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Questions and Answers
What is the typical compressive strength range of normal-weight concrete at 28 days?
What is the typical compressive strength range of normal-weight concrete at 28 days?
Which type of concrete is primarily used for its thermal insulating properties?
Which type of concrete is primarily used for its thermal insulating properties?
What is the unit weight range of structural lightweight concrete?
What is the unit weight range of structural lightweight concrete?
In which type of concrete is little or no reinforcing steel typically used?
In which type of concrete is little or no reinforcing steel typically used?
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What is the primary use of heavy weight concrete?
What is the primary use of heavy weight concrete?
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What defines no-slump concrete?
What defines no-slump concrete?
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Which of the following aggregates is used in structural lightweight concrete?
Which of the following aggregates is used in structural lightweight concrete?
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What is a characteristic of mass concrete?
What is a characteristic of mass concrete?
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What is the first step involved in the production of concrete?
What is the first step involved in the production of concrete?
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Which material's measurement is required to be accurate within ±1% during batching?
Which material's measurement is required to be accurate within ±1% during batching?
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What is the primary factor that affects the properties of hardened concrete?
What is the primary factor that affects the properties of hardened concrete?
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Which method is generally more accurate for measuring concrete ingredients?
Which method is generally more accurate for measuring concrete ingredients?
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What percentage accuracy is specified for measuring water during batching?
What percentage accuracy is specified for measuring water during batching?
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Which operation is involved after the mixing of concrete?
Which operation is involved after the mixing of concrete?
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In terms of accuracy, how much variance is allowed for aggregates in the batching process?
In terms of accuracy, how much variance is allowed for aggregates in the batching process?
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What is a recommended practice for mixing concrete for minor projects?
What is a recommended practice for mixing concrete for minor projects?
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What is the primary purpose of air-entraining agents in concrete?
What is the primary purpose of air-entraining agents in concrete?
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What effect do water-reducing agents have on concrete mix?
What effect do water-reducing agents have on concrete mix?
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How do retarders function in concrete applications?
How do retarders function in concrete applications?
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What is a key characteristic of accelerators used in concrete?
What is a key characteristic of accelerators used in concrete?
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Which of the following is NOT a function of pozzolans in concrete?
Which of the following is NOT a function of pozzolans in concrete?
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Which additive is known to be corrosive to metals in concrete?
Which additive is known to be corrosive to metals in concrete?
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What commonality do workability agents and water-reducing agents share in concrete mixtures?
What commonality do workability agents and water-reducing agents share in concrete mixtures?
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Which of the following statements about additives in concrete is correct?
Which of the following statements about additives in concrete is correct?
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What is the maximum capacity of standard truck mixers?
What is the maximum capacity of standard truck mixers?
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Which condition must aggregate meet to avoid affecting free water content in a concrete mix?
Which condition must aggregate meet to avoid affecting free water content in a concrete mix?
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What is one capability of truck mixers aside from mixing concrete?
What is one capability of truck mixers aside from mixing concrete?
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What method can be used to calculate the volume of plastic concrete produced?
What method can be used to calculate the volume of plastic concrete produced?
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What must be done if aggregate contains free water when calculating the volume of concrete mix?
What must be done if aggregate contains free water when calculating the volume of concrete mix?
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What is a characteristic of ready-mix concrete (RMC) mentioned in the content?
What is a characteristic of ready-mix concrete (RMC) mentioned in the content?
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How soon should concrete in truck mixers be discharged after mixing starts?
How soon should concrete in truck mixers be discharged after mixing starts?
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What is required for aggregate weight when calculating absolute volume?
What is required for aggregate weight when calculating absolute volume?
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What should be done to ensure proper mixing of concrete in a mixer?
What should be done to ensure proper mixing of concrete in a mixer?
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How often should the mixer drum speed be checked?
How often should the mixer drum speed be checked?
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What is a common method for cleaning the concrete mixer at the end of the day?
What is a common method for cleaning the concrete mixer at the end of the day?
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What is one of the primary functions of central batching plants?
What is one of the primary functions of central batching plants?
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What is the recommended mixing time for a 1 m3 mixer?
What is the recommended mixing time for a 1 m3 mixer?
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How should the consistency of mixed concrete be assessed?
How should the consistency of mixed concrete be assessed?
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What is essential to check before starting up the mixer?
What is essential to check before starting up the mixer?
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What role does a weight batcher play in the mixing process?
What role does a weight batcher play in the mixing process?
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What should the weights of sand and coarse aggregates be based on when using bagged cement?
What should the weights of sand and coarse aggregates be based on when using bagged cement?
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Why is it recommended to add ingredients by weight for batching concrete?
Why is it recommended to add ingredients by weight for batching concrete?
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What is the purpose of the water tank equipped with a dial gauge in a concrete mixer?
What is the purpose of the water tank equipped with a dial gauge in a concrete mixer?
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What adjustment is made to the coarse aggregate weight for the first batch of concrete?
What adjustment is made to the coarse aggregate weight for the first batch of concrete?
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How often should the water gauge in the mixer be recalibrated?
How often should the water gauge in the mixer be recalibrated?
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What is a common method for batching ingredients for small jobs?
What is a common method for batching ingredients for small jobs?
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What can happen if a clean mixer is not used for the first batch?
What can happen if a clean mixer is not used for the first batch?
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What is the main role of the mixer driver in batching concrete?
What is the main role of the mixer driver in batching concrete?
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Study Notes
Concrete Construction
- Concrete is a versatile, economical, and widely used construction material.
- Hardened concrete must meet design strength requirements, be uniform, waterproof, durable, and wear-resistant.
- Desirable properties of plastic concrete include workability and cohesiveness.
- Concrete is classified into various types based on application and density, including normal-weight, structural lightweight, lightweight insulating, mass, heavy weight, refractory, and architectural concrete.
- Normal-weight concrete has a unit weight ranging from 140 to 160 lb/ft³ (2243–2563 kg/m³).
- Structural lightweight concrete has a unit weight less than 120 lb/ft³ (1922 kg/m³).
- Lightweight insulating concrete has a unit weight from 15 to 90 lb/ft³ (240–1442 kg/m³).
- Mass concrete has a unit weight similar to regular concrete, used in structures like dams.
- Heavy-weight concrete uses heavy aggregates and is primarily used for nuclear radiation shielding.
- Refractory concrete is suitable for high-temperature applications like boilers and furnaces.
- Architectural concrete is exposed to view and is used for special shapes, designs, or surface finishes.
Concrete Components
- Aggregate is used to reduce the cost and shrinkage of concrete.
- Aggregate properties strongly impact the quality of the final concrete.
- Proper distribution and shape of aggregate particles are necessary for effective concrete.
- Aggregates need to be strong, resist freezing/thawing, and chemically stable.
- Water is essential for cement hydration and concrete workability.
- Water-cement ratios (typically 0.40 to 0.70 by weight) affect concrete strength, water tightness, and durability.
- Concrete additives include air-entraining agents, water-reducing agents, retarders, accelerators, pozzolans, and workability agents.
- Air-entraining agents enhance concrete resistance to freezing/thawing and scaling.
- Water-reducing agents increase workability and reduce water content
- Retarders delay concrete hardening, while accelerators increase early strength.
Concrete Production
- Batching (measuring ingredients) is crucial for quality concrete.
- Concrete ingredients are often measured by weight.
- Specifications often require ±1% accuracy for cement, ±2% for aggregates, ±1% for water, and ±3% for admixtures to ensure consistency.
- Batching on-site often uses small mixers, while central batching plants are used for large projects.
Batching and Mixing Equipment
- Concrete mixers, aggregate stockpiles, aggregate bins, and weight hoppers, belt conveyors, cement silos, water tanks, admixture tanks, control rooms, and ready-mix trucks are key equipment.
Estimating Mixer Production
- The absolute-volume method calculates batch volumes by summing absolute volumes of mix components.
- The saturated surface dry (SSD) condition is essential for proper aggregate weight calculations in determining batch sizes.
Advantages of Ready-Mixed Concrete
- Ready-mixed concrete offers speed, reduced labor, and material handling.
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Description
This quiz covers the essential properties and classifications of concrete used in construction. Learn about the different types of concrete, their unit weights, and their applications in various structural contexts. Understand the importance of design strength, durability, and workability in concrete mixtures.
