Name: concrete durability and water penetration
Uploaded: 2024-11-07T14:48:45.000Z
Duration: 1 min 25 s
Channel: JoVE

透過性とは、液体または気体がコンクリート中をどれだけ容易に移動できるかを指します。この特性は、液体を保持し、化学的劣化に抵抗する構造の不透過性を確保するために関連します。
コンクリートの透過性は、コンクリートサンプルの上部を除くすべての側面が密封されている基本的なラボテストで評価されます。次に、加圧水を上面に塗布します。
定常状態に達すると(約10日かかる場合があります)、特定の期間にわたってコンクリートの設定された厚さに浸透した水の量が記録されます。
標準的な標準重量骨材で構成されるコンクリートの場合、透過性はセメントペーストの多孔性によって決まります。
水和セメントペーストの透過性は、ゲル内の小さな細孔サイズによって決定されるだけでなく、より大きな毛細管細孔の存在によっても影響を受けます。
水和が進むと、もともと水で満たされていた空間の一部が塞がれてしまうため、セメントペーストの透過性が低下します。
水とセメントの比率が低い場合(通常は0.6未満)、毛細血管が分節化または分解され、流体の流れが妨げられるため、透過性が低下します。

コンクリートにおける透水性

Permeability of Concrete

コンクリートの透水性とは、液体やガスが材料をどれだけ容易に通過できるかを指します。この品質は、コンクリート構造物の防水性と耐久性、および化学攻撃に対する耐性を評価する上で非常に重要です。コンクリートの透水性は、比較実験室試験によって判定できます。これらのテストでは通常、コンクリートの試験片を側面から密閉し、圧力をかけて上面に水圧をかけ、通過する水の量を測定します。通常、このテストは 10 日間ほどかけて行われ、定常状態に達します。


 コンクリートの透水性は、水セメント比と水和度だけでなく、セメントペーストの空隙率にも影響され、これは細孔サイズの分布によって変わります。毛細管の空隙率は重要な役割を果たします。セグメント化された毛細管は、相互接続された毛細管に比べて透水性が低くなるためです。セメントペーストが水和し続けると、当初水で占められていた空隙が閉じられるため、透水性が低下します。耐久性のあるコンクリートの場合、水セメント比が低い方が有利で、透水性を早く低下させることができます。


 また、コンクリート混合物は密度が高く、透水性を低減するために粒度の整った骨材を使用する必要があることも指摘されています。さらに、養生方法や骨材のサイズなどの要因が透水性に影響を与える可能性があり、望ましい低透水性レベルに達するために霧養生などの特定の養生条件にさらさない限り、蒸気養生コンクリートは通常、湿潤養生コンクリートよりも透水性が高くなります。

透過性とは、液体または気体がコンクリート中をどれだけ容易に移動できるかを指します。この特性は、...

Education

JoVE Core

Civil Engineering

土木工学

Unit 1

ユニット1

コンクリートの透水性

KEY TERMS AND CONCEPTS

主要用語と概念

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 state is reached.

Several features of the concrete mix affect permeability. The water/cement ratio and the degree of hydration both matter. The porosity of the cement paste also plays a major role. Pore size distribution is important, and capillary porosity can change how easily water moves through the material.

Interconnected capillaries allow more flow than segmented capillaries, which reduce permeability. As cement paste hydrates, its permeability drops because voids that once held water are gradually closed. For more durable concrete, a lower water/cement ratio helps the mix reach low permeability sooner. A dense mix with well-graded aggregate also helps reduce permeability. Curing and aggregate size matter too. Steam-cured concrete usually has higher permeability than moist-cured concrete, although fog curing can be used in some cases to reach low permeability levels.

Concrete Durability and Water Penetration

concrete-durability-and-water-penetration

permeability of concrete

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

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 water moves through concrete, how permeability is tested in the lab, and why mix design and curing affect durability and water-tightness.

Concrete Durability and Water Penetration | 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

Concrete Durability and Water Penetration

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