Resonance flexural vibration(Fast Fourier Transform, FFT), ultrasonic wave(Pundit) and stress wave(Metriguard) techniques were examined as means of evaluating the static modulus of elasticity (MOE) and predicting the ...Resonance flexural vibration(Fast Fourier Transform, FFT), ultrasonic wave(Pundit) and stress wave(Metriguard) techniques were examined as means of evaluating the static modulus of elasticity (MOE) and predicting the modulus of rupture (MOR) of finger-jointed lumber specimens made with four kinds of Eucalyptus (Eucalyptus. citriodora, E. exserta, E. grandis x E. urophylla and E. grandis). Dynamic MOE was calculated from frequency and time obtained from forced vibrations and sounds induced in the four species of finger-jointed specimens. It was found that correlation coefficients between density and static MOE and dynamic MOE were statistically significant at the 0.01 level. And it was also found that the three nondestructive techniques can provide rapid and accurate means to determine the MOE, and the dynamic MOE was more accurate to predict static MOE than density. But the correlation coefficient between dynamic MOE, static MOE and MOR were lower than results reported by other researchers for solid wood, and were not statistically significant. It can be concluded that the three nondestructive techniques are useful for evaluating the MOE, but not suitable for predicting the MOR of finger-jointed.展开更多
In the present study,in order to investigate the effects of fly ash on the structural evolution and strength damage mechanism of Pisha-sandstone cement soil,unconfined compressive strength tests of Pisha-sandstone cem...In the present study,in order to investigate the effects of fly ash on the structural evolution and strength damage mechanism of Pisha-sandstone cement soil,unconfined compressive strength tests of Pisha-sandstone cement soil with different fly ash content levels and various ages were carried out.The apparent morphology,microstructures,and chemical compositions of the samples were observed and analyzed using ultra-depth three-dimensional microscopy,scanning electron microscopy,and XRD methods.The results revealed that the unconfined compressive strength levels of Pisha-sandstone cement soil samples displayed increasing trends with the increases in fly ash content and age.For example,when the fly ash content levels were increased from 12%to 15%,the strength of Pisha-sandstone cement soil had only slightly increased under the curing ages of 7,28,and 60 days.In addition,the unconfined compressive strength levels of the samples with 15%fly ash content only increased 0.02%,0.51%,and 0.54%,respectively,when compared with the samples containing 12%fly ash.It was observed that with the increases in the fly ash content,the number of pores on the outer surfaces of the samples were significantly reduced.Also,the height differences of cross-sectional gullies were reduced,and the apparent morphology was observed to be flatter.Since cement hydration creates a strong alkaline environment for reaction systems,the active degrees of the pozzolanic reactions of the fly ash were stimulated in this study.Moreover,a significant amount of the C-S-H gel phase and the stable five-membered ring structure of the mordenite and ettringite were generated,which connected the loose Pisha-sandstone particles to form a skeleton.The internal microstructures were then observed to be denser and more uniform.At the same time,the micro-pores were filled and refined by the unreacted micro-bead fly ash.Consequently,the defects in the internal microstructures were improved.Also,based on the Weibull distribution,a damage evolution model of the Pisha-sandstone cement soil was established.The analysis results of the damage variable D values during the initial damage stage,damage evolution stage,and residual damage stage of the damage process showed that the damage variables during all three stages displayed decreasing trends with the increases in the fly ash content levels and age.Therefore,based on this study’s findings,it was considered that the incorporation of fly ash could effectively improve the damage degrees of Pisha-sandstone cement soil under external force conditions.展开更多
Durability design of recycled high performance concrete（RHPC） is fundamental for improving the use rate and level of concrete waste as coarse recycled aggregate（CRA）. We discussed a frostdurability-based mix propo...Durability design of recycled high performance concrete（RHPC） is fundamental for improving the use rate and level of concrete waste as coarse recycled aggregate（CRA）. We discussed a frostdurability-based mix proportion design method for RHPC using 100 % CRA and natural sand. Five groups of RHPC mixes with five strength grades（40, 50, 60, 70 and 80 MPa） were produced using CRA with four quality classes, and their workability, 28 d compressive strengths and frost resistances（measured by the compressive strength loss ratio and the relative dynamic modulus of elasticity） were tested. Relationships between the 28 d compressive strength, the frost resistance and the CRA quality characteristic parameter, water absorption, were then developed. The criterion of a CRA maximum water absorption limit value for RHPC was suggested, independent of its source and quality class. The results show that all RHPC mixes achieve the expected target workability, strength, and frost durability. The research results demonstrate that the application of the proposed method does not require trial testing prior to use.展开更多
Extrusion-calendering method was developed to prepare single-polymer composites（SPCs） of ultrahigh molecular weight polyethylene（ UHMWPE） fabric reinforcing low density polyethylene（LDPE）.Differential scanning c...Extrusion-calendering method was developed to prepare single-polymer composites（SPCs） of ultrahigh molecular weight polyethylene（ UHMWPE） fabric reinforcing low density polyethylene（LDPE）.Differential scanning calorimeter（DSC） experiments were executed to determine the setup of extrusion temperature.Effects of the die temperature on the tensile and interfacial performances of SPCs were studied through the tensile and T-peel tests,respectively. The results showed that both tensile strength and modulus increased initially and decreased afterwards as the temperature increased. The peak values of tensile strength and modulus of PE SPCs,which are 10. 8 and 3. 5 times as high as those of the unreinforced LDPE respectively,were obtained at 150 ℃. Higher temperatures also give a positive effect on peel strength. Scanning electron microscopy（ SEM） and camera were also used to observe the morphology of the SPCs samples.展开更多
The pavement performance of epoxy resin modified asphalt mixtures was investigated by the Marshall test, the indirect tensile test, the rutting test, the three-pointed bending test and the composite beam fatigue test....The pavement performance of epoxy resin modified asphalt mixtures was investigated by the Marshall test, the indirect tensile test, the rutting test, the three-pointed bending test and the composite beam fatigue test. In comparison with the performance of epoxy resin modified asphalt mixtures, the performance of stone matrix asphalt mixtures （SMA10） was also investigated. The rutting test and composite beam fatigue test results show that the epoxy resin modified asphalt mixtures can improve permanent deformation and fatigue characteristics. They also show lower temperature susceptibility and greater resistance to moisture damage compared to the SMA10. Findings from the research indicate that the epoxy resin modified asphalt mixture provides an optional material for the pavement of long-span steel bridges in China due to profound performance and economic advantages.展开更多
Surface miner, a continuous mining machine, is being manufactured in India and abroad owing to enhanced demand of production in various mining industries like coal, limestone, gypsum, bauxite etc. Different types of s...Surface miner, a continuous mining machine, is being manufactured in India and abroad owing to enhanced demand of production in various mining industries like coal, limestone, gypsum, bauxite etc. Different types of surface miners are manufactured today based on cutting drum placement and design specifications. Selective mining without drilling and blasting, high production and small size products are some of the prominent attractive features obtained with these moving marvels. This machine can be used with good efficiency in soft to medium hard rock (100-120 MPa). This paper synthesizes the different applications, equipment models, features offered, operating methods, cutting performance assessment models as well as typical production performance of surface miner in coal and limestone mines of India. Engine hour metre reading, diesel and pick consumptions are linearly influenced by production. The emphasis for future research is also brought out.展开更多
基金This research is supported by ITTO Project PD 69/01 Rev.2(I) "Improved and diversified use of tropical plantation timber in China tosupplement diminishing supplies from natural forests".
文摘Resonance flexural vibration(Fast Fourier Transform, FFT), ultrasonic wave(Pundit) and stress wave(Metriguard) techniques were examined as means of evaluating the static modulus of elasticity (MOE) and predicting the modulus of rupture (MOR) of finger-jointed lumber specimens made with four kinds of Eucalyptus (Eucalyptus. citriodora, E. exserta, E. grandis x E. urophylla and E. grandis). Dynamic MOE was calculated from frequency and time obtained from forced vibrations and sounds induced in the four species of finger-jointed specimens. It was found that correlation coefficients between density and static MOE and dynamic MOE were statistically significant at the 0.01 level. And it was also found that the three nondestructive techniques can provide rapid and accurate means to determine the MOE, and the dynamic MOE was more accurate to predict static MOE than density. But the correlation coefficient between dynamic MOE, static MOE and MOR were lower than results reported by other researchers for solid wood, and were not statistically significant. It can be concluded that the three nondestructive techniques are useful for evaluating the MOE, but not suitable for predicting the MOR of finger-jointed.
基金This study was funded by the National Natural Science Foundation of China(Grant No.51869022).
文摘In the present study,in order to investigate the effects of fly ash on the structural evolution and strength damage mechanism of Pisha-sandstone cement soil,unconfined compressive strength tests of Pisha-sandstone cement soil with different fly ash content levels and various ages were carried out.The apparent morphology,microstructures,and chemical compositions of the samples were observed and analyzed using ultra-depth three-dimensional microscopy,scanning electron microscopy,and XRD methods.The results revealed that the unconfined compressive strength levels of Pisha-sandstone cement soil samples displayed increasing trends with the increases in fly ash content and age.For example,when the fly ash content levels were increased from 12%to 15%,the strength of Pisha-sandstone cement soil had only slightly increased under the curing ages of 7,28,and 60 days.In addition,the unconfined compressive strength levels of the samples with 15%fly ash content only increased 0.02%,0.51%,and 0.54%,respectively,when compared with the samples containing 12%fly ash.It was observed that with the increases in the fly ash content,the number of pores on the outer surfaces of the samples were significantly reduced.Also,the height differences of cross-sectional gullies were reduced,and the apparent morphology was observed to be flatter.Since cement hydration creates a strong alkaline environment for reaction systems,the active degrees of the pozzolanic reactions of the fly ash were stimulated in this study.Moreover,a significant amount of the C-S-H gel phase and the stable five-membered ring structure of the mordenite and ettringite were generated,which connected the loose Pisha-sandstone particles to form a skeleton.The internal microstructures were then observed to be denser and more uniform.At the same time,the micro-pores were filled and refined by the unreacted micro-bead fly ash.Consequently,the defects in the internal microstructures were improved.Also,based on the Weibull distribution,a damage evolution model of the Pisha-sandstone cement soil was established.The analysis results of the damage variable D values during the initial damage stage,damage evolution stage,and residual damage stage of the damage process showed that the damage variables during all three stages displayed decreasing trends with the increases in the fly ash content levels and age.Therefore,based on this study’s findings,it was considered that the incorporation of fly ash could effectively improve the damage degrees of Pisha-sandstone cement soil under external force conditions.
基金Funded by the National Natural Science Foundation of China(No.51278073)Prospective Joint Research Project of Jiangsu Province(No.BY2015027-23)State Key Laboratory for Geo Mechanics and Deep Underground Engineering,China University of Mining&Technology(No.SKLGDUEK1704)
文摘Durability design of recycled high performance concrete（RHPC） is fundamental for improving the use rate and level of concrete waste as coarse recycled aggregate（CRA）. We discussed a frostdurability-based mix proportion design method for RHPC using 100 % CRA and natural sand. Five groups of RHPC mixes with five strength grades（40, 50, 60, 70 and 80 MPa） were produced using CRA with four quality classes, and their workability, 28 d compressive strengths and frost resistances（measured by the compressive strength loss ratio and the relative dynamic modulus of elasticity） were tested. Relationships between the 28 d compressive strength, the frost resistance and the CRA quality characteristic parameter, water absorption, were then developed. The criterion of a CRA maximum water absorption limit value for RHPC was suggested, independent of its source and quality class. The results show that all RHPC mixes achieve the expected target workability, strength, and frost durability. The research results demonstrate that the application of the proposed method does not require trial testing prior to use.
基金Supported by the National Natural Science Foundation of China(51403019)
文摘Extrusion-calendering method was developed to prepare single-polymer composites（SPCs） of ultrahigh molecular weight polyethylene（ UHMWPE） fabric reinforcing low density polyethylene（LDPE）.Differential scanning calorimeter（DSC） experiments were executed to determine the setup of extrusion temperature.Effects of the die temperature on the tensile and interfacial performances of SPCs were studied through the tensile and T-peel tests,respectively. The results showed that both tensile strength and modulus increased initially and decreased afterwards as the temperature increased. The peak values of tensile strength and modulus of PE SPCs,which are 10. 8 and 3. 5 times as high as those of the unreinforced LDPE respectively,were obtained at 150 ℃. Higher temperatures also give a positive effect on peel strength. Scanning electron microscopy（ SEM） and camera were also used to observe the morphology of the SPCs samples.
基金The National Natural Science Foundation of China(No50578038)the PhDPrograms Foundation of Ministry of Education of China (No20050286008)
文摘The pavement performance of epoxy resin modified asphalt mixtures was investigated by the Marshall test, the indirect tensile test, the rutting test, the three-pointed bending test and the composite beam fatigue test. In comparison with the performance of epoxy resin modified asphalt mixtures, the performance of stone matrix asphalt mixtures （SMA10） was also investigated. The rutting test and composite beam fatigue test results show that the epoxy resin modified asphalt mixtures can improve permanent deformation and fatigue characteristics. They also show lower temperature susceptibility and greater resistance to moisture damage compared to the SMA10. Findings from the research indicate that the epoxy resin modified asphalt mixture provides an optional material for the pavement of long-span steel bridges in China due to profound performance and economic advantages.
文摘Surface miner, a continuous mining machine, is being manufactured in India and abroad owing to enhanced demand of production in various mining industries like coal, limestone, gypsum, bauxite etc. Different types of surface miners are manufactured today based on cutting drum placement and design specifications. Selective mining without drilling and blasting, high production and small size products are some of the prominent attractive features obtained with these moving marvels. This machine can be used with good efficiency in soft to medium hard rock (100-120 MPa). This paper synthesizes the different applications, equipment models, features offered, operating methods, cutting performance assessment models as well as typical production performance of surface miner in coal and limestone mines of India. Engine hour metre reading, diesel and pick consumptions are linearly influenced by production. The emphasis for future research is also brought out.
