Name: why concrete can fail around rebar
Uploaded: 2024-11-07T14:48:46.000Z
Duration: 1 min 27 s
Channel: JoVE

콘크리트 덩어리 내부에서는 pH가 약 13인 수산화칼슘의 높은 알칼리도가 수동성으로 알려진 상태인 보호용 산화철 층을 생성하여 강철 보강재를 부식으로부터 보호합니다.
다양한 전기화학적 전위로 인해 양극 및 음극 영역이 강철 표면에 형성됩니다.
이 영역은 수화 시멘트의 소금 용액에 의해 연결되어 전해질 역할을 합니다.
양극에서 양전하를 띤 철 이온은 염 용액에 용해됩니다.
대조적으로, 음전하를 띤 전자는 음극으로 이동하여 전해질에 흡수되고 물 및 산소와 반응하여 수산기 이온을 형성합니다.
수산화제2철은 수산기 이온이 철 이온과 결합할 때 형성됩니다. 이후 수산화제2철이 산화되면 녹이 형성됩니다.
또한, 주변 시멘트 페이스트의 염화물 이온은 양극 지점에서 염산을 형성하여 강철의 보호층을 파괴하고 공식 부식을 일으킵니다.
강철이 녹슬면 부피가 증가하고 압력을 가하여 콘크리트 균열 및 쪼개짐으로 이어질 수 있습니다.
에폭시 코팅 또는 아연 코팅된 강철을 사용하거나 콘크리트의 투과성을 줄이면 강철 부식을 줄일 수 있습니다.

철근의 부식

Corrosion of Reinforcement

콘크리트 내부의 철근 부식은 재료의 고유한 특성과 외부 요인에 영향을 받는 과정입니다. 콘크리트에 존재하는 수산화칼슘이 제공하는 약 13의 높은 pH 수준은 처음에는 표면에 수동적인 산화철 층을 형성하여 철근을 보호합니다.


 그러나 시간이 지나고 탄산화, 염화물 침투, 균열과 같은 특정 조건에서는 이 보호 상태가 손상될 수 있습니다. 강철에는 양극 및 음극 영역이라고 하는 서로 다른 전기화학적 전위를 가진 영역이 있습니다. 염을 함유한 수화된 시멘트 페이스트는 이러한 영역을 연결하는 전해질 역할을 합니다. 양극 영역에서 강철의 철은 전해질에 양전하 이온으로 용해되는 반면, 음극 영역에서는 주변 콘크리트의 물과 산소가 관여하는 반응에서 전자가 소모되어 하이드록실 이온을 생성합니다.


 이러한 하이드록실 이온은 용해된 철과 결합하여 수산화철을 생성하고, 이는 더 산화되어 녹이 됩니다. 염화물 이온의 존재는 이 과정을 악화시켜 보호 산화철 층을 공격하는 염산을 형성하여 국부적인 침식 부식을 초래합니다. 이 부식은 강철을 확장하여 콘크리트에 균열과 박리를 일으킬 수 있습니다.


 강철 보강재의 부식을 방지하기 위한 예방 조치로는 강철 자체에 에폭시나 아연과 같은 보호 코팅을 사용하거나 콘크리트의 품질을 개선하여 투과성을 낮추고 부식성 물질의 침투를 막는 방법이 있습니다.

콘크리트 덩어리 내부에서는 pH가 약 13인 수산화칼슘의 높은 알칼리도가 보호막을 만들어 강철 보강재를 부식으로부터 보호합니다.

Education

교육

JoVE Core

Civil Engineering

토목공학

Unit 1

제1단원

Permeability of Concrete

콘크리트의 투수성

KEY TERMS AND CONCEPTS

주요 용어 및 개념

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 regions, which creates a small electrochemical cell.

At the anodic regions, iron dissolves into the electrolyte as positively charged ions. At the cathodic regions, electrons are used in reactions with water and oxygen in the surrounding concrete to form hydroxyl ions. These hydroxyl ions combine with the dissolved iron to make ferric hydroxide, which then oxidizes into rust.

Chloride ions make the problem worse. They can cause localized pitting corrosion by forming hydrochloric acid that attacks the protective iron oxide layer. As rust builds up, the steel expands and can crack the concrete, leading to spalling.

Corrosion can be reduced in a few ways. Protective coatings such as epoxy or zinc can be applied to the steel. Another option is to improve concrete quality so it is less permeable and slows the entry of corrosive agents.

Why Concrete Can Fail Around Rebar

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 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

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 concrete’s high pH protects steel rebar, why carbonation and chlorides trigger rust, and how coatings and dense concrete help prevent cracking.

Why Concrete Can Fail Around Rebar | 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

Why Concrete Can Fail Around Rebar

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