Papers by Keyword: Pore Structure

Abstract: The pore structure of a material radically infuences its properties, such as strength, freeze-thaw resistance, capillarity or resistance to elevated temperatures. The character of the pore structure is also limiting for the intrusion of aggressive oxides into the material, which affects its service life. The paper describes how a crystalline additive influences the pore structure of cement mortars. It describes the effect of secondary crystallisation and the influence of the additon of PP fibers on the apparent porosity and the internal structure of the mortar. It also discusses the influence of aggressive conditions on the mortar’s pore structure.

Abstract: In order to raise up the the rate of multipurpose utilization of rich-silicon iron ore tailing (IOTP for short) and the preparation of ultra-high performance concrete(UHPC for short), the influence rules and mechanism of rich-silicon iron ore tailing powder replacing fly ash in UHPC were studied, the influences of different specific surface area and dosage of IOTP replacing fly ash on its strength and liquidity were tested. Moreover, the pore structure and hydration products morphology of UHPC were tested by MIP and SEM methods, respectively. The results show that when fly ash replaced by IOTP, the liquidity of UHPC will be increased. When alternative content of IOTP is less than 10%, proper specific surface area of IOTP can improve the strength and pore structure, it can get the best result when the alternative content is 5% and the specific surface area is 588m2/kg. However, when alternative content of IOTP is 15% or more, all of these properties of UHPC become worse. It proves that IOTP can be used in the preparation of UHPC and improve the properties of UHPC.

Abstract: Porous cordierite is among the special porous ceramic due to its extensive properties. In this research, porous cordierite was fabricated through gelcasting method. A mixture of raw materials (SiO₂, Al₂O₃ and MgO) was melted at 1550 °C followed by quenching in water to produce a glass. Then the formed glass powder were milled for 1, 3, 5, 7 and 9 hours to obtain various particle sizes of cordierite powder. Cordierite powder produced was then used to prepare 3-D porous cordierite ceramic using gelcasting method. The cordierite pellets were characterized. Surface morphology was analysed via Scanning Electron Microscope (SEM) to observe the pore structure of porous cordierite formed from powder with various particle sizes.

Abstract: The Jurassic continental shale from northern Qaidam basin was selected as the research object, through the analysis of X-ray diffraction (XRD), field emission scanning electron microscopy (SEM) and nitrogen adsorption experiment, the mineral composition and pore structure characteristics of Jurassic continental shale from the northern Qaidam basin have been investigated in detail. All shale samples studied are quite rich in clay minerals. The clay mineral content ranges from 59.8% to 83.3% with an average of 74.6%, and the brittle mineral content accounts for 16.5% to 39.3%. Nitrogen adsorption test results indicate that for mesopores and macropores of shale samples the average pore width is 2~200 nm, mainly centering on 10~50 nm, and the micropores of the shale samples have a centralized distribution of 0.5~1 nm. The shale samples show high specific surface areas of 4.6~15.2 m2/g. According to SEM results, interparticle mineral matrix pores are main pore type and slit-type pore are well developed.

Abstract: The alumina hollow fiber membranes were prepared by spinning and then sintering method. The dope solution was fabricated by using 1-methyl-2-pyrrolidone (NMP), dimethylsulfoxide (DMSO), dimethylacetamide (DMAc), and triethylphosphite (TEP) as solvents, which have different interaction rate with non-solvent. SEM analysis showed that the alumina hollow fiber membranes have different pore structure. In particular, the hollow fiber membranes prepared with DMSO, DMAc and NMP had finger structures. In contrast, when it was made with TEP, the membrane had a sponge structure. The gas permeability and the contact angle of each hollow fiber membranes were measured. The fabricated hollow fiber membranes were applied to the membrane contact process for the carbon dioxide absorption. The hollow fiber membranes prepared with TEP is had the highest carbon dioxide absorption characteristics. A higher carbon dioxide absorption activity of hollow fiber membranes prepared with TEP was suggested to be due to its gas permeability and hydrophobicity. In conclusion, it was confirmed that the higher gas permeation due to pore structure of the membrane had a favorable effect on the absorption performance.

Abstract: Concrete is widely used construction material for the development of built environment which consumes huge amount of cement, around 4.3 billion metric ton all over the world. Reinforced concrete construction exposed to harsh environment such as chloride bound air causes deterioration in concrete through its pore structure by corroding the steel bar. The use of pozzolanic material i.e. metakaolin (MK), fly ash (FA), silica fume (SF), nano silica (NS) can be used as partially cement replacing material which not only reduces the pores in concrete but improves the mechanical, durability properties and microstructure of concrete. This paper reviews various transport mechanisms involved in ingress of deleterious material and incorporation of MK, FA and NS in concrete and their effects on concrete mechanical and durability properties. However, the research work provides an extended approach to evaluate combine effect using MK, FA, and NS and to produce a concrete with more refined pore structure for aggressive environment.

Abstract: The porous structure of copper-cadmium oxide system produced by electrochemical synthesis using alternating current in ammonium chloride solutions with concentrations of 3 and 25 wt% was studied. It was shown that the composition of electrolysis products is represented by oxides of copper (I) and (II), hydroxides of cadmium; it depends on the current density and the solution concentration. The products of joint electrochemical oxidation of copper and cadmium obtained in ammonium chloride solution with concentrations of 3 and 25 wt% and current densities of 1 and 3 A/cm² are characterized by mesoporous structure.

Abstract: The aging of hydraulic concrete structure is a highly complicated problem. To reasonably evaluate the aging situation of a long-term operating concrete sluice, the core samples are obtained by field sampling from the sluice piers and the mercury injection experiment is carried out in this paper. The main objectives of this experimental investigation are to analyze the pore structure characteristics of the different parts in core samples and discuss the concrete aging rule of hydraulic concrete structure. The experimental results show that the aging of the hydraulic concrete has a certain relationship with the evolution of the concrete pore structure. It is feasible to use the pore structure of concrete to express the concrete aging of the hydraulic structure. The research in this paper will provide a basis for further study on the aging mechanism of the hydraulic concrete structure.

Abstract: Researched the influence of the pore structure and water absorption on the carbonization property with sulphoaluminate foamed cement as an example. The results showed that: Under the same levels of dry density, the smaller pore size, the higher the carbonation coefficient and the integrity of pore had the same effect. After the surface water-proofing, water absorption decreased by 10% on average, the time of carbonizing completely become longer, and carbonation coefficient was increased. And put forward the methods of improving the carbonation resistance properties of sulphoaluminate cement foam materials.

Abstract: Though discussed a lot, it remains a practical challenge to modeling pore structure in cement paste. The fractal approach shows a great advantage since it allows to generate complex pore structure via simple geometric iterations and to incorporate the wide scope of pores in a self-similar manner. In this paper, the solid mass fractal model is proposed for pore structure in cement paste. The parametric analysis is performed in conjunction with the porosimetric test. It is shown that the proposed solid mass fractal well describes pore structure in cement paste.