Controlling Temperatures in the Mass Concrete
Concrete Mix Control (Pre-Cooling Procedure): It is a preparation against the possible effect to the concrete properties and construction operations. When these factors are explained to the relevant persons engaged to these activities therefore measures will be taken to eliminate or minimize undesirable effects that possibly introduced. This method defines lists of possible unfavorable effects and prevents practices intended to minimize them. Among these practices are such important measures as a pre-cooling ingredient, consideration of concrete temperature as placed, transportation time and curing technique. The method of concrete temperature control will be proposed as follows:
Use of ice as part of mixing water2: This application is effective in reducing concrete temperature, because on melting alone, to absorb heat. The following measures will be applied:
v Spray cool water continually approximately at every 30 minutes interval to the course aggregate stock3. This will be done at least 2 hours in advance prior to mixing of concrete.
v Add ice as a part of mixing water for the concrete mix to reduce the water temperature. The ice will be added until the water temperature is reduced to reach 8-10 Celsius Degree. The amount of ice added to the water is dependent on the air temperature at the certain mixing day.
v Spray cool water to the trucks mixers to reduce the temperature of the trucks mixers.
v At the batching, the first batch of the concrete shall be checked its temperature. The water temperature will be continued to reduce until the concrete temperature is lower than 30 Celsius Degree prior to the delivering to the workface.
v The above process will be regularly done during the entire period of supply to ensure that the same degree of temperature always be maintained.
v At the workface upon a delivery of the concrete, the fresh concrete will be re-measured whether the temperature is still within the specified tolerance.
2 ACI 207 ,4R-93 : Cooling and Insulation System for Mass Concrete— 3.3.2 Using ice as batch water -One lb (kg) of ice absorbs 144 Btu’s (334 kJ) when it changes from ice to water; thus, the use of ice is one of the basic and most efficient methods to lower concrete placing temperatures. The earliest method involved the use of block ice that was crushed or chipped immediately before it was batched. Later methods utilized either ice flaking equipment, where ice is formed on and scraped from a refrigerated drum that revolves through a source of water; or equipment where ice is formed and extruded from refrigerated tubes and is clipped into small biscuit-shaped pieces as it is extruded.
3 ACI 207 ,4R-93 : Cooling and Insulation System for Mass Concrete— 3.4- Aggregate cooling Although most rock minerals have a comparatively low unit heat capacity, aggregates comprise the greatest proportion of concrete mixtures. Therefore, the temperature of the aggregates has the greatest influence on the temperature of the concrete. Under the most severe temperature conditions of construction, the objectives of a comprehensive temperature control program cannot be achieved without some cooling of the concrete aggregates. 3.4.3 Sprinkling of coarse aggregate stockpiles-Misting or sprinkling water onto coarse aggregate stockpiles is an inexpensive but limited means of reducing coarse aggregate temperatures. The amount of cooling that can be obtained depends upon the cooling effect of natural evaporation, which in turn, depends upon the ambient conditions of temperature, wind, and relative humidity.