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Which factor does NOT affect the strength of concrete?
What is a key component of Roman cement that distinguishes it from earlier types of concrete?
Which concrete durability issue is associated with the reaction between water and certain aggregates?
What defines the bond strength of concrete?
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Which ancient location is credited with an early form of concrete and utilized gypsum mortar?
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What is the relationship between tensile strength and compressive strength in concrete?
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What type of attack on concrete is primarily caused by exposure to seawater?
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Who was pivotal in the revival of hydraulic cement knowledge after the Fall of Rome?
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What role does gypsum play in the process of cement hydration?
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Which type of cement is characterized as hydraulic?
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What is the maximum particle size for fine aggregates?
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How do aggregates affect the performance of concrete?
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What distinguishes admixtures from additives in concrete?
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What percentage of total aggregate mass do coarse aggregates typically form?
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What is a disadvantage of using ready-mixed concrete?
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What is the primary purpose of using aggregates in concrete?
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Which property of good concrete ensures prevention of premature cracks?
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What is the function of hydraulic calcium silicates in Portland cement?
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What is an advantage of concrete over steel structures regarding maintenance?
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Which of the following factors negatively affects the uniformity of strength in concrete?
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What is a key feature of the '4-E' criteria for selecting construction materials?
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How does concrete perform under cyclic loading compared to steel?
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Which of the following is NOT a property of good concrete?
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What is a primary reason for using mixer trucks in ready-mixed concrete transport?
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What is the primary purpose of using accelerators in concrete?
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Which admixture would be most useful for concreting in hot weather?
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What is the role of superplasticizers in concrete mixtures?
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Which of the following materials are classified as pozzolans?
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How do mineral admixtures improve concrete strength?
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What is a possible outcome of using superplasticizers in mass concrete?
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What is a key characteristic of mineral admixtures or pozzolans?
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What advantage do set-retarders provide in concrete work?
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What is a key advantage of concrete structures in terms of vibration resistance?
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How does concrete behave at very low temperatures compared to steel?
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Which factor contributes to the economic advantages of using concrete?
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What is the energy saving percentage when producing 1 ton of concrete compared to steel?
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Which of the following incorrectly describes concrete's environmental impact?
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What density range defines lightweight concrete?
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Which type of concrete is primarily used for radiation shielding?
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Which of the following is NOT an advantage of concrete over steel structures?
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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!