Packing Density Research Articles

Microporous tungsten oxide spheres coupled with Ti3C2Txnanosheets for high-volumetric capacitance supercapacitors.

In the contemporary landscape of technological advancements, the burgeoning demand for portable electronics and flexible wearable devices has necessitated the development of energy storage systems with superior volumetric performance. Tungsten oxide (WO3), known for its high density and theoretical capacitance, is a promising electrode material for supercapacitors. However, low conductivity and poor cycling stability are still the key bottlenecks for its application. Herein, a novel composite comprising hollow porous WO3 spheres (HPWS) derived by template method was electrostatic self-assembled on the surface of the Ti3C2Tx nanosheets. The resulting electrodes exhibited ultra-high volumetric capacitance of 1930 F cm-3 at 1 A g-1 and rate capability of 46% at 50 A g-1, attributed to enhanced ion accessibility from microporous structure and electron transport from conductive network of Ti3C2Tx even at a high packing density of 3.86 g cm-3. Utilizing HPWS/Ti3C2Tx as the negative electrode and porous carbon as the positive electrode, the assembled asymmetric supercapacitor achieved an energy density of 31 Wh kg-1 at a power density of 650 W kg-1 with over 107% capacitance retention after 5000 cycles. This work provides a promising approach for developing next-generation supercapacitors with ultra-high volumetric capacitance.

Stress-relieved hollow porous carbon nanoring structures anchored with ZnCo2O4 nanoparticles towards super stable lithium storage

Stress-induced structural mechanical instability is a common occurrence in the electrode material during electrochemical cycling, especially for composite material systems. The structural mechanics engineering of nanocomposites comprising electrochemical active materials and carbon with novel structures holds great promise in addressing this issue. However, conventional carbonaceous materials often encounter challenges in long-term durability and high specific capacity stemming from their intrinsic uneven stress distribution and few active sites. Herein, finite element analysis reveals that the ring-like structure effectively mitigates stress concentration from expansion and possesses high packing density, outperforming traditional nanosphere and nanocube architectures. Accordingly, nanocomposites consisting of hollow porous nanostructured N-doped carbon nanorings (N-CNRs) anchored with bimetallic ZnCo2O4 nanoparticles are designed, which exhibit an extraordinary cycling performance for lithium storage with 96.4 % capacity retention following 1000 cycles and an impressively low storage degradation rate of 0.00357 % per cycle, as well as displaying an excellent specific capacity (1218 mA h/g at 0.1 A g−1) and outstanding rate performance (565 mA h/g at 5.0 A g−1). The well-engineered design nanocomposite features the synergistic effect of electrochemically active ZnCo2O4 nanoparticles integrated with structurally stable carbon nanorings for enhanced electrochemical performance.

Two-dimensional-lattice-confined single-molecule-like aggregates.

Intermolecular distance largely determines the optoelectronic properties of organic matter. Conventional organic luminescent molecules are commonly used either as aggregates or as single molecules that are diluted in a foreigner matrix. They have garnered great research interest in recent decades for a variety of applications, including light-emitting diodes1,2, lasers3-5 andquantum technologies6,7, among others8-10. However, there is still a knowledge gap on how these molecules behave between the aggregation and dilution states. Here we report an unprecedented phase of molecular aggregate that forms in a two-dimensional hybrid perovskite superlattice with a near-equilibrium distance, which we refer to as a single-molecule-like aggregate (SMA). By implementing two-dimensional superlattices, the organic emitters are held in proximity, but, surprisingly, remain electronically isolated, thereby resulting in a near-unity photoluminescence quantum yield, akin to that of single molecules. Moreover, the emitters within the perovskite superlattices demonstrate strong alignment and dense packing resembling aggregates, allowing for the observation of robust directional emission, substantially enhanced radiative recombination and efficient lasing. Molecular dynamics simulations together with single-crystal structure analysis emphasize the critical role of the internal rotational and vibrational degrees of freedom of the molecules in the two-dimensional lattice for creating the exclusive SMA phase. This two-dimensional superlattice unifies the paradoxical properties of single molecules and aggregates, thus offering exciting possibilities for advanced spectroscopic and photonic applications.

Cation-modulated permselectivity regulation of polyelectrolyte nanofiltration membranes for water purification

Polyelectrolyte multilayer (PEM) membranes fabricated by layer-by-layer (LBL) assembly have been widely adopted for nanofiltration (NF) due to their unique merits of highly tunable surface charge and pore size. However, current PEM membranes generally suffer from cumbersome preparation procedures and unsatisfying water permeance and/or solute retention rates, which stymie their practical applications. This study discloses a facile and effective method to deliberately regulate the interactions between polyelectrolytes and their LBL assembly behaviors by using cations with various valences and sizes as the modulators. Compared with the acquiescent background electrolyte NaCl, the PEMs modulated by divalent cations (i.e., Ca2+) exhibit intensified surface electronegativity with dense packing structures, and the resulting PEM membranes thus show high rejections for both inorganic salts (i.e., 94.0 % for Na2SO4) and negatively charged emerging micropollutants (EMPs) (i.e., 94.9 % and 99.9 % for tetracycline hydrochloride and perfluorododecanoic acid, respectively). In contrast, monovalent cations (i.e., Li+) lead to the formation of PEMs with loose structures and strong surface electronegativity, which endow the PEM membranes with a high water permeance of 15.0 LMH/bar and slightly reduced solute rejections. Nevertheless, the retention rates of Na2SO4 and perfluorooctanoic acid still surpass those obtained by the NaCl-modulated PEM membrane. Interestingly, trivalent cations such as Fe3+ and Al3+ are unable to facilitate the formation of an intact PEM. Characterization data and theoretical models imply that cations play a pivotal role in the stacking structure of PEMs through synergistically modulating polyelectrolyte-counterion interactions and the overcompensation and subsequent site diffusion of polyanions. This work demonstrates an effective approach to finely tune the nanostructure and permselectivity of the PEMs, which provides a valuable platform for the rational design of PEM NF membranes for effective separations of salts and EMPs.

Achieving Record C2H2 Packing Density for Highly Efficient C2H2/C2H4 Separation with a Metal–Organic Framework Prepared by a Scalable Synthesis in Water

AbstractAdsorptive C2H2/C2H4 separation using metal–organic frameworks (MOFs) has emerged as a promising technology for the removal of C2H2 (acetylene) impurity (1 %) from C2H4 (ethylene). The practical application of these materials involves the optimization of separation performance as well as development of scalable and green production protocols. Herein, we report the efficient C2H2/C2H4 separation in a MOF, Cu(OH)INA (INA: isonicotinate) which achieves a record C2H2 packing density of 351 mg cm−3 at 0.01 bar through high affinity towards C2H2. DFT (density functional theory) calculations reveal the synergistic binding mechanism through pore confinement and the oxygen sites in pore wall. The weakly basic nature of binding sites leads to a relatively low heat of adsorption (Qst) of approximately 36 kJ/mol, which is beneficial for material regeneration and thermal management. Furthermore, a scalable and environmentally friendly synthesis protocol with a high space‐time yield of 544 kg m−3 day−1 has been developed without using any modulating agents. This material also demonstrates enduring separation performance for multiple cycles, maintaining its efficacy after exposure to water or air for three months.

Crystal structure and structure-guided tunnel engineering in a bacterial β-1,4-galactosyltransferase

Lacto-N-neotetraose (LNnT), a representative oligosaccharide found in human milk, has been previously examined for its beneficial traits. However, the LNnT titer is limited by the efficient glycosyltransferase pathway, particularly with respect to the catalysis of rate-limiting steps. As data on the crystal structure of the key enzyme required for synthesizing LNnT are lacking, the synthesis of LNnT remains an uncertainty. Here, for the first time we report the three-dimensional structure of a bacterial β-1,4-galactosyltransferase, Aaβ4GalT, and analyze the critical role played by residues in its catalytic efficacy. Guided by structural insights, we engineered this enzyme to enhance its catalytic efficiency using structure-guided tunnel engineering. The mutant enzyme L5 (K155M/H156D/F157W/K185M/Q216V) so produced, showed a 50-fold enhancement in catalytic activity. Crystal structure analysis revealed that the mechanism underlying the improvement in activity was of the swing door type. The closed conformation formed by dense hydrophobic packing with Q216V-K155M widened and permitted substrate entry. Our results show that altering the tunnel conformation helped appropriately accommodate the substrate for catalysis and provide a structural basis for the modification of other glycosyltransferases.

Thermodynamic stabilities of NdFe3Al2, Nd5Fe17 and μ compounds and evolutions of microstructures and magnetic properties of Nd-Fe-Al alloys with nanocrystallites

In the Nd-Fe-Al ternary system, thermodynamic stabilities of three compounds, NdFe3Al2, Nd5Fe17 and μ, were determined by the equilibrated alloys, indicating that both NdFe3Al2 and μ ternary compounds are metastable phases, while Nd5Fe17 compound is a stable phase. Meantime, the microstructures of five representative as-cast alloy buttons are illustrated, which are consisted of crystalline phases and the complex of nanocrystallites + amorphous matrix (NCAM). The crystalline phases including Nd, Nd3Al, Nd2Fe17-xAlx and Nd6Fe13-xAl1+x as well as the nanocrystallites such as dhcp-Nd, fcc-Nd and Nd6Fe13-xAl1+x embedded in the amorphous matrix were observed. Particularly, it is concluded that the fcc-Nd nanocrystallites may be transformed from the fcc dense packing clusters of the amorphous matrix and/or dhcp-Nd nanocrystallites. The hard magnetic properties of these as-cast alloys can be attributed to NCAM and present a non-strict proportionate effect. The alloy composed of Nd + NCAM, with curie temperature (Tc) 515 K, displays the highest intrinsic coercivity Hci 305 kA/m and remanent magnetization Br 10.8 emu/g. Its good glass-forming ability is presented by the high ratio (Tx/Tm) 0.88 and the small interval (Tm-Tx) 105 K of the crystallization temperature (Tx) with the melting temperature (Tm). Since the present investigation focuses on phase stabilities, microstructural characterizations, magnetic properties and glass-forming ability of the Nd-Fe-Al alloys, the obtained results can provide a better understanding for advancing the design of the Nd-Fe-Al based hard magnets and amorphous materials.

Achieving Record C2H2 Packing Density for Highly Efficient C2H2/C2H4 Separation with a Metal-Organic Framework Prepared by a Scalable Synthesis in Water.

Adsorptive C2H2/C2H4 separation using metal-organic frameworks (MOFs) has emerged as a promising technology for the removal of C2H2 (acetylene) impurity (1%) from C2H4 (ethylene). The practical application of these materials involves the optimization of separation performance as well as development of scalable and green production protocols.Herein, we report the efficient C2H2/C2H4 separation in a MOF, Cu(OH)INA (INA: isonicotinate) which achieves a record C2H2 packing density of 351 mg cm-3 at 0.01 bar through high affinity towards C2H2. DFT (density functional theory) calculations reveal the synergistic binding mechanism through pore confinement and the oxygen sites in pore wall.The weakly basic nature of binding sites leads to a relatively low heat of adsorption (Qst) of approximately 36 kJ/mol, which is beneficial for material regeneration and thermal management. Furthermore, a scalable and environmentally friendly synthesis protocol with a high space-time yield of 544 kg m-3 day-1 has been developed without using any modulating agents. This material also demonstrates enduring separation performance for multiple cycles, maintaining its efficacy after exposure to water or air for three months.

Physical aspects of epithelial cell-cell interactions: hidden system complexities.

The maintenance of homeostasis and the retention of ordered epithelial cell self-organization are essential for morphogenesis, wound healing, and the spread of cancer across the epithelium. However, cell-cell interactions in an overcrowded environment introduce a diversity of complications. Such interactions arise from an interplay between the cell compressive and shear stress components that accompany increased cell packing density. They can lead to various kinds of cell rearrangement such as: the epithelial-to-mesenchymal cell state transition; live cell extrusion; and cell jamming. All of these scenarios of cell rearrangement under mechanical stress relate to changes in the strengths of the cell-cell and cell-matrix adhesion contacts. The objective of this review study is twofold: first, to provide a comprehensive summary of the biological and physical factors influencing the effects of cell mechanical stress on cell-cell interactions, and the consequences of these interactions for the status of cell-cell and cell-matrix adhesion contacts; and secondly, to offer a bio-physical/mathematical analysis of the aforementioned biological aspects. By presenting these two approaches in conjunction, we seek to highlight the intricate nature of biological systems, which manifests in the form of complex bio-physical/mathematical equations. Furthermore, the juxtaposition of these apparently disparate approaches underscores the importance of conducting experiments to determine the multitude of parameters that contribute to the development of these intricate bio-physical/mathematical models.

Role of the constriction angle on the clogging by bridging of suspensions of particles

Confined flows of particles can lead to clogging, and therefore failure, of various fluidic systems across many applications. As a result, design guidelines need to be developed to ensure that clogging is prevented or at least delayed. In this Letter, we investigate the influence of the angle of reduction in the cross section of the channel on the bridging of semidilute and dense non-Brownian suspensions of spherical particles. We observe a decrease of the clogging probability with the reduction of the constriction angle. This effect is more pronounced for dense suspensions close to the maximum packing fraction where particles are in contact in contrast to semidilute suspensions. We rationalize this difference in terms of arch selection. We describe the role of the constriction angle and the flow profile, providing insights into the distinct behavior of semidilute and dense suspensions. Published by the American Physical Society 2024

Proteome-Wide Assessment of Protein Structural Perturbations under High Pressure

One of the planet's more understudied ecosystems is the deep biosphere, where organisms can experience high hydrostatic pressures (30–110 MPa); yet, by current estimates, these subsurface and deep ocean zones host the majority of the Earth's microbial and animal life. The extent to which terrestrially relevant pressures up to 100 MPa deform most globular proteins—and which kinds—has not been established. Here, we report the invention of an experimental apparatus that enables structural proteomic methods to be carried out at high pressures for the first time. The method, called high-pressure limited proteolysis (Hi-P LiP), involves performing pulse proteolysis on whole cell extracts brought to high pressure. The resulting sites of proteolytic susceptibility induced by pressure are subsequently read out by sequencing the peptide fragments with tandem liquid chromatography–mass spectrometry. The method sensitively detects pressure-induced structural changes with residue resolution and on whole proteomes, providing a deep and broad view of the effect of pressure on protein structure. When applied to a piezosensitive thermophilic bacterium, , we find that approximately 40% of its soluble proteome is structurally perturbed at 100 MPa. Proteins with lower charge density are more resistant to pressure-induced deformation, as expected; however, contrary to expectations, proteins with lower packing density (i.e., more voids) are also more resistant to deformation. Furthermore, high pressure has previously been shown to preferentially alter conformations around active sites. Here, we show this is also observed in Hi-P LiP, suggesting that the method could provide a generic and unbiased modality to detect binding sites on a proteome scale. Hence, data sets of this kind could prove useful for training emerging artificial intelligence models to predict cryptic binding sites with greater accuracy. Published by the American Physical Society 2024

Diverse morphology and motility induced emergent order in bacterial collectives.

Microbial communities exhibit complex behaviors driven by species interactions and individual characteristics. In this study, we delve into the dynamics of a mixed bacterial population comprising two distinct species with different morphology and motility aspects. Employing agent-based modeling and computer simulations, we analyze the impacts of size ratios and packing fractions on dispersal patterns, aggregate formation, clustering, and spatial ordering. Notably, we find that motility and anisotropy of elongated bacteria significantly influence the distribution and spatial organization of nonmotile spherical species. Passive spherical cells display a superdiffusive behavior, particularly at larger size ratios in the ballistic regime. As the size ratio increases, clustering of passive cells is observed, accompanied by enhanced alignment and closer packing of active cells in the presence of higher passive cell area fractions. In addition, we identify the pivotal role of passive cell area fraction in influencing the response of active cells toward nematicity, with its dependence on size ratio. These findings shed light on the significance of morphology and motility in shaping the collective behavior of microbial communities, providing valuable insights into complex microbial behaviors with implications for ecology, biotechnology, and bioengineering.

Influence of doping soda-lime-silica glasses with Gd2O3, In2O3, and La2O3 on the enhancing of their physical, opto-mechanical and radiation shielding properties

A series of soda-lime-silicate glasses doped Gd2O3, In2O3, and La2O3 rare earth ions was prepared using the melt-quenching technique. The prepared glass samples are designed depending on a chemical composition of (15-X)Na2O – 30CaO – 55SiO2 –XM2O3, where X = 1.0 mol% and M = Ga (NCSG), In (NCSI), and La (NCSL). The amorphous state of the synthesized samples confirmed by XRD analysis, and structural changes were studied via density (ρg), molar volume (Vm), Oxygen molar volume (Vo), and Oxygen packing density (OPD). The mechanical and shielding attenuation parameters of the produced glasses were also projected. The ρg of prepared glasses increased from 2.742 to 2.829 g/cm3 as a result of M2O3-dopant with high molecular weight rare earth oxides. Whereas, the physical parameters Vm, Vo, and OPD were behave in the same trend. Elastic moduli were improved when Na2O replaced with M2O3. The M2O3/Na2O replacement led to increase stiffer and rigidity of the prepared glasses. The NCSL sample was possessed the lowest optical energy band (Eopt.) values (3.45 eV and 2.63 eV for direct and indirect transitions). The NCSL glass sample possessed the highest mass (MAC) and linear (LAC) absorption capacity. In addition, the same glass sample verified the lowest values of half-value layer (HVL) and mean free path (MFP). Thus, the sample coded as NCSL sample including La2O3 is a superior for optical and radiation shielding capacities among all studied glasses. Therefore, the studied glasses can be applied for several optical and radiation shielding applications.

Exploration of red and deep red Thermally activated delayed fluorescence molecules constructed via intramolecular locking strategy

Red and deep red (DR) organic light-emitting diodes (OLEDs) have garnered increasing attention due to their widespread applications in display technology and lighting devices. However, most red OLEDs exhibit low luminescence efficiency, severely limiting their practical applications. To address this challenge, we theoretically design four novel TADF molecules with red and DR luminescence using intramolecular locking strategies building upon the experimental findings of DCN-DLB and DCN-DSP, and their crystal structures are predicted with the lower energy and higher packing density. The photophysical properties and luminescence mechanism of six molecules in toluene and crystal are clarified using the first principles calculation and thermal vibration correlation function (TVCF) method. The proposed design strategy is anticipated to offer several advantages: enhanced electron-donating capabilities, more rigid structures, longer emission wavelengths and higher luminescence efficiency. Specifically, we introduce oxygen atoms and nitrogen atoms as intramolecular locks, and the newly developed DCN-DBF and DCN-PHC have redshifted emission, narrow singlet–triplet energy gap (ΔEST), fast reverse intersystem crossing rate and enhanced photoluminescence quantum yield (PLQY). Notably, DCN-DBF achieves both long wavelength emission and high efficiency, with emission peaks at 598 nm and 587 nm corresponding to PLQY of 52.13 % and 43.42 % in toluene and crystal, respectively. Our work not only elucidates the relationship between molecular structures and photophysical properties, but also proposes feasible intramolecular locking design strategies and four promising red and DR TADF molecules, which could provide a valuable reference for the design of more efficient red and DR TADF emitters.

Long-Chain Molecular Crystals Antimony(III) Alkanethiolates Sb(SCnH2n+1)3 (n ≥ 12): Synthesis, Crystal and Electronic Structures, and Supramolecular Self-Assembly via Secondary Interactions.

Currently, there is not much success in solving the molecular and crystal structures of long-chain metal alkanethiolate complexes [M(SCnH2n+1)m] at the atomic level. Taking Sb(SC16H33)3 (1) as an example, we herein disclose the structural characteristics of long-chain trivalent antimony(III) alkanethiolates Sb(SCnH2n+1)3 (n ≥ 12) by single-crystal X-ray crystallography. Specifically, the Sb atom is three-coordinated by alkanethiolate ligands and a slightly distorted triangular pyramid SbS3 core is formed owing to the unique intramolecular stereochemistry of three alkyl chains, namely, two of them almost parallel aligning and the third chain extending alone around the SbS3 core. We further determine the conformation, spatial orientation and packing density of alkyl chains in 1 along with a comparison to those in other long-chain crystalline systems, and reveal the roles of intermolecular van der Waals and Sb···S secondary interactions in molecular self-assembly, which enables 1 to be a layer-structured molecular crystal with a monoclinic P21/c unit cell. The band structures and the atomic orbital contributions to the valence band maximum and conduction band minimum for 1 have also been evaluated by DFT calculations and rationally correlated with its optical absorption property. This study will help understand and discover new structures and structure-property relations of long-chain chemical systems.

Structural, morphological, optical and down-conversion studies of NaLaMgTeO6:Dy3+ single phase phosphor for white light emitting applications and solar spectral converter for photovoltaic applications

Researches on rare earth activated phosphors in solid state lighting and enhancement in efficiency of solar cells pave attention to develop efficient phosphor materials. In the present work, Dy3+ doped NaLaMgTeO6 phosphors are synthesized using solid state reaction method. The structural studies using XRD analysis confirmed the successful formation of the compound. SEM analysis reveals that the particles are closely packed, which in turn exhibit intense luminescence intensity due to low scattering and high packing density. Elemental configuration were analyzed using EDS analysis. FTIR analysis revealed the vibrational bands of the host matrix. Optical energy bandgap was calculated using DRS spectra. The luminescence characteristics of the samples were investigated using excitation and emission spectra. Upon most intense 351 and 388 nm excitation, sharp yellow emission peak at 572 nm dominates blue emission at 478 nm, further reveals that Dy3+ ions occupy low symmetry site in the host lattice. The optimum concentration of Dy3+ in the present host is x = 0.04 mol and concentration quenching is due to dipole-quadrupole interaction of adjacent Dy3+ ions. The thermal quenching phenomenon is studied using temperature dependent photoluminescence analysis. The CIE chromaticity coordinates and CCT values conclude NaLaMgTeO6:Dy3+ phosphors are good candidate for cool near-white light emitting materials for outdoor illumination. The study on solar spectral response and down-conversion property of the synthesized phosphor demonstrate its applicability as solar spectral converters in solar cell applications.

Effect of GGBFS on the mechanical properties of metakaolin-based self-compacting geopolymer concrete

The focus of this study is the production and testing of a new self-compacting geopolymer concrete（SCGC）. The concrete has excellent self-compacting properties, mechanical properties and environmental advantages, showing great potential for engineering applications. Due to the high specific surface area of metakaolin (MK), it is challenging to produce a self-compacting geopolymer concrete using metakaolin as the main material. A self-compacting geopolymer concrete with excellent properties was produced by partially replacing metakaolin with ground granulated blast furnace slag (GGBFS). This innovation enriches the diversity of powder material choices for self-compacting geopolymer concrete. The experimental results showed that the addition of ground granulated blast furnace slag significantly enhanced the filling capacity and interstitial passage capacity and wet packing density of ground granulated self-compacting concrete. The best working performance of the concrete was achieved at 40 % GGBFS replacement. The test data were slump extension of 749 mm, T50 time of 3.23 s, V-funnel test time of 8.2 s, L-box test result of 0.96, and wet packing density of 1.946 g/cm3. With the increase in the replacement rate of the ground granulated blast furnace slag, the compressive strength of self-compacting ground polymer concrete and the split tensile strength showed a trend of increasing and then decreasing. The maximum compressive strength of 55.2 MPa and splitting tensile strength of 4.11 MPa were obtained when the substitution rate of ground granulated blast furnace slag was 20 %. The drying shrinkage of self-compacted geopolymer concrete was significantly increased by the addition of excess ground granulated blast furnace slag. The drying shrinkage was increased by 147 % at 40 % substitution rate compared to 0 % substitution rate. Scanning electron microscope (SEM) tests and thermogravimetric analysis were performed on all samples. At ground granulated blast furnace slag substitution rate of 20 %, a uniform and dense gel structure was formed inside. At 40 % ground granulated blast furnace slag substitution rate, the weight loss of the specimens reached 13.4 %, which was 4.22 % more than the control group with 0 % substitution rate. The results showed that GGBFS effectively promoted the generation of internal cementitious structures in SCGC. This study provides the necessary information for the development of metakaolin-based self-compacting geopolymer concrete and contributes to the popularization of metakaolin-based self-compacting geopolymer concrete. It will also broaden the scope of use of metakaolin in self-compacting geopolymer concrete, which will contribute to the diversification of building materials and the development of the construction industry towards a low-carbon and sustainable future.

Modeling of the effect of fibers on ECC slurry fluidity based on an amended water film thickness theory

Knowing the influence mechanisms of fibers on ECC slurry fluidity and implementing the prediction of ECC slurry fluidity attach vital significance to the design and application of ECC. Based on traditional water film thickness (WFT) theories, this paper introduces the difference in surface WFT of reactive fibers and binding material particles with excess water distribution coefficient and further gives a modified formula for water film calculation and a WFT based ECC fluidity model. Through 40 tests and fitting, the excess water distribution coefficient with respect to distinct fibers and relevant parameters of the ECC fluidity model are obtained. The results indicate that the new model is applicable to different types of fibers, and the fluidity of ECC slurry can be described using an equation, with the R2 of the new equation reaching 0.97. Finally, based on the proposed model, the impact of PP and PVA fibers on the fluidity of ECC slurry can be summarized in two aspects: the wedge effect of the fibers reduces the packing density of the ECC powder, leading to a decrease in the excess water ratio; the water distribution in the ECC slurry is altered by the fibers, resulting in a decrease in the water film thickness on the surface of the cementitious material particles, ultimately causing a decline in the fluidity of the ECC slurry.

Impact of polycarboxylate superplasticizer dosage on controlled low strength material flowability and bleeding: Insights from water film thickness

Civil excavation projects frequently yield substantial excess spoil, posing challenges to sustainable construction. This study explores repurposing such spoil for creating controlled low strength material (CLSM), emphasizing the novel use of polycarboxylate superplasticizer (PCE) to reduce the water requirement. The work also distinctively utilizes water film thickness (WFT) theory to elucidate the effects of PCE dosage and WFT on material properties, thereby advancing CLSM mix design. First, using an experimental approach, a series of fresh CLSM samples are prepared, with varying the water-to-solid ratio (W/S) and PCE dosage, to evaluate their packing density, WFT, flowability, and bleeding rate. It is demonstrated that both packing density and WFT experienced a non-linear increase with rising PCE dosage. Regression analysis of the experimental data reveals that the flowability and bleeding rate linearly increase with the rising WFT, and the enhancements are more pronounced at higher PCE dosage. Notably, at a given WFT, the impact of PCE dosage on flowability and bleeding rate reduce as WFT decreases. Additionally, the research identifies specific WFT thresholds correlating with maximum flowability and a 5% bleeding rate. These thresholds mark the critical point at which WFT ceases to influence flowability and delineate the maximum WFT that satisfies the bleeding rate requirements, respectively. These insights are important for optimizing the design of CLSM with PCE in terms of flowability and bleeding rate.

Rheology and hardened properties of eco-friendly ultra-high performance concrete paste: Role of waste stone powder fillers

Waste stone powder is the largest by-product generated during the production of manufactured sand, which causes environmental pollution and resource wastage due to its large accumulation and landfill disposal. In this study, the effectiveness of basalt powder (BP) was evaluated against that of limestone powder (LP) to verify its potential for use as a functional and environmentally-friendly filler in Ultra-High Performance Concrete (UHPC) compositions. The theories of wet packing density (WPD) and water film thickness (WFT) are introduced to investigate the effect of stone powder on hardened and rheological properties of UHPC. Results indicate that the WFT of the solid particle system (cement and stone powder) exhibits a direct correlation with the increase in stone powder content (up to 20 %). As the WFT increases, the shear resistance between particles is reduced, leading to a nonlinear decrease in the yield stress and plastic viscosity of the UHPC paste, thereby enhancing its flowability. More superplasticizer is adsorbed on the surface of BP, which weakens the gain effect of the superplasticizer in reducing the yield stress. Due to the increased WPD, a near-linear enhancement in the compressive strength of the paste is observed. Supplementary nucleation sites for C-S-H are provided by the surface of the stone powder, thus accelerating the early hydration kinetics of the UHPC paste and facilitating development of strength at an early age. When 20 % of cement is replaced by LP and BP, the carbon emission index of UHPC paste is reduced by 34.9 % and 21.7 %, respectively.