What Causes Your Concrete To Crack?
Concrete is a wonderful, hard-working material that’s widely used in homes and commercial buildings. However, this durable material can also be susceptible to cracking. Cracks in concrete can be caused by many factors. Understanding why they occur and what to do about it can help you avoid future issues.
1. Excessive Water
There are many reasons why your concrete might crack, but the primary cause is excessive water. The majority of residential concrete work involves a lot of water being added to the mix on the job site- this can significantly reduce the strength of the concrete. The excess water can be caused by an uneven sub-grade, an overly soft concrete mix, or a poor drainage system. Any of these factors can cause the concrete to settle and crack. Excessive water also decreases the cement to water ratio- which is critical for achieving a high quality concrete. Make sure the concrete is poured from a reliable contractor with experience in the field and who will know exactly what kind of water they are allowed to use on the job.
Shrinkage is the term used to describe a process that occurs as concrete dries and hardens. It’s not just a cosmetic problem — it can weaken the strength of the concrete and cause cracks to appear. Concrete shrinks when excess mixing water evaporates and the paste dries out. The drying shrinkage of concrete depends on the water to cementitious materials ratio, the aggregate content and the total water content in the concrete mix. This process can be controlled by using a more rigid concrete mix, adding a shrinkage-compensating or crack-reducing admixture and increasing the volume of stiff aggregate. These techniques also reduce the likelihood of void formation around formwork and reinforcing steel.
Impact is a term used to describe a wide range of forces, such as abrasion or percussive, that can cause concrete surfaces to damage. Depending on the type of force, the cracking patterns will vary. Abrasion occurs when objects on or underneath a surface continuously rub against the concrete, gouging it and sometimes causing small fractures. These are common in areas of traffic or heavy loads and can be prevented by proper concrete design. The cracks usually appear around the edges of the concrete and are typically referred to as abrasion or crazing cracks. The abrasion is caused by a combination of mechanical, chemical and thermal factors, such as hot, dry air. Another common impact on concrete is corrosion, which affects the reinforcing steel and can cause spalling or flaking. A small spall may look like a fine line, but it can indicate that the reinforcement is vulnerable to more severe corrosive forces. Depending on the impact, there are a variety of different repair options for cracked concrete. Understanding what the type of crack is, and how it occurred, can help identify which repairs are most effective. This can reduce the cost of repairs and the risk of future deterioration or damage to a structure, and possibly human life.
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