# 3D-Printed Concrete Bridges: Material, Design, Construction, and Reinforcement
## 4 Construction Techniques for 3D-Printed Concrete Bridges
### Construction Techniques  
This section reviews the construction methods used in 3D-printed concrete bridges, focusing on prefabrication and on-site assembly. Prefabricated methods involve printing structural components off-site in a controlled environment, allowing for precise quality control and optimized material usage. These components are transported to the construction site and assembled into the final structure. The Striatus Bridge demonstrates a prefabrication approach involving segmenting a digitally modeled arch into 53 individual voussoirs using a stereotomy process [13; 41]. Their technique ensured that contact surfaces experience primarily compressive forces, aligning with the principles of unreinforced masonry. Prefabricated segments were printed off-site and transported to the site for assembly. The construction process included preparing a foundation system with steel footings connected by tension ties supported by ground screws tailored to site constraints. A temporary scaffolding system accommodated the curved profile, supporting the segments during assembly. The segments were placed sequentially, with tension ties pre-tensioned before final positioning. The decentering process transferred structural loads from temporary supports to the ties and concrete segments, creating a stable, self-supporting structure. Another example of prefabrication is constructing a 4.7-m-long prestressed concrete bridge [25]. The bridge was divided into six equal-length units to facilitate transportation and printing logistics, each weighing approximately 80-90 kg. During assembly, the prefabricated units were supported on a simple brick bracket, and mortar was used to fill the joints between them, ensuring proper force transmission. The FloatArch Bridge also utilized prefabrication but integrated hybrid construction techniques to achieve a complex free-form design [18]. Segmented into nine components shown in Figure 5(a), the design used principal stress trajectories to ensure contact surfaces experienced perpendicular compressive forces. After curing, segments were transported and assembled with temporary and permanent supports. Steel cables served as tensile members, connecting the end segments cast conventionally. The absence of grout or mortar allowed for disassembly and potential reuse, emphasizing sustainability. [PERSON] et al. 's girder [16], which consisted of 18 prefabricated segments joined on-site with cast end blocks, is another example of a hybrid construction approach (the segments and their assembling are shown in Figure 4(b)). These segments were printed off-site. Traditional casting was utilized for the two end blocks, essential for anchoring the post-tensioning forces and joining the prefabricated segments. These components were fabricated on-site with conventional formwork, ensuring structural integrity in areas requiring reinforcement. Similarly, the Nijmegen 29-m bridge span was divided into five simply supported parts [24]. Prefabricated elements were transported to the site, glued together, and reinforced with traditionally cast concrete anchor blocks, while the columns utilized 3D-printed concrete \"lost formwork.\" The road bridge in Ukraine was also constructed using both prefabrication and traditional in-site casting [26]. To optimize material usage and structural efficiency, the bridge utilized prefabricated minimass beams and lattice slab concrete panels, topped with a cast-in situ slab. The minimass beams reliedon axial tension and compression rather than bending strength, while the lattice slabs served as permanent formwork and a safe working platform during construction. The construction of the 3D-printed concrete bicycle bridge in Gemert, Netherlands, further exemplifies this approach [23]. Due to facility limitations, the bridge's 6.5-m span was printed at the TU/e 3D concrete printing facility in six individual elements. The segments were designed to be rotated 90\({}^{\circ}\) after printing and assembled on-site.