Name: why concrete can fail around rebar
Uploaded: 2024-11-07T14:48:46.000Z
Duration: 1 min 27 s
Channel: JoVE

Dentro de una masa de hormigón, la alta alcalinidad del hidróxido de calcio con un pH de alrededor de 13 protege el refuerzo de acero de la corrosión mediante la creación de una capa protectora de óxido de hierro, un estado conocido como pasividad.
Debido a los diferentes potenciales electroquímicos, se forman regiones anódicas y catódicas en la superficie del acero.
Estas regiones se unen gracias a la solución salina del cemento hidratado, que actúa como electrolito.
Los iones ferrosos cargados positivamente del ánodo se disuelven en la solución salina.
Por el contrario, los electrones cargados negativamente se mueven al cátodo, son absorbidos por el electrolito y reaccionan con el agua y el oxígeno para formar iones hidroxilo.
El hidróxido férrico se forma cuando los iones hidroxilo se unen con los iones ferrosos. La oxidación posterior del hidróxido férrico conduce a la formación de óxido.
Además, los iones de cloruro en la pasta de cemento circundante forman ácido clorhídrico en puntos anódicos, rompiendo la capa protectora del acero y causando corrosión por picaduras.
Después de que el acero se oxida, aumenta de volumen y ejerce una presión que puede provocar grietas y desprendimientos del hormigón.
El uso de acero recubierto de epoxi o zinc o la reducción de la permeabilidad del concreto puede reducir la corrosión del acero.

corrosión del refuerzo

Corrosion of Reinforcement

La corrosión de las armaduras de acero dentro del hormigón es un proceso en el que influyen las propiedades inherentes del material y factores externos. El elevado nivel de pH de alrededor de 13, proporcionado por el hidróxido de calcio presente en el hormigón, protege inicialmente las armaduras de acero al promover la formación de una capa pasiva de óxido de hierro en su superficie.

Sin embargo, con el tiempo y en determinadas condiciones, como la carbonatación, la entrada de cloruros y el agrietamiento, este estado protector puede verse comprometido. El acero tiene zonas con diferentes potenciales electroquímicos, conocidas como regiones anódicas y catódicas. La pasta de hormigón hidratada, que contiene sales, actúa como un electrolito que conecta estas regiones. En las regiones anódicas, el hierro del acero se disuelve en forma de iones con carga positiva en el electrolito, mientras que en las regiones catódicas, los electrones se consumen en reacciones que involucran agua y oxígeno del hormigón circundante para producir iones hidroxilo.

Estos iones de hidroxilo se combinan con el hierro disuelto para crear hidróxido férrico, que se oxida aún más y se convierte en óxido. La presencia de iones de cloruro exacerba este proceso, lo que provoca corrosión por picaduras localizada al formar ácido clorhídrico que ataca la capa protectora de óxido de hierro. Esta corrosión puede expandir el acero, lo que provoca que el hormigón se agriete y se descascare.

Las medidas preventivas contra la corrosión del refuerzo de acero incluyen el uso de recubrimientos protectores como epoxi o zinc sobre el propio acero o la mejora de la calidad del hormigón para reducir su permeabilidad, dificultando así la entrada de agentes corrosivos.

Corrosión del refuerzo

Dentro de una masa de hormigón, la alta alcalinidad del hidróxido de calcio con un pH de alrededor de 13 protege el refuerzo de acero de la corrosión mediante la creación de un ...

Education

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JoVE Core

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Ingeniería Civil

Unit 1

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Permeability of Concrete

Permeabilidad del hormigón

KEY TERMS AND CONCEPTS

TÉRMINOS Y CONCEPTOS CLAVE

why concrete can fail around rebar

Steel reinforcement in concrete can corrode when its protective environment changes. Fresh concrete is highly alkaline because of calcium hydroxide, with a pH of about 13. That high pH helps form a passive iron oxide layer on the steel surface, which slows corrosion.

Over time, carbonation, chloride ingress, and cracking can weaken this protection. Concrete contains hydrated cement paste with salts, and it acts as an electrolyte. Different areas of the steel then behave as anodic and cathodic regions, which creates a small electrochemical cell.

At the anodic regions, iron dissolves into the electrolyte as positively charged ions. At the cathodic regions, electrons are used in reactions with water and oxygen in the surrounding concrete to form hydroxyl ions. These hydroxyl ions combine with the dissolved iron to make ferric hydroxide, which then oxidizes into rust.

Chloride ions make the problem worse. They can cause localized pitting corrosion by forming hydrochloric acid that attacks the protective iron oxide layer. As rust builds up, the steel expands and can crack the concrete, leading to spalling.

Corrosion can be reduced in a few ways. Protective coatings such as epoxy or zinc can be applied to the steel. Another option is to improve concrete quality so it is less permeable and slows the entry of corrosive agents.

Why Concrete Can Fail Around Rebar

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corrosion of reinforcement

Steel reinforcement in concrete can corrode when its protective environment changes. Fresh concrete is highly alkaline because of calcium hydroxide, with a pH of about 13. That high pH helps form a passive iron oxide layer on the steel surface, which slows corrosion. Over time, carbonation, chloride ingress, and cracking can weaken this protection. Concrete contains hydrated cement paste with salts, and it acts as an electrolyte. Different areas of the steel then behave as anodic and cathodic...

key terms and concepts

Learn how concrete’s high pH protects steel rebar, why carbonation and chlorides trigger rust, and how coatings and dense concrete help prevent cracking.

Why Concrete Can Fail Around Rebar | JoVE K12

JoVE Core Civil Engineering provides a foundational exploration of essential construction materials in civil engineering, focusing on bricks, stones, steel, wood, and concrete through easy-to-understand animated videos. This collection covers the properties, manufacturing processes, and practical applications of these materials. Additionally, the accompanied science-in-action videos demonstrate the research experiments performed in laboratories.

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Why Concrete Can Fail Around Rebar

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