41. The term “retarder” in cement refers to a chemical admixture used to:
a) Slow down the setting time
b) Extend the working time
c) Improve the workability
d) Speed up the setting time
View Answer
Correct answer: a) Slow down the setting time
Explanation: A retarder is a chemical admixture added to cement to slow down the setting time. It is useful in hot weather conditions or when a longer working time is needed.
42. The term “air entrainment” in cement refers to the process of:
a) Increasing the air content in concrete
b) Decreasing the air content in concrete
c) Controlling the water-cement ratio
d) Enhancing the workability of cement paste
View Answer
Correct answer: a) Increasing the air content in concrete
Explanation: Air entrainment is the process of intentionally incorporating tiny air bubbles into concrete to increase its resistance to freeze-thaw cycles and improve workability. This is achieved by using air-entraining agents or admixtures.
43. The term “plasticizer” in cement refers to a chemical admixture used to:
a) Increase the water-cement ratio
b) Improve the workability and flowability of the cement paste
c) Accelerate the setting time
d) Reduce the shrinkage of concrete
View Answer
Correct answer: b) Improve the workability and flowability of the cement paste
Explanation: A plasticizer, also known as a water-reducing admixture, is added to cement to improve its workability and flowability without significantly increasing the water-cement ratio. It enhances the ease of mixing, placing, and finishing of the concrete.
44. The term “superplasticizer” in cement refers to a chemical admixture used to:
a) Increase the water-cement ratio
b) Improve the workability and flowability of the cement paste
c) Accelerate the setting time
d) Enhance the compressive strength of concrete
View Answer
Correct answer: b) Improve the workability and flowability of the cement paste
Explanation: A superplasticizer, also known as a high-range water-reducing admixture, is used to significantly improve the workability and flowability of the cement paste without increasing the water-cement ratio. It allows for better placement and compaction of concrete.
45. The term “reinforced cement concrete” (RCC) refers to:
a) Concrete made with recycled materials
b) Concrete with added reinforcement bars or fibers
c) Concrete used for decorative purposes
d) Concrete with improved workability
View Answer
Correct answer: b) Concrete with added reinforcement bars or fibers
Explanation: Reinforced cement concrete (RCC) is a composite material consisting of concrete in which steel reinforcement bars or fibers are embedded. The reinforcement enhances the tensile strength and ductility of the concrete, allowing it to resistcracking and withstand higher loads.
46. The term “permeability” of concrete refers to its:
a) Ability to resist compression
b) Resistance to chemical attack
c) Resistance to temperature variations
d) Ability to allow the passage of fluids
View Answer
Correct answer: d) Ability to allow the passage of fluids
Explanation: Permeability refers to the ability of concrete to allow the passage of fluids, such as water or gases. Low permeability is desired to prevent water penetration, corrosion of reinforcement, and durability issues.
47. The term “workability” of concrete refers to its:
a) Strength and durability
b) Resistance to freeze-thaw cycles
c) Ability to be easily mixed, placed, and compacted
d) Resistance to chemical attack
View Answer
Correct answer: c) Ability to be easily mixed, placed, and compacted
Explanation: Workability refers to the ease and ability of concrete to be mixed, placed, and compacted with minimal effort. It relates to the concrete’s consistency, flowability, and ability to fill molds or formwork without segregation.
48. The term “curing” of concrete refers to the process of:
a) Adding admixtures to concrete mix
b) Mixing cement with aggregates and water
c) Applying a protective layer to the concrete surface
d) Providing a favorable environment for hydration and strength development
View Answer
Correct answer: d) Providing a favorable environment for hydration and strength development
Explanation: Curing is the process of maintaining adequate moisture and temperature conditions to facilitate the proper hydration and strength development of concrete. It ensures optimal hydration and enhances the durability and strength of the concrete.
49. The term “prestressed concrete” refers to a type of concrete in which:
a) The water-cement ratio is reduced for higher strength
b) Steel reinforcement is added to improve durability
c) Tensioned steel tendons or cables are incorporated to induce compressive stress
d) Lightweight aggregates are used to reduce the weight
View Answer
Correct answer: c) Tensioned steel tendons or cables are incorporated to induce compressive stress
Explanation: Prestressed concrete is a type of concrete in which steel tendons or cables are tensioned before the concrete is cast. The tensioning of tendons induces compressive stress in the concrete, which enhances its strength and resistance to bending and cracking.
50. The term “concrete mix design” refers to the process of:
a) Determining the proper water-cement ratio for concrete
b) Selecting suitable aggregates for concrete production
c) Proportioning and selecting the constituents of concrete mix
d) Determining the compressive strength of concrete
View Answer
Correct answer: c) Proportioning and selecting the constituents of concrete mix
Explanation: Concrete mix design involves proportioning and selecting the appropriate constituents of the concrete mix, including cement, aggregates, water, and admixtures, to achieve the desired properties and performance of the concrete. It considers factors such as strength requirements, workability, durability, and environmental conditions.
