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Concrete Engineering

COLD WEATHER CONCRETING

INTRODUCTION
The period developed when the mean day to day temperature falls below 40 C for more than three consecutive days is called cold weather and the concreting done in that period is referred to as cold weather concreting. However, special conditions are to be maintained when finishing, placing, curing, and protecting concrete from severe weather conditions. As during winter conditions can change abruptly, better planning in execution of the work is essential.

When concrete is in plastic state and it freezes, then strength reduces by 50% which in turn affects its durability and workability. Hence, it should be protected from freezing until it attains a minimum of 3.5 MPa.

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Self Compacting Concrete

INTRODUCTION
Self compacting concrete is a type of concrete that needs no mechanical vibration or any external source for vibration for its compaction. It can be placed under its own weight and it is cohesive much to be handled without bleeding or segregation. However, the circumstances under which it is made should be free from any kind of noise or any kind of vibration that may damage or alter the property of such concrete. Such concrete is used specially in places where compacting is difficult. Hence it has been gaining traction since its discovery and is more used in important works to ensure structural performance and safety. It is widely used in various important project sites, drilled shafts, retaining systems, pipes, conduits, columns, floor finishing and many more.
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What are various types of Admixtures?

INTRODUCTION
Admixtures are added to the concrete mix to reduce water content, accelerate or decelerate the setting property, make concrete light and modify concrete properties. They are added immediately before or during the mixing of concrete. Excessive amount of water may lead to excessive bleeding and segregation that is why admixtures are added to control such constituents of concrete. This imbalance makes the concrete weak and the strength will also be affected. Many admixtures provide the combination of Superplasticizers, plasticizers or air entrainers. In laboratories, the admixtures are added during concrete preparation but in field not much time can be given on mixing and making concrete appropriate for using quickly. Hence, admixtures are added in cement clinkers formation and then transported to the site for ready to use.
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Factors Affecting Strength And Workability Of Concrete

INTRODUCTION
Strength and workability are both dominating factors in the making of concrete. Strength can be increased by increasing cement content but this in fact reduces the workability. Moreover,the water content can be increased for better workability, but this affects the strength. Hence,a perfect balance is to be maintained for both strength and workability. Furthermore, besides cement and water content, some other factors contribute greatly, which will be discussed as follows.
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Methods of Concrete Mix Design For Medium Strength Concretes

INTRODUCTION
The available mix design methods are mostly dependent on charts, graphs and empirical relations from repetitive experiments following the same principle with a little bit of variations in different mix methods. Some of the commonly known design methods are-
1. Trial and Adjustment method of mix design
2. British DoE mix design method
3. ACI mix design method
4. Concrete mix proportioning-IS Guidelines
5. Rapid method for mix design
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