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

해수에 노출 된 콘크리트 구조물은 에트링자이트와 석고의 바늘 모양 결정이 용해되어 다공성을 증가시키고 강도를 감소시킵니다.
반대로, 팽창은 흘수선 위의 콘크리트 기공 내에서 염 결정화로 인한 압력으로 인해 발생할 수 있습니다.
그러나 염 용액은 모세관 작용을 통해 콘크리트를 통해 상승할 수 있으며 손상이 발생하여 콘크리트의 투과성이 중요함을 나타냅니다.
조수 지역의 콘크리트는 지속적인 습식-건조 주기로 인해 크게 저하되는 반면 물에 잠긴 콘크리트는 영향을 덜 받습니다.
콘크리트에 대한 바닷물 손상은 기공이 수산화마그네슘으로 막혀 입구를 막을 때 감소합니다.
수산화 마그네슘은 바닷물의 황산 마그네슘과 콘크리트 중의 수산화 칼슘의 반응으로 석고와 함께 형성됩니다.
때때로 바닷물은 염분 흡수로 콘크리트 손상을 일으켜 부식된 보강재 주변의 콘크리트에 균열을 일으킬 수 있습니다.
바닷물에 저항하기 위해 철근 콘크리트는 보강을 위한 2-3인치의 덮개가 필요하며 위에는 600lbs/yd³ 시멘트, 흘수선 아래에는 500lbs/yd³의 잘 압축된 평면 콘크리트가 필요합니다.

콘크리트에 대한 해수의 영향

Effect of Sea Water on Concrete

해수에 노출된 콘크리트는 에트링가이트와 석고의 용해와 같은 분해를 겪을 수 있으며, 재료의 다공성을 높이고 강도를 감소시킵니다. 반면, 콘크리트 기공 내의 염의 결정화는 특히 증발이 발생하는 수위 위에서 팽창을 일으킬 수 있습니다. 그럼에도 불구하고, 이 팽창은 콘크리트의 투과성으로 인해 해수가 구조물에 침투할 때만 발생합니다.


 조수 표식 사이의 구역에서 규칙적으로 습윤과 건조를 반복하는 콘크리트는 특히 위험에 처해 있으며 영구적으로 잠긴 구역보다 더 심하게 분해되는 경향이 있습니다. 해수로 인한 손상은 황산마그네슘과 수산화칼슘의 반응으로 콘크리트에 형성되는 수산화마그네슘의 침전으로 다소 완화되며, 이로 인해 기공이 막히고 다공성이 감소합니다.


 화학적 효과 외에도 해양 환경의 콘크리트는 서리, 파도 작용 및 마모로 인한 물리적 손상을 입을 수도 있습니다. 이러한 물리적 손상은 특히 콘크리트에 흡수된 염분이 철근 부식에 기여할 때 화학적 열화의 영향을 악화시킬 수 있습니다.


 해수로 인한 손상을 방지하기 위해 황산염 공격에 사용된 것과 유사한 조치를 권장합니다. 여기에는 투과성이 낮은 콘크리트를 사용하고 철근 위에 최소 5.08~7.62cm의 적절한 피복을 보장하는 것이 포함됩니다. 수위 위는 입방미터당 355.97kg, 수위 아래는 입방미터당 296.64kg의 시멘트 함량과 0.40~0.45 이하의 물-시멘트 비율이 권장됩니다. 또한 콘크리트를 철저히 압축하고 시공 조인트에서 정밀한 장인 정신을 발휘하는 것은 해수 공격에 대한 콘크리트의 내구성을 향상시키는 데 중요합니다.

해수에 노출 된 콘크리트 구조물은 에트링자이트와 석고의 바늘 모양 결정이 용해되어 다공성을 증가시키고 감소시킵니다.

Education

교육

JoVE Core

Civil Engineering

토목공학

Unit 1

제1단원

Permeability of Concrete

콘크리트의 투수성

KEY TERMS AND CONCEPTS

주요 용어 및 개념

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 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.

civil engineering

Seawater Damage and Concrete Durability

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