ACI Dry-Mix Nozzleman flashcards
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32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Dry-mix process
- A shotcrete method where dry cement, aggregate, and additives are mixed and conveyed pneumatically; water is added at the nozzle.
- Water-cementitious ratio
- The ratio of water to cementitious materials by mass; in dry-mix shotcrete, it is controlled at the nozzle and typically ranges from 0.35 to 0.45.
- Silica fume
- A very fine pozzolanic material added to dry-mix shotcrete to improve cohesion, reduce rebound, and increase strength and durability.
- Rebound
- Material that bounces off the surface during application; increases with greater nozzle distance, higher air pressure, or larger aggregate.
- Accelerator
- An admixture added to dry-mix shotcrete to reduce set time and increase early strength; typically chloride-free and dosed per manufacturer.
- Dry-mix gun
- Equipment that feeds pre-blended dry material into a high-velocity air stream for transport through the hose to the nozzle.
- Water ring
- A component at the nozzle that introduces water into the dry material stream; must provide even distribution for proper mixing.
- Air pressure at gun
- The compressed air pressure measured at the gun, typically 60–100 psi, adjusted for hose length, elevation, and material.
- Hose diameter
- The internal diameter of the material hose, typically 1.25 to 2 inches for dry-mix shotcrete; affects flow and pressure drop.
- Nozzleman communication
- Clear signals or radio contact between the nozzleman and gun operator to coordinate start, stop, and adjustments during shooting.
- Nozzle distance
- The distance from the nozzle tip to the surface; for dry-mix shotcrete, typically 3 to 6 feet to ensure proper compaction.
- Nozzle angle
- The angle between the nozzle and the surface; should be perpendicular (90 degrees) for proper compaction and minimal rebound.
- Water adjustment
- The nozzleman adjusts water at the nozzle to achieve a slightly dark, moist appearance without dry pockets or sagging.
- Shooting vertical work
- Application technique for vertical surfaces: start at the bottom and work upward, maintaining a consistent layer thickness.
- Overhead application
- Shooting overhead requires thinner layers and reduced water to prevent fall-out; use a consistent motion and avoid excessive build-up.
- Test panel
- A pre-construction mock-up that simulates field conditions, used to verify mixture, technique, and to obtain test specimens.
- Surface preparation
- Cleaning and roughening the substrate to remove loose material, dust, oil, and laitance; ensures proper bond.
- Saturated-surface-dry
- A substrate condition where pores are filled with water but no free water is on the surface; prevents absorption of mixing water.
- Bonding agent
- A material applied to a prepared substrate to improve adhesion of shotcrete, especially for repairs or cold joints.
- Curing
- Maintaining moisture and temperature to allow cement hydration; begins as soon as finishing is complete and continues for a specified period.
- Cold joint
- A joint formed when a new layer is placed against previously set shotcrete; requires roughening, cleaning, and bonding agent.
- Compressive strength
- The ability of shotcrete to resist axial loads; typically determined by testing cores from a test panel or in-place.
- Bond strength test
- A pull-off test (ASTM C1583) that measures the tensile adhesion of shotcrete to the substrate; minimum typically 100 psi.
- Thickness verification
- Checking applied shotcrete thickness using a depth gauge or cores; tolerance is typically plus or minus 1/4 inch.
- Delamination inspection
- Tapping the surface with a hammer to detect hollow sounds that indicate unbonded or delaminated shotcrete.
- Respirable crystalline silica
- Airborne particles from dry-mix materials that can cause silicosis; exposure is regulated by OSHA 29 CFR 1910.1053.
- PPE for nozzleman
- Personal protective equipment including NIOSH-approved respirator, safety glasses, face shield, gloves, and hearing protection.
- Compressed air safety
- Never exceed hose rated pressure; secure couplings with safety pins; do not stand in line with the hose.
- Waste disposal
- Contain rebound and wash water; prevent entry into storm drains; follow local environmental regulations.
- Dry, dusty material
- A troubleshooting symptom indicating insufficient water at the nozzle; check water pressure and water ring for blockage.
- Sagging or sloughing
- Excess water or thick layers cause material to sag; reduce water, reduce layer thickness, or increase accelerator.
- Clogged hose
- Blockage in the material hose; stop material feed, reduce air, and clear safely without looking into the hose end.