Electrochemical realkalisation for rehabilitation of reinforced concrete structures

Abstract

In steel reinforced and prestressed concrete structures depassivation of the reinforcing steel can take place due to carbonation of the concrete cover. Depending on humidity and oxygen availability subsequent corrosion reactions will be initiated. Such conditions require measures to exclude corrosion induced damages during the designed lifetime of the structure. In the last few years an electrochemical realkalisation treatment has been proposed as adequate rehabilitation technique for carbonated concrete. This temporary treatment should increase the pH-value of the concrete pore water solution due to penetration of alkaline electrolyte from the concrete surface as well as repassivate the reinforcement due to electrochemical reactions at the steel surface.In order to clarify the different mechanisms taking place during electrochemical realkalisation laboratory tests have been carried out using carbonated reinforced mortar specimens. The investigations were aimed at checking the influence of various parameters, e.g. treatment time and current density, as well as the efficiency and long-term durability of this rehabilitation method.In Stahl-und Spannbetonbauwerken kann durch die Carbonatisierung der Betonuberdeckung eine Depassivierung des Bewehrungsstahles eintreten. In Abhangigkeit vom Feuchtigkeits-und Sauerstoffangebot konnen anschlieaend Korrosionsreaktionen initiiert werden. Solche Bedingungen erfordem MaOnahmen, um korrosionsbedingte Schaden wiihrend der geplanten Nutzungszeit des Bauwerks zu vermeiden. In den letzten Jahren ist die elektrochemische Realkalisierung als Instandsetzungsverfahren ftir carbonatisierten Stahlbeton vorgeschlagen worden. Bei dieser temporaren Methode sol1 der pH-Wert der Betonporenwasserlosung durch das Eindringen eines alkalischen Elektrolyten von der Betonoberflache aus angehoben sowie eine Repassivierung der Bewehrung durch elektrochemische Reaktionen an der Stahloberflache erreicht werden.Um die verschiedenen Mechanismen, die wahrend der elektrochemischen Behandlung ablaufen, zu untersuchen, wurden Laborversuche an carbonatisierten Mijrtelelektroden durchgefuhrt. Ziel der Untersuchungen war, sowohl den EinfluB der verschiedenen Parameter, wie z.B. Behandlungszeit und Stromdichte, als auch die Wirksamkeit und die Dauerhaftigkeit dieser Behandlungsmethode zu klaren.

Influência Do Grau De Corrosão Das Armaduras Na Eficiência Do Método De Realcalinização Para Tratamento De Estruturas De Concreto Carbonatadas

“…Uma vez que a frente de carbonatação atinja a armadura e as condições de alcalinidade do concreto estejam abaixo de 11,5, faz--se importante recuperar a alcalinidade da solução contida nos poros do concreto de modo a prevenir e, até certo ponto, tratar a corrosão (MIETZ, 1998). Duas técnicas de realcalinização foram desenvolvidas com esse intuito, a realcalinização eletroquímica e a realcalinização passiva ou natural.…”

“…No primeiro caso, a alcalinidade é proporcionada no interior do concreto, por meio da aplicação de um campo elétrico entre a armadura e uma malha externa temporária (MIETZ, 1998). O tratamento por realcalinização eletroquímica foi desenvolvido na década de 1980, para tentar recuperar estruturas de concreto armado afetadas pela carbonatação.…”

Essential Factors For The Changes In Concrete During Electrochemical Extraction

“…As a result of the voltage applied, chloride ions are attracted towards the anode. Once they reach the surface, they move to the anolite and in consequence they are removed from the concrete [1][2][3][4][5][6][7][8][9][10][11][12][13][14] and [22][23]. Alsabry and Zybura in [20] described ion migration in the concrete pore fluid caused by an external electric field employing the solution to an inverse task of the diffusion equation.…”

Durability aspects of electrochemical realkalisation treatment

“…Literature contributions on the short-term effects of ER are relatively numerous, for instance in terms of the role of several parameters (as concrete composition and circulated charge) on concrete realkalisation and on corrosion conditions of steel reinforcement (Mietz 1995, Redaelli & Bertolini 2011, Tong et al 2012, Yeih & Chang 2005. Conversely, contributions regarding the long-term effects are few.…”