Maximum Particle Size Research Articles

TriPoD: Tri-Population size distributions for Dust evolution

Context. Dust coagulation and fragmentation impact the structure and evolution of protoplanetary disks and set the initial conditions for planet formation. Dust grains dominate the opacities, they determine the cooling times of the gas via thermal accommodation in collisions, they influence the ionization state of the gas, and the available grain surface area is an important parameter for the chemistry in protoplanetary disks. Therefore, dust evolution is an effect that should not be ignored in numerical studies of protoplanetary disks. Available dust coagulation models are, however, too computationally expensive to be implemented in large-scale hydrodynamic simulations. This limits detailed numerical studies of protoplanetary disks, including these effects, mostly to one-dimensional models. Aims. We aim to develop a simple – yet accurate – dust coagulation model that can be easily implemented in hydrodynamic simulations of protoplanetary disks. Our model shall not significantly increase the computational cost of simulations and provide information about the local grain size distribution. Methods. The local dust size distributions are assumed to be truncated power laws. Such distributions can be fully characterized by only two dust fluids (large and small grains) and a maximum particle size, truncating the power law. We compare our model to state- of-the-art dust coagulation simulations and calibrate it to achieve a good fit with these sophisticated numerical methods. Results. Running various parameter studies, we achieved a good fit between our simplified three-parameter model and DustPy, a state-of-the-art dust coagulation software. Conclusions. We present TriPoD, a sub-grid dust coagulation model for the PLUTO code. With TriPoD, we can perform twodimensional, vertically integrated dust coagulation simulations on top of a hydrodynamic simulation. Studying the dust distributions in two-dimensional vortices and planet-disk systems is thus made possible.

Low-dose cement stabilized large particle size graded crushed stone: Laboratory and field investigations

Compared with traditional graded crushed stone (GCS), the maximum aggregate size of large particle size GCS (LPS-GCS) is larger and the content of large-size aggregates is more, which can form an interlocking skeletal structure with a stronger bearing capacity. Nevertheless, LPS-GCS occasionally exhibits unstable performance, and one effective way to enhance LPS-GCS's mechanical and physical properties is to stabilize it with low-dose cement. In this study, four cement contents (1.5 %, 2.0 %, 2.5 %, and 3.0 %, by mass) were selected to form low-dose cement stabilized LPS-GCS (LCS-LPS-GCS) mixtures with a maximum aggregate particle size of 53 mm. Unconfined compressive strength (UCS) and compressive resilient modulus (CRM) tests were performed on LCS-LPS-GCS samples for different cement contents and curing times. Moreover, prediction models and correlations for the UCS and CRM at different curing times were established. Furthermore, a test road was used to evaluate the LCS-LPS-GCS's field compaction level and deflection. Laboratory test results indicated that while the California bearing ratio was significantly higher than that of conventional GCS, the maximum dry density of LPS-GCS designed in this study was close to that of conventional GCS. With the same cement content, LCS-LPS-GCS outperformed conventional GCS in terms of UCS and CRM. Based on the variation law of the mechanical properties, the ideal cement content should be around 2.5 %. There was a strong positive correlation between UCS and CRM scores from LCS-LPS-GCS. The UCS and CRM were appropriate to be predicted by exponential and growth functions models, respectively. The field investigations indicated that asphalt pavements reconstructed with LCS-LPS-GCS had high compaction and low deflection, resulting in better bearing capacity and durability. The results of this investigation can serve as a reference for the design and application of LCS-LPS-GCS base for long-lasting and resilient pavements.

Study on the Influence of Walnut Shell Coarse Particles on the Slurry Permeation and the Air Tightness of Filter Cake

Slurry shields rely on the formation of a compact filter cake to maintain excavation face stability and ensure construction safety. In strata with high permeability, significant slurry loss occurs, making filter cake formation and air tightness maintenance challenging. In this study, light organic walnut shell was selected as an additive coarse particle material for slurry. Slurries incorporating two types of coarse particles, sand and walnut shell, were prepared, and tests on slurry permeation and air tightness of the filter cake were conducted in three different strata. The results indicate that the addition of coarse particles effectively improves filter cake formation and air tightness in high-permeability strata. It is essential to use graded particles in highly permeable strata, with controlled maximum and minimum particle sizes. As the content of coarse particles increases, the air tightness of the filter cake initially increases and then decreases. Notably, the air tightness of filter cakes containing walnut shell is superior to those containing sand. Replacing sand with walnut shell as a slurry plugging material enhances filter cake quality in high-permeability strata. For highly permeable strata with a permeability coefficient greater than 1.0 × 10−3 m/s, an addition of 30 g/L to 40 g/L is recommended.

Numerical analysis on the performance of sodium chloride solution evaporative crystallization system driven by high-temperature heat pump

In the context of sustainable development, heat pump technology is increasingly recognized as a key method for enhancing the efficiency of evaporative crystallization processes. In this study, we propose a high-temperature heat pump evaporative crystallization system to facilitate the recycling of waste heat from secondary steam in low-vacuum and low-temperature evaporative crystallization, thereby achieving the cyclic utilization of condensation heat from secondary steam. The primary objective of this research is to develop a comprehensive mathematical model for the HPC system that investigate its operating performance under varying conditions, with the aim of promoting its practical application. The results demonstrate that by adjusting operating pressures, the temperature of the secondary steam can be controlled, allowing for regulation of the main particle size of the product. Specially, when maintaining the flow rate of the raw material liquid at 90 % of design condition, it is possible to achieve a maximum main particle size of 2.8 mm. Additionally, fluctuations in the flow rate of the raw material liquid significantly impact the cycle rate, with the optimum operating flow rate range identified as 75 % to 110 % of the rated value. The coefficient of performance of the system can achieve 5.85 under design conditions with a concentration of 4 % and flow rate of 310 kg/h. This research provides a theoretical foundation for the practical operation and commissioning of the HPC units.

Investigation on compressive strength and splitting tensile strength of manufactured sand concrete: Machine learning prediction and experimental verification

Due to experimental constraints, traditional strength prediction models for manufactured sand concrete (MSC) exhibit significant limitations and have a narrow range of applicability. To overcome these limitations and enhance prediction accuracy, this paper, based on the widespread application of machine learning in concrete performance research, employed four algorithms: Support Vector Regression (SVR), Random Forest Regression (RFR), Gradient Boosting (GB), and Extreme Gradient Boosting (XGB) to develop highly accurate and strongly generalizable models for predicting the compressive strength (CS) and splitting tensile strength (STS) ofMSC. The predictive performance of each model was evaluated, the influence laws of various factors were analyzed, and finally, macroscopic experiments were conducted to validate the models' prediction accuracy and generalization ability. The development of these models and the analysis of the influence laws of various factors on the strength of MSC provide a valuable reference for the mix design. The conclusions are as follows: (1) The XGB model demonstrates the highest prediction accuracy and strongest generalization ability for both the CS and STS of MSC, achieving R2 values of 0.98 and 0.94 on the testing set, respectively. (2) The CS and STS of MSC are primarily influenced by four factors: water-binder ratio (W/B), curing age (AGE), cement (C), and coarse aggregate (RI≥0.08869, RI: relative importance), showing a positive correlation with AGE and C, and a negative correlation with W/B. As the fly ash content, stone powder content, maximum particle size of coarse aggregate, and sand ratio increase, the CS and STS initially increase and then decrease. Appropriately increasing the fineness modulus of manufactured sand is beneficial to both CS and STS, while the addition of slag is beneficial to CS and harmful to STS. (3) The prediction accuracy and generalization ability of the XGB model are verified through three sets of macroscopic experiments: C30, C35, and C40. The relative errors of each set's predictions are less than 8 %. (4) A graphical user interface is constructed based on the XGB model, enhancing its practicality.

Grading scalping and sample size effects on critical shear strength of mine waste rock through laboratory and in-situ testing

Geotechnical stability analyses of mine waste rock (WR) piles require the critical friction angle (ϕcr) of the coarse blasted rock. However, due to the presence of oversized rock clasts, shear strength can only be characterized on small samples prepared using grading scaling techniques, such as scalping. Thus, considering a testing device able to handle samples of characteristic size D, the material should be scaled down to a maximum particle size dmax given by the minimum sample aspect ratio α = D/dmax. However, a practical concern about how far the size scale can be reduced while keeping representative results remains a matter of debate in the geotechnical community. International standards do not agree on the minimum recommended α, and its effects on the mechanical behavior remain poorly understood. This paper aims to investigate the grading effects and sample size effects on ϕcr of WR materials using the scalping technique, to provide insights on the minimum recommended α. Triaxial tests were conducted on loose and dense samples of diameters D = 150 and 300 mm. Samples were scalped from field material having dmax = 75 mm, to allow a range of α from 4 to 30. Additionally, one of the world largest in-situ direct shear boxes (120 × 120 × 38 cm3) was developed to test the same WR material. The results show that scalping is an appropriate technique to assess the critical shear strength of WR. The minimum α for ϕcr assessment in triaxial testing is not sensitive to grading nor sample size, but it is affected by sample density. The aspect ratio was found to be α ≥ 12 and α ≥ 16 for loose and dense samples, respectively. This finding advocates that α values recommended by worldwide standards, such as ASTM D7181-20, might be too low and should be revisited after comprehensive testing.

Experimental and molecular dynamics simulation of the synergistic mechanism of short-chain fluorocarbon surfactant and electrolyte on inhibiting coal dust pollution

This paper investigated the synergistic mechanism of short-chain fluorocarbon surfactant and electrolyte on inhibiting coal dust pollution via the experimental and molecular dynamics simulations Findings illustrated that the synergistic application of short-chain fluorocarbon and electrolyte achieves better dust suppression performance when compares with the individual application of FS-50 and FS-3100, the maximum suppression rates for FS-50 and FS-3100 after the addition of electrolytes are 94.48 % and 93.94 %, respectively. The addition of electrolyte reduces the diffusion coefficient of suppressants, and its effect on FS-3100 is much higher than on FS-50. The maximum particle size achieved by FS-50 reaches 304–344 μm, while only 238–269 μm and 269–306 μm are acquired by FS-3100. The smaller negative potential and the larger difference in EPE indicate that the addition of NaCl promotes the adsorption of H2O molecules by surfactants. Compared to FS-3100, FS-50 has a lower negative potential and a larger EPE difference, suggesting that FS-50 exhibits stronger reactivity and better ability of absorb ion hydrates and H2O molecules, and hence has superior agglomeration effect. The addition of NaCl also promotes the generation of more sodium hydrate ions and hydrated chloride ions, which enhances the ability of FS-3100 to absorb H2O. Compares with FS-50, due to special curved spatial configuration and the synergistic effect with electrolytes, FS-3100 could restrict the desorption of large numbers of H2O molecules more effectively, and therefore exhibiting better wettability.

Prediction of Ultra-High-Performance Concrete (UHPC) Properties Using Gene Expression Programming (GEP)

In today’s digital age, innovative artificial intelligence (AI) methodologies, notably machine learning (ML) approaches, are increasingly favored for their superior accuracy in anticipating the characteristics of cementitious composites compared to typical regression models. The main focus of current research work is to improve knowledge regarding application of one of the new ML techniques, i.e., gene expression programming (GEP), to anticipate the ultra-high-performance concrete (UHPC) properties, such as flowability, flexural strength (FS), compressive strength (CS), and porosity. In addition, the process of training a model that predicts the intended outcome values when the associated inputs are provided generates the graphical user interface (GUI). Moreover, the reported ML models that have been created for the aforementioned UHPC characteristics are simple and have limited input parameters. Therefore, the purpose of this study is to predict the UHPC characteristics while taking into account a wide range of input factors (i.e., 21) and use a GUI to assess how these parameters affect the UHPC properties. This input parameters includes the diameter of steel and polystyrene fibers (µm and mm), the length of the fibers (mm), the maximum size of the aggregate particles (mm), the type of cement, its strength class, and its compressive strength (MPa) type, the contents of steel and polystyrene fibers (%), and the amount of water (kg/m3). In addition, it includes fly ash, silica fume, slag, nano-silica, quartz powder, limestone powder, sand, coarse aggregates, and super-plasticizers, with all measurements in kg/m3. The outcomes of the current research reveal that the GEP technique is successful in accurately predicting UHPC characteristics. The obtained R2, i.e., determination coefficients, from the GEP model are 0.94, 0.95, 0.93, and 0.94 for UHPC flowability, CS, FS, and porosity, respectively. Thus, this research utilizes GEP and GUI to accurately forecast the characteristics of UHPC and to comprehend the influence of its input factors, simplifying the procedure and offering valuable instruments for the practical application of the model’s capabilities within the domain of civil engineering.

Crucial role of extracellular polymeric substances from anammox sludge in wastewater phosphorus recovery via magnesium phosphate crystallization

The magnesium phosphate (Mg-P) crystallization based on anaerobic ammonia oxidation is of interest for simultaneous nitrogen and phosphorus removal in wastewater treatment due to cost-effectiveness. Understanding the role of extracellular polymeric substances (EPS) in crystal growth is pivotal for bio-induced Mg-P crystallization. In this work, the effects of EPS in Mg-P crystallization were thoroughly investigated. Results indicated that EPS decreased the initial crystallization rate but slightly improved the final crystallization yield. The maximum removal efficiencies of Mg and P ions increased by 2.8 % and 3.1 %, respectively, when EPS concentration was 80 mg/L. Additionally, the presence of EPS enhanced Mg3(PO4)2·10 H2O production and facilitated the formation of larger rhombic plate-like structures crystals (maximum particle size increased by 215 %). Analysis of EPS composition changes during the crystallization process and characterization of the final crystals suggested that tryptophan-like proteins preferentially involved in the Mg-P crystallization process, while β-sheet proteins potentially influencing crystal morphology. Furthermore, the formation of phosphate ester groups, hydrogen bonding, and COOH-Mg2+ complexes were considered triggering factors for the interaction between EPS and Mg-P crystals. This study elucidated the underlying mechanism of EPS on Mg-P crystallization, further enhancing the understanding of the interaction between inorganic mineralization processes and microorganisms.

Macro–micro correlation analysis on the loess from Ili River Valley subjected to freeze–thaw cycles

The Ili River Valley in Xinjiang, China, is a typical seasonal frozen area where loess landslide disasters have become increasingly common during the freeze–thaw periods in recent years. This study analyzed the macroscopic mechanical strength and microstructure changes of the Ili loess under different freeze–thaw cycles (FTCs) through the post-freeze–thaw triaxial compression test on the unsaturated soil in laboratory. Apart from the scanning electron microscopy (SEM), and the nuclear magnetic resonance (NMR), the macro–micro correlation analysis and the cluster-principal component analysis were applied for the theoretical discussion. The results indicated that the cohesive force of the loess exhibits an initial decreases, followed by the increases, and eventually keep stable after various FTCs, while the internal friction angle showed the opposite developing trend before the final constant. Similar to the strong correlation between the cohesive force and the particle abundance, the internal friction angle is also closely related to the abundance and orientation fractal dimension of the loess particles. However, the principal component analysis results showed that cohesive force strongly correlates with the average maximum pore size and the pore size fractal dimension, for which the internal friction angle most strongly affected by the average maximum particle size. The possible reason is that the extracted principal components represent a class of microscopic parameters with the same or similar change trend, although there may be a certain offset between them. The mechanical deterioration of loess is attributed to the repeated frost heaving force and the migration potential caused by FTCs. The alterations of the microstructure accelerated the deterioration of the macroscopic mechanical properties of the loess, which further widens the understanding of the mechanism behind the deterioration of loess mechanical strength in the Ili River Valley under FTCs, and contributes to the prevention and management of the local landslide disasters.

Numerical simulation of sulfur particle agglomeration at bends of high sulfur natural gas gathering pipelines based on Euler–PBM coupling

Sulfur deposition can result in an increase in the wall thickness of high-sulfur natural gas gathering pipelines, leading to issues like unstable pipeline flow. It is crucial to reveal the aggregation of sulfur particles at key locations of high-sulfur natural gas gathering pipelines to predict the location and amount of sulfur deposition in the pipelines. In this paper, the Euler–PBM (Population balance model) coupling is used to establish a numerical simulation model of gas–solid two-phase pipe flow accompanied by sulfur particle agglomeration in the pipe bends, focusing on the influence of sulfur particle volume fraction, pipe inclination angle and inlet flow velocity on sulfur particles agglomeration behavior. The results show that the sulfur particles have a significant agglomeration effect at the bend of the collecting pipeline, and the agglomeration growth occurs to different degrees throughout the bend, and the main area of sulfur particles agglomeration is near the top wall of the pipeline, followed by other areas near the wall of the pipeline. When the inlet volume fraction of sulfur particles was increased from 0.05 to 0.25%, and the inclination angle of the pipe was increased from 30° to 90°, the distribution range of sulfur particle size after agglomeration became wider, and the maximum size of sulfur particles was 187.56 μm, and the effect of sulfur particle agglomeration was enhanced; the inlet flow rate was increased from 3.0 to 9.0 m/s, and the reduction range of sulfur particle size after agglomeration was 5.68–9.87 μm. The maximum particle size of sulfur particles also decreased, and the effect of sulfur particle agglomeration was weakened.

Enhanced aerobic granular sludge by thermally-treated dredged sediment in wastewater treatment under low superficial gas velocity

The positive contributions of carriers to aerobic granulation have been wildly appreciated. In this study, as a way resource utilization, the dredged sediment was thermally-treated to prepared as carriers to promote aerobic granular sludge (AGS) formation and stability. The system was started under low superficial gas velocity (SGV, 0.6 cm/s)for a lower energy consumption. Two sequencing batch reactors (SBR) labeled R1 (no added carriers) and R2 (carriers added), were used in the experiment. R2 had excellent performance of granulation time (shortened nearly 43%). The maximum mean particle size at the maturity stage of AGS in R2 (0.545 mm) was larger compared to R1 (0.296 mm). The sludge settling performance in R2 was better. The reactors exhibited high chemical oxygen demand (COD) and ammonia nitrogen (NH3-N) removal rates. The total phosphorus (TP) removal rate in R2 was higher than R1 (almost 15% higher) on stage II (93-175d). R2 had a higher microbial abundance and dominant bacteria content. The relative abundance of dominant species was mainly affected by the carrier. However, the enrichment of dominant microorganisms and the evolution of subdominant species were more influenced by the increase of SGV. The results indicated that the addition of carriers induced the secretion of extracellular polymeric substances (EPS) by microorganisms and accelerated the rapid formation of initial microbial aggregates. This work provided a low-cost method and condition to enhance aerobic granulation, which may be helpful in optimizing wastewater treatment processes.

Enhancement of terephthalic acid recovered from PET waste using a combination of citric acid and dimethyl sulfoxide extraction

This study aimed to develop an eco-friendly, cost-efficient, and practically viable method for extracting terephthalic acid (H2BDC) from polyethylene terephthalic (PET) waste. Dimethyl sulfoxide (DMSO) was combined with either citric acid (C6H8O7) or H2SO4 to enhance the particle size of H2BDC, and the optimum conditions during the acidification step were determined. Additionally, response surface methodology was employed to examine the influence and interaction of extractant (NaOH) concentration, hydrolysis temperature, and time on the optimal H2BDC yield and recovery ratio. Experimental results demonstrated that NaOH concentration significantly impacted both H2BDC yield and recovery ratio, surpassing the effects of hydrolysis temperature and time. Under optimal conditions involving a temperature of 200 °C and a 12 h reaction time with 5% NaOH, the model predicted a 100% yield and recovery ratio, which closely matched the experimental results of 99% and 100% for yield and recovery ratio, respectively. To enhance particle size, a combination of DMSO and C6H8O7 was more effective than H2SO4. The maximum particle size achieved was 57.4 µm under the following optimum conditions: premixing 5 M C6H8O7 with DMSO at a 35:75 mL ratio and maintaining a reaction temperature of 75 °C for 40 min. The study demonstrated the stability and consistency of the method. The H2BDC yield remained between 96 and 98% with high purity over eight consecutive cycles of using the DMSO and C6H8O7 mixture. The findings highlight the importance of integrating C6H8O7 and DMSO to enhance H2BDC quality, meeting commercial product criteria with evidence of high purity and large particle size. This method presents a promising solution for extracting H2BDC from PET waste, with potential implications for the recycling industry and a positive environmental impact.

Determining the Size of Representative Volume Elements for a Two-Dimensional Random Aggregate Numerical Model of Asphalt Mortar without Damage.

The size of the representative volume element (RVE) for the two-dimensional (2D) random aggregate numerical model of asphalt mortar in a non-destructive state, which directly affects the time required to simulate the linear viscoelastic behavior from asphalt mastic to asphalt mortar. However, in the existing literature, limited research has been conducted on the size determination of the numerical model RVE for asphalt mortar. To provide a recommended size for the typical 2D random aggregate numerical model RVE of asphalt mortar in a nondestructive state, this paper first applies the virtual specimen manufacturing method of asphalt concrete 2D random aggregate to asphalt mortar. Then, it generates numerical model RVEs of asphalt mortar with different maximum particle sizes, after which geometric and numerical analyses are conducted on these models. Finally, based on the geometric and numerical analysis results, the recommended minimum sizes of RVE for the 2D asphalt mortar numerical model are provided.

Stability of bubble-particle hetero-coagulates accessed by atomic force microscopy to understand the froth flotation of agglomerating hydrophobic fines

The key microprocesses, which determine the efficiency in froth flotation are the formation and breakage of particle-bubble hetero-coagulates. Agglomeration can be used to increase the recovery of fine particles < 20 µm. Here the stability of hetero-coagulates consisting of agglomerates and gas bubble determines the process performance. Therefore, the stability of agglomerate-bubble hetero-coagulates was accessed by atomic force microscopy (AFM) on particle-laden gas bubbles, agglomerates and pristine gas bubbles without particles in the interface. The force and work of adhesion from AFM measurements were compared to the detaching force and the detaching energy that act on agglomerate-bubble and particle-bubble hetero-coagulates under turbulent conditions, similar to those in a flotation cell. This comparison provides the maximum size of agglomerates and single particles that can remain attached to the gas bubbles at a given energy dissipation rate. The results suggest that the size of agglomerates attached to gas bubbles can grow beyond the Kolmogorov length, which limits the size of agglomerates under turbulent conditions. The findings are supported by in-line probe images of agglomerate-bubble hetero-coagulates that were captured in an aerated stirred tank under turbulent conditions. It was further shown that the particle detachment from particle-laden bubbles is governed by the deformation of the underlying gas bubble and the local particle coverage.

Study on compaction characteristics and mechanical model of dry crushing filling material under lateral confinement condition

The compaction characteristics and bearing capacity of dry filling materials in goaf have a significant influence on stope control and surface stability. Through acoustic emission monitoring and mechanical model analysis, a series of confined compression tests were conducted on crushed waste with varying particle sizes and Talbot coefficients. The deformation, fragmentation, and acoustic emission characteristics under corresponding working conditions were determined. The results indicate that the stress–strain curves of crushed stone with different particle sizes and Talbot coefficients exhibit similar nonlinear behavior during confined compression. However, the strain response varies with changing stress levels. By analyzing the slope change rate of the stress–strain curve, the lateral uniaxial compression process of waste rock can be divided into three deformation stages: rapid compression, stable crushing, and slow compaction. The compressive deformation characteristics of gravel differ based on particle size and Talbot coefficient. Specimens with a higher Talbot coefficient demonstrate stronger compressive resistance and weaker deformation resistance during initial compaction loading. Notably, the internal pressure structure strength is influenced by factors such as maximum particle size D, grading coefficient n, and particle size distribution continuity, rather than solely by the proportion of large particles. The evolution of acoustic emission signals and energy-time curve during waste rock confined axial compression synchronizes with the compaction process. Overall, compaction plays a critical role in maintaining the stability of goaf in dry crushed waste filling.

Influence of materials and processes on the robustness of apparent porosity control methods for fair-faced concrete

Fair-faced concrete is a new type of concrete that directly uses the surface of concrete as the facing, with good surface integrity, no chiseling and repairing after forming, and no need for decoration. In recent years, it has developed rapidly after being introduced into China, but there are some problems, the stability of pore control is difficult and the formation mechanism is insufficient. It also exists chromatic aberration. Aiming at the formation mechanism of apparent pores in fair-faced concrete, by changing raw materials and mix ratio of fair-faced concrete, adjusting raw materials, construction process and formwork parameters, this paper put forward the control interval of high robustness parameters of fair-faced concrete with few apparent pores and excellent aesthetic grade. It makes it possible to prepare fair-faced concrete repeatedly and stably with a good economy. It also has good guiding significance for practical projects. The material parameters included initial gas content, maximum particle size of coarse aggregate, plastic viscosity coefficient, initial dynamic yield stress and bleeding rate. Construction process parameters included vibration frequency, vibration time and vibration amplitude. Formwork parameters included release agents with different contact angles. The results show that the initial gas content of the fair-faced concrete slurry was 2%–3%, the particle size of the coarse aggregate was 5 mm–25 mm, the plastic viscosity coefficient of the fair-faced concrete slurry was 5 Pa·s-10 Pa s, the yield stress was 100 Pa–200 Pa, the water secretion rate was 8%–10 %, and the vibration frequency was 10,000 times/min-12,000 times/min. When the vibration time was 20 s–25 s, the vibration amplitude was 1.0 mm–1.2 mm, and the contact angle was 102°–112°, the apparent porosity of the fair-faced concrete could be controlled well.

Influence of Elevated Temperatures on the Compressive Strength of Concrete Made with Different Types of Aggregate

Concrete, the backbone of modern infrastructure, exhibits varying mechanical behaviour that depends on its components, with aggregates playing a crucial role in its strength and durability. This study aimed to investigate the influence of elevated temperatures on the compressive strength of concrete made with different types of aggregate. A comprehensive evaluation of concrete mixes was conducted using quartz, crushed clay bricks, crushed andesite, expanded clay and expanded glass coarse aggregates. For each coarse aggregate type, concrete mixtures were made with the same amount of Portland cement, water-cement ratio, natural sand, and superplasticizer. The effective water-cement ratio and cement content were kept constant in each concrete mixture. The grading and maximum particle size were the same in all concrete mixtures. The results revealed that the type of aggregate has a significant impact on the compressive strength and thermal resistance of concrete, with andesite-containing concrete exhibiting the highest residual strength after heating up to 800 °C and clay brick-concrete displaying the highest strength under elevated temperatures up to 1000 °C. The study also found that the age of concrete affects its strength at elevated temperatures, as concrete in the early stages of hydration is more susceptible to thermal cracking than concrete that has had more time to cure. Generally, the compressive strength of normal-weight aggregates depends on the strength of the parent rock. But in the case of fire (elevated temperature), the cement paste matrix loses its strength, and the aggregates effects become more significant.

Effect of flexible membrane in triaxial test on the mechanical behaviour of rockfill material using Discrete Element Method

The investigation of rockfill materials poses challenges due to their large particle size, associated high cost, and long laboratory testing duration. As a result, empirical correlations based on historical experimental studies are commonly used to design and analyse rockfill structures. However, the extensive use of rockfill in a wide range of applications and limited understanding of its mechanical behaviour emphasize the need for further research. These make it necessary to develop a robust technique capable of capturing key parameters such as particle shape and breakage, allowing for the simulation and study of large-scale assemblies with realistic boundary conditions. Given that the behaviour of rockfill is highly scale-dependent, primarily due to particle breakage, the simplified laboratory tests on the scaled-down assemblies can be misleading. Particle breakage is a fundamental phenomenon in the mechanical behaviour of rockfill and significantly affects shear strength, deformability, and porosity under different stress levels. The particle breakage is influenced by factors such as the rockfill’s maximum particle size, mineralogy, particle shape, gradation, and confining stresses. This study adopts a computationally efficient breakage method called the Modified Particle Replacement Method (MPRM) based on the Discrete Element Method. A Tile-Based Flexible Membrane (TBFM) for triaxial test modelling has been developed by employing segmental rectangular walls to create a deformable membrane. The effects of critical parameters, including particle shape, confining stress, membrane resolution, degree of flexibility, and the characteristic strength of the particles, are examined. The findings of the combined MPRM-TBFM approach demonstrate the significant influence of membrane flexibility on volumetric-related behaviour.Graphical

Effects of synthesis conditions on particle size and pore size of spherical mesoporous silica

The particle size and pore size of spherical mesoporous silica materials play significant roles in their application. However, relatively limited systematic research has been conducted on how preparation conditions influence these properties. In particular, the effects of some important factors have not been adequately studied, including reaction time, reaction temperature, and organic solvent type. In this work, octane and water were used as solvents, and tetraethyl orthosilicate was used as the silicon source to systematically study the effects of reaction time, reaction temperature, different organic solvents, octane/water mass ratio, styrene template concentration, and surfactant (cetyltrimethylammonium bromide, CTAB)/H2O mass ratio on the particle morphology, particle size, and pore size of silica. The results suggest that the above-mentioned neglected factors exert a substantial influence on both particle size and pore size. In the experimental temperature range, the pore diameter decreases and the particle size increases with increasing temperature. The maximum particle size and pore size are achieved after a reaction time of 3 h, and a further increase in reaction time leads to a smaller particle size and pore size. As the number of carbon atoms in the organic solvent decreases, the pore size also gradually increases. Styrene and organic solvents that dissolve in CTAB micelles are crucial factors in pore formation, while the aggregation of the swollen CTAB micelles influences the particle size. The changes in the pore structure stability and hydroxyl density of the synthesized samples in water were also studied. After undergoing water treatment at temperatures ranging from 20 to 60 °C for 72 h, both the pore structure and morphology remain relatively unchanged. When the temperature increases, the surface hydroxyl density exhibits a more pronounced increase in the presence of water. After water treatment for 5 h, the surface hydroxyl density reaches saturation.