Quality Control, Testing, Safety, and Repair
Core concepts
Quality control for wet-mix shotcrete covers the delivered mix (slump, air content, temperature, yield) and the in-place product (thickness, bond, strength, and consolidation). Test panels are the standard way to verify nozzleman technique and material performance: panels are shot under job conditions, cured, and cored or sawed for testing. Cores are used for compressive strength and thickness; bond is checked by hammer sounding, coring, or pull-off methods.
Thickness is verified by probing fresh material, by coring, or by pre-installed depth gauges. Consolidation and voids are found by sounding, coring, or visual inspection behind steel.
Safety is a major exam theme. The nozzleman and crew wear a respirator (silica dust), eye protection, hearing protection, gloves, and appropriate clothing. The nozzleman controls the safety of the spray zone - no one stands downrange of the stream. Compressed-air and pump systems must be depressurized and locked out before maintenance. Rebound is slippery and contains cement; clean it up. Watch for hose whipping if a coupling fails.
Repair of defective shotcrete: remove unsound material to sound substrate, prepare the surface (clean, rough, pre-wet), and replace with compatible material. Voids behind steel must be opened and filled, not just capped.
Traps
- Treating a test panel as optional paperwork - it is the primary verification of nozzleman competence.
- Assuming a visual pass means sound material; voids behind steel are often invisible.
- Forgetting that rebound is a hazard (slip and dust) and must be managed.
Worked example
A core from a production area shows a void at the rebar plane. Correct response: sound the area, remove unsound material back to sound shotcrete, prepare and pre-wet, and re-shoot the repair - do not simply trowel a patch over the surface.