Why Does Concrete Crack?
Cracks in concrete are common — but not all cracks mean something’s wrong. Understanding why they form helps you identify normal shrinkage versus damage that needs attention. Here’s a clear look at the main causes of cracking and what can be done to prevent it.
Shrinkage During Curing
As concrete cures, the water in the mix evaporates and the material shrinks slightly. When parts of the slab dry at different rates, internal tension builds, leading to small shrinkage cracks. These are common and typically cosmetic.
Temperature and Moisture Changes
Concrete expands in heat and contracts in cold. Seasonal changes, freeze-thaw cycles, and moisture fluctuations cause stress that can result in cracking. Proper joint placement helps control where this movement occurs.
Poor Base Preparation or Soil Movement
If the subbase isn’t properly compacted or the soil underneath shifts over time, the slab can move unevenly. This leads to structural cracking or settlement cracks. A solid, well-prepared base is critical to prevent this.
Excessive Load or Impact
Concrete has high compressive strength but limited flexibility. Heavy loads, dropped objects, or equipment can stress the surface beyond its capacity, creating cracks—especially in thin or unsupported areas.
Lack of Maintenance
Unsealed concrete is porous, allowing water, salts, and chemicals to enter. Over time, freeze-thaw expansion and corrosion can widen existing cracks. Regular cleaning and sealing help prevent long-term deterioration.
Preventing and Repairing Cracks
While some cracking is unavoidable, proper preparation, mix design, joint placement, and moisture control reduce the risk. If cracks develop, professional repair and sealing prevent further damage and restore surface integrity.
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