Name: concrete failure patterns under compression
Uploaded: 2024-11-07T14:48:30.000Z
Duration: 1 min 23 s
Channel: JoVE

圧縮力がコンクリートに作用しても、内部の欠陥の端には引張応力が存在し、破壊を引き起こすため、圧縮下でのコンクリートの挙動を理解することは非常に重要です。
一軸圧縮を受けると、コンクリートは通常、加えられた力の方向に平行に走る亀裂を発生させます。
平行亀裂は、圧縮方向に垂直に作用する局所的な引張応力から発生します。これに対して、せん断面の形成により角度のある亀裂が発生する場合があります。
コンクリート試験片が破断すると、通常、加えられた力に平行な2つの平面に沿って破損し、その結果、試験片は応力の方向と一致する細長い柱状破片に破損します。
二軸圧縮では、コンクリートは荷重に平行な平面に沿って破損することが多く、スラブのようなピースが作成されます。
一方、三軸圧縮は、破砕ではなく破砕をもたらし、異なる破壊メカニズムを示しています。
破壊パターンは、直接的な応力条件下でのみの挙動を示します。長さと幅の比率が2以上の試験片は、試験機のプラテンが通常導入する可能性のある追加の横方向の力を最小限に抑えます。

圧縮荷重下におけるコンクリートの挙動

Behavior of Concrete Under Compressive Load

コンクリートは、さまざまな圧縮荷重を受けると、特定の挙動を示します。これを理解することは、コンクリートの構造的完全性を理解する上で重要です。コンクリートが一軸圧縮を受けると、力の方向と平行に亀裂が生じる傾向があります。これらの平行亀裂は、圧縮方向と垂直に発生する局所的な引張応力によって生じます。さらに、せん断面の形成により、斜めの亀裂が生じることもあります。


 この一軸荷重下でコンクリート試験片が破壊されると、通常は力と一致する 2 つの平面に沿って分離し、応力方向を反映した細長い柱状の破片に砕けます。二軸圧縮下では、通常、荷重と平行な平面に沿って破壊が発生し、スラブ状の破片が生成されます。対照的に、三軸圧縮では、破砕挙動が起こり、破壊とは異なる破壊メカニズムを示します。


 観察された破壊パターンと挙動は、直接的な応力条件下でのコンクリートの反応のみを示しています。試験の精度を確保するには、試験片の長さと幅の比を 2 にする必要があります。これにより、試験機の圧版によって発生する可能性のある追加の横方向の力を回避することができます。この特定の設定により、コンクリートの圧縮応力に対する固有の反応を分離することができ、さまざまな建設用途におけるコンクリートの性能と耐久性を評価するために不可欠です。

圧縮下でのコンクリートの挙動は、圧縮力がコンクリートに作用しても、引張応力がコンクリートに存在するため、理解することが重要です...

behavior-of-concrete-under-compressive-load

Education

JoVE Core

Civil Engineering

土木工学

Unit 1

ユニット1

Strength of Concrete

コンクリートの強度

KEY TERMS AND CONCEPTS

主要用語と概念

concrete failure patterns under compression

Concrete failure patterns under compression show how the material responds to different kinds of direct stress. These patterns help explain concrete’s structural integrity. Under uniaxial compression, where force acts in one direction, cracks often form parallel to the load. These parallel cracks come from local tensile stress, which is pulling stress that appears perpendicular to the compression direction.

As uniaxial loading continues, angled cracks may also appear. These cracks are linked to shear planes, which are slanted surfaces where the material can slide and break. The specimen usually fractures along two planes that line up with the force. It then breaks into long, column-like fragments that follow the stress direction.

Concrete behaves differently under biaxial compression, where force is applied from two directions. In this case, failure usually occurs along a plane parallel to the loads. The broken pieces are often slab-like rather than column-like. Under triaxial compression, concrete shows crushing instead of fracturing, which points to a different failure mode.

These fracture patterns matter because they show how concrete responds to direct stress only. Test setup also affects the result. To reduce extra sideways forces from the testing machine platens, the specimen should have a length-to-width ratio of two. This helps isolate the concrete’s own compressive response and supports better testing of strength and durability for construction use.

Concrete Failure Patterns Under Compression

concrete-failure-patterns-under-compression

tensile strength considerations of concrete

tensile-strength-considerations-of-concrete

How Cracks Limit Concrete Strength

Concrete tensile strength is limited by tiny cracks inside the material. The cement paste itself can be much stronger in theory than it is in practice. In real concrete, the measured strength can be up to a thousand times lower than the theoretical value. These small cracks help explain that gap. When a load is applied, stress rises at the crack tips. This idea is described by Griffith's theory of brittle fracture. In brittle materials, cracks can grow quickly once the stress at their tips...

behavior of concrete under compressive load

Concrete failure patterns under compression show how the material responds to different kinds of direct stress. These patterns help explain concrete’s structural integrity. Under uniaxial compression, where force acts in one direction, cracks often form parallel to the load. These parallel cracks come from local tensile stress, which is pulling stress that appears perpendicular to the compression direction. As uniaxial loading continues, angled cracks may also appear. These cracks are linked...

porosity in cement paste

How Cement Curing Changes Porosity

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pore size distribution

Concrete Porosity and Durability

Concrete porosity and durability depend strongly on pore size distribution in hardened cement paste. Capillary pores are much larger than gel pores, and in partially hydrated cement paste they form a connected network that lowers strength and raises permeability. Higher permeability makes concrete more vulnerable to freeze-thaw damage and chemical attack. The risk also depends on the water-to-cement ratio. A higher ratio can leave more space for capillary pores to remain open. As cement...

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water cement ratio

Concrete Strength and Water Balance

Concrete strength depends on the balance between water and cement in the mix. This water-cement ratio is the weight of water compared with the weight of cement. It affects strength, durability, and how well concrete resists environmental stress. Abrams’ law shows that less water usually makes stronger concrete. Water is still needed for hydration, which is the chemical process that binds water and cement. It also helps the mix stay workable and compactable. Some water must be absorbed into the...

aggregate cement ratio

How Mix Ratio Changes Concrete Strength

The aggregate cement ratio changes how concrete performs. It is the weight of aggregate divided by the weight of cement in a concrete mix. This ratio affects strength, workability, and durability, so it is an important part of concrete design. A higher aggregate cement ratio makes the mix leaner. Lean mixes have less cement paste to coat and lubricate the aggregate, so they can be harder to work with. At the same time, they may increase strength because the concrete has less total porosity, or...

transition zone

Concrete Transition Zone and Its Porosity

The concrete transition zone is the thin region where aggregate meets cement paste. It has more pores than the surrounding material, so it is usually weaker at first. The bond around the aggregate comes mainly from Van der Waals forces, which are weak attraction forces between particles. When concrete is compacted, this zone often has a higher water-cement ratio near the aggregate. That extra water can form thin water films around the coarse aggregate. These films increase porosity and help...

relation between tensile strength and compressive strength of concrete

relation-between-tensile-strength-and-compressive-strength-of-concrete

Concrete Strength Testing: Tension vs. Compression

Concrete strength testing compares tensile strength and compressive strength. These two properties are related, but they do not rise at the same rate. Tensile strength usually grows more slowly than compressive strength, so the balance between them changes as concrete gets stronger. Several factors affect tensile strength measurements. The test method, specimen size and shape, aggregate texture, and moisture content can all change the result. Direct tension tests are difficult to perform...

fatigue strength of concrete

Concrete Fatigue Under Repeated Loads

Concrete fatigue describes how concrete can weaken or fail when loads are applied again and again, even when each load is below the material’s strength limit. This property matters because it affects the durability and service life of concrete structures. In materials science and engineering, fatigue is a key reason concrete may not last as long as expected under real use. Concrete can fail in two main ways through fatigue. Static fatigue, also called creep rupture, happens under a constant...

impact strength of concrete

Concrete Impact Resistance in Real Use

Concrete impact resistance matters when a material must handle repeated blows and sudden loads. It is important during pile driving, where concrete piles are driven into the ground. It also matters for machinery foundations that experience impulsive loads and for precast concrete parts that can be damaged during handling. Impact strength is measured by checking how well concrete absorbs energy from repeated impacts. A major sign of serious damage is when the concrete does not rebound after...

abrasion resistance of concrete

Concrete Wear Tests and Surface Durability

Concrete wear tests show how well a surface can stand up to abrasion and long-term use. Abrasion is the wearing away of a material by rubbing, scraping, or contact with moving solids. This property matters because concrete surfaces can lose material under vehicle traffic or when solids carried in water brush against them. The transcript describes three tests used to measure concrete abrasion resistance. In the revolving disc test, three plates rotate against the concrete, and silicon carbide...

reinforcements in concrete

Steel Bars in Concrete Structures

Steel bars in concrete structures help the material carry both compression and tension. Concrete is strong when it is squeezed, but it is weak when pulled. Rebar, or reinforcing steel bars, is placed inside the concrete to handle those tensile forces. Steel is a practical choice because it has a similar coefficient of thermal expansion to concrete. That means both materials expand and contract in a similar way as temperature changes. The steel used for reinforcement is usually made by a...

fiber reinforced concrete

Concrete Strength with Added Fibers

Fiber-reinforced concrete is concrete that includes added fibers to improve strength and durability. It uses hydraulic cement with fine or coarse aggregates, plus separated, non-continuous fibers mixed through the material. These fibers can come from steel, glass, and polymers, as well as natural sources such as sisal and cellulose or manufactured sources such as polypropylene and Kevlar. Steel fibers are often preferred because they are strong and tough. They help concrete resist cracking and...

prestressed concrete

How Concrete Is Preloaded for Strength

Prestressed concrete is a construction method that preloads concrete so it can handle more stress. High-strength steel strands are stretched before or after the concrete is loaded in service. The goal is to put the concrete into compression. That compression helps balance the tension the structure will face later. By reducing tension, prestressing helps limit cracks in the concrete. It can also let a structure carry greater loads or span longer distances than conventional reinforced concrete.

ferrocement

Ferrocement Mesh and Mortar Design

Ferrocement is a construction material made from dense layers of mesh or fine rods covered fully in cement mortar. It is a form of reinforced concrete, but it uses mesh instead of the larger steel bars found in standard reinforced concrete. This structure gives ferrocement its thin, flexible form. The material is built from wire meshes and a mortar made of cement and sand. The mortar is usually mixed in a 1:2 or 1:3 ratio. The water-to-cement ratio is kept between 0.40 and 0.45. This helps the...

non-destructive tests for concrete strength

non-destructive-tests-for-concrete-strength

Concrete Strength Checks Without Breaking It

Concrete strength can be checked without fully breaking the material. Two common methods are the rebound hammer test, also called the Schmidt hammer test, and the penetration resistance test, also called the Windsor Probe test. Both are used to estimate the strength of existing concrete. The rebound hammer test measures the hardness of the concrete surface and gives an indirect clue about strength. A spring-driven mass moves inside a tubular housing and strikes a plunger against the concrete.

key terms and concepts

Learn how concrete cracks, fractures, and crushes under uniaxial, biaxial, and triaxial compression, and why test shape matters.

Concrete Failure Patterns Under Compression | 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 Failure Patterns Under Compression

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