Concrete Properties and Durability

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Questions and Answers

Which factor does NOT affect the strength of concrete?

Aggregate-cement ratio

Water-cement ratio

Presence of air humidity (correct)

Temperature during mixing

What is a key component of Roman cement that distinguishes it from earlier types of concrete?

Gypsum

Hydraulic cement (correct)

Quicklime

Calcium carbonate

Which concrete durability issue is associated with the reaction between water and certain aggregates?

Alkali-aggregate reaction (correct)

Acid attack

Corrosion of reinforcement

Impact of age

What defines the bond strength of concrete?

The adhesion between the concrete and the reinforcement Signup and view all the answers

Which ancient location is credited with an early form of concrete and utilized gypsum mortar?

Egypt Signup and view all the answers

What is the relationship between tensile strength and compressive strength in concrete?

Tensile strength is typically lower than compressive strength Signup and view all the answers

What type of attack on concrete is primarily caused by exposure to seawater?

Corrosion of reinforcement Signup and view all the answers

Who was pivotal in the revival of hydraulic cement knowledge after the Fall of Rome?

John Smeaton Signup and view all the answers

What role does gypsum play in the process of cement hydration?

It increases the setting time by delaying hydration. Signup and view all the answers

Which type of cement is characterized as hydraulic?

Cement with hydration products stable in aqueous environments. Signup and view all the answers

What is the maximum particle size for fine aggregates?

4.75 mm. Signup and view all the answers

How do aggregates affect the performance of concrete?

They enhance volume stability and durability. Signup and view all the answers

What distinguishes admixtures from additives in concrete?

Admixtures are added during mixing, while additives are added at the manufacturing stage. Signup and view all the answers

What percentage of total aggregate mass do coarse aggregates typically form?

55%-70%. Signup and view all the answers

What is a disadvantage of using ready-mixed concrete?

It requires advance order and may lead to wastage. Signup and view all the answers

What is the primary purpose of using aggregates in concrete?

To add volume and reduce the cement content. Signup and view all the answers

Which property of good concrete ensures prevention of premature cracks?

Cohesiveness. Signup and view all the answers

What is the function of hydraulic calcium silicates in Portland cement?

To provide a source of binding during hydration. Signup and view all the answers

What is an advantage of concrete over steel structures regarding maintenance?

Concrete does not require treatment in normal environments. Signup and view all the answers

Which of the following factors negatively affects the uniformity of strength in concrete?

Segregation of the mix. Signup and view all the answers

What is a key feature of the '4-E' criteria for selecting construction materials?

Economic aspects are included. Signup and view all the answers

How does concrete perform under cyclic loading compared to steel?

Concrete has no significant issues related to local stress fields. Signup and view all the answers

Which of the following is NOT a property of good concrete?

Presence of honey-combs. Signup and view all the answers

What is a primary reason for using mixer trucks in ready-mixed concrete transport?

To enhance transportation efficiency and maintain mix workability. Signup and view all the answers

What is the primary purpose of using accelerators in concrete?

To speed up hardening and increase early strength Signup and view all the answers

Which admixture would be most useful for concreting in hot weather?

Set-retarders Signup and view all the answers

What is the role of superplasticizers in concrete mixtures?

To improve workability and reduce water-cement ratio Signup and view all the answers

Which of the following materials are classified as pozzolans?

Granulated blast furnace slag Signup and view all the answers

How do mineral admixtures improve concrete strength?

They chemically react with lime to form cementitious products Signup and view all the answers

What is a possible outcome of using superplasticizers in mass concrete?

Reduction of heat of hydration Signup and view all the answers

What is a key characteristic of mineral admixtures or pozzolans?

They consist of fine siliceous materials that react with lime Signup and view all the answers

What advantage do set-retarders provide in concrete work?

They prevent cold joints during layering Signup and view all the answers

What is a key advantage of concrete structures in terms of vibration resistance?

Greater self weight provides better damping resistance Signup and view all the answers

How does concrete behave at very low temperatures compared to steel?

Concrete maintains ductility while steel becomes brittle Signup and view all the answers

Which factor contributes to the economic advantages of using concrete?

Reduced labor costs and machinery requirements Signup and view all the answers

What is the energy saving percentage when producing 1 ton of concrete compared to steel?

82% Signup and view all the answers

Which of the following incorrectly describes concrete's environmental impact?

Toxic fumes emitted from surface coatings Signup and view all the answers

What density range defines lightweight concrete?

Density < 1800 kg/m3 Signup and view all the answers

Which type of concrete is primarily used for radiation shielding?

Heavy Weight Concrete Signup and view all the answers

Which of the following is NOT an advantage of concrete over steel structures?

Higher tensile strength compared to concrete Signup and view all the answers

Study Notes

Properties of Hardened Concrete

Strength influenced by several factors: water-cement ratio, aggregate-cement ratio, aggregate size and strength, compaction, mixing temperature, curing method, and age.
Tensile strength is a vital property of concrete, essential for structural integrity.
Compressive strength typically surpasses tensile strength in concrete; their relationship is key for structural design.
Bond strength of concrete impacts adhesion between aggregate and cement paste, crucial for overall durability.

Durability of Concrete

Permeability affects the absorption of water and chemicals, leading to potential damage.
Sulphate attack can weaken concrete, especially in environments rich in sulphate salts.
Attack by seawater poses risks due to chlorides and aggressive ions affecting the steel reinforcement.
Acid attack can chemically erode concrete, diminishing its durability.
Alkali-aggregate reaction may cause expansion and cracking, resulting from alkali-silica interactions.
Corrosion of reinforcement can lead to structural failures due to loss of steel strength and integrity.

History and Evolution of Concrete

Ancient uses dated back to 7000 BC in Israel; early forms of concrete were not hydraulic.
Egyptian mortar (2690 BC) combined quicklime, gypsum, and sand, also not hydraulic.
Romans advanced cement technology, introducing hydraulic cement using pozzolan, with the Pantheon dome (128 AD) as a major achievement.
John Smeaton revived Roman cement knowledge in the 18th century, marking the start of modern concrete use in engineering.

Properties of Cement

Cement is a powdered mix composed of lime and clay minerals, which develops binding properties through hydration.
Portland cement is the most common hydraulic cement, consisting of calcium silicates.
Gypsum is often added to regulate setting time.

Aggregates

Aggregate constitutes approximately 75% of concrete volume, enhancing its stability and durability.
Coarse aggregates have particle sizes larger than 4.75 mm, while fine aggregates are smaller than 4.75 mm.

Admixtures

Admixtures are utilized to modify concrete properties; they can be added during mixing.
Types include accelerators for early strength, set-retarders to delay setting times, water-reducers (superplasticizers) for improved workability, and mineral admixtures (pozzolans) that enhance strength and durability.

Production and Properties of Good Concrete

Good concrete must exhibit consistency, cohesiveness, uniform strength, and absence of cracks.

Advantages of Concrete over Steel Structures

Concrete offers superior maintenance (no corrosion), fire resistance, vibration damping, and thermal ductility.
Cost-effective due to the abundance and low cost of materials; requires less skilled labor.
Production of concrete saves energy compared to steel structures.

Types of Concrete

Normal Weight Concrete has a density of approximately 2400 kg/m³ and uses natural aggregates.
Light Weight Concrete is less than 1800 kg/m³, utilizing low-density aggregates.
Heavy Weight Concrete exceeds 3200 kg/m³, applied for radiation shielding.

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Description

Explore the various properties of hardened concrete, including the factors that affect its strength such as water-cement ratio and aggregate-cement ratio. This quiz also discusses the durability of concrete, addressing issues like permeability and resistance to chemical attacks. Test your knowledge on these essential concepts in concrete technology!