Name: seawater damage and concrete durability
Uploaded: 2024-11-07T14:48:45.000Z
Duration: 1 min 22 s
Channel: JoVE

Las estructuras de hormigón expuestas al agua de mar experimentan la disolución de los cristales en forma de aguja de ettringita y yeso, aumentando la porosidad y reduciendo la resistencia.
Por el contrario, la expansión puede ocurrir debido a la presión de la cristalización de la sal dentro de los poros del concreto por encima de la línea de flotación.
Sin embargo, la solución salina puede ascender a través del hormigón por capilaridad y se producen daños, lo que indica la criticidad de la permeabilidad del hormigón.
El hormigón en las zonas de marea se degrada significativamente debido a los constantes ciclos húmedo-seco, mientras que el hormigón sumergido se ve menos afectado.
El daño del agua de mar al concreto se reduce cuando los poros se obstruyen con hidróxido de magnesio y bloquean la entrada.
El hidróxido de magnesio se forma con yeso a partir de la reacción del sulfato de magnesio en el agua de mar con el hidróxido de calcio en el hormigón.
A veces, el agua de mar puede causar daños en el hormigón con la absorción de sal, lo que provoca el agrietamiento del hormigón alrededor del refuerzo corroído.
Para resistir el agua de mar, el concreto reforzado necesita de 2 a 3 pulgadas de cubierta para refuerzo y concreto plano bien compactado con cemento de 600 lbs/yd³ por encima y 500 lbs/yd³ por debajo de la línea de flotación.

efecto del agua de mar sobre el hormigón

Effect of Sea Water on Concrete

El hormigón expuesto al agua de mar puede sufrir degradaciones como la disolución de la ettringita y el yeso, aumentando la porosidad del material y disminuyendo su resistencia. Por el contrario, la cristalización de sales dentro de los poros del hormigón puede provocar una expansión, especialmente por encima de la línea de flotación, donde se produce la evaporación. No obstante, esta expansión solo se produce cuando el agua de mar, gracias a la permeabilidad del hormigón, consigue infiltrarse en la estructura.

El hormigón en las zonas entre las marcas de marea, que se someten a ciclos regulares de humectación y secado, está especialmente expuesto a riesgos y tiende a degradarse más gravemente que las zonas que permanecen sumergidas de forma permanente. El daño causado por el agua de mar se ve mitigado en cierta medida por la deposición de hidróxido de magnesio, que se forma en el hormigón por la reacción del sulfato de magnesio con el hidróxido de calcio, lo que provoca la obstrucción de los poros y la reducción de la porosidad.

Además de los efectos químicos, el hormigón en ambientes marinos también puede sufrir daños físicos debido a las heladas, la acción de las olas y la abrasión. Estos daños físicos pueden empeorar los efectos del deterioro químico, en particular cuando las sales absorbidas por el hormigón contribuyen a la corrosión del acero de refuerzo.

Para evitar daños causados ​​por el agua de mar, se recomiendan medidas similares a las que se utilizan contra el ataque de sulfatos. Estas incluyen el uso de hormigón con baja permeabilidad y asegurar una cobertura adecuada de al menos 5,08 a 7,62 centímetros sobre las barras de refuerzo. Se recomienda un contenido de cemento de 355,97 kilogramos por metro cúbico por encima de la línea de flotación y 296,64 kilogramos por metro cúbico por debajo, junto con una relación agua-hormigón de no más de 0,40 a 0,45. Además, lograr una compactación completa del hormigón y ejercer una técnica precisa en las juntas de construcción son fundamentales para mejorar la durabilidad del hormigón contra el ataque del agua de mar.

Efecto del agua de mar sobre el hormigón

Las estructuras de hormigón expuestas al agua de mar experimentan la disolución de los cristales en forma de aguja de etringita y yeso, aumentando la porosidad ...

Education

Educación

JoVE Core

Civil Engineering

Ingeniería Civil

Unit 1

Unidad 1

Permeability of Concrete

Permeabilidad del hormigón

KEY TERMS AND CONCEPTS

TÉRMINOS Y CONCEPTOS CLAVE

seawater damage and concrete durability

Seawater can damage concrete by changing its chemistry, increasing porosity, and lowering strength. In marine settings, concrete is exposed to dissolved salts and repeated wetting, so its durability depends on how much water can enter the material.

One major form of damage is the breakdown of ettringite and gypsum, two concrete minerals that can dissolve in seawater. As these materials are lost, the concrete becomes more porous. Salt can also crystallize inside pores, especially above the waterline where evaporation is stronger, and that crystallization can force the concrete to expand.

That expansion only happens when seawater gets into the concrete through its pore system. Concrete in the tidal zone, where it is repeatedly wet and dried, is often damaged more than concrete that stays fully submerged. Seawater attack is partly reduced when magnesium hydroxide forms inside the concrete. It forms from the reaction of magnesium sulfate with calcium hydroxide and can clog pores, which lowers porosity.

Marine concrete can also be harmed by physical forces such as frost, wave action, and abrasion. These effects can make chemical damage worse. Salt that enters the concrete may also help corrode reinforcing steel, which weakens the structure even further.

Protection starts with low-permeability concrete, so seawater has a harder time entering the structure. Recommended practice also includes at least 2 to 3 inches of concrete cover over reinforcement bars. A cement content of 600 pounds per cubic yard above the waterline and 500 pounds per cubic yard below, along with a water-cement ratio no higher than 0.40 to 0.45, helps improve durability. Good compaction and careful construction joints are also important.

Seawater Damage and Concrete Durability

permeability of concrete

Concrete Durability and Water Penetration

Concrete durability depends partly on how easily water and gases can move through it. This property, called permeability, is important for judging water-tightness and resistance to chemical attack in concrete structures. Permeability is measured with comparative lab tests. In a typical test, the sides of a concrete specimen are sealed, water pressure is applied to the top surface, and the amount of water that passes through is measured. The test is often run for about ten days until a steady...

sulfate attack on concrete

Concrete Damage from Sulfate Exposure

Concrete damage from sulfate exposure starts with a whitish discoloration, often first seen at the edges and corners. As the attack continues, the concrete can crack and spall. This deterioration happens when sulfates react with hardened concrete and create new compounds that take up more space than the materials they replace. Sulfates may enter concrete from soil, groundwater, or industrial effluents. Inside the concrete, they can form calcium sulfate and calcium sulfoaluminate. The reaction...

effect of sea water on concrete

Seawater can damage concrete by changing its chemistry, increasing porosity, and lowering strength. In marine settings, concrete is exposed to dissolved salts and repeated wetting, so its durability depends on how much water can enter the material. One major form of damage is the breakdown of ettringite and gypsum, two concrete minerals that can dissolve in seawater. As these materials are lost, the concrete becomes more porous. Salt can also crystallize inside pores, especially above the...

acid attack on concrete

Concrete Damage from Low pH Water

Concrete damage from low pH water happens when acids react with the hydrated cement paste. This reaction dissolves the paste, so the concrete becomes softer and weaker. The problem is often seen in chimneys, sewers, and industrial settings. The amount of damage depends on how acidic the water is. When pH falls below 6.5, the attack becomes more severe. A pH below 4.5 can cause major concrete damage. The rate of damage also depends on how fast hydrogen ions move through the cement gel. This...

alkali aggregate reaction in concrete

How Moisture Cracks Alkali-Reactive Concrete

Alkali-aggregate reaction in concrete can weaken a structure when siliceous minerals in the aggregate react with alkaline hydroxides from cement. The reaction makes an alkali-silica gel, which pulls in water and swells. As the gel expands inside the rigid cement paste, it creates pressure that can crack and disrupt the concrete. The damage comes from both osmotic hydraulic pressure and the swelling of the solid reaction products. Particle size also matters. Fine siliceous particles can cause...

corrosion of reinforcement

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...

key terms and concepts

Learn how seawater weakens concrete through salt attack, porosity, and steel corrosion, and how low-permeability mixes help protect marine structures.

Seawater Damage and Concrete Durability | 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.

civil engineering

Seawater Damage and Concrete Durability

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