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Questions and Answers
Water is not an important ingredient of concrete.
Water is not an important ingredient of concrete.
False (B)
Impurities in water may interfere with the setting of cement.
Impurities in water may interfere with the setting of cement.
True (A)
Sea water is suitable for mixing concrete.
Sea water is suitable for mixing concrete.
False (B)
Tap water is not acceptable for mixing concrete.
Tap water is not acceptable for mixing concrete.
Additive is a material which is added to the batch immediately before or during mixing.
Additive is a material which is added to the batch immediately before or during mixing.
Admixture is a material, other than cement, water and aggregates, that is not used as an ingredient of concrete.
Admixture is a material, other than cement, water and aggregates, that is not used as an ingredient of concrete.
One of the reasons for using chemical admixtures in concrete mixtures is to reduce the strength of concrete.
One of the reasons for using chemical admixtures in concrete mixtures is to reduce the strength of concrete.
Sea water increases the risk of corrosion of the reinforcement in reinforced concrete.
Sea water increases the risk of corrosion of the reinforcement in reinforced concrete.
Chemical admixtures are only used in reinforced concrete.
Chemical admixtures are only used in reinforced concrete.
Calcium chloride is suitable for use in reinforced concrete.
Calcium chloride is suitable for use in reinforced concrete.
Retarding admixtures are useful in concreting in cold weather.
Retarding admixtures are useful in concreting in cold weather.
Sugar is a common accelerating admixture.
Sugar is a common accelerating admixture.
Retarding action is exhibited by soluble copper salts.
Retarding action is exhibited by soluble copper salts.
ASTM C 494-10 requires Type B admixtures to retard the initial set by at least 2 hours.
ASTM C 494-10 requires Type B admixtures to retard the initial set by at least 2 hours.
Admixtures classified as Type D are only water-reducing.
Admixtures classified as Type D are only water-reducing.
Water-reducing admixtures can reduce the water content of the mix by up to 20 per cent.
Water-reducing admixtures can reduce the water content of the mix by up to 20 per cent.
The use of calcium chloride does not contribute significantly to the corrosion of steel reinforcement if concrete is well proportioned and well compacted.
The use of calcium chloride does not contribute significantly to the corrosion of steel reinforcement if concrete is well proportioned and well compacted.
Retarding admixtures can prolong the time during which concrete can be transported and placed.
Retarding admixtures can prolong the time during which concrete can be transported and placed.
Admixtures can be used to remedy poor quality mix ingredients.
Admixtures can be used to remedy poor quality mix ingredients.
Admixtures are added to the concrete mix in quantities larger than 5 per cent by mass of cement.
Admixtures are added to the concrete mix in quantities larger than 5 per cent by mass of cement.
Superplasticizers are less effective than traditional plasticizers in reducing water content in concrete.
Superplasticizers are less effective than traditional plasticizers in reducing water content in concrete.
The use of superplasticizers has made it possible to use high water-to-cement ratios in concrete.
The use of superplasticizers has made it possible to use high water-to-cement ratios in concrete.
Type A admixtures are accelerating.
Type A admixtures are accelerating.
Accelerating admixtures are used to slow down the early strength development of concrete.
Accelerating admixtures are used to slow down the early strength development of concrete.
Superplasticizers are relatively inexpensive due to their simple manufacturing process.
Superplasticizers are relatively inexpensive due to their simple manufacturing process.
Calcium chloride is a common retarding admixture.
Calcium chloride is a common retarding admixture.
Water-reducing admixtures can be used in pumped concrete or concrete placed by a tremie.
Water-reducing admixtures can be used in pumped concrete or concrete placed by a tremie.
The effectiveness of water-reducing admixtures depends only on the type of cement used.
The effectiveness of water-reducing admixtures depends only on the type of cement used.
Admixtures are classified by their function in concrete.
Admixtures are classified by their function in concrete.
Superplasticizers increase the workability of concrete by reducing the slump.
Superplasticizers increase the workability of concrete by reducing the slump.
Type F admixtures are high-range water-reducing and retarding.
Type F admixtures are high-range water-reducing and retarding.
Accelerators are beneficial in high temperatures to avoid shrinkage cracking.
Accelerators are beneficial in high temperatures to avoid shrinkage cracking.
The main action of superplasticizers is to attract cement particles and increase their density.
The main action of superplasticizers is to attract cement particles and increase their density.
Water-reducing admixtures can improve the workability of concrete at a given water-to-cement ratio.
Water-reducing admixtures can improve the workability of concrete at a given water-to-cement ratio.
Using an accelerator allows earlier finishing of the concrete surface and application of insulation for protection.
Using an accelerator allows earlier finishing of the concrete surface and application of insulation for protection.
Superplasticizers can be used to make high-performance concrete with strengths over 120 Mpa.
Superplasticizers can be used to make high-performance concrete with strengths over 120 Mpa.
Flowing concrete is subject to excessive bleeding or segregation.
Flowing concrete is subject to excessive bleeding or segregation.
The normal dosage of superplasticizers is between 5 and 10 litres per cubic metre of concrete.
The normal dosage of superplasticizers is between 5 and 10 litres per cubic metre of concrete.
Air-entraining admixtures are not used in concrete mixes.
Air-entraining admixtures are not used in concrete mixes.
Damp-proofing and waterproofing admixtures are used to improve the strength of concrete.
Damp-proofing and waterproofing admixtures are used to improve the strength of concrete.
Workability admixtures are used to increase the strength of concrete.
Workability admixtures are used to increase the strength of concrete.
Corrosion inhibiting admixtures are used to prevent corrosion of the reinforcement in reinforced concrete.
Corrosion inhibiting admixtures are used to prevent corrosion of the reinforcement in reinforced concrete.
Fungicidal, germicidal, insecticidal admixtures are used in concrete mixes to improve its strength.
Fungicidal, germicidal, insecticidal admixtures are used in concrete mixes to improve its strength.
Colouring admixtures are used to change the colour of the concrete.
Colouring admixtures are used to change the colour of the concrete.
Mould releasing agents are used to improve the strength of concrete.
Mould releasing agents are used to improve the strength of concrete.
Study Notes
Water in Concrete
- Water is an important ingredient in concrete that participates in the chemical reaction with cement
- The quality of water is important as impurities can interfere with cement setting, affect concrete strength, cause staining, and lead to corrosion of reinforcement
- Water fit for drinking, with a pH of 6 to 8, is suitable for concrete mixing and curing
- Sea water or water with high chloride content is not suitable for concrete as it can cause corrosion of reinforcement and efflorescence
Admixtures in Concrete
- Admixtures are materials added to concrete to achieve specific properties
- Chemical admixtures are added to the batch during or immediately before mixing
- Additives are materials added during cement clinker grinding at the cement factory
- Admixtures are used to:
- Achieve specific properties
- Maintain quality during mixing, transporting, placing, finishing, and curing
- Overcome emergencies during concreting operations
- Reduce costs
- Properly used admixtures can be beneficial, but they are no remedy for poor mix ingredients, incorrect proportions, or poor workmanship
Types of Admixtures
- Accelerating Admixtures:
- Accelerate early strength development of concrete
- Used in low-temperature concreting, precast concrete, and urgent repair work
- May result in too high a rate of heat development and shrinkage cracking at high temperatures
- Retarding Admixtures:
- Delay the setting of cement paste
- Useful in hot weather concreting to prevent cold joints
- Prolong the time for transporting, placing, and compacting concrete
- Water-Reducing Admixtures:
- Reduce the water content of the mix
- Permit reducing the water/cement ratio while retaining workability or improving workability
- Can be used in pumped concrete or concrete placed by a tremie
- Superplasticizers (High-Range Water Reducers):
- Permit reducing the water content up to 30% without reducing workability
- Allow using w/c ratios as low as 0.25
- Useful in high-performance concrete with fly ash, slag, and silica fume
- Other types of admixtures include:
- Air-entraining Admixtures
- Pozzolanic or Mineral Admixtures
- Damp-proofing and Waterproofing Admixtures
- Gas forming Admixtures
- Air-detraining Admixtures
- Alkali-aggregate Expansion Inhibiting Admixtures
- Workability Admixtures
- Corrosion Inhibiting Admixtures
- Bonding Admixtures
- Fungicidal, Germicidal, Insecticidal Admixtures
- Colouring Admixtures
- Concrete Curing Compounds
- Polymer Bonding Agents
- Polymer Modified Mortar for Repair and Maintenance
- Mould Releasing Agents
- Protective and Decorative Coatings
- Installation Aids
- Floor Hardeners and Dust-proofers
- Non-shrink High Strength Grout
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Description
This quiz explores the role of calcium chloride in concrete and its impact on steel reinforcement, including corrosion and setting delays.
