Effect of aggregate contamination with pyrite on reinforcement corrosion in concrete

https://doi.org/10.1016/j.engfailanal.2020.105116Get rights and content

Highlights

  • •

    Concretes with 5.0% of SO3 prevented the formation of the rebar passivating film.

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    Pyrite contamination induced low corrosion potential and high current density.

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    SEM images confirmed the presence of ettringite due to pyrite oxidation.

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    XRD test indicated a portlandite consumption of up to 80% in contaminated samples.

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    The wetting and drying cycle was more aggressive for the internal sulfate attack.

Abstract

This research aimed to evaluate the chemical and microstructure parameters of cement pastes and electrochemical parameters of concretes, both contaminated with different levels of SO3 (0.0%, 0.5%, 1.0% and 5.0%) due to the presence of pyrite. To evaluate the chemical and microstructural parameters, SEM and XRD tests were carried out in cement pastes, to detect the formation of deleterious products. The electrochemical parameters, such as corrosion potential, current density and electrical resistivity were measured in concrete samples to evaluate the reinforcements immersed in contaminated concretes and the susceptibility of these reinforcement concretes to the corrosion phenomenon. SEM and XRD tests, carried out up to 720 days, confirmed the presence of deleterious products, such as ettringite. The electrochemical analysis, which was performed during 1100 days, indicated significantly lower values of corrosion potential (around −600 mV) and higher values of current density (0.7 µA/cm2) for the reinforcement immersed in concrete with 5.0% of SO3. Finally, the research concludes the greater susceptibility of pyrite contaminated concretes with 5.0 of SO3 to the phenomenon of corrosion and the formation of deleterious products, therefore, being a harmful content for use in reinforced concrete elements.

Introduction

According to Pradhan (2014) [1], concrete reinforcement corrosion is the most significant deteriorating mechanism for the reinforcement of structures. As it is the largest occurring phenomenon, it deserves studies on the favorable factors of the mechanism and preventive measures for it.

Corrosion is defined as the deterioration of a material, usually metallic, through chemical or electrochemical action of the environment, associated or not with mechanical stresses. The interaction between the material and the environment causes harmful and undesirable changes suffered by the material, making it unsuitable for its use in construction [2].

In general, studies related to corrosion in concrete structures analyze the phenomenon from the carbonation viewpoint (pH reduction) or chloride concentration (ion diffusion), since these are the main aggressive agents responsible for the deteriorating mechanism [3]. However, a study from the viewpoint of sulfate presence in concrete mixtures is interesting, since sulfide-contaminated aggregates are available and there are differences in contaminant attack mechanism and its content limit that, so its use may not be harmful to the concrete [4].

Concrete structures far from urban centers usually require the use of local aggregates that might present contaminations such as pyrite. Those contaminations can affect directly the corrosion mechanism of the concrete structures. Although expansion, microcracking and loss of stiffness are essential during the evaluation of structures affected by sulfate attack [5], [6], the sulfate contamination could influence the steel passivation and induce the corrosion initiation even with no significant mechanical changes in the concrete. Therefore, this paper contributes to the understanding of the corrosion phenomenon associated with sulfate attacks that can occur due to internal contaminations such as pyrite.

This study aims to analyze, through chemical and electrochemical tests, the influence that the use of aggregates contaminated by sulfides on the behavior of cementitious composites regarding the phenomenon of corrosion. The chemical analysis (SEM and XRD) allows discussions on deleterious products formed in cement paste from 28 to 720 days of age. The electrochemical analysis (corrosion potential, current density and electrical resistivity) supports the discussions of the susceptibility to the corrosion phenomenon of concretes contaminated by sulfides, from 28 to 1100 days of age.

The hypothesis raised in this study is that the contamination of the samples by sulfides would leave the steel bars more susceptible to the phenomenon of corrosion, since one of the consequences of the attack is the consumption of Portlandite, a material responsible for maintaining the pH of the matrix and protecting the reinforcement [7], and also allows the formation of ettringite in the concrete [8]. Thus, the combined analysis of the chemical and electrochemical properties of the contaminated samples makes it possible to study the products formed due to the attack, as well as the behavior of the reinforcement concerning the corrosion mechanism. And finally, a contamination limit from the electrochemical perspective can be proposed.

Section snippets

Literature review

The deleterious reactions of concrete structures that contain sulfide in their composition start with the oxidation of the sulfide mineral. Pyrite, for example, in the presence of water and oxygen, oxidizes, forming iron hydroxide and sulfuric acid, as shown in Eq. (1) [9].FeS2+H2O+72O2→FeSO4+H2SO4

The by-products generated can react with the compounds present in the cementitious matrix and initiate new chemical reactions and forming products with volumes greater than the initial volume of

Materials and characteristics of mixtures

The experimental program of this study consisted of the molding of samples of contaminated reinforcement concretes for electrochemical tests and cement pastes for chemical and microstructural tests. The materials used in both mixtures were: cement, fly ash and pyrite as a contaminant.

The binder blend used was obtained by a composition of 65% of commercial cement, CPV ARI – NBR 16697 [18] equivalent to Type III – ASTM C150 [19], and 35% of fly ash, equivalent to ASTM C618 [20] class F. The final

Electrochemical analysis

Fig. 3(A) and (B) show the corrosion potential in wetting and drying cycle and tank conditions, respectively. For the corrosion risk analysis, the limits presented in ASTM C876 [48] are shown in Fig. 3 (low, uncertain and high). In the analysis of the formation of the passivating film, it was taken into consideration the change of risk range, high risk to uncertain risk, as mentioned by Koga et al. [49]. However, it is important to note that the classification referred to in ASTM C876 [48] was

Conclusions

The electrochemical tests confirmed the higher susceptibility to the steel corrosion in reinforced concretes with contamination of 5.0% of SO3. In the two exposure conditions, cycle and tank, it was not possible to point out the formation of the passivating film for the series of higher contamination in any condition. Also, after 1100 days, the 5.0% of SO3 series presented higher corrosion current density, 0.7 µA/cm2, (moderate level) and lower potential of corrosion, −600 mV, (high-risk zone).

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

The authors thank the support, as a scholarship, by Foundation Araucária, as well as the availability of the infrastructure and human resources made available by the Federal University of Paraná (PPGECC/UFPR-Brazil). Our gratitude also to the Center of Electron Microscopy of UFPR (CME/UFPR) by the support during the SEM tests.

Declaration of Competing Interest

The authors confirm that this work is unpublished and there is no declaration of interest. It strictly followed all ethical procedures and it has not been submitted to any other journal for publication.

References (70)

  • A.M. Elmoaty

    Four-years carbonation and chloride induced steel corrosion of sulfate-contaminated aggregates concrete

    Constr. Build. Mater.

    (2018)
  • D.A. Spears et al.

    Pyrite in UK coals: its environmental significance

    Fuel

    (1994)
  • A. Campos et al.

    Effects of an internal sulfate attack and an alkali-aggregate reaction in a concrete dam

    Constr. Build. Mater.

    (2018)
  • J. Gao et al.

    Durability of concrete exposed to sulfate attack under flexural loading and drying–wetting cycles

    Constr. Build. Mater.

    (2013)
  • J. Gong et al.

    Effects of sulfate attack and dry-wet circulation on creep of fly-ash slag concrete

    Constr. Build. Mater.

    (2016)
  • L. Jiang et al.

    Study of deterioration of concrete exposed to different types of sulfate solutions under drying-wetting cycles

    Constr. Build. Mater.

    (2016)
  • A. Blanco et al.

    Lessons learned about the diagnosis of pathologies in concrete dams: 30 years of research and practice

    Constr. Build. Mater.

    (2019)
  • W. Zhang et al.

    Effects of impressed current density on corrosion induced cracking of concrete cover

    Constr. Build. Mater.

    (2019)
  • F. Matalkah et al.

    Acid resistance and corrosion protection potential of concrete prepared with alkali aluminosilicate cement

    J. Build. Eng..

    (2018)
  • P. Linares-Alemparte et al.

    Porosity and electrical resistivity – based empirical calculation of the oxygen diffusion coefficient in concrete

    Constr. Build. Mater.

    (2019)
  • Z. Pan et al.

    Hydration products of alkali-activated slag-red mud cementitious material

    Cem. Concr. Res.

    (2002)
  • G.Y. Koga et al.

    A comparative study of mild steel passivation embedded in Belite-Ye’elimite-Ferrite and Portland cement mortars

    Electrochim. Acta

    (2018)
  • X.H. Sun et al.

    Electrochemical and microscopic investigation on passive behavior of ductile iron in simulated cement-mortar pore solution

    Constr. Build. Mater.

    (2017)
  • J. Williamson et al.

    The effect of simulated concrete pore solution composition and chlorides on the electronic properties of passive films on carbon steel bar

    Corros. Sci.

    (2016)
  • J.O. Iroh et al.

    Corrosion performance of polypyrrole coating applied to low carbon steel by an electrochemical process

    Electrochim. Acta

    (2000)
  • M. Moreno et al.

    Corrosion of reinforcing steel in simulated concrete pore solutions: effect of carbonation and chloride content

    Corros. Sci.

    (2004)
  • P. Garcés et al.

    Corrosion of steel reinforcement in structural concrete with carbon material addition

    Corros. Sci.

    (2007)
  • H. Nahali et al.

    Effect of phosphate based inhibitor on the threshold chloride to initiate steel corrosion in saturated hydroxide solution

    Constr. Build. Mater.

    (2014)
  • C. Andrade et al.

    Effects of some mineral additions to Portland cement on reinforcement corrosion

    Cem. Concr. Res.

    (2013)
  • S. Goni et al.

    Synthetic concrete pore solution chemistry and rebar corrosion rate in the presence of chlorides

    Cem. Concr. Res.

    (1990)
  • A. Poursaee et al.

    Reinforcing steel passivation in mortar and pore solution

    Cem. Concr. Res.

    (2007)
  • A. Alhozaimy et al.

    Significance of oxygen concentration on the quality of the passive film formation for steel reinforced concrete structures during the initial curing of concrete

    Cem. Concr. Compos.

    (2016)
  • W. Ouyang et al.

    Evolution of surface hardness of concrete under sulfate attack

    Constr. Build. Mater.

    (2014)
  • X. Wang et al.

    Stability and decomposition mechanism of ettringite in presence of ammonium sulfate solution

    Constr. Build. Mater.

    (2016)
  • P.K. Mehta

    Mechanism of sulfate attack on Portland cement concrete – another look

    Cem. Concr. Res.

    (1983)

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