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Corrosion protection of steel reinforcement by alternative binder types
With the aim of reducing the environmental impact of cement production, various approaches are being pursued worldwide to produce new types of binders as alternative for the mainly produced ordinary Portland cement (OPC). The properties of these alternative binders differ in different regards from standardized cement types. This characteristic has an influence on the expected durability of reinforced concrete components produced with new types of binder. The unique feature of this work lies in the fact that nine different types of alternative binders were examined about their possible applications and limitations in reinforced concrete. This enabled not only the comprehensive characterization of the corrosion-relevant properties but also an evaluation of the standardized testing and assessment methods with regard to their suitability for the different new types of binders. The alternative binder types under investigation are OPC-based composite cements, with alternative supplementary cementitious materials (SCMs) represented as calcined clays or steel slag as well as Calcium sulfoaluminate (CS̅A) cement and alkali-activated materials (AAMs) designed as low-calcium AAMs and high-calcium AAMs departed on the basis of their calcium content in the precursors. Moreover, a binder type based on hydrate phases (C-S-H) produced in an autoclave was in the scope of the investigations. The different approaches for alternative binder types are at different stages on their way from research application into the practical use in reinforced concrete. Therefore, these investigations contribute to the state of knowledge at different starting points, that are highlighted as follows. For the formulations, where the use in reinforced concrete is so far only subject to research, the first reported experimental findings regarding their influence on the passivation behavior of embedded steel were gained in this work. This applies for the use of a calcined illitic clay or steel slag as SCM in OPC and for the C-S-H binder as well. It was shown that they all guarantee the passivation of the steel reinforcement. The time until corrosion can be initiated due to carbonation or chloride ingress is a decisive factor when evaluating the binder performance. Therefore, the suitability of standardized test methods to quantify the duration of the initiation phase of corrosion of the reinforcement was evaluated for the different binder types. It was found that the rapid chloride migration test leads to a misevaluation of the binder types especially the ones with a lower pH value of the pore solution, because of the influence on the chemical reaction of usually applied indicator solutions. As promising alternative for indicator-based methods the Laser induced breakdown spectroscopy (LIBS) is proposed. With the introduction of new binder types, influencing factors on the microstructure, such as the often-referred water to cement (w/c) ratio on the porosity in OPC based concrete, can be assumed to not be universally valid for every new binder type, because of differing pore structures and pore solution compositions and binder characteristics. The formation factor, calculated from the total electric resistivity divided by the resistivity of the pore solution, is highlighted as universally suitable parameter to classify the permeability of the pore structure for aggressive species and the influence of the pore structure on other transport related processes. From the results of the investigations and the experience with the different binder types, recommendations for their testing, opportunities in the application in reinforced concrete and further research needs are derived.
Corrosion protection of steel reinforcement by alternative binder types
With the aim of reducing the environmental impact of cement production, various approaches are being pursued worldwide to produce new types of binders as alternative for the mainly produced ordinary Portland cement (OPC). The properties of these alternative binders differ in different regards from standardized cement types. This characteristic has an influence on the expected durability of reinforced concrete components produced with new types of binder. The unique feature of this work lies in the fact that nine different types of alternative binders were examined about their possible applications and limitations in reinforced concrete. This enabled not only the comprehensive characterization of the corrosion-relevant properties but also an evaluation of the standardized testing and assessment methods with regard to their suitability for the different new types of binders. The alternative binder types under investigation are OPC-based composite cements, with alternative supplementary cementitious materials (SCMs) represented as calcined clays or steel slag as well as Calcium sulfoaluminate (CS̅A) cement and alkali-activated materials (AAMs) designed as low-calcium AAMs and high-calcium AAMs departed on the basis of their calcium content in the precursors. Moreover, a binder type based on hydrate phases (C-S-H) produced in an autoclave was in the scope of the investigations. The different approaches for alternative binder types are at different stages on their way from research application into the practical use in reinforced concrete. Therefore, these investigations contribute to the state of knowledge at different starting points, that are highlighted as follows. For the formulations, where the use in reinforced concrete is so far only subject to research, the first reported experimental findings regarding their influence on the passivation behavior of embedded steel were gained in this work. This applies for the use of a calcined illitic clay or steel slag as SCM in OPC and for the C-S-H binder as well. It was shown that they all guarantee the passivation of the steel reinforcement. The time until corrosion can be initiated due to carbonation or chloride ingress is a decisive factor when evaluating the binder performance. Therefore, the suitability of standardized test methods to quantify the duration of the initiation phase of corrosion of the reinforcement was evaluated for the different binder types. It was found that the rapid chloride migration test leads to a misevaluation of the binder types especially the ones with a lower pH value of the pore solution, because of the influence on the chemical reaction of usually applied indicator solutions. As promising alternative for indicator-based methods the Laser induced breakdown spectroscopy (LIBS) is proposed. With the introduction of new binder types, influencing factors on the microstructure, such as the often-referred water to cement (w/c) ratio on the porosity in OPC based concrete, can be assumed to not be universally valid for every new binder type, because of differing pore structures and pore solution compositions and binder characteristics. The formation factor, calculated from the total electric resistivity divided by the resistivity of the pore solution, is highlighted as universally suitable parameter to classify the permeability of the pore structure for aggressive species and the influence of the pore structure on other transport related processes. From the results of the investigations and the experience with the different binder types, recommendations for their testing, opportunities in the application in reinforced concrete and further research needs are derived.
Corrosion protection of steel reinforcement by alternative binder types
Korrosionsschutz der Stahlbewehrung durch alternative Bindemittelarten
Achenbach, Rebecca (author) / Raupach, Michael (tutor) / Breit, Wolfgang (tutor)
2024-01-01
1 Online-Ressource : Illustrationen pages
Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2024; Aachen : RWTH Aachen University 1 Online-Ressource : Illustrationen (2024). = Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2024
Miscellaneous
Electronic Resource
English
Influence of Binder Materials Type on Corrosion Protection for Steel Reinforcement
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