Testing the temperature of fresh concrete is crucial in ensuring that it conforms to standard temperature specifications. This is because the temperature of the concrete plays a significant role in how it cures and gains final strength. Therefore, it is essential to measure the concrete temperature during its mixing and placing.
The American Society for Testing and Materials (ASTM) has established a method to determine the temperature of fresh concrete, which is outlined in ASTM C1064. This method involves using a calibrated thermometer to test the concrete temperature accurately.
To ensure that the concrete is of the desired quality, it is necessary to adhere to the temperature specifications provided by ASTM. By following the procedure outlined in ASTM C1064, construction professionals can accurately determine the temperature of fresh concrete and ensure that it meets the required standards.
Fresh Concrete Temperature-Test Apparatus
The temperature testing apparatus includes:
- Container
- Thermometer
- Scoop or shovel
1. Container
To ensure accurate temperature readings when testing concrete mixtures, it is important to use a container that provides sufficient space between the sides of the container and the thermometer. As a general guideline, this distance should be at least 3 inches.
Additionally, the depth of the container should be appropriate for the size of the aggregates used in the concrete mix. A good rule of thumb is to make the depth of the container three times the length of the largest aggregate. For example, if the largest aggregate used in the mix is 2 inches in length, then the depth of the container should be 6 inches to accommodate it properly. This will help ensure that the concrete mixture is thoroughly mixed and that temperature readings are accurate.
2. Thermometer
The thermometer should have the capability to accurately measure temperatures within the range of 30°F to 120°F. Specifically, it should be able to measure the temperature of concrete with a high degree of precision, with an accuracy of ±1°F.
Figure-1: Thermometer to test Concrete Temperature
It is essential to ensure that the thermometer is submerged into the concrete to a depth of at least 3 inches. This means that the stem of the thermometer must be at least 3 inches long in order to accurately measure the temperature of the concrete. Prior to conducting any tests on the concrete, it is important to always calibrate the thermometer to ensure accurate readings.
3. Scoop or Shovel
When it comes to mixing concrete, it is essential to have a scoop or shovel that can effectively serve its purpose. The tool must be able to scoop a sufficient and representative amount of concrete, ensuring that the mixing process is done correctly. This means that the scoop or shovel needs to be designed in a way that allows it to collect an appropriate amount of concrete each time it is used.
The process of mixing concrete requires precise measurements, and a poorly designed scoop or shovel can result in an inconsistent mix, leading to weak or brittle concrete. To avoid this, it is crucial to choose a scoop or shovel that is specifically designed for mixing concrete. This type of tool is usually made from sturdy materials, such as steel or plastic, and has a shape and size that allows for efficient mixing.
Overall, the right scoop or shovel can make a significant difference in the quality of the concrete produced. It is important to choose a tool that can scoop a representative amount of concrete and mix it thoroughly, ensuring that the final product is strong and durable. By selecting a well-designed scoop or shovel, the process of mixing concrete can be made more efficient and effective.
Procedure to Test Temperature of Fresh Concrete (ASTM C1064)
As per ASTM C172 standards, the concrete mix should be sampled and mixed thoroughly to ensure an accurate temperature reading that represents the entire sample. Once mixed, the thermometer should be inserted into the sample in a way that its stem is completely inside the mix and positioned 3 inches away from all sides of the container. Any space between the thermometer and the concrete should be closed by slowly pressing the concrete towards the instrument, taking care not to alter the nearby temperature reading.
For concrete mixes with a nominal aggregate size of less than 3 inches, the temperature reading should be taken after waiting for 2 to 5 minutes, and recorded to the nearest 1°F. However, for concrete mixes with a nominal aggregate size greater than 3 inches, it may take up to 20 minutes for the temperature to stabilize before the reading can be taken.
It is important not to read the temperature after removing the instrument from the concrete. The reading should be recorded in a designated book, and the thermometer should be cleaned using a sponge to remove any concrete stuck on it, ensuring it is prepared for the next test.
Figure-2: Testing Temperature of Fresh Concrete by Thermometer
Image Courtesy: SI Certs
The maximum limit for concrete temperature is determined by factors such as the type of materials used and the environmental conditions. According to ASTM C1064-86, the recommended range for concrete temperature is between 26.7°C and 35°C, although this can be adjusted based on project specifications.
When concrete is poured at a higher internal temperature, it can lead to a number of issues. These may include false compressive strength values, fast setting, the need for quick finishing, loss of entrained air, and cracks due to rapid evaporation.
On the other hand, if concrete is poured at a temperature lower than 25°F, it can freeze during the curing process, resulting in a significant reduction in compressive strength. This can lead to a highly brittle product, decreased curing and strength-gain rates, and cracks due to freezing and thawing.
FAQs
What is the temperature range of the thermometer to test concrete temperature?
According to the ASTM standards, a thermometer used for measuring the temperature of concrete must have the capability to measure temperatures within a range of 30°F to 120°F. Additionally, it must have an accuracy of ±1°F when measuring the temperature of concrete. This means that the thermometer must be able to provide a reading that is within one degree Fahrenheit of the actual temperature of the concrete. Adhering to these standards ensures that accurate temperature measurements are obtained for concrete, which is crucial for ensuring its quality and durability.
At what temperature does concrete freeze?
When concrete is being mixed and the temperature falls below 25°F, there is a risk that the mixture may freeze during the process. This is a concern because freezing temperatures can cause the water in the mixture to freeze, leading to expansion and cracking of the concrete. Additionally, frozen concrete may not set properly, which can compromise its strength and durability. It is therefore important to monitor the temperature during the mixing process and take appropriate measures to prevent freezing, such as using heated materials or mixing in a heated environment. By taking these precautions, the risk of freezing can be minimized, and the resulting concrete can be strong and long-lasting.
Does temperature affect concrete?
When concrete is poured at a higher internal temperature, it can lead to a false compressive strength value and cause the concrete to set faster. This requires quick finishing, and the loss of entrained air can lead to cracks due to quick evaporation. On the other hand, if the concrete mix is poured at a temperature lower than 25°F, it may freeze during the process, resulting in a significant reduction in its compressive strength. Such concrete mixes tend to be highly brittle, with a decrease in the rate of curing and strength gain. Moreover, cracks may develop due to freezing and thawing.