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The relative humidity represents the amount of water vapor in the air compared to the amount that air can hold.
Relative humidity in concrete is one of the critical parameters that should be considered before laying a floor. If concrete contains high relative humidity combined with excess moisture, it can cause floor failures and subsequently costly repairs and liabilities.
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Relative Humidity in Concrete
Relative humidity may be confused with moisture content in concrete, but they are distinctly different. The relative humidity is the amount of water in a vapor form, while the moisture is the amount of water in a liquid state.
Understanding humidity is important because high humidity can lead to various concrete damages, such as delamination of a concrete floor.
Factors Increasing Relative Humidity in Concrete
Several factors can increase the relative humidity in concrete, and their influence can extend for six months or more after concrete pouring. These factors are mentioned below:
- The initial quantity of water in a concrete mixture
- Surrounding conditions like high ambient relative humidity, additional source of water, cold temperature, and limited air movement
- Wet curing
- Utilization of pozzolans, like silica fume, that tends to retain water, and hence concrete requires a long time to dry.
- Insufficient moisture barrier in a slab on grade leading outside temperature to penetrate the slab.
It is important to note that sealing concrete before the completion of bleeding traps extra moisture in the concrete. The moisture evaporates and creates pressure on the concrete below the flooring, which causes damage and deterioration of the material.
How Does High Relative Humidity Affect Concrete Flooring?
High relative humidity causes a reduction in concrete strength. It also increases the pH in concrete, which compromises the integrity of concrete and flooring materials. The flooring material may experience various deteriorations, which are mentioned below:
1. Delamination of concrete floor
2. Blistering of epoxy coating
3. Adhesive re-emulsification
4. Cracking, curling, or bubbling of flooring materials.
How to Prevent Concrete Floor Failures Due to High Humidity?
Allocate Time for Concrete Drying
Measurement of relative humidity in concrete is essential to prevent flooring failures. Failures occur when newly-placed concrete is topped or overlayed with flooring materials when the concrete is not dried completely, and relative humidity is still high.
So, a common solution is to wait till relative humidity decreases. For this purpose, the relative humidity should be monitored, and when it gets to a specific level, it will be safe to install flooring.
Several techniques are available to estimate relative humidity in concrete, such as anhydrous calcium chloride (CaCl) testing, the hood method, the plastic sheet method, and the use of hand-held moisture meters.
These methods take measurements on a surface or near a concrete surface, while the internal relative humidity is still unknown. A more accurate and reliable evaluation of relative humidity can be achieved using in-situ relative humidity testing.
Use Low Water-Cementitious Material Ratio
Optimizing concrete mixtures and using low water-cementitious materials can help concrete dry quickly and install flooring materials. Additionally, covering concrete with polythene sheeting will help in proper curing and eliminate the need to add extra water for curing. Curing water will extend the drying period of concrete. Lastly, the use of curing compounds should be avoided.
Moisture Migration System
It is not practical to wait until relative humidity in concrete is reduced due to time constraints, damaged damp-proof membrane, or lack of a damp-proof membrane. In this case, using a moisture migration system may solve the problem.
The surface-applied moisture migration system can reduce the vapor transmission rate to an acceptable level. Nonetheless, a decision to completely rely on such a system should be studied carefully.
FAQs
The relative humidity in concrete is the amount of water vapor in the air compared to the amount that air can hold.
Relative humidity in concrete is one of the critical parameters that should be considered before laying a floor. For instance, monitoring and controlling relative humidity is essential in applying flooring. If concrete contains high relative humidity combined with excess moisture, it can cause floor failures and subsequently costly repairs and liabilities.
1. The initial quantity of water in a concrete mixture.
2. Surrounding conditions like high ambient relative humidity, additional source of water, cold temperature, and limited air movement.
3. Wet curing.
4. Utilization of pozzolans, like silica fume, that tends to retain water, and hence concrete requires a long time to dry.
5. Insufficient moisture barrier in a slab on grade leading outside temperature to penetrate the slab.
High relative humidity leads to several damages in concrete floors which are:
1. Delamination of concrete floor
2. Blistering of epoxy coating
3. Adhesive re-emulsification
4. Cracking, curling, or bubbling of flooring materials.
Several techniques are available to estimate relative humidity in concrete, such as anhydrous calcium chloride (CaCl) testing, the hood method, the plastic sheet method, and the use of hand-held moisture meters.
These methods take measurements on a surface or near a concrete surface, and internal relative humidity is still unknown. A more accurate and reliable evaluation of relative humidity can be achieved using in-situ relative humidity testing.
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