3.1 Fresh Concrete Field Sampling (ASTM C172) & Temperature Measurement (ASTM C1064)

3.1 Fresh Concrete Sampling & Temperature Measurement

A concrete test represents only the concrete sampled. Identify the delivery, the approved sampling location, adjustments already made, and the element the sample represents. Model IBC Table 1705.3 item 6 addresses concrete specimen fabrication and slump, air and temperature testing before placement. Item 7 separately addresses inspection during placement. ACI 318-19 Section 26.12.1.1 assigns acceptance sampling and testing to qualified personnel and specifies point-of-delivery samples for standard-cured acceptance strength tests.

Obtain a representative ASTM C172/C172M-14a sample

For a revolving drum mixer or agitator, take at least two portions at regularly spaced intervals in the middle of discharge after the water and admixtures have been added and the required mixing is complete. Avoid the very first and last portions. Note 3 explains the intent with guidance to sample between 10% and 90% discharge. The operative requirement is a representative composite from the middle portion.

Pass a clean receptacle through the entire stream or divert the entire stream into it. Regulate drum discharge with drum speed so the gate does not screen out larger particles. Combine portions in a suitable container and remix with a shovel only enough to make the composite uniform. Protect it from evaporation and contamination. Use at least 1 ft³ for strength specimens. Smaller samples can suffice for routine slump, air or temperature checks. A C94 preliminary sample and the C172 composite for acceptance are separate operations.

For wet-sieving under Section 6, collect the sample before sieving, remove the retained oversized aggregate without wiping off its adhering mortar, then briefly remix the passing fraction and test promptly. Follow the method-specific instructions for reporting results and any required calculation for the full mixture. The cylinder mold and sieving choice must also meet ASTM C31.

Track the three C172 clocks

For example, collect the first truck portion at 10:02 and the final portion at 10:13. The 11-minute interval is within 15 minutes. Start the three fresh-property tests by 10:18. If the composite was formed at 10:14, begin molding by 10:29. Prepare apparatus before sampling and record the actual times.

Measure fresh concrete temperature

Under ASTM C1064/C1064M-17, use a device accurate to ±1°F over the specified 30°F to 120°F range. Verify accuracy at least annually or when questioned at two temperatures at least 30°F apart, using the specified traceable reference device. For a sample in a separate container, dampen the container and provide enough concrete in every direction around the sensor for at least 3 inches of cover and at least three times the nominal maximum coarse aggregate size. When temperature is the only test, C1064 permits sampling without a composite.

1. Place the end of the sensing portion at least 3 inches into the fresh concrete. Use the surrounding clearance to limit influence from the container, ambient air or adjacent surfaces.
2. Gently press concrete around the device where it enters the surface to close the gap.
3. Leave it in place for at least 2 minutes and at most 5 minutes. Read without withdrawing the sensor.
4. Record to the nearest 1°F, or the method's 0.5°C increment if using SI.

The method measures temperature at the time of the test. Concrete with nominal maximum aggregate larger than 3 inches can require additional time for heat transfer between aggregate and mortar, as discussed in the method's significance section. Compare the measured result with the limit in the governing documents. If a stated 95°F limit applies and the valid result is 98°F, record the 3°F exceedance and report it through the approved process.

If the project specifies additional sampling at a pump outlet, record that location and apply its specified criteria. Keep the separately required point-of-delivery strength acceptance sampling traceable. If water was permitted after an initial slump check, complete the required remixing and obtain the acceptance composite from the adjusted load.