Name: concrete damage from sulfate exposure
Uploaded: 2024-11-07T14:48:45.000Z
Duration: 1 min 29 s
Channel: JoVE

O concreto submetido ao ataque de sulfato normalmente exibe uma aparência esbranquiçada distinta, muitas vezes perceptível pela primeira vez nas bordas e cantos, com rachaduras e descamação subsequentes.
A fissuração no concreto resulta devido à permeabilidade aprimorada, permitindo que a água com sulfato se infiltre na estrutura.
O sulfato infiltrado forma sulfato de cálcio e sulfoaluminato de cálcio, que ocupam mais espaço, fazendo com que o concreto endurecido se expanda e se quebre, levando a problemas como deslocamento das paredes do edifício devido à pressão lateral exercida por uma laje em expansão.
O solo ou a água subterrânea são a fonte usual de sulfatos, como sulfatos de sódio, potássio, magnésio, amônio e cálcio, que causam danos ao entrar em contato com o concreto.
Os testes de laboratório para a resistência do concreto ao ataque de sulfato envolvem a imersão ou alternância de amostras de umedecimento e secagem em soluções de sulfato de sódio ou magnésio ou uma combinação de ambos.
O impacto é medido pela perda de força, expansão, perda de peso ou exame visual da amostra.
A utilização de cimento resistente a sulfato ou a redução do hidróxido de cálcio na pasta de cimento hidratado e a fundição de concreto denso com uma proporção água-cimento mais baixa aumentam a defesa do concreto contra o ataque de sulfato.

ataque de sulfato no concreto

Sulfate Attack on Concrete

O ataque de sulfato no concreto é um processo de deterioração caracterizado por uma descoloração esbranquiçada começando nas bordas e cantos, acompanhada de rachaduras e lascas. Esse fenômeno ocorre quando os sulfatos reagem com os componentes do concreto endurecido formando, compostos como sulfato de cálcio e sulfoaluminato de cálcio, que ocupam mais espaço do que as substâncias que substituem, fazendo com que o concreto se expanda e se rompa.

Sulfatos de fontes como solo, águas subterrâneas ou efluentes industriais penetram no concreto, e sua reação produz gesso e etringita. Essa reação é semelhante à da fabricação de cimento, onde o gesso previne a pega instantânea ao reagir com aluminato tricálcico. No entanto, no concreto endurecido, essa reação é indesejável, pois pode levar a danos estruturais.

A resistência ao ataque de sulfato é um aspecto crítico que geralmente é testado pela imersão de amostras de concreto em soluções de sulfato. Esse método permite a observação de alterações na amostra, como redução de resistência, expansão e perda de peso. A inspeção visual também é uma ferramenta valiosa na identificação de danos. O uso de cimento com baixo teor de aluminato tricálcico, como cimento resistente a sulfato e cimento misturado, pode aumentar significativamente a resistência do concreto ao ataque de sulfato. A durabilidade do concreto contra-ataque de sulfato também depende de atingir uma baixa relação água-cimento para baixa permeabilidade, um fator crucial para reduzir a probabilidade de danos.

Ataque de sulfato no concreto

O concreto submetido ao ataque de sulfato normalmente exibe uma aparência esbranquiçada distinta, muitas vezes perceptível pela primeira vez nas bordas e cantos, com subsequente ...

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Permeability of Concrete

Permeabilidade do Concreto

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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 also produces gypsum and ettringite, which expand and disrupt the hardened structure.

This process is related to the role of gypsum during cement manufacture. There, gypsum reacts with tricalcium aluminate to help prevent flash set. In hardened concrete, the same kind of reaction becomes harmful and can weaken the structure.

Engineers test sulfate resistance by immersing concrete samples in sulfate solutions. They then look for strength reduction, expansion, and weight loss. Visual inspection is also important because surface changes can help reveal damage.

Concrete can resist sulfate attack better when it uses cement with low tricalcium aluminate content. Sulfate-resisting cement and blended cement are both useful options. A low water-cement ratio also helps by lowering permeability, which reduces the chance of sulfate damage.

Concrete Damage from Sulfate Exposure

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 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 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...

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 sulfate exposure damages concrete, causes whitening, cracking, and spalling, and how resistance is tested and improved with low-permeability cement.

Concrete Damage from Sulfate Exposure | 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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Concrete Damage from Sulfate Exposure

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