Concrete floors and slabs are susceptible to moisture, which can cause various issues such as discoloration, hindered polymerization of products, and even delamination of bonded coating systems. It is crucial to conduct moisture and vapor tests to determine the presence and amount of moisture in the concrete, as appropriate measures can then be implemented to eliminate or minimize its negative effects.
To measure concrete moisture, there are several methods available that provide both qualitative and quantitative results. The plastic sheet test, as per ASTM D 4263, is a qualitative method that determines whether there is moisture present in the concrete slab. On the other hand, the calcium chloride test, in accordance with ASTM F 1869, is a quantitative method that measures the amount of moisture and vapor transmission in the concrete. By utilizing these methods, the level of moisture in the concrete can be determined and necessary actions can be taken to prevent any potential damages.
Concrete Moisture and Vapor Test Methods
1. Plastic Sheet Test (ASTM D 4263)
A test method involving the use of plastic sheet is utilized to detect the presence of moisture in concrete. This particular method is considered appropriate in situations where there is a plan to apply coatings onto the surface of the concrete. It is imperative that the test is conducted before the application of the coating to ensure that the concrete is sufficiently dry.
Required Materials
There are two items mentioned in the given context: a tape and a transparent square polyethylene sheet. The tape has a width of 51 mm, while the polyethylene sheet has a size of 460 mm x 460 mm and a thickness of 0.10 mm.
The tape’s width is specifically stated as 51 mm, but there is no information about its length, color, or other characteristics. It is possible that it is an adhesive tape used for various purposes such as packaging, sealing, or labeling.
On the other hand, the transparent square polyethylene sheet is described in more detail. Its size is given as 460 mm x 460 mm, which means that it has the same length and width. It is also stated to be transparent, which suggests that it is see-through and allows light to pass through. The material of the sheet is identified as polyethylene, a type of plastic that is commonly used for packaging and various applications due to its durability and flexibility. The thickness of the sheet is specified as 0.10 mm, which indicates that it is relatively thin and may be used for covering or wrapping items.
Test Frequency
The testing requirement for concrete surfaces involves conducting one test for every 46 square meters of floor, wall, or ceiling. This means that if a surface measures more than 46 square meters, multiple tests will need to be conducted to cover the entire area.
To ensure comprehensive testing of vertical surfaces, it is recommended that a minimum of one test be conducted for every 3 meters of vertical rise. This testing should begin within 300 mm of the floor and cover all elevations. By conducting tests in this manner, any potential issues or defects can be identified and addressed as needed.
Test Procedure
To conduct the moisture test, tightly tape a plastic sheet onto the concrete surface, making sure that all edges are properly sealed, as shown in Fig.1. Leave the plastic sheet in place for at least sixteen hours. After the designated time, carefully remove the plastic sheet, as shown in Fig. 2. Inspect the underside of the plastic sheet and the concrete surface for any presence of moisture. You can do this by wiping your finger on both the concrete surface and the underside of the plastic sheet to feel for any moisture. If the concrete surface is moist, it may feel cooler to the touch and appear darker in color.
Fig. 1: Tape the sheet on the concrete surface
Fig. 2: Remove the Sheet and Inspect its Underside and Concrete Surface for moisture
Limitations of plastic sheet test
The test results obtained after leaving the sheet in place for 16 hours do not fully capture the moisture movement from the bottom to the top of the slab. This is because the limited time frame only reflects the surface-level changes. Therefore, the test results may not be an accurate representation of the overall moisture condition of the slab.
It is important to note that the moisture detected under the plastic sheet could be attributed to condensation caused by the dew-point temperature of the slab surface. This phenomenon may not necessarily indicate moisture flow within the slab. Hence, it is crucial to consider other factors that could affect the test results and obtain a more comprehensive understanding of the moisture condition of the slab.
2. Calcium Chloride Test (ASTM F 1869)
The ASTM F 1969 is a standard test method that determines the moisture vapor emission rate from bare concrete floors. This test can be performed on concrete floors located above-grade, on-grade, or below-grade. The results of this test provide a numerical value that indicates the amount of moisture vapor being emitted from the surface of the concrete floor. This information is used to determine if the concrete floor is suitable for installing resilient floor coverings.
The purpose of the calcium chloride test method is to quantify the rate of moisture vapor that is being emitted from concrete floors. This test is particularly useful in determining if a concrete floor is suitable for receiving resilient floor coverings. By measuring the moisture vapor emission rate, this test can provide valuable information about the potential for moisture-related issues such as mold growth or floor covering failure.
The ASTM F 1969 test is a reliable and widely accepted method for measuring moisture vapor emission from concrete floors. It is an essential step in determining the suitability of a concrete floor for the installation of resilient floor coverings. By providing a quantitative value, this test can help prevent potential moisture-related issues and ensure the longevity of the floor covering system.
Required Materials
The scenario involves a plastic dish with a diameter of 69mm and a height of 15-20mm that contains 16g of anhydrous calcium chloride. The dish comes with a lid that can be sealed around the circumference using pressure-sensitive tape.
In addition, a transparent cover with a height of 38mm and flanges measuring 12mm around the perimeter is needed to seal off the test area of the floor. The cover is required for the purpose of conducting tests.
Finally, a scale that is capable of measuring up to 0.1g is necessary for the experiment. The scale will be used to obtain accurate measurements during the test.
Test Frequency
When testing an area of up to 100 square meters, it is recommended to choose three different locations for the test. However, if the area exceeds 100 square meters, an additional test location should be added for every 100 square meters or fraction thereof. This ensures a more comprehensive and accurate assessment of the area being tested. By selecting multiple test locations, any potential issues or variations in the results can be identified and addressed. It is important to choose the test locations carefully to ensure they are representative of the entire area being tested. The tests should also be conducted using appropriate methods and equipment to ensure reliable and accurate results.
Test Procedure
was carefully prepared by using abrasive cleaning methods to thoroughly eliminate any foreign substances. This process involved meticulous cleaning techniques to ensure that the surface was free from any debris, dirt, or other contaminants that could potentially affect the quality and durability of the concrete. The abrasive cleaning method used was effective in removing all unwanted materials from the surface, leaving it clean, smooth, and ready for further treatment or application. By employing this meticulous approach, the concrete surface was thoroughly cleaned and properly primed for subsequent steps in the construction or finishing process.
Fig. 3: Clean Concrete Surface
To determine the weight of the dish, calcium chloride, lid, and tape, you need to place all of these items on a weighing scale and measure their combined weight. Make sure to handle the items carefully and place them gently on the scale to avoid any damage or inaccurate readings. Once all the items are on the scale, read the weight displayed on the scale and record it to the nearest 0.1 gram for accurate measurement. This will give you the total weight of the dish, calcium chloride, lid, and tape combined.
Fig. 4: Weigh the Dish
Starting weight, time, date, and test location will be recorded before proceeding. Next, the dish will be opened and placed on the designated concrete surface that has been prepared for the test.
Fig. 5: Open the Dish and Place it on the Concrete Surface
To secure the plastic cover over the dish, make sure it is properly placed on top of the dish. Then, using the preformed sealant tape that is already attached to the flanges, fasten the plastic cover tightly to the concrete surface. This will ensure that the cover is securely sealed and prevents any moisture or debris from entering the dish. The sealant tape is designed to provide a watertight seal, keeping the dish protected and functioning optimally.
Fig. 6: Place a Plastic Cover Over the Dish
After the specified time period of 60 to 72 hours has elapsed, it is recommended to carefully cut a hole in the plastic cover of the dish. This can be done using appropriate tools or equipment, ensuring safety precautions are taken. Once the hole is made, the plastic cover can be removed from the dish, allowing access to the contents inside. It is important to exercise caution while cutting the hole and removing the cover to avoid any potential hazards or contamination of the dish. Proper disposal or recycling of the plastic cover should be done in accordance with local regulations and guidelines.
Fig. 7: Cut a Hole in Plastic Cover
After filling the dish, carefully place the lid back on top, ensuring it is securely attached with the pressure-sensitive tape. Make sure the lid is properly aligned with the dish to create a tight seal. Once the lid is securely in place, use a scale to weigh the sealed dish again. This step will help ensure that the weight of the dish, including its contents, is accurately measured and recorded. The pressure-sensitive tape will help maintain the integrity of the seal, preventing any leakage or contamination during subsequent handling or transportation. Accurate weighing is crucial in many scientific, culinary, and industrial applications where precise measurements are required for accurate results.
Fig. 8: Place the Lid and Seal the Dish and Weigh it Again
Calculation
The MVER, or moisture vapor emission rate, can be calculated using a specific expression.
The MVER, or moisture vapor emission rate, is a measure of the amount of moisture that is released from a concrete surface over time. It is calculated by determining the change in mass (weight gain) of an anhydrous calcium chloride (CaCl2) dish in grams, which is placed on the concrete surface. The contact area of the flanged cover on the concrete, minus the area of the CaCl2 dish, is used to calculate the effective contact area (A) in square meters. The exposure time (T) is measured in hours.
3. Other Methods
ACI 302.2 R-06 includes several other types of concrete moisture tests in addition to those already mentioned. These tests are as follows:
The Relative humidity test (ASTM F 2170 and F 2420), the Electrical resistance test (which has no ASTM standard test method), the Electrical impedance test (which also has no ASTM standard test method), the Mat test (which also has no ASTM standard test method), the Qualitative calcium chloride test (which also has no ASTM standard test method), and the Primer or adhesive strip test (which again has no ASTM standard test method).
These tests are intended to provide additional ways to measure concrete moisture beyond what has already been discussed. The Relative humidity test, for example, is designed to measure the moisture level inside a concrete slab. The Electrical resistance and impedance tests use electrical currents to determine moisture levels, while the Mat test involves placing a special mat on the concrete surface and then measuring the moisture content of the mat. The Qualitative calcium chloride test involves placing a special chemical on the concrete surface and then observing any changes that occur over time. Finally, the Primer or adhesive strip test involves applying a primer or adhesive strip to the concrete surface and then measuring moisture levels over time.