NAME________________________
CONCRETE QUIZ 1
- Distinguish between cement and concrete.
- Name at least three items you have encountered today which are concrete.
- What are the major ingredients for concrete, and what role do they play?
- What is meant by "workable?" Why is it important for concrete to be workable?
- Give an example of an aggregate. What is the practical use for this aggregate in making concrete?
NAME _____________________________
CONCRETE QUIZ 2
- What can be used to slow the hardening of concrete (give example?) Why would slowing this process be desirable?
- What can be used to speed the hardening of concrete (give example?) Why would speeding up this process be desirable?
- Suppose you were in charge of building a skyscraper. What would be your choice for aggregate and why?
NAME______________________________
CONCRETE QUIZ 3
- What will happen to concrete if it dries out too quickly?
- Suppose you were to be the chief designer in charge of building a concrete ship to carry people overseas. What aggregate might you choose to put in your concrete and why?
- Explain what the dormancy period of fresh concrete is. How do contractors make use of the dormancy period?
- Explain how can you measure the consistency of freshly mixed concrete?
NAME________________________
CONCRETE QUIZ 4
- Briefly discuss the importance of a proper water to cement ratio.
- Explain the purpose of a superplasticizer in making concrete.
- Why should gloves be worn when mixing concrete? Be specific.
- Water is important in making concrete, however, it can also be harmful to concrete. Explain this statement.
NAME KEY
CONCRETE QUIZ 1
- Distinguish between cement and concrete.
Cement is a component of concrete. Cement and water make the "glue" which holds concrete together.
- Name at least three items you have encountered today which are concrete.
Answers will vary.
- What are the major ingredients for concrete, and what role do they play?
cement- reacts with water to form "glue"
water- reacts with cement, the amount also determines strength
aggregate- makes concrete stronger, more durable, and less costly
- What is meant by "workable?" Why is it important for concrete to be workable?
Cement which is workable is able to be poured into forms without difficulty. A slump test is used to measure workability.
- Give an example of an aggregate. What is the practical use for this aggregate in making concrete?
gravel, sand, vermiculite, perlite,
Aggregate makes the concrete stronger and cheaper.
NAME__KEY________________________
CONCRETE QUIZ 2
- What can be used to slow the hardening of concrete (give example?) Why would slowing this process be desirable?
Sugar can be added to the concrete to retard hardening. For example, if the concrete needs to be transported a long distance, then a retarding admixture would be desired.
- What can be used to speed the hardening of concrete (give example?) Why would speeding up this process be desirable?
Calcium chloride solution can be added to speed the hardening of concrete. For example, in cold weather it is desirable to speed up the hardening process and produced higher heat of hydration.
- Suppose you were in charge of building a skyscraper. What would be your choice for aggregate and why?
The aggregate would depend upon how the concrete is to be used in the building. Lightweight aggregates like shale are used for insulating properties. However, normal weight aggregate would be required for strength. Availability and economy of aggregate are important, too.
NAME__KEY________________________
CONCRETE QUIZ 3
- What will happen to concrete if it dries out too quickly?
Concrete will most likely crack due to drying shrinkage. The hydration reaction which strengthens concrete will be halted from lack of water resulting in weaker concrete.
- Suppose you were to be the chief designer in charge of building a concrete ship to carry people overseas. What aggregate might you choose to put in your concrete and why?
A lightweight aggregate would be desirable for building a ship needing to float. However, the boat would be dangerous because of poor tensile properties of concrete. It would have to be reinforced to be safe.
- Explain what the dormancy period of fresh concrete is. How do contractors make use of the dormancy period?
The dormancy period of fresh concrete is the period during which the concrete is in a plastic state and the reaction is very, very slow. This state lasts from 1 to 3 hours and allows contractors to transport concrete to the job site and consolidate it before it hardens. After the dormancy period, the hydration reaction accelerates, and the concrete sets and becomes hard.
- Explain how can you measure the consistency of freshly mixed concrete?
A slump test can be performed on freshly mixed concrete to determine its consistency. This is done by pouring it into an inverted cup with the bottom cut out. Once the cup is removed, the concrete is observed. It is desirable that the concrete stay 50-75% of its original height for good workability.
NAME__KEY__________________
CONCRETE QUIZ 4
- Briefly discuss the importance of a proper water to cement ratio.
The water to cement ratio determines the strength of concrete. The less water that is used to obtain a workable concrete, the more strength the resulting hardened concrete will have. However, remember that workability is lost if water to cement ratio is too low.
- Explain the purpose of a superplasticizer in making concrete.
A superplasticizer is an admixture which is used to make concrete more workable with the use of less water. Using a superplasticizer will result in a stronger concrete because less water is used.
- Why should gloves be worn when mixing concrete? Be specific.
Gloves should be worn while mixing concrete because one of the products of the hydration reaction is calcium hydroxide, a base. In fact, upon mixing concrete, the pH rises to 12 which means the solution is strongly basic. This can burn, irritate, and dry out the skin.
- Water is important in making concrete, however, it can also be harmful to concrete. Explain this statement.
Water transports harmful substances that lead to concrete degradation. Water is the central issue in freeze-thaw damage of concrete.
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