Thin Area Research Articles

Role of lamp type in conventional batch and micro-photoreactor for photocatalytic hydrogen production.

The use of an irradiation source with a homogeneous distribution of irradiation in the volume of the reaction mixture belongs to the essential aspects of heterogeneous photocatalysis. First, the efficacy of six lamps with various radiation intensity and distribution characteristics is contrasted. The topic of discussion is the photocatalytic hydrogen production from a methanol-water solution in the presence of a NiO-TiO2 photocatalyst. The second section is focused on the potential of a micro-photoreactor system-the batch reactor with a micro-reactor with a circulating reaction mixture, in which the photocatalytic reaction takes place using TiO2 immobilized on borosilicate glass. Continuous photocatalytic hydrogen generation from a methanol-water solution is possible in a micro-photoreactor. This system produced 333.7 ± 21.1µmol H2 (252.8 ± 16.0mmol.m-2, the hydrogen formation per thin film area) in a reproducible manner during 168h.

Generation of adaptive hexahedral meshes from surface and voxel geometric models

We present a modification of the developed hexahedral mesh generator from voxel data which allows constructing adaptive computational meshes. Construction of the refinement field is based on geometry features of the described model when it has a large thickness difference in dimensions or small and thin areas. A universal criterion for cells refinement is proposed which gives the possibility of its use in the case of volumetric (voxel) and surface (STL) representations of the model geometry. The refinement templates that provide conformal mesh closure are described. The results of the algorithm performance are given.

A precision dimple grinder-polisher produced by 3D printing

A precision dimple grinder-polisher has been designed and constructed using 3D printing. The purpose of the device is to produce a thin central area in 3 mm round samples for transmission electron microscopy before ion milling to electron transparency. The device can be self-made by any laboratory with a 3D printer for scientific research or teaching, and when combined with recycling and use of biodegradable filaments it can help labs reach their sustainable development goals. A novel sample holder design allows sample alignment without a monocular and thickness detection by light transmission. Novel solutions are developed for aligning the grinding disc and sample rotation motors and for fixing the polishing cloth to the polishing disc. The diameter-depth relationship is investigated for steel and plastic grinding discs. Design principles and materials are discussed, and the tool is evaluated by preparing samples from copper, silicon and tungsten, which are then examined in the transmission electron microscope to evaluate their quality.

Effects of thickness profile and inner/outer of localized thin area defects on the remaining strength of pressure equipment

When encountering pressure equipment with a structural defect such as a local thinning defect (LTA), a critical question often arises regarding the safety of continued operation. This is primarily determined by the strength at the LTA zone, as it represents the weakest point of the structure. The remaining strength factor (RSF) is proposed as an indicator to evaluate the remaining strength and life of pressure equipment when a severe LTA is identified. The API 579/ASME FFS standard offers a series of practical engineering approaches for field engineers to follow, which have achieved great success. However, it has been found that the simpler Level 1 and Level 2 approaches sometimes fail to differentiate between LTAs on the inner or outer surface of the pressure equipment, yielding identical numerical processes and results. Moreover, the use of critical thickness profiles to replace the actual thickness profile in analysis can lead to overly optimistic estimation of the RSF, posing a potential danger when the RSF is close to the allowable limit. Key issues investigated in this study include: (a) discrepancies caused by the use of simplified critical thickness profiles or parabolic profiles, as API 579 suggested, on the RSF; (b) differences in RSFs when the same LTA is on the inner and outer wall; and (c) comparisons of membrane stress and bending stress, as well as their influences on the RSF at the cross-section of the vessel wall. It can be concluded with certainty that all simplified geometries (CTP and PTP) tend to underestimate the RSF and should be used with caution. Additionally, the actual remaining strength of the outer LTA was found to be slightly lower than that of the inner LTA of identical size. Therefore, when remaining life and derating for prolonged operation are of interest, finite element analysis on pressure equipment with the LTA is recommended.

Convective organization and 3D structure of tropical cloud systems deduced from synergistic A-Train observations and machine learning

Abstract. We are building a 3D description of upper tropospheric (UT) cloud systems in order to study the relation between convection and cirrus anvils. For this purpose we used cloud data from the Atmospheric InfraRed Sounder and the Infrared Atmospheric Sounding Interferometer and atmospheric and surface properties from the meteorological reanalyses ERA-Interim and machine learning techniques. The different artificial neural network models were trained on collocated radar–lidar data from the A-Train in order to add cloud top height, cloud vertical extent and cloud layering, as well as a rain intensity classification to describe the UT cloud systems. The latter has an accuracy of about 65 % to 70 % and allows us to build objects of strong precipitation, used to identify convective organization. This rain intensity classification is more efficient to detect large latent heating than cold cloud temperature. In combination with a cloud system analysis, we found that deeper convection leads to larger heavy rain areas and a larger detrainment, with a slightly smaller thick anvil emissivity. This kind of analysis can be used for a process-oriented evaluation of convective precipitation parameterizations in climate models. Furthermore, we have shown the usefulness of our data to investigate tropical convective organization metrics. A comparison of different tropical convective organization indices and proxies to define convective areas has revealed that all indices show a similar annual cycle in convective organization, in phase with convective core height and anvil detrainment. The geographical patterns and magnitudes in radiative heating rate interannual changes with respect to one specific convective organization index (Iorg) for the period 2008 to 2018 are similar to the ones related to the El Niño–Southern Oscillation. However, since the interannual anomalies of the convective organization indices are very small and noisy, it was impossible to find a coherent relationship with those of other tropical mean variables such as surface temperature, thin cirrus area or subsidence area.

Multiple Scratching: An Atomistic Study

Using molecular dynamics simulation, we investigate multiple scratching processes in which a tip moves through a groove that has already been formed during a previous scratch. We use a conical indenter such that the friction coefficient is independent of the scratch depth. First, a single scratch to a depth of 4 nm is compared with a 2-cycle scratch in which a scratch at depth 2 nm is followed by a second scratch to the full depth of 4 nm. We observe that the second cycle shows a smaller friction coefficient as long as the tip moves through the pre-formed groove without touching the front end. In addition, we studied 5 cycles of scratching, in which the scratch depth was increased by 2 nm in each cycle. These results confirm and generalize the findings for the 2-cycle scratch. A constant-load 2-cycle scratch simulation emphasizes that the reduction in transverse load—and, consequently, in the friction coefficient—is caused by the fact that, despite a large normal area supporting the normal load, only a thin area is available to resist the transverse movement of the scratch tip. The work done during scratching is in good approximation proportional to the scratch volume showing that the transverse hardness is approximately constant in all scratch processes investigated here.

Direct and indirect damage zone of radiofrequency ablation in porcine lumbar vertebra.

To explore the direct and indirect heat damage zone of radiofrequency ablation (RFA) in porcine vertebrae and to verify the safety of RFA in a vascularized vertebral tumor model. RFA was performed in the porcine lumbar vertebrae. Magnetic resonance (MR) imaging, hematoxylin and eosin (HE), and terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) were used to assess the extent of direct and indirect injuries after RFA. The cavity of lumbar vertebrae was made, and the adjacent muscle flap was used to fill the cavity to make a vertebrae tumor model. RFA was performed in the vascularized vertebral tumor model. T1-weighted images showed a hypointensive region in the center surrounded by a more hypointensive rim on day 0 and 14. T2-weighted images showed that RFA zone was hypointensive on day 0. On day 7, hypointensity was detected in the center surrounded by a hyperintensive rim. HE showed that the RFA zone could be clearly observed on day 14. Thin bone marrow loss areas were seen around the RFA zone, which was consistent with the hyperintensive rim on the T2-weighted images. TUNEL showed a large number of apoptotic cells in the RFA zone. During RFA in the vertebral tumor model, the temperature of all monitoring positions was less than 45 °C. Using in vivo experiments, the effective zone of RFA was evaluated by MR imaging and pathology, and the direct and indirect damage range were obtained. The safety of RFA was verified by RFA in a vascularized vertebral tumor model.

Ultrathin Anterolateral Thigh Free Flap: An Adipocutaneous Flap with the Most Superficial Elevation Plane.

Although many efforts have been made to create thinner anterolateral thigh (ALT) flaps, their thickness varies among patients, and the flap may be still too thick to match shallow defects. The authors successfully harvested an ALT flap through the most superficial elevation plane, the superficial fat layer, which was useful to match the shallow defects. All patients who underwent ALT free flap reconstruction for upper and lower distal extremity defects were divided retrospectively into groups by ALT flap elevation plane: thin, above the deep fascia; superthin, at the superficial fascia; and ultrathin, through the superficial fat. Preoperative computed tomographic angiography and duplex ultrasonography planning were used for all patients. Anatomical characteristics of donor subcutaneous tissue and surgical details, including flap thickness, flap size, and incidence of flap necrosis were compared among the groups and between sexes. The average deep and superficial fascial depths were 16.7 and 10.8 mm, 12.5 and 8.2 mm, and 9.1 and 5.6 mm ( P < 0.05), and the average flap thickness was 5.8 mm, 7.9 mm, and 7.8 mm ( P = 0.29) in the ultrathin, superthin, and thin ALT groups, respectively. No significant intergroup differences existed in flap size or complications. The deep and superficial fascia were located significantly deeper in female patients (9.4 and 6.0 mm in male patients and 14.9 and 9.6 mm in female patients, respectively). With precise preoperative planning, the most superficially elevated, ultrathin ALT flap can achieve optimal reconstructions of thin body areas. Female patients with thicker thighs and patients with a high body mass index would benefit from this flap. Therapeutic, IV.

Variability Assessment of the Performance of MoS2-Based BioFETs

Two-dimensional material (2DM)-based Field-Effect Transistors (FETs) have been postulated as a solid alternative for biosensing applications thanks to: (i) the possibility to enable chemical sensitivity by functionalization, (ii) an atomically thin active area which guarantees optimal electrostatic coupling between the sensing layer and the electronic active region, and (iii) their compatibility with large scale fabrication techniques. Although 2DM-based BioFETs have demonstrated notable sensing capabilities, other relevant aspects, such as the yield or device-to-device variability, will demand further evaluation in order to move them from lab-to-fab applications. Here, we focus on the latter aspect by analyzing the performance of MoS2-based BioFETs for the detection of DNA molecules. In particular, we explore the impact of the randomized location and activation of the receptor molecules at the sensing interface on the device response. Several sensing interface configurations are implemented, so as to evaluate the sensitivity dependence on device-to-device variability.

Chemical strengthening behavior of a glass substrate having locally different thickness

To understand the effect of chemical strengthening process on irregular geometry, a partially thinned glass substrate was strengthened according to the ion-exchange conditions, and the strengthening properties and the dimensional changes of the partially thinned glass were analyzed using a surface stress meter and a 3-dimensional analyzer. The results revealed that the compressive stress (CS) measured at a thin area of the glass substrate having different thicknesses was affected by the CS of a thick zone, and consequentially the CS of the thin zone was bigger than that measured at a same thickness glass. It was also found that the dimensional changes across the thin zone after chemical strengthening were relatively big, and as a result, it caused a physical deformation on the thin area due to the interference in the thick area.

Mapping of Active Frazil and Sea Ice Production in the Northern Hemisphere, With Comparison to the Southern Hemisphere

AbstractFrazil ice in the coastal polynyas has been increasingly recognized as important for efficient sea ice production, associated dense water formation, transport of particulate matter and consequent biological production. However, it has not been well understood where and to what degree active‐frazil areas occur in the Northern Hemisphere polynyas. We presented the first mapping of active frazil in the Northern Hemisphere, using sea ice data during September–May for 2002/2003–2010/2011, created from an Advanced Microwave Scanning Radiometer for the Earth Observing System thin ice algorithm that can detect active frazil areas. The North Water, Northeast Water, Anadyr, and St. Lawrence Island polynyas were found to have a relatively high occurrence rate of active frazil compared with other polynyas. We improved the estimation of sea ice production by discriminating between active frazil and thin solid ice and found that previous algorithms tended to overestimate sea ice production, particularly for polynyas dominated by thin solid ice such as the Okhotsk Northwestern polynya. We also made the first global comparison of polynya characteristics for all the major coastal polynyas. The annual ice production rate is 3–4 m yr−1 in the Northern Hemisphere polynyas and 6–9 m yr−1 in the Antarctic coastal polynyas. This large difference is mainly explained by the less frequent occurrence of active frazil and thin ice areas in the Northern Hemisphere polynyas owing to a lower occurrence of strong wind events.

Metallography on a sickle fragment from the Drassburg/Burgenland hoard find

Abstract The Drassburg Bronze Age hoard find (approx. 25 kg) also comprises some sickles and sickle fragments. One of these sickle fragments was provided for metallographic examinations. A XRF analysis revealed 94.5 wt.% Cu, 4.31 wt.% Sn, 0.61 wt.% Pb, and 0.12 wt.% S in the alloy. It can therefore be attributed to tin bronzes. The material has a uniform dendritic microstructure. Higher concentrations of Sn, S, and Pb were measured in the interdendritic areas. This suggests a precipitation of the phases Pb and Cu2S from the residual melt. Klemm II etching also revealed the dendritic areas which exhibited different orientations. Deformations were observed in thin edge areas of the sickle fragments. They were introduced in the course of mechanical postprocessing of the bronze or during its use. The surface of the sickle exhibits a patina with a layered structure and a thickness of up to 500 μm. The Sn contents measured in the outer layers are somewhat higher than in the inner layers.

Kinematic Modes Identification and Its Intelligent Control of Micro-Nano Particle Manipulated by Acoustic Signal

In this paper, the dynamics of a micro-nano particle on the micro-thin plate driven by an acoustic signal was investigated, including the particle kinematics mode, kinematics equation, and trajectory control. According to Newton’s kinematic theorem, analyzing the forces acting on the particle, the kinematic modes of the driven particle are distinguished with specific mathematical conditions, which are classified as slide, bounce, and stable modes strictly planned on a thin plate area. Based on the theory of kinematic modal analysis, the simulation results reveal the distribution rules of particle motion modes against the driving signal or plate geometry. The particle kinematics equation governing the sliding movement on the thin plate was then derived in light of the interaction between the particle and driving signal, based on which, the particle trajectory was drawn and analyzed in detail. For the purpose of controlling the particle trajectory, the control problem was designed in accordance with a linear active disturbance rejection controller (LADRC). Further, a guidance law was proposed, and the corresponding controller was designed to realize the linear trajectory following.

(Invited) Lithium Recovery from Geothermal Brines

Lithium is a critical raw material for developing current lithium-ion batteries and prospective next-generation batteries. Its reserves are concentrated in a handful of countries. It is primarily extracted from continental brines, wherein Li+ is relatively concentrated (0.3 –1.5 wt%) in a complex mixture of many more components with relatively large water solubilities.Current practices to extract lithium from continental brines involve evaporation, i.e., >90% of water. Eventually, the concentration of Li+ intensifies up to 6–7%, in a brine which follows numerous chemical processing steps, to ultimately produce battery-grade lithium chemicals. Despite being the easiest and currently most cost-effective practices, these are inefficient and unsustainable (chemical-intensive, requires extensive land use and time, and delivers large volumes of waste), especially in the context of the sharp increase in the demand for lithium that is already happening and is expected to endure in the coming decades.To sustainably meet the future demand for lithium, it is imperative to develop more efficient extraction methods, which are faster, less climate/weather reliant, minimize waste production, and especially deal with water differently than current industrial processing (i.e., circumventing evaporation). Besides being applicable to concentrated lithium brines, characteristic of primary extraction, these methods should especially be applicable to dilute brines (i.e., geothermal, oilfield, seawater, wastewater,—which contain 0.01–0.3 mg of Li+ per L of brine), as these have more recently prospected for Li recovery. Together with lithium recycling from spent batteries, these hold the promise of delocalizing raw lithium sourcing.New extraction technologies have emerged within the past decade, including adsorption and the use of membranes. In addition to being insufficient for an effective recovery, some alternatives seem to imply a harsher environmental impact than current practices, whereas others would be disadvantageous to treat the large volumes of fluid associated with lithium extraction. Especially, electrochemical methods for Li+ recovery are (re)surging.[1] The use of Li+ insertion electrodes coupled to membranes and membrane electrolysis are notoriously thriving.[1,2] However, the first approach bears the limitation of requiring extremely thin and large area electrodes to process large brine volumes, and the second one suffers from being energy-intensive, plus current investigations show the constant addition of chemicals for pH adjustment, and produce chloride- and hypochlorite-anions rich solutions which are neither economic nor sustainable.[2] Furthermore, in membrane electrolysis swelling of the ion exchange membrane could be an issue[3] that has not been addressed in Li+ recovery studies; if excessive, this could lead to membrane deformations and ultimately to the blockage of the flow channels within the reactor. Despite the aforementioned limitations, electrochemical methods are a more sustainable and versatile option, with latent competitiveness vs. current industrial practices. Thus, ideal solutions should have the added value of circumventing the limitations of the state-of-the-art electrochemical approaches mentioned above. This aim was pursued in the present work.Gas diffusion electrodes (GDEs) are broadly used in electrochemical energy-conversion devices, such as fuel cells and metal-air batteries, as well as in electrolyzers aiming at chemical synthesis, like in the chlor-alkali industry, hydrogen peroxide production, CO2 conversions to fuels and fine chemicals, or N2 reduction to ammonia. Recently, the use of GDEs was pioneered for metal recovery in a process named gas-diffusion electrocrystallization (GDEx).[4–7] This talk will explain the underlying principles of GDEx and its successful application in the recovery of highly dilute lithium (<300 mg L-1) in synthetic brines containing up to 150 mg L-1 NaCl, as well as in real geothermal brines with Li+ concentrations below 50 mg L-1. Up to 50% of direct lithium extraction from the brine can be achieved, selectively, forming solid materials with lithium concentrations >0.5%, which are promising as a starting material for the direct conversion into battery-grade lithium hydroxide or carbonate.

The practicability of different preparation of mandibular molar restored by modified endocrown with intracanal extension: Computational analysis using finite element models

Background and objectivePost-core-crown (PCC) and endocrown are two common restorative methods for severely damaged molars, but exhibit disadvantages. This study aimed to explore the practicability of modified endocrown with a 2 mm intracanal extension (MED) to restore defective teeth using finite element analysis (FEA). MethodsFive groups of numerical models of mandibular molars restored by three MEDs, a PCC, and a routine endocrown after root canal treatment were devised by FEA software. We constructed 4 mm, 3 mm, and 2 mm thickness of MED restorations to restore mandibular molars that were prepared to 1 mm, 2 mm, and 3 mm from the cemento-enamel junction (CEJ). Furthermore, PCC and routine endocrown were used to compare the stress distribution with MED. Lithium disilicate glass-ceramics (EMAX) and resin nanoceramics (LU) were considered restorative materials, and a vertical load of 600 N and an oblique load of 200 N were applied to the restorations. ResultsIn three MEDs by LU, 2 mm thickness of restoration generated the highest stress on prepared teeth, while the thickness of EMAX did not significantly influence the stress value. MED by LU generated higher stress around the CEJ, and reduced the stress on the middle and lower root compared to MEDs by EMAX, PCC by EMAX, and PCC by LU. MED by EMAX caused lower stress around the CEJ, and generated higher stress in the chamber walls after extended root canals compared with MED by LU, endocrowns by LU, and endocrowns by EMAX. There was an evident stress concentration at the last but one layer, which was a thin area of the tooth root in all restorative models. ConclusionsThe use of modified endocrown may be considered an effective restorative method to restore defective mandibular molar, but suitable restorative material must be selected based on the tooth preparation method and deficiencies in the tooth structure.

Evaluation of Cultivated Land Quality in Semiarid Sandy Areas: A Case Study of the Horqin Zuoyihou Banner

Objective: The evaluation of cultivated land quality from the regional perspective and the clear level and change in cultivated land quality in the whole region can better guide the construction of cultivated land quality, carry out scientific optimization allocation, improve grain production capacity, and promote the sustainable use of cultivated land. Research methods: The utilization of local resources and natural conditions were comprehensively considered, and the evaluation was carried out from the four dimensions of ecology, quantity, spatial structure and scale to comprehensively reflect the level of regional cultivated land utilization. Results: (1) The cultivated land quality level of the Horqin Zuoyihou Banner is low, and the pressure of regional water resources is great. Some cultivated land is located in the area with poor natural conditions, and there are many thin and narrow cultivated areas of land. The area of cultivated land that can be carried by regional water resources under current irrigation is 184,492.17 hm2, and that under water-saving irrigation is 259,703.72 hm2, which are lower than the current cultivated land areas. (2) During the study period, the total amount and spatial distribution of cultivated land changed greatly, and there were good natural conditions and utilization conditions of newly added cultivated land, but the quality of cultivated land from the regional perspective showed a downward trend. The dynamic attitude of cultivated land change was 0.99%. (3) According to the evaluation results, the cultivated land was divided into the following four categories: priority protection type, optimization and coordination type, gradual conversion type and priority conversion type, which accounted for 34.18%, 30.59%, 28.83% and 6.40% of the total cultivated land area, respectively. Conclusions: There is a sharp contradiction between the supply and demand of water resources, and the quality of cultivated land in the region is low and shows a downward trend, which is not conducive to the sustainable use of regional land resources. In this regard, the Horqin Zuoyihou Banner should actively curb the growth of cultivated land, develop water-saving irrigation processes, strengthen ecological environment protection, and systematically optimize the layout of cultivated land on the premise of ensuring ecological security according to the actual conditions of different regions.

Analytical Methods and GAPI Assessment Used for the Determination of Toxic Metals in Commercial Cosmetic Products: A Review

Background: The toxic metal content of cosmetics causes worry because of the daily and repeated use of these products, which are placed over thin and sensitive areas of the skin such as the face, eyelids, and lips. Objective: Toxic metals like Fe, Cr, Hg, Cu, Cd, Ni, and As are determined in various types of cosmetics such as colour cosmetics, hair cosmetics, body and face care products, and herbal cosmetics. Last studies estimate that in commercial cosmetics toxic metals might present in amounts making a risk to human health. Methods: Many analysis methods used for determining toxic metals in cosmetics were established. The instruments involving FAAS, ICP-AES, ICP–MS, Hydride generation, Cold vapor, and CE spectrometers with many novel methods were described in this review. Green analytical methods should be developed for determining toxic metals in cosmetics and particularly during the preparation of analytical cosmetic samples. Results: The most tools used for assessing analytical protocols related to green analytical chemistry are GAPI (Green Analytical Procedure Index). GAPI gives good information on the safety of analytical chemistry procedures, depending on the five pentagrams shaped with three color symbols that can be used (green, yellow, and red) referring to low, medium to high impact, respectively. Conclusion: This review offers an overview, analytical chemistry methods and instruments used for the estimation of toxic metals in cosmetics and their GAPI assessment.

Spatiotemporal Trace of Human Behaviors and Responses Pertaining to Winter Storm Dylan

This study highlights how Winter storm Dylan plays a significant role in human behaviors and responses according to a multitude of periods, geographical scales, census regions, sociodemograhpic, and regional characteristics. This study finds that people show different behaviors and responses according to periods, states, and regional characteristics. Second, tweets are relatively uploaded across the US states during the winter storm week, compared to the pre-winter storm and post-winter storm weeks. Third, regions play an important role in displacements. Minnesota and Massachusetts exhibit 5.1 and 1.8 times more displacements than Montana. Fourth, while total employment is negatively associated with displacements, jobs per household and regional diversity are positively associated with them. The dense business areas show 0.4 times less displacements than the thin business areas, and places that have many workers per household and high regional diversity show 2.3 and 1.6 times more displacements than the other places.

Experimental Investigation of Self Compacting Concrete Beams Strengthened with Steel Fibre Reinforcement

The project mainly aims at studying the mechanical and durability characteristics of the self-compacting steel fibre reinforced concrete with recycled aggregate as coarse aggregate and ecosand as fine aggregate replacement by conducting compressive strength test, consistency test, split tensile strength test, flexural strength test, water absorption test. The project also deals with the comparison of properties of the proposed self-compacting concrete with mentioned replacements with that of existing conventional concrete. For this experiment, M40 grade concrete is used and steel fibre is incorporated and ecosand is used. Conventional concrete tends to present a problem with regard to adequate consolidation in thin sections or areas of congested reinforcement, which leads to a large volume of entrapped air voids and compromises the strength and durability of the concrete.

Experimental Investigation of Steel Fibre Reinforced Self Compacting Concrete using ECOSAND

The project mainly aims at studying the mechanical and durability characteristics of the self-compacting steel fibre reinforced concrete with recycled aggregate as coarse aggregate and ecosand as fine aggregate replacement by conducting compressive strength test, consistency test, split tensile strength test, flexural strength test, water absorption test. The project also deals with the comparison of properties of the proposed self-compacting concrete with mentioned replacements with that of existing conventional concrete. For this experiment, M40 grade concrete is used and steel fibre is incorporated and ecosand is used. Conventional concrete tends to present a problem with regard to adequate consolidation in thin sections or areas of congested reinforcement, which leads to a large volume of entrapped air voids and compromises the strength and durability of the concrete.