Papers by Keyword: Gas Permeability

Abstract: For evaluating the crack state on solid bridge joint on site, the relationship between gas permeability and crack width of joint concrete is studied both on material and structural levels in this article. In laboratory tests, gas permeability tests on concrete samples with macrocrack are performed, the relationship between the relative gas permeability rate k/k₀ and the relative variation of crack width a_c is established combining with regression analysis, the fitting curve equation is . when a_c increases by 1.125×10^-2 mm, the gas permeability increases about 10 times compared with the initial state. In field tests, “pulse tests” are performed on bridge joint based on 3 embedded pulse probes to measure the evolution of gas permeability during bridge operation. The results show, firstly, the gas permeability of joint concrete are in the order of 10^-16~10^-19 m², which indicates a good compaction performance; Secondly, an order of magnitude increase of gas permeability of one probe in different ages, or the fact that the gas permeability at one position in solid joint is obviously larger than the other positions, these phenomena indicate the existence of original defects, or the possibility of macrocrack appearance from microcracks, and the crack width increases by about 0.01 mm.

Abstract: Micro-and mesoporous ceramics demonstrate promising properties for applications in energy-and environment-related fields. Due to their high thermal and chemical stability, they are particularly suited for separation in harsh thermal or chemical environments, e.g. as membrane materials for the separation of gas mixtures. In this work, we present the use of a preceramic poly(vinyl)silazane in combination with organic molecular porogens for the generation of micro-/mesoporous non-oxide ceramic structures. Microporosity is generated during the pyrolytic conversion process, while the addition of molecular porogens, to be removed during the heat-treatment, enables further control of the micro-/mesopore structure. A systematic investigation of various porogens showed the suitability of polystyrene for this purpose. Based on these findings, the pore structure and pore connectivity of polysilazane/polystyrene-derived structures were evaluated using gas physisorption and small angle X-ray scattering techniques. This material was further investigated by preparing asymmetric membranes consisting of micro-/mesoporous polysilazane/polystyrene-derived layers on porous ZrO₂/TiO₂ supports. The potential for gas separation applications was then demonstrated by single-gas permance evaluation of the generated structures at temperatures up to 300 °C.

Abstract: This paper presents the results of an experimental investigation on gas flow and Klinkenberg effect in coal. An anthracite coal sample is subjected to a range of effective stress conditions in order to investigate a general trend of coal permeability reduction with an increase in effective stress. Based on the measured values of permeability at different mean gas pressures for constant effective stress conditions, intrinsic values of permeability in the range 0.2 – 1.5 mD and gas slip factors are determined using the Klinkenberg plot. Using measured gas permeability and calculated intrinsic permeability values, an assessment of the mean gas pressure required to minimize the Klinkenberg effect is conducted.

Abstract: Two approaches can be used to study the size effect: one based on the change in sample size, and the other based on the variation in the aggregates size. The main objective of this research was to study the second approach. We studied 6 various concrete mixes and each test was repeated three times. For each material, uniaxial cyclic compressive tests have been performed to investigate the behaviour of concrete in a partially damaged state. The specimens were submitted to three levels of loading corresponding to 30, 60 and 80% of the maximal compressive strength. The damage indicator chosen is the decrease of Young’s modulus and the tightness indicator is the gas permeability. Results show that the concrete composition and more particularly the aggregate size have an important influence on the mechanical and transfer properties of concretes.

Abstract: An experimental campaign is carried out to study the effect of drying shrinkage and temperature on multi-directional gas permeability of dry concrete. Thermal loadings up to 250°C are applied on concrete samples in cylinder (11×22) and dog-bone forms (total length of 61 cm). Samples are sliced for permeability measurements. Permeabilities in longitudinal and radial directions are addressed. The cylinder samples are first sliced then dried or heated whilst the dog-bone samples are first dried or heated then sliced. The average of initial intrinsic permeability for the slices (5 cm height, 11 cm diameter) obtained from the (11×22) samples is found isotropic and equal to 2.93×10^-17 m2. In this case, drying shrinkage is isotropic. Furthermore, it is shown that for the dog-bone samples, drying shrinkage may induce micro-cracks preferentially in a certain direction which induces permeability anisotropy. Finally, the evolution of the normalized intrinsic permeability with respect to initial permeability versus temperature is found isotropic. An exponential fitting of intrinsic permeability versus temperature is found based on experimental measurements.

Abstract: The durability of concrete depends on its ability to prevent the ingress of aggressive chemical species. Transport properties of concrete, mainly permeability, play a key role in assessing and predicting the durability of reinforced concrete structures. This paper presents an experimental study on gas permeability of concrete influenced by environmental humidity and test depth. Gas permeability of concrete were measured both under dry condition and air-water balance by Cembureau method. A fine linear relationship between gas permeability coefficient and porosity of concrete blocks is shown in this article.

Abstract: This paper is focused on clarifying behaviour of concrete at elevated temperature with employing new test set-up constructed at Institute of Building Construction and Technology, Vienna University of Technology. This unique test set-up allows measuring gas permeability of different building materials such as concrete or ceramic at both high temperature (up to 400°C) and pressure (up to 6 bars). Present paper illustrates a new set up for permeability measurement during the heating and cooling and different testing procedures and evaluation of their influence on results.

Abstract: A biodegradable poly-lactic acid (PLA)/Sepiolite nanocomposite films were prepared by the thermo-compression and solvent-casting methods, and barrier properties (water-vapor and gas barrier) were evaluated. By introducing sepiolite into PLA, the properties of nanocomposite films improved until a certain amount (1.5% wt). By increasing sepiolite loading, nanoparticles tented to agglomerate and gas permeability (GP) decreased. According to the results, the nanocomposite films prepared by the thermo-compression method were more brittle but strong due to the formation of more crystals; while solvent-casted films were more ductile due to the presence of solvent, which may act as a plasticizer, as evidenced by the results of the GP.

Abstract: Aerogels are porous materials with potential applications in fields ranging from thermal insulation, catalyst support, filters, electrical storage, components in optical devices, mechanical damping all the way to drug release. However, careful reliable characterization is the base for both, understanding of fundamental structure - property relationships as well as a directed development of materials and composites for specific applications. The review therefore addressed severe problem upon aerogel characterization that have been identified in the past and presents reliable non-destructive alternatives and novel methods that can be applied for the characterization of aerogels as well as their gel precursors.

Abstract: Hong Kong-Zhuhai-Macao Bridge, the main structure is immersed tube tunnel bridge, its design life of 120 years, to find a suitable detection method is essential to assess the durability of the tunnel to ensure quality. TORRENT detection method and concrete testing radar combining such a large cross-section of the tunnel concrete structures nondestructive testing, test results show that the combination of these two methods on its own merits, the principle can efficiently detect large section structure permeability. NDT permeability through the tunnel to achieve effective assessment of the quality of concrete.