Concreting in Hot Weather: Things You Need To Know

The United Kingdom, renowned for its temperate climate and often characterised by its mild, damp weather, has experienced a notable shift in recent years. Global climate change is influencing weather patterns worldwide. Concrete pouring in hot weather presents significant challenges that construction professionals must understand and prepare for. Above all, these heat waves can have significant implications for various sectors, including construction.

To ensure the successful execution of projects in such extreme environments, construction professionals must carefully navigate the intricacies of concreting in hot weather.

The Impact of Heat on Concrete Quality and Strength

As the concrete undergoes the process of cement hydration, it goes through a crucial phase of strengthening. This process involves the bonding of water with the concrete mixture, forming crystals within the concrete. To have optimal durability, proper curing concrete in hot weather techniques are essential. It may span several weeks or longer. Also, some major issues can arise during hot weather concreting:

• The high temperature causes rapid water evaporation from the concrete surface, leading to drying out. Further, this can result in weaker concrete, making it susceptible to cracks, chips, and other structural problems.
• Warm conditions can accelerate the drying process, which possibly causes the concrete to become weak or soft. Does concrete dry faster in hot weather? Yes, and this rapid drying can compromise the final strength of the concrete due to insufficient moisture during hydration.
• The increased heat may adversely affect the concrete’s performance during the critical initial curing period.
• Also, concreting in severe weather may reduce 28-day strength by up to 10% compared to optimal conditions.

How to Minimise the Effect of Hot Weather?

By adequately scheduling and implementing effective strategies, it is possible to pour concrete at a higher temperature without compromising its quality. To control the concrete’s temperature in such conditions, the following tips can be employed:

• Specialised Mix Design: Opt for a concrete mix designed for hot weather applications to enhance its performance and resilience.
• Temperature-Controlled Mixing: Make necessary adjustments to the mixture and utilise chilled mixing water to regulate the temperature during the mixing process.
• Surface Preparation: Further, dampen the substrate before placing the concrete to prevent excessive water evaporation from the mixture.
• Chemical Additives: Incorporate a retarding admixture to slow down the setting time of the concrete, allowing sufficient time for proper placement and finishing.
• Strategic Timing: Schedule the concrete pouring in hot weather early in the morning or late in the afternoon when the ambient temperatures are lower. Further, it minimises the risk of rapid evaporation.
• Environmental Controls: Settle sunshades around the concrete area to shield it from direct rays and maintain a cooler environment for better curing.
• Workforce Planning: If feasible, increase the number of workers involved in the process to expedite the finishing and confirm that the concrete is worked with promptly.

How to Keep My Concrete Mix Cool During Hot Weather?

Keeping your concrete mix cool during hot weather is essential for achieving optimal strength and durability. Here are effective strategies that professionals use to manage concrete temperature during hot conditions.

1. Water Temperature Management

The simplest way to control concrete temperature begins with your mixing water. Start by using cold water when preparing your concrete mix. The cooler the initial water temperature, the longer it will take for the concrete to heat up during hydration.

For more extreme conditions, consider these additional techniques:

• Replace a portion of the mixing water with ice or chilled water
• Store water in shaded areas or refrigerated containers before mixing
• Aim for a water temperature between 45°F (7°C) and 65°F (18°C)

2. Site Preparation and Environmental Controls

Creating a favorable environment for your concrete pour can significantly impact the success of your project during hot weather.

Before placing concrete, thoroughly wet the subgrade or formwork to create a cooler environment and prevent rapid moisture absorption from the mix. This simple step helps maintain the concrete’s workability for longer periods.

Controlling the environment around your concrete can make a substantial difference:

• Erect temporary shade structures over the pour site
• Install windbreaks to minimise hot, dry winds that accelerate evaporation
• Use shading nets over freshly laid surfaces to lower surface temperatures
• Schedule concrete pouring in hot weather for early morning or evening when temperatures are cooler

3. Chemical Admixtures and Special Mix Designs

Modern concrete technology offers several solutions specifically designed for hot weather applications:

Incorporate chemical retarders into your concrete mix to slow down the setting time, allowing for extended placement and finishing periods. These admixtures are particularly beneficial when working in extreme heat conditions.

Hydration control admixtures can regulate the hydration process, reducing the heat generated during curing. This helps prevent thermal cracking and improves the final strength of the concrete structure.