4.1 ASTM C1064 Purpose, Equipment, and Timing
Key Takeaways
- ASTM C1064 measures the temperature of freshly mixed hydraulic-cement concrete during field testing.
- The temperature measuring device must be accurate, readable, and verified on the required schedule or whenever accuracy is in doubt.
- Temperature measurement must be completed within 5 minutes after obtaining the sample when measured from a sample.
- The result is reported to the required accuracy, commonly the nearest 1 degree F or 0.5 degree C.
Temperature as a Fresh-Concrete Property
ASTM C1064 covers measuring the temperature of freshly mixed hydraulic-cement concrete. Temperature matters because it affects slump loss, setting time, air stability, finishing behavior, curing risk, and specification compliance. A temperature result is also a snapshot. If the technician waits too long, measures near the edge of a shallow sample, or reads a device before it stabilizes, the value may describe the environment more than the concrete.
The equipment requirement is a common written-exam target. The temperature measuring device must be suitable for concrete, readable to the required increment, and accurate within the required tolerance over the expected range. ACI study materials and field practice commonly emphasize accuracy within plus or minus 1 degree F, or plus or minus 0.5 degree C, and reporting to the nearest 1 degree F or 0.5 degree C. The device must be verified at least every 12 months and whenever accuracy is in doubt.
When temperature is measured in a sample obtained under C172, the measurement must be completed within 5 minutes after the sample is obtained. That means the thermometer cannot be at the bottom of a toolbox while the technician finishes slump first. Temperature equipment should be ready before sampling, especially in hot, cold, windy, or fast-paced placements.
| C1064 item | Required habit | Exam risk |
|---|---|---|
| Device accuracy | Use a verified concrete thermometer | Confusing readability with accuracy |
| Verification | Check annually and when accuracy is doubtful | Using a damaged or dropped device |
| Sample timing | Complete measurement within 5 minutes | Waiting until after long test delays |
| Reporting | Record to nearest required increment | Overstating precision |
| Field use | Keep sensor embedded while reading | Reading after removing the device |
The test may be performed in the sampled concrete, in a transporting unit, or in placed concrete when there is enough surrounding concrete for a valid reading. The controlling idea is that the sensing portion must be embedded in concrete and shielded from ambient air. A thin smear of concrete on a probe or a reading taken against the side of a metal container is not a reliable concrete temperature.
Performance-exam success comes from calm setup. Have the thermometer available, know the verification status, insert it correctly, press concrete around the stem, wait for stabilization within the allowed window, read while embedded, and record the result accurately. The procedure is short, so mistakes usually come from rushing or assuming that any quick number is acceptable.
Field memory list:
-
Verify the thermometer before field use and after damage or doubt.
-
Start temperature work promptly after sampling.
-
Embed the sensor in enough concrete to isolate it from air.
-
Wait for stabilization but stay within the maximum reading time.
-
Report the temperature without adding unsupported precision.
What does ASTM C1064 measure?
How often should the temperature measuring device be verified at a minimum?
When temperature is measured from a C172 sample, when must the measurement be completed?