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The temperature of fresh concrete can be determined as per ASTM C1064 to ensure the concrete's conformity with standard temperature specifications. The method employs a calibrated thermometer to test the concrete temperature.
The temperature of the concrete affects the way it cures, and the final-strength gain. Hence, it is necessary to test the temperature of the concrete during its mixing and placing.
This article explains the procedure to test fresh concrete temperature as per ASTM C1064.
Fresh Concrete Temperature-Test Apparatus
The temperature testing apparatus includes:
- Scoop or shovel
The container used for the test must be big enough to have a minimum distance of 3 inches between the sides of the container and the thermometer.
As a thumb rule, the depth of the container must be thrice the length of the largest aggregate used in the concrete mix. If the length of the largest aggregate used is 2 inches, then the container's depth must be 6 inches.
The thermometer must be able to measure the temperature range of 30°F to 120°F. It must measure the temperature of concrete up to an accuracy of ±1°F.
The thermometer must be submerged to a minimum depth of 3 inches into the concrete. Therefore, the stem of the thermometer must be at least 3 inches long. Always calibrate the thermometer before testing the concrete.
3. Scoop or Shovel
A scoop or shovel used must serve the purpose of mixing the concrete. It must scoop a representative amount of concrete.
Procedure to Test Temperature of Fresh Concrete (ASTM C1064)
- The concrete mix is sampled as per ASTM C172 and mixed thoroughly. Proper mixing ensures that the sample provides a temperature reading that is representative of the whole sample.
- After mixing, place the thermometer into the sample so that the instrument is 3 inches away from all the sides of the container. Always insert the thermometer in a way that its stem is completely inside the mix.
- Try to close any space formed between the thermometer and the concrete. It can be done by slowly pressing the concrete towards the instrument, ensuring the nearby temperature does not alter the reading.
- For a concrete mix with a nominal aggregate size of less than 3 inches, the temperature is read after waiting for 2 to 5 minutes. The reading is recorded to the nearest of 1°F. But in the case of a concrete mix with a nominal size greater than 3 inches, it normally takes 20 minutes for the temperature to stabilize, following which the temperature reading is taken.
- Do not read the temperature after taking out the instrument.
- Record the reading in the book and clean the thermometer using a sponge. Clean the concrete stuck on the instrument and keep it prepared for the next test.
The concrete temperature limit is dependent on the type of materials and the environmental conditions. ASTM C1064-86 has set a maximum limit of concrete temperature between 26.7°C and 35°C. This can be modified as per project specifications.
The concrete mix poured at a higher internal temperature can face the following issues:
- False compressive strength value
- Fast setting
- Need for quick finishing
- Loss of entrained air
- Cracks due to quick evaporation
- The product is highly brittle
- Curing and strength-gain rate decreases
- Cracks due to freezing and thawing
As per ASTM standards, the thermometer must be able to measure the temperature range of 30°F to 120°F. It must measure the temperature of concrete up to an accuracy of ±1°F.
The concrete mix poured at a temperature lower than 25°F might freeze during the process.
The concrete mix poured at a higher internal temperature faces the following issues:
1. False compressive strength value
2. Fast setting
3. Need for quick finishing
4. Loss of entrained air
5. Cracks due to quick evaporation
The concrete mix poured at a temperature lower than 25°F might freeze during the process. This reduces the compressive strength to half. The issues faced by such concrete mixes are:
1. The product is highly brittle
2. Curing and strength gain rate decreases
3. Cracks due to freezing and thawing