Changes In Air Content Research Articles

Effect of pumping process on the properties of 3D printed concrete containing air-entraining agent

Using 3D printing technology in the construction industry is growing rapidly due to its numerous advantages. However, understanding various influencing factors on this technique is crucial. Among these, the concrete pumping process can significantly impact printed concrete’s properties. The results indicate that the pumping process can alter the structure of void spaces, reduce the air content, and increase the compressive strength of concrete. Mainly, the mechanisms of mechanical entrapment, reduction of air content and increase of hydration kinetics respectively cause these changes in air content and compressive strength due to pumping. In the control samples, the fresh air content decreased by 47% and the compressive strength increased by 4.3%. The creation of stable air bubbles using air-entraining agents can lead to a decrease in change of air content and compressive strength. By using 0.12% air-entraining agent, the drop in air content due to pumping reached about 23–25%. It also appears that, depending on the amount of entrained air in the mixture, pumping can affect its flowability differently. Highlights The pumping process is an essential component in 3D printed concrete, so it is necessary to see the effect of this process on the properties of printed concrete, especially its fresh properties. Although the addition of an air-entraining agent can help concrete resist freezing and thawing cycles, what matters is the air content in the hardened state. Concrete pumping can change the structure of concrete voids and affect its various properties.

MEASUREMENT OF WATER RETENTION OF PEAT SOIL IN CANAL BLOCKING USING PRESSURE PLATE CHAMBER

Measuring air retention in constructed canal blockage is critical for determining changes in air content after canal blocking. The purpose of this study is to assess the influence of changes in levels on air retention values measured at three depths, namely 0-20 cm, 20-40 cm, and 40-60 cm, at four transect sampling stations created at a distance of 10 m to 260 m from the canal block. Changes in bulk density, porosity, and peat volume affect groundwater. Peat soil samples were collected from burned peatlands, and canal blocks were constructed. A pressure plate chamber was used to assess air retention. The findings of the investigation revealed that the air retention pattern of peat soil at 16 test sample locations was at maximum at PF 0.2 at each depth. At higher pressures (pF 2-4.2), peat groundwater is strongly bonded by peat soil particles. The average bulk density of peat is 0.2 2 and the porosity value is 86.79%. The higher the air content at each pF value has no influence on the porosity and bulk density values. Changes in air content between pF 2.0 and 4.2 lower average peat volume by 7.4%. The size of this value is assumed to be determined by the peat's type, maturity, and decomposition value

Robust HU-based CT ventilation from an integrated mass conservation formulation.

Computed tomography (CT) ventilation algorithms estimate volume changes induced by respiratory motion. Existing Hounsfield Unit (HU) methods approximate volume change from the measured HU variations between spatially corresponding voxel locations within a temporally resolved CT image pair, assuming that volume changes are caused solely by changes in air content. Numerical implementations require a deformable image registration to determine the inhale/exhale spatial correspondence, a preprocessing lung volume segmentation, a preprocessing high‐intensity vessel segmentation, and a post‐processing smoothing applied to the raw volume change estimates obtained for each lung tissue voxel.PurposeWe introduce the novel mass‐conserving volume change (MCVC) method for estimating voxel volume changes from the HU values within an inhale/exhale CT image pair. MCVC is based on subregional volume change estimates that possess quantitatively characterized and controllable levels of uncertainty. MCVC is therefore robust to small variations in DIR solutions and the resulting ventilation images are overall more reproducible. In contrast to existing HU methods, MCVC does not require a preprocessing lung vessel segmentation or pre/post‐processing Gaussian smoothing.MethodsSubregional volume change estimates are defined in terms of mean density ratios. As such, the corresponding uncertainty is characterized using Gaussian statistics and standard error analysis of the sample density means. A numerical solution is obtained from the MCVC formulation by solving a constrained linear least squares problem defined by a series of subregional volume change estimates. Reproducibility of the MCVC method with respect to DIR solution was assessed using expert‐determined landmark point pairs and inhale/exhale phases from 10 four‐dimensional CTs (4DCTs) available on http://www.dir-lab.com. MCVC was also compared to the robust Integrated Jacobian Formulation (IJF), a transformation‐based ventilation method.ResultsThe ten Dir‐Lab 4DCT cases were registered twice with the same DIR algorithm, but using different degrees of freedom (DIR 1 and DIR 2). Standard HU ventilation (HUV) and MCVC ventilation images were computed for both solutions. The average spatial errors (300 landmarks per case) for DIR 1 ranged between 0.74 and 1.50 mm, whereas for DIR 2 they ranged between 0.68 and 1.18 mm. Despite the differences in spatial errors between the two DIR solutions, the average Pearson correlation between the corresponding HUV images was 0.94 (0.03), while for the MCVC images it was 1.00 (0.00). The average correlation between MCVC and IJF ventilation over the ten test cases was 0.81 (0.14), whereas for HUV and IJF it was 0.56 (1.11).ConclusionWhile HUV is robust to DIR solution, its implementation depends on heuristic Gaussian smoothing and vessel segmentation. MCVC is based on subregional volume change measurements with quantifiable and controllable levels of uncertainty. The subregional approach eliminates the need for Gaussian smoothing and lung vasculature segmentation. Numerical experiments are consistent with the underlying mathematical theory and indicate that MCVC ventilation is more reproducible with respect to DIR algorithm than standard HU methods. MCVC results are also more consistent with the robust IJF method, which suggests that incorporating robustness leads to more consistent results across both DIRs and ventilation algorithms.

Impact of aeration change and beam arrangement on the robustness of proton plans.

This study determines the impact of change in aeration in sinonasal cavities on the robustness of passive‐scattering proton therapy plans in patients with sinonasal and nasopharyngeal malignancies. Fourteen patients, each with one planning CT and one CT acquired during radiotherapy were studied. Repeat and planning CTs were rigidly aligned and contours were transferred using deformable registration. The amount of air, tumor, and fluid within the cavity containing the tumor were measured on both CTs. The original plans were recalculated on the repeat CT. Dosimetric changes were measured for the targets and critical structures. Median decrease in gross tumor volume (GTV) was 19.8% and correlated with the time of rescan. The median change in air content was 7.1% and correlated with the tumor shrinkage. The median of the mean dose D mean change was +0.4% for GTV and +0.3% for clinical target volume. Median change in the maximum dose D max of the critical structures were as follows: optic chiasm +0.66%, left optic nerve +0.12%, right optic nerve +0.38%, brainstem +0.6%. The dose to the GTV decreased by more than 5% in 1 case, and the dose to critical structure(s) increased by more than 5% in three cases. These four patients had sinonasal cancers and were treated with anterior proton fields that directly transversed through the involved sinus cavities. The change in dose in the replanning was strongly correlated with the change in aeration (P = 0.02). We found that the change in aeration in the vicinity of the target and the arrangement of proton beams affected the robustness of proton plan.

Effects of Pitch-Based Short Carbon Fibers on the Workability, Unit Weight, and Air Content of Mortar Composite

Pitch is a viscoelastic polymer material consisting of aromatic hydrocarbons. It is used to produce carbon fibers with sheet-like crystal structures. The aim of the work presented in this paper was to evaluate the effects of pitch-based short carbon fibers on the workability, unit weight, and air content of freshly mixed mortar composite. Experimental investigation was carried out on five different types of mortar composite, including a control mortar. Four mortar composites were prepared including pitch-based short carbon fibers with 1–4% volume contents. The fresh mortar composites were tested to determine their slump, inverted slump cone flow (flow time, mass flow, and volume flow), unit weight, and air content. In addition, the correlation between the slump and flow time of various mortar composites was determined. It was found that the slump decreased with the increasing volume content of carbon fibers. The flow time of mortar composite increased, and therefore its mass flow and volume flow decreased with a greater volume content of carbon fibers. The slump was strongly correlated with the flow time, with a correlation coefficient of 0.9782. Furthermore, the unit weight of the fresh mortar composite decreased due to the incorporation of carbon fibers. However, amongst the different carbon fiber reinforced mortar composites, the mortar with 3% fiber volume content provided the highest unit weight. The air content results were consistent with the unit weight results. The change in air content of various mortar composites followed a trend reciprocal to that of unit weights. When the overall effects of carbon fibers were compared, it was observed that the fiber volume content higher than 3% resulted in a significantly low workability and provided a much lower unit weight with greater entrapped air content.

Spontaneous lung pathology in a captive common marmoset colony (Callithrix jacchus).

Data on spontaneous pathology are substantially scarce for common marmosets, compared to other laboratory animals, but is essential for the interpretation of histological findings in the context of toxicological and experimental studies. Especially if common marmosets are used as experimental animals in respiratory research, detailed knowledge on the spectrum, occurrence, and incidence of spontaneous histopathological pulmonary lesions in this non-human primate species is required. In this study, lung tissue of 638 common marmosets from the marmoset colony of the German Primate Center was examined histologically. The analysis revealed a high incidence of predominantly mild and multifocal interstitial pneumonia (32.99 %) of unknown etiology in most cases. Only few marmosets exhibited lobar pneumonia (1.41 %) and bronchopneumonia (0.94), which were mainly caused by bacterial pathogens such as Bordetella bronchiseptica and Klebsiella pneumoniae. Lung immaturity and atelectasis were common histological findings in newborn marmosets. Typical background lesions included anthracosis (8.15 %), hemosiderosis (1.72 %), extramedullary hematopoiesis (11.6 %), mineralization (10.97 %), and inflammatory cell foci (10.34 %). In addition, three cases of pulmonary arteriopathy (0.47 %) and 1 case of foreign-body granuloma (0.16 %) were detected in the marmoset study cohort. The high prevalence of circulatory disturbances (congestion, edema, hemorrhage) and changes in air content (secondary atelectasis, alveolar emphysema) could partly be explained by euthanasia-related artifacts or agonal changes. The present study provides a comprehensive overview of the range and incidence of spontaneous pulmonary histopathology in common marmosets, serving as valuable reference data for the interpretation of lung lesions in toxicological and experimental marmoset studies.

Lobe based image reconstruction in Electrical Impedance Tomography.

Electrical Impedance Tomography (EIT) is an imaging modality used to generate two-dimensional cross-sectional images representing impedance change in the thorax. The impedance of lung tissue changes with change in air content of the lungs; hence, EIT can be used to examine regional lung ventilation in patients with abnormal lungs. In lung EIT, electrodes are attached around the circumference of the thorax to inject small alternating currents and measure resulting voltages. In contrast to X-ray computed tomography (CT), EIT images do not depict a thorax slice of well defined thickness, but instead visualize a lens-shaped region around the electrode plane, which results from diffuse current propagation in the thorax. Usually, this is considered a drawback, since image interpretation is impeded if 'off-plane' conductivity changes are projected onto the reconstructed two-dimensional image. In this paper we describe an approach that takes advantage of current propagation below and above the electrode plane. The approach enables estimation of the individual conductivity change in each lung lobe from boundary voltage measurements. This could be used to monitor disease progression in patients with obstructive lung diseases, such as chronic obstructive pulmonary disease (COPD) or cystic fibrosis (CF) and to obtain a more comprehensive insight into the pathophysiology of the lung. Electrode voltages resulting from different conductivities in each lung lobe were simulated utilizing a realistic 3D finite element model (FEM) of the human thorax and the lungs. Overall 200 different patterns of conductivity change were simulated. A 'lobe reconstruction' algorithm was developed, applying patient-specific anatomical information in the reconstruction process. A standard EIT image reconstruction algorithm and the proposed 'lobe reconstruction' algorithm were used to estimate conductivity change in the lobes. The agreement between simulated and reconstructed conductivity change in particular lobes were compared using Bland-Altman plots, correlation plots and linear regression. To test the applicability of the approach in a realistic scenario, EIT measurements of a patient suffering from cystic fibrosis (CF) were carried out. Conductivity changes in each lobe generate specific patterns of voltage change. These can be used to estimate the conductivity change in lobes from measured boundary voltage. The correlation coefficient between simulated and reconstructed conductivity change in particular lobes is r>0.89 for all lobes. Unknown position of the electrode plane leads to over- or underestimation of reconstructed conductivity change. Slight mismatches (±5% of the forward model height) between the actual position of the electrode plane and the position used in the reconstruction model lead to regression coefficients of 0.7 to 1.3 between simulated and reconstructed conductivity change in the lobes. The presented approach enhances common reconstruction methods by providing information about anatomically assignable units and thus facilitates image interpretation, since impedance change and thus ventilation of each lobe is directly determined in the reconstructions.

On the potential of coupling air content and O 2/N 2 from trapped air for establishing an ice core chronology tuned on local insolation

The potential to access an ice core chronology tuned on local insolation has been demonstrated for the first time in the work of M. Bender (2002) linking the variations of O 2/N 2 ratios in the air trapped in the Vostok ice with local (78°S) summertime insolation. More recently, it has been shown that the long-term changes in air content, V, recorded in ice from the high Antarctic plateau are also dominantly imprinted by the local summer insolation ( Raynaud et al., 2007). This paper presents a new V record from Vostok, which is compared with the published Vostok O 2/N 2 record for the same period of time (160–390 ka BP) by using the same spectral analysis methods. The spectral differences between the two properties and the possible mechanisms linking them with insolation through the surface snow structure and the close-off processes are discussed. The main result of our study is that the two experimentally independent local insolation proxies lead to absolute (orbital) timescales, which agree together within less than 1 ka on average. This result strongly adds credibility to the total content and the O 2 to N 2 ratio of the air trapped in ice as reliable and complementary tools for accurate dating of existing and future deep ice cores.

The local insolation signature of air content in Antarctic ice. A new step toward an absolute dating of ice records

An accurate chronology of ice cores is still needed for interpreting the paleoclimatic record and to understand the relation between insolation and climate. A new domain of research in this area has been stimulated by the work of M. Bender linking the record of N 2/O 2 ratio in the air trapped in the ice with the local insolation. Here we investigate the potential of the air content of polar ice, V, as another and complementary ice proxy of local insolation. We propose that the long-term changes in air content recorded in ice from the high Antarctic plateau is dominantly imprinted by the local summer insolation. The V measurements covering the last 440,000 yr and obtained along the EPICA DC (EDC) ice core are presented. 86% of the variance observed in the V record can be explained neither by air pressure nor by temperature changes, and then should reflect properties influencing the porosity at close-off other than temperature. A wavelet analysis indicates a dominant obliquity period (around 41 ka) over the last 440 ka. We propose a mechanism, which can account for the observed anti-correlation between local insolation and V and explain how the local insolation, via the integrated summer insolation, can affect the near-surface snow structure and consequently the porosity at close-off. The V and the integrated summer insolation changes show high coherency over all the record and a variable phase relationship with a maximum phase difference of about 4000 yr around 200 ka ago. The phase difference may reflect the difference between the EDC2 chronology based on an inverse dating method and an accurately dated insolation curve. Our work, by proposing a new and complementary ice proxy for local insolation should eventually contribute to the establishment of an absolute dating of the ice paleo-record.

Dielectric behavior of pulmonary edema induced in the rat lung

The dielectric properties (conductivity, kappa and relative permittivity, epsilon) of excised rat lung are modified by lung air and water content. The measurements of these quantities were made over the frequency range of 10 kHz to 100 MHz with an open-ended coaxial probe. The following relationships were analyzed in an oleic acid-induced pulmonary edema model using 18 animals: the spectra of kappa, epsilon and the loss tangent as a function of lung air and water content. Secondly, an isolated-perfused lung system was produced to induce a gradual increase in lung water. The time course of kappa, epsilon and the loss tangent for one excised lung was analyzed. The principal findings were: (i) a decrease in kappa and epsilon with increasing air content, (ii) an increase in kappa and epsilon with increasing water content, and (iii) a good correlation between lung water content and maximum loss tangent that was insensitive to changes in air content. We conclude that this technique could provide a quantitative assessment of lung water during pulmonary edema formation.

Air Change in Hydraulic Concrete Due to Pumping

The air content of concrete plays an important role in the durability of concrete. Excess air may reduce the strength of the concrete, while inadequate air will result in premature deterioration of the concrete due to scaling caused by freeze–thaw cycles and deicing chemicals. Pumping of hydraulic concrete has been a common practice for placing concrete. Although the air content before pumping is relatively easy to control, the air change during pumping has not been well understood. The purpose of this study was to investigate the change in air content of hydraulic concrete caused by pumping. Air content and other properties of concrete before and after pumping were measured at 36 construction projects in two phases. Analysis on data from 31 projects in Phase I indicated that most concrete experiences air loss because of pumping. Many factors could be behind this air loss. Analysis on data from five control projects in Phase II indicated that sampling methods had a moderate effect on the air change. Errors in measurement were minimal for certified testers and calibrated pots. The air change of concrete was significantly affected by the configuration of the boom, in addition to the air content before pumping. Attachments to the boom played key roles in reducing the air loss. Two mathematical models were developed for the prediction of air loss.

Evaluation of in vivo total and regional air content and distribution in primate lungs with high-resolution CT.

The authors sought to determine whether gray-scale quantitative information from high-resolution computed tomography (CT) could reliably yield estimates of lung air content and help determine changes in air content with lung inflation and deflation. High-resolution CT images (n = 40) of lungs of two anesthetized monkeys were obtained after inflation with known air volumes. Percentage air content was calculated for each voxel, and lung volumes and patterns of air distribution were determined. When corrected for pressure and temperature, high-resolution CT-based volumes correlated closely with inflation volumes (r = .99; standard error = 3.4%). Patterns of regional change in air content demonstrated known patterns of ventilation. Although the high-spatial-frequency algorithm used in high-resolution CT enhances edges of structures and improves visualization of anatomic detail, gray-scale values from the same high-resolution CT data set remain a reliable index of regional lung attenuation.

Investigation of Fiber-Reinforced Concrete for Use in Transportation Structures

Results are presented of a laboratory investigation to determine the properties of fiber-reinforced concretes (FRCs) with steel (hooked-end), polypropylene (monofilament and fibrillated), and the recently introduced polyolefin fibers (monofilament) for application in pavements and bridge deck overlays. Concrete properties in the unhardened and hardened states were evaluated and compared. Although the ultimate splitting tensile strength, compressive strength, and first-crack strength were higher in most of the FRCs, when strength values were adjusted for changes in air content, only a few batches had higher strengths. The addition of fibers resulted in great improvements in flexural toughness and impact resistance. Three FRC pavement overlays were applied in Virginia in 1995. The FRCs used in the projects were similar to those used in the laboratory investigation, with similar fiber volumes, types, and sizes. To implement the findings of the study successfully, the performance of the FRC pavement overlays is being monitored.

Testing Fly Ash in Mortars for Air-Entrainment Characteristics

Abstract When fly ash is used in the production of air-entrained concrete, it can affect the dosage requirement of air-entraining admixture (AEA) needed to produce the desired air content. ASTM C 618 provides a uniformity requirement for the dosage of AEA needed with a particular fly ash, and ASTM C 311 provides a test to determine compliance with the requirement. In a study of fly ash uniformity, the C 311 test was found to be ineffective in evaluating the effect of fly ash characteristics on AEA dosage requirement. The problem with the C 311 test is traced to the high levels of AEA which are required in the test and is illustrated by the use of AEA dosage versus air content curves. Modifications to the C 311 test are proposed wherein an admixture dosage is selected from the AEA dosage versus air content curve. This dosage is then used to test successive fly ash samples, and changes in air content of the test mix illustrate the variations in AEA requirement caused by the fly ash. An additional modification permits the evaluation of the fly ash's potential to lose entrained air over time.