The drier and longer days are a boon for the construction industry during the summer months, but building concrete structures in hot, and especially dry weather comes with unique challenges such as slump loss, rapid set times and excessive surface moisture evaporation. The wind is also an issue in this environment as it exacerbates the accelerated evaporation process. One or combination of the above can cause excessive shrinkage resulting in cracking, and other issues such as placing and finishing difficulties. These all lead to different defects in concrete structures. However, with some forethought and planning, the challenge of working in the heat can be mitigated.
Let’s have a closer look at these challenges and their solutions:
Accelerated Slump Loss
Slump loss is directly related to the reduction of the free water in fresh concrete reduced mainly by hydration of the cement and evaporation. Conditions that accelerate the rate of moisture loss and the rate of cement hydration, such as high ambient and concrete temperature, low relative humidity and high wind speed, can accelerate the rate of slump loss.
All concrete has slump loss, or it would never harden, but the workability and consistency of the concrete mix need to allow for placing and finishing the concrete. In a normal environment, the concrete gradually loses its entire slump and then proceeds to harden. Excessive heat can lead to an abnormally high rate of slump loss. There are several ways to manage this.
A common solution is retempering, or the addition of water and remixing of concrete. However, retempering can reduce the strength of the concrete due to an increase in the water/cement ratio. In addition, excess water will also cause an increase in shrinkage and result in cracking, increased permeability, dusting and scaling. Hence, retempering with water can minimize the slump loss issue, however, it might also adversely affect the strength and durability. More appropriate solutions include cooling the mix to lower the concrete’s temperature which slows slump loss and also the use of an admixture to control the set time.
Plastic Shrinkage Cracking
High temperature, low humidity, and the wind will increase the speed of evaporation of surface moisture and increase the possibility of plastic shrinking and cracking. To avoid this, keep concrete temperature low, dampen substrate and forms, erect temporary windbreaks, sunshades and use fog sprays to keep the humidity high and the air temperature low. Using evaporation retarder, adding appropriate fiber, and placing concrete early in the morning and late in the afternoon also helps reduce plastic shrinkage cracks.
Faster Set Times
Hot weather impacts the setting time of concrete by accelerating the hydration and causing it to dry too quickly. The hotter the weather, the faster concrete will dry, which will make finishing more difficult and increases the chance of cracking in the final product. The hydration can also be controlled by using an admixture which retards the setting time, enhances concrete performance and allows you to better balance your concrete’s set time.
Concrete Management Tips in Hot Environments
To produce durable concrete and manage challenges arising from working in high-temperature environments, consider these tips to protect your concrete:
- Don’t let tight deadlines tempt you to order or try to place more ready-mixed concrete than you can finish and cover.
- Make sure you have enough labor and equipment to place concrete quickly. Delays and prolonged agitation lead to higher concrete temperatures and slump loss.
- Mixers, chutes, pump lines and other equipment in contact with the mix should be shaded, covered with wet burlap or painted white to reduce solar heat.
- On windy days, install windbreaks.
- Use refrigerated water, ice, or liquid nitrogen to cool the mix during batching.
- Consider beginning the job in the afternoon to capitalize on lower evening temperatures.
- Ensure each ready-mix truck carries additional superplasticizer for temperature-related slump loss.
- To protect against premature water loss, wet down substrates before pouring concrete.
- Spray aggregate piles to keep them cool and damp.
- Immediately following final finishing, begin the wet curing process, using specifications produced by the American Concrete Institute (ACI), found in ACI 308R-01 – Guide to Curing Concrete).
- And finally, utilize Kryton’s Krystol Internal Membrane (KIM)®. This admixture is specifically designed to address many of the challenges arising from concrete construction in the heat. The primary function of KIM® is to act as a concrete waterproofer, thereby enhancing the durability of the concrete. By managing the heat of hydration, KIM® can reduce shrinkage and cracking by up to 25 percent and assist in internal curing that ultimately leads to a more durable and waterproof concrete structure.
Kryton’s KIM® Admixture can Take the Heat
An example of how Kryton’s KIM® has performed well in a hot environment is the Emirates Airlines Call Center in Dubai. The project was on a tight schedule and needed to be completed in August when temperatures can soar to the high 40°C range. Kryton’s KIM was selected as the waterproofing system in place of membranes: the entire raft slab, retaining walls, and a drinking water tank was cast with Kryton’s KIM® dosed concrete. The project was delivered on schedule in large part because of the efficiency of the hot weather concreting process assisted by Kryton’s KIM® concrete waterproofing admixture.
Krystol Internal Membrane (KIM)® will help you navigate heat challenges. External membrane systems must be installed on site and are prone to site challenges such as unfavorable weather and temperature conditions, inadequate surface preparation and poor workmanship resulting in missed areas, loss of adhesion and failure of seams or welds. In contrast, KIM admixture avoids all of these risks because as a permanent part of the concrete mass, it is invulnerable to damage and because it does not require installation, it removes the potential for human error.
In addition, by controlling the heat of hydration, KIM® can reduce shrinkage and cracking which ultimately leads to a more durable and waterproofed concrete structure. Not only does KIM® give you crucial benefits during hot weather concreting, it’s also the most reliable concrete waterproofing concrete product available for your project.