As one who promotes choosing process before product, I believe that the success of any project also depends on matching the appropriate equipment to the process/product chosen. Specialty equipment offers several opportunities to achieve effective results. This article will discuss the predampener, a machine used in dry-mix shotcrete application.
In wet-mix shotcrete application, the water- cement ratio (w/c) is controlled prior to discharge into the mixer-pump apparatus. High-velocity air pressure propels the mixture to the receiving surface. In a dry-mix shotcrete application, the w/c is controlled by the nozzleman. Because it is not desirable for the nozzleman to introduce all the water at the water ring, a predampener must be used to ensure proper hydration of the cement.
The predampener facilitates the process as follows: the bagged product, or œsuper sack material, is dropped into the predampener™s front hopper and moved by an auger system through a fine mist of water that dampens the product prior to it being dropped into the shotcrete gun and propelled by compressed air up to the nozzle, where the appropriate amount of additional water is then added.
When shotcrete is delivered by a ready-mix concrete truck, the mixture is already predampened from the moisture in the sand. Avoid the use of