An Application Process that Can Speed Things up a Bit
On most large-scale infrastructure projects, concrete work is a slow, but vital part of the job, especially during the project’s early stages. Excavating the site, building and placing the formwork, pouring and finishing the concrete, and waiting for the material to set and bond make traditional cast-in-place construction a timely and labor-intensive method. Many owners and contractors are gushing over an old, but new-and-improved technology that can significantly speed and simplify on-site placement of structural concrete: pre-mixed concrete sprayed in place at high velocity, called Shotcrete.
Long-timers might remember a decades-old spray concrete technique, sometimes called gunite, that is similar, but different in important ways, both in its application technique and its quality and benefits. As described in The Balance Small Business, “With the gunite method, the dry concrete ingredients are placed into a hopper and then pushed out pneumatically through a hose to a nozzle. The nozzle operator then controls the addition of water at the nozzle, turning the dry ingredients into concrete that is fully mixed by the time the material hits the host surface. This gives the operator control over the water content being put into the mix, allowing for a better placement process without the need for additional accelerators. It is the recommended method when the process involves frequent stops during the application process.”
In contrast, it continues, “Wet-mix Shotcrete uses fully mixed concrete and sends it through a hose and nozzle without additional water. This is the most commonly used process, as it produces less rebound (material that falls to the ground and is wasted) and dust compared to dry-mix gunite. The greatest advantage of the wet-mix process is that larger volumes can be placed in less time.”
The Secret Is in the Mix
According to a Concrete Construction newsletter, “The wet-mix permits better control and more versatile mix designs than the dry-mix process. Any type of admixture such as an air-entraining, water-reducing and/or set-controlling agent can be used. Thorough mixing of the ingredients is easier to achieve. More accurate control of the mix proportions is possible. The mix proportions for the wet-mix process are about the same as for the dry-mix process. The entire mix is premixed to a slump suitable for the work.”
Concrete Quality Still Remains Influential to Outcome
In either method, it’s important to accurately control the physical and chemical properties by ensuring the proper proportion of water is contained in the mix to maintain appropriate application consistency as well as achieve the specified slump, finish and strength in the finished product.
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