Construction Materials Questions and Answers for Entrance exams on “Placing of Concrete”.
1. The concrete is contained in a timber or steel casing for a certain period after its placing, this casing is known as the ____________
Clarification: The shuttering, formwork or moulds is to be removed when concrete has Harden sufficiently to support its own weight. The formwork should be designed in such a way that it can be easily removed and used again.
2. A ___________ consists of a watertight pipe of diameter about 250 mm to 300 mm.
Clarification: The pipe extends from the level of working platform to the lowest point where concrete is to be deposited. The bottom of the Tremie is provided with the concrete block which is forced out when concrete starts.
3. A _____________ is provided at the top of the Tremie to receive the concrete.
Clarification: It is necessary to keep the bottom end of the Tremie sufficiently deep in the fresh concrete so as to prevent the entry of water in the Tremie. A Hopper is provided at the top to receive the concrete which goes through the Tremie into the water.
4. __________ method is not in common use in case of placing concrete underwater.
Clarification: Tremie Method consist of spreading course aggregate underwater and then the salary of cement and sand its food through the pipe so as to replace the water in the voids of the coarse aggregate.
5. The ____________ is the most effective process of repairing concrete work which has been damaged due to enquiry work or other reasons.
Clarification: In Guniting method, the surface to be treated is cleaned and washed, the nozzle of gun is generally kept at a distance of about 750 mm to 850 mm from the surface to be treated and the velocity of nozzle varies from 120 m/sec to 160 m/sec.
6. The _________ is a mixture of cement and sand, the usual proposition being 1:3.
Clarification: A cement gun is used to deposit the Gunite on the concrete surface under a pressure off about 22 N/cm2 to 30 N/cm2. The cement is mixed with slightly moist sand and the necessary water is added as the mixture comes out from the cement gun.
7. It is observed that in cold weather, the curing is _________ in the initial stages of the setting of concrete.
Clarification: The slow curing of concrete results in higher ultimate strength. The concrete should be cured adequately especially when humidity is low and heat is used to control the temperature.
8. While placing concrete in hot weather, the aggregate should be _____________ to bring down the temperature of concrete.
b) Pre cooled
Clarification: In summer, the usual mistake made while placing concrete is the addition of extra water to the mixture as well as the finish concrete surface. Such an extra water resistance the strength and other properties of concrete.
9. In cold weather conditions, the temperature of concrete should not be allowed to fall below ___________ for at least 3 days after its placing.
a) 5° C
Clarification: At the time of placing, the temperature of concrete should be between 15° Celsius to 25° Celsius and it should not be allowed to come into contact with water having a temperature of 35° Celsius.
10. The ___________ are open at top and their bottoms are provided with openable doors.
Clarification: The concrete is put up in the bucket and it is covered by means of Canvas to protect it from water when bucket is being lowered point. When bucket reaches the desired depth, the bottom doors are opened out and concrete is allowed to drop slowly.
Construction Materials for Entrance exams,