The 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 geometry. 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 3D-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 strain-hardening 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.

Despite all the recent advances in the development of 3D concrete printing, this technology still has many unresolved problems. In most of the completed projects with the application of 3D concrete printing, the focus was mainly on mastering the printing of vertical walls, while horizontal structural elements were produced with conventional methods, i.e., 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.

Pervious concrete is a stormwater management practice used in the United States, Europe, China, Japan, and many other countries. Yet, the design of pervious concrete mixtures to balance strength and permeability requires more research. Sphere packing models of pervious concrete were used in compressive strength testing simulations using the discrete element method with a cohesive contact law. First, three mixtures with varied water-to-cement (w/c) ratios and porosities were used for model development and validation. Next, an extensive database of simulated compressive strength and tested permeability was created, including 21 porosities at three w/c ratios. Analysis of the database showed for pavement applications where high permeability and strength are required, advised porosity is 0.26-0.30, producing average strengths of 14.4, 11.1, and 7.7 MPa for w/c ratios of 0.25, 0.30, and 0.35. The model can guide the mixture design to meet target performance metrics, save materials and maintenance costs, and extend the pavement life.

The rapid growth of the construction industry in Asia and the consequent updating of design specifications put forward higher performance requirements for structural components, which results in a large number of existing shear walls that are not compliant with the current seismic standards. A prospective retrofitting method, which is based on replacing the existing boundary concrete or attaching external boundary columns to nonconforming shear walls, is experimentally studied. Four shear-wall specimens were designed according to the current Chinese design code: one using plain concrete boundary columns and three using ultra-high-toughness boundary columns (UHTBCs), adopting three different strengthening strategies relevant to the boundary size and the connection form. Cyclic performance, damage patterns due to UHTBCs, and connection form are discussed based on the experimental results, from which it was ascertained that shear walls with UHTBCs show improved seismic performance, compatible with the requirements of the current seismic design code, even for the reduced-boundary UHTBCs and non-connection specimens. The predictive equation for the sectional moment capacity of shear walls with UHTBCs was discussed as a practical tool for retrofitting applications. This study highlights the most important features of a rapid retrofitting measure to improve the resilience of existing nonconforming shearwall structures, while also proving to be an effective measure for newly constructed structures.

Recently, hybrid reinforcement by combining steel with fiberreinforced polymer (FRP) bars has emerged as a new system in reinforced concrete (RC) constructions. This reinforcement system can effectively overcome the ductility and serviceability challenges of FRP-RC structures. A total of 11 full-scale bridge-deck slabs were constructed and tested. The test parameters were reinforcement type, ratio, arrangement, and slab thickness. Moreover, a comparison between the experimental and predicted deflections from design provisions was carried out to verify the efficiency of the models for hybrid RC sections. Based on test results, hybrid RC slabs exhibited ductility leading to an ample warning before failure rather than brittle shear failure observed for FRP-RC slabs. In addition, hybrid RC slabs displayed good stiffness, serviceability, and load-carrying capacity. Furthermore, test results give an average bond-dependent coefficient, kb, of 1.27, close to the 1.2 recommended by ACI CODE-440.11-22. In addition, some modifications were proposed to shear equations available in\ different design codes to be valid for hybrid RC members without shear reinforcement.