Concreting is the process of mixing, placing, compacting, and curing concrete to form a strong and durable structure. It is a vital part of construction work, whether for pavements, buildings, bridges, or any other infrastructure. The success of concreting heavily depends on external factors, especially the weather. While cold weather presents its own challenges, hot weather concreting demands special attention to avoid compromising the strength and quality of the finished product.

What is Hot Weather Concreting?

Hot weather concreting refers to performing concrete work in environmental conditions that adversely affect the properties and performance of fresh or hardened concrete. According to international guidelines, this typically means:

• Ambient temperatures above 30°C
  
• Low relative humidity
• High wind speeds
• Solar radiation or heated forms/surfaces

Together, these conditions accelerate water evaporation and concrete setting, which may reduce durability and workability if not properly controlled.

What is Concreting?

Concreting is the process of mixing, transporting, placing, compacting, and curing concrete to form strong, durable structures. As a vital element in modern construction, concreting must be carefully managed to ensure safety, stability, and longevity.

Why is Hot Weather a Concern in Concreting?

High temperatures increase the rate of cement hydration, causing the concrete to set rapidly. This limits finishing time and may lead to surface defects. The combination of heat, dry air, and wind causes excessive water loss, leading to early shrinkage cracks and reduced long-term strength.

What Happens to Concrete if it is Too Hot?

• Premature stiffening
  
• Plastic shrinkage and surface cracking
  
• Delayed or incomplete hydration
  
• Long-term durability issues

Is Concrete Good for a Hot Climate?

Concrete is suitable for hot climates if designed and cured correctly. When mixed with appropriate materials and protected from excessive heat, concrete offers high thermal mass, which helps regulate building temperatures and improves energy efficiency. However, poor practices in hot conditions can lead to serious durability issues.

Factors Influencing Hot Weather Concreting

1. Air Temperature – Directly affects hydration rate and evaporation.
2. Concrete Temperature – Ideal maximum is below 32°C.
3. Humidity and Wind – Influence the rate at which surface moisture evaporates.
4. Formwork and Surface Temperatures – Can contribute to rapid setting if exposed to sun.

Precautions in Hot Weather Concreting

Pre-Concrete Planning

• Use chilled water or partially replace mixing water with ice.
• Store aggregates in shade and keep them moist before mixing.
• Use retarding admixtures to delay setting and improve workability.
• Avoid cement types with high heat of hydration.
  

During Placement

• Place concrete during cooler parts of the day (early morning/evening).
• Use sunshades, windbreaks, and fogging equipment around the site.
• Reduce transportation time to avoid early stiffening.

Post-Placement Measures

• Start curing immediately to maintain surface moisture.
• Apply wet burlap, curing compounds, or misting systems.
  
• Continue curing for at least 7–14 days.
  

Effect of High Temperature on Curing

Proper curing is essential for strength and durability. In hot weather:

• Rapid evaporation reduces surface moisture required for hydration.
• Inadequate curing leads to weak surface zones (scaling, dusting).
• Increased temperature gradients cause differential shrinkage and cracking.

Prevention Tips

• Start curing immediately using water curing, wet hessian, or curing membranes.
• Maintain moist conditions for at least 7–14 days.

Undesired Outcomes in Hot Weather Concreting

• Plastic shrinkage cracks
  
• Thermal cracking
  
• Surface crusting
  
• Segregation due to rapid drying
  
• Poor compaction due to short workability window
  
• Low final compressive strength
  
• Reduced bond between layers or joints

Impact of Hot Weather on Concreting

Effect of High Temperature on Setting Time

In hot weather conditions, the initial and final setting times of concrete are significantly affected due to the accelerated rate of hydration.

🔹 Initial Setting Time

The initial setting time is the period during which concrete begins to stiffen. High ambient and material temperatures can reduce this time by up to 30–50% compared to standard conditions. This means there is less time for placing, compacting, and finishing the concrete before it starts to harden.

• Standard (at 20°C): ~45–75 minutes

• Hot weather (30–35°C+): ~20–40 minutes

🔹 Final Setting Time

This is when the concrete becomes hard enough to bear some load or finishing work. High temperatures can significantly shorten this phase, leaving little to no margin for correction or reworking.

• Standard: ~6–8 hours

• Hot conditions: as low as 3–5 hours

Key Implications

• Increased risk of cold joints if delays occur between pours

• Difficulties in finishing large slabs or complex formwork

• Poor bond strength at construction joints due to premature stiffening

• Accelerated setting may lead to reduced workability and surface defects

Preventive Measures

• Use retarding admixtures to delay the setting process

• Keep materials cool (shaded storage, chilled water)

• Ensure faster placement and compaction

• Limit batch sizes in extremely hot weather to allow for manageable placement within setting time

Effect of Hot Weather on Total Construction Cost

Poor planning in hot weather concreting leads to:

Unmanaged hot weather = Higher costs + Lower quality + Health risk

Effect of Heat on Manpower

High heat doesn’t just affect concrete—it affects the people working with it:

• Heat stress and dehydration reduce worker efficiency.
• Increased chances of fatigue, dizziness, and heatstroke.
• Labourers may rush work, compromising finish quality.

Workforce Safety Tips

• Schedule work during cooler hours (early mornings/evenings).
• Provide shaded rest areas, hydration breaks, and PPE designed for hot climates.

Best Practices for Hot Weather Concreting

• Conduct trial mixes to optimise the design.
• Use insulated or reflective formwork.
• Employ self-curing or shrinkage-reducing admixtures.
• Monitor concrete and ambient temperatures regularly.
• Train workers on rapid placement and finishing techniques.

Advantages of Hot Weather Concreting

• Faster early strength gain (if curing is well-managed)
• Longer daylight hours for construction activities
• No risk of freezing during placement or early curing
  Disadvantages of Hot Weather Concreting
• Risk of thermal and shrinkage cracking
  
• Increased need for water and admixtures
  
• Rapid loss of workability
  
• Labour fatigue and health risks
  

Relevant IS Codes for Hot Weather Concreting

🔹 IS 456:2000 – Plain and Reinforced Concrete – Code of Practice

• Clause 14 deals with Concrete under Special Conditions, including hot weather.

• Provides guidance on temperature control, curing, and precautions.

🔹 IS 7861 (Part 1):1975 – Hot Weather Concreting

• Specifically addresses procedures, precautions, and recommended practices for concreting in high temperatures.

🔹 IS 7861 (Part 2):1981 – Cold Weather Concreting

• While focused on cold conditions, it complements Part 1 for comprehensive seasonal concreting practices.

Conclusion🎯

Hot weather concreting is a common challenge in global construction—but one that can be expertly managed with the right knowledge and planning. While excessive heat accelerates setting and increases the risk of defects, following good concreting practices ensures strong, durable, and crack-free structures.

FAQs: Hot Weather Concreting

Q1: What temperature is too hot for concreting?

Concrete placement should be avoided when ambient temperatures exceed 30°C, unless proper precautions are in place.

Q2: Can I pour concrete in direct sunlight?

It’s not recommended. Direct sunlight increases surface temperature and evaporation. Use shading or pour in cooler periods.

Q3: How can I cool concrete during mixing?

Use chilled water, ice flakes, or pre-cooled aggregates. Shade storage bins and silos to lower material temperature.

Q4: How does wind affect hot weather concreting?

Wind accelerates evaporation, increasing the chance of plastic shrinkage cracks. Use windbreaks to reduce exposure.

Q5: Can concrete cure without water in hot weather?

No. Without moisture, hydration stops prematurely, weakening the structure. Continuous curing is essential in heat.

Q6: Should I add more water to increase workability?

No. Adding water on site can damage the water-cement ratio and reduce strength. Use plasticisers or retarders instead.