How can a temperature rise affect air content in fresh concrete?

• A. Higher temperatures can influence air content readings and may cause readings to differ from those at lower temperatures, affecting durability.
• B. Temperature rise has no effect on air content.
• C. Air content increases proportionally with temperature in all cases.
• D. Color change is a more significant concern than air content.

Answer: (A)

Air content readings in fresh concrete are affected by temperature because the test relies on measuring gas volumes, which change with temperature and with how the paste and any air-entraining agents behave as heat varies. When the concrete gets hotter, gas volume changes and the effectiveness of the air-void system can shift, so the reading you obtain can differ from what you'd get at cooler temperatures even if the actual amount of entrained air is the same. This means a temperature rise can lead to readings that don’t reflect the true air content at standard conditions, potentially impacting durability decisions. To get accurate results, tests are performed at or adjusted to a standard temperature, or temperature corrections are applied, so the measured air content reliably represents the fresh concrete’s performance in service.