American Concrete Institute (ACI) Practice Exam

Measuring the temperature of freshly mixed concrete requires enough time for the thermometer to come to equilibrium with the concrete. Right after mixing, the concrete is still adjusting and the sensor has a finite response time, so a very short immersion won’t give a stable, representative reading. Leaving the sensor in the mix for about 2 to 5 minutes allows the temperature to stabilize and provides an accurate value at placement. If you pull it out too quickly (30 seconds or 1 minute), the reading may still be influenced by surface contact or transient conditions; waiting much longer (like 10 minutes) isn’t necessary and could allow ambient conditions or ongoing mixing to alter the reading. This 2–5 minute window balances accuracy with practical field timing and aligns with standard procedures for determining the temperature of fresh concrete.