In This Short Article We Covers,
- What Is Meant By Shrinkage
- Types Of Shrinkage
WHAT IS SHRINKAGE OF CONCRETE
- Shrinkage Is the decrease in volume of concrete in the absence of load with time.
- In the plastic stage, concrete shrinks in volume due to absorption of water or loss of water.
- Due to bleeding, the surface water evaporate rapidly causing shrinkage and this uneven shrinkage causes shrinkage cracks.
- Shrinkage depends upon the efficiency of curing method as well as water cement ratio and water added.
- Shrinkage can reduce by using low water cement ratio, pre-saturated aggregate, water tight and non-absorbents.
TYPES OF SHRINKAGE
- Plastic shrinkage.
- drying shrinkage.
- carbonation shrinkage.
- Autogenously shrinkage.
If volume reduction in concrete occurs before, it becomes hard or still in plastic stage, called as plastic shrinkage.
The reduction in volume of concrete that occurs primarily due to moisture loss after the concrete has hardened is known as drying shrinkage.
Carbon dioxide present in the atmosphere reacts in the presence of water with hydrated cement.
Calcium hydroxide [Ca(OH)2] gets converted to calcium carbonate and also other cement compounds are decomposed.
Such a complete decomposition of calcium compound in hydrated cement is chemically possible even at the low pressure of carbon dioxide in normal atmosphere.
Carbonation penetrates beyond the exposed surface of concrete very slowly.
The rate of penetration of carbon dioxide depends also on the moisture content of the concrete and the relative humidity of the ambient medium.
Carbonation is accompanied by an increase in weight of the concrete and by shrinkage.
Autogenously shrinkage, also known as “basic shrinkage”
It is the shrinkage due to chemical reactions between cement with water, known as hydration, and do not include environmental effects such as temperature and moisture changes.
Its magnitude is usually ignored in concretes with w/c ratio more than 0.40.
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Author & Editor Of This Blog.
Founder Of “KPSTRUCTURES”