pH-dependent chloride desorption isotherms of Portland cement paste

Teymouri, Mohammad; Shakouri, Mahmoud; Vaddey, Naga Pavan

doi:10.1016/j.conbuildmat.2021.125415

Cited by 16 publications

(4 citation statements)

References 36 publications

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“…Most of the physically bound chlorides are generally attributed to chloride ions bound in the ion-exchange sites of CSH and CASH. This bound mechanism differs as the composition of CSH and CASH is affected by the calcium to silicon (Ca/Si) ratio or calcium ion concentration in concrete formulations [31,[42][43][44][45]. Most of the physically adsorbed chloride is adsorbed by CASH gel; the chloride adsorption by CH, ettringite, and Friedel's salt is neglected because of their small surface area compared to CSH or CASH binder gels [46,47].…”

Section: Physical Chloride Binding Of Specimens Containing Mkmentioning

confidence: 99%

“…The cation of chloride salt (e.g., Ca 2+ , Mg 2+ ) has been shown to make a noticeable difference in chloride binding [57]. Neat OPC paste, MK-supplemented materials, and LC3 materials exposed to CaCl 2 and MgCl 2 were found to have more bound chloride ions than when exposed to the same concentration of chloride in NaCl solutions (see Figure 10) [42,57,69,108,109,114]. This elucidates a potential cation type effect on the chloride adsorption where an increasing positive charge of the surface of C(A)SH and a higher calcium concentration [44,50,57,89] as well as an increase in AFm formed is apparent [57].…”

Section: Cationmentioning

confidence: 99%

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A Review on the Effect of Metakaolin on the Chloride Binding of Concrete, Mortar, and Paste Specimens

et al. 2022

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Chloride binding is a complex phenomenon in which the chloride ions bind with hydrated Portland cement (PC) phases via physical and chemical mechanisms. However, the current utilization of clays as (Al)-rich supplementary cementitious materials (SCMs), such as metakaolin (MK), can affect the chloride-binding capacity of these concrete materials. This state-of-the-art review discusses the effect of clay-based SCMs on physical and chemical chloride binding with an emphasis on MK as a high-reactivity clay-based SCM. Furthermore, the potential mechanisms playing a role in physical and chemical binding and the MK effect on the hydrated cement products before and after exposure to chloride ions are discussed. Recent findings have portrayed competing properties of how MK limits the physical chloride-binding capacity of MK-supplemented concrete. The use of MK has been found to increase the calcium silicate hydrates (CSH) content and its aluminum to silicon (Al/Si) ratio, but to reduce the calcium to silicon (Ca/Si) ratio, which reduces the physical chloride-binding capacity of PC-clay blended cements, such as limestone calcined clay cements (LC3). By contrast, the influence of MK on the chemical chloride capacity is significant since it increases the formation of Friedel’s salt due to an increased concentration of Al during the hydration of Portland cement grains. Recent research has found an optimum aluminum to calcium (Al/Ca) ratio range, of approximately 3 to 7, for maximizing the chemical binding of chlorides. This literature review highlights the optimal Al content for maximizing chloride binding, which reveals a theoretical limit for calcined clay addition to supplementary cementitious materials and LC3 formulations. Results show that 5–25% of replacements increase bound chloride; however, with a higher percentage of replacements, fresh and hardened state properties play a more pivotal role. Lastly, the practical application of four binding isotherms is discussed with the Freundlich isotherm found to be the most accurate in predicting the correlation between free and bound chlorides. This review discusses the effects of important cement chemistry parameters, such as cation type, sulfate presence, carbonation, chloride concentration, temperature, and applied electrical fields on the chloride binding of MK-containing concretes—important for the durable formulation of LC3.

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Section: Physical Chloride Binding Of Specimens Containing Mkmentioning

confidence: 99%

Section: Cationmentioning

confidence: 99%

A Review on the Effect of Metakaolin on the Chloride Binding of Concrete, Mortar, and Paste Specimens

et al. 2022

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“…Moreover, Ref. [37] studied the chloride adsorption on the C-S-H, but attributing to the electrostatic charges the binding ability, which changes with the nature of the cation. However, Ref.…”

Section: Introductionmentioning

confidence: 99%

Finite Boundary Conditions Due to the Bar Presence in the Model of Chloride Penetration

Tavares

Andrade

2022

Materials

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The chloride penetration is usually modelled through the application of a solution of Fick’s second law of diffusion, based on the assumption of semi-infinite boundary conditions. However, the presence of the bars, on whose surface the chlorides accumulate, makes this assumption incorrect. As the time progresses, the chlorides in the steel/concrete interface increase in concentration more than the chlorides overpassing the bar position without obstacles. This circumstance, although previously studied, has not been introduced in common practice, in spite of it supposes early reaching of the chloride threshold. The study in this paper shows a deterministic analysis of the chloride diffusion process by the finite element method (FEM) which numerically solves Fick’s second law, taking into account the accumulation of the chlorides on the bar surface. Several examples are calculated and factors between the finite/semi-infinite solutions are given. These factors depend on the cover depth and the diffusion coefficient, and with less importance, on the diameter of the bar, which make it unfeasible to propose a general trend.

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“…A drop in the pH level of pore solution in OPC concrete results in the decomposition of calcium hydroxide (CH), calcium silicate hydrate (CSH), and ettringite at the pH of 12.6, 10.7, and 10.5, respectively [ 5 ]. Continuation of this process results in the dissolution and/or decomposition of components such as CH and CSH and influences the chloride binding mechanism [ 6 ]. A product of such reactions, calcium salts, will reduce the compressive and flexural strength of OPC concrete.…”

Section: Introductionmentioning

confidence: 99%

The Effect of Mixture Proportion on the Performance of Alkali-Activated Slag Concrete Subjected to Sulfuric Acid Attack

et al. 2022

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Long-term deterioration and durability concerns in harsh environments with acidic attacks are considered as the weaknesses of ordinary Portland cement (OPC) concrete. Although the performance of alkali-activated slag concrete (AASC) has been reported to be superior in acidic environments, there is a poor understanding regarding the impacts of diverse mix design parameters on AASC durability in an acidic environment. This research aims to understand the impact of mix design parameters on the durability of AASC in the sulfuric acid (H2SO4) environment with pH = 3. The type of alkaline solution, the molarity of alkaline solutions, the weight ratio of alkaline solutions to slag, and the weight ratio of NaOH to Na2SiO3 are mix design parameters investigated in this study. The compressive strength reduction and weight loss were monitored from early ages up to 180 days. Moreover, an OPC concrete sample was produced as a reference.

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pH-dependent chloride desorption isotherms of Portland cement paste

Cited by 16 publications

References 36 publications

A Review on the Effect of Metakaolin on the Chloride Binding of Concrete, Mortar, and Paste Specimens

A Review on the Effect of Metakaolin on the Chloride Binding of Concrete, Mortar, and Paste Specimens

Finite Boundary Conditions Due to the Bar Presence in the Model of Chloride Penetration

The Effect of Mixture Proportion on the Performance of Alkali-Activated Slag Concrete Subjected to Sulfuric Acid Attack

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