationship between the electrical resistance test and corrosion intensity (Fig. 13a) in self-compacting and ordinary concrete samples reveals that the correlation between the electrical resistance test and corrosion current intensity is 90% for self-compacting concrete samples. When ordinary concrete is used, this correlation decreases to 82%. In Fig. 13b, which illustrates the correlation between RCPT test results and the rate of corrosion intensity, self-compacting concrete specimens exhibit a 96% correlation, while ordinary concrete specimens show an 86% correlation. The correlation between the diffusion test in self-compacting concrete and the rate of corrosion intensity (Fig. 13c) is 87%, higher than the correlation results observed in ordinary concrete. The relationship between other tests and the rate of corrosion intensity in Table 5 confirms the stronger association between the results of self-compacting concrete and the rate of corrosion intensity. Based on the evaluation results, it is evident that self-compacting concrete has a more significant relationship in determining the intensity of corrosion in almost all tests, with higher correlation values compared to ordinary concrete samples. Consequently, employing self-compacting concrete can better control the extent of steel corrosion in reinforced concrete.

3.13 Comparison of the Effect of Self-Compacting Concrete Performance on Corrosion of Ordinary and Pre-Rusted Rebar

Table 6 summarizes the performance of self-compacting and ordinary concrete on the corrosion intensity of different rebars in reinforced concrete at 91 days. According to the results of concrete quality tests, the SSZ0.4 sample outperformed all other samples, while sample C0.5 had the lowest rating. Consequently, these two samples were selected as representing the best and worst concrete quality, respectively, to assess the impact of concrete quality on the corrosion of various rebars. The findings in the table indicate that when rebar S1 is used to reinforce concrete, corrosion is reduced by 97% in SSZ0.4 (self-compacting concrete) compared to C0.5 (ordinary concrete). This reduction ranges from 93 to 55% in samples S2–S6. When different rebars are employed, the influence of concrete quality on steel corrosion reveals that as the amount of rust on the rebar surface increases, the effect of concrete quality on corrosion intensity diminishes. However, concrete quality still affects the severity of corrosion. This finding emphasizes that, in addition to concrete quality, the condition of rebar corrosion in reinforced concrete plays a significant role. Therefore, employing high-quality self-compacting concrete can significantly reduce steel corrosion in reinforced concrete. However, it is crucial to closely monitor and examine the condition of the rebar surface before manufacturing reinforced concrete samples.

Table 6 The effect of SCC quality on corrosion of different rebars in concrete
Full size table

4 Conclusions

This study aimed to investigate the impact of self-compacting concrete quality on corrosion reduction in reinforced concrete when pre-rusted rebar is used. The key findings of this investigation are summarized below:

  1. 1.

    When pre-rusted rebar is employed in reinforced concrete, the intensity of steel corrosion is closely related to tests measuring the chloride diffusion coefficient, rapid chloride permeability, and rapid chloride migration. This relationship is 10–15% stronger when self-compacting concrete is utilized than regular concrete.

  2. 2.

    Incorporating supplementary cement materials and reducing the ratio of the water to cementitious material in self-compacting concrete resulted in a 13–48% greater reduction in corrosion risk compared to similar samples in ordinary concrete.

  3. 3.

    Properties associated with chloride diffusion in concrete, such as the chloride ion diffusion coefficient, chloride ion accelerated penetration, and chloride ion migration coefficient, strongly influenced the corrosion of pre-rusted steel in reinforced concrete. In these aspects, self-compacting concrete outperformed ordinary concrete, leading to lower corrosion levels in rebars with different degrees of pre-rust.

  4. 4.

    Self-compacting concrete exhibited superior mechanical properties and durability parameters compared to ordinary concrete.

  5. 5.

    Apart from concrete quality, the condition of the rebar surface in terms of rust also impacts the corrosion of pre-rusted rebar in reinforced concrete. Factors such as proximity to the sea and proper storage methods for rebar significantly influence the corrosion of the rebar surface and, consequently, steel corrosion in reinforced concrete.