Concreting in hot weather

3. Curing Practices for Hot Weather Concreting

Proper curing is essential to ensure adequate hydration and prevent premature drying, which can lead to cracking and reduced strength. In hot weather, curing practices should be modified to extend the moisture retention period:

Moist Curing: Continuously maintain a wet surface over the concrete for at least 7 days, preferably 14 days. This can be achieved by ponding water, using water-soaked burlap, or applying curing compounds.

Membrane Curing: Apply a monomolecular or multimolecular membrane curing compound to the concrete surface to reduce evaporation and maintain moisture content.

Fog Curing: Utilize fogging nozzles to continuously spray a fine mist of water over the concrete surface.

Suggested Reading: For more information on Types of concreting methods and Hydrophobic material click.

4. Jobsite Management for Hot Weather Concreting

Effective jobsite management practices are critical to ensure the success of concreting in hot weather:

Planning and Scheduling: Carefully plan the concreting sequence and schedule work during the coolest times of the day.

Communication and Coordination: Ensure clear communication and coordination among all project stakeholders, including concrete suppliers, subcontractors, and inspectors.

Site Preparation: Prepare the site by wetting the subgrade, forms, and reinforcement to minimize water absorption from the concrete mix.

Temperature Monitoring: Continuously monitor ambient, concrete, and subgrade temperatures to adjust curing and placement practices accordingly.

Worker Safety: Implement appropriate heat stress mitigation measures to protect workers’ health and safety.

By implementing these strategies, concreting projects can be successfully executed even in hot weather conditions, ensuring the quality, durability, and long-term performance of concrete structures.

Disadvantages of concrete drying in hot weather

Hot weather throws several disadvantages at concrete drying, impacting its quality and overall performance. Here’s a breakdown of the key issues:

Rapid Evaporation: High temperatures accelerate the rate at which water evaporates from the concrete surface. This disrupts the hydration process, which is crucial for concrete to gain strength.

Reduced Workability: Rapid water loss makes the concrete stiffer and harder to work with. This can lead to difficulties in achieving proper finishing and consolidation, potentially creating weak spots or uneven surfaces.

Plastic Shrinkage Cracking: As the surface loses water quickly, it shrinks at a different pace compared to the interior. This mismatch can cause cracks to appear on the surface, often referred to as plastic shrinkage cracks. These cracks can compromise the concrete’s strength and aesthetics.

Increased Risk of Thermal Cracking: Hot weather can also lead to excessive internal heat buildup within the concrete. This internal heat, combined with shrinkage from drying, can cause thermal cracking. These cracks can be deeper and more detrimental to the structural integrity of the concrete.

Reduced Strength: All the factors mentioned above contribute to a reduction in the final strength of the concrete. Without proper hydration and proper finishing, the concrete won’t achieve its full potential strength.

Does air affect the quality of concrete?

Yes, air does affect the quality of concrete, but it depends on the type and amount of air. Here’s the breakdown:

Intentionally Entrained Air: This is beneficial and  a common practice.  Small, evenly distributed air bubbles are introduced into the concrete mix through admixtures. These air bubbles provide several advantages:

Improved Freeze-thaw Resistance: When water freezes, it expands. The air bubbles provide space for this expansion, preventing the concrete from cracking. This is especially important in climates with frequent freezing and thawing cycles.

Workability: Air entrainment helps make the concrete mix more workable, which means it’s easier to place and finish.

Entrapped Air: This is  unwanted air and can negatively impact concrete quality. It occurs when air gets trapped in the mix during mixing or placement.  Entrapped air voids are typically larger and more irregularly shaped compared to intentionally entrained air bubbles.  Here’s how it can affect concrete:

Reduced Strength: Large air voids act like weak points in the concrete, reducing its overall strength.

Increased Permeability: Entrapped air can create pathways for water and other substances to penetrate the concrete, potentially leading to durability issues.

In summary: The presence of air in concrete is not inherently bad.  In fact,  intentionally entrained air is a  desirable feature. However, entrapped air is detrimental and should be minimized through proper mixing and consolidation techniques.

Conclusion in hot weather:

Concreting in hot weather requires extra attention and specific strategies to overcome the challenges it presents. While hot weather can accelerate the setting time, it also leads to rapid moisture loss and other issues that can compromise the final strength and durability of the concrete.

By following these key points, you can ensure successful concreting even in hot weather:

Adjust the mix design to include a lower heat of hydration cement, a lower water-to-cement ratio, and appropriate admixtures.

Employ proper placement techniques such as scheduling for cooler hours, using chilled concrete, and protecting the fresh concrete surface.

Implement effective curing practices like extended wet curing, membrane curing, or fog curing to maintain moisture content.

Practice meticulous jobsite management that includes planning, communication, temperature monitoring, and worker safety measures.

By taking these precautions, you can mitigate the disadvantages of hot weather concreting and achieve a high-quality, long-lasting concrete structure.