Name: concrete impact resistance in real use
Uploaded: 2024-11-07T14:48:31.000Z
Duration: 1 min 21 s
Channel: JoVE

衝撃を伴うコンクリート杭を地面に打ち込むか、取り扱い中にプレキャストコンクリート要素に突然の負荷や意図しない衝撃に耐える機械のコンクリート基礎を検討してください。
コンクリートは、これらの衝撃に耐えるのに十分な強度を備えている必要があります。コンクリートの衝撃強度を評価するには、繰り返しの衝撃に対する耐性とエネルギーを吸収する能力を決定する必要があります。
具体的には、コンクリートがリバウンドを示さなくなる前にコンクリートが許容する衝撃の数は、重大な損傷を示しています。
衝撃強度は、角張った形状の粗い骨材や粗い表面を持つ骨材を用いた混合物で増加し、曲げ強度との関係を示しています。
コンクリートの衝撃強度と圧縮強度は、骨材の種類とその保管条件によって関連し、異なります。たとえば、水中に貯蔵されたコンクリートは、乾燥した状態で貯蔵されたコンクリートよりも衝撃強度が低くなります。
骨材の最大サイズを小さくし、ポアソン比を低くし、弾性率を低くすることで、コンクリートの衝撃強度を高めることができます。
適切な衝撃強度を得るには、コンクリート混合物に1立方ヤードあたり670ポンド未満のセメント含有量を使用することが有益です。

コンクリートの衝撃強度

Impact Strength of Concrete

コンクリートの衝撃強度は、杭打ち時や衝撃荷重を受ける機械基礎を支える際の加わる力に対する材料の耐久性を反映する重要な指標です。また、プレキャストコンクリート部​​品を取り扱う際にも、偶発的な損傷を防ぐために不可欠です。衝撃強度は、コンクリートの繰り返し衝撃に対する耐性とエネルギー吸収能力を観察することで評価されます。コンクリートが打撃を受けても反発を示さなくなることは、コンクリートが重大な損傷を受けていることを示す重要な指標です。


 コンクリート混合物の配合は衝撃強度に影響し、粗骨材は角張っていて表面が粗いため、衝撃強度が高くなります。このような混合物は結合力が強く、圧縮強度だけでなく材料の曲げ強度にも大きく寄与すると考えられています。コンクリートの保管条件も衝撃強度を変える可能性があり、湿った状態では乾燥状態での保管に比べて強度が下がるのが一般的です。


 衝撃強度を向上させるには、最大骨材サイズを小さくし、弾性係数とポアソン比が低い骨材を選択します。また、衝撃強度を最適化するには、セメント含有量が 1 ㎥ あたり 355.97 ㎏ を超えないコンクリート混合物を使用することが推奨されます。これらの調整により、コンクリートが受ける可能性のある動的かつ潜在的に損傷を与える力に対して、コンクリートの弾力性を高めることができます。

衝撃を伴うコンクリート杭を地面に打ち込むか、突然の負荷や意図しない衝撃に耐える機械のコンクリート基礎を検討することを検討してください...

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 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 being struck. That response shows how much impact energy the material can take before it fails.

The concrete mix has a strong effect on impact strength. Coarse aggregates that are more angular and have rougher surfaces usually increase impact strength. These mixes suggest a stronger bond and are thought to contribute more to flexural strength, which is resistance to bending, than to compressive strength alone.

Storage conditions also matter. Concrete kept in wet conditions usually has lower impact strength than concrete stored dry. Impact resistance can be improved by using a smaller maximum aggregate size and aggregates with a lower modulus of elasticity and Poisson’s ratio. For the best result, the mix should also use no more than 670 pounds of cement per cubic yard.

Concrete Impact Resistance in Real Use

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

behavior-of-concrete-under-compressive-load

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...

porosity in cement paste

How Cement Curing Changes Porosity

Cement curing changes porosity in the hardened paste. Porosity means the void spaces inside concrete. These spaces affect both strength and durability. When water and cement react, hydration forms a semi-solid paste that traps water in different ways. Some of that water becomes combined water. It makes up about 23% of the cement's dry mass. Other water stays as gel water, which fills very small voids called gel pores. Gel pores account for about 28% of the cement gel volume. The...

total voids in concrete

Concrete Voids and Strength

Concrete voids affect both strength and permeability. They include gel water, capillary pores, and entrapped air. In hydrated cement paste, gel water is held within the cement hydration products. Physically entrapped or adsorbed water also supports the hydration process. As cement hydrates, the space needed for the products from a cubic centimeter of cement is estimated to double. Capillary pores are the open spaces left inside the hydrated paste. Their size depends mainly on the...

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...

microcracking in concrete

How Concrete Cracks Before Failure

Concrete can develop tiny cracks before any outside load is applied. These microcracks usually form at the boundary between coarse aggregate and hydrated cement paste. They often result from small volume changes caused by stress-strain differences, heat, and moisture movement. At first, these microcracks stay stable. They usually do not grow much until the concrete reaches about 30 percent of its ultimate strength. As the load rises, the material can begin to change more quickly. When...

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 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 impact resistance is affected by mix design, aggregate shape, storage conditions, and cement content in pile driving and machinery foundations.

Concrete Impact Resistance in Real Use | 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 Impact Resistance in Real Use

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