Name: freeze-thaw damage in concrete
Uploaded: 2024-11-07T14:48:50.000Z
Duration: 1 min 27 s
Channel: JoVE

Estruturas de concreto em climas frios, como meios-fios úmidos à beira da estrada, retêm a umidade, tornando-as vulneráveis à ação do gelo e danos subsequentes.
Os sais de degelo usados nos meios-fios atraem mais água para o concreto, piorando os danos durante os ciclos de congelamento e descongelamento à medida que as temperaturas flutuam.
O principal problema decorrente da ação do gelo é a incrustação da superfície, onde a água penetra na estrutura porosa do concreto e permanece dentro.
À medida que as temperaturas caem e a água congela, a expansão da água congelada exerce pressão sobre o concreto. Essa pressão pode fazer com que a camada externa do concreto rache e lasque.
Outro problema significativo é a rachadura em D, um tipo de dano próximo às bordas e juntas. Essas rachaduras em forma de D indicam problemas estruturais mais profundos, ameaçando a resistência do concreto.
O concreto sem vazios arrastados pelo ar, que fornecem espaço para a expansão da água durante o congelamento, sofre danos graves devido a repetidos ciclos de congelamento e descongelamento.
Cada ciclo faz com que o concreto se expanda, levando a mais rachaduras e, eventualmente, a lascas, que é um processo destrutivo, que separa fragmentos de concreto da estrutura e reduz significativamente a resistência estrutural do concreto.

ação do gelo no concreto

Frost Action on Concrete

Estruturas de concreto em climas frios, como aquelas ao longo das estradas, podem reter umidade. Essa umidade as torna suscetíveis a danos relacionados ao gelo quando as temperaturas caem abaixo de zero. Adicionar umidade piora os danos durante as flutuações de temperatura, levando a congelamento e degelo repetidos. Sais de degelo, espalhados sobre essas estruturas para derreter o gelo, aumentam o ciclo de congelamento e degelo e atraem ainda mais umidade para o concreto.

Esse ciclo de congelamento e degelo causa principalmente incrustações na superfície, onde a água penetra no concreto e congela, expandindo e exercendo pressão. Essa pressão pode fraturar a camada superficial do concreto, resultando em rachaduras e lascas. Quando a água nos poros do concreto congela, ela pode criar um desequilíbrio termodinâmico com a água do gel ao redor, fazendo com que mais água entre e congele, aumentando assim a pressão. Além disso, a pressão osmótica dos sais na água pode forçar mais água para dentro dos poros, intensificando a pressão durante os ciclos de congelamento e degelo.

Mais profundamente no concreto, podem se desenvolver rachaduras em durabilidade perto das bordas e juntas. Essas rachaduras profundas em formato de D indicam problemas significativos de durabilidade com o concreto. O concreto sem vazios com ar incorporado é mais vulnerável a ciclos de congelamento e degelo. Esses vazios são pequenos espaços dentro do concreto que agem como amortecedores, permitindo que a água congelada se expanda sem causar danos. Sem esses vazios, a expansão resulta em mais rachaduras e, eventualmente, leva à lascamento, que ocorre quando partes do concreto se quebram, enfraquecendo a estrutura.

Ação do Gelo no Concreto

Estruturas de concreto em climas frios, como meios-fios úmidos à beira da estrada, retêm a umidade, tornando-as vulneráveis à ação do gelo e danos subsequentes.
O degelo ...

Education

JoVE Core

Civil Engineering

Engenharia Civil

Unit 1

Unidade 1

Freezing and Thawing in Concrete

Congelamento e Degelo em Concreto

KEY TERMS AND CONCEPTS

TERMOS E CONCEITOS-CHAVE

freeze-thaw damage in concrete

Freeze-thaw damage in concrete is a major problem in cold climates. Roadside concrete and other outdoor structures can hold moisture, and that water can freeze when temperatures drop below freezing. When the weather changes again and again, repeated freezing and thawing can weaken the concrete over time.

De-icing salts can make the damage worse. These salts are spread on ice to help melt it, but they also pull more moisture into the concrete and add to the freeze-thaw cycle. One common result is surface scaling, which happens when water enters the concrete, freezes, and expands. The expansion creates pressure that can crack the surface and cause chips.

The pressure can also build inside the pores of the concrete. When pore water freezes, it can create a thermodynamic imbalance with the surrounding gel water, so more water moves in and freezes. Salt in the water can add osmotic pressure, which pushes even more water into the pores. In deeper parts of the concrete, D-cracking can form near edges and joints. These deep, D-shaped cracks show serious durability problems.

Concrete without air-entrained voids is most vulnerable to this kind of damage. Air-entrained voids are tiny spaces in the concrete that act like buffers and give freezing water room to expand. Without them, the expanding ice causes more cracks and can lead to spalling, where pieces of concrete break away and weaken the structure.

Freeze-Thaw Damage in Concrete

frost action on concrete

Freeze-thaw damage in concrete is a major problem in cold climates. Roadside concrete and other outdoor structures can hold moisture, and that water can freeze when temperatures drop below freezing. When the weather changes again and again, repeated freezing and thawing can weaken the concrete over time. De-icing salts can make the damage worse. These salts are spread on ice to help melt it, but they also pull more moisture into the concrete and add to the freeze-thaw cycle. One common result...

frost resistant concrete

Protecting Concrete from Freeze-Thaw Damage

Concrete can break down during freeze-thaw cycles, so frost resistance matters in cold weather. When water inside concrete freezes, it expands and can create internal pressure that leads to cracking. Builders use several strategies to reduce that damage and keep concrete strong. One key method is air entrainment, which adds tiny air bubbles to the mix. These small voids give ice room to expand, so pressure inside the concrete stays lower. The amount of entrained air is usually about 4% to 7%...

air-entraining agents

Freeze-Thaw Protection in Concrete

Air-entraining agents help concrete resist damage in cold climates. They also improve the workability of the mix. Their main role is to reduce cracking when freezing and thawing happen again and again. These agents work by adding tiny air bubbles to the concrete. The bubbles give water room to expand when temperatures drop. They also lower the surface tension of water, which helps form stable, small bubbles instead of weak, accidental voids. The goal is to create many small, evenly spread air...

measurement of air content in concrete

Concrete Air Content Testing Methods

Concrete air content testing helps show how much air is trapped in fresh concrete. This matters because air content affects structural integrity and durability. It is especially important for concrete used in places with severe weather. Proper air content also helps concrete resist freeze-thaw cycles and can improve workability and strength. Several ASTM standards describe how to measure air content in fresh concrete. The pressure method, ASTM C231, is the most common. It uses a sealed chamber...

effects of air-entrainment in concrete

Air Bubbles and Freeze Resistance in Concrete

Air bubbles in concrete help the mix resist damage from freeze-thaw cycles. Air entrainment adds tiny air pockets that work as internal voids. These voids give freezing water room to expand. That reduces internal stress and helps prevent cracks. This protection matters in places with repeated freezing and thawing. Without enough space for expanding ice, concrete can deteriorate faster over time. Air-entrained concrete is designed to limit that repeated stress. It helps protect the structure...

key terms and concepts

Learn how freeze-thaw cycles, de-icing salts, and trapped moisture damage concrete, causing surface scaling, D-cracking, and spalling in cold climates.

Freeze-Thaw Damage in Concrete | 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

Freeze-Thaw Damage in Concrete

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