Aggregate Sources Research Articles

Optimization of fly ash and slag binder systems for pavement concrete mixtures in Indiana

This paper summarizes a research study on the optimization of concrete pavement mixtures in Indiana. The goal of this research was to select an optimum (in terms of paste content and the replacement level of pozzolanic materials) composition for two types of mixtures: portland cement mixtures containing Class C fly ash and portland cement mixtures containing ground granulated blast furnace slag (GGBFS). The variables studied included the total volume of paste in the mixture (21 – 25%) and the level of cement replacement by either fly ash (14 – 30% of total weight of cementitious materials) or GGBFS (20 – 40% of total weight of cementitious materials). The water:cementitious materials ratio was kept constant at 0.44 and the total mass of cementitious materials varied from 272 to 323 kg/m3 (458 to 545 lb/yd3) for fly ash mixtures and from 274 to 326 kg/m3 (462 to 550 lb/yd3) for GGBFS mixtures. The test matrix of concrete mixtures was statistically designed, analyzed and optimized using of Response Surface Methodology (RSM) in order to find the most desirable combinations of variables studied. A total of 20 different concretes (including two control, cement-only mixtures) were produced and tested in the laboratory. The optimal mixtures were found to contain, respectively, ~29% of fly ash and ~21% of paste, and ~36% of slag and ~21% of paste. However, in anticipation of potential problems with workability while using variable aggregate sources it is recommended that the proposed paste content be increased to 22% for fly ash and to 23% for slag mixtures.

Novel technique to produce porous thermochromic VO2 nanoparticle films using gas aggregation source

Vanadium dioxide (VO2) is a phase transition material that undergoes semiconductor-to-metal transition at the temperature of about 68 °C. This extraordinary feature triggered intensive research focused on the controlled synthesis of VO2. In this study, we introduce and investigate an original linker- and solvent-free strategy enabling the production of highly porous VO2 nanoparticle-based films. This technique combines a gas-phase synthesis of vanadium nanoparticles and their subsequent atmospheric pressure thermal oxidation. It is shown that the thermochromic behaviour of such produced nanomaterial is at the fixed oxidation temperature strongly dependent on the oxidation time. Concerning this, it was found that there exists an optimal oxidation time (60 s in our study) that assures the production of crystalline VO2 nanoparticles with the highest, reproducible and temporally stable semiconductor-to-metal transition with the resistive switching ratio close to 2 orders of magnitude and dramatic switching of optical properties in the near infra-red spectral region.

Tailored Functionalization of Plasmonic AgNPs/C:H:N:O Nanocomposite for Sensitive and Selective Detection

ABSTRACTWe report here on the development of tailored plasmonic AgNPs/C:H:N:O plasma polymer nanocomposites for the detection of the pathogenic bacterium Borrelia afzelii, with high selectivity and sensitivity. Silver (Ag) nanoparticles, generated by a gas aggregation source, are incorporated onto a C:H:N:O plasma polymer matrix, which is deposited by magnetron sputtering of a nylon 6.6. These anchored Ag nanoparticles propagate localized surface plasmon resonance (LSPR), optically responding to changes caused by immobilized pathogens near the nanoparticles. The tailored functionalization of AgNPs/C:H:N:O nanocomposite surface allows both high selectivity for the pathogen and high sensitivity with an LSPR red‐shift Δλ > (4.20 ± 0.71) nm for 50 Borrelia per area 0.785 cm2. The results confirmed the ability of LSPR modulation for the rapid and early detection of (not only) tested pathogens.

Porous metal/metal-oxide nanostructured coatings produced using gas aggregation sources of nanoparticles as recyclable SERS active platforms

Porous metal/metal-oxide nanostructured coatings produced using gas aggregation sources of nanoparticles as recyclable SERS active platforms

Chloride ingress and carbonation assessment of mortars prepared with recycled sand and calcined clay-based cement

A promising and economical route for the reduction of the environmental impact generated by Ordinary Portland Cement (OPC) and Construction and Demolition (C&D) waste could be possible using Recycled Sand (RS) with Limestone Calcined Clay Cement (LC3). This research study presents an experimental investigation based on the comparison between LC3 and CEM II binders mixed with natural sand and two types of recycled sand (substitution rate 50 vol%). Mechanical and durability properties of the different mortars were examined through compression and flexural strength tests, capillary water absorption, Mercury Intrusion Porosimetry (MIP), fog chamber salt spray exposure and immersion in chloride solution condition to evaluate water-soluble and acid-soluble chloride contents, and carbonation assessment by natural and accelerated methods. According to experimental results, LC3 containing 70 % of clinker and a calcined clay to limestone ratio of 2:1 exhibits superior compressive strength compared to CEM II for both natural and recycled sands and significantly enhances the resistance against chloride ions ingress and carbonation. These results demonstrate that LC3 binder with 70 % clinker is a promising material to produce LC3 blends with adequate durability against carbonation and chloride ions ingress, particularly when recycled sand is used as a source of fine aggregate.

Suitability of aggregate recycled from concrete pavements for layers made of unbound and cement bound mixtures

The paper presents research on the possibility of utilizing materials recycled from concrete pavements through crushing them in crushers and re-incorporating into pavement courses. From the economic and technical points of view crushed concrete waste can be an alternative source of aggregates, replacing natural aggregates. Crushed concrete was tested with regard to the current requirements which aggregates applied in layers made of unbound and cement bound mixtures must meet. Concrete rubble is shown to be suitable a material for re-incorporation into pavement road surface courses and limitations on the use of such materials are indicated.

Effect of pre-wetting treatment for waste waterglass foundry sand on the properties of alkali-activated slag

Waste waterglass foundry sand (WwFS) is a solid waste generated by the foundry industries that is commonly discarded in landfills and has urgent needs for disposal and recycling. Accordingly, this study suggests using WwFS as aggregates source for the preparation of alkali-activated slag mortars (AASM). Two different pre-wetting methods (24 h pre-wetting at 20°C and 1~6 h pre-wetting at 70°C) were used to treat WwFS and compared their performances with adding quartz sand and dried WwFS mortars. Compared to WwFS mortars without pre-wetting treatment, the compressive strengths of WwFS mortars containing WwFS pre-wetting in water at 70°C at 28d were increased by 1.3~10.0%, and the C-(A)-S-H average elastic modulus was increased by 16%. This study confirmed the feasibility of using hot water pre-wetted WwFS as the single aggregate source for AASM, which is important for the large-scale utilization of WwFS.

Multicore@shell nanoparticle synthesis from a single multicomponent target by gas aggregation source

Synthesis of multifunctional nanomaterials is known as a critical challenge in advanced nanoscience. Multicore@shell nanostructures are generated here via a gas phase synthesis approach. To achieve this objective, we used conventional DC magnetron sputtering in conjunction with a gas aggregation chamber. We employed a customized Au-Ti target to produce metal-metal oxide multicore@shell nanoparticles (NPs) with tunable properties. The deposited NPs were characterized with regard to their chemical composition, morphology, structural status, NP size distribution and optical properties. The obtained data clearly confirms that the crystalline Au cores are encapsulated in a TiOx matrix in each individual NP. Furthermore, the chemical composition and size distribution of the NPs can be affected by the operating pressure. Our approach provides a versatile route with many different possibilities to synthesize multicore@shell NPs from a variety of composite targets for well-desired applications including environmental, optical/plasmonic, and energy.

Evaluation of Physical Properties of Aggregates: A Case Study on Aggregate Sources around Kathmandu Valley

Aggregates play a crucial role in construction works, and this research aims to characterize aggregates from different sources in the Kathmandu Valley, considering factors such as particle size, shape, water absorption, and toughness, resistance to abrasion, crushing value, and impact value. The study investigated identifying and testing aggregates from the sources around and within Kathmandu Valley. A preliminary survey identified nine quarries around Kathmandu Valley based on accessibility to the valley and the highest producers (regarding materials volume). Coarse aggregate samples were collected from Dukuchap (Lalitpur), kaldhunga (Kavre), Bogati Panauti (Kavre), Aagra Khola (Makwanpur) and Melamchi (Sindhupal Chowk. Fine aggregates were collected from Melamchi (Sindhupal Chowk), Belkhu (Dhading), and Sankhu (Kathmandu). Evaluation of physical properties of aggregates included fineness modulus test, water absorption test, crushing value test, Impact value test, silt content test, Flakiness and Elongation test, and abrasion resistance test. Upon meticulous evaluation of the collected samples, it was observed that Fineness Modulus, specific gravity, water absorption, materials finer than 75μm and silt content of the sources were found in between the respective range of (1.97 to3.49), (2.53 to2.62), (1.05 to1.96) % and (1.74 to 5)% and (1.21 to 11.04) respectively. Similarly, specific gravity, water absorption, flakiness index, abrasion value, impact value, and crushing value of coarse aggregates were found in the range of (2.65-2.72), (0.36-1.07)%,(15.03-18.41)%,(15.94-41.52)%,(15.23-34.31)% and(13.55-28.68)% respectively.

A systematic review of the extant literature on the Tanzanian e-government services for economic development

This paper investigates the existing Tanzanian e-government services for economic development through a systematic review of the literature. The main objective is to examine researchers’ articles on e-government services towards achieving the Tanzanian economic growth as well as the current issues and trends on e-government globally. Specifically, this study aims to answer three research questions on: what are the functional e-government services in Tanzania? What is the level of Tanzanian e-government service performance? And what are the factors influencing Tanzanian e-government service performance for economic development? A systematic literature search was conducted on four aggregate data sources, which included Google Scholar, ResearchGate, CORE, and Refseek. A combination of search key terms was employed to obtain the data sources from 2015 to 2022. One hundred and five articles were found by the combined search and screened, resulting to eighteen articles that were recommended for the study. Content and Microsoft Excel computer application were used to analyse the screened data sources. The findings reveal that, a number of functional services is offered and considered potential for revenue collection and contribute to the nation's economic development. Nevertheless, Tanzania has improved and dynamically advanced to the transaction level of e-government implementation where the majority of the citizens interact for services and information. However, factors related to the activeness of the platforms, accessibility, usability, infrastructure, security issues, privacy, and technical support services among others, were identified to influence the performance of Tanzanian e-government services and thus call attention to the government in addressing these issues.

Unsupervised multi-source domain adaptation via contrastive learning for EEG classification

Individual differences in electroencephalography (EEG) present significant challenges for subject-independent EEG classification in brain–computer interfaces (BCIs). Existing domain adaptation methods often address individual differences by merging all source domains indistinguishably into a single source and aligning features between this aggregate source and the target domain. Neglecting the relationships between different source domains would hinder the model’s adaptability and generalization. Therefore, we propose a method called Contrastive Learning-based Unsupervised multi-source Domain Adaptation (CLUDA) for learning subject-independent representations in motor imagery. Our method not only aligns the conditional distributions of each source domain with the target domain but also reduces discrepancies among the source domains using contrastive learning, thus learning more generalized domain-invariant representations. Specifically, CLUDA effectively eliminates semantic variances by maximizing the similarity between positive pairs (same class) and minimizing the similarity between negative pairs (different classes) across subjects. Finally, we validated CLUDA on four motor imagery datasets and consistently achieved state-of-the-art performance.

Laser Metal Printing from Nanoparticles Prepared by a Gas Aggregation Source.

This study demonstrates the use of nanoparticles prepared by a gas aggregation source for fabricating structures by combining laser sintering and ablation. At first, the morphology and optical properties of prepared nanoparticle coatings were characterized. Then, the response of coatings to laser irradiation at different powers or exposure times was studied by in situ time-of-flight mass spectrometry, followed by scanning electron microscopy measurements of the resulting structures. By comparing the numbers of detected Ag ions, that were ablated and desorbed, with changes in morphology after irradiation, the optimum conditions for laser sintering and ablation of Ag nanoparticle coatings were found. As a proof of concept we fabricated micromirrors from sintered metal, microwires from both sintered metal and interconnected nanoparticles, and arbitrary metallic bulky or nanoparticle patterns. Vacuum compatibility and the possibility of fabrication of both metallic and nanoparticle structures in one step predetermines applications of developed method in electronics or sensing.

Assessing cracking resistance and threshold limits of bituminous mixtures with IDEAL-CT and predictive modeling techniques

This paper presents a comprehensive study to establish the threshold limit of CTIndex for the Marshall mixes. The study also aims to assess the impact of different design factors on the cracking resistance of bituminous mixtures using the Indirect Tensile Asphalt Cracking Test (IDEAL-CT) test. This study considers 2 different aggregate sources, 2 different gradations, 5 different types of Design Aggregate Gradation (DAG), 3 binder types, and 5 levels of compactive effort. The test results show that higher cracking resistance can be achieved using a smaller nominal maximum size of the aggregate (NMAS), finer gradation, modified binder, and decreased compactive effort with aggregates having low abrasion and absorptive characteristics. This study also comprehends the influence of volumetric parameters of the bituminous mixes on fracture resistance. It was found that at a particular Optimum Binder Content (OBC), higher bulk specific gravity of the compacted specimen (Gmb) and voids filled with asphalt (VFA) result in reduced CTIndex, specifying poor cracking performance. While higher air voids (AV) and voids in mineral aggregate (VMA) lead to increased CTIndex, indicating better-cracking resistance. Statistical analysis tools were used to evaluate the significance of the influential factors that are affecting the cracking potential of the mix. Different Machine learning models were also developed to predict CTIndex based on the design factors considered in the study. The random forest (RFR) model showed strong accuracy, reflected by low Mean Absolute Error (MAE=3.16), Mean Absolute Percentage Error (MAPE=9.57), Root Mean Square Error (RMSE=4.23), and a high coefficient of determination (R²=0.95) value, notifying a precise fit and reliable predictions. Additionally, a GUI has been also developed to enhance the practical usability of the model for wider usage. Further, the present study proposes the threshold value of CTIndex for the selection of crack-resistant bituminous mixtures. Moreover, the study investigated the correlation between laboratory and field compaction methods and validated the initial threshold specification of CTIndex for the Marshall mixes. Despite of the variations in different compaction methodologies and specimen thickness, a strong positive correlation (R² > 0.76) between laboratory and field cores of BC-1 and DBM-2 indicates that the performance criteria are adequate and justified.

Investigation of Performance of Copper Slag and Ore Tailings Novel Trial Self-compacting Concrete Mixtures

A non-conventional concrete with the properties of flow-ability, filling-ability, and passing-ability without any need for mechanical compaction but flow under self-weight is known as self-compacting concrete. This study developed trial mixtures for self-compacting concrete (SCC) using locally available waste products. The copper slag and ore tailings from Bamangwato Concessions Limited Mine in Selebi-Phikwe, Botswana were used as source of fine aggregate, and fines substitute. Eight mix proportions were developed with the quantities of cement, granite, copper slag, ore tailings and water-cement ratio as variables. The mix proportions were developed in accordance with recommendations from American Concrete Institute (ACI 237R-07) and fresh SCC properties (flow ability, passing ability, filling-ability, and segregation) were performed to assess the performance of the mixes. It was observed that the range of slump flow values were between (500 – 750 mm), V-funnel values (1.46 – 7.46 s), passing-ability of (0.76 – 1.0). The hardened properties of SCC (strength and density) were between 8.1 and 33.3 MPa, and 2093 to 2406 kg/m3) respectively. It could be concluded that SCC produced from mine wastes (copper slag and ore tailings) is found suitable for the use in unreinforced and normal concrete applications.

To Analysis the Feasibility of Utilization of Modified Recycled Aggregate for Recycled Cement Bound Mixtures (A Review)

Construction and Demolition (C&D) wastes are generated through the demolition of concrete structures, and they are often discarded into the open area causing environmental problems. Various components such as bricks, concrete, steel, wood, etc., are generated through the demolition of structures. Perhaps the necessity of construction materials, especially aggregates, increases rapidly due to urbanization and industrialization. Construction activities mainly depend on natural resources as a source of raw materials, leading to ecological imbalance. So, the construction industries tend to depend on alternative materials as the source of aggregates in concrete production. Recycling C&D wastes and using them as aggregates will be a viable option to counteract the problems mentioned above. The recycled aggregates are broken fractions of C&D wastes with smeared cement particles adhered to on the surface of natural aggregates. In this study, recycled aggregates were collected from a 20-year- old demolished building at the university and recycled into fractions of 1.18 mm~2.36 mm and 10 mm~20 mm and replaced for both fine aggregates and coarse aggregates. However, the poor quality of recycled aggregates resulting from the presence of adhered mortar affects the properties of the concrete. Thus, this paper aims to improve the property of recycled aggregates through surface treatments. Though various treatments were developed either to remove or coat the adhered mortar surface on the recycled aggregates, this study uses microbes in conjunction with advanced mixing approach techniques to improve the quality of recycled aggregates and properties of the recycled aggregate concrete (RAC). This paper finds Feasibility of Utilization of Modified Recycled Aggregate in various construction work by study the different Literature review and articles

Marginal Aggregates: The Role of Clays.

Clays are components in the fine portion of aggregates, less than 75 microns in size (micro-fines), which are usually washed away when producing coarse or fine (manufactured sand) aggregates in quarries. When marginal sources of aggregates are being used, the content of this washed portion can be quite high, and there is an incentive to keep as much of it in the aggregate, including the clays. The present paper presents a comprehensive treatment of the role of clays in terms of the characterization of their composition and quantification of their effects on the rheological and mechanical properties of cementitious systems, as well as the means to mitigate deleterious influences. It is shown that the strategy for neutralizing the effect of micro-fines containing clays on increased water demand in concrete can be quantified in terms of the combination of their content in concrete and their nature as characterized by the methylene blue value (MBV); this is a more rational approach to considering their influence than their content in specific aggregates as specified in standards. The effect of low and medium MBV aggregates on the water requirement can be neutralized by lignosulfonates when their content in the concrete is below a threshold value of about 150 kg/m3; polycarboxylates (PC) are required at higher contents; for high MBV aggregates, a combination of PC and clay mitigating admixture (CMA) is required. It is also demonstrated that with proper treatment, such micro-fines can be turned into useful fillers, enhancing the strength of concrete and thus also serving as a means for reducing cement content.

Catalytic Heaters at Oil and Gas Sites May be a Significant yet Overlooked Seasonal Source of Methane Emissions.

Successful reduction of oil and gas sector methane emissions to meet near-zero intensity targets requires the identification and mitigation of all possible sources. One potentially important source is catalytic heaters, which have largely escaped attention in regulatory and mitigation efforts despite being ubiquitous at upstream production sites in cold climate regions. This study reports direct in situ measurements of the exhaust streams of 38 natural gas-fired catalytic heaters at upstream production sites in British Columbia, Canada. All heaters in the sample showed consistently poor methane conversion with mean destruction efficiencies of 61 ± 5% while releasing 235 [+31/-28] g of methane per cubic meter of fuel. Although individual units are generally small methane sources (mean of 0.28 ± 0.04 kg/h), their prevalence means they could represent 6% of the total provincial upstream methane inventory and as an aggregate methane source could be 5× more significant than abandoned wells. Notably, these heaters are seasonal sources whose emissions would be missed in measurement campaigns occurring solely in summer months. However, additional measurements from a small number of heat medium burners demonstrate that, where feasible, methane emissions can be reduced by approximately 425× by replacing catalytic heaters with centralized heat systems.

Overexpression of long noncoding RNA DUXAP8 inhibits ER-phagy through activating AKT/mTOR signaling and contributes to preeclampsia

Preeclampsia (PE) is a life-threatening pregnancy-specific complication with controversial mechanisms and no effective treatment except delivery is available. Currently, increasing researchers suggested that PE shares pathophysiologic features with protein misfolding/aggregation disorders, such as Alzheimer disease (AD). Evidences have proposed defective autophagy as a potential source of protein aggregation in PE. Endoplasmic reticulum-selective autophagy (ER-phagy) plays a critical role in clearing misfolded proteins and maintaining ER homeostasis. However, its roles in the molecular pathology of PE remain unclear. We found that lncRNA DUXAP8 was upregulated in preeclamptic placentae and significantly correlated with clinical indicators. DUXAP8 specifically binds to PCBP2 and inhibits its ubiquitination-mediated degradation, and decreased levels of PCBP2 reversed the activation effect of DUXAP8 overexpression on AKT/mTOR signaling pathway. Function experiments showed that DUXAP8 overexpression inhibited trophoblastic proliferation, migration, and invasion of HTR-8/SVneo and JAR cells. Moreover, pathological accumulation of swollen and lytic ER (endoplasmic reticulum) was observed in DUXAP8-overexpressed HTR8/SVneo cells and PE placental villus trophoblast cells, which suggesting that ER clearance ability is impaired. Further studies found that DUXAP8 overexpression impaired ER-phagy and caused protein aggregation medicated by reduced FAM134B and LC3II expression (key proteins involved in ER-phagy) via activating AKT/mTOR signaling pathway. The increased level of FAM134B significantly reversed the inhibitory effect of DUXAP8 overexpression on the proliferation, migration, and invasion of trophoblasts. In vivo, DUXAP8 overexpression through tail vein injection of adenovirus induced PE-like phenotypes in pregnant rats accompanied with activated AKT/mTOR signaling, decreased expression of FAM134B and LC3-II proteins and increased protein aggregation in placental tissues. Our study reveals the important role of lncRNA DUXAP8 in regulating trophoblast biological behaviors through FAM134B-mediated ER-phagy, providing a new theoretical basis for understanding the pathogenesis of PE.

N-Alkanes formed by methyl-methylene addition as a source of meteoritic aliphatics

Aliphatics prevail in asteroids, comets, meteorites and other bodies in our solar system. They are also found in the interstellar and circumstellar media both in gas-phase and in dust grains. Among aliphatics, linear alkanes (n-CnH2n+2) are known to survive in carbonaceous chondrites in hundreds to thousands of parts per billion, encompassing sequences from CH4 to n-C31H64. Despite being systematically detected, the mechanism responsible for their formation in meteorites has yet to be identified. Based on advanced laboratory astrochemistry simulations, we propose a gas-phase synthesis mechanism for n-alkanes starting from carbon and hydrogen under conditions of temperature and pressure that mimic those found in carbon-rich circumstellar envelopes. We characterize the analogs generated in a customized sputter gas aggregation source using a combination of atomically precise scanning tunneling microscopy, non-contact atomic force microscopy and ex-situ gas chromatography-mass spectrometry. Within the formed carbon nanostructures, we identify the presence of n-alkanes with sizes ranging from n-C8H18 to n-C32H66. Ab-initio calculations of formation free energies, kinetic barriers, and kinetic chemical network modelling lead us to propose a gas-phase growth mechanism for the formation of large n-alkanes based on methyl-methylene addition (MMA). In this process, methylene serves as both a reagent and a catalyst for carbon chain growth. Our study provides evidence of an aliphatic gas-phase synthesis mechanism around evolved stars and provides a potential explanation for its presence in interstellar dust and meteorites.

Tracing the vertical migration of exogenous cadmium in soil by seasonal freeze-thaw event using rare earth elements

Environmental behaviors of heavy metal in soil are strongly influenced by seasonal freeze-thaw events at the mid-high altitudes. However, the potential impact mechanisms of freeze-thaw cycles on the vertical migration of heavy metal are still poor understood. This study aimed to explore how exogenous cadmium (Cd) migrated and remained in soil during the in-situ seasonal freeze-thaw action using rare earth elements (REEs) as tracers. As a comparison, soil which was incubated in the controlled laboratory (25 °C) was employed. Although there was no statistically significant difference in the Cd levels of different soil depths under different treatments, the original aggregate sources of Cd in the 5–10 cm and 10–15 cm soil layers differed. From the distributions of REEs in soil profile, it can be known that Cd in the subsurface of field incubated soil was mainly from the breakdown of >0.50 mm aggregates, while it was mainly from the <0.106 mm aggregates for the laboratory incubated soil. Furthermore, the dissolved and colloidal Cd concentrations were 0.47 μg L−1 and 0.62 μg L−1 in the leachates from field incubated soil than those from control soil (0.21 μg L−1 and 0.43 μg L−1). Additionally, the colloid-associated Cd in the leachate under field condition was mainly from the breakdown of >0.25 mm aggregates and the direct migration of <0.106 mm aggregates, while it was the breakdown of >0.50 mm and the direct migration of <0.106 mm aggregates for the soil under laboratory condition. Our results for the first time provided insights into the fate of exogenous contaminants in seasonal frozen regions using the rare earth element tracing method.