Shotcrete process is to use compressed air to convey the pre-dampened mix through delivery hose to the nozzle to project the material onto the sprayed surface under high velocity, and then to form concrete support layer after the projected material coagulates and hardens. At the shotcrete nozzle, air is added. The air from the shotcrete nozzle provides several functions, including to propel the mix at a higher velocity and to spread the mix out into a cone-shaped spray pattern. Since the shotcrete is being propelled at a high velocity, compaction occurs as the shotcrete particles accumulate on the application surface. Increasing the air can mean higher shotcrete velocity and better compaction, which leads to denser concrete that exhibits greater compressive strength and less permeability.
With shotcrete the W/C ratio is controlled at the batch plant or at the mixing station. The concrete needs to be plastic enough to pump. Since low W/C ratios produce a more durable and water-resistant mix, water-reducing agents are often used. In general, a W/C ratio under 0.5 produces a more durable and waterproof mix. Since the concrete is pumped wet, the process is also known as Wet-Mix and Wet.
Shotcrete/Gunite –Both Shotcrete and Gunite open up new methods of concrete construction. Sprayed concrete lets you go vertical with concrete without all the formwork needed for poured in place concrete.
One distinct advantage of either the shotcrete or gunite system over hand-application is the water/cement (W/C) ratio of the in-place concrete. A benefit of shotcrete and gunite(gunite machine)is that the in-place W/C ratio is usually less than a mix that was not pneumatically applied. One of the reasons for this is that more water is evaporated during the spraying process than is evaporated with the trowel process.
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