If you look around, you will see that concrete is universally used as a building material in many areas. Concrete is a highly durable and widely used construction material and it is relatively cheap and long lasting. It is made up of cement, aggregates such as sand and gravel, and water. When these components are mixed together, they form a strong and hard material that can withstand heavy loads and harsh environmental conditions. However, one of the biggest threats to the long-term durability of concrete is water. Water is always on the attack.
Water is one of the most damaging agents to concrete, and it is relentless. It can cause a range of problems, including cracking, spalling, scaling, discoloration and corrosion of reinforcing steel. These problems can significantly reduce the strength and integrity of concrete structures, making them more susceptible to damage and failure over time. We see this damage daily when we inspect residential foundation. Sometimes it is hard to appreciate the accrued damage that water and time can bring about.
There are several reasons why water is so damaging to concrete. In this article, we will explore the various mechanisms and reasons through which water can harm concrete.
One of the primary ways in which water damages concrete is through chemical reactions. When water comes into contact with concrete, it can react with the cement to form a chemical compound known as calcium hydroxide. This reaction is known as hydration and is essential for the strength and hardening of concrete. However, if the concrete is exposed to water for an extended period of time, this reaction can continue, leading to the formation of additional calcium hydroxide. You may notice a “white chalk” on concrete which is an indication that this degradation has started. Many people erroneously think this is mold, but it is not. It is the deterioration of the concrete substrate.
Another way in which water damages concrete is through freeze-thaw cycles. In western Pennsylvania, where we are located, this is a huge problem. Many homes are brutally attacked by this phenomenon. When water enters the pores and cracks of concrete, it can freeze during cold weather. As water freezes, it expands, putting pressure on the surrounding concrete. This can cause the concrete to crack and deteriorate, especially if the freeze-thaw cycle occurs repeatedly over time.
Freeze-thaw cycles can be particularly damaging to concrete structures that are exposed to water and have low permeability. When water enters the pores of low-permeability concrete, it can become trapped and unable to escape. When the water freezes, it can expand and cause significant damage to the concrete.
In addition to cracking and spalling, freeze-thaw cycles can also weaken the bond between the concrete and any reinforcing steel that may be present. This can increase the risk of corrosion and further deterioration of the concrete.
Corrosion of reinforcing steel
One of the most significant ways in which water damages concrete is through corrosion of reinforcing steel. Reinforcing steel, also known as rebar, is used to provide additional strength to concrete structures. Reinforced steel is ubiquitous in the building trades and is a commonplace practice in most construction. When concrete is exposed to water, it can penetrate the concrete and reach the reinforcing steel. Over time, this can cause the steel to corrode and weaken, reducing the overall strength and integrity of the structure. Commonly your will see a damage piece of concrete where the concrete has fallen off down to the rebar rods. This is because the rods, usually made out of steel, rust and expand. This creates outward pressure relative to the position of the rebar nd pushes off the loose concrete. This creates a negative cycle as more exposed steel will rust more, quicker than before, and push off more concrete. This is the demise of many concrete structures.
Corrosion of reinforcing steel occurs due to a combination of factors, including exposure to water, oxygen, and chlorides. When these elements come into contact with the steel, they can cause it to rust and corrode. As the steel corrodes, it can expand and put pressure on the surrounding concrete, causing it to crack and deteriorate.
Corrosion of reinforcing steel is particularly problematic in concrete structures that are exposed to seawater or deicing salts.
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