Glossary of 3D concrete printing

Plain definitions of the terms used in 3D concrete printing, printable materials and digital fabrication.

A

Accelerator
An accelerator is a chemical admixture that shortens the setting time of a cement-based mix or speeds up its early strength development.
Additive construction
Additive construction is the application of additive manufacturing to buildings and building components, forming them layer by layer from a digital model instead of casting them in formwork.

B

BIM (Building Information Modelling)
Building Information Modelling (BIM) is the practice of designing, coordinating and managing a building through a shared digital model that carries both geometry and non-geometric information such as materials, quantities and responsibilities.
Binder jetting
Binder jetting in construction is a particle-bed additive process in which a print head deposits liquid binder or activator onto successive thin layers of powder, hardening only the component.
Buildability
Buildability is the ability of a freshly deposited mix to retain its shape and carry the weight of subsequent layers without excessive deformation, buckling or collapse.

C

Cable-driven printer
A cable-driven printer is a construction 3D printer in which the print head is suspended and positioned by several winch-driven cables anchored around the working volume.
Cold joint
A cold joint is a weakened interface formed when fresh material is placed onto concrete or mortar that has already stiffened too far for the two to merge into a continuous mass.
Curing
Curing is the process of maintaining adequate moisture and temperature in freshly placed concrete so that cement hydration can continue and the material develops its intended strength and durability.

D

Digital fabrication
Digital fabrication is the manufacture of physical components directly from digital geometry using computer-controlled machines.

E

Extrudability
Extrudability is the ability of a fresh cement-based mix to be pumped through a delivery line and leave the nozzle as a continuous filament of constant cross-section.
Extrusion
Extrusion in concrete printing is the process of forcing fresh mortar through a shaped nozzle under pressure so that it leaves the nozzle as a continuous filament of defined cross-section.

F

Formwork-free construction
Formwork-free construction is the production of concrete geometry without moulds or shuttering, the fresh material holding its own shape as it is placed.

G

G-code
G-code is a numerical control programming language consisting of sequential commands that specify machine movements, feed rates and tool functions.
Gantry printer
A gantry printer is a construction 3D printer in which the print head is carried on a rigid frame of linear axes that spans the build area, moving the nozzle in three directions.
Geopolymer
A geopolymer is a binder formed when an aluminosilicate precursor reacts with an alkaline activator to produce a hardened aluminosilicate network.
Green strength
Green strength is the strength of a cementitious material in its fresh, unhardened state, which determines how much load a deposited layer can carry before the binder has set.

I

In-situ printing
In-situ printing is 3D concrete printing carried out on the construction site itself, so that walls and other elements are built directly in their final position instead of being produced elsewhere and transported.
Interlayer bond
Interlayer bond is the tensile and shear adhesion developed between two successive layers of a printed concrete element, normally the weakest plane in the hardened part.

L

Layer height
Layer height is the vertical thickness of a single deposited layer in a print, determined by the nozzle opening, the extrusion rate and the travel speed of the print head.
Layer lines
Layer lines are the horizontal ridges visible on the face of a 3D-printed concrete element, formed by the profile of each successive deposited bead.
LC3 (limestone calcined clay cement)
LC3, or limestone calcined clay cement, is a blended cement combining Portland clinker with calcined clay, limestone and gypsum.

N

Nozzle
A nozzle in concrete printing is the shaped outlet at the end of the print head through which fresh mortar is extruded, defining the width and profile of the deposited filament.

O

Open time
Open time is the period after mixing during which a printable mortar remains pumpable and extrudable, and during which a deposited layer still bonds well to the layer placed on it.

P

Parametric modelling
Parametric modelling is a design method in which geometry is described by parameters and relationships rather than by fixed, manually drawn shapes.
Post-tensioning
Post-tensioning is a prestressing method in which steel tendons are stressed after the concrete has hardened, putting the element into compression so that it can resist tensile forces in service.
Precast concrete
Precast concrete is concrete cast or otherwise formed into finished elements at a location other than their final position in the works, then transported and installed.
Print path continuity
Print path continuity is the property of a toolpath in which each layer is deposited as a single uninterrupted movement, avoiding the stops, restarts and travel moves that introduce defects into a printed element.
Printable mortar
A printable mortar is a fine-aggregate cement-based mix designed to be pumped through a delivery line, extruded through a nozzle and to retain its shape without formwork.

R

Reinforcement strategies in 3D printing
Reinforcement strategies in 3D concrete printing are the methods used to give a printed element tensile and shear capacity, since the printing process itself leaves no room for a conventional reinforcement cage.
Robotic arm printing
Robotic arm printing is 3D concrete printing in which the nozzle is carried by a multi-axis industrial robot arm that can orient the print head freely in space.

S

Set on demand
Set on demand is a 3D concrete printing strategy in which the change from pumpable to stiff is triggered at or near the nozzle, usually by dosing an accelerator into the flowing mix.
Shotcrete 3D printing
Shotcrete 3D printing is an additive construction process in which successive layers are sprayed onto the build surface by a compressed-air nozzle rather than extruded as a filament.
Shrinkage cracking
Shrinkage cracking is cracking caused by the volume reduction that concrete undergoes as it loses water or as cement hydrates, when that contraction is restrained by the element's geometry, its supports or its own stiffer parts.
Slicing
Slicing is the step that converts a solid three-dimensional model into a stack of layers and the machine instructions needed to print each of them.
Superplasticiser
A superplasticiser is a high-range water-reducing admixture that disperses cement particles so a mix stays workable at a low water to binder ratio.
Supplementary cementitious materials (SCM)
Supplementary cementitious materials, abbreviated SCM, are fine materials used in place of part of the Portland clinker in a cement-based mix.
Surface finish of printed concrete
Surface finish in 3D concrete printing is the final condition of an element's visible face, ranging from the ribbed as-printed texture left by the nozzle to surfaces that are troweled, ground, polished, rendered or coated after printing.

T

Thixotropy
Thixotropy is the property of a material whose viscosity falls reversibly while it is being sheared and recovers once it is left at rest, without any change in composition.
Toolpath
A toolpath is the programmed route that a printer head follows through space, defining the order, direction and speed with which material is deposited to form each layer.

V

Viscosity-modifying admixture (VMA)
A viscosity-modifying admixture, abbreviated VMA, is an admixture that raises the viscosity and cohesion of the paste phase of a cement-based mix.

Y

Yield stress
Yield stress is the shear stress that must be exceeded before a fresh cementitious material begins to flow, below which the material behaves as a solid.