Blog – Construction Drying

How Humidity and pH Affect Concrete Degradation

Moisture-related problems in concrete flooring amount to over $1 billion in damages each year. Concrete is porous by nature. The more porous it becomes the more potential there is for moisture-related damage, which leads to problems such as high pH levels and carbonation. Relative humidity levels in concrete directly affect its pH levels. This means that pH levels rise as relative humidity levels increase. For this reason, optimal humidity for concrete drying is necessary to ensure the building material’s integrity during and after its installation.

pH and Its Affect on Concrete

A neutral pH is 7, which is what you find in natural freshwater. Anything above 7 is alkaline, and anything below is acidic. Portland cement, concrete’s binding agent, has a pH of 11, making it alkaline. For cement to effectively hold the various components within it, it should have a pH of around 11. The problem is that Portland cement does not resist many acidic compounds well. As the pH of acids decreases below 6.5, concrete deterioration increases. Solutions with a pH of 3 or lower are the most harmful. The more concrete deteriorates, the more porous it becomes.

Causes of excess moisture in concrete include:

  • Too much water in the concrete mix
  • Not allowing concrete to dry and cure long enough
  • Rainfall
  • Leaks
  • Lack of adequate climate control
  • Concrete sweating
  • Landscaping that does not divert water away from a building’s foundation

Interactive pH

In addition to degradation, one of the largest implications of increased pH levels in concrete is the failure to adhere to the floor covering. For a floor covering installation to be successful over a concrete slab, the concrete and flooring adhesive’s pH must be compatible. Otherwise, the adhesive’s bond will ultimately fail. Similarly, when relative humidity levels in concrete increase due to excess moisture, pH levels within the concrete increase, which could result in flooring adhesive-related failure.

Carbonation

Water that contains bicarbonate ions with free carbon dioxide dissolves the calcium carbonate in concrete. In essence, cement in the concrete reacts with the carbon dioxide in the air or water. This effect is known as carbonation. The acidic reaction sometimes occurs when concrete is exposed to salts or acid rain.

Carbonation lowers concrete’s pH, affecting its ability to hold the components within it together. When exposed to acidic environments, concrete dissolves into sand and rocks. This effect is dangerous in buildings because the carbonation in concrete may eventually affect steel reinforcements and attack their protective layer of iron oxide, leading to corrosion. As steel corrodes, it can expand up to six times its size. The resulting pressure can cause the already weakened concrete around it to break and crack. 

Preventing pH Problems in Concrete

Concrete manufacturers create regional guidelines for contractors to follow, as some areas have different pH levels, precipitation levels, hydrogen ion concentrations, and relative humidity levels. Follow these guidelines and create the optimal humidity for concrete drying with the custom temporary environmental control solutions from Polygon. These solutions ensure that water vapor from the wet concrete rises from the bottom of the slab to the top in a manner that isn’t too fast or too slow, so it hydrates and strengthens properly, and keeps your project on schedule. Contact Polygon to learn more and schedule a complimentary consultation.  

[Photo from Rachel Haller via CC License 2.0]

Degraded concrete

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