Search

Shotcrete 3D Printing (SC3DP) applies concrete layer by layer using a wet‐spray process. The resulting hardened concrete properties of the applied SC3DP layers (e.g. height, width or mechanical strength) are largely dependent on the selected material and process parameters. In this context, the nozzle geometry is an important influencing parameter. During printing, the velocity of the shotcrete jet is significantly influenced by the nozzle outlet diameter. Therefore, in the present study, the effect of the nozzle outlet diameter (15 ‐ 30 mm) is investigated with regard to the resulting layer homogeneity, i.e. local density and aggregate distribution in the cross‐section, and hardened concrete properties, i.e. flexural strength. By analysing the manufactured specimens, an uneven distribution of the aggregate is observed horizontally across the cross‐section of the layers. An accumulation of aggregate is present in the core of the layer resulting in a cement paste‐rich region in the edge areas. This leads to increased local densities in the core of the specimen. The application of the concrete with small nozzle outlet diameters results in the highest local densities and the highest flexural strength. [ABSTRACT FROM AUTHOR]

Utilization of an Electromechanical impedance (EMI) technique with Piezoelectric (PZT) sensors has showed potential for Structural Health Monitoring (SHM). The changes in mechanical structure via flexural bending and cracking can be detected by monitoring the deviations in electrical impedance signals recorded with embedded PZT sensors. This paper has conducted a comprehensive study on the potential of an EMI technique with embedded PZT sensors with 3D Concrete Printing (3DCP) structures subjected to flexural bending test until plastic failure. The impact of different Piezoelectric housing methods and materials has been studied comprehensively through the monitoring of EMI signals. Experimental results indicate that material housing types and thickness affect the sensitivity of EMI readings but also performed as a reinforcement when a load is directly applied. The embedded PZT sensors with the EMI technique have shown strong potential to address the cost and lifecycle challenges posed by traditional construction methods as the insertion of PZT sensors seamlessly functions with 3DCP workflows. Further developmental work can be carried out to address the sensitivity of the sensor, performance as a reinforcement, and installation automation. The results proved that the coated sensors could detect fractures in 3DCP concrete with decreased sensitivity on thicker coating layers through the variance in materials and coating thickness in the paper. [ABSTRACT FROM AUTHOR]

In Singapore, there is an increasing need for independence from manpower within the Building and Construction (B&C) Industry. Prefabricated Prefinished Volumetric Construction (PPVC) production is mainly driven by benefits in environmental pollution reduction, improved productivity, quality control, and customizability. However, overall cost savings have been counterbalanced by new cost drivers like modular precast moulds, transportation, hoisting, manufacturing & holding yards, and supervision costs. The highly modular requirements for PPVC places additive manufacturing in an advantageous position, due to its high customizability, low volume manufacturing capabilities for a faster manufacturing response time, faster production changeovers, and lower inventory requirements. However, C3DP has only just begun to move away from its early-stage development, where there is a need to closely evaluate the process parameters across buildability, extrudability, and pumpability aspects. As many parameters have been identified as having considerable influence on C3DP processes, monitoring systems for feedback applications seem to be an inevitable step forward to automation in construction. This paper has presented a broad analysis of the challenges posed to C3DP and feedback systems, stressing the admission of process parameters to correct multiple modes of failure. [ABSTRACT FROM AUTHOR]

• W1.5 shows superior interlayer bonding and flexural strength. • Optimal stand-off distance is 13.5 mm to 15 mm. • Lattice beam achieved a failure load of 49.01 kN with flexural failure. This paper presents the optimal selection of cable reinforcement for concrete 3D-printed lattice beam. It also addresses key challenges associated with interlayer bonding and flexural strength of 3D printed elements. Three different types of reinforcement including 1.6 mm and 2 mm diameter rebar, (R1.6 & R2) and 1.5 mm wire (W1.5) with seven strings were evaluated with different stand-off distances of 10–20 mm. The interlayer bonding and flexural strength were investigated to determine the most effective reinforcement configuration. Results show that W1.5 reinforcement exhibited higher interlayer bonding and flexural strength as compared with R1.6 and R2. Subsequently, the optimal reinforcement configuration (W1.5) was embedded in a concrete 3D-printed lattice beam. The lattice beam was structurally evaluated using four-point testing, demonstrating an ultimate load-carrying capacity of 49.01 kN with a mid-span displacement of 2.99 mm. Moreover, it exhibited flexural failure with no premature failures such as inter-layer delamination. [ABSTRACT FROM AUTHOR]

• The dummy layer reduces geometry deviations and maximizes interlayer bonding. • The dummy layers significantly enhance the interlayer bonding of the top layer. • After introducing a dummy layer, geometrical deviation notably reduces. This paper presents the effect of dummy layers in concrete 3D printing to enhance interlayer bonding and reduce geometrical deviations. The specimens were printed by varying numbers of dummy layers at different layer heights using the optimized printing parameters. The impact of dummy layers on interlayer bonding was determined using a split tensile test and the geometrical deviations were analyzed using a 3D-scanning technique. Results demonstrate that significant improvement was found in interlayer bonding, notably at the top layer. For instance, by adding two dummy layers in specimen H10D2, the difference between the top and middle layers bond strength was reduced from 42.57% (i.e., for specimen H10D0) to 0.79%. Moreover, the dummy layers effectively minimized the geometrical deviations by achieving the desired layer dimensions in the top layer of specimens. [ABSTRACT FROM AUTHOR]

Among the several geometry and process-related characteristics that determine the ultimate product quality of 3D printed concrete, one that has gained considerable importance is the height/thickness of the individual layers. Layer height dictates the number of interlayer interfaces, and influences the properties of the layer and the interfaces (both interlayer and inter-filament), for a given mixture and printer characteristics. This paper examines the influence of layer height on the constitutive response and failure of 3D printed concrete specimens under compression, investigated along the direction of layer build-up (or perpendicular to the layer interfaces), which is the dominant plane of loading in 3D printed walls and columns. Plain and steel fiber-reinforced wall elements with two different layer heights (7.5 mm and 15 mm) are printed, from which cylindrical and prismatic specimens are extracted and tested. The uniaxial compressive strength is seen to decrease with increasing layer height. The constitutive relationships of the specimens with different layer heights, along with volumetric strains, enable the extraction of crack initiation stress and unstable crack propagation stress, which are influenced by layer height and the presence of fiber reinforcement. The unstable crack propagation stress is lower than the peak stress, and it decreases with increasing layer height. Digital image correlation (DIC) is used to demonstrate the dominant effect of inter-filament interfaces on the crack propagation response and resultant failure. • Examination of the influence of layer heights on compressive response. • Dependence of critical stress states on layer heights. • Dominant effect of inter-filament interfaces on crack propagation. • Accounting for layer heights in conjunction with material design for better performance. [ABSTRACT FROM AUTHOR]

• Interaction between inter-filament void, bonding, & geometric deviation is studied. • Investigated the influence of different printing parameters using RSM. • High speed & low extrusion with 1/8N d overlapping are optimal printing parameters. This study presents the effect of different printing parameters including printing speed, extrusion rate, and inter-filament overlapping distance on inter-filament bonding, inter-filament voids, and geometrical deviation in concrete 3D printed structures using Response Surface Methodology. Moreover, this study adopts a central composite design to generate a set of experimental runs and develop a second-order polynomial equation to quantify the effect of printing parameters. Results show that high inter-filament bonding with minimal inter-filament void and geometrical deviation can be achieved at high printing speed and low extrusion rate with 1/8N d (2.5 mm) inter-filament overlapping distance. [ABSTRACT FROM AUTHOR]

Existing approaches from design to concrete 3D-printing fabrication can customize the shapes of compression-dominated concrete arches and vaults but has limited applications due to high facility requirements such as a robotic arm and a reconfigurable print bed for fabricating overhanging geometries. Therefore, there is a need to develop an alternative design-to-fabrication approach for 3D printers without such facility requirements. In this paper, concrete blocks were designed as prismatic shapes which could be customized by a most basic, gantry-based 3D printer with a flat print bed and could be assembled to a larger 3D arch structure designed based on stability and strength analyses. The feasibility of such approach was demonstrated by lab prototyping. Reduced facility requirements in this approach allow 3D-printing to be more widely applied for customizing compression-dominated structures. With further design method innovation in the future, this design-to-fabrication approach can be extended for compression-dominated structures with more complex geometries. • Concrete 3D-prinitng of compression-dominated structures with basic facility • Customized design 3D arch fabrication was proposed from 2.5D segments. • Incorporation of analyses at pre/post-assemble stage with design of modular arch • Compensating dimension offset in segment assembling reduces arch dimension errors. [ABSTRACT FROM AUTHOR]

In the current study, we examine the effect of using natural and recycled coarse aggregates in designing 3D printable concrete. We assessed the rheological behaviourusing a dynamic shear rheometer, and it was observed that the addition of coarse aggregates significantly decreased the yield stress and marginally lowered the plastic viscosity. This was attributed to the increase in the paste and water film thickness with the addition of larger aggregates. Therefore, a reduction in the superplasticizer dosage is required to obtain coarse aggregate mixtures with similar yield stress and buildability to the control mixture. The mechanical properties were evaluated by using beam and cube samples cut out from printed wall elements. A marginal decrease in compression and flexural strength was observed for both the mixtures with natural and recycled coarse aggregates. The total and autogenous shrinkage assessment was performed using mould cast prismatic specimens, while the shrinkage cracking potential was evaluated using the restrained ring test. The coarse aggregate mixtures showed lower total and autogenous shrinkage. Notably, the addition of the saturated recycled aggregates significantly lowered the autogenous shrinkage, possibly due to internal curing. As a result, a relatively lower strain rate factor and slower development of tensile stresses occurred in the restrained shrinkage test, increasing the cracking age for the coarse aggregate mixtures. The current study, therefore, shows good potential for using natural and recycled coarse aggregates in 3D printable concrete. [ABSTRACT FROM AUTHOR]

This paper investigates an approach of 3D printing lightweight concrete elements using extrusion of hollow-core filaments. Two different filament shapes of rectangular hollow shape and U-shape were printed by using customised nozzles. The primary challenge in hollow-core 3D printing is the extrudability and the stability of the overhang of the filament at fresh state. The stability of the overhang was assessed by determining the viscosity recovery rate and yield strength growth rate of the mix with nanoclay as a thixotropic additive. The mix containing 0.2 wt% of nanoclay has shown good extrudability and enhanced stability of the overhang. The hollow-core 3D printed elements have shown a reduced density of 1369.6 kg/m3 and 1701.7 kg/m3, compared to 2114.1 kg/m3 obtained for solid-core printing. The compressive strength and the Modulus of Rupture (MoR) of hollow-core filaments evaluated at different directions reveal a significant strength loss in perpendicular and lateral directions due to the effective bond area reduction between filaments. The thermal performance of 3D printed panels assessed using simulated test room experiments reports that the hollow-core panels have high thermal inertia due to increased insulation capacity. However, the lack of thermal energy storage has resulted in high indoor temperature in these test rooms. [ABSTRACT FROM AUTHOR]

Buildability is the ability to 3D print by adding concrete layer by layer continuously to the required level without significant deformation or collapse of the freshly printed component. This paper presents a systematic review of the reported studies to improve the buildability of concrete. The paper also presents original concepts and some results for improving the buildability of geopolymer concrete. Two methods to enhance the buildability are discussed: (1) Additives during initial mixing of concrete (2) Buildability enhancement at the print-head by an intervention (set-on-demand). The former method is the most widely studied, however, it affects the pumpability. The latter includes mixing accelerators, heating, ultrasonication, or magnetorheological control, performed at the print-head to rapidly increase the yield strength of the material immediately prior to extrusion. This method does not affect the pumpability of the mix until it reaches the print-head. Finally, the prospects of a new set-on-demand method are presented. • Buildability enhancement is achieved by interventions at initial mixing and at the print head. • Strength development in fresh concrete is due to re-flocculation (physical) and setting (chemical). • Enhancement at initial mixing is constrained by the pumpability limitations. • Most developed set-on-demand approach is by mixing accelerators at the print-head. • Similar approach to attain on demand setting of geopolymer concrete is discussed in detail. [ABSTRACT FROM AUTHOR]

Foundation piles that are made by concrete 3D printers constitute a new alternative way of founding buildings constructed using incremental technology. We are currently observing very rapid development of incremental technology for the construction industry. The systems that are used for 3D printing with the application of construction materials make it possible to form permanent formwork for strip foundations, construct load-bearing walls and partition walls, and prefabricate elements, such as stairs, lintels, and ceilings. 3D printing systems do not offer soil reinforcement by making piles. The paper presents the possibility of making concrete foundation piles in laboratory conditions using a concrete 3D printer. The paper shows the tools and procedure for pile pumping. An experiment for measuring pile bearing capacity is described and an example of a pile deployment model under a foundation is described. The results of the tests and analytical calculations have shown that the displacement piles demonstrate less settlement when compared to the analysed shallow foundation. The authors indicate that it is possible to replace the shallow foundation with a series of piles combined with a printed wall without locally widening it. This type of foundation can be used for the foundation of low-rise buildings, such as detached houses. Estimated calculations have shown that the possibility of making foundation piles by a 3D printer will reduce the cost of making foundations by shortening the time of execution of works and reducing the consumption of construction materials. [ABSTRACT FROM AUTHOR]

This paper provides a comprehensive review of the material behaviour for extrusion-based concrete 3D printing spanning from the early age to long-term performance. We begin with a discussion on the recent progress on the understanding of early-age behaviour. Following this, the mechanical response in the hardened state, and the different strategies to introduce reinforcement are reviewed. Finally, we present insights and perspectives on the transport mechanisms in printed concrete to assess the long-term performance, and also discuss the overall impact of construction by concrete 3D printing on sustainability. [ABSTRACT FROM AUTHOR]