Why Does Reinforced Concrete Crack When the Casting Dry? Here's the Technical Cause

In the construction world, cracking of concrete after the casting process is often a major concern. Many people immediately blame the quality of the concrete, even though the reinforcing steel also plays a crucial role in preventing structural cracks.

So, why can reinforcing steel "fail" and the concrete still crack when the casting dries? Here's a technical explanation you need to know to avoid making mistakes in your project.

1. Reinforcing Steel Quality Doesn't Meet Standards
Reinforcing steel functions as reinforcement that resists tensile forces in concrete. If the quality of the reinforcing steel is low—for example, it doesn't meet SNI standards, its material content is not homogeneous, or its strength is below specifications—then its bonding strength to the concrete is weakened.

As a result, when the concrete experiences natural shrinkage (shrinkage) as it dries, the reinforcing steel is unable to withstand the tension, resulting in cracks.

Solution: Use high-quality, SNI-certified reinforcing steel from a trusted distributor.

2. Improper Reinforcement Placement and Spacing
Technical errors in the field, such as excessive spacing of reinforcing steel, positioning steel not according to the working drawings, or reinforcement shifting during casting, can cause uneven load distribution.

When the concrete dries and receives preload, poorly reinforced areas are more susceptible to hairline cracks and even structural cracks.

Solution: Ensure that the rebar is installed according to the structural details and securely secured with binding wire.

3. Rebar Diameter Doesn't Match Structural Calculations
Rebar diameters smaller than specified are often used for cost efficiency. However, the diameter of the rebar significantly affects the concrete's ability to withstand tensile forces.

If the rebar diameter is too small, its tensile strength will not be sufficient to withstand the movement of the concrete during the drying process.

Solution: Follow the engineer's structural calculations and do not reduce the rebar specifications.

4. Inadequate Bond Between Rebar and Concrete
Rebar surfaces that are heavily rusted, oily, or dirty can compromise the bond between the rebar and concrete. This can cause slippage between the concrete and the rebar, which can lead to cracking as the concrete begins to harden.

Solution: Use rebar with good surface condition and store the material in a protected area before use.

5. Suboptimal Concrete Curing
While not entirely the fault of the reinforcing steel, a poor curing process (concrete allowed to dry too quickly) can increase the risk of cracking. In this situation, the reinforcing steel works harder to withstand the shrinkage stress of the concrete.

If the quality of the reinforcing steel is less than optimal, cracking will occur more easily.

Solution: Cure according to standards so that the concrete and reinforcing steel work optimally as a single structure.

Conclusion
Cracking of concrete during curing is not only a matter of the concrete mix, but is also greatly influenced by:

Rebar quality

Reinforcing steel specifications and diameter

Field installation techniques

Synergy between concrete and reinforcing steel

Using quality, standard-compliant reinforcing steel is the first step to preventing serious structural problems.

Use Quality Reinforcing Steel for Safer Projects
PT Intisumber Bajasakti provides quality reinforcing steel, meeting SNI standards, and is ready to support your various construction project needs—from small scale to large-scale industries.

📞 Phone: 021-66675999
🌐 Website: intisumberbajasakti.com
✉️ Email: info@intisumberbajasakti.com

Contact our team now for a consultation on the best product and material solutions for your project.

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