Geopolymer is characterized by high strength, denseness, low thermal conductivity, and resource conservation, and it meets the needs of coarse-grained fill improvement for high-speed railway roadbed engineering in terms of seismic safety and feasibility of resource acquisition. The unconfined compression strength tests of geopolymer-stabilized fine-grained fillings with different mixing ratios of metakaolin and alkali-activator and the dynamic triaxial tests of geopolymer-stabilized coarse-grained fillings with different rock block contents and confining pressures were carried out. The mixing ratio of raw material and alkali activator for composing metakaolin-based geopolymer and their optimum mixing ratio in fine-grained fillings were analyzed. The impacts of rock block content and confining pressure on the dynamic characteristics of the geopolymer-stabilized coarse-grained fillings were discussed. The results indicated that the optimum ratio of metakaolin and alkali activator for composing geopolymer was 2:1, and their optimum content in fine-grained fillings was 15%; the maximum dynamic shear modulus of geopolymer-stabilized coarse-grained fillings had an approximately linear relationship with the rock block content and a non-linear relationship with the confining pressure; when the shear strain was normalized, the dynamic shear modulus ratios of the geopolymer-stabilized coarse-grained fillings were distributed in a narrow band, while the damping ratio showed a relatively high dispersion in values. The results of this study can provide the design parameter basis for the application and popularization of geopolymer-stabilized coarse-grained fillings.

Ethylene propylene diene monomer (EPDM) possessing nonpolar groups exhibits low dielectric loss and is one of the candidates for fabricating flexible dielectric materials. Incorporation of high amount of ceramics is commonly used to improve dielectric properties of EPDM. However, the high volume fraction makes EPDM rigid and enhances the complex viscosity of composite materials during manufacturing processes. In this study, high-barrier graphene (HBG), which is highly lamellar and thin (lamellar/thickness is approximately 3300), was selected as filler. The study aims to investigate the influence of low-loading HBG on the rheological, vulcanization, dielectric, mechanical, thermal and electric properties of EPDM. In this work, the Raman spectrum shows that the grain size and layer number of HBG is 70 nm and 3–4, respectively. Rheological measurement shows that 3

Reducing cement consumption by reutilizing solid wastes in soil stabilization and eliminating the residual by-product of cement hydration as much as possible could effectively improve the mechanical performance and economic benefits of problematic soils in underground engineering practices. This study employed red mud and phosphogypsum as additives to improve the engineering performance of cemented silty sands. A series of chemical, mechanical, and microstructural tests were conducted to investigate the optional mixing ratio of red mud and phosphogypsum to replace cement in silty sand stabilization, the strength improvement of silty sand with different total dosages of the composite binder (the mixture of cement, red mud, and phosphogypsum), the ratios of water to the composite binder, and curing ages compared with that stabilized with only ordinary Portland cement, and their mechanical performance enhancement mechanism. The results show that red mud and phosphogypsum could replace about 1/3 of cement consumption to the maximum in soil stabilization. The optional mixing ratio of cement: red mud: phosphogypsum for silty sand stabilization was 16:7:1. Compared with pure cement-stabilized silty sands, the silty sand stabilized with the composite binder achieved a superior mechanical performance at the initial age but a relatively slow increase over the curing age when the binder consumption was the same. The tensile and shear strength of silty sands stabilized with the composite binder were similar to that of only cement. The gradually disappeared calcium hydroxide and the downsized pores illustrated in microstructural observation implied that adding red mud and phosphogypsum in silty sand stabilization could not only compact the internal structure of the soil but also make up the defects of drying shrinkage and shrinkage cracking induced by the by-products of cement hydration. The results of this study can provide a reference for the resourceful utilization of red mud and phosphogypsum and for saving cement consumption in engineering practices.

The high moisture content and low strength of dredged soft soils result in significant difficulties in directly reutilizing them in engineering. Improving their mechanical properties effectively and achieving re-utilization with the maximum benefit in engineering is the key to disposing of dredged soils with high moisture content. This study investigated the influences of cement and steel slag ratio, moisture content, the maximum particle size of steel slag, and curing age on the compressive strength of dredged silty clay in a plastic flow state. The performance improvement of dredged silty clay stabilized with cement and steel slag was discussed by comparing to related previous studies. The strengthening mechanism of dredged soils stabilized with cement and steel slag was explored by microstructural observation. The results show that when the ratio of cement to steel slag was 9:6; namely, using steel slag to replace 40% of cement, the strength properties of dredged silty clay stabilized by cement and steel slag could ensure the minimum requirements of the project greater then 100 kPa, and their economics could achieve the best results. The finer the particle size of steel slag was, the better the stabilization effect was. The compressive strength of dredged silty clay stabilized by cement and steel slag with particle sizes of less than 0.075 mm was 1.06 times, 1.10 times, and 1.16 times that of 0.25 mm, 1 mm, and 2 mm and increased linearly over curing ages earlier than 28 days. The compressive strength of dredged silty clay stabilized by cement and steel slag cured for 28 days was 2.44 times, 1.59 times, and 1.36 times that of 3, 7, and 14 days, respectively. The evolution of microstructural characteristics showed that the internal pore sizes of dredged soil decreased the structural compactness increased significantly due to the formation of more calcium silicate hydrate and other agglomerated flocculent gel materials from the further reaction between steel slag and cement hydration products. The results of this study can provide technological parameters for the re-utilization of dredged soil stabilized with cement and steel slag.

In this study, 1-wt% fluorinated couple agents were firstly used to modify the surface of high barrier graphene platelets (HBG). Then the modified HBG were incorporated into ethylene propylene diene monomer (EPDM). Due to high lamellar size/thickness ratio (about 3300), untreated HBG (HBG-un) increase the complex viscosity of EPDM composites. The surface modification of HBG by heptadecafluoro-decyl-triethoxy silane (17F) can reduce the surface energy of HBG and then decrease the complex viscosity of EPDM/HBG-un from 21,000 to 13,000 Pa s (about 40% decrease) at 1.7 Hz. Due to the increased physical entanglement and C=C bonds, HBG-un can increase the tensile and tear strength of EPDM control by about 3 and 2 times, respectively. The surface modification of 17F can slightly reduce the tensile and tear strength of EPDM/HBG-un by 9% and 8%, respectively. HBG-un can increase the thermal conductivity and dielectric constant of EPDM control by 17% and 2.8 times increase, respectively. Surface modification of 1-wt% 17F can remarkably reduce the dielectric loss of EPDM/HBG-un by 50% at 20 MHz, slightly affecting the dielectric constant and thermal conductivity. In addition, HBG-un can decrease the volume and surface resistivity of EPDM control by 2 and 1 order of magnitude, respectively, while 1-wt% 17F can both increase the surface and volume resistivity of EPDM by one order of magnitude.

Geopolymer binder has the advantages of early strength, fast solidification, high volume stability, and low permeability. It is beneficial to improve the mechanical performance of silty sands, saving cement consumption and being environmentally friendly. However, the strength improvement of silty sand stabilized with steel slag-based geopolymer was significantly controlled by their material composition and technical parameters. This study conducted a series of unconfined compression tests to investigate the material composition of steel slag-based geopolymer binders and their reasonable mixing ratio for silty sand stabilization. The optimum mixing ratio of precursor (steel slag) to alkaline activator (the combination of Na2SiO3 and CaO) and the optimum dosage of steel slag-based geopolymer for silty sand stabilization were explored. The strengthening mechanism of geopolymer-stabilized silty sands was discussed based on microstructural images and elemental concentrations of primary components observed by SEM and EDS. The results show that when the mass ratio of steel slag : Na2SiO3 : CaO was 80:35:21, and the steel slag-based geopolymer material was 15%, the silty sand could achieve the best mechanical performance improvement. The microstructural characteristics of geopolymer-stabilized silty sands at different curing ages illustrated that the compactness and integrity of silty sand structures were enhanced over the curing age. The improving cementitious contact among particles and enlarging particle size was responsible for the strength improvement of silty sand. This research can provide a reference for applying steel slag-based geopolymer in silty sand stabilization in engineering practices.

Geopolymer binders are adjudged as the latest wave of sustainable alkali-activated materials for soil stabilization due to their excellent bonding properties. This study applied metakaolin as a precursor for synthesizing the geopolymer binder by employing the mixture of quicklime and sodium bicarbonate as an alkali activator. The optimal mass mixing ratio of the alkali activator, metakaolin, and silty clay was determined by unconfined compression tests. The stabilization mechanisms of the geopolymer binder were measured by x-ray diffraction and Fourier transform infrared spectroscopy. The microstructural characteristics of the geopolymer-stabilized silty clay were observed by scanning electron microscopy with an energy dispersive x-ray spectroscopy and mercury intrusion porosimetry test for understanding the strengthening mechanism of the silty clay after the treatment. Results indicate that the optimal mass mixing ratio of the alkali activator, metakaolin, and silty clay is 1:2:17, and the unconfined compressive strength of the geopolymer-stabilized silty clay reaches the maximum value of 0.85 MPa with adding 15 wt% of the geopolymer binder. Diffraction patterns show an insufficient polymerization of the geopolymer binder in the silty clay in the early days but a rapid synthesis of aluminosilicate gels after that. The new asymmetrical stretching vibration peaks signified the formation of aluminosilicate networks and are responsible for the strength improvement of the silty clay. Microstructural analyses further confirm the formation of aluminosilicate gels and their positive impacts on the structure of the silty clay over curing age.

For dielectric elastomers, the high loading of high k ceramic fillers can increase the dielectric constant of elastomers, but their Young’s modulus can also be greatly increased and the high loading of filler increases the complex viscosity of composites during manufacturing process. In this study, graphene platelets (GE) fabricated by plasma-enhanced chemical vapor deposition (PECVD) is used to improve the dielectric constant of ethylene propylene diene monomer (EPDM)-based elastomer. The dependence of the cure, electrical, rheological, dielectric and mechanical properties of EPDM-based elastomers on amount of GE is analyzed. It is found that the addition of 0.5% graphene platelets can increase the dielectric constant of EPDM control from 2.0 to 6.6 (230% increase) at 10 3 Hz, with little change of electric resistivity. Moreover, the addition of 0.5% graphene platelets decreases the complex viscosity of EPDM control from 48,000 to 16,500 Pa S (1.9 times decrease) at 1.7 Hz. Compared to EPDM control, the 0.5% graphene increase the relative ratio of dielectric constant to Young’s modulus by 180%.

The issue of high driving voltages limits the commercial application of dielectric elastomer transducers, but increasing dielectric permittivity and reducing the Young’s modulus of elastomers is a means of lowering this driving voltage. However, dielectric elastomer fabrication, which fulfills simultaneously high dielectric permittivity and a low Young’s modulus, is difficult. In this study, we explore the combined usage of ionic liquids and glycerol as soft fillers with high dielectric permittivity in silicone-based elastomers. We also fabricate a foamed structure in silicone elastomers to lower further the Young’s modulus of the elastomers. Surprisingly, it is found that nitrogen atoms in the cations of ionic liquids (ILs) do not inhibit the platinum (Pt)-catalysed hydrosilation of silicone elastomers when ILs are dissolved in glycerol. The effect of molecular structure and the amount of ILs on the electrical breakdown strength, rheological, dielectric and mechanical properties of silicone-based elastomers is analysed herein. Compared to the pure elastomer, the combined usage of 5% 1-butyl-4-methylpyridinium tetrafluoroborate with 10% glycerol can improve the relative ratio of dielectric permittivity to the Young’s modulus almost eleven-fold at a given electrical field below the electrical breakdown field.

The environmentally friendly technology of high-frequency ultrasonic processes with the mostly concerned frequencies of 200 kHz and 400 kHz were applied and investigated systematically for BPA degradation in both pure water and river water mediated conditions. Investigations were carried out examining the effects of crucial parameters determining the system efficiency and BPA degradation mechanisms. Results proved that BPA was efficiently degraded via the oxidation by .OH. The 400 kHz ultrasonic process demonstrated much stronger capability in generating .OH and corresponding higher efficiency in BPA degradation based on electron spin resonance analysis. Increasing solution volume could increase the radical yields, and the temperature increase rate (dT/dt) showed linear relationship with k(obs). In addition, the degradation of BPA with different concentrations was for the first time found controlled by different limiting factors, in which the degradation only with higher concentrations (>= 0.02 mM) conformed to the Langmuir-Hinshelwood mechanism. More acidic condition and the bulk temperature of about 40 degrees C favored BPA degradation. The presence of NO3-, SO42-, and Cl- demonstrated minor influence while CO32-, HCO3- and NO2- showed significant inhibition, and the effects of different anions also depended on their concentrations. The degradation rate decreased 23% when river water was used as the matrix. Furthermore, both hydroxylation of the benzene ring and attack on the connecting carbon were found to be the reaction pathways, and the latter was proposed to be more dominant. (C) 2019 Elsevier Ltd. All rights reserved.

For the field of flexible electronic materials, titanium carbide (TiC) is still a new member that needs to be further investigated. In this study, the effects of surface modification, TiC content and ethylene alpha olefins (POE) amount on dielectric properties of ethylene propylene diene copolymer (EPDM) are investigated in detail. The addition of 20% modified TiC particles can improve the dielectric constant of EPDM control from 2.4 to 8.7 (360% increase) at 105 Hz. However, the complex viscosity of EPDM control increases by 6.4 times at 1.7 Hz and the volume resistivity decreases by 3 order of magnitude. Moreover, the thermal conductivity of EPDM control only increase by 17%. By comparison, the 20% POE not only increases the dielectric constant of EPDM/TiC (10/2) from 8.7 to 13.5 (55% increase) at 105 Hz, with slight decrease of volume resistivity, but also decreases the complex viscosity of EPDM/TiC (10/2) from 1.19 × 105 Pa·S to 5.78 × 104 Pa·S (51% decrease) at 1.7 Hz. Meanwhile, the addition of 20% POE can further enhance the thermal conductivity of EPDM/TiC (10/2) from 0.281 W/(m·K) to 0.416 W/(m·K) (48% increase).

ABSTRACTThe aim of this study is to improve the dielectric and mechanical properties of HDPE/BaTiO3 composites by binary BaTiO3 particles, when the volume fraction of BaTiO3 is constant. In this study, it was found that the pack density of binary BaTiO3 particles in HDPE/BaTiO3 composite relies on particle ratio and volume fraction of small particles. It is found that the addition of 50 vol % 1600 nm BaTiO3 particles can boost the dielectric constant of HDPE control from 2 to 30 (14 times higher) at 40 Hz and 19 (8.5 times higher) at 40 MHz, respectively. When the particle ratio was 4, the substitution of 10 vol % 1600 nm BaTiO3 particles by 10 vol % 400 nm BaTiO3 particles can further enhance the dielectric constant of HDPE/L‐BT (10/10) from 30 to 50 (67% increase) at 40 Hz and from 19 to 42 (121% increase) at 40 MHz, respectively, without greatly influencing the volume resistivity of HDPE composites. In addition, the thermal conductivity of HDPE with binary BaTiO3 particles were all above 2.0 W/(m•K). © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 1101–1108

In order to fabricate barium titanate (BaTiO3) particles with high purity, small particle size and narrow distribution of particle size, the synthesis methods and doping elements should be properly selected. Compared to polar polymers, non-polar polymers have advantages on the fabrication of miniaturized and lightweight electronic devices, due to excellent process-ability and little endogenous heat generated in the electric field. To avoid the aggregation of BaTiO3 particles in polymer matrix, several nanometer thick organic coating on the BaTiO3 surface is needed. What's more, the alignment of BaTiO3 and hybrid use of fillers can further improve the dielectric properties of polymer/BaTiO3 composites.

ABSTRACTIn this study, mica, treated by three types of coupling agents, isopropyl trioleic titanate (NDZ105), 3‐aminopropyltriethoxysilane (KH550), and vinyltrimethoxysiloxane homopolymer (SG‐Si6490), were utilized to improve the properties of ethylene propylene diene monomer (EPDM)/barium titanate (BaTiO3) composites. It is found that the addition of untreated mica can increase the complex viscosity, while the KH550 modified mica can reduce the complex viscosity. Compared to single usage of coupling agent SG‐Si6490, the hybrid usage of KH550 and SG‐Si6490 can further increase the tensile strength of EPDM/BaTiO3/SG‐Si6490 treated mica (70/20/10) from 9.10 to 11.01 MPa (22% increase). The untreated mica can increase the interfacial polarity and improve the dielectric constant of EPDM/BaTiO3 (70/30) from 7 to 9 at 40 MHz (28% increase). Moreover, the KH550 treated mica can enhance the thermal conductivity of EPDM/BaTiO3 (70/30) from 0.323 W m−1 K−1 to 0.446 W m−1 K−1 (38% increase). In the meantime, the increased crosslink density caused by coupling agents can increase the volume resistivity of EPDM composites. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44833.

In this study, ethylene propylene diene monomer (EPDM)/barium titanate (BaTiO3)/mica (or graphite) composites with different volume fraction of mica (or graphite) were prepared by two-roll milling process. Thermal conductivity, crosslink density, cure, rheological, mechanical and dielectrical properties of composites were investigated. The results of rheological properties indicated that the 15 vol% mica made the complex viscosity of EPDM/BaTiO3 compound to become non-sensitive to varying shear. In terms of mechanical properties, only 5 vol% graphite flakes remarkably improved the tensile strength of EPDM/BaTiO3 (70/30) from 7.47 MPa to 13.20 MPa (76% increase). By comparison, the 20 vol% mica just increased the tensile strength of EPDM/BaTiO3 (70/30) to 12.10 MPa. In addition, 20 vol% graphite flakes boosted the thermal conductivity and dielectric constant of EPDM/BaTiO3 (70/30) from 0.323 W m(-1) K-1 and 7.1 at 40 MHz to 2.421 W m(-1) K-1 (749% increase) and 70 at 40 MHz (almost 1000% increase), respectively. The excellent electric and thermal performance was attributed to the mobile n electrons in graphite flakes. (C) 2017 Elsevier Ltd. All rights reserved.

The aim of the study was to use carbon fibers and carbon blacks to improve the thermal conductivity, mechanical and dielectric properties of ethylene propylene diene monomer (EPDM)/barium titanate (BaTiO3) composites. It was found that 7.5 vol% carbon blacks, with high specific surface area, can make complex viscosity of EPDM/BaTiO3 compound to become non-sensitive to varying shear. Due to the sulfuric atom and C=C groups on surface of carbon blacks, 10 vol% carbon blacks can enhance the tensile strength and tear strength of EPDM/BaTiO3 (70/30) from 9.00 MPa and 21.06 kN m−1 to 14.32 MPa (59% increase) and 30.02 kN m−1 (43% increase). It was found that the 10 vol% spherical carbon blacks with high specific area can partially contact BaTiO3 and fill the gap between BaTiO3 particles to increase thermal conductivity and dielectric constant of EPDM/BaTiO3(70/30) from 0.323 W m−1 K−1and 7 at 5 MHz to 0.632 W m−1 K−1 (95% increase) and 746 (106 times increase) at 5 MHz, respectively. When the filler content was 10 vol%, carbon blacks and carbon fibers can decrease the volume resistivity of EPDM/BaTiO3 (70/30) from 2.23 × 1013 to 6.37 × 105 Ω m (eight order of magnitude drop) and 4.25 × 1011 Ω m (two order of magnitude drop), respectively.

This paper studies how the addition of Carbon nanotubes (CNT) influencing the properties, especially the mechanical properties and colorimetry of ethylene propylene diene rubber (EPDM)/SiO 2 composites. The results show that the increased content of CNT can turn EPDM/SiO 2 composites from lighter, redder, and yellower to darker, greener and bluer, respectively. The total color change (ΔE) of EPDM/SiO 2 composites would be acceptable when the CNT content is below 3%. When the CNTs content reaches 4%, the tensile strength of EPDM is the maximum.

This paper studies how the addition and various content of Carbon nanotube (CNT) affecting the properties, especially the color difference of ethylene propylene diene rubber (EPDM)/ CaCO3 composites. The results show that the increased content of CNT can turn EPDM/CaCO3 composites from lighter, greener, and bluer to darker, redder and yellower, respectively. The total color change (ΔE) of EPDM/CaCO3 composites is acceptable, when the content of CNT is less than 2wt%. The optimum tensile strength of EPDM composites can be gained, when the content of CNT is 3%.

In this study, 3-Aminopropyltriethoxysilane (KH550) with polar amino groups is applied to modify the surface of Barium titanate (BaTiO3) particles. When volume fraction of BaTiO3 further increases to 50 vol%, the dielectric constant and loss of HDPE control increase from 2.5 and 0.02 to 18.5 and 0.10 at 10 MHz, respectively, with the volume resistivity of HDPE control decreasing from 3.6 × 1013 Ω m to 3.5 × 1011 Ω m. The increased amount of modified BaTiO3 can increase the flexural strength and modulus HDPE composites from 8 and 90 MPa to 14 and 780 MPa, respectively. However, the increase of modified BaTiO3 can restrict mobility of HDPE chains and decrease the crystallinity of HDPE composites.

In this work, three types of coupling agents: isopropyl trioleic titanate (NDZ105), vinyltriethoxysilane (SG-Si151), 3-aminopropyltriethoxysilane (KH550) were applied to modify the surface tension of Barium titanate (BaTiO3) particles. The Fourier transform infrared (FT-IR) spectra confirm the chemical adherence of coupling agents to the particle surface. The long hydrocarbon chains in NDZ105 can cover the particle surface and reduce the polar surface tension of BaTiO3 from 37.53 mJ/m(2) to 7.51 mJ/m(2), turning it from hydrophilic to oleophilic properties. The short and non-polar vinyl groups in SG-Si151 does not influence the surface tension of BaTiO3, but make BaTiO3 have both hydrophilic and oleophilic properties. The polar amino in KH550 can keep BaTiO3 still with hydrophilic properties. It is found that SG-Si151 modified BaTiO3 has the lowest interaction with HDPE matrix, lowering the storage modulus of HDPE composites to the greatest extent. As for mechanical properties, the polar amino groups in KH550 on BaTiO3 surface can improve the adhesion of BaTiO3 with HDPE matrix, which increases the elongation at break of HDPE composites to the greatest extent. In terms of electrical properties, the polar amino groups on surface of BaTiO3 can boost the dielectric properties of HDPE/BaTiO3 composites and decrease the volume resistivity of HDPE/BaTiO3 composites. The aim of this study is to investigate how functional groups affect the rheological, mechanical and electrical properties of HDPE composites and to select a coupling agent to produce HDPE/BaTiO3 composites with low dielectric loss, high dielectric constant and elongation at break. (C) 2015 Elsevier B.V. All rights reserved.