On leaching mechanisms of major and trace elements from concrete - Carbonation, exposure to deicing salt and external sulphates

Beddoe, R.E.; Müllauer, W.; Heinz, D.

doi:10.1016/j.jobe.2021.103435

Cited by 5 publications

(4 citation statements)

References 24 publications

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“…These ill effects reduce the service life of concrete, and detached heavy metal ions pollute the surrounding environment [49]. The leaching process is usually controlled by diffusion from within the concrete and ongoing surface dissolution mechanisms [50]. Alkalis in cement matrices are released by diffusion, but calcium release is mainly due to the dissolution of surface portlandite and, at a pH less than 12.4, decalcification of the CSH gel.…”

Section: Runoff Characteristicsmentioning

confidence: 99%

“…Figure 8 shows the percentage of removal of these metal ions from concrete samples in each cycle and the subsequent change in the pH of the percolated solutions. The removal of lead and zinc in non-carbonated samples The leaching process is usually controlled by diffusion from within the concrete and ongoing surface dissolution mechanisms [50]. Alkalis in cement matrices are released by diffusion, but calcium release is mainly due to the dissolution of surface portlandite and, at a pH less than 12.4, decalcification of the CSH gel.…”

Section: Runoff Characteristicsmentioning

confidence: 99%

“…The release of alumina from carbonated concrete is very low because the solubility control is transferred to aluminum hydroxide (i.e., gibbsite). In contrast, ettringite in carbonated concrete dissolves so that additional silicates are released by diffusion out of the carbonated layer [50]. Although percolated water has a pH that exceeds the maximum permissible limits of drinking water according to the WHO standards [51], several soils below the concrete pavement have a modest self-buffering capacity for the attenuation of high-pH water [52].…”

Section: Runoff Characteristicsmentioning

confidence: 99%

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Evaluation of the Performance of Pervious Concrete Inspired by CO2-Curing Technology

Muthu,

Sadowski

2024

Applied Sciences

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Urban runoff is acidic in nature and mainly consists of heavy metals and sediments. In this study, the pervious concrete samples were cured in a CO2-rich environment and their performance under runoff conditions was evaluated by passing different solutions containing clay particles, heavy metal ions, and acid species. The compressive strength of these samples was reduced by up to 14% when they were cured in water instead of a CO2 environment. Heavy metal ions, including lead and zinc, in the simulated runoff were adsorbed in these pervious concrete samples by up to 96% and 80% at the end of the experiment, but the acid species in this runoff could leach calcium ions from the cement components during passage. Clay particles in the runoff were trapped in the flow channels of samples, which marginally reduced the percolation rate by up to 14%. Concrete carbonation reduced the release of calcium ions under runoff conditions, and zinc removal was relatively lower because of the nonavailability of hydroxyl sites in the interconnected pore structure. The weight and strength losses in the carbonated concrete samples were relatively lower at the end of the acid storage experiment, suggesting that CO2 curing reduces cement degradation in aggressive chemicals. The SEM and tomography images revealed the degraded microstructure, while the XRD results provided data on the mineralogical changes. CO2 curing improves the strength gain and service life of pervious concrete in runoff environments.

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Section: Runoff Characteristicsmentioning

confidence: 99%

Section: Runoff Characteristicsmentioning

confidence: 99%

Section: Runoff Characteristicsmentioning

confidence: 99%

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Evaluation of the Performance of Pervious Concrete Inspired by CO2-Curing Technology

Muthu,

Sadowski

2024

Applied Sciences

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“…Another possibility is renewing periodically the leaching solution and controlling the pH in the interval [8,24,25]. Studies often consider the composition of water in order to combine different attack mechanisms, e.g., an external sulphate attack and leaching [26][27][28], or focus on specific in situ cases [1,29]. Therefore, to the authors' knowledge, there is currently no consensus on the type of performance-oriented leaching test that can easily be used with mineral water to obtain useful insights into water-induced cementitious material degradation.…”

Section: Introductionmentioning

confidence: 99%

Experimental Investigation on the Effects of Mineral Water Composition on the Leaching of Cement-Based Materials

Pouyanne,

Boudache,

Hilloulin

et al. 2024

Materials

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The common phenomenon observed for concrete in aggressive water is leaching, which involves the dissolution of cement hydration products. Many studies have focused on leaching in demineralised water or acid attacks, but mineral water still deserves further investigation. In most standards, the aggressiveness of a given water body is determined by its pH and not its composition. The effect of the calcium content of the water on degradation is yet to be determined. In this paper, the leaching of Portland cement-based mortar was induced by two types of drinking water with different calcium contents and buffer capacity in controlled conditions. The Langelier saturation index (LSI) was used to describe water aggressiveness based on the calco-carbonic equilibrium. The studied waters had the same pH but LSIs of +0.5 and −1.0 corresponding to scaling with respect to aggressive water; demineralised water was used as a reference. Microstructural damage was checked by TGA and X-ray microtomography. Macroscopic measurements were used to monitor global degradation. The soft water caused a 53% deeper deterioration of the mortar sample than the hard water. Soft water-induced leaching was found to be similar yet slower to leaching via demineralised water (with a mass loss of −2.01% and −2.16% after 200 days, respectively). In contrast, hard water induced strongly time-dependent leaching, and the damage was located close to the surface. The roughness of leached specimens was 18% higher in hard water than in soft water. The formation of calcite on the sample surface not only affects the leaching rate by creating a protective surface layer, but it could also act as a calcium ion pump.

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Passivation performance of Nb microalloyed rebar in concrete carbonation environments with different pH

Zeng,

Gu,

Wang

et al. 2024

Sci Rep

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In this study, XPS sputtering depth, SEM and electrochemical tests (CV, EIS, M-S, i-t, DPP) were used to study the structural composition and formation mechanism of surface passive film of Nb microalloyed rebar in SCPS with different pH. The results showed that after passivation for 10 d in SCPS with different pH, compared with CS rebar, the stability and compactness of surface passive film of 34Nb rebar gradually increased with the decreases of pH. Firstly, with the decreases of pH, the outer layer of surface passive film of 34Nb rebar was composed of Fe oxides and Fe hydroxides, and the inner layer was composed of Fe oxides and Nb oxides, thus increasing the mass ratio of Fe 3+ /Fe 2+ and Nb 2 O 5 /(NbO 2 + NbO). Secondly, with the decreases of pH, the addition of Nb promoted the formation of Fe oxides in 34Nb rebar, obtaining the excellent R ct , E corr and E p . Finally, with the decreases of pH, the addition of Nb promoted the enrichment of Nb oxides in 34Nb rebar, inhibiting the degradation of Fe oxides, and the passive film exhibited the P-N type semiconductor, thus significantly decreasing the carrier density and enhancing the passivation rate of 34Nb rebar.

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On leaching mechanisms of major and trace elements from concrete - Carbonation, exposure to deicing salt and external sulphates

Cited by 5 publications

References 24 publications

Evaluation of the Performance of Pervious Concrete Inspired by CO2-Curing Technology

Evaluation of the Performance of Pervious Concrete Inspired by CO2-Curing Technology

Experimental Investigation on the Effects of Mineral Water Composition on the Leaching of Cement-Based Materials

Passivation performance of Nb microalloyed rebar in concrete carbonation environments with different pH

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