Understanding the Types of Concrete Cracking in Construction
Concrete is one of the most widely used construction materials in the world. It offers strength, durability, and versatility, making it ideal for a range of structures from homes and roads to skyscrapers and dams. However, one of the most common issues faced during and after construction is cracking in concrete.
While cracking is not always a sign of structural failure, understanding the different types of concrete cracks and their causes is essential for proper construction, maintenance, and repair. In this post, we’ll explore the major types of concrete cracks, what causes them, and how they can be managed or prevented.
 |
Types of Concrete Cracking in Construction |
Why Does Concrete Crack?
Before diving into the types of cracks, it’s important to understand why concrete cracks. Concrete is a composite material made of cement, aggregates (like sand and gravel), and water. As it hardens and gains strength, several internal and external factors can cause stress in the concrete. When this stress exceeds the tensile strength of concrete, cracking can occur.
Common causes of concrete cracking include:
- Shrinkage (both plastic and drying)
- Thermal expansion and contraction
- Settlement of the subgrade
- Overloading
- Corrosion of reinforcing steel
- Poor construction practices
1. Plastic Shrinkage Cracks
When it happens: Within the first few hours after concrete placement
Reasons: Rapid loss of water from the surface during initial setting
Plastic shrinkage cracks are among the earliest types of cracks that can occur. They form while the concrete is still plastic (before it has hardened). When water evaporates too quickly from the surface often due to high temperatures, wind, or low humidity—the surface dries faster than the inner layers, causing tensile stress and cracking.
Appearances:
- Thin, short, and shallow cracks
- Typically appear in parallel patterns
Preventions:
- Use windbreaks or sunshades
- Apply curing compounds immediately after finishing
- Avoid placing concrete during the hottest part of the day
2. Thermal Cracks
It happens: Within the first few days or later due to temperature changes
Reasons: Temperature gradients causing expansion and contraction
Concrete expands when heated and contracts when cooled. If the structure cannot freely expand or contract, internal stress builds up. This can lead to cracking, especially in mass concrete structures where temperature differences between the core and the surface are significant.
Appearance:
- Typically occur at points of restraint or poor joint placement
- Straight or diagonal cracks
Prevention:
- Proper temperature control during curing
- Control the heat of hydration for mass pours
- Use expansion joints
3. Drying Shrinkage Cracks
When it happens: Days to weeks after placement
Reasons: Volume reduction as concrete loses moisture
As concrete cures and dries over time, it shrinks due to loss of moisture. If the movement is restrained by the subgrade, formwork, or reinforcement, tensile stresses develop, leading to drying shrinkage cracks.
Appearances:
- Can extend through the full depth of the slab
- Often random in pattern
Preventions:
- Use proper curing techniques
- Use shrinkage-reducing admixtures.
- Design joints to accommodate movement
4. Cracks Due to Corrosion of Reinforcement
When It happens: Months or years after construction.
Reasons: Rust formation from moisture or chloride attack.
When steel reinforcement inside concrete begins to rust, it expands up to six times its original volume. This causes internal pressure that cracks and spalls the surrounding concrete.
Appearance:
- Horizontal or vertical cracks along the line of rebar
- Often accompanied by rust stains or surface delamination
Preventions:
- Use corrosion-resistant reinforcement
- Ensure adequate concrete cover over rebar
- Avoid exposure to salt or chemicals.
5. Settlement Cracks
When it happens: Shortly after concrete is placed.
Reason: Uneven settlement of the concrete surface or supporting soil
Settlement cracks occur when the concrete settles over a weak or poorly compacted subgrade or around embedded items like pipes or rebar. This can also happen if the formwork is not properly supported.
Appearance:
- Often seen near columns, walls, or other restraints
- Irregular and vertical displacement at cracks
Preventions:
- Use proper reinforcement placement and support
- Ensure proper compaction of subgrade
- Avoid excessive vibration.
6. Structural Cracks
When it happens: Any time during the life of the structure.
Reason: Overloading, design flaws, or foundation movement.
These are the most serious types of cracks as they may compromise the integrity of the structure. Structural cracks are often wide and deep and may continue to grow over time. They can be caused by design errors, unexpected loads, seismic activity, or foundation settlement.
Appearances:
- May appear diagonally on walls or vertically on columns
- Wide, continuous cracks
Preventions:
- Ensure accurate structural design
- Use proper load calculations
- Monitor and maintain foundation integrity.
7. Map Cracking or Pattern Cracking
When it happens: Over time due to surface shrinkage.
Reason: Surface drying or carbonation over time.
Map cracking is a pattern of interconnected cracks, often due to shrinkage or long-term deterioration. It can also occur due to alkali-silica reaction or carbonation, especially in exposed surfaces.
Appearances:
- Occurs mainly on surface plaster or top layer
- Resembles a road map.
Prevention:
- Ensure proper curing and maintenance
- Use quality materials
- Apply protective coatings to exposed concrete.
8. Crazing
When it happens: Soon after finishing.
Reason: Rapid drying of the surface.
Crazing is characterized by a network of very fine, shallow cracks on the surface of concrete. Though not structurally dangerous, it affects appearance and may indicate poor curing or finishing practices.
Appearance:
- Only visible when surface is wet or under light
- Spider web or map-like pattern.
Prevention:
- Avoid over-troweling
- Use proper curing practices
- Reduce water-cement ratio.
9. Diagonal Cracks in Beams and Columns
When it happens: Under heavy loads or seismic stress.
Reason: Shear failure or flexural stress.
Diagonal cracks in structural members like beams and columns can indicate excessive stress or inadequate reinforcement. These are often critical and require immediate attention.
Appearance:
- May appear near supports or midspan
- Diagonal cracks at 45-degree angles.
Prevention:
- Follow design codes strictly
- Provide sufficient shear and flexural reinforcement
- Monitor and inspect regularly.
10. Expansion Cracks
When it happens: Due to temperature changes or moisture.
Reason: Lack of movement joints.
Concrete expands with heat and moisture. If no allowance is made for this movement such as expansion joints cracks will occur to relieve the stress.
Appearance:
- Often vertical or angled
- Cracks near corners or at long, unbroken spans.
- Allow for thermal movement in design
- Install expansion joints at appropriate intervals
Final Thoughts
Concrete cracking is a natural and often unavoidable phenomenon. However, understanding the types of cracks, their causes, and how to prevent or control them is key to building safe and long-lasting structures.
Proper design, construction practices, and maintenance can go a long way in minimizing cracks and preserving the aesthetic and structural integrity of concrete elements.
If you're a builder, engineer, or homeowner, knowing these crack types can help you identify problems early and seek the right solutions before small issues become major failures.