The best plan for hot weather concreting is to balance between quality, costs, and your available resources.
As weather conditions and curing behavior are hard to predict, continuous checking and monitoring the concrete temperature and strength is key to ensure efficient curing and take action when needed. An easy way to observe the concrete curing is with the use of wireless concrete sensors. Those can measure and monitor the curing over the whole project time and give real-time insight into the actual conditions.
In the steps below we have gathered our tips for each phase of the concrete process:
To truly succeed under warm conditions the planning and coordination should start in the initial phases of the concrete manufacturing process. Planning for these can save a lot of time and money later on in the project.
A good starting point is to consider the temperature conditions on site. Questions such as:
Once you have the answers to these questions it will be much easier to understand the equipment and personnel requirements for your project.
Hot weather concreting might require additional equipment such as water pumps, additional electric generators, lighting equipment (if working before the sun rises or when the sun sets) and other tools. One of the key issues in this type of conditions is that an equipment breakdown or delay may cause huge problems as the concrete will lose fluidity (also known as slump) quickly and harden much faster than under normal conditions. As discussed earlier, this can lead to a reduced quality of the cast, when the concrete is not curing effectively.
After knowing the expected weather conditions on-site, the concrete mix design can help to reduce the associated risks with hot-weather concreting:
When designing a concrete mix for hot weather concreting it is recommended to reduce the use of cement, within a reasonable margin, while still satisfying the strength and durability requirements. This will reduce the heat emission and slow down the rate of cement hydration as well as minimize the thermal expansion and the risk of cracks. An additional benefit of reducing the cement content is lower CO2 emissions for the concrete mix used, for a more eco friendly construction project.
Some admixtures, such as fly ash or GGBS (Ground Granulated Blast-furnace Slag), may be used to delay the setting time and reduce the heat emission from the cement hydration process.
One of the most successful techniques in warm weather is to reduce the temperature of the concrete mix by cooling it down. This can be done in multiple ways, and ACI recommends the following techniques:
These techniques have the potential to reduce the concrete’s temperature by 0,5 °C to 11 °C depending on the chosen technique. It is worth noting that the cost of the different techniques presented above differ considerably depending on the required equipment, personnel expertise, project location, etc.
It is important to minimize the transportation time as much as possible and reduce the risk of delays to prevent early concrete setting problems. These could range from the concrete mix hardening in the mixing truck to the added difficulty of pumping the concrete due to high rigidity.
Warm weather conditions may increase the moisture evaporation rate and reduce the setting time. This means that the concrete mix starts to solidify quicker and becomes harder to handle. Therefore, the period to place, finish and cure the concrete will be shorter than under other conditions.
To avoid the high temperatures that can negatively influence your concrete strength, move the pouring time tolater at night or early in the morning. This way the concrete can cure for some time without the influence of the hot temperatures. For this strategy to work, it is important to coordinate well with the batching plant and the subcontractors.
The main goal during the curing phase is to guarantee that the cement hydration proceeds successfully in order to achieve the maximum strength potential of the concrete mix. The two most important things to avoid are moisture loss and excessive temperatures.
There are many curing techniques to maintain water content and prevent moisture loss in casted concrete:
These help to preserve the moisture within the concrete and assure that the cement will hydrate fully. Cured concrete has a higher final strength, reduced risk of surface cracking and higher durability than concrete that has not been cured.
To be able to check if the measures are effective, continuous checks of the curing and temperature are important. This can be done with data loggers or, an even better option, using wireless concrete sensors. These can be used to measure and monitor the concrete temperature, maturity and strength development continuously. Doing this will allow you to take the required actions to prevent big temperature differentials, surface drying or accelerated rate of hydration. This will minimize the risk of thermal cracking, drying shrinkage and surface flaking all of which can affect the durability and strength of your concrete.