9 Causes of Cracks in RC Slabs

7 Causes of Cracks in Reinforced Concrete Slabs

7 Causes of Cracks in Reinforced Concrete Slabs: Numerous variables, such as poor concrete quality, insufficient structural design, insufficient steel bar spacing, wide slab span, and inadequate aggregates, contribute to the formation of cracks and fissures in RCC slabs. While concerns relating to faulty structural design may be prevented at the design stage of the project, the other aspects can be avoided during the building stage.

1. Concrete with Poor Quality

Decreasing the concrete’s quality is one of the factors that contribute to the development of cracks in RC slabs. Inadequate concrete quality leads in decreased concrete strength, more precisely, tensile strength. As a consequence, concrete’s tensile strength achieves its maximum value at very low stress magnitudes.

Incorrect water-cement ratios, insufficient concrete mixing, poor concrete placing, and insufficient consolidation are all problems that might threaten the quality of the concrete. As a result, prepare and pour concrete according to the specified mix specifications and adhere to the right concrete placement techniques.

2. Unsafe 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.

Cracks in Reinforced Concrete Slabs
Patterns of Cracks in Slabs


When the space between primary and distribution reinforcement exceeds the specified spacing, fractures in the RCC slab may emerge.

3. Flexural Cracks

After the hardening condition, these cracks may emerge in reinforced concrete components. Flexural cracks are vertical fractures that originate in the member’s strain zone and extend to the member’s neutral axis. The width of these fissures is often greater towards the member’s mid-span. This is because the zone of greatest reinforcing strain occurs there.

Flexural fractures occur when the tensile tension produced by bending surpasses the concrete’s tensile strength. This is strictly a design problem, and the designer is solely responsible for controlling the breadth of flexural cracks.

Providing a suitable area of reinforcing steel in relation to the load effects on the concrete component prevents flexure cracking.

4. Inadequate Concrete Cover

Inadequate concrete cover decreases the level of protection necessary for steel bars. As a consequence of chloride assaults, steel corrosion occurs, resulting in concrete cracking along steel bars.

Cracks and corrosion in edge of slab 
Cracks and corrosion in edge of slab (source)

5. Shrinkage Cracking

Shrinkage fissures often appear from months to three or four years after casting, depending on the pace of drying. Moisture loss from new concrete results in a volume drop. If any external or internal constraint opposes the shrinking movement, tensions will occur. When the stress surpasses the concrete’s tensile strength, fractures form. Particularly sensitive are thin parts with a wide surface area, such as slabs. Drying out happens at the surface, and hence the first layer to be damaged is the surface layer. The surfaces of large cross-section components may fracture due to the restraint provided by the concrete’s inner section. Concrete close to corners and edges is especially susceptible to cracking due to moisture leakage from neighboring surfaces. There is no conventional pattern for drying shrinkage cracking since the cracks emerge whenever shrinkage movement is restricted.

6. Formwork Errors

Inadequate formwork installation may also contribute to the formation of cracks in the reinforced concrete slab.

7. Durability Issues

The correct choice of concrete constituents, such as aggregate, is critical for minimizing the likelihood of crack initiation in RC slabs. Cracking may occur when alkali-aggregate is used in concrete.

When reinforced concrete slabs are created under adverse environmental circumstances, such as coastal locations, sulfate attacks occur.

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