ACI 306R-16 Guide to Cold Weather Concreting

ACI 306R-16 Guide to Cold Weather Concreting. 3.1—Objectives The objectives of cold weather concreting practices are to: (a) Prevent damage to concrete due to early-age freezing. When no external water is available, the degree of saturation of newly placed concrete decreases as the concrete matures and the mixing water combines with cement during hydra- tion. Additionally, mixing water is lost to evaporation even at cold temperatures. Under such conditions, the degree of saturation falls below the critical saturation. Critical satura- tion is the level at which a single cycle of freezing can cause damage. The degree of saturation falls below critical satura- tion at the approximate time the concrete attains a compres- sive strength of 500 psi (3.5 MPa) (Powers 1962). At 50°F (10°C), most well-proportioned concrete mixtures reach this strength within 48 hours. The temperature of concrete is measured in accordance with ASTM C1064/C1064M. (b) Ensure that the concrete develops the required strength for safe removal of forms, shores, and reshores, and for safe loading of the structure during and after construction. (c) Maintain curing conditions that promote strength devel- opment without exceeding the recommended concrete temper- atures in Table 5.1 by more than 20°F (–7°C) and without using water curing, which may cause critical saturation at the end of the protection period, thus reducing resistance to freezing and thawing when protection is removed (5.1). (d) Limit rapid temperature changes, particularly before the concrete has developed suffcient strength to withstand induced thermal stresses. Rapid cooling of concrete surfaces or large temperature differences between the exterior and interior region of structural members can cause cracking and can be detrimental to strength and durability. At the end of the required period (Chapter 7), gradually remove insula- tion or other protection so the surface temperature decreases gradually during the subsequent 24-hour period (7.5). (e) Provide protection consistent with the durability of the structure during its design life. Satisfactory strength for 28-day, standard-cured cylinders is of no consequence if the structure has surfaces and corners damaged by freezing, dehydrated areas, and cracking from overheating because of inadequate protection, improper curing, or careless workmanship. Similarly, early concrete strength achieved by the use of calcium chloride (CaCl 2 ) is not serviceable if the concrete cracks excessively in later years because of disruptive internal expansion due to corrosion of reinforce- ment (11.2). Short-term gains in construction economy on concrete protection should not be obtained at...