Several Factors Causing Cracks

Several factors like poor concrete quality, improper structural design,
inappropriate steel bar spacing, large slab span, improper aggregates, etc. are
responsible for the development of cracks in RCC slabs. While the issues
pertaining to improper structural design can be eliminated in the design stage,
the other factors can be avoided in the construction stage of the project.
What are the Causes of Cracks in Reinforced Concrete
Slab?
1. Poor Concrete Quality
Compromising with the concrete quality is one of the reasons for crack developments
in reinforced concrete slabs. Poor concrete quality results in lower concrete strength,
specifically, the tensile strength. As a result, the tensile strength of concrete reaches its
maximum limit at a very low magnitude of stress.
Incorrect water to cement ratio, inadequate concrete mixing, improper placement of
concrete, and insufficient consolidation are factors that can jeopardize the concrete
quality. Therefore, prepare and pour concrete according to the designated mix and
follow proper concrete placement procedure.
2. Improper Structural Design
Another cause of crack development in an RCC slab is the low reinforcement ratio
due to errors in the design stage. A lower reinforcement ratio yields a lower slab
capacity to support loads. As a result, the RCC slab cracks at smaller loads.
Figure-1: Patterns
of Cracks in Reinforced Concrete Slabs Due to Improper Structural Design
3. Wrong Steel Bars Spacing
When the spacing between primary and distribution reinforcement is greater than the
designated spacing, then cracks may develop in the RCC slab.
4. Insufficient Concrete Cover

Insufficient concrete cover reduces the required protection for steel bars. As a
result, chloride attacks would cause steel corrosion, leading to cracking of concrete
along steel bars.
Figure-2: Cracks Due to Insufficient Concrete Cover
5. Improper Curing
Improper curing of concrete may cause concrete shrinkage and subsequently initiate
cracks. Moreover, it could reduce the strength of the concrete. The cracks due to
improper curing can be shallow fine cracks that are parallel to each other.
Figure-3: Shrinkage Cracks Appear on Slabs are Parallel to

each Other
6. Large Slab Span

When the span of the slab is longer than that of applicable standards, then the
development of cracks, especially flexural cracks, is highly likely.
7. Errors in Formwork Placement

Improper installation of formworks could also be one of the reasons for crack
development in the RCC slab.
8. Wrong Material Selection

The selection of right concrete constituent, such as aggregate, is essential in reducing
the risk of crack initiation in the reinforced concrete slab. The use of alkali-aggregate
in concrete can cause the development of cracks. The map of cracks due to alkali-
aggregate is shown below.
Figure-4: Cracks in Reinforced Concrete slab Due to Alkali-

aggregate reactions
9. Severe Environmental Conditions

Sulfate attacks occur when the reinforced concrete slab is constructed in harsh
environmental conditions, like, coastal areas. The pattern of cracks due to sulfate
attack can be observed in the following figure.
Figure-5: Cracks Caused by Sulfate Attack
FAQs
What are the causes of cracks in reinforced concrete slabs?
Several factors like poor concrete quality, improper structural design, inappropriate
steel bar spacing, insufficient concrete cover, large slab span, improper aggregates,
and inadequate curing regime are responsible for the development of cracks in RCC
slabs.
How does poor concrete quality lead to crack development in
reinforced concrete slabs?
Compromising with the concrete quality is one of the reasons for crack developments
in reinforced concrete slabs. Poor concrete quality results in lower concrete strength,
specifically tensile strength. As a result, the tensile strength of concrete is surpassed at
a lower stress than expected.
How do environmental conditions initiate cracks in Reinforced
concrete slabs?
Sulfate attacks occur when the reinforced concrete slab is constructed in harsh
environmental conditions, like, coastal areas. The sulfate attack causes crack
development in concrete.

Several Factors Causing Cracks

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Several Factors Causing Cracks

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Several factors like poor concrete quality, improper structural design,

pertaining to improper structural design can be eliminated in the design stage,

4. Insufficient Concrete Cover

Figure-2: Cracks Due to Insufficient Concrete Cover

Figure-3: Shrinkage Cracks Appear on Slabs are Parallel to

6. Large Slab Span

7. Errors in Formwork Placement

8. Wrong Material Selection

Figure-4: Cracks in Reinforced Concrete slab Due to Alkali-

9. Severe Environmental Conditions

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