Hot Weather Concrete Resources

6/18/2025

Hot weather concreting can be a challenge – to make your next hot weather concreting project a success, ACI has various resources & learning tools available.

ACI PRC-305-20: Guide to Hot Weather Concreting defines hot weather as, “one or a combination of the following conditions that tends to impair the quality of freshly mixed or hardened concrete by accelerating the rate of moisture loss and rate of cement hydration or otherwise causing detrimental results: high ambient temperature; high concrete temperature; low relative humidity; and high wind speed.”

So, does that mean that concrete can’t be placed on a sunny day when it’s hot outside? No, but hot weather can create problems in delivery, mixing, placing, and curing concrete that can adversely affect the properties and serviceability of the concrete, so precautions need to be taken.

Hot Weather Effects on Concrete
Various adverse effects on the properties and serviceability of concrete are brought on by hot weather. Among them are:

• Effect on strength—Concrete mixed, placed, and cured at elevated temperatures normally develops higher early strengths, but 28-day strength may be reduced.
• Effect of proper curing—Inadequate curing combined with high placement temperatures impairs the hydration process and reduces strength.
• Effect of surface drying—The probability of plastic shrinkage cracking increases whenever the environmental conditions increase evaporation or when the concrete has a reduced bleeding rate. Plastic shrinkage cracking is frequently associated with hot weather concreting in arid climates but is seldom a problem in hot and humid climates where relative humidity is rarely less than 80%.
• Effect on air entraining—Increases in concrete temperature will generally reduce the amount of entrained air in the concrete.

Hot Weather Concrete Problems
Potential problems for concrete in the freshly mixed state include:

• Increased water demand.
• Increased rate of slump loss and corresponding tendency to add water at the job site.
• Increased rate of setting, resulting in greater difficulty with handling, compacting, and finishing, and a greater risk of cold joints.
• Increased tendency for plastic shrinkage and thermal cracking.
• Increased difficulty in controlling entrained air content.

Concrete Damage Caused by Hot Weather
Damage to concrete caused by hot weather can never be fully alleviated. Potential deficiencies to concrete in the hardened state can include:

• Decreased strengths resulting from higher water demand.
• Increased tendency for drying shrinkage and differential thermal cracking from either cooling of the overall structure, or from temperature differentials within the cross section of the member.
• Decreased durability resulting from cracking.
• Greater variability of surface appearance, such as cold joints or color difference, due to different rates of hydration or different water-cementitious material ratios (w/cm).

ACI Hot Weather Resources

ACI Publications:

ACI PRC-305-20: Guide to Hot Weather Concreting:

This guide defines hot weather, discusses potential problems, and presents practices intended to minimize them. These practices include selecting materials and proportions, precooling ingredients, and batching. Other topics discussed include length of haul, consideration of concrete temperature as placed, facilities for handling concrete at the site, and, during the early curing period, placing and curing techniques, and appropriate testing and inspection procedures in hot weather conditions.

ACI SPEC-305.1-14(20) Specification for Hot Weather Concreting:

Provides requirements for hot weather concreting that the architect/engineer can apply to any construction project involving hot weather concreting by citing it in the project specification.

Online Learning - ACI University Courses:

On-Demand Course: Hot Weather Concrete:

This webinar will discuss the current state-of-the-art developments regarding hot weather concrete, the impact of new materials and construction practices on the risk of damage from hot weather.

On-Demand Course: State-of-the-Art Developments in Hot Weather Concreting:

This webinar will discuss the current state-of-the-art developments regarding hot weather concrete, the impact of new materials and construction practices on the risk of damage from hot weather.

On-Demand Course: Impact of Hot Weather Conditions on Concrete Repairs (Part 1):

Repairing concrete in hot weather requires planning to ensure a successful project. This course will assist contractors, material suppliers, and specifiers with practical information on planning, constructing, and designing successful concrete repairs in hot weather.

On-Demand Course: Impact of Hot Weather Conditions on Concrete Repairs (Part 2):

Repairing concrete in hot weather requires planning to ensure a successful project. This course will assist contractors, material suppliers, and specifiers with practical information on planning, constructing, and designing successful concrete repairs in hot weather.

On-Demand Course: Hot Weather Concrete – Best Practices and Lessons Learned:

This presentation will cover best practices and examples from projects where pre-cooling measures, moisture controls, mixture adjustments, and admixture technologies have been implemented to reduce adverse effects to the concrete under hot, drying conditions. Case studies from large infrastructure projects in North America will be shown to describe different cost-effective ways to improve constructibility of field operations in hot weather.

Free Online Education Presentations:

Hot Weather Concrete Specification Choices to Achieve Architectural Concrete Results by Richard Szecsy

Hot Weather Concreting in South Louisiana by TJ Harris

Breaking the Ice: Controlling SCC in Hot Weather by Stacia Van Zetten

The Hot Weather Concrete Committee develops and reports information on hot weather concreting.

View all ACI information on Hot Weather Concreting here.