A metakaolin(Mk)-based geopolymer cement from Tunisian Mk mixed with different amounts of silica fume(SiO_2/Al_2O_3 molar ratio varying between 3.61 and 4.09) and sodium hydroxide(10M) and without any alkali silicate ...A metakaolin(Mk)-based geopolymer cement from Tunisian Mk mixed with different amounts of silica fume(SiO_2/Al_2O_3 molar ratio varying between 3.61 and 4.09) and sodium hydroxide(10M) and without any alkali silicate solution, is developed in this work. After the samples were cured at room temperature under air for 28 d, they were analyzed by X-ray diffraction(XRD), Fourier transform infrared(FTIR) spectroscopy, environmental scanning electron microscopy, mercury intrusion porosimetry, ^(27)Al and ^(29)Si nuclear magnetic resonance(NMR) spectroscopy, and compression testing to establish the relationship between microstructure and compressive strength. The XRD, FTIR, and ^(27)Al and ^(29)Si NMR analyses showed that the use of silica fume instead of alkali silicate solutions was feasible for manufacturing geopolymer cement. The Mk-based geopolymer with a silica fume content of 6 wt%(compared with those with 2% and 10%), corresponding to an SiO_2/Al_2O_3 molar ratio of 3.84, resulted in the highest compressive strength, which was explained on the basis of its high compactness with the smallest porosity. Silica fume improved the compressive strength by filling interstitial voids of the microstructure because of its fine particle size. In addition, an increase in the SiO_2/Al_2O_3 molar ratio, which is controlled by the addition of silica fume, to 4.09 led to a geopolymer with low compressive strength, accompanied by microstructures with high porosity. This high porosity, which is responsible for weaknesses in the specimen, is related to the amount of unreacted silica fume.展开更多
Let D C RN （N≥3）, be a smooth bounded domain with smooth boundary 3D. In this paper, the existence of boundary blow-up weak solutions for the quasilinear elliptic equation Δpu -= Ak（x）f（u） in D（λ 〉 0 and 1 ...Let D C RN （N≥3）, be a smooth bounded domain with smooth boundary 3D. In this paper, the existence of boundary blow-up weak solutions for the quasilinear elliptic equation Δpu -= Ak（x）f（u） in D（λ 〉 0 and 1 〈 p 〈 N）, is obtained under new conditions on k. We give also asymptotic behavior near the boundary of such solutions.展开更多
Over the past two decades,there have been enormous advances in lattice Boltzmann(LB)numerical simulation and modelling.The lattice Boltzmann method has become a practical and promising tool for many fluid problems.A m...Over the past two decades,there have been enormous advances in lattice Boltzmann(LB)numerical simulation and modelling.The lattice Boltzmann method has become a practical and promising tool for many fluid problems.A majority of recent studies have relied on numerical computations of isothermal flows.However,much less efforts have been devoted to complex thermal flows,such as flows in porous media subjected to external magnetic force,flows with temperature-dependent properties.In this paper,an overview is made based on some accomplishments in these numerical endeavours.Along with the paper’s sections,the state-of-the-art trend and the LBM advances in modelling and in computational aspects for specific classes of problems of major interest will be fully touched on.Concluding remarks are given and the axis of our future studies will be traced.展开更多
文摘A metakaolin(Mk)-based geopolymer cement from Tunisian Mk mixed with different amounts of silica fume(SiO_2/Al_2O_3 molar ratio varying between 3.61 and 4.09) and sodium hydroxide(10M) and without any alkali silicate solution, is developed in this work. After the samples were cured at room temperature under air for 28 d, they were analyzed by X-ray diffraction(XRD), Fourier transform infrared(FTIR) spectroscopy, environmental scanning electron microscopy, mercury intrusion porosimetry, ^(27)Al and ^(29)Si nuclear magnetic resonance(NMR) spectroscopy, and compression testing to establish the relationship between microstructure and compressive strength. The XRD, FTIR, and ^(27)Al and ^(29)Si NMR analyses showed that the use of silica fume instead of alkali silicate solutions was feasible for manufacturing geopolymer cement. The Mk-based geopolymer with a silica fume content of 6 wt%(compared with those with 2% and 10%), corresponding to an SiO_2/Al_2O_3 molar ratio of 3.84, resulted in the highest compressive strength, which was explained on the basis of its high compactness with the smallest porosity. Silica fume improved the compressive strength by filling interstitial voids of the microstructure because of its fine particle size. In addition, an increase in the SiO_2/Al_2O_3 molar ratio, which is controlled by the addition of silica fume, to 4.09 led to a geopolymer with low compressive strength, accompanied by microstructures with high porosity. This high porosity, which is responsible for weaknesses in the specimen, is related to the amount of unreacted silica fume.
基金We are indebted to Prof. A. Daaloul, Secretary of State to the Minister of Agriculture and Water Resources, in charge of Hydraulic Resources and Fishing （Tunisia）, for helping us to achieve this work. We thank Prof. J. Hatchett from the Kansas State University （ Manhattan, USA） for providing plant material. This study was morally and financially supported by the ＂Minlstére de la Recherche Scientifique, de la Technologie et du Développement des Compétences＂ （Tunisia） and the ＂ Direction Générale de la Recherche Scientifique et de la Rénovation Technologique au Ministére de l＇Enseignement Sup6rieur＂ （Tunisia）.
文摘Let D C RN （N≥3）, be a smooth bounded domain with smooth boundary 3D. In this paper, the existence of boundary blow-up weak solutions for the quasilinear elliptic equation Δpu -= Ak（x）f（u） in D（λ 〉 0 and 1 〈 p 〈 N）, is obtained under new conditions on k. We give also asymptotic behavior near the boundary of such solutions.
文摘Over the past two decades,there have been enormous advances in lattice Boltzmann(LB)numerical simulation and modelling.The lattice Boltzmann method has become a practical and promising tool for many fluid problems.A majority of recent studies have relied on numerical computations of isothermal flows.However,much less efforts have been devoted to complex thermal flows,such as flows in porous media subjected to external magnetic force,flows with temperature-dependent properties.In this paper,an overview is made based on some accomplishments in these numerical endeavours.Along with the paper’s sections,the state-of-the-art trend and the LBM advances in modelling and in computational aspects for specific classes of problems of major interest will be fully touched on.Concluding remarks are given and the axis of our future studies will be traced.
