Aggregate Volume Research Articles

Sorting out the effect of credit supply

We document that banks that cut lending more during the Great Recession were lending to riskier firms ex-ante. To understand the aggregate implications of this sorting pattern, we build an assignment model in which banks have heterogeneous costs to take on risky loans and firms have different credit risks. In the model, aggregate loan volume depends on the entire distribution of bank holding costs and firm credit risks. We then use our model to recover the change in the distribution of bank holding costs during the Great Recession and show that it explains two-thirds of the decline of aggregate loan volume during this period.

Türkiye Ekonomisinde Bankacılık Sektörü Tarafından Yaratılan Yurt İçi Kredi Hacmi İle Ekonomik Büyüme Arasındaki İlişki: ARDL Sınır Testi Yaklaşımı

Banks are one of the most important elements of the financial system. Banks are organizations that are involved in the development of the money market by ensuring the collection of savings in the economy, transferring surplus funds to economic units that need funds. Banks expand the money supply through the credit channel and ensure that savings are converted into investments in the economy. Increasing investments in the country will contribute to production and employment. The rise in the number of goods and services produced will also lead to development in the rate of economic growth. From this point of view, this study analyzes the short and long-run effects of the aggregate domestic credit volume created by deposit banks, development and investment banks, and participation banks on economic growth in the Turkish economy by adopting the autoregressive distributed lag bounds testing (ARDL) approach for quarterly data covering 2008:01-2022:02 periods. As a result of the analysis, a cointegration relationship has been found between the aggregate domestic credit volume and economic growth. It is concluded that there is no long-term relationship between the aggregate domestic credit volume and economic growth, but they are in a relationship in the short term.

The investigation of shrinkage cracking of paste and mortar based on the eccentric ring test and multiphysics simulation

The eccentric ring test presents a novel approach to evaluating the occurrence of shrinkage cracking in cementitious materials. The eccentric ring test has been confirmed to induce cracks on the thin sides of the specimen. However, the underlying mechanism behind this cracking phenomenon remains inadequately explored. In this study, the eccentric ring test is used to examine cement paste with different water-cement (w/c) ratios and mortar with varying aggregate volume fractions. The examination focuses on the influence of surface sealing and immersion curing on shrinkage cracking. The integrated shrinkage model, which is applicable to both autogenous shrinkage and drying shrinkage, is introduced to simulate the shrinkage of cementitious materials. The shrinkage cracking of eccentric specimens is further investigated through a multiphysics coupling analysis that considers shrinkage, humidity field, and stress field. The simulation results show that the humidity decreases more rapidly on the thinner sides during the shrinkage of the eccentric ring. The circumferential stress in the specimen is much greater than the radial stress. Additionally, the tensile stress in the circumferential direction exceeds 4 MPa on the outer ring. As the drying time increases, the circumferential tensile stress on the thin sides of the eccentric ring develops more rapidly, resulting in cracking on the thin side. The eccentric ring test is practicable in ordinary concrete and high-strength concrete, and the simulation is of significance in examining the cracking risk of concrete pipes and some thin wall components since these components are sensitive to the shrinkage cracking.

Workability, Mechanical Properties, and Microstructure Analysis of Bottom Ash Mortar Reinforced with Recycled Tire Steel Fiber

Recycled tire steel fiber (RTSF) is added to mortar with pre-wetted bottom ash (BA) to enhance the mechanical properties of the mortar, in addition to providing an internal curing effect. This work investigated the mechanical properties of BA mortar, such as the compressive strength, splitting tensile strength, and flexural strength, including the heat of reactions and the total shrinkage, considering different contents of BA (i.e., 10%, 20%, and 30% replacements by volume of fine aggregate) and recycled steel fiber (RSF, i.e., 0.5% and 1.0% by volume). The results showed that BA reduced all mechanical properties; however, it increased the degree of hydration by raising the heat peak of hydration in the first 7 days, increasing the amount of calcium hydroxide at 28 days, and significantly refining the pore structure during the curing period. Regarding the effects of RTSF, the bridging effect positively affected the compressive strength, splitting tensile strength, and flexural strength of the mortar with 30% BA when 1% RTSF was added, increasing them by 25%, 46%, and 40%, respectively. Moreover, adding 1% RTSF reduced the total porosity of the mortar with 30% BA from 17.2% to 14.8%.

Study on pumping wear characteristics of concrete pipeline based on CFD-DEM coupling

Concrete pumping, integral to building construction, governs pipeline durability and overall construction efficiency. This study advances the traditional methods by employing the CFD-DEM coupling technique, a pioneering approach that integrates the irregular shape of coarse aggregates, capturing the intricacies of concrete pumping in pipelines. Beyond identifying primary wear areas and quantifying wear magnitudes, this research unveils a quadratic progression in average wear over time. The most pronounced wear appears in the pipeline’s bent sections. Notably, pumping speed, more influential than aggregate volume fraction, is pivotal to pipeline wear. Minimized speeds increase blockage risks, notably at elbows, while augmented speeds intensify wear. An optimal speed range between 2 and 3 m/s is deduced. Additionally, as the aggregate volume fraction surges, wear amplifies and blockages frequent. Hence, an aggregate volume fraction between 15 and 20% emerges as the recommendation.

Behaviour of carbon or glass FRP-confined rubberised concrete under monotonic compression

This paper presents a comparative assessment of the compressive behaviour of rubberised concrete (RuC) confined with FRP jackets. In total, three RuC mixes were investigated with rubber content of 6%, 12% and 18% of the total aggregate volume, as well as a conventional concrete mix as a reference. A total of 100 cylindrical concrete specimens (Ø100 × 200 mm) subjected to monotonic axial compression were tested. Confinement scheme comprised 1 or 2 FRP layers of either carbon or glass uniaxial fabric. The mechanical properties, stress–strain behaviour, and confinement effectiveness ratios were assessed. The discussion includes a comparative assessment of the influence of rubber content, confinement and the type of fibre of the fabrics used on the aforementioned properties. The efficiency of analytical models in predicting the experimental results was also investigated. The results revealed a significant reduction of the compressive strength when crumb rubber was used as mineral aggregate replacement in concrete. FRP confinement of RuC was able to mitigate the reduction in compressive strength. Confinement of RuC with glass or carbon FRP jackets having similar axial rigidity resulted in similar stress–strain behaviour, which was mostly affected by the rubber content. Existing analytical models were able to predict the experimental results with moderate accuracy.

Ophthalmology procedure trends in the United States during the COVID-19 pandemic.

To evaluate the relationship between the COVID-19 pandemic and ophthalmic procedural volume. A retrospective cohort study using TriNetX, a federated electronic health record's research network was done. Monthly Current Procedural Terminology-specific volumes per healthcare organization were clustered chronologically to calculate average volumes into 3-month seasons to calculate average procedural volumes. An aggregate of the total pandemic period (March 2020-August 2021) was compared to corresponding figures in pre-pandemic timeframes. Intravitreal injections were the most prevalent procedure in this time period with 320,106 occurrences. Phacoemulsification cataract surgery was the second most prevalent (N = 176,095) procedure. From March 2020 to August 2021, a mean pandemic volume of 266.7 (SD = 15) was observed, a 5% decrease (p < 0.05) in procedures compared to the pre-pandemic mean of 280.8 (SD = 26.1). Spring 2020 exhibited the sharpest seasonal decrease in procedural volume (- 88%). The largest count of statistically significant increases in procedure volume was in Spring 2021 (+ 18%). The aggregate mean volume per HCO showed significant decreases for 11 out of 17 procedures in the 12month March 2020-February 2021 timeframe and significant decreases for 10 out of 17 procedures over the 18-month March 2020-August 2021 pandemic period. This study highlights the relative inverse relationship between COVID-19 cases and ophthalmic procedure volume in America. Quantifying ophthalmic procedure trends is important in retrospectively assessing surgical disruptions and prospectively accommodating delayed surgeries. Furthermore, awareness of these trends could help ophthalmologists prepare should similar disruptions occur in the setting of future pandemics or national disasters.

Holopelagic Sargassum aggregations provide warmer microhabitats for associated fauna

Drifting aggregations of Sargassum algae provide critical habitat for endemic, endangered, and commercially important species. They may also provide favorable microclimates for associated fauna. To quantify thermal characteristics of holopelagic Sargassum aggregations, we evaluated thermal profiles of 50 aggregations in situ in the Sargasso Sea. Sea surface temperature (SST) in the center of aggregations was significantly higher than in nearby open water, and SST differential was independent of aggregation volume, area, and thickness. SST differential between aggregation edge and open water was smaller than those between aggregation center and aggregation edge and between aggregation center and open water. Water temperature was significantly higher inside and below aggregations compared to open water but did not vary inside aggregations with depth. Holopelagic Sargassum aggregations provide warmer microhabitats for associated fauna, which may benefit marine ectotherms, though temperature differentials were narrow (up to 0.7 °C) over the range of aggregation sizes we encountered (area 0.01–15 m2). We propose a hypothetical curve describing variation in SST differential with Sargassum aggregation size as a prediction for future studies to evaluate across temporal and geographic ranges. Our study provides a foundation for investigating the importance of thermal microhabitats in holopelagic Sargassum ecosystems.

Effects of the particle morphology and volume fraction of coarse aggregate on the mechanical properties of concrete

The morphology and volume fraction of coarse aggregate particles significantly influence the mechanical characteristics of concrete. This paper presents the development of a numerical model for pebble concrete by combining experiments with the discrete element method. The mesoscopic parameters between mortars and the contact surface between mortars and aggregates in the model were calibrated by comparing simulated stress–strain relationships with experimental data from pebble concrete. Subsequently, the model and mesoscopic parameters were validated by comparing them with experimental results. The obtained mesoscopic parameters were then utilized in the numerical modeling of uniaxial compression for single-shaped coarse aggregate concrete. Results showed that the peak stress of the elliptical aggregate concrete was 2.8 MPa higher than that of the oblate spherical aggregate concrete, leading to more cracks and severe damage in the former. Thus, elliptical aggregates proved more suitable as coarse aggregates for concrete than oblate spherical aggregates. Furthermore, the study investigated the influence of ellipsoidal aggregate volume fraction on concrete strength. The compressive strength reached the highest when the volume fraction of ellipsoidal aggregate was 57%. Therefore, the ideal coarse aggregate volume fraction was determined to be 57%. These results offer valuable insights into designing concrete mix proportions.

Studying the rheological features, mechanical properties and flexural toughness of the WSFRSCC by varying the coarse aggregate volume

The low tensile strength of concrete structures requires studying the effects of fibers on the performance of fresh and hardened concretes where finding the right amount of coarse aggregates is a challenge in the concrete industry. This study has addressed the effects of increasing the volumes of wavy steel fibers (0.15, 0.3 and 0.45%) and coarse aggregates (30, 40, 50 and 60%) on fresh concrete parameters and Self-Compacting Concrete (SCC) strength and fracture characteristics. Results have shown that using wavy steel fibers has negative effects on the properties of the fresh SCC because its efficiency and flowability are reduced, and increasing the coarse aggregate volume has positive effects because the rheological properties are improved. On the other hand, increasing the wavy steel fiber volume will improve the compressive strength in concretes containing 50 and 60% coarse aggregates. Only in 60% coarse-aggregate concretes, increasing the fiber volume from 0.15 to 0.45% will slightly reduce the wavy steel fiber reinforced self-compacting concrete (WSFRSCC) tensile strength. Increasing the coarse aggregate volume (30% – 60%) will improve the elasticity modulus of specimens with fixed percent fiber. Comparison of ASTM C 1609, JSCE SF-4 and JG/T 472-2015 methods revealed that the latter could well provide a thorough understanding of the variations of the flexural toughness of the WSFRSCC due to the demarcation of the pre- and post-peak load areas.

Mechanical properties and flexural behaviour of green light weight concrete beams exposure to salty soils

This paper presents an experimental investigation on the mechanical properties, durability and flexural behaviour of green concrete beam when subjected to harsh environments by using recycled building materials. Concrete resistance to external aggressive environmental condition is one of the most significant characteristics to maintain the concrete durability. The fundamental goal of this study is to understanding the performance of green lightweight concrete beam of (10×10×40 cm) under two different severe saline conditions; Ground Water Condition (GWC) and Severe Saline Clay Soil Condition (SSC) that contain chlorides and sulfates at concentrations like to those existing in groundwater and soil of the southern and middle parts of Iraq. In this research, in addition to normal concrete; three basic categories of green lightweight concrete are used: structural, non-structural and moderate strength using recycled of clay bricks and themestone blocks as coarse Light Weight Concrete (LWA) by a replacement ratio of (0, 50 and 100) % volume of natural coarse aggregate. All green Light Weight Aggregate Concrete (LWAC) beams and related specimens for mechanical properties were subjected to GWC, SSC and Laboratory Air Condition (LAC) for till (3, 6 and 9 months) after twenty-eight days of curing by tap water. Compressive strength, splitting tensile strength and density were also studied. The results obtained offered that the GWC and SSC have impacted the performance of all concrete beam types negatively with exposure age. The decadence was more for non-structural green LWAC beam. It is found that the resistance of beams contains bricks aggregate to GWC and SSC was a better than the other types of the green LWAC, the percentage decreases in failure load were 15.47% and 13.31% at 9 months of exposure to GWC and SSC measured relative to concrete beam exposed to LAC, respectively. Under the effect of aggressive conditions till 3 months, the results clarified that the improvement rate in the mechanical properties of the green LWAC were increased with age in comparison with ordinary concrete. The percentage reduction in compressive, splitting tensile strength and density at 9 months were ranged between (8.70-17.05) %, (14.71-36.50) % and (0.11-3.98) %, respectively measured relative to the same specimens in LAC.

Axial behaviour of steel tubes infilled with rubberised alkali‐activated concrete

AbstractThis study investigates the axial compressive behaviour of concrete filled steel tubes with rubberised alkali‐activated concrete as infill. A high‐strength slag‐based alkali‐activated concrete mix is chosen as a reference and rubber contents of 0, 30 and 60% replacements by volume of natural aggregates are considered. Steel tubes with circular and square cross‐sections having length‐to‐diameter/width ratios of 2 and 4 are investigated. The maximum axial capacity and the axial load‐shortening response are observed. The results show a reduction in the axial capacity and elastic stiffness of the confined specimens with higher rubber content. The circular tube sections provide greater confinement to the concrete core, evidenced from the higher ultimate stress, in comparison with the square tube sections. Circular confined specimens also exhibit a softer post‐peak axial load‐shortening response when compared to the square confined specimens. The axial capacity and overall behaviour of the confined specimens with the same cross‐section is generally similar for specimens with length‐to‐diameter/width ratios of 2 and 4, with a slight reduction in the axial stiffness for the taller specimens. Eurocode 4 axial strength design expressions for concrete filled steel tubes are shown to be applicable for the specimens tested in this study.

The Effect of the ASEAN FTA on Intra-Regional Trade in Lao PDR

Purpose - This study aims to estimate the effects of the Association of South-East Asian Nations Free Trade Area (AFTA) on international trade in Lao People’s Democratic Republic (PDR) Design/Methodology/Approach - This study empirically analyzes the effects of AFTA on Lao PDR’s intra-regional trade with ASEAN countries using a gravity model by employing panel data from ten ASEAN countries from 1990 to 2017.&#x0D; Findings - This paper finds that joining AFTA positively affects aggregate trade volume and exports of Lao PDR. However, joining AFTA does not positively impact Lao PDR’s imports.&#x0D; Research Implications - With a very limited number of studies on the effect of AFTA on Lao PDR, most previous studies examine the effect on Lao PDR using a subset of ASEAN countries. This paper contributes to the literature by being the first to empirically analyze the effect of AFTA on intra-regional trade in Lao PDR with all ten ASEAN member countries. The findings of the study suggest that further extending FTA networks with other countries will promote Lao PDR’s trade and its access to the international market.

Refined simulation of bond-slip behavior between ribbed steel and concrete: Effects of initial stress and temperature

The bond performance between steel and concrete exposed to fire is influenced by many factors, including the presence of an initial load before the temperature increase. To investigate such effect, a 3-D refined simulation model is presented accounting for the heterogeneity of concrete at the mesoscopic level and the external geometry of ribbed steel bars. The rationality and validity of the refined simulation model and of the multi-step analysis were verified by comparison with existing experimental data. Subsequently, the effects of aggregate gradation and distribution, initial loading level and temperature on the bond behavior were analyzed. The load transfer mechanism at the steel–concrete interface as a function of temperature under different loading levels is captured and discussed. It is found that the influence of aggregate grading and distribution on the bond-slip curve can be ignored under the aggregate volume fraction set in this work. Additionally, results show that the damage initially concentrates at the rib tip of the deformed steel bars, with an increase across the concrete section as the slip increases, as it could be expected. However, the bond stress and both stress and strain of steel at the same position decrease as the temperature increases. Finally and most importantly, it is found that the heating and loading sequence induce a different damage evolution inside the specimen, with a significant effect on the bond stiffness, the plateau portion of the bond stress-slip curve and the bond strength associated to a given critical temperature.

Fast and intelligent measurement of concrete aggregate volume based on monocular vision mapping

Fast and intelligent measurement of concrete aggregate volume based on monocular vision mapping

Phase segmentation in X-ray CT images of concrete with implications for mesoscale modeling

X-ray computed tomography (XRCT) is a valuable tool for characterizing the microstructure of concrete and for developing 3D mesoscale numerical models directly from experimental data. However, the results of imaging and subsequent modeling are reliable only if individual phases can be identified and segmented accurately. Siliceous aggregates and cement paste are difficult to separate in XRCT images because of their similar X-ray attenuation coefficients. This work examines the quality of aggregate phase segmentation in XRCT images using (1) a standard deviation thresholding approach and (2) a random forest classification. Both approaches were validated with ground truth data for concrete samples with different aggregate volume fractions. Our findings show that either approach may successfully be used to segment aggregate phases if appropriate post-processing is performed. However, our results emphasize the critical need to preserve both aggregate size and shape during post-processing as illustrated through mesoscale modeling.

Strains of high-performance and ordinary concretes depending on the cement paste volume and the w/c ratio

The test results of 15 high performance concretes (HPCs) and ordinary concretes allowed to explain the influence of different volumes of cement paste on shaping the deformation properties of concrete under temporary compressive load. Increasing the volume of the paste by 100 dm3/m3 and reducing the volume of coarse aggregate at the same time reduces the modulus of elasticity and significantly increases the compressive strain at the peak stress. When increasing the volume of cement paste, smaller changes in properties were observed in ordinary concretes than in HPCs, modulus of ordinary concrete elasticity decreased by 4–9%, and compressive strains at the peak stress increased by 18–23%. However, in HPCs the changes are greater. Modulus changes are 7–28% and strains at the peak stress changes are from 19% to 41% at w/c = 0.25. It was found that the compressive strength of all concretes with the smallest volume of cement paste at each w/c ratio from 0.25 to 0.60 was the highest. Increasing the volume of cement paste in concretes for each w/c ratio causes a large increase in the compressive strains at peak stress.Hence, the likely causes of changes in the examined properties are the reduced adsorption of water on the smaller surface area of the aggregate, which dries less bulk cement paste, increasing the aggregate-cement paste interfacial transition zone (ITZ) width, which is visible on the scanning electron microscopy (SEM) images taken. When the volume of the aggregate is larger and the volume of the paste is smaller, as a result of water adsorption by the larger surface area of the aggregate grains, the actual (effective) w/c ratio in bulk paste decreases, resulting in improved strength and deformation properties.

Enhancement of the three-dimensional interfacial layer of a rocky desertification soil using a red mud-based fertilizer

Red mud, a solid waste of alumina extraction from bauxite, was used as a compost carrier to prepare a geological fertilizer. It was amended at proportions of 0, 5%, 10%, 15% and 50% by weight (g/kg) to improve a rocky desertification soil (classified as lime soil) productivity. Through the simulation of different rain intensity (15, 50, and 90 mm/h) with three precipitation rates (1000, 2000, 3000 mm), soil chemical and physical properties, such as soil organic matter (SOM), total nitrogen (TN), ammonia nitrogen (AN), nitrate nitrogen (NN), total potassium (TK), available potassium (AK), total phosphorus (TP), available phosphorus (AP), bulk density and aggregates were tested and analyzed. In addition, a three-dimensional evaluation and analysis of the improvement attributed to the geological fertilizer was conducted. The results showed that the soil loss could be maintained in the range of 19%–72% under rainfall intensities. In addition, the reduction rate of soil clay content was less than 20%, and the lowest reduction rate of SOM, TN, TP and other nutrient was only 4% at the application rate of 5%–50%. The BD of the 0–20 cm top soil decreased progressively from 1.2 to 0.9 g/cm3, while the water-stable aggregate volume increased by 45%–76%. The red mud-based fertilizer enhanced the ability of the rocky desertification soil to resist rainfall erosion and infiltration in amended soil profiles. Considering the trends of nutrient losses and effects on the soil structure, the application rate of 15% by weight (g/kg) was best for improving the rocky desertification soil productivity.

Clarifying the effects of volume proportion and surface area of aggregate on chloride diffusivity of concrete through microstructural design

Increasing the aggregate proportion usually reduce the chloride diffusivity of concrete, but may also increase the chloride diffusivity as more interfacial transition zone (ITZ) is introduced with increased surface area of aggregate. Since both packing density and surface area of aggregate varied simultaneously with its particle size distribution (PSD), effects of volume proportion and surface area of aggregate on the chloride diffusivity of concrete has not been clarified separately yet. In the present study, we established a database containing over 500,000 aggregate PSDs and their corresponding packing density and specific surface area using the Compressible Packing Model (CPM) and photogrammetric 3D reconstruction. By individually controlling target volume proportion or surface area of aggregate, effects of aggregate volume proportion and surface area on the mechanical properties and chloride diffusivity of concrete were evaluated. Then an empirical equation, in consideration of aggregate size-dependent ITZ thickness the tortuosity, was proposed to describe the relationship between chloride diffusion coefficient and aggregate proportion and surface area, and a strategy for aggregate PSD optimization was provided to meet chloride diffusivity requirement, which offer an approach for enhancing the chloride resistance of concrete.

Coaxially swirled porous disks flow simultaneously induced by mixed convection with morphological effect of metallic/metallic oxide nanoparticles

This study focuses on the numerical modeling of coaxially swirling porous disk flow subject to the combined effects of mixed convection and chemical reactions. We conducted numerical investigations to analyze the morphologies of aluminum oxide (Al2O3) and copper (Cu) nanoparticles under the influence of magnetohydrodynamics. For the flow of hybrid nanofluids, we developed a model that considers the aggregate nanoparticle volume fraction based on single-phase simulation, along with the energy and mass transfer equations. The high-order, nonlinear, ordinary differential equations are obtained from the governing system of nonlinear partial differential equations via similarity transformation. The resulting system of ordinary differential equations is solved numerically by the Runge–Kutta technique and the shooting method. This is one of the most widely used numerical algorithms for solving differential equations in various fields, including physics, engineering, and computer science. This study investigated the impact of various nanoparticle shape factors (spherical, platelet and laminar) subject to relevant physical quantities and their corresponding distributions. Our findings indicate that aluminum oxide and copper (Al2O3-Cu/H2O) hybrid nanofluids exhibit significant improvements in heat transfer compared to other shape factors, particularly in laminar flow. Additionally, the injection/suction factor influences the contraction/expansion phenomenon, leading to noteworthy results concerning skin friction and the Nusselt number in the field of engineering. Moreover, the chemical reaction parameter demonstrates a remarkable influence on Sherwood’s number. The insights gained from this work hold potential benefits for the field of lubricant technology, as they contribute valuable knowledge regarding the behavior of hybrid nanofluids and their associated characteristics.