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

As estruturas de concreto expostas à água do mar experimentam a dissolução dos cristais em forma de agulha de etringita e gesso, aumentando a porosidade e reduzindo a resistência.
Por outro lado, a expansão pode ocorrer devido à pressão da cristalização do sal dentro dos poros do concreto acima da linha d'água.
No entanto, a solução salina pode subir através do concreto por ação capilar e ocorrem danos, indicando a criticidade da permeabilidade do concreto.
O concreto nas zonas de maré se degrada significativamente devido aos constantes ciclos úmidos e secos, enquanto o concreto submerso é menos afetado.
Os danos causados pela água do mar ao concreto são reduzidos quando os poros entopem com hidróxido de magnésio e bloqueiam a entrada.
O hidróxido de magnésio é formado com gesso a partir da reação do sulfato de magnésio na água do mar com o hidróxido de cálcio no concreto.
Às vezes, a água do mar pode causar danos ao concreto com absorção de sal, levando a rachaduras no concreto ao redor da armadura corroída.
Para resistir à água do mar, o concreto armado precisa de 2 a 3 polegadas de cobertura para reforço e concreto plano bem compactado com cimento de 600 lbs/yd³ acima e 500 lbs/yd³ abaixo da linha d'água.

efeito da água do mar no concreto

Effect of Sea Water on Concrete

O concreto exposto à água do mar pode sofrer degradação como a dissolução de etringita e gesso, aumentando a porosidade do material e diminuindo sua resistência. Em contraste, a cristalização de sais dentro dos poros do concreto pode causar expansão, particularmente acima da linha d'água, onde ocorre a evaporação. No entanto, essa expansão só acontece quando a água do mar, possibilitada pela permeabilidade do concreto, consegue se infiltrar na estrutura.

O concreto em áreas entre as marcas de maré, que passam por ciclos regulares de umedecimento e secagem, está particularmente em risco e tende a se degradar mais severamente do que as áreas que permanecem permanentemente submersas. O dano da água do mar é um pouco atenuado pela deposição de hidróxido de magnésio, que se forma no concreto pela reação do sulfato de magnésio com hidróxido de cálcio, levando ao entupimento dos poros e à redução da porosidade.

Além dos efeitos químicos, o concreto em ambientes marinhos também pode sofrer danos físicos devido à geada, ação das ondas e abrasão. Este dano físico pode piorar os efeitos da deterioração química, particularmente quando os sais absorvidos pelo concreto contribuem para a corrosão do aço de reforço.

Para evitar danos causados ​​pela água do mar, medidas semelhantes às usadas contra o ataque de sulfato são recomendadas. Isso inclui usar concreto com baixa permeabilidade e garantir uma cobertura adequada de pelo menos 5,08 a 7,62 cm sobre as barras de reforço. Um teor de cimento de 355,97 kg/m^3 acima da linha d'água e 296,64 kg/m^3 abaixo, juntamente a uma relação água-cimento de não mais que 0,40 a 0,45, é aconselhável. Além disso, obter uma compactação completa do concreto e exercer um artesanato preciso nas juntas de construção são essenciais para aumentar a durabilidade do concreto contra o ataque da água do mar.

Efeito da água do mar no concreto

As estruturas de concreto expostas à água do mar experimentam a dissolução dos cristais em forma de agulha de etringita e gesso, aumentando a porosidade e reduzindo ...

Education

JoVE Core

Civil Engineering

Engenharia Civil

Unit 1

Unidade 1

Permeability of Concrete

Permeabilidade do Concreto

KEY TERMS AND CONCEPTS

TERMOS E CONCEITOS-CHAVE

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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