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

Concrete subjected to sulfate attack typically exhibits a distinct whitish appearance, often first noticeable at the edges and corners, with subsequent cracking and flaking.
Cracking in concrete results due to enhanced permeability, allowing water with sulfate to infiltrate the structure.
The infiltrated sulfate forms calcium sulfate and calcium sulfoaluminate, which take more space, causing hardened concrete to expand and break apart, leading to issues like shifting of building walls due to lateral pressure exerted by an expanding slab.
Soil or groundwater is the usual source for sulfates, such as sodium, potassium, magnesium, ammonium, and calcium sulfates, which lead to damage when coming in contact with concrete.
Laboratory tests for concrete&#39;s resistance to sulfate attack involve immersing or alternate wetting and drying samples in sodium or magnesium sulfate solutions or a combination of both.
The impact is gauged by the specimen&#39;s loss of strength, expansion, weight loss, or visual examination.
Utilizing sulfate-resistant cement or reducing the calcium hydroxide in hydrated cement paste and casting dense concrete with a lower water-cement ratio boosts concrete&#39;s defense against sulfate attack.

sulfate attack on concrete

Sulfate Attack on Concrete

Sulfate attack on concrete is a deterioration process characterized by a whitish discoloration beginning at the edges and corners, accompanied by cracking and spalling. This phenomenon occurs when sulfates react with the components of hardened concrete, forming compounds like calcium sulfate and calcium sulfoaluminate which occupy more space than the substances they replace, causing the concrete to expand and disrupt.
Sulfates from sources like soil, groundwater, or industrial effluents penetrate the concrete, and their reaction produces gypsum and ettringite. This reaction is similar to the one in cement manufacture where gypsum prevents flash set by reacting with tricalcium aluminate. However, in hardened concrete, this reaction is undesirable as it can lead to structural damage.
The resistance to sulfate attack is a critical aspect that is usually tested by immersing concrete samples in sulfate solutions. This method allows for the observation of changes in the specimen, such as strength reduction, expansion, and weight loss. Visual inspection is also a valuable tool in identifying damage. The use of cement with a low tricalcium aluminate content, such as sulfate-resisting cement and blended cement, can significantly enhance the concrete&#39;s resistance to sulfate attack. The durability of concrete against sulfate attack also relies on achieving a low water-cement ratio for low permeability, a factor that is crucial for reducing the likelihood of damage.

Concrete subjected to sulfate attack typically exhibits a distinct whitish appearance, often first noticeable at the edges and corners, with subsequent ...

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Permeability of Concrete

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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...

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...

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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...

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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 offers a foundational exploration of essential construction materials such as bricks, stones, steel, wood, and concrete, along with fluid mechanics topics like flow over immersed bodies, open channel flow, and dimensional modeling. It also covers key surveying concepts, including leveling, traverse adjustments, curve design, topographic mapping, and geospatial technologies (GPS & GIS). Science-in-action videos showcase laboratory research on materials, fluids, and surveying practices in real-world engineering systems.

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Concrete Damage from Sulfate Exposure

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