scholarly journals Lightweight Cement Conglomerates Based on End-of-Life Tire Rubber: Effect of the Grain Size, Dosage and Addition of Perlite on the Physical and Mechanical Properties

Materials ◽  
2021 ◽  
Vol 14 (1) ◽  
pp. 225
Author(s):  
Andrea Petrella ◽  
Michele Notarnicola
Keyword(s):  
Grain Size ◽  
End Of Life ◽  
Compression Tests ◽  
Tire Rubber ◽  
Impact Compression ◽  
Weight Percentage ◽  
Deep Groove ◽  
Mechanical Strengths ◽  
The Impact ◽  
Thermal Conductivities

Lightweight cement mortars containing end-of-life tire rubber (TR) as aggregate were prepared and characterized by rheological, thermal, mechanical, microstructural, and wetting tests. The mixtures were obtained after total replacement of the conventional sand aggregate with untreated TR with different grain sizes (0–2 mm and 2–4 mm) and distributions (25%, 32%, and 40% by weight). The mortars showed lower thermal conductivities (≈90%) with respect to the sand reference due to the differences in the conductivities of the two phases associated with the low density of the aggregates and, to a minor extent, to the lack of adhesion of tire to the cement paste (evidenced by microstructural detection). In this respect, a decrease of the thermal conductivities was observed with the increase of the TR weight percentage together with a decrease of fluidity of the fresh mixture and a decrease of the mechanical strengths. The addition of expanded perlite (P, 0–1 mm grain size) to the mixture allowed us to obtain mortars with an improvement of the mechanical strengths and negligible modification of the thermal properties. Moreover, in this case, a decrease of the thermal conductivities was observed with the increase of the P/TR dosage together with a decrease of fluidity and of the mechanical strengths. TR mortars showed discrete cracks after failure without separation of the two parts of the specimens, and similar results were observed in the case of the perlite/TR samples thanks to the rubber particles bridging the crack faces. The super-elastic properties of the specimens were also observed in the impact compression tests in which the best performances of the tire and P/TR composites were evidenced by a deep groove before complete failure. Moreover, these mortars showed very low water penetration through the surface and also through the bulk of the samples thanks to the hydrophobic nature of the end-of-life aggregate, which makes these environmentally sustainable materials suitable for indoor and outdoor elements.

scholarly journals Environmentally Sustainable Cement Composites Based on End-of-Life Tyre Rubber and Recycled Waste Porous Glass

Materials ◽  
2019 ◽  
Vol 12 (20) ◽  
pp. 3289 ◽  
Author(s):  
Andrea Petrella ◽  
Rosa Di Mundo ◽  
Sabino De Gisi ◽  
Francesco Todaro ◽  
Claudia Labianca ◽  
...  
Keyword(s):  
End Of Life ◽  
Cement Paste ◽  
Porous Glass ◽  
Raw Materials ◽  
Compression Tests ◽  
Impact Compression ◽  
Environmentally Sustainable ◽  
Deep Groove ◽  
Complete Failure ◽  
Recycled Waste

In this paper, environmentally sustainable cement mortars were prepared with end-of-life tyre rubber (TR) and recycled waste porous glass (PG) as aggregates in order to obtain lightweight products characterized by renewable and not-pretreated materials specifically for indoor applications. The secondary raw materials were added as partial and/or total replacement of the conventional sand aggregate. The resulting lightweight specimens were characterized by rheological, mechanical, thermal, microstructural and wettability tests. Fine tyre rubber aggregates affected the cohesiveness of the composites, as opposite to coarse tyre rubber and porous glass. The flexural and the compressive strengths of the porous glass samples were higher than the tyre rubber samples because of the higher stiffness and good adhesion of the glass to the cement paste as observed by microstructural observations. On the contrary, an unfavorable adhesion of the tyre aggregates to the cement paste was observed, together with discrete cracks after failure without separation of the two parts of the specimens. The latter result can explain the best results obtained by tyre rubber mortars in the case of impact compression tests where the super-elastic properties of the elastomeric material were evidenced by a deep groove before complete failure. Moreover, the thermal conductivity decrease of the lightweight porous TR and PG composites was in the range of ~80–90% with respect to the sand-based samples, which suggests that they can be used as plasters and masonries, and, in the case of tyre rubber specimens, outside applications are not excluded as observed from the wettability tests.

scholarly journals Research On Water-Immersion Softening Mechanism of Coal Rock Mass Based on Split Hopkinson Pressure Bar Experiment

2021 ◽  
Author(s):  
Zhiyuan Liu ◽  
Gang Wang ◽  
Jinzhou Li ◽  
Huaixing Li ◽  
Haifeng Zhao ◽  
...  
Keyword(s):  
Moisture Content ◽  
Coal Sample ◽  
Split Hopkinson Pressure Bar ◽  
Water Immersion ◽  
Compression Tests ◽  
Hopkinson Pressure Bar ◽  
Impact Compression ◽  
Split Hopkinson ◽  
Pressure Bar ◽  
The Impact

Abstract The coal mining process is affected by multiple sources of water such as groundwater and coal seam water injection. Understanding the dynamic mechanical parameters of water-immersed coal is helpful to the safe production of coal mines. The impact compression tests were performed on coal with different moisture contents by using the ϕ50 mm Split Hopkinson Pressure Bar (SHPB) experimental system, and the dynamic characteristics and energy loss laws of water-immersed coal with different compositions and water contents were analyzed. Through analysis and discussion, it is found that: (1) When the moisture content of the coal sample is 0%, 30%, 60%, the stress, strain rate and energy first increase and then decrease with time; (2) When the moisture content of the coal sample increases from 30% to 60%, the stress "plateau" of the coal sample disappears, resulting in an increase in the interval of the compressive stress and a decrease in the interval of the expansion stress. (3) The increase of the moisture content of the coal sample will affect its impact deformation and failure mode. When the moisture content is 60%, the incident rod end and the transmission rod end of the coal sample will have obvious compression failure, and the middle part of the coal sample will also experience expansion and deformation. (4) The coal composition ratio suitable for the impact experiment of coal immersion softening is optimized.

Experimental Study of Equation of State for Concrete

2012 ◽  
Vol 174-177 ◽  
pp. 566-569
Author(s):  
Zhu Zhang ◽  
Yan Juan Jin
Keyword(s):  
Equation Of State ◽  
Time Pressure ◽  
Pressure Gauge ◽  
Rate Sensitivity ◽  
Compression Tests ◽  
Concrete Material ◽  
Impact Compression ◽  
Stress Peak ◽  
Shock Hugoniot ◽  
The Impact

In order to study dynamic mechanical properties of concrete, the impact compression tests of concrete material under three different velocities are conducted using a light gas gun. Flyer and target are made of the same material, the manganin pressure gauge is used to measure the time-pressure curves of the samples. The measured time-pressure curves show that the stress peak will increase with the increase of flyer speed, and the stress peak at different locations will decrease with the increase of dissemination distance. It illustrate that concrete material has obvious rate sensitivity and energy dissipation characteristics. Then, through further analysis of the experimental data, the shock hugoniot relationship is determined, that is a linear relationship between the shock wave speed and the wave particle velocity. Based on the shock hugoniot data of the concrete, the high-pressure polynomial equation of state is fitted.

scholarly journals Impact-Rubbing Dynamic Behavior of Magnetic-Liquid Double Suspension Bearing under Different Protective Bearing Forms

Processes ◽  
2021 ◽  
Vol 9 (7) ◽  
pp. 1105
Author(s):  
Jianhua Zhao ◽  
Lanchun Xing ◽  
Sheng Li ◽  
Weidong Yan ◽  
Dianrong Gao ◽  
...  
Keyword(s):  
Dynamic Behavior ◽  
Ball Bearing ◽  
Magnetic Liquid ◽  
Electromagnetic System ◽  
Fixed Ring ◽  
Deep Groove ◽  
Deep Groove Ball Bearing ◽  
Protection Devices ◽  
Hydrostatic System ◽  
The Impact

The magnetic-liquid double suspension bearing (MLDSB) is a new type of suspension bearing, with electromagnetic suspension as the main part and hydrostatic supports as the auxiliary part. It can greatly improve the bearing capacity and stiffness of rotor-bearing systems and is suitable for a medium speed, heavy load, and frequent starting occasions. Compared with the active electromagnetic bearing system, the traditional protective bearing device is replaced by the hydrostatic system in MLDSB, and the impact-rubbing phenomenon can be restrained and buffered. Thus, the probability and degree of friction and wear between the rotor and the magnetic pole are reduced drastically when the electromagnetic system fails. In order to explore the difference in the dynamic behavior law of the impact-rubbing phenomenon between the traditional protection device and hydrostatic system, the dynamic equations of the rotor impact-rubbing in three kinds of protection devices (fixed ring/deep groove ball bearing/hydrostatic system) under electromagnetic failure mode are established, and the axial trajectory and motion law of the rotor are numerically simulated. Finally, the dynamic behavior characteristics of the rotor are compared and analyzed. The results show that: Among the three kinds of protection devices (fixed ring/deep groove ball bearing/hydrostatic system), the hydrostatic system has the least influence on bouncing time, impact-rubbing force, and impact-rubbing degree, and the maximum impact-rubbing force of MLDSB is greatly reduced. Therefore, the protective bear is not required to be installed in the MLDSB. This study provides the basis for the theory of the “gap impact-rubbing” of MLDSB under electromagnetic failure, and helps to identify electromagnetic faults.

Model of Microstructure Development in Hot Deformed Magnesium Alloy AZ31 Type

2013 ◽  
Vol 197 ◽  
pp. 232-237 ◽  
Author(s):  
Dariusz Kuc ◽  
Eugeniusz Hadasik
Keyword(s):  
Grain Size ◽  
Flow Stress ◽  
Magnesium Alloy ◽  
Rolling Process ◽  
Microstructure Development ◽  
Compression Tests ◽  
Magnesium Alloy Az31 ◽  
Hot Rolling Process ◽  
Alloy Type ◽  
Relaxation Curves

The paper presents a model of microstructure changes elaborated for magnesium alloy type AZ31. In previous papers, the function of flow stress was defined on the basis of uniaxial hot compression tests. On the basis of marked relaxation curves and quantitative tests of structure the softening indicators were defined together with elaboration of equations which describe the changes in the grain size. Marked coefficients of equations were introduced in the code of simulation program. Calculations were conducted for given temperature values from 450 ÷ 250°C and strain rate from 0.01 to 10 s-1, which correspond with rolling temperature range of this alloy. Prepared model will allow the proper choice of parameters in hot rolling process of this alloy to achieve the assumed microstructure.

Effects of oxygen content on microstructure and impact toughness of high heat input flux-cored wire weld metals

2018 ◽  
Vol 115 (4) ◽  
pp. 410
Author(s):  
Fengyu Song ◽  
Yanmei Li ◽  
Ping Wang ◽  
Fuxian Zhu
Keyword(s):  
Grain Size ◽  
Impact Toughness ◽  
Weld Metal ◽  
Oxygen Content ◽  
Heat Input ◽  
High Heat ◽  
Cored Wire ◽  
Weld Metals ◽  
High Heat Input ◽  
The Impact

Three weld metals with different oxygen contents were developed. The influence of oxygen contents on the microstructure and impact toughness of weld metal was investigated through high heat input welding tests. The results showed that a large number of fine inclusions were formed and distributed randomly in the weld metal with oxygen content of 500 ppm under the heat input condition of 341 kJ/cm. Substantial cross interlocked acicular ferritic grains were induced to generate in the vicinity of the inclusions, primarily leading to the high impact toughness at low temperature for the weld metal. With the increase of oxygen content, the number of fine inclusions distributed in the weld metal increased and the grain size of intragranular acicular ferrites decreased, which enhanced the impact toughness of the weld metal. Nevertheless, a further increase of oxygen content would contribute to a great diminution of the austenitic grain size. Following that the fraction of grain boundary and the start temperature of transformation increased, which facilitated the abundant formation of pro-eutectoid ferrites and resulted in a deteriorative impact toughness of the weld metal.

Recrystallization and Grain Growth during Alloy 718 Processing

2007 ◽  
Vol 539-543 ◽  
pp. 3094-3099
Author(s):  
Nho Kwang Park ◽  
Jeoung Han Kim ◽  
Jong Taek Yeom
Keyword(s):  
Grain Size ◽  
Grain Growth ◽  
Heat Treatments ◽  
Grain Structure ◽  
Alloy 718 ◽  
Compression Tests ◽  
Δ Phase ◽  
Grain Boundary Characteristics ◽  
The Difference ◽  
Boundary Characteristics

In Alloy 718 ingot cogging process, dynamic and metadynamic recrystallizations, and static grain growth occur, and also the presence of δ phase plays a key role in controlling the grain size. In this study, the evolution of grain structure in VIM/VAR-processed Alloy 718 ingots during post-cogging heat treatments is dealt with. Compression tests were made on VIM/VAR-processed Alloy 718 ingot at temperatures between 900oC ~ 1150oC. Heat treatments were made on the compression-tested specimens, and the variation of grain size was evaluated. Constitutive equations for the grain growth are established to represent the evolution of microstructures. Special attention is paid to the evolution of grain structure under the condition of dynamic and metadynamic recrystallizations, and grain growth. The grain growth rate depends mainly on the presence of δ-phase below the δ-solvus temperature, and on the difference in the grain boundary characteristics above it.

A Case–Control Study Evaluating the Impact of Dedicated Palliative Care Training on Critical Care Interventions at the end of Life

2021 ◽  
pp. 082585972110374
Author(s):  
Jee Y. You ◽  
Lie D. Ligasaputri ◽  
Adarsh Katamreddy ◽  
Kiran Para ◽  
Elizabeth Kavanagh ◽  
...  
Keyword(s):  
Palliative Care ◽  
Critical Care ◽  
High Risk ◽  
End Of Life ◽  
Poor Prognosis ◽  
Medical Interventions ◽  
Risk Of Death ◽  
Before And After ◽  
The Difference ◽  
The Impact

Many patients admitted to intensive care units (ICUs) are at high risk of dying. We hypothesize that focused training sessions for ICU providers by palliative care (PC) certified experts will decrease aggressive medical interventions at the end of life. We designed and implemented a 6-session PC training program in communication skills and goals of care (GOC) meetings for ICU teams, including house staff, critical care fellows, and attendings. We then reviewed charts of ICU patients treated before and after the intervention. Forty-nine of 177 (28%) and 63 of 173 (38%) patients were identified to be at high risk of death in the pre- and postintervention periods, respectively, and were included based on the study criteria. Inpatient mortality (45% vs 33%; P = .24) and need for mechanical ventilation (59% vs 44%, P = .13) were slightly higher in the preintervention population, but the difference was not statistically significant. The proportion of patients in whom the decision not to initiate renal replacement therapy was made because of poor prognosis was significantly higher in the postintervention population (14% vs 67%, P = .05). There was a nonstatistically significant trend toward earlier GOC discussions (median time from ICU admission to GOC 4 vs 3 days) and fewer critical care interventions such as tracheostomies (17% vs 4%, P = .19). Our study demonstrates that directed PC training of ICU teams has a potential to reduce end of life critical care interventions in patients with a poor prognosis.

Development of Model for Acoustic Noise Generated from Bedload in Rivers 

2021 ◽  
Author(s):  
Mohamad Nasr ◽  
Thomas Geay ◽  
Sébastien Zanker ◽  
Recking Alain
Keyword(s):  
Grain Size ◽  
Size Distribution ◽  
Impact Velocity ◽  
Acoustic Noise ◽  
Acoustic Power ◽  
Bedload Transport ◽  
Empirical Formulas ◽  
Impact Rate ◽  
Flux Measurements ◽  
The Impact

<p>Quantifying bedload transport is important for many applications such as river management and hydraulic structures protection. Bedload flux measurements can be achieved using physical sampler methods. However, these methods are expensive, time-consuming, and difficult to operate during high discharge events. Besides, these methods do not permit to capture the spatial and temporal variability of bedload transport flux. Recently, alternative measuring technologies have been developed to continuously monitor bedload flux and grain size distribution using passive or active sensors. Among them, the hydrophone was used to monitor bedload transport by recording the sounds generated by bedload particles colliding on the river bed (referred as self-generated noise SGN). The acoustic power of SGN was correlated with bedload flux in field experiments. To better understand these experimental results and to estimate measurement uncertainties, we developed a theoretical model to simulate the SGN. The model computes an estimation of the power spectral density (PSD)by considering the contribution of all signals generated by impacts between bedload particles and the riverbed, and accounting for the attenuation of the acoustic signal between the source and the hydrophone position due to river propagation effects,. In this model, we</p><p>The energy of acoustic noise generated from the collision between two particles is mainly dependent on the transported particles' diameter and the impact velocity. We tested different empirical formulas for the estimation of the number of impact (impact rate) and the impact velocity depending on particle size and hydraulic conditions. To characterize the acoustic power losses as a function of distance and frequency, we used an attenuation function which was experimentally calibrated for different French rivers.</p><p>We tested the model on a field dataset comprising acoustic and bedload flux measurements. The results indicate that the PSD model allows estimating acoustic power (in between a range of one order of magnitude) for most of the rivers considered.  The model sensitivity was evaluated. In particular, we observed that it is very sensitive to the empirical formulas used to determine the impact rate and impact speed. In addition, special attention should be kept in mind on the assumption of the grain size distribution of riverbed which can generate large variability in some rivers particularly in rivers with a significant sand fraction.</p>

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