10.11
Hot Weather Concreting
In dry and hot conditions, placing fresh concrete at high temperatures accelerates the setting and leads to rapid evaporation of water from the concrete, which can cause cracking.
Preferably, the concrete's temperature in hot weather conditions should not exceed 60 degrees Fahrenheit.
This is achieved by reducing the cement content, using Sulfate-free aggregates with less moisture absorption, incorporating set-retarding admixture, adding ice to the mixing water, and ensuring its complete melting before the concrete mixing is completed.
Additionally, on hot weather sites, precautions include shading the aggregate stockpiles from direct sunlight, spraying them with water to facilitate cooling by evaporation, burying the water pipes, and painting concrete handling equipment and tanks white to reflect sunlight.
Formwork is sprayed with water before the concrete is placed, and the placement is done during the cooler evening hours.
After placement, the concrete may be covered with white-colored plastic sheeting to protect it from the sun and rapid evaporation.
Lastly, in dry weather conditions, wetting the concrete and allowing evaporation of water facilitates good curing and cooling.
Concreting at elevated temperatures accelerates the hydration process, leading to quicker setting but potentially reducing the long-term strength of the concrete structure. Additionally, low air humidity fosters rapid moisture loss from the concrete, resulting in reduced workability, pronounced plastic shrinkage, and a higher likelihood of crazing.
Mitigating the heat increase in concrete can be economically achieved by shading aggregate stockpiles to prevent heating from solar radiation, burying water pipes, and painting exposed pipes and tanks white to reflect heat. Lowering the cement content in the mix can reduce the total heat released from hydration; in this case, the decrease in workability due to less cement content can be compensated by selecting aggregates with low absorption rates and minimal impurities. Adjusting workability and setting time is also possible through the application of set-retarding admixture. Incorporating ice into the mixing water helps to control the temperature. It is crucial, however, to ensure the ice is completely dissolved during the mixing process.
It is advisable to place the concrete within 45 to 60 minutes after mixing on dampened formworks and during the cooler evening hours. Post-placement, it is crucial to ensure the evaporation rate does not exceed 0.25 kg/m2per hour on the concrete surface. To protect the concrete from excessive daytime heat, it should be covered. During dry conditions, wetting the concrete can provide dual benefits of cooling and promoting effective curing.
In dry and hot conditions, placing fresh concrete at high temperatures accelerates the setting and leads to rapid evaporation of water from the concrete, which can cause cracking.
Preferably, the concrete's temperature in hot weather conditions should not exceed 60 degrees Fahrenheit.
This is achieved by reducing the cement content, using Sulfate-free aggregates with less moisture absorption, incorporating set-retarding admixture, adding ice to the mixing water, and ensuring its complete melting before the concrete mixing is completed.
Additionally, on hot weather sites, precautions include shading the aggregate stockpiles from direct sunlight, spraying them with water to facilitate cooling by evaporation, burying the water pipes, and painting concrete handling equipment and tanks white to reflect sunlight.
Formwork is sprayed with water before the concrete is placed, and the placement is done during the cooler evening hours.
After placement, the concrete may be covered with white-colored plastic sheeting to protect it from the sun and rapid evaporation.
Lastly, in dry weather conditions, wetting the concrete and allowing evaporation of water facilitates good curing and cooling.
- Hot Weather Concreting - The process where concrete setting is affected by hot weather conditions.
- Hydration Process - The reaction that binds together cement and water in the concrete mix.
- Retarding Admixture - Substance to slow down concrete setting time in hot weather.
- Workability - Ease with which concrete can be mixed, placed, and finished.
- Aggregate Stockpiles - Stored piles of sand, gravel, or crushed stone in the concrete mix.
- Define Hot Weather Concreting – Describe the challenges and methods in this context (e.g., hot concrete).
- Contrast Normal Weather vs Hot Weather Concreting – Discuss the differences in processes (e.g., hot and cold weather concreting).
- Explore Examples – Detail how to correctly concrete in hot conditions (e.g., watering concrete in hot weather).
- Explain Using Retarding Admixture – Overview of this method in reducing concrete setting time.
- Apply in Practice – Discuss how these concepts can be practically used in construction.
- [Question 1] What is 'hot weather concreting' and how does it affect the hydration process?
- [Question 2] What is a 'retarding admixture' and how does it adjust the setting time?
- [Question 3] How does the concept of 'workability' change in hot weather concreting?
From Chapter 10:
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