Which of the following is NOT a factor of hot weather concreting?

• A. High ambient temperature
• B. High concrete temperature
• C. High relative humidity
• D. Solar radiation

Answer: (C)

In hot weather concreting, the main concerns are those that increase temperature and moisture loss in the concrete, which speeds up setting and can cause plastic shrinkage cracks. High ambient temperature raises the air and concrete temperatures, speeding hydration and reducing the time you have to work with the mix. High concrete temperature itself drives faster setting and can worsen early stiffening and thermal cracking. Solar radiation heats the concrete surface, further increasing evaporation and surface temperature, which compounds drying and shrinkage issues.

High relative humidity, on the other hand, tends to reduce evaporation from the concrete surface. While humidity can influence curing, it is not a factor that intensifies hot-weather problems; in fact, higher humidity mitigates some of the evaporation losses that are problematic in hot conditions. Therefore, high relative humidity is not a factor of hot weather concreting.