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One of the problems I see in dry process the nozzle man have a tendency to shoot too dry. Rebond is up and water cement ratio is too low for good compaction and hydration. When using accelerator the water is more important because it takes water to make the accelerator work. I see nozzle man try to shoot without enough water especially when shooting overhead.
The other problem I see is not enough volume of air. I have seen too small hose from the air compressure to the gun so they increase air pressure, this does not work. The bull those between compressor and gun should be same size as material hose at 100 PSI using air motor. 100 PSI will operate the air motor and for safety if a hose plugs. You have a hydraulic motor; air pressure can be reduced at the compressor to 80 PSI, for safety.
I am reading the specs for a job that I have been hired by the contractor as a consultant; it reads when shooting down the material, “turn up the air”. From a safety standpoint, this is an accident waiting to happen. The nozzle man can kink the hose, causing it to expand and break loose any material built up.
Both processes work for placing good quality concrete. Being a good nozzle man in one process does not mean you are qualified in the other process there are some things that may be similar, but other things are different. 50’ of 2 inch wet gun hose, taking in the account of surge-weight of concrete-and weight of hose, equals about 1000 pounds. Dry gun hose will float on water when shooting; wet gun nozzle man basically turns air full on and maintains angle and distance. Dry gun nozzle man has to also concentrate on controlling water
For the dry gun, the nozzle man has a lot more nozzles to choose from. 1 1/2 inch and 2 inch are used the most often; however there is 1 inch to 2 1/2 inch available I have shot material from very fine tune as much as 30% 3/8 gravel in the mix. I had shot dirt with 1 sack cement yd3 and mixes that will make 10,000 PSI concrete.
Probably one of the most unique jobs was shooting 1 1/2 inch of concrete on a 100 year old ship that was 70 feet long, 24 feet beam and a draft of 12 feet. It went back in the water sitting higher than when it came into dry dock.
Nozzleman need to check the water ring and make sure all the hoes are clean. I have seen welding tip cleaners used. This could enlarge the holes, and cause more water to be injected on side with water valve and less water opposite the water valve. I like a piece of wire to clean holes.
I trained 2 nozzleman for a job that didn’t pass the ACI exam. The first thing we discussed was the nozzle. When I asked about the water ring, they said “water water ring?”
I have in my collection of “don’ts” several nozzle bodies that ware wore out on the inside because they were used without a water ring. I have water rings with holes drill out the ¼” to get more water to the mix. This lets all the water in the on our side and dry on