Beton‐3D‐Druck durch selektive Ablage Mechtcherine, Viktor; Nerella, Venkatesh Naidu
Beton- und Stahlbetonbau,
January 2019, Letnik:
114, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Das Interesse am digitalen Betonbau steigt rapide an, damit auch die Erwartungen an diese neue, vielversprechende Technologie. Die Methoden der digitalen Fertigung mit Beton gewinnen immer weiter an ...Reife, sodass weltweit bereits mehrere Pilotprojekte realisiert werden konnten. Jedoch sind noch etliche Hürden zu nehmen, bevor der 3D‐Druck mit Beton und andere digitale Bauverfahren in die Baupraxis überführt werden können. Eine der größten Herausforderungen ist die Erarbeitung einer praxistauglichen Vorgehensweise zur Festlegung, Einstellung und Prüfung der erforderlichen Materialeigenschaften von frischem und erhärtendem Beton. Die Schwierigkeiten bei der Gestaltung der rheologischen Eigenschaften von Frischbeton ergeben sich aus unterschiedlichen, zum Teil entgegengesetzten Anforderungen, die durch maßgebende technologische Schritte – Materialförderung, Formung, Ablage und Belastung durch darauffolgende Betonschichten – bestimmt werden. Zu durchdenken und neu zu definieren sind auch einschlägige Methoden der Materialcharakterisierung. Der vorliegende Aufsatz konzentriert sich auf diese Fragestellungen im Kontext der mit großem Abstand am häufigsten verwendeten digitalen Fertigungsmethode, nämlich dem 3D‐Druck durch selektive Betonablage. Die Gedankengänge, theoretischen Grundlagen und Empfehlungen hinsichtlich der Materialprüfung lassen sich allerdings sinngemäß auch auf andere Verfahren übertragen.
3D‐concrete‐printing by selective deposition – Requirements for fresh concrete and testing
The interest in digital concrete construction is rapidly increasing, as well as the expectations of this new, promising technology. The methods of digital fabrication with concrete are becoming ever more mature, so that several pilot projects have already been realized worldwide. However, there are still some hurdles to overcome, before 3D‐printing with concrete and other digital construction processes can be transferred to construction practice. One of the biggest challenges is the development of a practice‐oriented approach for determining, adjusting and testing the required material properties of fresh and hardening concrete. The difficulties in designing the rheological properties of fresh concrete result from different, sometimes conflicting requirements, which are determined by decisive technological steps – material conveying, shaping, depositing and loading by subsequent concrete layers. To think through and to redefine are also relevant methods of material characterization. This article focuses on these issues in the context of what is by far the most commonly used digital manufacturing method, namely 3D‐printing by selective concrete deposition. However, the conceptual reasoning, theoretical foundations and recommendations with regard to material testing can be analogously applied to other methods.
Massive rotator cuff tears constitute 10% to 40% of rotator cuff tears. Surgical repair is challenging, with high retear rates (20% to 90%). The aim of this study was to develop a new surgical ...technique to perform an interpositional expanded polytetrafluoroethylene (ePTFE) patch repair for massive and/or irreparable rotator cuff tears that minimizes arthroscopic knot tying without compromising repair strength. (1) Twelve 30×50 mm ePTFE patches and no.2 sutures (450 mm length) were either sterilized in an autoclave for 15 minutes at 130°C and 120 kPa, or left unsterilized. The sutures and patches were then pulled to failure in an Instron Materials Testing System to verify the effect of sterilization on the biomechnical properties. (2) A “Slide and Grip” technique was developed for synthetic patch interpositional repair and compared with our standard “Weave” technique. Autoclaving had no effect on patches (486±15 N vs. 491±15 N; mean±SEM) or sutures. Both “Weave” and “Slide and Grip” techniques had similar repair strengths (279±22 vs. 248±15 N). However, the “Slide and Grip” technique was much faster to perform than the (12.3±1.0; vs. 21.5±1.0 min; mean±SEM) (P<0.0001). A novel technique for the ePTFE patch repair of massive rotator cuff tears provided 40% reduction in operative time with similar pullout strength compared with the “Weave” technique.
This paper presents a laboratory evaluation of plant-produced asphalt mixtures containing the control hot-mix asphalt (HMA) and four warm-mix asphalt (WMA) technologies: an organic additive ...(Sasobit®) and three foaming processes (Advera®, low-emission asphalt, and Gencor). These asphalt mixtures were produced using a single binder performance grade (PG 64-22) and 9.5-mm nominal maximum aggregate size Superpave mix design compacted to 75 design gyrations. Dynamic modulus (E*), flow number, and Hamburg wheel-track tests were utilised to evaluate the mechanical properties of the asphalt mixtures. The PG of the asphalt binders containing the WMA technologies was also verified. In addition, their rheological properties were evaluated using shear modulus master curves and multiple stress creep recovery tests. It was found that the asphalt binder containing Sasobit® technology increased the continuous high-temperature binder grade by 6°C and measured higher elastic properties. In general, the asphalt mixture prepared with Sasobit® technology and the control HMA mixture measured higher stiffness than those prepared with the other WMA technologies and measured the highest dynamic modulus rutting parameter and fatigue cracking parameter. In addition, these mixtures demonstrated increased resistance to rutting and moisture damage. Statistical analysis indicated that the binder rheological properties, WMA dosage rates, and production temperatures influenced the performance of the WMA mixtures.
The behavior of three copolymers high density polyethylene at high rate loading was investigated. Namely, one unimodal type (HDPE-1) and two bimodal type. Structure of PE samples was characterized by
...13
C NMR (Carbon-13 nuclear magnetic resonance). The Taylor impact test was used. Specimens in form of a cylinder (14 mm in diameter and 50 mm in length) were fired against a steel bar. Striking velocities achieved up to 116 m/s. No permanent strain of these specimens was detected. Numerical simulation of these tests showed that the material behavior is probably viscoelastic. Results showed that there was no difference in the impact behavior of tested polymers. This conclusion was obtained both for the results in the time domain and the frequency domain.
Based on previous works on polymers and regular bitumens, a new method for determining the molecular weight distribution (MWD) of asphaltic paving binders, using the phase angle (
) of the complex ...modulus measured in the linear viscoelastic domain, has been developed in this paper. MWDs of pure petroleum bitumens, natural bitumens, modified bitumens and artificially aged bitumens are calculated by this method and compared with MWDs obtained by gel permeation chromatography. The two methods give comparable results, but the δ-method developed here is more sensitive to the molecular weight of species. This method is very simple to implement, and seems a powerful tool in the determination of MWD of bitumens, in the visualisation and repartition of modifiers in the bitumen matrix and in the ageing monitoring and quantification.
With the rapid growth in the manufacturing industry and increased urbanization, higher amounts of composite material waste are being produced, causing severe threats to the environment. These ...environmental concerns, coupled with the fact that undergraduate students typically have minimal experience in research, have initiated the need at the UAE University to promote research among undergraduate students, leading to the development of a summer undergraduate research program. In this study, a recycling methodology is presented to test lab-fabricated Carbon-Fiber-Reinforced Polymer (CFRP) for potential applications in industrial composite waste. The work was conducted by two groups of undergraduate students at the UAE University. The methodology involved the chemical dissolution of the composite waste, followed by compression molding and adequate heat treatment for rapid curing of CFRP. Subsequently, the CFRP samples were divided into three groups based on their geometrical distinctions. The mechanical properties (i.e., modulus of elasticity and compressive strength) were determined through material testing, and the results were then compared with steel for prompt reference. The results revealed that the values of mechanical properties range from 2 to 4.3 GPa for the modulus of elasticity and from 203.7 to 301.5 MPa for the compressive strength. These values are considered competitive and optimal, and as such, carbon fiber waste can be used as an alternate material for various structural applications. The inconsistencies in the values are due to discrepancies in the procedure as a result of the lack of specialized equipment for handling CFRP waste material. The study concluded that the properties of CFRP composite prepreg scrap tend to be reusable instead of disposable. Despite the meager experimental discrepancies, test values and mechanical properties indicate that CFRP composite can be successfully used as a material for nonstructural applications.
Steel-fiber-reinforced concrete is a composite material which is becoming more and more widely employed in building construction, due to its better resistance to cracking and to crack propagation ...with respect to plain concrete. Its mechanical behavior strongly depends on the choice of fiber properties and their volume fraction in the concrete mixture. As any material used in building construction, the "on-site" test of its properties represents a very important task. Often, this requires the employment of noninvasive and nondestructive measurement procedures that have to be carried out directly in situ. In this paper, a new method for the estimation of the fiber density and their average orientation is presented. The measurement technique is based on the employment of a probe that is sensitive to the magnetic properties of the steel fibers. The performance of the method has been theoretically and experimentally analyzed.
Fiber blends have the potential to improve the mechanical and sustainability credentials of steel fiber‐reinforced concrete (SFRC), but at which ratios these can work is not known a priori. This ...paper investigates the uniaxial tensile stress–strain (
σ − ε) relationship of blended SFRC using manufactured steel fibers on their own, or blended with sorted steel fibers recycled from end‐of‐life tires (recycled tire steel fiber RTSF), at total fiber dosages of 30, 35, and 45 kg/m3. The accuracy of two
σ − ε relations proposed by RILEM TC 162‐TDF and Model Code 2010 is assessed using the experimental results from concrete prisms. By using nonlinear finite element (FE) analysis, it is found that the RILEM approach can lead to significant overestimation (up to 72%) of peak flexural load and energy absorption capacity (up to 39%), while the Model Code 2010 can provide a rather accurate prediction of the energy absorption capacity and some overestimation (less than 34%) of the peak flexural load. Inverse FE analysis is used to determine indirectly the uniaxial tensile
σ − ε relations of the examined SFRC mixes, and a simplified trilinear relation for SFRC is proposed. It is concluded that the tensile strength of SFRC with RTSF at a low total fiber dosage is only marginally improved by fiber addition, and the postcracking tensile strengths at different strains can be determined directly from residual flexural tensile strengths (f
Ri) of prisms.
Background
During cardiogenic shock blood circulation is minimal in the human body and does not suffice to survive. The extracorporeal life support system (ECLS) acts as a miniature ...heart-lung-machine that can be temporarily implanted over major vessels e.g. at the groin of the patient to bridge cardiogenic shock. To perform this procedure in an emergency, a proper training model is desirable. Therefore, a 3-dimensional-printable (3D) material must be found that mimics large vessel needle penetration properties. A suitable test bench for material comparison is desirable.
Methods
A test setup was built, which simulated the clinically relevant wall tension in specimens. The principle was derived from an existing standardized needle penetration test. After design, the setup was fabricated by means of 3D printing and mounted onto an universal testing machine. For testing the setup, a 3D printable polymer with low Shore A hardness and porcine aorta were used. The evaluation was made by comparing the curves of the penetration force to the standardized test considering the expected differences.
Results
3D printing proved to be suitable for manufacturing the test setup, which finally was able to mimic wall tension as if under blood pressure and penetration angle. The force displacement diagrams showed the expected curves and allowed a conclusion to the mechanical properties of the materials. Although the materials forces deviated between the porcine aorta and the Agilus30 polymer, the graphs showed similar but still characteristic curves.
Conclusions
The test bench provided the expected results and was able to show the differences between the two materials. To improve the setup, limitations has been discussed and changes can be implemented without complications.
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