Concrete is one of the most common building materials used in new construction, particularly for flooring. The material constantly interacts with the environment around it, so influences such as temperature and humidity affect the moisture levels within it. Just as water is a vital ingredient when mixing concrete, excessive amounts of it can create numerous problems. The most common sources of excess moisture in concrete are free water—too much water in the concrete mixture—and moisture rising from below a slab. Because of the costly issues that may result from excess moisture in concrete construction, humidity control is an essential preventive and corrective measure.
How High Humidity Affects Concrete
- Increased pH levels: Relative humidity levels directly affect the pH levels in concrete. For this reason, concrete manufacturers create regional guidelines for installers to follow, as some areas in the country are drier and have different field pH levels. When relative humidity levels are high, the moisture increases the concrete’s pH levels. Incidentally, the interaction compromises the concrete’s integrity and the integrity of any adhesive or coating materials applied to it.
- Decreased strength: When relative humidity levels increase, the compressive strength of concrete decreases, affecting its durability.
- Microbial growth: Moisture creates the ideal conditions for the growth of mold, mildew, and bacteria. When mold and bacteria grow and reproduce within the concrete, they affect its strength. At the same time, the organisms may affect the health of the individuals within the affected area.
Sweating Slab Syndrome
In concrete construction, humidity control can prevent sweating slab syndrome, an event that occurs when moisture develops on the surface of concrete slabs within a building. In addition to increasing the moisture levels within the concrete, sweating slab syndrome poses a serious safety risk to individuals and transport machinery. Not only may individuals slip and fall, but the slippery concrete could also prevent machinery with wheels from stopping during transport operations.
Dew point condensation is often the cause of sweating slab syndrome. When warm, humid air enters a building or structure through vents, windows, or doors, it diffuses throughout the structure and condenses on concrete if the temperature is at or below the dew point. The effect is similar to condensation forming on a glass that contains a cold beverage.
In some instances, salt deposits on concrete slabs lead to sweating slab syndrome. Salt is hygroscopic and naturally attracts moisture from the air. When the salt is within the concrete, it holds water molecules within the air. This generally occurs when there is no vapor retarder under the slab or a lack of proper air circulation. When the concrete sweats because of the salts within it, salt deposits may remain on the surface. If one does not immediately clean the salt, individuals or the wheels of material handling equipment could track the salt to other areas of a property.
Concrete Construction: Humidity Control
Excessive moisture affects concrete the most when there is a lack of air circulation and climate control. The best preventive measure is to identify and correct humidity problems before the installation of flooring or surface coatings. After concrete cures, temporary humidity and temperature solutions will help mitigate moisture problems and their damaging effects. Polygon provides a variety of custom solutions that create the ideal environmental conditions as concrete cures and the following adhesives or surface coatings dry. The use of temporary humidity control measures also creates conditions that prevent moisture from forming on the surface of the concrete. To learn more about temporary humidity control solutions, contact a Polygon representative today.
[Photo from Matthew Paul Argall via CC License 2.0]
