The water absorption test is a method used to measure the rate at which water is absorbed by both the outer and inner surfaces of concrete. This test involves observing the change in mass of concrete samples as they absorb water over a period of time, with only one side of the specimen being exposed to water. To conduct this test, samples of concrete can either be taken from drilled cores or molded into cylinders. Before the test is performed, the samples should be saturated and weighed. The rate of absorption can be calculated at various distances from the surface that is exposed to water.
Factors Influencing Water Absorption of Concrete
Concrete mix proportions, chemical admixtures, and supplementary cementitious materials all play a crucial role in determining the properties and performance of concrete. The composition and physical properties of the cementitious component and the aggregates used in the mix also influence the overall quality of the concrete. Additionally, the entrained air content, which is the amount of air deliberately incorporated into the mix, can impact the durability and freeze-thaw resistance of the concrete.
The type and duration of curing also have significant effects on the strength and durability of concrete. The curing process involves maintaining an adequate level of moisture and temperature for a specified period to allow for proper hydration and strength gain. Factors such as the degree of hydration, which is the extent to which the cementitious materials have reacted with water, and the presence of microcracks can further influence the strength and durability of the concrete.
Concrete surface treatments such as sealers or form oil can affect the appearance, durability, and longevity of the concrete surface. The placement method, including consolidation and finishing, is also critical in ensuring that the concrete achieves the desired strength and durability. Finally, the concrete moisture condition at the time of testing can affect the test results and the interpretation of the data obtained.
Purpose
The objective of the water absorption test is to measure the speed at which hydraulic cement concrete absorbs water. This test is conducted to evaluate the concrete’s ability to withstand exposure to moisture, as excess water absorption can lead to reduced durability and strength over time. The test involves exposing the concrete to water for a specified duration and measuring the weight gain of the sample. By determining the rate of water absorption, engineers and construction professionals can make informed decisions about the appropriate use and maintenance of the concrete in various applications.
Tools and Materials
The equipment list provided includes several items necessary for conducting a scientific experiment or measurement involving the use of support devices, rods, pins, or other tools. Additionally, a top-pan balance, accurate to at least ±0.01 g, is required for precise weight measurements. A timing device is also necessary to ensure accurate measurements of time.
To maintain a clean and controlled environment during the experiment, paper towels or cloths can be used for cleaning surfaces, and an environmental chamber may be required to regulate temperature, humidity, or other environmental factors. To store samples or materials, polyethylene storage containers are recommended to prevent contamination or damage.
For accurate measurements of size or dimensions, a caliper can be used, and sealing materials like duct tape or aluminum tape may be necessary to seal containers or prevent leakage. Finally, a plastic bag or sheeting can be used to cover materials and prevent exposure to the external environment. Overall, this equipment list is essential for conducting a successful scientific experiment or measurement with precision and accuracy.
Concrete Sample Preparation
Concrete specimens used for testing can either be drilled cores or molded cylinders. To ensure standardization, they should have a diameter of 100 ±6 mm and a length of 50 ±3 mm. The test result is obtained by averaging the test results of at least two samples. It is important to ensure that the test surfaces are at the same distance from the original exposed surface of the concrete.
To prepare the drilled core specimens obtained from the field for testing, they should be vacuum saturated. Before conducting the absorption test, it is necessary to measure the mass of each specimen to the nearest 0.01 g. The next step is to place the test samples in an environmental chamber set at a temperature of 50 ± 2 degrees and a relative humidity of 80 ±3 % for three days.
Once the environmental conditioning is complete, the specimens should be placed in sealable containers with enough space between the sample and the container wall to allow for free airflow around the specimen. These containers are then stored at a temperature of 23 ±2 degrees for a minimum of 15 days before conducting the absorption test.
During the absorption test, the specimens are subjected to tap water conditioned to the same temperature as the storage temperature. This procedure is carried out at a temperature of 23 ±2 degrees.
Vacuum-saturation Procedure
To begin the process, the specimen should be placed directly into a vacuum desiccator with both end faces of the sample exposed. The desiccator should then be sealed and the vacuum pump started, maintaining the vacuum for three hours.
Next, a separatory funnel should be filled with de-aerated water. With the vacuum pump still running, the water stopcock should be opened and enough water should be drained into a container to cover the specimen. Once the specimen is covered, the water stopcock should be closed and the vacuum pump should be allowed to run for an additional hour.
After the additional hour has passed, the vacuum line stopcock should be closed, and the pump turned off. The vacuum line stopcock should then be turned to allow air to re-enter the desiccator.
Finally, the specimen should be soaked in a beaker of water for 18 ± 2 hours.
Water Absorption Test Procedure
To conduct the test, follow these steps:
- Retrieve the specimens from the storage container and weigh them to the nearest 0.01 g.
- Measure at least four diameters of the specimen at the surface that will be exposed to water, and calculate the average diameter.
- Seal the side surface of the specimens with appropriate seal material, and seal one end that will not be exposed to water with a plastic sheet secured by an elastic band or an equivalent system.
- Weigh the sealed specimen and record it as the initial mass.
- Prepare the specimen support at the bottom of the pan, and fill the pan with tap water until it rises approximately 3 mm above the specimen supports (see Figure-1). This water level needs to be maintained throughout the test.
- Start the timing device, and place the unsealed surface of the specimen on the supports in the pan. Record the time and date of the initial contact of the specimen with the water.
- Record the mass of the specimen at the time intervals provided in Table-1.
- After recording the mass, remove the concrete specimen from the pan. If the contact time is less than 10 minutes, stop the timing device, and wipe off any surface water with a dampened paper or cloth. Invert the specimen to prevent the wet surface from contacting the balance pan. Weigh the specimen within 15 seconds of removing it from the pan. Finally, place the specimen back on the support in the pan and restart the timing device.
Table-1: Time interval for Recording the Mass of Concrete Specimen
| Time interval | Tolerances |
| 60 second | 2 second |
| 5 minutes | 10 second |
| 10 minutes | 2 minutes |
| 20 minutes | 2 minutes |
| 30 minutes | 2 minutes |
| 60 minutes | 2 minutes |
| Every hour up to 6 hours | 5 minutes |
| Once a day up to 3 days | 2 hours |
| Day 4 to 7 3 measurements 24 hours apart | 2 hours |
| Day 7 to 9 One measurement | 2 hours |
Calculations
The absorption rate of concrete can be calculated using the following expression, represented by Equation 1. This equation uses the change in specimen mass, mt, in grams at time t, the exposed area of the specimen, a in mm2, and the density of the water, d in g/mm3. The initial rate of water absorption is determined by finding the slope of the line that is the best fit to I plotted against the square root of time for all the points from 1 minute to 6 hours. Similarly, the secondary rate of water absorption can be calculated by finding the slope of the line that is the best fit to I plotted against the square root of time for all the points from 1 day to 7 days. These rates of water absorption are important parameters to measure for concrete testing and analysis.
FAQs
What is water absorption rate test (sorptivity test) of hydraulic-cement concrete?
The provided definition describes a testing technique used to estimate the rate of water absorption, or sorptivity, in hydraulic cement concrete. This method involves measuring the increase in mass of a concrete specimen over time as it absorbs water, with only one surface of the specimen exposed to the water source. The rate of absorption can be determined from the data collected during this test.
How do you calculate the water absorption rate of concrete?
To calculate the water absorption rate of a concrete specimen, a specific formula can be used. The formula involves dividing the change in mass of the concrete specimen by the area of the sample that is exposed to water. The result of this calculation is then multiplied by the density of water. This provides an accurate measurement of the rate at which the concrete is absorbing water. By determining the water absorption rate of a concrete sample, it is possible to gain insights into its durability and potential for water damage.
What are the factors that influence water absorption of concrete?
- The proportions of the mixture used in concrete play a crucial role in determining its strength and durability. The right ratio of cement, water, and aggregates is necessary for achieving the desired properties of the finished product. Different applications may require different mixture proportions, so it’s essential to consult experts to determine the appropriate ratios.
- Entrained air is an important factor to consider when making concrete. This refers to the tiny air bubbles trapped within the mixture. These bubbles can help enhance the durability of concrete by reducing its susceptibility to freeze-thaw cycles, abrasion, and other forms of damage.
- The moisture condition of concrete can affect its strength and durability. If the concrete is too wet or too dry, it may not achieve the desired properties. Therefore, it’s important to maintain the right moisture levels throughout the curing process to ensure optimal strength and durability.
- Curing is the process of allowing concrete to harden and reach its full strength potential. The type and duration of curing can have a significant impact on the final properties of the concrete. Proper curing can help enhance the durability and strength of concrete, and prevent cracking and other forms of damage.
- The composition and physical properties of cement materials and aggregates used in concrete can affect its strength and durability. The quality and consistency of these materials must be carefully monitored to ensure the desired properties of the finished product.
- Chemical admixtures and supplementary cementitious materials can be added to concrete to enhance its properties. These additives can improve workability, increase strength, and reduce the risk of cracking and other forms of damage.
- Concrete surface treatments, such as sealers, can help protect the material from environmental factors and extend its lifespan. These treatments can improve the durability of concrete and prevent moisture intrusion and other forms of damage.
- The presence of microcracks in concrete can affect its durability and strength. These small cracks can lead to larger cracks over time, eventually causing the concrete to fail. Therefore, it’s essential to monitor for and address microcracks in concrete.
- The method of concrete placement, including compaction and finishing, can affect its final properties. Proper compaction and finishing can help enhance the strength and durability of concrete, while improper methods can lead to cracking and other forms of damage.
- The degree of cement hydration refers to the amount of water used in the concrete mixture and the length of time allowed for the cement to cure. Proper hydration is necessary for achieving the desired strength and durability of the finished product.