In concrete construction, temperature isn’t just a comfort factor — it’s a performance driver. When temperatures rise, so does the risk of problems with workability, strength, durability, and cracking. That’s why understanding mix temperature, heat of hydration, and the use of chilled mix water is critical — especially during hot weather.
What Is Mix Temperature?
Mix temperature refers to the temperature of freshly mixed concrete at the time of batching and delivery. It is influenced by a combination of factors, including:
- The ambient air temperature
- The temperature of water, cement, and aggregates
- Time spent in the mixer or in transport
- Solar exposure of materials (e.g., sun-heated aggregate stockpiles)
In normal conditions, mix temp. typically ranges from 60°F–80°F. In hot weather, it can easily exceed 90°F if not properly controlled.
Why 90°F Is a Critical Threshold
Once concrete mix temperatures climb above 90°F (32°C), a number of issues can arise:
- Accelerated setting – Concrete sets faster, reducing workability and finishing time.
- Increased water demand – Workers may add water to improve slump, which can weaken the mix.
- Reduced long-term strength – Faster hydration can harm the final strength of the concrete.
- Higher cracking risk – Rapid evaporation and thermal stresses raise the likelihood of plastic shrinkage or thermal cracking.
- Durability concerns – Improperly cured hot-weather concrete is more prone to surface scaling and long-term degradation.
Mix Temperature vs. Heat of Hydration
Though often confused, mix temperature and heat of hydration are two distinct — but related — concepts:
| Concept | Mix Temperature | Heat of Hydration |
| Definition | Temperature of freshly mixed concrete | Heat released as cement reacts with water |
| Timing | At mixing and placement | During curing (especially in the first 72 hours) |
| Purpose | Affects workability and early performance | Impacts internal temperature rise & cracking risk |
| Affected By | Ingredients + ambient conditions | Cement type, mix design, curing conditions |
Higher mix temperatures accelerate the rate of hydration, which can lead to higher internal heat and increased thermal stress—particularly in large or mass pours.
Using Chilled Water to Manage Mix Temperature
One of the most effective ways to control mix temperature in hot weather is to use chilled mix water. This simple step can significantly reduce the temperature of the entire batch.
Benefits of Chilled Mix Water:
- Lowers initial mix temperature to safer levels, often keeping it well below the 90°F threshold
- Improves workability and setting time, allowing more time for placing and finishing
- Reduces risk of early-age cracking and strength loss
- Helps meet project specs in DOT, commercial, and industrial applications
Conclusion
Managing mix temperature is not just a matter of comfort—it’s essential to achieving strong, durable, and reliable concrete, especially in hot weather. Understanding the relationship between mix temperature, heat of hydration, and the tools available—like chilled water—empowers producers and contractors to make smart, proactive decisions on every job.
When the temperature rises, so should your awareness. And with the right approach, even the hottest days can produce the highest-quality results.
