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

Seawater-exposed concrete structures experience the dissolution of the needle-shaped crystals of ettringite and gypsum, increasing porosity and reducing strength.
Conversely, expansion can occur due to pressure from salt crystallization within the concrete&#39;s pores above the waterline.
However, the salt solution can ascend through the concrete via capillary action, and damage occurs, indicating the criticality of the concrete&#39;s permeability.
Concrete in tidal zones degrades significantly from constant wet-dry cycles, whereas submerged concrete is less affected.
Sea water damage to concrete is reduced when pores clog with magnesium hydroxide and block the entry.
Magnesium hydroxide is formed with gypsum from the reaction of magnesium sulfate in sea water with calcium hydroxide in concrete.
Sometimes, seawater can cause concrete damage with salt absorption, leading to cracking of concrete around the corroded reinforcement.
To resist seawater, reinforced concrete needs 2 to 3 inches of cover for reinforcement and well-compacted plane concrete with 600 lbs/yd&#179; cement above and 500 lbs/yd&#179; below the waterline.

effect van zeewater op beton

Effect of Sea Water on Concrete

Beton dat wordt blootgesteld aan zeewater kan degraderen, zoals het oplossen van ettringiet en gips, waardoor de porositeit van het materiaal toeneemt en de sterkte afneemt. Daarentegen kan de kristallisatie van zouten in de poriën van het beton uitzetting veroorzaken, met name boven de waterlijn waar verdamping optreedt. Niettemin vindt deze uitzetting alleen plaats wanneer zeewater, mogelijk gemaakt door de permeabiliteit van het beton, erin slaagt de structuur te infiltreren.

Beton in gebieden tussen getijden lijnen, die regelmatige cycli van bevochtiging en droging ondergaan, lopen een bijzonder groot risico en hebben de neiging om ernstiger te degraderen dan gebieden die permanent onder water blijven. De schade door zeewater wordt enigszins verzacht door de afzetting van magnesiumhydroxide, dat zich in het beton vormt door de reactie van magnesiumsulfaat met calciumhydroxide, wat leidt tot verstopte poriën en verminderde porositeit.

Naast chemische effecten kan beton in mariene omgeving ook fysieke schade oplopen door vorst, golfslag en slijtage. Deze fysieke schade kan de effecten van chemische achteruitgang verergeren, met name wanneer zouten die door het beton worden geabsorbeerd bijdragen aan de corrosie van wapeningsstaal.

Om schade door zeewater te voorkomen, worden maatregelen aanbevolen die vergelijkbaar zijn met die tegen sulfaataantasting. Deze omvatten het gebruik van beton met een lage permeabiliteit en het verzekeren van een goede dekking van ten minste 5,08 tot 7,62 centimeter over de wapeningsstaven. Een cementgehalte van 355,97 kilogram per kubieke meter boven de waterlijn en 296,64 kilogram per kubieke meter eronder, samen met een water-cement verhouding van niet meer dan 0,40 tot 0,45, wordt geadviseerd. Daarnaast is het bereiken van een grondige verdichting van het beton en het uitoefenen van nauwkeurig vakmanschap in constructievoegen van cruciaal belang om de duurzaamheid van beton tegen zeewater aantasting te verbeteren.

Effect van zeewater op beton

Seawater-exposed concrete structures experience the dissolution of the needle-shaped crystals of ettringite and gypsum, increasing porosity and reducing ...

Education

JoVE Core

Civil Engineering

Civiele techniek

Unit 1

Permeability of Concrete

Doorlatendheid van beton

KEY TERMS AND CONCEPTS

BELANGRIJKE TERMEN EN CONCEPTEN

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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