Q: How do I know when to use hot weather concreting techniques?
A: ACI 305 defines hot weather as any combination of conditions that impairs concrete quality by increasing the moisture loss or rate of hydration. Those conditions include high ambient temperature, high concrete temperature, low humidity, wind speed, and solar radiation. This is admittedly somewhat vague, so use Fig. 2.1.5 in ACI 305 to estimate moisture loss and take precautions when the rate of evaporation is lower than 0.2 pounds per square foot per hour.