Concrete Mixtures

Topics: Concrete, Reinforced concrete, Deformation Pages: 2 (451 words) Published: December 22, 2012
CE 4201 (Reinforced Concrete)
BSCE-4November 14, 2012

Assignment #1: Chapter 1(Introduction)

1. Name several admixtures that are used in concrete mixes. What is the purpose of each? Air-entraining admixtures are used to increase concrete’s resistance to freezing (relieves the pressure in concrete) and thawing (results to less cracking) and provide better resistance to the deteriorating action of de-icing salts. Accelerating admixtures are used to reduce curing time and protect the concrete and the earlier removal of forms. Retarding admixtures are used to slow the setting of the concrete and to retard temperature increases. They are also used to enhance bonding together of pours. Superplasticizers are used to produce workable concretes with higher strengths while using the same amount of cement. Waterproofing materials are used to retard the penetration of water into porous concretes.

2. What is Poisson’s ratio, and where can it be of significance in concrete work? Poisson’s ratio is the ratio of concrete’s lateral expansion (due to compressive loads) to its longitudinal shortening. It is considered in the analysis and design of arch dams, tunnels, and other statically indeterminate structures.

3. What factors influence the creep of concrete?
Long-terms loads (like sustained compressive loads) result to creep in concrete. The amount of creep depends largely on the amount of stress. Other factors include: curing time, strength, temperature, humidity, cement-water paste percentage, reinforcement, and size of concrete.

4. What steps can be taken to reduce creep?
Lengthen curing time of concrete. Control exposure to high temperatures. Prefer higher humidity areas. Lessen the amount of cement-water paste. Add more reinforcements to compression areas of concrete. Design large concrete members (large volume-to-surface area ratio).

5. What is the effect of creep in reinforced concrete columns that are subjected to axial compression loads?...
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