Shotcrete Rules we Live by
These are the rules that apply on every job we run, whatever the site, the mix or the machine. Each one has a reason behind it, and we teach these reasons on our courses. The site's own rules, the ground control plan and the SWMS sit above everything.
At the Agi Truck
Water is never added to correct slump. The only water that goes into a load is the allowable water printed on the docket, and no water if none is printed on the docket. Added water that is not in the mix design, lowers the strength the designer relies on.
A load is retempered once, with plasticiser to the manufacturer's procedure, before discharge. Once discharge starts the volume left in the bowl is not known, so the dose cannot be worked out and the load can be overdosed. If retempering does not bring the load into the specified slump range, it is rejected, and the rejection is recorded with the reason.
The slump is checked on arrival, before discharge, and the load is accepted or rejected on that reading. The temperature is recorded with it.
At the Nozzle
Air on before accelerator on. Accelerator off before the concrete stops. The nozzle is pointed at the floor and away from people whenever the air, accelerator or pump is running.
The nozzle is held at 90 degrees to the substrate, 1.0 to 1.5 m away by hand and 1 to 2 m from a robotic rig. The angle is opened only to fill behind steel and brought straight back.
The accelerator dose rate comes from the mix design and pre trials and is worked out as a percentage of the total binder. Overdosing of accelerator costs 28 day strength permanently.
Rebound is never sprayed over and never put back through the hopper. The area is cleared before spraying, and spraying runs in horizontal bands from the bottom up so rebound falls below the band being sprayed. More air does not cut rebound. It can make it worse.
No pass goes on thicker than the material will carry. Any deep holes or overbreak should be filled first.
Concrete Delivery Line
Every coupling on the concrete line, the air line and the accelerator line has a whip check or safety pin for clamps. Every hose is rated above the pump's maximum concrete pressure, and the line is checked end to end before spraying.
The baseline pressure is noted after priming. A sharp spike of more than 10-15 bar above it is treated as a blockage forming. Nobody raises the pressure or the engine revs to push a blockage through. Nobody opens a coupling until the pump has been stopped, the pressure relieved by reversing, the pump isolated, the air line bled and zero verified at more than one gauge (check for dead). Nobody straddles a line to open it, and nobody stands in the line of fire.
Nobody passes under the boom, and no other work goes on in the heading during spraying. The exclusion zone are well defined and respected.
Test Panels and the Ground Conditions
Test panel are sprayed from the same load, at the same time, in the same orientation as the actual job. A square panel is sprayed at the production dose. It is not moved within 18 hours and it is at the laboratory within 48. A specimen can be rejected before it is tested if it was not sprayed correctly or has been damaged, but just never because of its final result.
Re-entry is set by strength, not by time. Nobody stands under fresh shotcrete until the re-entry tests reach the minimum site requirement, generally 1 MPa, and any other ground support is installed. heat and time passed is not evidence of strength.
The pre-start covers the carrier, the boom, the pump and the compressor, and the operator completes and signs it before commencing. Nobody signs for something they did not do or did not see.
Anyone can give the stop signal, and it is always obeyed.
These controls are part of what we teach on the EFNARC nozzle operator courses, Robotic and Hand Spraying. The course pages have the modules and the enquiry form.
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