Why are cracks in concrete bad?

Non-structural cracks do not affect the integrity and strength of the concrete structure, but they do affect the aesthetics of the concrete structure. However, if left untreated, they can become a problem, as they can serve as a passage for the penetration of materials into the concrete structure.

Why are cracks in concrete bad?

Non-structural cracks do not affect the integrity and strength of the concrete structure, but they do affect the aesthetics of the concrete structure. However, if left untreated, they can become a problem, as they can serve as a passage for the penetration of materials into the concrete structure. When concrete is still in its plastic state (before hardening), it is full of water. As the slab loses moisture during curing, it shrinks.

As the concrete shrinks, the slab may crack to relieve stress. Shrinkage cracks are common and can appear as soon as a few hours after the slab has been poured and finished. They do not normally pose a threat to the structure. This category covers the behaviour of concrete whose shape can no longer be altered without damage.

It includes cracks caused by drying shrinkage as well as those resulting from temperature movements that occur in all materials exposed to the weather. Unless the structure in question allows movement of its members without the development of excessive stresses, extensive cracking can often occur. Crazing cracks after hardening may be the result of excessive buoyancy that tends to draw water and cement to the surface, resulting in weak concrete subject to high shrinkage stresses. More often, they are the result of poor curing.

Other cracks that occur after hardening may be due to lack of adequate reinforcement at corners, insufficient depth of concrete over reinforcement bends, nesting of reinforcing steel in the concrete, or lack of expansion and contraction joints. I am often asked about cracks in concrete foundations. Many owners get nervous when they see cracks in concrete and wonder if they are bad or dangerous. While it is a natural reaction to worry when you see something cracked, the reality is that 95 percent of cracks in concrete are harmless and are nothing to worry about.

Plastic shrinkage cracks Probably the most common reason for first cracks in concrete is plastic shrinkage. This water takes up space and makes the slab a certain size. As concrete is a very rigid material, this shrinkage creates stress in the concrete slab. As the concrete shrinks, it is dragged along its granular sub-base.

This impediment to its free movement creates a tension that can literally pull the slab apart. When the stress is too great for the hardened concrete, the slab cracks to relieve the stress. Especially in hot climates, shrinkage cracks can appear as soon as a few hours after the slab has been poured and finished. While there are many reasons for concrete slabs to crack, most do not lead to serious foundation or structural problems; however, there are times when cracks are a warning sign of foundation or other problems.

In these cases, the homeowner or buyer should check other things in the house to help determine the severity. Excess water in the concrete mix can also increase the likelihood of cracks. When placing concrete, avoid adding additional water to the mix. Excess water will evaporate from the concrete, causing further shrinkage.

Be sure to choose the right concrete mix for your project. Concrete provides structures with strength, stiffness and resistance to deformation. However, these characteristics mean that concrete structures lack the flexibility to move in response to environmental or volume changes. Cracking is often the first sign of concrete deterioration.

However, it is possible for deterioration to occur before cracks appear. Cracking can occur in both hardened and fresh, or plastic, concrete as a result of volume changes and repeated loading. The bad news about typical floating slab construction (where the soil is not compacted) is that anything that causes settlement of the soil poses a risk of cracking and settlement of the slab. Flooding, seepage or simply poor management of roof and surface runoff can send water under a building, causing settlement of the loose soil.

This cracking is the result of a combination of factors that influence the magnitude of the tensile stresses that cause it. The repair method should be selected based on an assessment of the crack and the objective(s) of the repair. If concrete loses moisture from its surface too quickly, it will shrink (faster than the concrete below the surface) causing a condition known as a map crack. Plastic shrinkage cracks occur when wind speed, low relative humidity, high ambient temperature, or a combination of all three, cause water to evaporate from the surface of the concrete faster than it can be replaced by bleeding into the surface.

Review the types of cracks in floor slabs in the previous article and you will have a better idea of the range of damage and the distinction between commetic and more severe cracks in concrete. After fixing all concrete cracks, consider adding an epoxy coating to the garage floor. A cold joint is intentionally placed in the concrete by the contractor when pouring the concrete. Once you understand the cause and significance of the cracks, you should apply the appropriate repair method(s).

If the cracks are rust stained, run lengthwise, are more than hairline cracks, or are worsening, it would be wise to consult a structural engineer. As this settlement occurs, the slab will often develop some cracks due to this settlement, but in the bigger picture, these will not normally be of great concern either. The wire mesh usually comes in rolls or sheets and is placed in the concrete slab, approximately in the centre of the slab; in a 4-inch thick slab it would be about 5 inches from the top and 5 inches from the bottom of the slab. The control joints create a weak spot in the slab so that when the concrete shrinks, it cracks at the joint rather than randomly throughout the slab (see figure).

This increase in volume increases the pressure on the concrete and causes radial cracks as the concrete fails under tensile stresses. I would use a flexible concrete-coloured sealant to keep water out of the joint between the concrete steps and the wood-sided house wall. They haven't gotten worse since you bought the house, but you need to keep them clear of debris so that grass and other plants can't take root and widen the cracks.

Riley Ryan
Riley Ryan

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