Hot weather conditions can greatly impact every aspect of the production and placement of concrete, from its initial creation to the final stages of application. This is due to several factors, including an increase in the rate of hydration, which can result in faster hardening and setting times. Additionally, hot weather can cause increased movement of moisture both from within and on the surface of the concrete, which can negatively affect its long-term strength and durability.
It’s important to note that the impact of hot weather on concrete is not solely dependent on temperature alone. Factors such as relative humidity and wind speed can also play a significant role in how the concrete sets and hardens. The combined effect of these variables can result in significant variations in the final product, which can have implications for its structural integrity and overall performance over time.
Effect of Hot Weather on Concrete
Following table shows the effect of hot weather on different stages of concrete production and placement :
| Stage | Effect |
| Production | Increased water demand for given workability, Increased difficulty in controlling entrained air content |
| Transit | Loss of water by evaporation, Increased rate of loss of workability |
| Placing, finishing and curing | Loss of water by evaporation, Increased rate of loss of workability, Increased rate of setting, Increased tendency to plastic shrinkage cracking, Higher peak temperature during hydration leading to increased tendency to cracking and lower long-term strength |
| Long-term | Lower strength, Decreased durability, Variable appearance |
1. Higher Water Demand
In hot weather conditions, fresh concrete is prone to losing moisture, which can have a negative impact on its workability. To counteract this, more water is needed to maintain the desired level of workability. However, increasing the amount of water used in the concrete mixture can lead to issues such as reduced strength and increased permeability. Therefore, it is important to find a balance between maintaining workability and ensuring the concrete’s overall quality and durability. This can be achieved by using admixtures or adjusting the proportions of other materials in the mix. By carefully managing the amount of water used in hot weather conditions, the workability of the concrete can be maintained without sacrificing its long-term performance.
2. Rapid Loss of Workability
Concrete is a commonly used construction material that is known for its durability and strength. However, during hot weather conditions, the properties of concrete can be affected. One of the main issues is that the rate of hydration, which is the chemical reaction between cement and water, increases in hot weather. This can cause the concrete to set too quickly and lose its workability, making it difficult to handle and shape.
In addition to the increased rate of hydration, hot weather can also cause the concrete to lose moisture more quickly. This can happen due to evaporation caused by high temperatures, low humidity, and strong winds. As a result, the concrete can become too dry, making it difficult to work with and increasing the risk of cracking.
Overall, it is important to take measures to protect concrete during hot weather conditions to ensure its quality and durability. This may involve adjusting the mix design of the concrete to account for the faster rate of hydration and loss of moisture, as well as using techniques such as shading, misting, and covering to minimize the impact of hot weather on the concrete.
3. Decrease in Concrete Setting Time
The rapid hydration reaction of concrete results in a significant decrease in its initial setting time. This, in turn, reduces the available time for tasks such as transit, placing, and finishing. As a result, the work must be completed in a shorter amount of time than if the setting time were longer. This can present a challenge for those working with concrete as they must ensure that they are able to complete the necessary tasks within the limited time frame. Therefore, it is important for individuals working with concrete to be aware of the properties and behavior of the material in order to work efficiently and effectively.
4. Plastic Shrinkage Cracks
Evaporation is a process by which a liquid turns into vapor or gas. In the case of concrete, the rate of evaporation is affected by different factors such as temperature, wind speed, and relative humidity. When these factors increase, the rate of evaporation also increases. This means that when the temperature is high, the wind is strong, and the relative humidity is low, the rate of evaporation of water from the surface of the concrete also increases.
When freshly placed concrete bleeds, it means that the water from the mixture moves towards the surface of the concrete member. However, due to the increased rate of evaporation, this moisture dries up quickly, faster than the rate at which it is replaced by the bleeding action. This can lead to the development of plastic shrinkage cracks on the surface of the concrete. These cracks can compromise the structural integrity of the concrete and cause other problems in the long run.
Therefore, it is important to consider the environmental conditions during the concrete placement and curing process. Proper measures should be taken to control the temperature, wind speed, and relative humidity to prevent the rapid evaporation of water from the concrete surface. This can be done through the use of shading, windbreaks, and the application of curing compounds or water to keep the surface moist. By taking these precautions, the risk of developing plastic shrinkage cracks can be significantly reduced, ensuring the durability and longevity of the concrete structure.
5. Strength of Concrete
When the temperature rises, the rate of hydration reaction in concrete increases as well. This results in the concrete gaining greater early strength. However, this increase in temperature can also have negative consequences for the long-term strength of the concrete. As the concrete loses moisture over time, its workability decreases, making it more difficult to compact. This decrease in workability can lead to a reduction in the concrete’s long-term strength.
6. Durability of Concrete
In hot weather conditions, the workability of concrete is adversely affected. The high temperature causes the concrete to dry out quickly, which makes it difficult to work with. To combat this problem, more water is typically added to the mix. However, this can lead to the generation of pores within the concrete. When the moisture evaporates, these pores become empty spaces, which makes the concrete porous. This porosity negatively impacts the durability of the concrete, and can ultimately lead to structural damage. Therefore, it is important to take measures to mitigate the effects of hot weather on concrete, such as using shade or misting to keep the surface temperature down, and using alternative materials to reduce the need for water.
Placing Concrete in Hot Weather
Hot weather can cause problems for concrete, especially when the temperature rises between 75ºF and 100ºF. In particular, low relative humidity and high wind velocity can exacerbate these issues when combined with the harsh sun and high temperature. As a result, it is crucial to take steps to mitigate these conditions and prevent potential problems.
One effective way to cool concrete is to cool the aggregates. This can be done by simply sprinkling them with water and allowing the evaporation process to cool them. However, there are also other methods available, such as using ice or injecting liquid nitrogen into the mixer. It is important to note, however, that these methods can add cost to the concrete.
In addition to cooling the concrete, contractors should also be prepared to prevent rapid drying by providing sunshades, windbreaks, and other means. By taking these steps, it is possible to minimize the potential for problems caused by hot weather and ensure that the concrete sets and cures properly.
Basic Guides for Hot Weather Concreting
When preparing to work with concrete during hot weather, it’s essential to plan in advance and have all necessary equipment and materials ready beforehand. It’s important to keep the subgrade and forms moist to prevent them from absorbing water from the mix, and to use sunshades and windbreaks whenever possible. Additionally, it’s crucial to have everything prepared before the ready-mix truck arrives to avoid making the truck wait.
Effective communication with the ready-mix concrete provider is key to ensure coordination between the contractor and the producer. Once the concrete is ready, it should be placed, struck off, and darbyed immediately. To prevent rapid drying, crusting, plastic shrinkage, and rubber sets, evaporation retardants, fogging or misting with water, or a vapor-proof sheet can be used after screeding.
Temporary covers, like continuously moistened burlap, can be placed over the fresh concrete and removed in small sections immediately ahead of the finishers. Substituting a burlap drag or broom finish will eliminate other high-risk finishing practices, such as smooth trowel finish. Curing should take place when the surfaces are hard enough to resist marring.
To ensure the concrete is adequately protected, it should be sealed with a good, quality sealer for a minimum of 30 days after placing and curing. Lastly, it’s important to remember to protect the crew in high temperatures by drinking plenty of fluids and being careful with long exposure to the sun.