Measuring the Temperature of Fresh Concrete

Apparatus

1. Container: The material of the container should be non-absorptive material. Size of container is to be large enough to ensure that at least 75mm of concrete will exist around the sensor of the temperature measuring device in all directions. In addition, the thickness of concrete around the thermometer shall be > 3 times the nominal maximum size of coarse aggregate.
2. Temperature measuring device (thermometer): The precision of the used thermometer shall enable accurate determination of the temperature of fresh concrete in the range of 1.0 to 48.0°C with an accuracy of ± 0.5°C. The length of the temperature measuring device has to allow its immersion into concrete to a minimum depth of 75 mm. 
3. Reference Thermometer: The reference thermometer should have an accuracy of ± 0.5°C at the verification points specified below. 
4. Scoop: for filling the container and properly handling the concrete.

Calibration of Thermometer

Thermometers that will be used to measure the temperature of fresh concrete should undergo an annual calibration, or if there is a question regarding the accuracy of the thermometer. Calibration is performed by measuring the temperature readings using the thermometer at two temperatures that are at least 30°F apart. The calibration can be performed in oil or any other appropriate baths that have uniform density:

1. Keep the bath temperature consistent within ± 0.5°C during the testing duration.
2. Have both the temperature and reference thermometers kept in the bath for at least 5 minutes prior to reading temperatures.
3. Continuously circulate the bath liquid to ensure a uniform temperature.

Sampling Concrete

1. The temperature of freshly mixed concrete may be determined within the transporting equipment as long as at least 75 mm of concrete can be maintained around the sensor in all directions.
2. Temperature may be obtained after concrete placement considering the formwork as the container.
3. If the concrete truck or formworks are not used as containers, a concrete sample shall be taken and filled in the sample container. The sampling starts with dampening (with water) the sample container just before the sampling (according to ASTM C172).

Procedure for Measuring the Temperature of Fresh Concrete

1. Complete the temperature measurement of the freshly mixed concrete within 5 min after obtaining the sample.
2. Put the thermometer in the freshly mixed concrete in such a way that allows the surrounding of the temperature sensor by 75 mm of concrete in all directions. 
3. Gently press the concrete around the thermometer at the surface of the concrete to close any void that may cause the ambient air temperature to affect the reading.
4. Keep the temperature measuring device in the freshly mixed concrete for at least 2 minutes or until the temperature reading stabilizes, then read and record the temperature.
5. Clean the thermometer with a sponge before going for the next point.

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