ACI 305R-20 Guide to Hot Weather Concreting

ACI 305R-20 Guide to Hot Weather Concreting. 1.2—Scope This guide identifes problems associated with hot weather concreting and describes practices that alleviate these poten- tial adverse efects. These practices include suggested prepa- rations and procedures for use in general types of hot weather construction, such as pavements, bridges, and buildings either cast in place or precast. Temperature, volume changes, and cracking problems associated with mass concrete are treated more thoroughly in ACI 207.1R, 207.2R, and 224R. 3.3—Practices for hot weather concreting Good judgment is necessary to select procedures that appropriately blend quality, economy, and practicability. The procedures selected will depend on type of construction, characteristics of the materials being used, and the experience of the local industry in dealing with high ambient tempera- ture, high concrete temperatures, low relative humidity, and high wind speed. The most serious difculties occur when personnel placing the concrete lack experience in constructing under hot weather conditions or in doing the specifc type of construc- tion. Last-minute improvisations are rarely successful. Early preventive measures should be applied with the emphasis on materials evaluation, advanced planning and purchasing, and coordination of all phases of work. Planning in advance for hot weather involves development of an appropriate concrete mixture and a detailed plan for mixing, trans- porting, placing, protecting, curing, and testing of concrete. Precautions to avoid plastic shrinkage cracking are impor- tant. The potential for thermal cracking, either from overall volume changes or from internal restraint, should be antici- pated, properly assessed, and mitigated. Typical methods to minimize and to limit crack size and spacing include: proper use and timely installation of joints; increased amounts of reinforcing steel; and practical limits on concrete temperature. Some adjustments to concrete mixtures that have been successful in hot weather conditions include: using a reduced cement content; using a low-heat- of-hydration cement; the selection and dosage of appropriate chemical admixtures; the use of supplementary cementitious materials to replace cement; and the use of synthetic micro- fbers and macrofbers. Developing a comprehensive plan and procedures for use in hot weather concreting conditions include the following practices and measures used to reduce or avoid the potential problems of hot weather concreting, as discussed in detail in Chapters 4 to 6.ACI 305R pdf download.