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Số người truy cập: 36,932,891

 Determination of diffusivities of dissolved gases in saturated cement-based materials
Tác giả hoặc Nhóm tác giả: Quoc Tri Phung; Norbert Maes; Diederik Jacques; Elke Jacop; Arno Grade; Geert De Schutter; Guang Ye
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Nơi đăng: Concrete Repair, Rehabilitation and Retrofitting IV, CRC Press; Số: -;Từ->đến trang: 1019-1027;Năm: 2015
Lĩnh vực: Khoa học công nghệ; Loại: Bài báo khoa học; Thể loại: Quốc tế
TÓM TẮT
Diffusion is an important property for characterizing concrete durability because it governs the penetration of aggressive substances (Cl-, SO42-, O2, CO2) responsible for degradation. However, data on the diffusion of substances (other than Cl-) in concrete are very scarce due to time and resource consuming measurements. This work describes a method to determine the diffusion coefficients of dissolved gases in saturated cement-based materials in order to study the effects of degradation on the transport properties. The proposed method is adapted from the technique used to determine the diffusivity of clay materials. The method is based on a through-diffusion methodology and allows simultaneous determination of diffusivities of two dissolved gases diffusing in opposite directions. A cement plug is mounted between two water reservoirs pressurized by two different gases at equal pressure (~ 1 MPa) to avoid advection. The changes in the dissolved gas concentration (at the opposite sides) are measured indirectly via gaseous phases which are in equilibrium with aqueous phases according to Henry's law. Additionally, a simple 1-D diffusive transport model (based on 1st and 2nd Fick’s laws) is developed to interpret the experimental data. The concentrations at outlet and inlet are used as inputs for the model, and the diffusivity is obtained by a fitting procedure. Experiments were performed on intact and carbonated cement (CEM I) paste samples with a gas combination: He and Xe. The results showed that the proposed method is providing reliable results within a reasonable experimental time and is useful to study the effects of degradation on the transport properties of cementitious materials. Carbonation resulted in a lower diffusivity.
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ABSTRACT
Diffusion is an important property for characterizing concrete durability because it governs the penetration of aggressive substances (Cl-, SO42-, O2, CO2) responsible for degradation. However, data on the diffusion of substances (other than Cl-) in concrete are very scarce due to time and resource consuming measurements. This work describes a method to determine the diffusion coefficients of dissolved gases in saturated cement-based materials in order to study the effects of degradation on the transport properties. The proposed method is adapted from the technique used to determine the diffusivity of clay materials. The method is based on a through-diffusion methodology and allows simultaneous determination of diffusivities of two dissolved gases diffusing in opposite directions. A cement plug is mounted between two water reservoirs pressurized by two different gases at equal pressure (~ 1 MPa) to avoid advection. The changes in the dissolved gas concentration (at the opposite sides) are measured indirectly via gaseous phases which are in equilibrium with aqueous phases according to Henry's law. Additionally, a simple 1-D diffusive transport model (based on 1st and 2nd Fick’s laws) is developed to interpret the experimental data. The concentrations at outlet and inlet are used as inputs for the model, and the diffusivity is obtained by a fitting procedure. Experiments were performed on intact and carbonated cement (CEM I) paste samples with a gas combination: He and Xe. The results showed that the proposed method is providing reliable results within a reasonable experimental time and is useful to study the effects of degradation on the transport properties of cementitious materials. Carbonation resulted in a lower diffusivity.
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