Electrochemical chloride extraction on reinforced concrete contaminated external chloride: Efficiencies of intermittent applications and impacts on hydration products

Nguyen, Thi Hai Yen; Trần, Mẫn Văn; Pansuk, Withit; Cao, Nguyen Thi; Bui, Van Hong Linh

doi:10.1016/j.cemconcomp.2021.104076

Cited by 18 publications

(8 citation statements)

References 27 publications

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“…The TGA spectra that describes the influence of NH 4 HSO 4 and NaHSO 4 on the hydration products of the fly ash cement paste after 1 d and 28 d is shown in Figure 7 . The decomposition peak of ettringite and C-S-H gel was at 70–100 °C, while the decomposition peak of calcium hydroxide occurred between 420 and 475 °C [ 23 ]. The calcium hydroxide production in the cement paste samples that contained NH 4 HSO 4 and NaHSO 4 was observed to be lower than that in samples without sulfate after one day, which is consistent with the XRD test results, supporting the theory that NH 4 + and H + consume a portion of the available calcium hydroxide.…”

Section: Resultsmentioning

confidence: 99%

Performance of Cement Paste with Denitrified Fly Ash Containing NH4HSO4

Wang

Qin

et al. 2022

Materials

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The denitrification process was completed in coal-fired power plants, resulting in the fly ash containing NH4HSO4. When this kind of fly ash with ammonia was applied to cement and concrete, there could be phenomena such as a retarded setting time, decreased compressive strength, and volume expansion. This paper mainly investigated the influence of fly ash containing NH4HSO4 on the properties of fly ash cement paste, and pastes with NaHSO4 were set as the control samples. The research on Na+ in cement hydration was studied. The influence of NH4HSO4 content in fly ash on the properties of fly ash cement paste was also investigated. It was found that NH4+ could greatly affect the properties of fly ash cement paste, such as significantly reducing the fluidity, prolonging the setting time, decreasing the compressive strength, increasing the drying shrinkage, decreasing the total heat released during the hydration, and affecting the content of calcium hydroxide hydrate. Increasing the ammonia content of the denitrified fly ash would reduce fluidity, retard its setting time, increase the porosity of the cement stone, and increase the number of pores with large sizes in the fly ash cement paste. The increase of porosity and pores with large sizes in cement decreases the compressive strength and increases the drying shrinkage of the fly ash cement paste.

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Section: Resultsmentioning

confidence: 99%

Performance of Cement Paste with Denitrified Fly Ash Containing NH4HSO4

Wang

Qin

et al. 2022

Materials

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“…According to the above analysis, the electrochemical repair can effectively remove chloride ions in concrete. However, many studies show that ECR will not only eliminate harmful chloride ions, but also have adverse effects on reinforced concrete structure, such as reducing the bonding strength between reinforcing bar and concrete (Nguyen et al, 2021), making the reinforcing bar more fragile . Meanwhile, Na + and K + ions in the concrete solution will also aggregate near the reinforcing bar, causing concrete ASR harm.…”

Section: Effect Of Cathode Location On Ecrmentioning

confidence: 99%

A numerical study of chloride migration in concrete under electrochemical repair

Chen

Zhang

Ming³

et al. 2023

Proceedings of the Institution of Civil Engineers - Structures

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Electrochemical repair (ECR) is one of the most effective methods of removing chloride from offshore engineering structures to improve their durability. The diffusion of chloride and electrochemical migration are key stages in this process. In this work, a new numerical chloride migration–diffusion model was established using the Nernst–Planck equation. The distributions of free chloride ions in concrete in the stages of free chloride diffusion and ECR were simulated and the effects of the external potential and cathode position on ECR efficiency were analysed. The results showed that ECR can effectively remove chloride ions from concrete. After 12 weeks of ECR, the chloride removal efficiency was more than 66%. With an increase in the repair time, the ECR efficiency decreased gradually. In the initial stage of ECR, the chloride concentration on the rebar surface decreased rapidly. After 4 weeks of ECR, the chloride concentration tended to stabilise. The ECR efficiency also improved with an increase in external potential increases, with the chloride concentration on the reinforcing bar surface decreasing rapidly. When cathodes are set on both sides of the concrete, the ECR time should be extended and the external potential should be increased to achieve a better repair effect.

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“…Changes in the distribution of chloride ion concentration in concrete are used to evaluate the effectiveness of chloride extraction treatment [ 34 , 35 ]. Sensors placed inside concrete to measure its resistance or conductivity are also used.…”

Section: Introductionmentioning

confidence: 99%

Effect of Imperial Smelting Process Slag Addition in Self Compacting Concrete Concrete on the Efficiency of Electrochemical Chloride Extraction

et al. 2023

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This paper presents the analysis of how ISP slag addition affects the effectiveness of chloride extraction from self-compacting concrete. Corrosion processes were initiated by chloride ions added to concrete by the method accelerated with an electric field. Corrosion of reinforcement was monitored using the method of linear polarization resistance (LPR). Polarization measurements of steel reinforcement and chloride profiles were analysed to evaluate the effectiveness of electrochemical extraction. Microstructural analysis was conducted on a specimen of concrete after migration and extraction of chlorides. The presence of chloride ions and the application of an electric field during migration were tested with respect to the changed microstructure of concrete evaluated on the basis of image analysis using a scanning electron microscope (SEM). The research contributes to a better understanding of the corrosion processes caused by the presence of chloride ions in concretes in which ISP slag was used as a substitute for sand in various amounts. Thanks to the treatments of concrete with already corroding reinforcement bars, it can be concluded that the moderate replacement of sand with ISP slag limited to 25% allows for the effective inhibition of corrosion processes taking place in these concretes. However, it is not possible to completely withdraw already started corrosion processes in steel. The observations of the microstructure of concrete in which sand was completely replaced with ISP slag indicate that after prolonged use of the chloride extraction process, we can expect a change in the microstructure and the formation of ettringite, which may cause the concrete structure to burst. The obtained information will contribute to the development of modelling methods for chloride ion extraction from a wide range of currently used concretes.

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Electrochemical chloride extraction on reinforced concrete contaminated external chloride: Efficiencies of intermittent applications and impacts on hydration products

Cited by 18 publications

References 27 publications

Performance of Cement Paste with Denitrified Fly Ash Containing NH4HSO4

Performance of Cement Paste with Denitrified Fly Ash Containing NH4HSO4

A numerical study of chloride migration in concrete under electrochemical repair

Effect of Imperial Smelting Process Slag Addition in Self Compacting Concrete Concrete on the Efficiency of Electrochemical Chloride Extraction

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