DRYING SHRINKAGE - Printable Version

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DRYING SHRINKAGE - C M Dordi - 07-01-2022

DRYING SHRINKAGE
The driving force for drying shrinkage is evaporation of water from the hydrated cement paste which is exposed to air with a relative humidity lower than that within the capillary pores and the hydrated paste. This driving force depends on the size and shape of the pores and their continuity. It also depends on the relative humidity of the ambient air. The loss of water causes a decrease in volume and consequently causes drying shrinkage.

CAUSES
Both drying shrinkage and creep originate from the same source i.e. the C-S-H paste. It is seen from the above that loss of physically absorbed water from C-S-H results in shrinkage strain. When hydrated cement paste is subjected to a sustained stress the C-S-H will lose a large amount of physically absorbed water depending on the magnitude and duration of the applied stress and the paste will show a creep strain. 

The removal of absorbed water is the main cause of both drying shrinkage and creep strains in concrete. The difference is that drying shrinkage is mainly due to differential RH between the concrete and its surrounding while creep is mainly due to sustained applied stress. 

COMMON LOCATIONS

1 Thin slab (Reinforced or not reinforced)
2 Concrete pavements or roads
3 Thin walls.

TIME OF APPEARANCE
1 Within few days or weaks
2 After several months.

PRIMARY CAUSES
1 In efficient joints in case of pavement or concrete roads
2 In adequate curing.
3 Poor quality aggregates (porous and weak).

SECONDARY CAUSES
1 High cement and water content
2 Use of mineral and chemical admixtures.

REMEDIAL I PREVENTIVE MEASURES
1 Reduce water and cement content.
2 Improve curing.
3 Use dense and strong aggregates.

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