Visualization of the three-dimensional structure and stress field of aggregated concrete materials through 3D printing and frozen-stress techniques
TL;DR: In this article, the authors used 3D printed models based on X-ray microfocus computed tomography (CT) imaging of a concrete sample to replicate its complex aggregate structure in a transparent matrix, and the associated three-dimensional stress field is visually characterized at mesoscale through uniaxial compression tests and photoelastic techniques that incorporate a threedimensional frozen-stress test to analyse the effects of randomly distributed aggregates.
About: This article is published in Construction and Building Materials.The article was published on 2017-07-15. It has received 53 citations till now. The article focuses on the topics: Stress field & Stress concentration.
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TL;DR: In this article, an optimal basalt fiber content was determined basing firstly on suitable printability and then on mechanical performance using a self-developed 3D printer for extrusion of the cementitious material and also for mechanical enhancement of fiber alignment along the print direction.
224 citations
TL;DR: In this paper, the authors reviewed 3D printing techniques that are currently being used in commercial 3D printers and summarized three latest development of largescale 3D printer systems and identified their relationships and limiting factors.
Abstract: In recent few years, significant improvement has been made in developing largescale 3D printer to accommodate the need of industrial-scale 3D printing. Cementitious materials that are compatible with 3D printing promote rapid application of this innovative technique in the construction field with advantages of cost effective, high efficiency, design flexibility and environmental friendly. This paper firstly reviews existing 3D printing techniques that are currently being used in commercial 3D printers. It then summarizes three latest development of largescale 3D printing systems and identifies their relationships and limiting factors. Thereafter, critical factors that are used to evaluate the workability and printable performance of cementitious materials are specified. Easy-extrusive, easy-flowing, well-buildable, and proper setting time are significant for cementitious material to meet the critical requirements of a freeform construction process. Finally, main advantages, potential applications and the prospects of future research of 3D printing in construction technology are suggested. The objective of this work is to review current design methodologies and operational constraints of largescale 3D printing system and provide references for optimizing the performance of cementitious material and promote its responsible use with largescale 3D printing technology.
146 citations
TL;DR: In this paper, the meso-mechanics of granite specimens containing pre-existing holes with different ligament angles (the angle between the line connecting the centers of two holes and the horizontal direction, and set as β = 0, 45 and 90°) after different temperature treatments (T = 25, 150, 300, 450, 600, 750 and 900 ǫ).
89 citations
TL;DR: In this article, a 3D printable cement mixture containing 40% mining tailings was proposed and the influence of paste age on the buildability of forty-layer structure was evaluated, as well as bending resistance of prism specimen sawed from the printed structure.
Abstract: The innovative 3D printing has been successfully applied to layeredly build-up construction-scale structures through the extrusion of various cementitious materials. Favourable buildability of fresh cement mixture and the hardened properties of the printed structures are essential requirement for the application of 3D concrete printing. This paper firstly proposed a 3D printable cement mixture containing 40% mining tailings. The influence of paste age on the buildability of forty-layer structure was evaluated, as well as the bending resistance of prism specimen sawed from the printed structure. The bonding between layers is a critical factor that influences the structural capacity. In particular, the weak bonding interface formed in the layered extrusion process was identified through high-resolution X-ray CT scanning. It is necessary and desirable for the cement paste to perform both well buildability and mechanical performances. Thereafter, a proper amount of viscosity modify agent (VMA) was used to improve the structural integrity by increasing the contact behaviour between the adjacent extruded layers. Meanwhile, the impact of curing method on the hardened properties of 3D printed structures was accessed. Results indicated that the prepared tailing mortar achieved sufficient buildability to be used in an extrusion-typed 3D printer at the paste age of 45 min. The mould-cast specimens process flexural strength of 7.87 MPa. In contrast, the flexural strength of printed specimens values 5.22 MPa and 12.93 MPa, respectively, after the addition of 1.5% VMA and 90 °C steam curing.
66 citations
Cites background from "Visualization of the three-dimensio..."
...In recent few years, various 3D printing techniques have been developed and pave a promising way for the optimal design of complex solid models and the guidance to real engineering practices (Ju et al. 2017a, b)....
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TL;DR: Measurements of the normal and tangential grain-scale forces inside a two-dimensional system of photoelastic disks that are subject to pure shear and isotropic compression show the underlying differences between these two stress states.
Abstract: Interparticle forces in granular media form an inhomogeneous distribution of filamentary force chains. Understanding such forces and their spatial correlations, specifically in response to forces at the system boundaries, represents a fundamental goal of granular mechanics. The problem is of relevance to civil engineering, geophysics and physics, being important for the understanding of jamming, shear-induced yielding and mechanical response. Here we report measurements of the normal and tangential grain-scale forces inside a two-dimensional system of photoelastic disks that are subject to pure shear and isotropic compression. Various statistical measures show the underlying differences between these two stress states. These differences appear in the distributions of normal forces (which are more rounded for compression than shear), although not in the distributions of tangential forces (which are exponential in both cases). Sheared systems show anisotropy in the distributions of both the contact network and the contact forces. Anisotropy also occurs in the spatial correlations of forces, which provide a quantitative replacement for the idea of force chains. Sheared systems have long-range correlations in the direction of force chains, whereas isotropically compressed systems have short-range correlations regardless of the direction.
1,052 citations
TL;DR: In this article, a mathematical procedure using spherical harmonic functions is described to characterize concrete aggregate particles and other particles of the same nature in 3D X-ray tomography images, and three main consequences of this procedure are mathematical classification of the shape of aggregates from different sources, comparison of composite performance properties to precise morphological aspects of particles, and incorporation of random particles into manyparticle computational models.
493 citations
TL;DR: In this article, the composites formed using main rapid prototyping processes such as Selective Laser Sintering/Melting, Laser Engineered Net Shaping, Laminated Object Manufacturing, Stereolithography, Fused Deposition Modeling, Three Dimensional Printing and Ultrasonic Consolidation are discussed.
436 citations
TL;DR: In this paper, three dimensional imaging of capillary porosity allowed the connectivity and tortuosity of the pore network to be studied, and it was shown that the degree of connectivity of the porosity is sensitive to both the spatial resolution of the images and the evolution of contrast resolution during ageing of the cement.
322 citations
TL;DR: In this paper, the authors describe the mechanical behaviour of FDM parts by the classical laminate theory (CLT) and experimentally measure the values of the elastic modulus in the longitudinal and transverse directions to the fibre (E1, E2), the Poisson's modulus (ν12), and the shear modulus(G12) in order to reach this objective.
316 citations