ACI 207.4R-20 Report on Cooling and Insulating Systems for Mass Concrete

ACI 207.4R-20 Report on Cooling and Insulating Systems for Mass Concrete. Postcooling systems require embedded temperature- sensing devices (temperature sensors or resistance ther- mometers) to provide special information for the control of concrete cooling rates. It is considered best practice to monitor temperature of concrete components, fresh concrete, and post-cooling system temperatures. Various technologies are available for monitoring temperatures. Typical methods include manual thermometers, wired temperature sensors, wired temperature sensor/datalogger systems, and wire- less temperature sensor/datalogger systems. Typical reso- lution of these devices is 2°F (1°C). Similar instruments provide data to evaluate the degree of protection aforded by insulation. Other instruments used to measure internal volume change, stress, strain, and joint movement have been described (Carlson 1970; USACE EM 1110-2-4300). CHAPTER 2—PRECOOLING SYSTEMS 2.1—General Reducing the temperature of the fresh concrete at place- ment is one of the most important and efective ways to reduce thermal stresses and cracking. Generally, the lower the temperature of the concrete when it passes from a plastic or as-placed condition to an elastic state upon hardening, the lower the tendency toward cracking. In massive structures, the reduction of the placing temperature will lower the peak temperature of the hardened concrete by a similar amount (ACI 207.2R). 2.3.1 Chilled batch water—One lb of water absorbs 1 Btu when its temperature is raised 1°F. Similarly, 1 kg of water absorbs 4.18 kJ when its temperature is raised 1°C. A unit change in the temperature of the batch water has approxi- mately fve times the efect on the temperature of the concrete as a unit change in the temperature of the cement or aggregates. This is due to the higher specifc heat of water with respect to the other materials. Equipment for chilling water is less complicated than ice-making equipment, and it avoids problems that can be encountered with handling and feeding ice to the mixer. Its consideration is always indicated whether solely for chilling batch water or in combination with other aspects of a comprehensive temperature control program, such as inundation cooling of coarse aggregates, cold classifying of fne aggregate, or postcooling of hard- ened concrete with embedded cooling coils.ACI 207.4R pdf download.