Papers by Keyword: Pore Structure

Abstract: The difference of movable fluid saturation of tight sandstone gas reservoir is researched, with transverse relaxation time (T₂) distribution derived from nuclear magnetic resonance technique (NMR). This article newly calculate T₂ cutoff value and elaborate the influence of pore structure on the occurrence characteristics of movable fluid. The study had revealed T₂ spectrum distribution includes the following types: (1) wide and flat single peak; (2) left single peak; (3) high left peak with low right peak. Movable fluid saturation is low, with class IV and class V movable fluid mainly. Pore structure control properties and percolation ability of rock reservoir and whether oil could be driven out depends on throat parameters of interconnected pores. Movable fluid saturation is low with bigger pore throat ratio, narrower pore throat distribution and higer pore structure heterogeneity.

Abstract: Aiming at the problem of the Alpine, high altitude and other complex environment in the northwest area, and lack of concrete mix and durability data in this harsh environment. Based on the real engineering project, the effect of W/C and the content of cementitious materials on concrete performances were studied, the strength, impermeability and frost resistance of concrete which was mixed respectively two kinds of water reducer and maintained in standard condition and outdoor condition were Studied comparatively. The pore structure of cement paste which was added respectively two kinds of water reducer were also analyzed. The results show that: The self-made polycarboxylate superplasticizer has the effect of low temperature and early strength, and it also can ameliorate the internal pore structure of the sample and improve the impermeability and frost resistance, and improve the durability of concrete.

Abstract: This paper adopted the vacuum sintering technology to prepare titanium fiber porous material with a three-dimensional spatial network fiber backbone and connectivity pore structure. With the help of fractal geometry theory and scanning and digitizing the image, the fractal research of pore-structure in porous titanium fibers is executed and we studied the influence of adopting the box-counting dimension method to calculate the fractal dimension. Additionally, we determined the quantitative relationship between fractal dimension and the porosity of the porous in titanium fiber, while described the physical meaning of the fractal dimension.

Abstract: The surface area and pore distribution of activated carbons (ACs) were characterized by nitrogen adsorption isotherms at 77 K, and double layer capacitors were assembled to demonstrate the electrochemical performance. With 1 mol·L^-1 tetraethylammonium tetrafluoroborate dissolved in acetonitrile (Et₄NBF₄/AN) as electrolyte, electrochemical methods including cyclic voltammetry (CV) and galvanostatic charge-discharge tests were used to evaluate the capacitors. Results show that the surface area has a limited effect on the specific capacitance of ACs and the increaing of mesoporous content can decrease the capacitance decay rate at large discharge current. When current increases from 0.15A·g^-1 to 9.6A·g^-1, the minimum specific capacitance decay rate of mesoporous ACs is 10.93%, while that of the microporous ACs is 15.21%;the contributions of mesoporous surface area to the specific capacitance drop from 10.10 to 9.95μF·cm^-2, while that of microporous surface area drop from 5.68 to 4.21μF·cm^-2.

Abstract: The pore structure of Portland cement pastes cured under different hydrothermal regimes was analyzed. Pore size distribution (PSD), hydraulic permeability coefficient (HK) and porosity (P) were found depending on temperature and steam pressure. With increasing hydrothermal characteristics, the pore structures degraded causing the depletion in compressive strength. Then, blast furnace slag (BFS) and silica fume (SF) were added to PC and cured under similar conditions. It was found that the pore structure was greatly improved. The effect of hydrothermal curing may be interpreted by the intensity and position of the peak, by the length and bimodal characteristic of PSD. The maximum concentration of pores of reference cement paste lies in the range 10 – 103 nm, and changes progressively to the size < 10 nm with increasing addition of BFS and SF. This behavior is attributed mainly to the presence of SF. Microstructure analysis shows hydrate products like needle CSH and CASH, which were stable under hydrothermal curing.

Abstract: The article presents the research results of modifying antifreeze influence on the pore structure formation of dry mortars in terms of adhesive and base layers of external thermal insulation composite systems within different temperature regimes of hardening.

Abstract: This paper tested the pore structure, capillary water absorption and impermeability of cement mortars modified with three polymers respectively, establishing the relationship between the pore structure and waterproof performance. The results show that with the polymer dosage growing, especially as the polymer/cement ratio (m_p/m_c) increases from 0% to 5%, the reduction in the capillary water absorption and the penetration depth of water into mortar is significant. In the m_p/m_c range of 0%~20% the open porosity presents a gradual decrease trend. The capillary water absorption and the penetration depth of water into mortar show linear growth and exponential growth respectively with the open porosity increasing.

Abstract: The effect of bittern on alkali-activated slag (AAS) cement and OPC was studied by testing on the strength and pore structure of the specimens stored in artificial bittern solution at certain periods. The experimental results show that the (AAS) cement exhibits excellent resistance to chemical attack of bittern. The significant increase of strength of (AAS) mortar stored in bittern solution was observed with the soaking time, and the strength increases very quickly before 27 d. But the strength of OPC decreases fast after17d. The more the contents of NaOH activator in AAS cement, the more the strength gained. And the more the contents of activator, the less porosity is. Curing the AAS cement in bittern environment leads to a reduction in the total pore volume and to a refinement of the pore structures.

Abstract: The present study concerns a development of cement-free concrete using ground granulated blast-furnace slag (GGBS) with alkali-activators such as KOH, NaOH, and Ca (OH)₂. To find out the development among three different activators, the concentration of hydroxyl ion was kept 0.5%, 1.0%, 1.5%, 2.0% and 3.0% by weight of binder irrespective of cations. The setting time was measured by penetration resistance immediately after casting of mortar. The development of compressive strength was measured at 7, 14, 28, and 91 days. The pore structure of cement-free mortar was examined by the mercury intrusion porosimetry (MIP) and rapid chloride penetration test (RCPT). Simultaneously, grew sample was used to microscopically observe at the XRD. For strength of cement-free mortar, mixed with KOH or NaOH was as high as OPC at 3.0 % by weight of binder. However, the compressive strength of cement-free concrete mixed with 3.0 % Ca (OH)₂ by weight of binder had just half strength of OPC mortar. Cement-free concrete activated with NaOH and Ca (OH)₂ had higher total pore volume, however, it had lower ionic penetrability due to the pore type which mostly consist of gel pores. For pore structure of cement-free mortar mixed with KOH, the total volume had similarity to that of OPC mortar, however, it had lower penetrability. Therefore, it may have higher resistance to chloride transport than that of OPC mortar.

Abstract: In this study, a modified pore structure of cement based material with respect to a path for ingressive ions was established. Of pores in a concrete, gel pores and other entrapped air voids were excluded from modelling the pore structure as no interests are given due to the ions immobilization of cement paste media. To setup the pore structure, the linear traverse method (LTM) was used to distribute air voids along the traverse line in a hexahedron cement paste structure, followed by including entrained air voids to fill up the least space of the cement matrix and making a network of the air voids through capillary pores at the variation in the diameters. Then the mercury intrusion porosimetry (MIP) was used to iteratively approach an accordance rate with calculated one from the above way to get into appropriate convergence value. As a result, for the OPC specimen the developed model shows a somewhat relevant value of 42.4 % of the accordance rate compared to empirical one and 64.24 of the ratio of ionic path to original distance within a concrete.