What Causes Concrete to Crack

Concrete is one of the most widely used construction materials, known for its strength and durability. Cracked concrete is a common sight, but it doesn’t have to be an inevitable one. Understanding the various factors that contribute to concrete cracking, from external weather conditions to internal material properties, empowers you to take preventative measures and safeguard the integrity of your concrete structures.

Table of Contents:

Concrete cracks can be classified into three main categories: external, internal, and structural factors. External factors include temperature fluctuations, moisture, and chemicals, while internal factors relate to shrinkage and setting. Structural factors include overloading and inadequate reinforcement. Let us explore each of them.

External Factors Causing of Concrete Cracks

Temperature Fluctuations

Concrete naturally expands and contracts with temperature changes. This constant movement can cause internal stress, leading to cracking, especially during rapid changes. For example, a 20°C overnight temperature drop can put significant strain on the material.

Moisture and Humidity

While concrete needs water to cure properly, too much water or excessive moisture can weaken it and make it more susceptible to cracking. Conversely, drying out too quickly due to rapid evaporation can also lead to shrinkage and cracking. Aiming for a moderate moisture content during the curing process is crucial.

Chemicals and De-icing Salts

Concrete is vulnerable to chemical attacks, particularly from de-icing salts like calcium chloride and sodium chloride. These chemicals corrode the concrete, weakening it and increasing the risk of cracks over time. Consider using alternative de-icing methods that are less harmful to concrete, whenever possible.

Internal Factors Causing of Concrete Cracks


Concrete naturally shrinks as it dries and cures, up to 0.5% or more. This shrinkage can create internal stress, leading to cracks. Using a mix with appropriate water content helps minimize shrinkage.

Setting and Curing

Proper setting (initial hardening) and curing (ongoing strength development) are crucial for strong concrete. If the concrete sets too quickly or slowly, it can become weak and susceptible to cracking. Additionally, improper curing, such as rapid drying due to lack of moisture, can significantly increase the risk of cracks and reduce the concrete’s strength.

Poor Mix Design

The mix ratio of cement, aggregates, and water plays a critical role in concrete strength. An incorrect mix ratio, whether too wet, too dry, or with improper proportions, can lead to a weak concrete structure more prone to cracking.

Structural Factors Causing of Concrete Cracks


Concrete is strong, but it has limits. If a structure is overloaded by exceeding its designed weight capacity, the concrete can crack under the excessive pressure. For example, a concrete slab not designed for heavy vehicles might crack under the weight of a truck.

Inadequate Reinforcement

Steel reinforcement is often used in concrete to provide additional strength by distributing and resisting internal stresses. If the concrete is not adequately reinforced, it can crack under stress. For example, a concrete beam without proper reinforcement might crack under the weight of a load.

Design Flaws

Structures with design flaws can lead to stress concentrations in the concrete, increasing the risk of cracking. For example, a concrete column not properly designed to support the load above it might crack under the stress.

Preventive Measures for Concrete Cracks

Proper Mix Design

  • Correct Proportions: Ensure the mix contains the right proportions of cement, aggregates, and water. Too much water weakens the concrete, while too little can make it difficult to work with. Opt for a mix designed for the specific application and environmental conditions.
  • Quality Materials: Use high-quality materials for enhanced durability and strength. Low-quality materials can deteriorate prematurely and crack.
  • Admixtures: Consider additives like plasticizers, superplasticizers, and air-entraining agents to improve workability, strength, and durability.
  • Cement Type: Choose the appropriate cement type based on the application and environment. For example, sulfate-resistant cement is suitable for high-sulfate environments.
  • Aggregate Size and Shape: Use well-graded, clean aggregates with appropriate sizes and shapes to minimize voids and maximize concrete strength.

Adequate Reinforcement

  • Steel Reinforcement: Incorporate steel reinforcement (rebar or wire mesh) for additional strength and stress prevention.
  • Proper Placement: Ensure correct placement of reinforcement within the concrete for maximum support and to avoid weak spots.
  • Corrosion Protection: Protect reinforcement from corrosion with epoxy-coated or galvanized rebar or anti-corrosion coatings.

Proper Curing Methods

  • Moisture Control: Keep the concrete moist during curing to prevent rapid drying. Cover it with a damp cloth or plastic sheeting.
  • Curing Time: Allow the concrete to cure for the appropriate time, typically ranging from 7 to 28 days, depending on type and environment.
  • Curing Compound: Use curing compounds or membrane-forming agents to retain moisture and prevent premature drying.

Joint Placement and Design

  • Control Joints: Incorporate control joints to allow movement and relieve stress, controlling where cracks occur and preventing random cracking.
  • Expansion Joints: Use expansion joints to accommodate temperature-related expansion and contraction. Fill them with flexible material to allow movement without damage.
  • Saw-Cut Joints: Create saw-cut joints in hardened concrete for crack control and aesthetics. Fill them with suitable joint filler.

Maintenance and Repair

  • Regular Inspections: Conduct regular inspections to identify early signs of cracks or damage. Early detection prevents small issues from becoming major problems.
  • Timely Repairs: Repair any cracks or damage promptly to prevent further deterioration. This might involve filling cracks with suitable material, or patching damaged areas.
  • Protective Coatings: Apply protective coatings (sealers or waterproofing compounds) to the concrete surface to prevent moisture ingress and chemical attacks.


Understanding what causes concrete to crack and taking steps to prevent them can save you time, money, and frustration in the long run. By following the simple tips outlined in this guide, you can help ensure that your concrete remains strong, durable, and crack-free for years to come. Remember, even small cracks can lead to bigger problems down the line, so proactive measures are key.

For extra peace of mind and expert advice, consider consulting professionals like Ener-Spray. They offer a wealth of knowledge and solutions specifically tailored to preventing and repairing concrete cracks, ensuring your structures stay strong and beautiful for years to come.

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