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5/13/2015
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Cooling a Concrete Truck Hot weather concreting is defined by ACI 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 hot weather concreting is concreting on a sunny day? In fact, hot weather concrete is as much to do with wind speed as what the concrete temperature is. Hot Weather Effects on Concrete Various adverse effects on the properties and serviceability of concrete are brought on by hot weather: Effect on strength—Concrete mixed, placed, and cured at elevated temperatures normally develops higher early strengths than concrete produced and cured at lower temperatures Effect of proper curing—Laboratory tests have demonstrated the adverse effects of high temperatures with a lack of proper curing on concrete strength. The longer the delay between casting of the cylinders and placing them into standard moist storage, the greater the strength reduction. Effect of surface drying—Plastic shrinkage cracking is frequently associated with hot weather concreting in arid climates. Effect of evaporation—Plastic shrinkage cracking is seldom a problem in hot and humid climates where relative humidity is rarely less than 80%. 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 Injection of liquid nitrogen into concrete truck 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). Typical Hot Weather Concrete Evaporation Protection Measures Damage to concrete caused by hot weather can never be fully alleviated. Potential deficiencies to concrete in the hardened state can include: Fogging Evaporation retarders Wet Burlap Wind breaks Protection of QC specimens Coordination with other project requirements Hot weather concreting can be a challenge – to minimize the disadvantages, and make your next hot weather concreting project a success, ACI has various learning tools available. ACI 305.1-14 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. ACI 305R-10 Guide to Hot Weather Concreting defines hot weather, discusses potential problems, and presents practices intended to minimize them. As part of ACI’s strategic plan, ACI proactively gathers and shares information on transformational ideas, practices, and techniques. ACI’s Hot Weather Concrete Committee develops and reports information on hot weather concreting. Web Sessions
Cooling a Concrete Truck
Hot weather concreting is defined by ACI 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 hot weather concreting is concreting on a sunny day? In fact, hot weather concrete is as much to do with wind speed as what the concrete temperature is.
Hot Weather Effects on Concrete Various adverse effects on the properties and serviceability of concrete are brought on by hot weather:
Hot Weather Concrete Problems Potential problems for concrete in the freshly mixed state include:
Injection of liquid nitrogen into concrete truck
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:
Typical Hot Weather Concrete Evaporation Protection Measures Damage to concrete caused by hot weather can never be fully alleviated. Potential deficiencies to concrete in the hardened state can include:
Hot weather concreting can be a challenge – to minimize the disadvantages, and make your next hot weather concreting project a success, ACI has various learning tools available.
ACI 305.1-14 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. ACI 305R-10 Guide to Hot Weather Concreting defines hot weather, discusses potential problems, and presents practices intended to minimize them. As part of ACI’s strategic plan, ACI proactively gathers and shares information on transformational ideas, practices, and techniques. ACI’s Hot Weather Concrete Committee develops and reports information on hot weather concreting.
Web Sessions
ACI University Course: 305.1-14 Updates to Hot Weather Concrete Specification
This webinar from covers the updated ACI 305.1-14 Specification for Hot Weather Concrete. The webinar addresses changes to the specification, calculation of evaporation rate to mitigate plastic shrinkage cracking, and provides an overview of the current state of the art of hot weather concrete.
ACI University Course: Guide to Hot Weather Concreting: Chapter 5 Production and Delivery; Chapter 6 Placing and Curing
This module is based on chapters 5 and 6, excerpted from ACI 305R-10, “Guide to Hot Weather Concreting,” address production, delivery, placement, and curing of concrete under hot weather conditions. Planning, cooling methods, controlling fresh properties, and retempering issues faced during production and delivery are considered.
Publications
ACI 305R-10 Guide to Hot Weather Concreting ACI 305.1-14 Specification for Hot Weather Concreting ASCC-1(05): The Contractor's Guide to Quality Concrete Construction - Third Edition
Journal Articles
Impact of Extremely Hot Weather and Mixing Method on Changes in Properties of Ready Mixed Concrete during Delivery
Effects of Liquid Nitrogen Cooling on Fresh Concrete Properties
View all ACI information on Hot Weather Concreting
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