Shrinkage Cracks & Prevention

Reasons for Concrete Shrinkage
Figure: Shrinkage Cracks
The best strategy to tackle any problem is to eliminate the factors that lead to the given issue, such as
concrete shrinkage in this case. The following factors are the culprit for concrete shrinkage.
1. Excess Water in Concrete
The workability and handling of concrete needs an adequate amount of water, but the free water in
the concrete is precisely the essential cause of concrete shrinkage.
2. Environmental Factors
Environmental factors like temperature, humidity, and wind velocity are also responsible for concrete
shrinkage.
3. Concrete Quality
Concrete quality with respect to w/c ratio, cement content, heat of hydration, aggregate, and
compaction level.
4. Geometry of Structural Member
Geometrical factors such as the surface-area-to-volume ratio of concrete and depth of concrete can
influence concrete shrinkage greatly. The concrete members smaller in size would suffer higher
shrinkage compared to larger structural members.
Besides, the larger the concrete surface, the wider the concrete area exposed to the environment,
and, as a result, the possibility of shrinkage is higher.
How to Reduce Shrinkage of Concrete at Construction Site?
1. Reduce Water Quantity
The reduction of water quantity can play a crucial role in the reduction of drying shrinkage, but
practice reasonable cautions to maintain workability needed to place and compact concrete. Tests
have shown that decreasing water to cement ratio from 0.45 to 0.35 leads to the reduction of concrete
shrinkage by 50%.
Surface crazing on walls and slabs is an excellent example of shrinkage from drying on a small scale.
Crazing usually occurs when the surface layer of the concrete has higher water content than that of
the interior concrete. The result is a series of shallow, closely spaced, fine cracks.
Reduce both drying shrinkage and settlement cracking by decreasing the concrete's water content as
the wall is placed from the bottom to the top. Using this procedure, bleed water from the lower
portions of the wall will tend to equalize the water content within the wall. This procedure needs
careful control and proper consolidation.
2. Add Additives
The addition of additives is another strategy to decrease concrete shrinkage. Water reducing
admixture and shrinkage reducing admixture can play a crucial role in reducing the shrinkage of
concrete.
The former reduces water content and concrete shrinkage, and the latter declines the internal effect
of shrinkage. Additionally, use shrinkage reducing admixture, which compensates for concrete
shrinkage by creating expansive crystals.
3. Aggregate
Use the optimum practical quantity of aggregate in the concrete mix to reduce drying shrinkage to
minimum possible value. The higher the aggregate stiffness, the more effective it is in reducing the
shrinkage of the concrete. That is why concrete containing sandstone aggregate has a higher shrinkage
rate—about twice that of concrete containing granite, basalt, or limestone.
4. Protect Concrete Surface from Rapid Drying
Fig : Protect Concrete Surface from rapid dryimg
Covering concrete surface would reduce or eliminate the influence of environmental factors on
concrete until the curing process begins. The use of ice or chilled water can help to decline batched
concrete temperature. Employ temporary windbreaks during windy days to decrease wind velocity.
5. Time of Concreting
The selection of proper time for concreting may reduce concrete shrinkage, especially plastic
shrinkage. For instance, pour concrete at night during summer to avoid high temperatures that
concrete may be exposed to during the daytime.
6. Proper Concrete Compaction
Compact concrete properly to avoid shrinkage of concrete. Prevent concrete re-tempering at the
construction site since it increases drying shrinkage because of the increase of water content.
7. Proper Curing
The adoption of proper curing mechanisms can reduce concrete shrinkage. Adequate curing allows
concrete to hydrate appropriately and gain designated strength.
Reinforced concrete slabs would particularly benefit from adequate curing because it enables the
concrete to achieve higher tensile capacity before drying out take place. Steam curing can reduce
concrete shrinkage.
8. Adequate Contraction Joints and Steel Detailing
Proper placement of contraction joints in combination with appropriate detailing of steel bars can
reduce the detrimental effect of concrete shrinkage; control crack development.

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Reasons for Concrete Shrinkage

Figure: Shrinkage Cracks

1. Excess Water in Concrete

4. Geometry of Structural Member

4. Protect Concrete Surface from Rapid Drying

Fig : Protect Concrete Surface from rapid dryimg

6. Proper Concrete Compaction

8. Adequate Contraction Joints and Steel Detailing

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