ACI 306R-10 Guide to Cold Weather Concreting

ACI 306R-10 Guide to Cold Weather Concreting. 3.3—Economy Experience shows the overall costs of adequate protection for cold weather concreting are not excessive, considering what is required and the resulting benefits. The owner should decide whether the extra costs of cold weather concreting operations are a profitable investment or if it is more cost effective to wait for mild weather. Neglecting protection against early freezing can cause immediate destruction or permanently weakened concrete. Therefore, if cold weather concreting is performed, adequate planning, protection from low temperatures, and proper curing are essential. CHAPTER 4—GENERAL REQUIREMENTS 4.1—Planning The general contractor, construction manager, concrete contractor, concrete supplier, specific materials suppliers, testing laboratory representative, and owner or architect/ engineer should meet in a preconstruction conference to define in clear terms what cold weather concreting methods will be used. This guide provides a basis for the contractor to select specific methods to satisfy the minimum requirements during cold weather concreting. Plans to protect fresh concrete from freezing and to maintain temperatures above the recommended minimum values should be made well before freezing temperatures are expected to occur. Equipment and materials should be at the work site before cold weather is likely to occur, not after concrete is placed and its temperature approaches the freezing point. 5.1—Placement temperature During cold weather, control the concrete mixing temper- ature as described in Section 5.2. When placing concrete, the temperature should not fall below the values in Line 1 of Table 5.1. Determine the placement temperature of concrete according to ASTM C1064/C1064M. The more massive the concrete section, the less rapidly it loses heat. Lower minimum placement temperatures are recommended for larger concrete sections, and for massive structures, it is especially beneficial to have low placement temperatures (ACI 207.1R). Concrete temperatures much higher than the Line 1 values do not result in a proportionally longer protection against freezing because the rate of heat loss is greater for larger temperature differentials. Higher temperatures require more mixing water, increase the rate of slump loss, may cause quick setting, and increase thermal contraction. Rapid moisture loss from exposed surfaces of flatwork may cause plastic shrinkage cracks. Rapid moisture loss can occur from surfaces exposed to cold weather because of the low absolute humidity of the cold air (ACI 302.1R). Keep the temperature of concrete as placed as close to the recommended minimum value as practicable. Placement temperatures should not be higher than...