Experimental Study on the Effect of Corrosion-inhibiting Admixtures on Chloride Corrosion Resistance of Concrete

Compared to the different types of rust inhibitors, The effects of the internal and external coating corrosion inhibitors on the corrosion resistance of concrete were studied. The impact of the mixed rust inhibitor on the working performance, compressive strength and chloride ion permeability coefficient of concrete was investigated. The results show that the working performance, late mechanical properties, and resistance to chlorine salt erosion of concrete are better than those of reference concrete after adding the anti-rust agent. Comparing the effects of 2% and 4% internal rust inhibitors on the corrosion resistance of chloride ions, based on the control group, the chloride ion diffusion coefficient of concrete with 2% and 4% rust inhibitors decreases to the original 15.1% and 37.0%, respectively. Concrete’s chloride ion diffusion coefficient with external rust inhibitor decreases to 62.5%. In addition, the internal corrosion inhibitor has a specific water-reducing component, which reduces the water consumption of concrete and improves the compactness of concrete itself, thus improving the corrosion resistance of concrete.


Introduction
Organic steel bar rust inhibitors can use the porous structure of concrete through the concrete pores, with gas-liquid dual-phase diffusion to reach the surface of the steel bar, forming a compelling protective film, so the organic steel bar rust inhibitor can not only be mixed into the raw material of concrete for use but also can be directly coated on the concrete surface, through the spontaneous penetration process to reach the surface of the steel bar.Finally, the surface of the steel bar is formed into a film to realize the protection of the steel bar, which is the penetration (migration) type rust inhibitor [1][2][3].Cortec is the first company in the United States to combine gas phase corrosion inhibitors with other organic rust inhibitors to protect reinforced concrete, regarded as the most promising technology in concrete structure repair [4][5][6][7][8].
Liu Xixu et [9] al. developed a MA anticorrosive and rust inhibitor, which can significantly improve the corrosion resistance of reinforced concrete, promote the development of strength, and have a good compensation shrinkage effect.Chen Bei et [10] al studied the effect of corrosion inhibitor on the compressive strength, sulfate corrosion resistance, chlorine corrosion resistance and other properties of concrete, as well as cement hydration products.The test results show that the corrosion inhibitor not only contributes to its mechanical properties, but also participates in the hydration reaction, making the product structure more compact and improve durability.Xu Junwei [11] studied and analyzed the effects of different amounts of alcoholamine rust inhibitors and calcium nitrite on the potential change law of steel bars, charge transfer resistance, porosity and the types of hydration products by using the rebar electrode potential method, electrochemical AC impedance spectroscopy, dry-water method, SEM, XRD and other test methods.Ma Shihao [12] analyzed the corrosion mechanism of chlorine salts on reinforced concrete structures in a Marine environment and discussed the critical role of composite rust inhibitors in improving the durability of reinforced concrete structures.Guo Qun [13] studied anodic rust inhibitors Na2CrO4 and Na2MoO4, cathodic rust inhibitors benzotriazole (BTA) and N, n-dimethylethanolamine (DMEA), and composite rust inhibitors, Etc.The corrosion degree and corrosion rate of steel bars in carbonized concrete were studied using natural potential, corrosion area rate, weight loss rate and electrochemical method [14].The results show that a composite rust inhibitor's effect on steel bars' corrosion rate was better than that of a single rust inhibitor.
According to the previous research results [15][16][17], two kinds of organic and inorganic rust inhibitors were used in the test.The effect between different types of rust inhibitors and different amounts of rust inhibitors on the working properties, mechanical properties, and resistance to chloride salt corrosion of concrete were studied.

Raw materials
The raw materials for the preparation of concrete, such as cement, sand and stone, are in line with the "Pebble and crushed stone for construction" (GB/T14685) and "sand for Construction" (GB/T14684).The stone material is limestone.The particle size is 5-25mm.The cement label is P Ⅱ 42.5, the water-reducing agent is 3301C-HM03, the grade I fly ash, and the slag powder is S95.Rust inhibitor is provided by Beijing Mengtai Building Materials outlet store, including liquid rebar embroidery agent (admixture type) and liquid rebar embroidery agent (migration type) two kinds, admixture type embroidery agent added to the concrete, the amount of cement 2~4%.Liquid rebar embroidery inhibitor (migration type) spray on the outer surface of concrete, a kilogram of spray twice can be constructed 2.5~3 square meters, are constructed following the instructions.

Mix proportion ratio
The benchmark concrete mix proportion ratio is DZ40, and the internal mixed rust inhibitor mix ratio is Table 1.DZ40N02 is the number of concrete specimens mixed with 2% rust inhibitor.DZ40N04 is the number of concrete specimens mixed with 4% rust inhibitor; DZ40WC is the number of concrete specimens coated with rust inhibitor.

Test Methods
With the same mix proportion ratio of concrete, the effects of different types of rust inhibitors and different content of rust inhibitors on chloride ion corrosion resistance were studied.The differences in chloride ion transport performance and mechanical properties of concrete may be determined, and the suitable internal rust inhibitor for Huangmaohai bridge concrete was selected.By simulating the actual service environment of Huangmaohai traffic engineering and combining with the actual service performance indicators, an indoor accelerated test was carried out to compare, test and analyze the influence of each promotion technology on the durability behavior of concrete and a material durability promotion scheme suitable for different parts of concrete was proposed.The amount of hydrophobic compound is 30 kg per cubic meter, which is added in place of the same water quality in the concrete mixing process.
The inner reinforcement rust inhibitor content in the concrete mixing process is 0, 2%, and 4%, respectively, as shown in Figure .1.The outer rust inhibitor is cured for seven days, and the pouring surface of the concrete specimen is polished with fine sandpaper, the surface is painted, and the surface is semi-dry before the second brushing.The penetrant crystalline material is also cured for seven days, and the pouring surface of the concrete specimen is treated with fine sandpaper, and then the surface is painted.External silane (GW) is applied by continuous spraying technology to achieve saturated impregnation, and the treated area should have a "smooth" effect of at least 5 seconds.
The test mould is  100mm×50mm.The maximum particle size of aggregate is not greater than 25mm.The specimen should be covered with plastic film and moved to the standard curing room immediately after moulding.The specimens should be removed within 24h±2h and then immersed in the standard curing room.After 28 days of curing, the chloride ion penetration resistance test (RCM method) was carried out according to GB-T50082-2009, " Standard for test methods of long-term performance and durability of ordinary concrete ".

Effect of rust inhibitor on the working performance of concrete
Concrete was prepared according to the mix ratio in Table 1, the concrete slump was measured, and the compressive strength value of standard curing to 3d, 7 d and 28 d was measured.The test results are shown in Table 2. To test the effect of rust inhibitor on the working performance of concrete, the amount of water-reducing agent is the same, and the slump of concrete becomes more significant with the increase of the amount of rust inhibitor, indicating that rust inhibitor has a specific increase in fluidity as a liquid.The test selected rust inhibitor, the antiseptic component, has a specific water-reducing component, so the concrete with the water-reducing agent content is low can ensure that the benchmark concrete has the same initial slump.Hence, the water-reducing agent content is lower than the benchmark concrete.

Effect of rust inhibitor on mechanical properties of concrete
Table 2, Figures 2 and 3 show that concrete's working and mechanical properties have been improved after adding anti-corrosion and rust inhibitors.The 3d and 7d compressive strength values of concrete doped with rust inhibitor are lower than the benchmark compressive strength values, but with the extension of curing age, the strength of concrete doped with rust inhibitor at 28 d age is higher than the benchmark compressive strength of concrete without rust inhibitor.Because the filler of rust inhibitor is slag powder and fly ash, the activity index is lower than that of cement, so the early strength of concrete doped with rust inhibitor is low.With the extension of curing time, the activity of slag powder and fly ash was gradually released, and the dense component made the concrete structure more compact so that the later strength of the concrete gradually increased.At 28 days, the compressive strength of concrete with rust inhibitor exceeded that of the benchmark concrete.

Effect of rust inhibitor on chloride ion penetration resistance of concrete
The test results are shown in Table 3, Figures 4, 5 and 6.When the same proportion of concrete specimens was used to test different additives on chloride ion erosion, it was found that the chloride ion diffusion coefficient of concrete specimens was 7.83×10 -12 m 2 /s without rust inhibitor.The influence of different contents of 2% and 4% of rust inhibitor on chloride ion corrosion resistance was compared.When a 2% inhibitor was used, the chloride ion diffusion coefficient decreased to 15.1% of the original.When a 2% rust inhibitor was used, the chloride ion diffusion coefficient decreased to 37.0%, indicating that the amount of rust inhibitor was not better and that 2% should be added.Comparing the influence of different types of rust inhibitors on the ability to resist chloride ion erosion, the chloride ion diffusion coefficient of the outer coating type rust inhibitor is 4.89×10 -12 m 2 /s, which is reduced to 62.5% of the original, and the effect is not good compared with the inner coating type rust inhibitor.

Conclusion
This paper studied the effects of the rust inhibitor on the working performance, compressive strength, and the chloride ion permeability coefficient of concrete.Compared with the effects of internal and external rust inhibitors on the corrosion resistance of concrete to chloride salt, details are as follows.
(1) The rust inhibitor has a particular water reduction, which can improve the working performance of concrete.The early age strength is small, and the strength increases later.
(2) The chloride ion diffusion coefficient of concrete mixed with 2% and 4% rust inhibitor decreases to 15.1% and 37.0%, respectively.The inner rust inhibitor improves the pore structure and compacting degree of concrete, and the chloride ion diffusion coefficient becomes smaller, which has good resistance to chloride salt erosion.
(3) Compared with the original concrete, the chloride ion diffusion coefficient with the outer coating rust inhibitor decreased to 62.5%, indicating that the outer coating rust inhibitor can also improve the resistance of concrete to chloride salt erosion.However, the effect is less than that of the inner mixed rust inhibitor.
(4) Compared with the internal and external rust inhibitor construction, the internal rust inhibitor construction is more superficial.It can be put in the concrete during the mixing process.The external rust inhibitor needs to be polished and brushed after the concrete hardens, which can improve the durability of the concrete structure in service.

Figure 2 .
Figure 2. Effect of Rust Inhibitor on Workability.Figure 3. Effect of Rust Inhibitor on Strength.

Figure 3 .
Figure 2. Effect of Rust Inhibitor on Workability.Figure 3. Effect of Rust Inhibitor on Strength.

Figure 4 .
Figure 4. Test process of chloride ion penetration depth.

Figure 5 .
Figure 5.The penetration depth of chloride ions.

Table 1 .
Concrete mix proportion ratio

Table 2 .
The working and mechanical properties of concrete.