International Concrete Abstracts Portal

Biochar properties—in particular, its fineness and ability to absorbwater—can be exploited to modify the rheological behavior ofcementitious conglomerates and improve the hydration of cementpaste under adverse curing conditions, such as those related tothree-dimensional (3-D) concrete printing. Regarding the freshstateproperties, the study of rheological properties, conductedon cementitious pastes for different biochar additions (by weightof cement: 0, 1.5, 2, and 3%), highlights that the biochar inducesan increase in yield stress and plastic viscosity. The investigationof mechanical properties—in particular, flexural and compressivestrength—performed on mortars evidences the internal curingeffect promoted by biochar additions (by weight of cement: 0, 3,and 7.7%). In fact, compared to the corresponding specimens curedfor the first 48 hours in the formwork, specimens with biochar addition cured directly in air are characterized by a drastically lowerreduction in compressive strength than the reference specimens—that is, approximately 36% and 48%, respectively. This interestingresult can also be exploited in traditional construction techniqueswhere faster demolding is needed.

In this study, fabric formwork is used to cast I-shaped and non-prismatic tapered reinforced concrete (RC) beams that have up to a 40% reduction in concrete volume, resulting in lower embodied CO₂, compared to a rectangular prismatic beam. The primary aim of this research is to use distributed sensing to characterize the behavior of these shape-modified beams to an extent that was not previously possible and compare their behavior to that of a conventional rectilinear beam. Four RC beams (a rectangular control and three fabric-formed sections) were tested in three-point bending. Distributed fiber optic strain sensors were used to measure strains along the full length of the longitudinal reinforcement, and digital image correlation was used to acquire crack patterns and widths. The results indicate that fabric-formed RC beams can achieve the same load carrying capacity as conventional rectilinear prismatic beams and meet serviceability requirements in terms of crack widths and deflections. The longitudinal reinforcement strains along the full length of the specimens were captured by Canadian concrete design equations as they account for the effects of both flexure and shear on reinforcement demand.

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.