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ACI 306R Document Information:
Title
Cold Weather Concreting
American Concrete Institute
Publication Date:
Jan 1, 1988
Scope:
INTRODUCTION
Definition of cold weather
This report describes construction procedures which, if properly followed, can result in concrete placed in cold weather of sufficient strength and durability to satisfy intended service requirements. Concrete placed during cold weather will develop these qualities only if it is properly produced, placed, and protected. The necessary degree of protection increases as the ambient temperature decreases.
Cold weather is defined as a period when, for more than 3 consecutive days, the following conditions exist: 1) the average daily air temperature is less than 40 F (5 C) and 2) the air temperature is not greater than 50 F (10 C) for more than one-half of any 24-hr period.* The average daily air temperature is the average of the highest and the lowest temperatures occurring during the period from midnight to midnight. Cold weather, as defined in this report, usually starts during fall and usually continues until spring.
Objectives
The objectives of cold weather concreting practices are to:
prevent damage to concrete due to freezing at early ages. When no external water is available, the degree of saturation of newly placed concrete decreases as the concrete gains maturity and the mixing water combines with cement during hydration. Under such conditions, the degree of saturation falls below the critical level (the degree of water saturation where a single cycle of freezing would cause damage) at approximately the time that the concrete attains a compressive strength of 500 psi (3.5 MPa) (Powers 1962). At 50 F (10 C), most well-proportioned concrete mix- tures reach this strength during the second day.
assure that the concrete develops the required strength for safe removal of forms, for safe removal of shores and reshores, and for safe loading of the structure during and after construction.
maintain curing conditions that foster normal strength development without using excessive heat and without causing critical saturation of the concrete at the end of the protection period.
limit rapid temperature changes, particularly before the concrete has developed sufficient strength to withstand induced thermal stresses. Rapid cooling of concrete surfaces or large temperature differences between exterior and interior members of the structure can cause cracking, which can be detrimental to strength and durability. At the end of the required period, insulation or other means of protection should be removed gradually so that the surface temperature decreases gradually during the subsequent 24-hr period (see Section 5.5).
provide protection consistent with the intended serviceability of the structure. Concrete structures are intended for a useful life of many years. The attainment of satisfactory strength for 28-day, stan dard-cured cylinders is irrelevant if the structure has corners damaged by freezing; dehydrated areas; and cracking from overheating because of inadequate protection, improper curing, or careless worltmanship. Similarly, early concrete strength achieved by indiscriminate use of excessive calcium chloride is of no avail if the concrete becomes excessively cracked in later years because of the likelihood of disruptive internal expansion due to alkali-aggregate reaction or of possible corrosion of reinforcement (see Section 8.1). Short-term construction economy should not be obtained at the expense of long-term durability.
Principles
This report presents recommendations to achieve the objectives listed in Section 1.3 (Schnarr and Young 1934a and 1934B). The practices and procedures described in this report stem from the following principles concerning cold weather concreting:
Concrete that is protected from freezing until it has attained a compressive strength of at least 500 psi (3.5 MPa) will not be damaged by exposure to a single freezing cycle (Powers 1962).
Concrete that is protected as in Section 1.4.1 will mature to its potential strength despite subsequent exposure to cold weather (Malhotra and Berwanger 1973). No further protection is necessary unless a certain strength must be attained in less time.
Where a specified concrete strength must be attained in a few days or weeks, protection at temper- atures above 50 F (10 C) is required. See Chapters 5 and 6.
Except within heated protective enclosures, little or no external supply of moisture is required for curing during cold weather. See Chapter 8.
Under certain conditions, calcium chloride should not be used to accelerate setting and hardening because of the increased chances of corrosion of metals embedded in concrete or other adverse effects. See Chapter 9.
Times and temperatures given in this report are not exact values for all situations and they should not be used as such. The user should keep in mind the primary intent of these recommendations and should use discretion in deciding what is adequate for each particular circumstance.
Economy
Experience has shown that the overall costs of adequate protection for cold weather concreting are not excessive, considering what is required and the resulting benefits. The owner must decide whether the extra costs involved in cold weather concreting operations are a profitable investment or if it is more cost effective to wait for mild weather. Neglect of protection against early freezing can cause immediate destruction or permanently weakened concrete. Therefore, if cold weather concreting is performed, adequate protection from low temperatures and proper curing are essential.
*The values in SI units are direct conversions of the in.-lb values. They do nor necessarily represent common metric ranges or sizes. For practical application. The user should adjust them to conform with local practice.
Keywords:
- subgrade preparation
- calcium chloride
- insulation
- in-place testing
- accelerating admixtures
- compressive strength
- age
- durability
- aggregates
- cold weather
- concrete construction
- materials handling
- formwork (construction)
- curing
- protection
- temperature
- concretes
- heating
- freeze-thaw durability
- form removal
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