ACI Shotcrete Inspector key terms

Concrete or mortar conveyed through a hose and pneumatically projected at high velocity onto a receiving surface, where it consolidates on impact and bonds to the substrate.

A shotcrete method in which the dry cement and aggregate are mixed and conveyed pneumatically, with water added at the nozzle just before projection onto the surface.

A shotcrete method in which all ingredients, including water, are mixed before entering the delivery line, and the fully mixed material is pumped and projected with compressed air at the nozzle.

Material that bounces off the receiving surface during shotcrete placement and is not incorporated into the finished work; it is typically richer in coarse aggregate and lower in cement content than the applied mix.

The trained operator who controls the shotcrete nozzle, adjusting angle, distance, and motion to achieve proper compaction, adhesion, and uniform thickness of the applied material.

The orientation of the nozzle relative to the receiving surface during placement; it is generally held close to perpendicular so the material compacts on impact and rebound is minimized.

The standoff between the nozzle tip and the receiving surface during shotcrete application, typically kept within a recommended range so the stream stays coherent and achieves proper consolidation.

An admixture added to shotcrete, often at the nozzle, to shorten setting time and increase early strength, especially important for overhead and vertical applications.

A very fine pozzolanic byproduct of silicon metal production added to shotcrete to improve cohesion, reduce rebound, increase strength, and lower permeability.

A material such as fly ash, slag, or silica fume used in partial replacement of portland cement to improve workability, durability, or reduce heat of hydration in shotcrete mixtures.

The mass ratio of water to total cementitious material in a shotcrete mixture, a key factor controlling strength, durability, and permeability of the hardened material.

The distribution of particle sizes in the sand and coarse aggregate used in shotcrete; proper gradation affects pumpability, rebound, and the quality of the applied layer.

Discrete fibers, such as steel or synthetic, added to shotcrete to improve toughness, flexural strength, and resistance to cracking and impact.

A factory-proportioned dry shotcrete material supplied in bags, requiring only the addition of water and mixing before placement, which improves consistency and quality control.

The maximum stress a hardened shotcrete specimen can sustain under axial loading, typically determined from cores or test panels and used to verify mixture acceptance.

A sample of shotcrete applied under field conditions to a form or substrate, from which specimens are cut or cored for testing strength, thickness, and other properties.

The extraction of cylindrical specimens from hardened in-place shotcrete or test panels using a core drill, used to verify thickness, strength, and bond.

The measure of adhesion between applied shotcrete and the receiving substrate or between successive layers, often evaluated by pull-off testing or core examination.

The process of cleaning, roughening, and wetting the receiving surface before shotcrete placement to ensure adequate bond and prevent contamination or delamination.

Moistening the substrate before shotcrete application so it does not absorb water from the fresh material, helping prevent rapid drying and poor bond.

An abrasive surface-cleaning method used to remove laitance, dirt, and loose material from concrete substrates, creating a roughened profile that promotes shotcrete bond.

The complete embedding of reinforcement, such as rebar or mesh, within shotcrete so that no voids or shadowing remain behind the bars, ensuring bond and corrosion protection.

A placement defect in which reinforcement blocks the shotcrete stream, leaving voids or low-density material behind the bar and reducing encapsulation and structural performance.

Shotcrete material that misses the intended target and lands elsewhere, representing waste and a potential contamination or cleanup issue on the project.

The stage in the setting of shotcrete at which the material begins to stiffen and lose workability, marking the point after which further finishing becomes difficult.

The stage at which shotcrete has hardened sufficiently to resist penetration and support limited loading, following initial set in the setting progression.

The process of maintaining adequate moisture and temperature in freshly placed shotcrete so cement hydration can continue, developing strength and durability.

The ease with which fluids pass through hardened shotcrete, influenced by water-cementitious materials ratio, compaction, and curing, and important for durability.

A separation or loss of bond between shotcrete and the substrate or between layers, often detected by sounding and requiring repair.

A nondestructive inspection technique in which the surface is tapped with a hammer to detect hollow or delaminated areas by the resulting sound.

The process of removing defective shotcrete and restoring the area with new material to meet thickness, bond, and durability requirements.

The ability of fiber-reinforced shotcrete to absorb energy and deform without failing, often measured by flexural load-deflection testing of panels.

The formation of fissures in shotcrete from shrinkage, thermal movement, or structural stress, which can reduce durability and require monitoring or repair.

Safety gear such as helmets, eye protection, respirators, gloves, and hearing protection worn by shotcrete crews to prevent injury from rebound, dust, and noise.

Airborne crystalline silica particles generated during dry-mix shotcreting and surface preparation, which can cause silicosis and require dust controls and respiratory protection.

Trial placement and testing of the proposed shotcrete mixture, equipment, and crew before production work to verify that the specified properties can be achieved.