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

El concreto sometido al ataque de sulfato generalmente exhibe una apariencia blanquecina distintiva, a menudo perceptible primero en los bordes y esquinas, con el consiguiente agrietamiento y descamación.
El agrietamiento en el hormigón se produce debido a una mayor permeabilidad, lo que permite que el agua con sulfato se infiltre en la estructura.
El sulfato infiltrado forma sulfato de calcio y sulfoaluminato de calcio, que ocupan más espacio, lo que hace que el hormigón endurecido se expanda y se rompa, lo que provoca problemas como el desplazamiento de las paredes del edificio debido a la presión lateral ejercida por una losa en expansión.
El suelo o las aguas subterráneas son la fuente habitual de sulfatos, como sulfatos de sodio, potasio, magnesio, amonio y calcio, que provocan daños al entrar en contacto con el hormigón.
Las pruebas de laboratorio para determinar la resistencia del concreto al ataque de sulfato implican sumergir o alternar muestras de humectación y secado en soluciones de sulfato de sodio o magnesio o una combinación de ambas.
El impacto se mide por la pérdida de fuerza, la expansión, la pérdida de peso o el examen visual del espécimen.
El uso de cemento resistente a los sulfatos o la reducción del hidróxido de calcio en la pasta de cemento hidratado y la fundición de hormigón denso con una menor relación agua-cemento aumenta la defensa del hormigón contra el ataque de sulfatos.

ataque de sulfatos al hormigón

Sulfate Attack on Concrete

El ataque de sulfatos al hormigón es un proceso de deterioro que se caracteriza por una decoloración blanquecina que comienza en los bordes y esquinas, acompañada de agrietamiento y desconchado. Este fenómeno ocurre cuando los sulfatos reaccionan con los componentes del hormigón endurecido, formando compuestos como el sulfato de calcio y el sulfoaluminato de calcio que ocupan más espacio que las sustancias a las que sustituyen, provocando la expansión y rotura del hormigón.

Los sulfatos de fuentes como el suelo, las aguas subterráneas o los efluentes industriales penetran en el hormigón y su reacción produce yeso y etringita. Esta reacción es similar a la que se produce en la fabricación de hormigón, donde el yeso evita el fraguado instantáneo al reaccionar con el aluminato tricálcico. Sin embargo, en el hormigón endurecido, esta reacción es indeseable, ya que puede provocar daños estructurales.

La resistencia al ataque de sulfatos es un aspecto crítico que generalmente se prueba sumergiendo muestras de concreto en soluciones de sulfatos. Este método permite observar cambios en la muestra, como reducción de resistencia, expansión y pérdida de peso. La inspección visual también es una herramienta valiosa para identificar daños. El uso de hormigón con un bajo contenido de aluminato tricálcico, como hormigón resistente a sulfatos y hormigón mezclado, puede mejorar significativamente la resistencia del concreto al ataque de sulfatos. La durabilidad del concreto contra el ataque de sulfatos también depende de lograr una baja relación agua-hormigón para una baja permeabilidad, un factor que es crucial para reducir la probabilidad de daño.

Ataque de sulfatos al hormigón

El hormigón sometido al ataque de sulfato suele presentar un aspecto blanquecino distintivo, que a menudo se nota por primera vez en los bordes y las esquinas, ...

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

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.

civil engineering

Concrete Damage from Sulfate Exposure

Description

Transcript

Tags