Additive manufacturing and digital fabrication bring new horizons to concrete and cement-based material construction. 3D printing inspired construction techniques that have recently been developed at ...laboratory scale for cement-based materials. This study aims to investigate the role of the structural build-up properties of cement-based materials in such a layer by layer construction technique. As construction progresses, the cement-based materials become harder with time. The mechanical strength of the cement-based materials must be sufficient to sustain the weight of the layers subsequently deposited. It follows that the comparison of the mechanical strength, which evolves with time (i.e. structural build-up), with the loading due to layers subsequently deposited, can be expected to provide the optimal rate of layer by layer construction. A theoretical framework has been developed to propose a method of optimization of the building rate, which is experimentally validated in a layer-wise built column.
•Using a fast setting binder, it is possible to print an earth-based mortar.•Alginate is an efficient binder to enables earth printing.•3D printing can make an earth-based material with compressive ...strength in the same order of conventional cob earth.•Young modulus and yield stress evolution of the material govern the maximum printing rate.
Due to its low environmental impact, earth construction has received much consideration in recent years. Nevertheless, its development remains limited due to low production rate. Recent developments have been made to improve earth-based materials mix-design and processing methods. Simultaneously, digitally based construction methods have been introduced in the field of construction especially for cement-based materials application. Among these new techniques, the so-called 3D printing by extrusion deposit has been the most intensively studied. In this study, we assess the possibility of adapting this technique to earth-based material. After making the earth’s rheological behaviour suitable for 3D printing, a laboratory-scale printing has been carried out and the printed samples have been mechanically tested.
The Large Hadron Collider forward (LHCf) experiment is designed to use the LHC to verify the hadronic-interaction models used in cosmic-ray physics. Forward baryon production is one of the crucial ...points to understand the development of cosmic-ray showers. We report the neutron-energy spectra for LHC s=7 TeV proton–proton collisions with the pseudo-rapidity η ranging from 8.81 to 8.99, from 8.99 to 9.22, and from 10.76 to infinity. The measured energy spectra obtained from the two independent calorimeters of Arm1 and Arm2 show the same characteristic feature before unfolding the detector responses. We unfolded the measured spectra by using the multidimensional unfolding method based on Bayesian theory, and the unfolded spectra were compared with current hadronic-interaction models. The QGSJET II-03 model predicts a high neutron production rate at the highest pseudo-rapidity range similar to our results, and the DPMJET 3.04 model describes our results well at the lower pseudo-rapidity ranges. However, no model perfectly explains the experimental results over the entire pseudo-rapidity range. The experimental data indicate a more abundant neutron production rate relative to the photon production than any model predictions studied here.
This article offers a comprehensive overview of the underlying physics relevant to an understanding of materials processing during the various production steps in extrusion-based 3D concrete printing ...(3DCP). Understanding the physics governing the processes is an important step towards the purposeful design and optimization of 3DCP systems as well as their efficient and robust process control. For some processes, analytical formulas based on the relevant physics have already enabled reasonable predictions with respect to material flow behavior and buildability, especially in the case of relatively simple geometries.
The existing research in the field was systematically compiled by the authors in the framework of the activities of the RILEM Technical Committee 276 “Digital fabrication with cement-based materials”. However, further research is needed to develop reliable tools for the quantitative analysis of the entire process chain. To achieve this, experimental efforts for the characterization of material properties need to go hand in hand with comprehensive numerical simulation.
Today, the extrusion-based 3D printing of concrete is a potential breakthrough technology for the construction industry. It is expected that 3D printing will reduce the cost of construction of civil ...engineering structures (removal of formwork) and lead to a significant reduction in time and improve working environment conditions. Following the use of this additive manufacturing layer-wise process, it is required to change the way concrete structures are designed and reinforced, especially for the parts of the structure under tension loads. Indeed, the extrusion-based concrete 3D printing process does not allow for the production of conventional reinforced concrete, and there is a need to develop other ways of compensating for the low mechanical performances of concrete, particularly in tension. In this study, the reinforcement of printed structures by using steel nails through the deposited layers of fresh concrete was investigated. Additionally, three-layer and 10-layer samples were reinforced with nails with varying inclination and spacing. The results show that inclined nails can be used to provide a flexural strengthening of the printing material in different directions.
The differential cross sections for inclusive neutral pions as a function of transverse and longitudinal momentum in the very forward-rapidity region have been measured at the LHC with the LHC ...forward detector in proton-proton collisions at sradical=2.76 and 7 TeV and in proton-lead collisions at nucleon-nucleon center-of-mass energies of super()sNNradical=5.02TeV. Such differential cross sections in proton-proton collisions are compatible with the hypotheses of limiting fragmentation and Feynman scaling. Comparing proton-proton with proton-lead collisions, we find a sizable suppression of the production of neutral pions in the differential cross sections after subtraction of ultraperipheral proton-lead collisions. This suppression corresponds to the nuclear modification factor value of about 0.1-0.3. The experimental measurements presented in this paper provide a benchmark for the hadronic interaction Monte Carlo simulation codes that are used for the simulation of cosmic ray air showers.
We focus in this paper on a potential correlation between yield stress and bleeding. We suggest that the conditions under which a fresh cement paste is able to display a yield stress result from the ...competition between Brownian motion and colloidal interactions whereas the conditions under which the suspension is stable result from the competition between colloidal interactions and gravity. These competitions highly depend on the solid volume fraction of the system and on the polymer surface coverage. The correlation between yield stress and bleeding is therefore very indirect and difficult to use in practice.
In this work, we propose to extend the Ovarlez and Roussel model, for estimating lateral form pressure exerted by fresh concrete, to low casting rates and long duration formwork filling. In this ...case, the assumption of a linear increase of the concrete yield stress with time at rest is imprecise. This assumption is valid for approximately 1 h at rest after placing and may lead to an overestimation of the lateral pressure for a longer period. Based on chemical arguments and experimental observations, it has been shown that the yield stress increases exponentially over time. The same fundamental physical assumptions made by Ovarlez and Roussel are used to predict the lateral pressure exerted on formwork. Comparison of the proposed model with experimental measurements shows that, pressure can be predicted with an accuracy comparable to the Ovarlez and Roussel model for casting times less than 1 h.
Summary
Recently, diets low in carbohydrate content have become a matter of international attention because of the WHO recommendations to reduce the overall consumption of sugars and rapidly ...digestible starches. One of the common metabolic changes assumed to take place when a person follows a low‐carbohydrate diet is ketosis. Low‐carbohydrate intakes result in a reduction of the circulating insulin level, which promotes high level of circulating fatty acids, used for oxidation and production of ketone bodies. It is assumed that when carbohydrate availability is reduced in short term to a significant amount, the body will be stimulated to maximize fat oxidation for energy needs. The currently available scientific literature shows that low‐carbohydrate diets acutely induce a number of favourable effects, such as a rapid weight loss, decrease of fasting glucose and insulin levels, reduction of circulating triglyceride levels and improvement of blood pressure. On the other hand some less desirable immediate effects such as enhanced lean body mass loss, increased urinary calcium loss, increased plasma homocysteine levels, increased low‐density lipoprotein‐cholesterol have been reported. The long‐term effect of the combination of these changes is at present not known. The role of prolonged elevated fat consumption along with low‐carbohydrate diets should be addressed. However, these undesirable effects may be counteracted with consumption of a low‐carbohydrate, high‐protein, low‐fat diet, because this type of diet has been shown to induce favourable effects on feelings of satiety and hunger, help preserve lean body mass, effectively reduce fat mass and beneficially impact on insulin sensitivity and on blood lipid status while supplying sufficient calcium for bone mass maintenance. The latter findings support the need to do more research on this type of hypocaloric low‐carbohydrate diet.
•An inhomogeneous turbulent boundary condition can model a cylindrical film-cooling hole.•The model also improves the predictions for laidback and fanshaped laidback holes.•The spatial inhomogeneity ...is particularly important for the near-hole behaviour of the flow.•Turbulence injection is crucial to immediately trigger the transition of the jet.
In many industrial applications, the mechanical integrity of a surface operating under large thermal loads is ensured by injecting a cold fluid through a series of hole along the surface, forming a thin film of cool fluid shielding the solid surface from external heat. An accurate prediction of the heat transfer provided by these so-called film-cooling systems is crucial to ensure the durability of the cooled surfaces. However, the large-eddy simulation of film-cooling systems is complex and expensive because the in-hole flow must be meshed and simulated. To address this difficulty, the modelling of the film-cooling jet by mean of a dedicated boundary condition has recently been proposed. This paper investigates several potential improvements for this type of model in four geometries: an inclined cylindrical hole, a fanshaped hole and two fanshaped laidback holes. The analysis focuses on the comparison of a spatially uniform injection to a model taking into account velocity and temperature spatial variations at the hole exit. The study also compares a non-turbulent injection to a model with synthetic turbulence injection. The comparisons are first performed using a fine mesh to validate the approach, then using a coarse mesh representative of a mesh that could be used to simulate a cooled nozzle guide vane. The results show that both spatial inhomogeneity and turbulence injection significantly improve the cooling effectiveness predictions in a wide variety of cases. The spatial inhomogeneity is especially crucial for the near-hole behaviour of the flow while turbulence injection is particularly important when the destabilisation of the jet by the crossflow is not sufficient to immediately trigger transition. Using a very coarse mesh, the turbulent mixing is observed to be underestimated with all examined boundary-condition models and the behaviour of the jet is not correctly described for some of the configurations investigated. Although not sufficient, non-negligible improvements are nevertheless obtained with an inhomogeneous turbulent injection compared to the baseline uniform model.
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