Temperature of Freshly Mixed Concrete
Thermometer and placement
Temperature is a simple test with strict details. Use a thermometer with accuracy of at least ±1°F (±0.5°C) and a range that covers the expected concrete temperature. The concrete sample must be at least 3 in. (75 mm) deep, and the thermometer must be immersed at least 3 in. (75 mm) into the concrete and kept at least 3 in. from the container walls. Leave it in place for at least 2 minutes, then read it while the thermometer is still in the concrete. Record to the nearest 1°F (0.5°C).
Sample conditions
Measure temperature on a representative sample within 15 minutes of sampling. Protect the sample from direct sunlight, wind, and hot or cold surfaces; these can change the reading. Do not measure in a thin layer, in a small cup, or by holding the thermometer in your hand. If the thermometer was stored in a hot truck or a cold box, let it equilibrate with the concrete.
Traps and rule of thumb
A common trap is reading too soon: a thermometer may appear stable after 30 seconds but still be drifting. Another trap is measuring the container wall instead of the concrete, or measuring a sample that sat in the sun. Do not use an infrared surface thermometer for acceptance.
Rule of thumb: 3 in. deep, 3 in. immersion, 3 in. from the side, 2 minutes, read in place. Worked example: after 45 seconds the display shows 72°F, but after the full 2 minutes it stabilizes at 76°F. Record 76°F, not 72°F.