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Why Does Concrete Crack After Pouring?

Concrete is a building material that has been utilized for centuries and continues to be the foundation of many structures. Despite its popularity and durability, concrete can crack after being poured, which can lead to costly repairs or even structural collapse if left unresolved.

Cracking in concrete is often caused by a variety of factors, such as thermal expansion and contraction due to temperature variation, settling due to gravity, drying shrinkage from water evaporation, improper curing techniques, or incorrect mix designs.

Each factor alone or combined with other factors could potentially cause cracking in freshly-poured concrete; however, it is important to understand each one separately in order to identify the best solution for preventing cracks before they occur.

The Chemistry of Concrete

Concrete is a composite material made up of an aggregate and binder which, when combined with water, forms the hardened product. The aggregate consists of sand, gravel or crushed stone while the binder is cementitious in nature most commonly using Portland Cement.

As the concrete cures through hydration, a series of chemical reactions occur that lead to changes in volume as well as strength development over time. This process can be affected by environmental factors such as temperature fluctuations and moisture content.

When these conditions are not ideal for curing, cracking may result due to differences between external forces on the material and its internal capacity for shrinkage compensation.

Too Much Water in the Mix

Concrete is a composite material composed of water, aggregate, and cement.

pouring water on a cement mix

If too much water is added to the concrete mix before pouring it into its final form, the resulting structure will be porous and weak due to an excess of free-flowing water in the mixture.

This can lead to cracking as the concrete hardens because not enough cement is available to bond all the components together properly.

Additionally, when air bubbles are trapped during the mixing or placing of the concrete, they create spaces that weaken the structural integrity and accelerate early shrinkage cracks.

Poor Installation Techniques

The poor installation techniques often used to create concrete can result in cracking. These techniques include:

  • inadequate preparation of the base or sub-base,
  • insufficient curing time, and
  • incorrect use of reinforcing materials.

When these steps are not followed correctly, the resulting concrete is more likely to crack as it ages due to shrinkage and temperature changes.

Furthermore, if the original mix design was flawed either by inexperienced personnel or a lack of proper ingredients, then this too will increase susceptibility to cracks over time.

Thus, errors during installation can have long-term implications for concrete structures that may not be immediately apparent when first poured.

Temperature Fluctuations After Pouring

Inadequate application of correct installation techniques is only part of the reason why concrete may crack after it has been poured. Temperature fluctuations can also play a role in cracking, as sudden temperature changes cause material expansion and contraction which can create stress on the concrete.

This type of damage to freshly laid concrete is more common in climates where there are significant variations between night and day temperatures or when large amounts of rainfall shortly after pouring.

When such conditions occur, measures should be taken to protect the fresh concrete from exposure to extreme heat or cold that could lead to cracking.

Shrinkage Cracks

Concrete shrinks as it cures, leading to shrinkage cracks. As the curing process continues, these shrinkage cracks will form and widen. The development of such cracks is caused by a decrease in volume due to water evaporation, temperature changes and other chemical reactions that occur during the process of concrete hardening.

When the surface of fresh concrete has dried before the inner layers have had time to catch up with the hydration process, cracking may also result from thermal expansion or contraction brought on by extreme temperatures. Additionally, incorrect placement of joints can lead to uneven drying, resulting in additional cracks.

To reduce the risk of concrete shrinkage cracking, proper curing methods should be employed and adequate joint spacing should be followed during placement.

Settlement Cracks

Settlement cracks are a common cause of concrete cracking after pouring. This type of crack occurs when the soil beneath the slab undergoes consolidation due to moisture, erosion or other causes.

It is typically caused by poor compaction prior to the pour, changes in moisture content that occur during curing, differential shrinkage between various parts of the slab, inadequate reinforcement steel bars used for support and stabilization, and reactive soils with high clay content causing swelling and heaving.

The best way to avoid settlement cracks is to ensure proper preparation before pouring, including compacting properly, using adequate reinforcement steel bars and testing reactive soils. Furthermore, controlling moisture levels throughout the curing process can also help minimize this type of concrete damage.

Excessive Weight on the Concrete

Cracking of reinforced concrete

A further cause of cracking in concrete is excessive weight on the surface.

When a heavy object such as equipment or furniture is placed onto freshly laid concrete, it can result in significant damage to the surface and its underlying structure due to the immense pressure applied by the item. This often causes fracturing of the top layers, resulting in visible cracks which may worsen over time if left unresolved.

It is important for builders and contractors to ensure that any items being moved onto fresh concrete are kept light and well-distributed across the entire surface area to prevent this kind of structural damage from occurring.

Corrosion of Steel Reinforcement

In addition to the excessive weight on concrete, corrosion of steel reinforcements can also cause cracking. The presence of moisture and oxygen accelerates the oxidation process which leads to rust formation on the steel bars embedded in it. This weakens the structure of reinforced concrete, making it more prone to cracking.

When choosing a reinforcing material for concrete structures, one should consider:

  1. The type of environment where the structure will be built;
  2. How much corrosion protection is needed;
  3. Cost implications associated with protective coatings or treatments;
  4. Maintenance efforts are required over time to prevent corrosion.

It is essential that these factors are taken into account as failure to do so could lead to structural damage due to corrosion in the long run.

Inadequate Curing

When concrete is poured, the cement paste begins to hydrate and harden. If it is not adequately cured by controlling temperature and moisture levels during this process, shrinkage cracks can form in the hardened material.

Poor curing of concrete also results in decreased strength and durability as well as increased porosity, permeability, and absorption. These effects may be further exacerbated if poor workmanship or inadequate materials were used initially when mixing the concrete.

The result of these processes can cause a variety of cracking patterns that can appear on walls or pavements after pouring.

Improper Joints

Furthermore, improper joints can also be a cause of concrete cracks. Joints are typically used to control cracking and provide extra strength for the slab. When not done correctly, joints will weaken the structure and lead to uneven loading on one side or another, which causes the slab to crack.

Poor joint design can result in shrinkage cracks due to a lack of reinforcement at vulnerable areas when drying occurs. To ensure that proper joints are established, it is important to use an experienced professional who has experience with correctly designing these structures.

Concrete cracking is a common problem that can be caused by several factors.

It is important to understand the chemistry of concrete and ensure proper installation techniques, such as avoiding too much water in the mix or temperature fluctuations after pouring.

Furthermore, reinforcing steel bars should be used and adequate curing processes completed. Lastly, excessive weight on the concrete or corrosion of reinforcement steel can cause cracking and inadequate joints will weaken the structure.

By following these tips and taking into consideration the type of environment, cost implications, maintenance efforts, and joint design when installing concrete structures, one can ensure a stronger and more durable finish.

If you need assistance with a concrete project, Big Easy Concrete can help. We are experienced in concrete installation and more and can help you design and build any concrete project in the Greater Louisiana area. Contact us today to get started!

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