The 3D printing of cementitious materials allows you to completely rethink the construction according to an additive approach, by optimizing the production of custom components and minimizing the use of cement towards the minimum environmental impact.

The opportunities of 3D printing are increasingly entering the current construction market because they offer new technical construction solutions, while integrating design and function, aesthetics and efficiency. 3D printing can really revolutionize the conventional serial production by cutting industrialization times and product modification according to design needs, each time different.

3D printing is a production process that requires particular care in the design phase in light of the continuous balance that is established between the printing process and the material change of state. The rheology of the material, in the fresh state, together with the design geometry are decisive for the material to be self-supporting during the extrusion phase. For this reason it is suggested to design 3D models with interconnections and overhangs not exceeding 15 degrees on the vertical plane.

Consider designing highly stable components with a planar base surface at least equal to the largest section. No supports are inserted in concrete printing because otherwise they would become an integral part of the printed object. An integrated approach is preferred between form, stability and final function, by taking advantage of stiffness by shape, articulated infills and a good compromise between overall weight and printing volume. For 3D modeling we recommend software (Rhinoceros, Blender, Autocad) capable of creating closed objects (brep, mesh), while for slicing we recommend Simplify3D software that is included in the WASP 3MT LDM purchase.

Concrete 3D printing consists of the following operating phases: mixing and preparation of the material, startup of the 3D printer for the preliminary setup and preparation of the pumping system (filling the pump hopper with the fresh mixture, analog setting of the physical parameters of the material of printing). The extrusion takes place in a closed and controlled setting inside the printer; during the printing operation it is necessary to feed the pumping system with material, checking the filling level inside the pump hopper.

Once printing is finished, it is possible to extract the underlying surface, and consequently the printed object, using a transpallet or a forklift. Given the strong aggressiveness of cement mixtures, the entire pumping system needs to be washed with running water. It is mandatory to carry out cleaning operations far from the printer and the control unit.

The mixing of the cement mixture can be carried out using a cement mixer or continuous mixer, with minimum batches of use of 40 liters. In the case of packaged premixed mortar, it is only necessary to add the amount of water that makes the material in the fresh state easily workable in a range of time comparable to that before extrusion (consider at least 60 minutes). In the case of self-packaged mixing, consider the use of a concrete mixer with total batches not exceeding 80 liters. The guidelines for the mix design go to the next point.

The cement mixture suitable for 3D printing consists of the following main components: cement (CEM 32.5 / 42.5 R), silica river sand (maximum grain size 1 mm), water, viscosity modifying and super plasticizing admixtures (to promote pumpability and maintaining the consistency suitable for extrusion). The quantities of each single constituent depend on multiple factors such as: the expected performance, the containment of shrinkage, the programmed workability and setting time for printing, the specific weight. Consider a water/cement ratio = 0.3 and cement/sand ratio = 0.5.

Upon specific request and on the occasion of each installation, we prepare a cement mixture validated by our experience in the field. We can provide the indications of the mix design and the availability on the local market of the necessary products, considering only the possible shipment of chemical admixtures to reduce the carbon footprint of the shipment.

It is possible to use in the mixture polymeric fibers (PP, PVA) with a length not exceeding 2 cm. There are both anti-shrinkage fibers to limit the shrinkage during extrusion and reinforcement fibers to increase the tensile strength of the printed product. The excessive quantity of fibers can affect negatively on the mixture workability. Steel fibers are not currently supported by the pumping system.

Cementitious mixtures require an environment at a temperature not exceeding 25-30°C. For this reason it is recommended to work in closed laboratories with partial air conditioning.

The recommended nozzle diameter range for 3D printing of cement mixtures is 18-30 mm. The layer height varies from 9 to 15 mm, considering the layer/nozzle height ratio = 0.5. The thickness of the single layer varies from 20 to 40 mm, considering the partial expansion when laying the material. The nozzle diameter range of clay-based mixes is 8-18 mm.

The maximum printing volume is a cylinder with diameter D = 1 m and height h = 1 m from the ground. The use of a printing surface base affects the maximum height only.

Each mixture has specific hardening and setting times depending on the basic components present in the mix. In addition to the chemical composition, further incident factors are both of chemical-physical origin (amount of water, water temperature) and of operational-environmental origin (adequate mixing, air temperature, time interval prior to extrusion). It is recommended to use materials with workability times of over 60 minutes.

After each print session, or in any case at intervals of more than 30 minutes between one activity and another, the continuous feeding system needs to be washed with running water, according to a simple automatic cleaning procedure. The entire continuous feeding system, extruder included, can be easily disassembled and washed in an area adjacent to the work area, equipped with an adequate wastewater collection system. It is mandatory to carry out cleaning operations far from the printer and the control unit.

Current international academic research is focusing on defining mechanical behavior and quantifying the strength of 3D printed elements. The compressive and tensile strengths vary mainly depending on the mixture used and on the orientation of the layering planes of the printed object once installed.

3D concrete printing allows the construction of walls, architectural cladding systems and sculptural works in a contemporary approach of modular assembly. Thanks to 3D technology, the production of large elements, even with a high formal complexity, takes on a significant and increasingly viable role in achieving solutions that are difficult to reach or even impracticable with traditional techniques. It is in fact possible to design and produce construction modules with different shapes, functions and materials.

The minimum space required for the installation of WASP 3MT LDM consists of a surface area of 5,5 mt x 2,5 mt x h 3,60 mt. It is recommended to notify our technical staff in case of obstacles of the workspace, both at floor and ceiling level.

The operator dedicated to 3D printing operations must have followed the first use course, scheduled for the day after installation. The operator does not require special training in the field of chemistry of materials but must know the principles underlying the operation of the 3D printer and the pumping system in full awareness of the risks arising from the use of cement.

Consultancy is the basis of the customer’s training and support service both in the phase prior to the purchase of the printer and in the subsequent phase. We provide a consultancy service on the following areas: 3D modeling, slicing optimization, feasibility study and optimization of the extrusion material.