International Concrete Abstracts Portal

Despite all the recent advances in the development of threedimensional (3-D) concrete printing (3DCP), this technology still has many unresolved problems. In most of the completed projects with the application of 3DCP, the focus was mainly on mastering the printing of vertical walls, while horizontal structural elements were produced with conventional methods—that is, using formwork, which reduces the level of technology automation, or using prefabricated elements, which makes the construction dependent on their availability and supply. In this contribution, the authors propose new methods of manufacturing slabs and beams directly on site by extruding concrete onto a textile reinforcement mesh laid on a flat surface. Specimens obtained from a slab produced following this method were used for mechanical testing and investigation of the concrete-reinforcement interface zone. Finally, as proof of the feasibility of the proposed approach, a demonstrator representing a full-scale door lintel was manufactured.

Extrusion-based concrete printing technology allows the fabrication of permanent formwork with intricate shapes, into which fresh concrete is cast to build structural members with complex geometries. This significantly enhances the geometric freedom of concrete structures without the use of expensive temporary formwork. In addition, with proper material choice for the permanent formwork, the load-bearing capacity and durability of the resulting structure can be improved. This paper investigates the concrete printing of permanent formwork for reinforced concrete (RC) beam construction. A three-dimensional (3-D)-printable engineered geopolymer composite or strain-hardening geopolymer composite (3DP-EGC or 3DP-SHGC), recently developed by the authors, was used to fabricate the permanent formwork. The 3DP-EGC exhibits strainhardening behavior under direct tension. Two different printing patterns were used for the soffit of the permanent formwork to investigate the effect of this parameter on the flexural performance of RC beams. A conventionally mold-cast RC beam was also prepared as the control beam for comparison purposes. The results showed that the RC beams constructed using the 3DP-EGC permanent formwork exhibited superior flexural performance to the control beam. Such beams yielded significantly higher cracking load (up to 43%), deflection at ultimate load (up to 60%), ductility index (50%), and absorbed energy (up to 107%) than those of the control beam. The ultimate load was comparable with or slightly higher than that of the control beam. Furthermore, the printing pattern at the soffit of the permanent formwork was found to significantly influence the flexural performance of the RC beams.

To ensure a successful outcome when using cementitious materials during three-dimensional (3D) printing operations, the effects of chemical admixtures on rheological and setting behavior must be carefully adjusted to accommodate the needs for pumping, extrusion, deposition, and self-sustainability without the support of formwork. This paper highlights potential solutions offered by chemical admixtures, while discussing various testing methods and important influencing parameters. The impact of commercial polymers on viscosity, initial yield stress, thixotropy, and their variations over time are reported. Influencing factors, such as mixing energy and material interactions, are discussed. Accelerating and strength-enhancing admixtures are used to illustrate the adjustment of setting and early strength development of concrete. Understanding the possibilities of modifying fresh concrete properties will help to improve the robotic construction process as well as the design or adaptation of the printing equipment.

Three-dimensional (3D) printing, also known as additive manufacturing, is a revolutionary technique, which recently has gained a growing interest in the field of civil engineering and the construction industry. Despite being in its infancy, 3D concrete printing is believed to reshape the future of the construction industry because it has the potential to significantly reduce both the cost and time of construction. For example, savings between 35 and 60% of the overall cost of construction can be achieved by using this technique due to the possibility of relinquishing the formwork. Moreover, this innovation would free up the architectural gesture by offering a wider possibility of shapes. However, key challenges should be addressed to make this technique commercially viable. The effect of mixture composition on the rheological properties of the printed concrete/mortar is vital and should be thoroughly investigated. This paper investigates the effect of using red mud, nanoclay, and natural fibers on the fresh and rheological properties of 3D-printed mortar. The rheological properties were evaluated using the penetrometer test, flow table test, and cylindrical slump test. The estimated yield stress values were then calculated based on the cylindrical slump test. Further, relationships between the tested parameters were established. The main findings of this study indicate that the use of an optimum dosage of a nanoclay was beneficial to attain the required cohesion, stability, and constructability of the printed mortar. The use of natural fibers reduced pulp flow by improving cohesion with a denser fiber network and reducing the cracks. With respect to red mud, it may be appropriate for printable mortar, but more testing is still required to optimize its use in a printable mixture. A printability box to define the suitability of mixtures for 3D printing was also established for these mixtures.

Digital fabrication and automated manufacturing technologies have been explored for civil engineering applications in the recent past and have rapidly gained momentum. Research and industrial development activities have been primarily focused on three-dimensional (3D) printing of concrete using the basic principle of extrusion along a predefined, automatically guided path. While the automated placement and shaping of concrete has advanced and has been refined significantly, the installation of reinforcement in the concrete is still largely done using traditional methods by manual placement of conventional steel reinforcing bar in a cavity between 3D-printed walls of formwork, which is subsequently filled by conventional cast-in-place concrete or grout. The concept for the construction of a structure in an entirely automated, digitally controlled process using alternative methods of structural reinforcement is currently still to be developed. Structural reinforcement is a key requirement in any efficient and economical concrete structure, and it is a challenge to invent a process for placing this reinforcement using an automated process in line with the printing process of concrete.