Importance of Fluid and Quickly Freezing Materials

On-site robotic construction, particularly with fluid and fast-setting clay and concrete mixtures, plays a crucial role in the future of 3D-printed housing. The choice of material is critical not only for structural strength but also for the overall success of the printing process.

Why Fluid and Rapid-Setting Materials Matter

Material selection in 3D printing construction is critical for several key reasons:

1. Flowability (Rheology):
   The material must flow easily through the printer nozzle and be deposited in uniform layers. This property is directly related to water content, additives, and the size and shape of aggregates (such as sand or gravel).
2. Rapid Setting:
   Each printed layer must achieve sufficient stiffness to support subsequent layers. Without this, structures can collapse or deform. This is especially critical when printing tall walls. Rapid-setting additives in cement- or clay-based mixes ensure this property.
3. Sufficient Strength:
   Once hardened, the material must meet the required levels of compressive and tensile strength to serve as a load-bearing component.
4. Open Time (Workability Duration):
   The material must remain workable in the printer’s reservoir or pumping system long enough to complete the printing process without setting prematurely.

Clay-Based Mixtures

Clay is attracting attention in 3D-printed construction due to its natural and sustainable properties. However, it presents certain technical challenges:

1. Setting Time:
   Natural clay can take a long time to dry. To address this, faster-drying clay mixes are developed using small amounts of cement, geopolymer, or drying accelerators.
2. Water Content:
   Adequate water is required for flowability, but excess water reduces strength and increases shrinkage.
3. Shrinkage:
   Clay tends to shrink as it dries, which can lead to cracking. This can be mitigated with fiber reinforcements or special aggregates.
4. Structural Strength:
   On its own, clay may not provide sufficient load-bearing capacity for multi-story structures. In such cases, clay can serve as a formwork to be filled with concrete or be used in hybrid solutions such as clay–polymer composites.

Example:
Projects like “Pylos” demonstrate how local soil, water, and binders can be combined in clay-based mixtures to print large-scale architectural components.

Concrete-Based Mixtures

Concrete is a natural candidate for 3D printing due to its ubiquity in construction. However, traditional concrete is not suitable for this technology. Specially formulated 3D printing concretes have therefore been developed:

1. High Flowability:
   The mix must be easily pumpable and pass through the nozzle. This is typically achieved using superplasticizers.
2. High Buildability:
   Each printed layer must hold its shape without collapsing under its own weight. This is achieved with rapid-set accelerators and viscosity-modifying agents.
3. Rapid Setting:
   The goal is for the concrete to begin setting within minutes during the printing process, requiring precise control of setting times.
4. Aggregate Size:
   To avoid nozzle blockages, aggregate size is reduced compared to conventional concrete, usually kept under 2 mm.
5. Strength:
   The hardened concrete should match or exceed the mechanical performance of conventional concrete.

Example:
Numerous research centers and companies are developing high-performance 3D-printable concretes reinforced with nanomaterials, special polymers, and fibers.

Integration with Robotic Systems

To utilize these specialized materials effectively, robotic systems must also be equipped with advanced capabilities:

1. Precision Control:
   Robotic arms must deposit material in accurate, repeatable layers.
2. Material Delivery System:
   Powerful pumps and mixers are required to deliver a consistent, homogeneous mixture to the nozzle.
3. Sensors and Real-Time Feedback:
   Environmental conditions (temperature, humidity) and material properties (viscosity, setting time) must be monitored and adjusted dynamically during the print.
4. Mobility (For On-Site Construction):
   For large-scale structures, robots should be integrated with mobile platforms or flexible systems like cable-driven setups to allow movement across the construction site.