Electrostatic self-assembly method (ESAM) was used to prepare bentonite supported-nano titanium dioxide photocatalysts. The materials were characterized by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). Methyl orange was used to estimate the photocatalytic activity of the materials. The effects of the calcination temperature and silane dosage on the photocatalytic activity of the samples were investigated. The experimental results show that the bentonite facilitates the formation of anatase and restrains the transformation of anatase to rutile. Part of nano-size TiO2 particles insert into the galleries of bentonite. The photocatalysts exhibit a synergistic effect of adsorption and photocatalysis on methyl orange. Photocatalysts prepared by ESAM method exhibit higher photocatalytic activity and better recycle ability than those of the traditional method.
Polyurethanes/multi-walled carbon nanotube (PU/CNT) composites were prepared with a help of ultrasonically dispersing CNT in the traditional procedure of synthesizing polyurethane. In this case, the various loading levels, sizes and surface-modified groups were considered to regulate the mechanical performances of the PU/CNT nanocomposites. Moreover, the structure and mechanical properties of all the PU/CNT nanocomposites were investigated by attenuated total reflection-Fourier transform infrared spectroscopy, dynamic mechanical analysis, scanning electron microscope, transmission electron microscope, and tensile testing. The experimental results showed that a moderate loading-level of 0.1wt% and a diameter of 10–15 nm for CNT could produce the maximum tensile strength and elongation while it was worth noting that the surface carboxylation of CNT could further enhance the tensile strength and elongation of the PU/CNT nanocomposites.
Ag modified ZnO (Ag/ZnO) nanocrystals were prepared by a facile and low temperature wet chemical method. The phase structures, morphologies, and optical properties of the as-prepared samples were characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), the Brumauer-Emmett-Teller (BET) surface area, UV-vis diffuse reflectance spectroscopy and photoluminescence (PL) spectra, respectively. The photocatalytic performance of Ag/ZnO with diffent Ag contents was measured with the degradation of methyl orange (MO) at room temperature under UV light irradiation. The experimental results indicated that the well-crystalline ZnO nanopaticles with a size of ca. 4.5 nm exhibited a high photocatalytic activity for the degradation of MO with the apparent rate constant (k) of 1.57 ×10−2 min−1, and the photocatalytic activities of ZnO were further enhanced by modification with silver. When the Ag loading was 3mol%, Ag/ZnO showed the highest photocatalytic acitivity with a k value of 5.452×10−2 min−1, which is 3.5 and 2.5 time more than that of ZnO and commercial P25, respectively.
The effects of photostabilizers of ultraviolet absorbers (UVA), hindered amine light stabilizer (HALS) and pigment on surface color change and mechanical properties of weathered wood-flour/polyethylene (HDPE) composites were investigated. After being added UVA with high UV absorbance, the WPC exhibites better ability to resist color fading and mechanical property loss. High molecular weight HALS is found to be the most effective in controlling long term fading and yellowing changes. Pigments cover the composites for remaining the original color after weathering regardless of less contribution to mechanical property. Addition of photostabilizer and pigment together show great synergism in decreasing color fading and flexural property loss.
The normal temperature corrosion of VC coating on the substrate of Cr12MoV prepared by TD process was tested in 5% NaCl aqueous solution, its surface morphologies and corrosion components after salt spray were observed with SEM and EDS, respectively, and the effects of salt spray on micro-structures of VC coating were analyzed. Moreover, the invalidation mechanism of VC coating after salt spray and its effect on substrate material were discussed. The experimental results shown that the uniformity and integrity of VC coating surface are destroyed by salt spray for 120 h, a large number of the pits are produced on the coating surface, and the coating falls off, which speeds corrosion breakage of its substrate; the oxidated film on its surface becomes rougher, broken and discontinuous, and falls off easily, which reduce the ability of resistance salt spray; the failure modes of VC coating after salt spray are expressed with falling off of oxidated film, stress concentration and pore effect and so on, the corrosion breakage of oxidated fi lm is the corrosion result of deoxidization corrosion from oxygen and HCl produced by NaCl and vapor.
The influences of titanium modification on the solidification behavior, shrinkage characteristic and primary austenite refinement of cast steel ZG270-500 smelted in intermediate frequency induction furnace were studied. 0.15wt% titanium modification increased the fluidity of the steel liquid, enhanced the feeding capacity of cast steel, changed the dispersed shrinkage porosity to concentrated shrinkage cavity, turned the coarse dendrites into fine equiaxed grain structures and greatly reduced the primary austenite grain size. By scanning electron microscope (SEM) and energy disperse spectroscope (EDS) analysis, it was found that titanium combined with carbon to be solid phase particles TiC, with high melting point, to promote the primary austenite nucleation authentically by non-spontaneous nucleating. The crystal lattice match growing model between γ-Fe and TiC was established. The mechanism of TiC heterogeneous nucleating existed in that the primary austenite grew up by {111}γ-Fe parallel to the closest packed plane {111}TiC in the crystal orientation 〈110〉γ-Fe//〈211〉TiC. The crystal planes mismatch $\delta _{\{ 111\} _{\gamma - Fe} }^{\{ 111\} _{TiC} } $ and the lowest orientation mismatch $\delta _{\{ 110\} _{\gamma - Fe} }^{\{ 110\} _{TiC} } $ were 8.18%. and 2.25% respectively, almost achieving complete coherent lattice match growing of austenite on TiC.
In order to produce the hear-resistant inner layer of hot-forging die, the plasma spraying and plasma re-melting and plasma spray welding were adopted. Substrate material was W6Mo5Cr4V2, including 10%, 20%, 30% tungsten carbide (WC) ceramic powder used as coating material to obtain different Nickel-based WC alloys coating. Micro-structure and micro-hardness analysis of the coating layer are conducted, as well as thermophysical properties for the coating layer were measured. The experimental results show that the coating prepared with 70%Ni60, 30%WC powder has the best properties with plasma spray welding, in which the micro-hardness can achieve 900HV, meanwhile it can improve the thermal property of hot-forging die dramatically.
The corrosion behavior of Al-Zn-Sn-Ga alloy in 3.5% NaCl solution was investigated by corrosion morphology observation and electrochemical testing. The experimental results show that there exist three stages during the course of corrosion. At the initial stage, pitting occurs surrounding the precipitates, which is driven by the galvanic couple effect. At the middle stage, pitting rapidly extends toward the horizontal direction, forming the shallow circular structure caused by the deposition of Ga ions around Sn. At the final stage, the new active sites led to the continuous corrosion of the alloy.
The stress corrosion cracking(SCC) behaviour of 7A52 aluminum alloy in air and in 3.5% NaCl solution was researched by slow strain rate test(SSRT) and SEM-EDS. The SCC susceptibility was estimated with the loss of the reduction in area. The experimental results indicate that the SCC susceptibility of 7A52 aluminum alloy in 3.5% chloride solution is the highest at strain rate of 1×10−6 s−1. The lowest one is under the condition of 1×10−5 s−1. Stress concentration and anode dissolving around Al-Fe-Mn intermetallics initiate micropores which will result in microcracks. The existence of intermetallics in the microstructure may play an important role in understanding the SCC initiation mechanisms of 7A52 aluminum alloy.
Ir coatings were deposited on the heat-treated C/C composites and graphite by double glow plasma. Microstructure and morphology of the coating and substrate were observed by SEM and TEM. The effect of the surface treatment for the carbon structural materials on the microstructure of the coating was investigated. Many large gaps and pores appeared on the surface of the substrates after heat treatment. The Ir coating did not fully covered on the surface of heat-treated C/C composite and graphite substrates because of the large gaps and pores on the surface of substrates. The Ir coating exhibited excellent ablation resistance at super-high temperature. After super-high temperature ablation, the coating kept the integrity, but the coating was weekly bonded to the substrates. Some microcracks and micropores appeared on the surface of as-ablated coating. The Ir coating would need thick enough to cover and fill the large microgaps and micropores on the surface of the heat-treated C/C and graphite substrates.
With the aid of hydrogen permeating devices, the hydrogen permeation behaviors of X52 pipeline steel in NACE A solution with saturated H2S/CO2 were studied under the conditions of different ambient temperatures and pH values, and the hydrogen permeation behaviors of X52 pipeline steel in weld seam zone were comparatively studied. The experimental results show that the hydrogen permeation coefficient value is directly proportional to the time required for reaching the saturation anode current and inversely proportional to the saturation anode current, and the hydrogen permeation coefficient is influenced by the corrosion scales; the temperature is directly proportional to the saturation anode current, and the hydrogen permeation coefficient is influenced by the temperature and corrosion scales, heat-affected zone and matrix zone in NACE A solution with saturated H2S/CO2 at normal temperature. The hydrogen permeation coefficient in weld seam zone is larger than that in heat-affected zone which is further larger than that in matrix zone.
Different morphologies of β-FeOOH were prepared by hydrothermal synthesis using NaH2PO4 as structural modifier. The rod-shaped, straw-like and flower-like products could be controllably obtained. The as-obtained products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and Ultraviolet-visible (UV-Vis) absorption spectroscopy. The experimental results show that the morphology manipulation could be achieved by adding different amounts of NaH2PO4. XRD pattern indicates that the asprepared sample is the pure tetragonal phase of β-FeOOH. UV-Vis absorption spectra of the products are affected by their morphologies, which shows that both the rod-shaped and straw-like β-FeOOH have outstanding absorption ability on the whole UV area (200–400 nm), which will have vast application prospects in UV protection.
The surface condition, some properties and ion releasing behavior of cobalt-chromium (Co-Cr) dental alloy formed by selective laser melting (SLM) technique were investigated. Before porcelain fused firing, the surface condition of the Co-Cr alloy was observed using a scanning electron microscope (SEM), and then the density and hardness were examined. After porcelain fused firing, the interface of porcelain and alloy was observed, and then the metal-ion release of the samples was tested. SLM technique provides Co-Cr alloy higher hardness than casting method. After degassing-oxidation procedure and porcelain fused firing, the interface of the alloy and porcelain showed excellent combination. Co ion was more than Cr ion released from SLM Co-Cr alloy, the amounts of Co and Cr ions were safe according to ISO security criterion. Considering the properties before and after porcelain fused sintering process, SLM technique is suitable for dental Co-Cr alloy restoration.
The aim of the present work was to investigate the swelling behavior and the in vitro release of acemetacin and bovine serum albumin from alginate gel beads crosslinked with Ca2+ or Ba2+. The release profiles suggested that the extent of swelling of the alginate beads played an important role in the release of drug. Small drugs are mainly released via diffusion through the alginate gel matrix. Compared with small drugs, large molecule drugs are difficult to diffuse through the pores of the matrix bead until the beads swell to a certain extent to provide enough large pores. The Ba2+ crosslinked alginate beads showed slower release rate compared with the Ca2+ crosslinked alginate beads, whether loaded the large molecules or small drugs. In conclusion, the Ba2+ crosslinked alginate beads are considered more suitable than Ca2+ crosslinked alginate beads for using as a sustained release vehicle especially for large molecule drugs.
The AgBr powder was prepared by a hydrothermal method via a reaction of AgNO3 with hexadecyltrimethy ammonium bromide (CTAB), namely, CTAB-assisted synthesis method. The selective-adsorption ability of the AgBr samples for the MO was evaluated in a MO and Rhodamine B mixed solution via ultraviolet-visible spectra. Compared with the AgBr sample prepared from NaBr solution, it was found that the AgBr powder synthesized by CTAB-assisted method exhibited high selective-adsorption performance for the MO in the MO-RhB mixed system. After aged for 60 min, the MO could be efficiently removed by CTABassisted AgBr powder. Considering the potential wide applications of the selective adsorption, the CTABassisted AgBr provides a new and efficient method for the removal of various dyes and is possible to be widely used in industries.
The molecular geometry, electronic structure, thermochemistry and infrared spectra of [Mg(CHZ)3](ClO4)2 and [Mg(CHZ)3](NO3)2 were comparatively studied using the Heyd-Scuseria-Ernzerhof (HSE) screened hybrid density functional with 6–31G** basis set. The experimental results show that the complexes have six-coordinated octahedron feature, and the metal-ligand interactions are predominantly ionic in nature. The calculated heats of formation predict that [Mg(CHZ)3](NO3)2 is more stable than [Mg(CHZ)3](ClO4)2. Detailed NBO analyses indicate that the ligand-anion interaction plays an important role in the stability for these two energetic complexes. Moreover, the stretching vibration frequencies of N-H bonds shift to lower wave number compared to the free CHZ ligand, which are caused by the delocalizations from N-H bond orbital to lone-pair electron antibond orbital of magnesium.
Polycarboxylate (PC) superplasticizers with different chemical structures were synthesized through free radical co-polymerization reaction. A total organic carbon analyzer was used to investigate adsorption behaviors of PCs, and to evaluate influences of soluble salts on absorption properties of PCs. It is found that adsorption ratios of PCs on cement particles decrease greatly with the addition of Na2SO4; the adsorption ratio of ethers PC with Hydroxyethyl methacrylate (HEMA) group first increases then decreases with the addition of NaCl; the adsorption ratio of esters PC with short side chains first decreases then increases, while the adsorption ratio of ethers PC with HEMA group decreases with the addition of CaCl2; the adsorption ratio of esters PC with short side chains decreases with the addition of Ca(NO3)2; AlCl3 causes the decrease of the adsorption ratio of ethers PC with HEMA group.
Long chain semiaromatic polyamides with high molecular weight were synthesized by the reactions of undecanediamine with various aromatic diacids, and characterized by fourier transform infrared spectra (FT-IR) and nuclear magnetic resonance (1H-NMR). The thermal behaviors were determined by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The solubility, dynamic mechanical, physical and mechanical properties of the polyamides were also investigated. The experimental results show that the polyamides with high molecular weights are obtained only the PH value of the polyamides salt are in the range of 7.2–7.4. The melting temperatures and the glass transition temperatures of the polyamides increase with the increase of the rigidity of aromatic diacids, and are near to those of poly(nonamethyleneterephthalamide) (PA9T).
Liquid carboxyl-terminated poly(butadiene-co-acrylonitrile)(CTBN)-epoxy resin(EP) prepolymers were prepared with different contents of CTBN. The chemical reactions between EP and CTBN were characterized by Fourier ransform infrared (FTIR) spectroscopy and gel permeation chromatography (GPC). The scanning electron micrograph (SEM) and dynamic mechanical analysis (DMA) of curing films showed phase separation, and the rubber particles were finely dispersed in the epoxy matrix. Mechanical properties analysis of curing films showed that impact strength and elongation at break increased significantly upon the addition of CTBN, indicating good toughness of the modified epoxy resins. Thermogravimetric analysis (TGA) showed that the incorporation of CTBN had little effect on the thermal stability of EP. Fusion-bondedepoxy (FBE) powder coatings modified with CTBN-EP prepolymers were prepared. The experimental results demonstrate the ability of CTBN-EP prepolymers, toughening technology to dramatically enhance the flexibility and impact resistance of FBE coatings without compromising other key properties such as corrosion protection.
A new Nylon 11 (PA11)/polyethylene-octene (POE) blends compatibilized by maleic anhydride grafted mixture polyethyleneocten (POE-g-MAH) was prepared through melt blending method. The isothermal crystallization kinetics and melting behaviors of PA11/POE blends were investigated in detail by differential scanning calorimetry (DSC) and polarized optical microscope. The n values of PA11 blending with POE or POE-g-MAH are almost similar with pure PA11, which indicates that the effect of POE and POE-g- MAH on nucleation and growth of PA11 crystal is slight. The overall crystallization rate of PA11/POE blends are higher than ones of pure PA11 at the same crystallization temperatures, but they decrease significantly when POE-g-MAH is added into PA11/POE blends. DSC heating curves of both PA11 and its blends exhibit two melting peaks, but the two melting peak become weaker when POE-g-MAH is add into PA11/POE blend systems. And the spherulite size is reduced signifi cantly by the addition of POE-g-MAH compared with pure PA11 and PA11/POE blends.
Calcium carbonate with three-dimensional chrysanthemun flower-like structure was successfully prepared from calcium chloride and sodium carbonate ethanol/water mixed solution by a simple precipitation method, using trisodium citrate as crystal modifier. The experimental results show that the three-dimensional structure of chrysanthemun flower-like calcium carbonate is built up with several symmetrical micrometer multi-layer petals arranged around the multi-layer pancake-liked center, and the micrometer center and petals are assemblied by a large number of nanometer spherical particles with size 10–20 nm. It is found that the amount of trisodium citrate, the ethanol volume content has an important influence on the formation of this morphology. A possible mechanism is proposed to explain the formation of three-dimensional chrysanthemun flower-like calcium carbonate according the results. Scanning electron microscopy (SEM), X-ray powder diffraction (XRD), flourier transform infrared spectroscopy (FT-IR), thermogravimety analysis (TG), transmission electron microscopy (TEM) equipped with energy-dispersive X-ray (EDX), and selected area electron diffraction (SAED) were used to characterize the crystals.
Dense and submicron-grained NiAl-Al2O3 composite was fabricated by pulse current auxiliary sintering (PCAS). Its microstructure was analyzed by XRD, SEM and TEM, and its mechanical behavior was evaluated through compression test and fracture toughness test. The average grain sizes of NiAl and Al2O3 are about 200 nm and 100 nm respectively. The Al2O3 particles dispersed in NiAl matrix, forming intergranular structure and intragranular structure. During sintering, Al2O3 particles were remarkably spherized due to the unique sintering mechanism of PCAS, which is beneficial to the improvement of toughness. The NiAl-Al2O3 composite exhibits high compressive yield strength, whether at room temperature or elevated temperature. Its room-temperature (23 °C) and elevated-temperature (1 200 °C) compressive yield strength are up to 2 050 MPa and 140 MPa, respectively. Meanwhile, its fracture toughness is significantly enhanced, which is up to 8.2 MPa/m1/2. It is suggested that the main strengthening-toughening mechanisms are grain refinement strengthening and Al2O3 dispersion strengthening. The fracture of larger NiAl grain is the transgranular cleavage and this is induced by crack tip deflection and grain boundary weakening which are caused by intergranular and intragranular Al2O3 particles, respectively.
A multipoint excitation experiment system of the 1Cr18Ni9 steel plate-pipe network as the main vibration body was established, which used transient flow produced by the wave exciter to excite the 1Cr18Ni9 steel plate-pipe network to vibrate. The experimental results show that the 1Cr18Ni9 steel plate vibrates in three dimensions. The vibrations of the particles of the steel plate distributing along the pipe’s axial have phase differences and take place near the cylinder side first. Therefore, it is a multipoint vibration mode. The amplitude of the 1Cr18Ni9 steel plate increases as the system pressure increases and decreases as the wave exciter’s frequency decreases. The vibration intensity of the particles of the 1Cr18Ni9 steel plate close to the cylinder is the strongest and the amplitude is the highest in Y direction at a given system frequency. The vibration intensity of the particles close to the wave exciter is the strongest and the amplitude is the smallest in Z direction at a given system pressure.
Effect of rare earth alloy modification on properties and microstructure of high carbon equivalent gray cast iron was investigated. The experimental results show that in the way of mechanical property, when the addition of rare earth alloy is 0.2% and 0.3%, the tensile strength of cast iron increases. In the way of microstructure, the addition of rare earth alloy increases the number of primary austenite dendrites, reduces secondary dendritic arm spacing, and changes the eutectic size and quantity. When rare earth alloy is added into gray cast iron, the morphology and quantity of graphite play a major role on the improvement of tensile strength.
Polyacrylamide-urea-sulfanilamide(PUS) was prepared as a novel heavy metal ions chelator and successfully used to simultaneously remove heavy metals from wastewater effluents. The effects of reaction parameters (sodium hydroxide, material ratio, temprature and contact time) were monitored to specify the best synthesis conditions. PUS was chemically characterized by means of infrared spectroscopy (FTIR) and ultraviolet-visible (UV-Vis). The simultaneous chelation performance of PUS towards selected heavy metals ions, Ni2+, Cu2+, Pb2+, Zn2+, Cd2+ was discussed, showing that Ni2+, Cu2+, Pb2+, Zn2+ could be better chelated. It is indicated that the synthesized PUS is a potential remediation material when used for the treatment of wastewater containing metal ions.
The microstructure and dielectric properties of Ag(Nb0.8Ta0.2)1−x(Mn0.5W0.5) xO3 (x=0, 0.04, 0.08, 0.12, 0.16) ceramic system were investigated. The Ag(Nb0.8Ta0.2)1−x(Mn0.5W0.5) xO3 ceramics were prepared by the traditional solid-state reaction method and were characterized by X-ray diffraction (XRD), scanning electron microscopy(SEM) and Raman spectrometer. The sintering ability and dielectric properties of Ag(Nb0.8Ta0.2)1−x (Mn0.5W0.5) xO3 were found to be improved with the doping of Mn4+ and W6+ ions. The densification temperature of Ag(Nb0.8Ta0.2)1−x(Mn0.5W0.5) xO3 ceramics decreased from 1 080 °C to 1 000 °C when x increased from 0 to 0.16. Ag(Nb0.8Ta0.2)1−x(Mn0.5W0.5) xO3 ceramic was found to have the best dielectric properties when x=0.08, larger permittivity (ɛ=547) and smaller dielectric loss (tanδ=0.00156).
The paving segregation of asphalt mixture was closely related to the structure size and using parameters for the screw distributor of paver, and the paving uniformity of the mixture was determined by the screw blade diameter, pitch, and the position of the mixture in the screw distributor. Through researching the kinematics of the mixture in the screw distributor, the mathematical model was established, and the mathematical model was related with structural parameters, used parameters and material parameters. Through the mathematical model, the various parameters on the screw distributor job performance were analyzed, and the unstable area, meta-stable area and stable area were determined. In the project, the full-scale test in actual project was conducted by using the AC25 mixture. By changing the using parameters compare the paving operations, the results show that, the reasonable parameter will greatly improve the uniformity of paving, and the surface proportion of structural depth of mixture decrease from the 2.13 to 1.60.
The electrical resistance, flexural strength, and microstructure of carbon fiber reinforced cement composites (CFRC) were improved greatly by adding water-redispersible latex powder. The electrical resistance of CFRC was investigated by two-probe method. The input range of CFRC based strain sensors was therefore increased, whereas electrical resistance was increased and remained in the perfect range of CFRC sensors. The analysis of scanning electron microscopy indicated that elastic latex bridges and a latex layer existed among the interspaces of the adjacent cement hydration products which were responsible for the enhancement of the flexural strength and electrical resistance. The formation mechanism of the elastic latex bridges was also discussed in detail. The continuous moving of two opposite interfaces of the latex solution-air along the interspaces of the adjacent hydrated crystals or colloids was attributed to the formation of the elastic latex bridges.
Circulating fluidized bed combustion (CFBC) fly ash was mixed with cement or lime at a different ratio as a stabilizer to stabilize lake sludge. In order to understand the influences of stabilizers on the lake sludge properties, tests unconfined compressive strength, water stability and SEM observation were performed. The experimental results show that with the increase of the curing time, the strength of all the stabilized specimens increase, especially the samples containing cement. The strength of the specimens is decreased with the increasing of the CFBC fly ash/cement ratio, the optimum ratio between CFBC fly ash and cement is 2:3. The water stability of CFBC fly ash-cement based stabilizers is higher than those of cement and lime. Moreover, the lake sludge stabilization mechanism of CFBC fly ash-cement based stabilizers includes gelation and filling of the hydration products, i e, C-S-H gel and the AFt crystal, which act as benders to solidify those particles together and fill in the packing void of the aggregates.
A kind of piezoresistive response extraction method for smart cement-based composites/ sensors was proposed. Two kinds of typical piezoresistive cement-based composites/sensors were fabricated by respectively adding carbon nanotubes and nickel powders as conductive fillers into cement paste or cement mortar. The variation in measured electrical resistance of such cement-based composites/sensors was explored without loading and under repeated compressive loading and impulsive loading. The experimental results indicate that the measured electrical resistance of piezoresistive cement-based composites/sensors exhibits a two-stage variation trend of fast increase and steady increase with measurement time without loading, and an irreversible increase after loading. This results from polarization caused by ionic conduction in these composites/sensors. After reaching a plateau, the measured electrical resistance can be divided into an electrical resistance part and an electrical capacity part. The piezoresistive responses of electrical resistance part in measured electrical resistance to loading can be extracted by eliminating the linear electrical capacity part in measured electrical resistance.
Morphology characteristics of mix aggregates with crushed air-cooled blast furnace slag (SCR) and crushed limestone (LCR) with 5–20 mm and 20–40 mm gradation were represented by numerical parameters including angularity number (AN) and index of aggregate particle shape and texture (IAPST). The effect of mix aggregates containing SCR on compressive strength and splitting tensile strength of concrete was investigated. Fracture characteristics of concrete, interfacial structure between aggregates and matrix were analyzed. The experimental results show that porous and rough SCR increases contact area with matrix in concrete, concave holes and micro-pores on the surface of SCR are filled by mortar and hydrated cement paste, which may increase interlocking and mechanical bond between aggregate and matrix in concrete. SCR can be used to produce a high-strength concrete with better mechanical properties than corresponding concrete made with LCR. The increase of AN and IAPST of aggregate may enhance mechanical properties of concrete.
In order to understand the strength developing law of the epoxy asphalt mixture, a curing reaction model of the epoxy asphalt binder was proposed based upon the thermokinetic analysis. Given some assumptions, the model was developed by applying the Kissinger law as well as Arrhenius equation, and the differential scanning calorimetry was performed for estimating the model parameters. To monitor the strength development of the epoxy asphalt mixture, a strength test program was employed and then results were compared to those produced from the proposed model. The comparative evaluation shows that a good consistency exists between the outputs from test program and the proposed model, indicating that the proposed model can be used effectively for simulating the curing reaction process for the epoxy asphalt binder and predicting the strength development for the epoxy asphalt mixture.
Effects of polycarboxylate-type superplasticizer (PC) molecular structure on the hydration heat of tricalcium silicate (C3S) paste and polymerization degree of hydration products (C-S-H gel) were researched by using TAM AIR isothermal microcalorimetry (TA) and 29Si nuclear magnetic resonance (NMR). Methoxy polyethylene glycol-methacrylates-based polycarboxylate superplasticizers with different side chain lengths and main chain lengths were employed. PC molecules with shorter main chain or longer side chains caused stronger retardation of C3S early hydration and lesser increase of C3S 3 d hydration degree. NMR measurement indicated that the incorporation of PC increased the hydration degree of C3S paste and the polymerization degree of silicon-oxygen tetrahedron of C-S-H gel. The tendency for C3S 7 d hydration degree to improve was more pronounced while PC molecules with longer main chain or shorter side chain were added. Whereas, PC molecules with longer main chains or longer side chains increased the 7 d polymerization degree of C-S-H gel.
The adsorption of superplasticizers in fly ash blended cement paste and its rheological effects were investigated. It is shown that the absorption of superplasticizer on portland cement particles is very different from that on fly ash particles. The fly ash particles have smooth surfaces and are negatively charged, so its adsorption capacity is weaker than the portland cement particles. The amount of adsorbed SP in the fly ash blended cement paste depends highly on the replacement proportion of portland cement with fly ash, and to a much less extent on the nature of the fly ash. However, the amount of adsorbed superplasticizer does not correspond well the ζ-potential of the solid particles, due the strong adsorbing capacities of the Portland cement particles. When fly ash replaces portland cement in the paste, the rheological behavior is radically changed, which is closely related to the fineness and density of the ash. The packing and agglomeration of the solid particles are the controlling factors on the rheological parameters of the fresh paste, instead of the amount and type of adsorbed superplasticizer.
Through the fast freeze-thaw cycle test, accelerated carbonation test, and natural carbonation test, the durability performance of lining concrete under combined action of freeze-thaw cycle and carbonation were studied. The experimental results indicate that freeze-thaw cycle apparently accelerates the process of concrete carbonation and carbonation deteriorates the freeze resistance of concrete. Under the combined action of freeze-thaw cycle and carbonation, the durability of lining concrete decreases. The carbonation depth of lining concrete at tunnel openings under freeze-thaw cycles and tunnel condition was predicted. For the high performance concrete with proposed mix ratio, the lining concrete tends to be unsafe because predicted carbonation depth exceeds the thickness of reinforced concrete protective coating. Adopting other measurements simultaneously to improve the durability of lining concrete at the tunnel openings is essential.
The uniaxial compressive response of steel-polypropylene hybrid fiber reinforced concrete (HFRC) and steel fiber-reinforced concrete (SFRC) was analyzed under high strain rate loading with a 74 mm diameter split Hopkinson pressure bar (SHPB). The experimental investigation focused on recorded data and resulted in distinguishing the strain rate that mobilized different ductility of steel-polypropylene hybrid fiber reinforced concrete (HFRC) and steel fiber-reinforced concrete (SFRC). 64 specimens of HFRC and SFRC with higher static compressive strength were tested at the strain rates changing from 20 to 120 s−1. The static compressive strength and dynamic stress-strain curves of the two materials were obtained at 4 different strain rates and the failure stress, and peak strain and peak toughness were also analyzed. The results show that HFRC has quite good dynamic mechanical property and clear strain-rate effect, and the failure mechanism of HFRC and SFRC was also compared based on the specimens’ failure modes in static and dynamic compressive tests.
Small stone asphalt mixture (SSAM) was designed by Bailey method and coarse aggregate voids-filling method. The optimum asphalt content was determined by Marshal test. Surface texture depth for SSAM with different voidage, and the BPN of SSAM and SMA before after wet track abrasion were measured. The experimental results indicate that the surface texture depth increases with the decreasing of asphalt aggregate ratio. The SSAM with the optimal asphalt content has a good skid resistance. BPN of asphalt mixture decreases with the increasing of wearing time, but the extent of reduction is different. The reduction rate of BPN for SSAM is smaller than that of SMA, indicating that SSAM has a good skid resistance attenuation capacity. Finally, the other properties of SSAM are also evaluated, showing that the splitting strength and modulus and SSAM are higher than those of SMA, and the other properties of SSAM, such as high-temperature performance and water stability can also satisfy the technical requirements.
To test self healing capability of asphalt binders, three asphalt specimens (pure asphalt, modified asphalt and aged asphalt) were prepared. Every specimen was tested by dynamic shear rheometer (DSR). The temperature sweeps result indicates that both aging and SBS modifying influence the self healing capability of asphalt binder. The fatigue-heal-fatigue test was introduced to study the self healing capability of asphalt in its serving periods. Furthermore, three different periods (0.5 h, 1 h, 3 h) were set up to study the influence of rest time on fatigue time. It is concluded that longer rest time, less load will delay the appearance of cracks and extend the service life of asphalt binders.
The article aimed to study the durability of steel fiber reinforced concrete under the coupled sewage-loading according to compressive strength, flexural strength, compressive strength corrosion coefficient, flexural strength corrosion coefficient, compressive strength balance coefficient, flexural strength balance coefficient. Through the homemade load frame applied to design specimens, the pre-loading level are equivalent the damage intensity of 0%,10%,30% and 50% four different ways. The experimental results show that the performance of concrete down gradually and sustaining load aggravated the degree of domestic sewage attacking concrete after six month; under different stress states, the more loading levels, the more serious domestic sewage attacked the steel fiber reinforced concrete. It is proved that the concrete damage can be inhibited by adding the steel fiber, when steel fiber volume fraction is 1.0%, the corrosion resistance of concrete is best.
Dynamic rheological properties of asphalt modified by Supramolecular UV resistant material—layered double hydroxides(LDHs) was studied by means of the dynamic shear rheometer (DSR) test. Two typical base asphalts were chosen and modifi ed by 2 different LDHs contents. DSR tests were performed on the original samples, samples after exposed to outdoor and samples after the artifi cial accelerated UV aging tests respectively to analyze the rheological properties. It is found that when the LDHs content is between 3wt% and 5wt% of asphalt weight, the high temperature performance and fatigue resistant property of the modifi ed asphalt become better, the UV aging resistance properties are improved.