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In this paper, epoxy acrylate/nickel-plated carbon nanotubes composites with different structural orientations (X, Z) were prepared by digital light procession 3D, and the orientation of nickel-plated carbon nanotubes in the magnetic field and its effect on the mechanical properties of the composites were systematically studied. The scanning electron microscope shows the orientation of the fiber in the magnetic field. The experimental results show that the mechanical properties and friction coefficient of the material show obvious anisotropy, but the anisotropy of wear rate is not obvious. The tensile strength of the X sample is about 18% higher than that of the Z sample when the content of nickel-plated carbon nanotubes was 0.15 wt%. The impact strength of the X sample is about 15% higher than that of the Z sample when the content of Ni-MWNTs was 0.1 wt%. The friction coefficient on the plane (X, Y) is about 20% lower than that on the plane (Y, Z) when the content of carbon nanotubes is 0.05 wt%.

To improve the wear resistance of polyimide (PI), surface modification was developed. In this study, the tribological properties of graphene (GN), graphene oxide (GO), and KH550-grafted graphene oxide (K5-GO) modified PI were evaluated by molecular dynamics (MD) at the atomic level. The findings indicated that the addition of nanomaterials can significantly enhance the friction performance of PI. The friction coefficient of PI composites decreased from 0.253 to 0.232, 0.136, and 0.079 after coating GN, GO and K5-GO, respectively. Among them, the K5-GO/PI exhibited the best surface wear resistance. Importantly, the mechanism behind the modification of PI was thoroughly revealed by observing the wear state, analyzing the changes of interfacial interactions, interfacial temperature, and relative concentration.

Purpose The purpose of this paper is to investigate the effect of SiO2 on the tribological properties of polytetrafluoroethylene (PTFE) composites from an atomic level. Design/methodology/approach Effect of SiO2 on the tribological properties of PTFE sliding against Cu was studied by molecular dynamics (MD) simulations to explore the inherent mechanisms from an atomic level. Findings SiO2 had a higher interaction energy with PTFE than copper, which contributed to an increase of interfacial temperature and velocity with severe adhesive wear on the PTFE molecules. Originality/value This study reveals the mechanism of SiO2 on the friction and wear behavior of PTFE by MD simulation.

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In this study, lightweight ultra-high-performance concrete (L-UHPC) was prepared by using SP to replace part of the cement. The main study investigated the effect of the amount of SP on the spread diameter, apparent density and mechanical properties of L-UHPC. The mechanism of the effect of SP on the hydration product of L-UHPC was studied and the pore structure of L-UHPC was also analyzed. The results show that the incorporation of SP can effectively improve the spread diameter and reduce the apparent density of L-UHPC to a certain extent. With the increase in SP content, the compressive strength of L-UHPC at 7 days of age did not change significantly. However, the compressive strengths at 3 and 28 days of age changed significantly. When the amount of SP was less than 12%, there was no significant decrease flexural and compressive strength at 28 days of age. However, the flexural and compressive strength of L-UHPC gradually decreased when the amount of SP was greater than 12%. The microstructure shows that SP can reduce the content of portlandite. This is mainly due to the fact that the addition of SP improved the stacking compactness of L-UHPC and promoted secondary hydration reactions. The content of portlandite and the hydration degree of cement were reduced. At the same time, the exothermic hydration of L-UHPC with SP was less, the hydration process was slow, and the exothermic rate of initial hydration was low. An appropriate amount of SP can effectively improve the pore structure of L-UHPC and significantly reduce the pore volume of harmful pores (50~200 nm). SP can make the L-UHPC structure more compact and has a positive effect on the development of L-UHPC strength.

The nanostructure and chloride binding capacity evolution of C-A-S-H gel exposed to aggressive solutions were investigated, utilizing 29Si NMR, 27Al NMR, SEM-EDS, and XRD techniques. The experimental results show that while Cl− ions show a smaller effect on the microstructure of C-A-S-H sample, and SO42− ions can react with C-A-S-H, resulting in decreasing Ca/Si and Al[4]/Si for the C-A-S-H gel (i e, decalcification and dealuminization). The presence of Mg2+ ions can aggravate the decalcifying and dealuminizing effects of SO42− ions on the C-A-S-H. With decreasing Ca/Si ratio and aluminum substitution for the original C-A-S-H gel, the depolymerization degree of silicate tetrahedra increases and the calcium aluminosilicate skeleton strengthens. C-A-S-H gel with lower Ca/Si ratio and higher Al[4]/Si ratio shows gentler nanostructure evolution under chemical attack, i e, improving thermodynamic stability under chemical attack. Furthermore, the chloride binding capacity of C-A-S-H gel is decreased after the sulfate attack. Aluminum substitution can also help C-A-S-H gel resist the degraded chloride binding capacity induced by sulfate attack.

The compositions and contents of phases in cement paste soaked in sodium sulfate solution changing with time were investigated in this study. First of all, the porosities in cement paste specimens over time were measured by an in situ X-ray computed tomography (X-ray CT) test. Cement hydration and sulfate erosion occur simultaneously during the soaking process of cement paste specimens in sodium sulfate solution. Therefore, the hydration behaviour and the erosion of sulfates in cement paste were combined in a new way to establish an X-CT–hydration–deterioration model, which was used to calculate the variations of the volume fractions of the phases in cement paste. Subsequently, the volume fractions of each phase were used to calculate the elastic moduli of cement paste specimens with the bulk modulus, shear modulus of each phase and a self-consistent (SC) method. Afterward, the calculated elastic moduli were compared with the experimental results obtained by uniaxial compression test and the error values were 1% for 28 d, 2·5% for 88 d and 5% for 148 d, which were all within 5%, indicating that the advanced X-CT–hydration–deterioration model combined with the SC method can successfully predict the elastic modulus of cement paste eroded in sodium sulfate solution.

A new hot mixed epoxy asphalt system was developed. The reaction process of epoxy resin was characterized by Fourier transform infrared spectroscopy (FTIR). The viscosity was investigated by Brinell viscometer when epoxy resin was mixed with asphalt. The glass transition temperature (Tg), homogeneity, thermal stability and viscoelasticity of epoxy asphalt were analyzed by differential scanning calorimetry (DSC), metallographic microscope, thermogravimetric (TG) and dynamic mechanical analysis (DMA). The results showed that the viscosity of epoxy resin modified asphalt reached 1 000 mPa·s for more than 180 minutes at 180 °C, while the best construction process is mixing at 180 °C for 2 hours and curing at 60 °C for 4 days. The particle size of asphalt is less than 50 µm. In addition, the mechanical properties of the materials are uniform within the specified pavement thickness.

Structure and mechanical properties of Calcium silicate hydrate (C-S-H) at a molecular level act as “DNA” of cement-based construction materials. In order to understand loading resistance capability of C-S-H gel, research on molecular dynamics (MD) was carried out to simulate the uniaxial tension test on C-S-H model along x, y, and z directions. Due to the structure and dynamic differences of the layered structure, the C-S-H model demonstrates heterogeneous mechanical behavior. On an XY plane, the cohesive force can reach 4 GPa which is mainly provided by the Ca-O and Si-O ionic-covalent bonds. The good plasticity of calcium silicate sheet is attributed to the silicate branch structure formation and the recovery role of interlayer calcium atoms. However, in z direction, C-S-H layers connected by the unstable H-bonds network, have the weakest tensile strength 2.2 GPa. This results in the brittle failure mode in z direction. The relatively low tensile strength and poor plasticity in z direction provides molecular insights into the tensile weakness of cement materials at macro-level.

The water absorption and desorption processes of different types of lightweight aggregates were studied. Subsequently, the influences of pre-wetting lightweight aggregates on compressive strength, microhardness, phase composition, hydration parameters and micromorphology of the cement pastes were investigated. The results showed that the water absorption and desorption capacities of the lightweight aggregates increased with the decrease of the densification degree. With the addition of pre-wetting lightweight aggregates, the compressive strength of the cement pastes would increase. Moreover, the enhancement effect was more obviously with the desorption capacity of pre-wetting lightweight aggregates increasing. Especially, sample S1 with pre-wetting red-mud ceramisites had the highest compressive strength, of which increased to 49.4 MPa after 28 d curing age. The reason is that mainly because the addition of pre-wetting lightweight aggregates can promote the generation of C–S–H gels in the interfacial zone, and the hydration degree of the interfacial zone increases with the water desorption of pre-wetting lightweight aggregates increasing. It is contributed to optimize the microstructure to enhance microhardness of the interfacial zone, resulting in the compressive strength of the cement-based materials improving. Therefore, the pre-wetting lightweight aggregates with high porosity and strength are the potential internal curing agents for high-strength lightweight concretes.

Purpose This paper aims to study the effect of different rare earth oxide on the tribological properties of polyimide (PI) nanocomposites based on the CNT and GO reinforcements. Design/methodology/approach The PI nanocomposites filled with different rare earth oxide based on the carbon nanotubes and graphene oxide were designed and prepared by hot press sintering. The mechanical and tribological properties of PI nanocomposites were carried out, and their reinforcement mechanisms were discovered. Findings Rare earth oxide had a weak influence on the impact strength of PI nanocomposites. Filling La2O3 can dramatically reduce the friction coefficient and wear rate of PI nanocomposites. Originality/value The PI nanocomposites filled with rare earth oxide based on the CNT and GO reinforcements were designed, and their mechanical and tribological properties were studied.

This study examines the mechanical performance, deformability properties and rheological properties of a newly developed waterborne epoxy resin (WER)-modified emulsified asphalt (WE/A) binder for micro-surfacing. Two types of WER, semi-flexible and rigid, were used to modify the binder. Furthermore, the modification mechanism was investigated using the fluorescent microscope test and the scanning electron microscope (SEM). In addition, the pavement performance at micro-surfacing was studied using the wet wheel wear resistance test, the pendulum friction test and the slurry rutting test. The results indicated that with a small content (

Purpose The purpose of this paper is to study the mechanism and effect of rare earth oxides on the properties of Cr2O3-TiO2 coating. Design/methodology/approach Cr2O3-TiO2 coatings with different proportion of CeO2 were deposited by atmospheric plasma spraying on aluminum alloy 7005. The mechanical, microstructure and tribological properties were studied. Findings The addition of CeO2 could improve the micro-hardness; decrease porosity, wear rate and surface roughness of the coating; and increase the bonding strength between the coating and substrate. The wear mechanism is a mixture of abrasive and adhesive wear. Originality/value The addition of CeO2 could refine microstructure, and promote the formation of solid solution structure, and then affect the properties of coatings.

In order to improve the transfer efficiency of the travelling wave ultrasonic motor (TRUM), the advanced polyimide-based (PI) frictional materials with high friction coefficient and elastic modulus were designed and prepared by hot press sintering. The friction coefficient of PI composite sliding against phosphor bronze was investigated by a flat-on-flat pattern tribo-meter simulated the running conditions of the TRUM. Besides, the micro-dimples with diameter of 300 μm and area density of 7.06% were fabricated on the surface of PI composites by laser ablation. The friction coefficient of the textured PI interface further increased compared to the smooth PI or polytetrafluoroethylene (PTFE) interface. Therefore, the mechanical output torque, rotational speed and transfer efficiency of the TURM with new frictional materials and surface texture were correspondingly improved. The enhancement mechanisms were discussed by analyzing the changes in friction coefficient and contact sate of the tribo-pairs.

The thermodynamic stability of sulfate ions on synthesized calcium aluminosilicate hydrate (C-A-S-H) microstructure with different Ca/Si ratios and Al/Si ratios was investigated by XRD, SEM-EDS, 29Si and 27Al nuclear magnetic resonance (NMR) and thermodynamic modeling. The results indicate that sulfate attack leads to both decalcification and dealumination for C-A-S-H gels, and the amount of corrosion products (gypsum and ettringite) decreased gradually with decreasing Ca/Si ratios of C-A-S-H. Sulfate ions can also promote the polymerization degree of C-A-S-H gels, improving its resistance to sulfate attack. Moreover, the 4-coordination aluminum (Al[4]) in C-A-S-H, 5-coordination aluminum (Al[5]), 6-ccordination aluminum (Al[6]) in TAH (third aluminum hydrate) and Al[6] in monosulfate or C-A-H (calcium aluminate hydrate) can be transformed into Al[6] in ettringite by sulfate attack. Furthermore, through thermodynamic calculation, the decrease of Ca/Si ratios and increase of Al/Si ratios can improve the thermodynamic stability of C-A-S-H gels under sulfate attack, which agrees well with the experiment results.

In order to gain a molecular-level insight on the structure and performance of cement-based materials in high temperature environment, this paper investigates the structure, dynamics and mechanical properties of their main hydration product, calcium aluminosilicate hydrate (C-A-S-H), at elevated temperatures by using reactive molecular dynamics simulation. The results show that rising temperature can destroy the H-bond network of interlayer water molecules in C-A-S-H, leading to pronounced expansion of the interlayer regions. Meanwhile, interlayer water molecules lose its glassy water dynamics and exhibit dramatically high diffusivity with rising temperature. In addition, the calcium atoms show inhomogeneous dynamics at high temperature. At 1500K, the interlayer calcium atoms can escape from their coordination “cages” and diffuse, while the motion of those located in the principal layer are restricted by the Si–O and Al–O bonds throughout the simulation. Furthermore, reactive force field couples the mechanical response and chemical reaction during the uniaxial tensile test for C-A-S-H gel. The de-polymerization and hydrolytic reaction happens frequently in the deformed C-A-S-H gel at high temperature, resulting in degradation of stiffness and strength. On the other hand, the atomic rearrangement at elevated temperature contributes to the re-connection of broken chemical bonds, enhancing ductility of C-A-S-H.

Insulated polyimide (PI) composites filled with short glass fibers (SGF), polytetrafluoroethylene (PTFE), SiO2, and polyphenylene (PPL) are specially designed, prepared, and the tribological properties are systematically investigated with references to the special requirements for frictional materials used in ultrasonic motors. The hardness and thermal decomposition temperature of the insulated PI composites are comparable to that of conductive PI composites. However, these insulated materials present excellent friction and wear performance, especially under high loads and speeds. Scanning electron microscopy (SEM) analysis of the worn surface indicates that adhesive and fatigue wear dominate the wear mechanisms.

In this study, the cement paste corroded in sodium sulfate solution was regarded as a three-phase composites composing of unhydrated cement particles, reaction products and pores on meso-scale. First of all, based on the results of the in-situ X-ray Computed Tomography (X-ray CT) test, a three-dimensional (3D) meso-scale finite element (FE) model of the cement paste specimen was established. Subsequently, homogenization methods were used to calibrate the mechanical parameters (elastic modulus, Poisson's ratio and strength) of the model and the constitutive relations of unhydrated cement particles and reaction products were modified. Finally, the failure process of the cement paste specimens conducted by the uniaxial compression test was simulated. The results showed that the compressive strength of the cement paste specimens experienced a process of increasing first and then decreasing with the increase of corrosion time, caused by the combination of cement hydration and sulfate ion corrosion. Additionally, the simulation results and the uniaxial compression test results were in good agreement, indicating that the modified constitutive relations were effective and the 3D meso-scale numerical simulation can well predict the uniaxial compression test of cement paste specimen under the corrosion of sodium sulfate.

In this paper, the microstructure and resistance to chloride ion penetration of ultra-high-performance concrete (UHPC) prepared from lightweight aggregate (LWA) were studied through simulation and experiment. The effects of LWA with different particle sizes on the chloride ion transport properties of lightweight ultra-high-performance concrete (L-UHPC) were discussed through simulation test results. The random delivery model of LWA in L-UHPC was established by MATLAB, and the model was introduced into COMSOL. Through the comparative analysis of experimental data and simulation results, the repeatability of the proposed model and the simulation accuracy were verified. The results show that when the LWA particle size changes from 0.15–4.75 mm to 0.15–1.18 mm, the width of interfacial transition zone (ITZ) and the overall porosity of L-UHPC decrease. This is because the large particle size LWA has more open pores with larger pore diameters and related interconnections, which are potential channels for chloride ion transport. Therefore, the chloride ion transport properties in L-UHPC are inhibited, which is manifested by the “tortuosity effect” of the LWA.