Question

Consider the following forms of water in a hydrated cement paste:

1. Capillary water

2. Chemically combined water

3. Interlayer water

4. Adsorbed water

Which of the above forms of water will on its/their removal, cause shrinkage of the paste?
1. 1, 2 and 3
2. 1, 2 and 4
3. 2, 3 and 4
4. 1, 3 and 4

Answer 1

Correct Answer - Option 4 : 1, 3 and 4

Concept:

Shrinkage in concrete: It can be defined as a decrease in either length or volume of concrete material resulting from changes in moisture content or chemical changes.

Shrinkage is time-dependent and its value includes plastic shrinkage, autogenous shrinkage, drying shrinkage.

• Plastic shrinkage is contraction in volume due to water movement from the concrete while still in the plastic state or before it sets. Loss of water by evaporation from the surface of the concrete in different layers or by the absorption by aggregate or subgrade is believed to be the reason for plastic shrinkage.
• Drying shrinkage is the contraction in volume due to loss in moisture from the concrete while drying. It is the loss of capillary water and water held in gel pores that cause the change in the volume.
• Autogenous shrinkage is the change in volume due to the chemical process of hydration of cement, exclusive of effects of applied load, and change in either thermal condition or moisture content.

Thus, the cause of shrinkage in hydrated cement paste is due to the removal of moisture in the form of capillary water, interlayer water, and adsorbed water.

The chemically combined water does not take part in shrinkage and cannot be removed by the process of shrinkage.