With rising world temperatures due to global warming, the job of concrete operators in hot, arid and tropical climates just got more challenging. Concrete placement in hot summer months or in regions of the world with constant high temperatures like Central & South America, the Middle East, Africa, South East Asia and Australia requires comprehensive planning, precise rapid execution and close monitoring during the finishing and curing phases.
What temperature range can be considered hot for fresh concrete pouring? Whenever the temperature reaches above 77 or 90 degrees Fahrenheit, a plan and specific measures should be put in place to remedy the damaging effect of such temperature. Consider that an increase of 20 degrees Fahrenheit can shrink the setting time to about 50 percent!
Placing fresh concrete in high temperatures impacts just about every step of the process, from concrete handling, the placing, setting and curing time. In addition, the high temperature also affect the cement mixture itself, the concrete equipment used to batch and transport the concrete. All of the above factors must be considered and addressed when designing a plan for the job.
Some of the main risks are accelerated cement hydration (which can cause plastic shrinkage and cracking), higher water-cement ratio that could cause reduce strength and slump loss.
Below are some measures that can be taken to reduce risks of plastic cracking and lower strength:
- Hire a crew experienced in rapid concrete placing in these hot conditions.
- Check forecast temperatures (day highs and night lows) and plan the job on the best days.
- Make sure you have adequate water availability on the site.
- Order or rent sunshades from the sun prior to pouring to reduce the surface temperature.
- Schedule wind screens in areas prone to high winds conditions.
- Rent misting or fogging equipment.
- Schedule your crew and pouring at the coolest times of the day (early morning and night time).
- Select the proper cool concrete mixture and set retarders for the job.
- In temperatures above 90° F the use of liquid nitrogen on the batching truck.
- Mist cool water on subgrade forms and steel reinforcement prior to placing.
- Have chilled water on hand to adjust the slump when needed.
- Check the rate of evaporation, the relative humidity and the concrete temperature with the help of a Nomogram. This is optional when operating in temperatures below 80° F but a must for temperatures above 90° F.
- Poor softer concrete so that it can be placed more rapidly but don’t add too much water to the mix.
- Choose proper curing methods (set retarders and water reducers) and apply when the concrete finishing is done.
SETTING, FINISHING & CURING
- Use retardant admixtures during the setting time.
- Make sure finishing is complete (when the surface sheen has disappeared) before starting the curing process (minimum 3 days).
- Never add water to concrete during the 3 days of finishing!
- Install sunshades, wind screen, misters or foggers to protect the concrete during the curing process.
Following the above recommendations, with proper planning and careful execution, placing concrete in hot weather conditions can be successfully achieved. Have any questions on concrete mix or equipment? Give us a call at: (503)283-2105