ACI Shotcrete Inspector flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

Shotcrete definition

Mortar or concrete pneumatically projected at high velocity onto a surface, consolidating on impact; placed by dry-mix or wet-mix process.

Dry-mix process

Cement and aggregate are mixed dry and conveyed pneumatically to the nozzle, where water is added immediately before projection onto the surface.

Wet-mix process

All ingredients, including water, are pre-mixed before pumping to the nozzle; water content is controlled at the batch plant rather than at the nozzle.

Silica fume role

A very fine pozzolan added at roughly 5-12% of cementitious mass; it increases cohesion, reduces rebound, and improves strength and impermeability.

Accelerator function

An admixture that shortens set time so shotcrete gains early strength and adheres, especially on overhead and vertical surfaces; alkali-free types are preferred.

Fiber reinforcement dose

Steel or synthetic fibers added by volume, commonly around 30-60 kg/m3 for steel, to improve toughness and crack resistance; not a substitute for structural steel.

Nozzle distance rule

The nozzle is held roughly 0.9-1.5 m (3-5 ft) from the surface; too far reduces impact velocity and increases rebound and overspray.

Nozzle angle rule

The nozzle is held perpendicular to the surface, deviating no more than about 15 degrees from normal, to maximize compaction and minimize rebound.

Wet-mix pumping equipment

A piston or rotor-stator concrete pump delivers pre-mixed shotcrete through a hose to the nozzle, where compressed air accelerates the stream.

Dry-mix feeding equipment

A pressure vessel or rotary gun meters dry material into a compressed-air stream that carries it through the hose to the water ring at the nozzle.

Nozzleman motion

A steady circular or elliptical sweeping motion builds uniform thickness; dwelling in one location creates lumps and shadowed, under-filled areas.

Rebound definition

Material that bounces off the surface during spraying; it is higher for dry-mix and overhead work and must never be reused in the work.

Compressed air requirement

Dry-mix typically needs about 7-10 m3/min at 0.5-0.7 MPa at the nozzle; insufficient air causes surging and poor consolidation.

Surface preparation

Substrate must be clean, sound, and free of dust, oil, and loose material; concrete is roughened to provide mechanical bond before spraying.

SSD substrate condition

Saturated-surface-dry means the substrate is moist but has no free water, so it neither draws mixing water from nor adds water to the shotcrete.

Surface profile CSP

Concrete surface roughness classified by Concrete Surface Profile (CSP) numbers; shotcrete typically requires a CSP 5-7 profile for adequate bond.

Single-pass thickness

Maximum thickness applied in one pass, roughly 50-75 mm on walls and about 25-50 mm overhead; thicker buildup uses multiple lifts.

Overhead placement

Apply in thin lifts and allow initial set between lifts to prevent sagging and fall-out; the first material goes into corners and behind reinforcement.

Cold joint treatment

Construction interfaces are square-cut or tapered, cleaned, roughened, and wetted before resuming placement to restore continuity and bond.

Test panel purpose

Field-sprayed panels replicate job conditions; cores cut from them are tested for compressive strength and inspected for thickness and bond.

Core diameter minimum

Compressive strength cores are typically at least 75 mm (3 in) in diameter, trimmed, capped, and tested in compression per project specification.

Field strength acceptance

Field-cured strength commonly must reach about 70-85% of design or laboratory strength to account for field variability and rebound effects.

Thickness verification

Thickness is checked by probe, core, or depth gauge; the average must meet the specified thickness and no single point may fall below the stated minimum.

Bond strength check

Assessed by pull-off test or core inspection; a continuous bond line with no visible delamination or hollow sound is required.

Curing requirement

Curing begins promptly after final set using wet curing, moist cover, or curing compound to prevent plastic and drying shrinkage cracking.

Defect removal

Voids, delamination, honeycomb, and low-strength shotcrete are removed back to sound material with square edges before any repair material is placed.

Repair material compatibility

Repair material must match the parent shotcrete in strength, modulus, and thermal expansion to prevent debonding and cracking at the interface.

Silica dust protection

Crystalline silica is a health hazard; controls include wetting, ventilation, and NIOSH-approved respirators for dry-mix dust exposure.

Compressed air hazard

Never look into a nozzle or stand in line with a pressurized hose; lines are depressurized before clearing plugs to avoid struck-by injury.

ACI 506 reference

ACI 506 is the Guide to Shotcrete and ACI 506.2 the Specification for Shotcrete; they govern materials, application, and inspection practice.

ASTM C1140 scope

Covers making and testing shotcrete test panels in the field, including spraying, curing, and core extraction for strength evaluation.

Nozzleman qualification

Nozzlemen are typically certified through an approved program before production work; the inspector verifies current qualification and technique.