4. CONTROL OF CONCRETE TRANSPORT AND PLACEMENT

摘要

Concrete may be transported from the concrete plant to the point of the placement by several means as a function of distance, rate of placement and environmental factors. The method of transport may affect the workability of the concrete and may cause segregation. Transportation and handling equipment should not only have the required capacity but also be capable of being adapted to different mixes and should be designed to minimise segregation. Checks are required to ensure that the method of concrete transport will not adversely affect the fresh concrete properties such as may be induced by drying, wetting or segregation. The specification may simply require a maximum workability loss as the means of controlling drying during transport, account having been taken of workability loss due to water absorption by the aggregate and other causes. A range of acceptable workabilities at the point of placement should normally take care of water gain from rain or other sources. Some specifications will also include requirements for covering open trucks and conveyors to prevent moisture loss or gain and heat gain during transport.