Understanding the Causes of Concrete Cracking
However, it is necessary to understand some of the causes of the cracks before taking preventive measures. There are various causes of cracks, each requiring a different solution.
- Shrinkage: The concrete contracts as it hardens because of the evaporation of water. The drying and setting processes result in a reduction in the volume of water, and hence in the volume of concrete. If this shrinkage is not controlled, it is likely to crack, which needs to be avoided at all costs.
- Temperature Changes: Concrete is sensitive to temperatures and undergoes changes in size depending on the temperature of its surrounding environment. The effects of heat are that it causes the material to expand, while the effects of cold are that it causes the material to contract. Such expansion and contraction can put pressure on the material’s surface, leading to cracks.
- Improper Mixing: This is when the concrete is not mixed properly, and this may result in the concrete having poor strength and therefore the weak areas that are prone to cracking. The proportion of water to cement also influences concrete strength, and the use of low-quality materials will impact it as well.
- Excessive Load: This is a factor that can lead to cracking of a concrete surface, especially if it is overloaded beyond its capacity. This is especially so with driveway, walkway, and floor surfaces that are likely to be used by heavy vehicles or equipment.
- Poor subgrade preparation: The ground on which concrete is laid is known as the subgrade, and this should be well prepared. A weak or poorly compacted subgrade can cause the ground to subside or shift, leading to cracks in the concrete surface.
- Moisture Issues: Water is one of the most important elements in the construction process of concrete, but it is also one of the most dangerous elements that can cause more harm to the concrete. During curing, the presence of moisture beneath or on the concrete surface can create pressure, leading to cracking. Water can also degrade concrete over time, which leads to deterioration of the material.
Proper Concrete Mix and Placement
To avoid cracking, it is important to follow the following steps when handling concrete: mixing and placing. The ratio of cement, water, and aggregates (fine aggregate-sand, coarse aggregate-gravel or crushed stone) should be proper. It is a ratio of water to cement, and the problem is that if the water-to-cement ratio is high, the mixture becomes weak, and if it is low, it becomes difficult to work with. Compact the concrete uniformly to prevent cracks and promote uniform curing. Ensure that the aggregates used are clean and free from contaminants, and do not tamper with the mixture after it has been poured. It should be allowed to settle on its own and de-aired so that a strong and crack-free surface is formed.
Reinforcement Techniques
Preventing cracks is another major factor where the right reinforcement of the concrete used in construction can be employed. Reinforcement assists in spreading surface stresses and minimizes crack formation resulting from shrinkage, thermal expansion, and other forces.
- Rebar and Wire Mesh: The steel used for reinforcement comes in the form of rebar or reinforcing bars or wire mesh in the construction of concrete structures. This imparts tensile strength to the concrete and prevents it from cracking under pressure. Rebar should be placed in the middle of the slab, while the wire mesh can be used in small projects such as parking lots or pathways.
- Fibers in Concrete: The addition of synthetic or steel fibers to the concrete mix can reduce cracking. These fibers improve concrete’s tensile strength, thereby reducing the likelihood of cracks. This is particularly useful when dealing with surfaces under heavy pressure or subjected to high temperatures.
Control Joints and Expansion Joints
To control concrete surface shrinkage and expansion, it is necessary to incorporate control joints and expansion joints, respectively. These joints are incorporated into the concrete structure to accommodate its expansion and contraction without developing cracks.
- Control Joints: These are designed cracks that are provided in the concrete to control the direction and location of cracking. These joints are normally placed at specific distances and can be created by using a saw or a trowel to scratch the concrete surface before it hardens. Control joints are used to prevent and contain random cracking since the concrete will crack at the joints intentionally.
- Expansion Joints: Expansion joints are provided in concrete structures to permit free movement of concrete due to thermal movements. These joints are typically used in large slabs, such as highways, bridges, and the foundations of buildings and structures. Expansion joints are also sealed with a compressible material to ensure that the pressure exerted on them does not cause strain on the concrete and, consequently, the formation of cracks.
Curing and Moisture Control
Curing concrete is one of the critical steps that help prevent cracks. Curing enables the concrete to gain strength over time because it protects it from drying out quickly by keeping it in a wet condition.
- Water curing: After placing the concrete, it is advisable to cover it with water for at least 7 days, particularly if the weather is hot. This can be achieved by using water sprays on the surface or placing wet burlap or a plastic sheet on the concrete surface to retain moisture.
- Curing Compounds: In the instances where water curing is inconvenient, curing compounds can be used to cover the concrete surface to retain water. These compounds create a barrier that helps the concrete maintain the right moisture content during curing.
- Over-wetting: Although water is essential in the curing process, excessive water can cause the surface to crack. Prevent water on the surface, which can dry and cause shrinkage cracks.
Proper Subgrade Preparation
The surface on which the concrete is poured is just as crucial as the material itself. A good subgrade is required to support the concrete load and prevent any movement that could cause cracking of the concrete surface.
- Compaction: The ground on which the concrete is to be placed should be compacted to ensure that it can support the structure well. So if the soil is loose or uncompact, it is likely to settle unevenly, leading to cracks. Among them, the subgrade must be compacted well to provide a good base for the concrete.
- Leveling: The subgrade should be leveled before laying concrete. If the surface is uneven, stress points will form, leading to concrete cracking. Level the area with leveling tools to ensure the ground is flat and properly leveled for the building’s construction.
Conclusion
To avoid cracks in concrete surfaces, proper craftsmanship should be observed throughout mixing, placing, reinforcement, and curing. It is important to understand the causes of cracking and prevent them to avoid damaging concrete surfaces and prolong their lifespan. Some vital factors in subgrade preparation, jointing, and curing are as follows. By following the above preventive measures, you can protect concrete surfaces from cracking and help ensure they remain strong and durable for a long time.