45 Questions
Water is not an important ingredient of concrete.
False
Impurities in water may interfere with the setting of cement.
True
Sea water is suitable for mixing concrete.
False
Tap water is not acceptable for mixing concrete.
False
Additive is a material which is added to the batch immediately before or during mixing.
False
Admixture is a material, other than cement, water and aggregates, that is not used as an ingredient of concrete.
False
One of the reasons for using chemical admixtures in concrete mixtures is to reduce the strength of concrete.
False
Sea water increases the risk of corrosion of the reinforcement in reinforced concrete.
True
Chemical admixtures are only used in reinforced concrete.
False
Calcium chloride is suitable for use in reinforced concrete.
False
Retarding admixtures are useful in concreting in cold weather.
False
Sugar is a common accelerating admixture.
False
Retarding action is exhibited by soluble copper salts.
False
ASTM C 494-10 requires Type B admixtures to retard the initial set by at least 2 hours.
False
Admixtures classified as Type D are only water-reducing.
False
Water-reducing admixtures can reduce the water content of the mix by up to 20 per cent.
False
The use of calcium chloride does not contribute significantly to the corrosion of steel reinforcement if concrete is well proportioned and well compacted.
True
Retarding admixtures can prolong the time during which concrete can be transported and placed.
True
Admixtures can be used to remedy poor quality mix ingredients.
False
Admixtures are added to the concrete mix in quantities larger than 5 per cent by mass of cement.
False
Superplasticizers are less effective than traditional plasticizers in reducing water content in concrete.
False
The use of superplasticizers has made it possible to use high water-to-cement ratios in concrete.
False
Type A admixtures are accelerating.
False
Accelerating admixtures are used to slow down the early strength development of concrete.
False
Superplasticizers are relatively inexpensive due to their simple manufacturing process.
False
Calcium chloride is a common retarding admixture.
False
Water-reducing admixtures can be used in pumped concrete or concrete placed by a tremie.
True
The effectiveness of water-reducing admixtures depends only on the type of cement used.
False
Admixtures are classified by their function in concrete.
True
Superplasticizers increase the workability of concrete by reducing the slump.
False
Type F admixtures are high-range water-reducing and retarding.
False
Accelerators are beneficial in high temperatures to avoid shrinkage cracking.
False
The main action of superplasticizers is to attract cement particles and increase their density.
False
Water-reducing admixtures can improve the workability of concrete at a given water-to-cement ratio.
True
Using an accelerator allows earlier finishing of the concrete surface and application of insulation for protection.
True
Superplasticizers can be used to make high-performance concrete with strengths over 120 Mpa.
True
Flowing concrete is subject to excessive bleeding or segregation.
False
The normal dosage of superplasticizers is between 5 and 10 litres per cubic metre of concrete.
False
Air-entraining admixtures are not used in concrete mixes.
False
Damp-proofing and waterproofing admixtures are used to improve the strength of concrete.
False
Workability admixtures are used to increase the strength of concrete.
False
Corrosion inhibiting admixtures are used to prevent corrosion of the reinforcement in reinforced concrete.
True
Fungicidal, germicidal, insecticidal admixtures are used in concrete mixes to improve its strength.
False
Colouring admixtures are used to change the colour of the concrete.
True
Mould releasing agents are used to improve the strength of concrete.
False
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
This quiz explores the role of calcium chloride in concrete and its impact on steel reinforcement, including corrosion and setting delays.
Make Your Own Quizzes and Flashcards
Convert your notes into interactive study material.
Get started for free
