Abstract: There are some reinforced concrete structures exposed to severe environmental conditions might require maintenance or strengthening. Many of these severe circumstances are the result of extreme climate conditions such as low temperature, freeze–thaw action, fire attack, and exposure to deicing salts. Because of this, the environmental durability of both the repair materials and methods used in rehabilitation applications are of utmost importance. A small fire can reach 250°C, while a common blaze can easily produce temperatures of around 800°C. In major conflagrations the temperature can even reach 1100°C. At this level, the heat affects most materials, provoking the spontaneous combustion of some of them and affecting the resistance of others. However, very little research has been performed in evaluating the environmental durability of strengthening materials for concrete members. Very little work has been done on the effects of freeze–thaw cycling on bonding and repair materials.
In this study, ultra high performance concrete (UHPC) was used to investigate the effect of strengthening concrete members by fire-damage test or freeze-thaw test. The results show that the mechanical properties of UHPC possess high strength, toughness, and freeze-thaw resistance. The CFRP (carbon fiber reinforced plates) wrapping specimens exposed at 300 °C showed totally failure with the deterioration of the adhesive. The UHPC with bonding 10 mm thickness specimens exposed at 400 °C and duration of 1 hour still in good shape. The UHPC with 1-cm or 2-cm thickness on strengthening concrete members could be obtained specific retrofit effects. The performance of UHPC specimens is better than those of CFRP wrapping specimens during high temperature exposure. The results of slant shear tests show that the bond strength of PC/PC, UHPC/PC and UHPC/UHPC decreased significantly after 600 freeze–thaw cycles or high temperature exposure.
Abstract: The TG and DTG curves of self-made ZnO precursor were studied by the thermo-gravimetric analysis method in N2 atmosphere from 25°C to 650°C at the heating rate of 5, 10 and 15°C/min. The TG curve showed that the decomposition process started at about 150°C and finished at 300°C, in accordance with the temperature range of the decomposition from basic zinc carbonate to zinc oxide. The first level chemical reaction based on Coats-Redfern method was applied to estimate the activation energy of the decomposition. The correlation factor was about 0.99, and the calculated average activation energy was 33.89kJ/mol. Active zinc oxides were perpetrated by microwave heating at 350°C for 30min. Their composition and surface morphology were investigated by using scanning electron microscope and X-ray diffraction and its quality can reach the first-grade standard of HG/T2572-94.
Abstract: Chitosan fibers(CSf) andCaSiO3 were incorporated into a poly (L-lactic acid)/hydroxyapatite (PLLA/HA) matrix as reinforcements to prepare scaffold composites with adequate strength and high porosity for bone tissue engineering combined with emulsion freeze drying technique. The structural morphology of the composites was observed by scanning electron microscope (SEM). The porosity was tested by liquid substitute method. The mechanical property was measured. The effects of addition of CSf and CaSiO3 on composites were also discussed. Simulated body fluid (SBF) experiments were conducted to assess the bioactivity of the composites. The chemical components of resultants on surfaces after the immersion in SBF were analyzed by fourier transform infrared spectroscopy (FTIR). The results show that the composites with high connectivity have pore sizes of 100~250μm, a porosity of 60%~80%, compressive strength of 3.5~8.0MPa. In the SBF tests, Chitosan fiber reinforced PLLA/HA-CaSiO3 composite degraded stably, meanwhile, the formation of a layer of bone-like apatite on the surfaces of the samples indicated a good bioactivity. Studies suggest the feasibility of using CSf reinforced PLLA /HA-CaSiO3 composite for bone tissue engineering.
Abstract: In order to solve the toxicity problem of gallic acid and its esters as food antioxidant,using the advantages of microcrystalline cellulose security and not to be absorbed by the body, a new type of polymeric anti-oxidants was exploited. Gallic acid microcrystalline cellulose ester was prepared by indirect esterification method ,which gallic acid and microcrystalline cellulose were used as raw materials. The structures of reaction materials and products were characterized and its oxidation resistance, stability, acute toxicology were studied by infrared spectroscopy, X-ray diffraction spectroscopy, scanning electron microscopy .The results showed that: gallic acid microcrystalline cellulose ester was successfully synthesized ; its ability to remove all kinds of free radicals was higher than or approximate equal to gallic acid; suitable for room temperature storage, high temperature sterilization, ultraviolet sterilizer, pH3.0~9.0,under these conditions it was stability;it was non-toxic substance, the safety was higher than gallic acid and gallic acid propyl. This study established the technical foundation for the further development of a new type of functional macromolecular compound which could be used for antioxidation.
Abstract: By changing gel and electrode shape, many different actuators could be invented. In the previous papers, we have reported that Maxwell stress generated in the PVC gels was expected as the results of polarization response of charges, and it mainly took place between the gel and the anode due to the accumulated negative charges on surface of the PVC gel near anode. Due to the existence of the Maxwell force, the PVC gel will be deformed asymmetrically and resulted in creep deformation along the anode. In this paper, we conducted some mechanical experiments and investigated the modulus of PVC gels with varied contents of plasticizer DBA. It was found that PVC gels were separated to two layers obviously after applied an electrical field. Near the anode, the layer (L1) was thinner and softer than other layer (L2) due to the transfer of plasticizer to the anode. This phenomenon was also confirmed by a fluorescence microscope. The displacement of gel in both sides near electrodes was different, and then a bending force was generated due to the force of electrical field. On the other hand, the recovery time of the deformed gel depended on the contents of plasticizer. The longer recovery time was observed for the lower content of plasticizer. The Young’s modulus of PVC gels in tensile becomes small after applied an electrical field and the gels became to be deformed easily.
Abstract: Chirped fiber Bragg grating (CFBG) sensors were embedded within the adhesive bondline of single-lap CFRP-GFRP bonded composite joints. The effect of disbond propagation (as a consequence of fatigue loading) on the reflected spectra from the CFBG sensor has been studied. As the disbond propagates, thermal strains generated during the bonding of the joint at elevated temperature are released and, as a consequence, a peak in the reflected spectra of the CFBG sensor can be seen. Using a transparent GFRP adherend, it has been possible to demonstrate that there is reasonable agreement between the position of the peak in the reflected spectrum and the disbond front position in the bonded joint.
Abstract: M-type hexaferrites Ba(ZnZr)xFe12-2xO19 (x=0, 0.5, 1.0, 1.5) powders, have been synthesized by molten salt method, where x varies from 0 to 1.5 in steps of 0.5. X-ray diffraction (XRD), field emission scanning electron microscope (FESEM) and vibrating sample magnetometer(VSM) were used to analyze the structures and magnetic properties. The results showed that, the magnetoplumbite structures for all samples calcining at 1100°C have been formed. The magnetic hysteresis loop measurements of the hexagonal ferrites powders showed that the saturation magnetization (Ms), the remanent magnetization (Mr), and the coercitivity (Hc) of ferrites depend strongly on the chemical compositions of materials. The data showed that the max Hc was obtained when substitution of x=1.0 (Hc=63.9 Oe), while the best Ms was obtained when substitution of x=0.5 (Ms=54.02 emu/g). Zn and Zr substitutions greatly modified the magnetic properties of BaM hexaferrite.
Abstract: The pyrophyllite used in this study was from Taishun County(Wenzhou,China). The surface of pyrophyllite was modified by coating with N-(n-butyl)-3-aminopropyltrimethoxysilane (BAPTS) coupling agent and utility of the BAPTS-modified pyrophyllite was investigated as an adsorbent for removal of Pb(II) ions from aqueous solutions. XRD and SEM analysis were used to characterise the surface modification. It can be clearly observed that the pyrophyllite looses its aculeated surface structure and gains more smooth morphology. It was observed that the BAPTS -modified pyrophyllite adsorbed approximately 94.50% of Pb(II) ions at an initial concentration of 10 mg/l and an amount of BAPTS of 2.0%.
Abstract: In this study, pure Al2O3-2SiO2 powders for a geopolymer were prepared by a sol-gel method, alkali-activation tests and alkali-dissolvability of the powders were carried out, and structure of the powders and alkali-activated products was investigated by 29Si and 27Al MAS NMR and SEM. Results showed that higher alkali-activation reactivity (higher compressive strengths of alkali-activated products) appeared in the powders heat-treated between 600-800 °C and alkali-dissolvability trend was different from that of alkali-activation tests. There were clear correlations between microstructure of alkali-activated products and alkali-activation reactivity and Al environment of the powders. It was found that high strength was related to a dense, fine grained microstructure. Such a structure was found in the alkali-activated products synthesized with the powders with high 5-coordinated Al contents. In addition, the peaks attributed to 5-coordinated Al were strengthened with the rise of heat-treated temperature of the powders.
Abstract: Fluorene and its derivatives which have an aromatic biphenyl structure with wide energy gap in the backbone and high luminescent efficiency have been drawn much attention to materials chemists and device physicists. In this research, 9,9-Bis(methoxycarbonylethy)fluorene and fluorene-containing polyester were prepared and their chemical structure and properties were initially studied. Furthermore, It is found that this fluorene-containing polyester might be a promising candidate for electroluminescent materials due to its excellent luminescent properties, solubility, film-forming property and thermal stability.