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 Challenges in measuring permeability of cementitious materials – towards a promising method
Tác giả hoặc Nhóm tác giả: Quoc Tri Phung, Norbert Maes, Diederik Jacques
Nơi đăng: 5th International workshop on the testing of low permeability materials, Belgium; Số: -;Từ->đến trang: -;Năm: 2016
Lĩnh vực: Chưa xác định; Loại: Báo cáo; Thể loại: Quốc tế
TÓM TẮT
Permeability is a fundamental material property for characterizing concrete durability because it determines the penetration of aggressive substances responsible for degradation under a pressure gradient. However, measuring permeability of cementitious materials is not a trivial task as is discussed in this work by an extended review of both direct and indirect permeability measurement methods. One of the main challenges is to cope with the continuous change in microstructure as a result of hydration of early age cementitious materials. Therefore, an appropriate method for measuring permeability and its change due to chemical degradation processes requires a short measurement time. With a need to have a flexible and sensitive method suitable for measuring permeability changes due to chemical degradation of concrete, we proposed a new method which meets three requirements: short measurement time; reliability and being simple enough to apply. The proposed method is very flexible and it is convenient to do further tests on the same sample. The samples can be decoupled after the test and connected to another setup in which the diffusivity can be tested or to perform degradation (e.g. carbonation, leaching) tests. After a degradation test, the samples can again be connected to the permeability setup to study the effect of degradation on the permeability. A sequence of different tests on the same sample is possible by quick couplings which help to disconnect the permeability cell (embedded sample inside) from the rest of measurement device and recouple it to another set up compatible with the permeability cell. The novelty of the method is that steady-state conditions are controlled by applying a constant water flow rather than the applied pressure gradient because the measurement accuracy of the pressure is much higher of the extremely low flow. A pressure gradient of around 5 to 10 bar is applied by controlling the pressure at both sides of a saturated cement-based core embedded in a permeability cell. When the flow almost reaches steady state, the constant pressure mode is changed to the constant flow mode. The pressure and water flow are controlled by precise Syringe pumps. Tests were performed on hardened cement pastes with water/cement ratio ranging from 0.325 to 0.6 to verify the proposed method. The validity of Darcy's law was confirmed by the permeability measurements with various flow rates performing on very permeable cement paste sample. The results showed that the proposed method is giving reliable results within a reasonable experimental time (one week for permeability coefficient of 10-13 m/s).
ABSTRACT
Permeability is a fundamental material property for characterizing concrete durability because it determines the penetration of aggressive substances responsible for degradation under a pressure gradient. However, measuring permeability of cementitious materials is not a trivial task as is discussed in this work by an extended review of both direct and indirect permeability measurement methods. One of the main challenges is to cope with the continuous change in microstructure as a result of hydration of early age cementitious materials. Therefore, an appropriate method for measuring permeability and its change due to chemical degradation processes requires a short measurement time. With a need to have a flexible and sensitive method suitable for measuring permeability changes due to chemical degradation of concrete, we proposed a new method which meets three requirements: short measurement time; reliability and being simple enough to apply. The proposed method is very flexible and it is convenient to do further tests on the same sample. The samples can be decoupled after the test and connected to another setup in which the diffusivity can be tested or to perform degradation (e.g. carbonation, leaching) tests. After a degradation test, the samples can again be connected to the permeability setup to study the effect of degradation on the permeability. A sequence of different tests on the same sample is possible by quick couplings which help to disconnect the permeability cell (embedded sample inside) from the rest of measurement device and recouple it to another set up compatible with the permeability cell. The novelty of the method is that steady-state conditions are controlled by applying a constant water flow rather than the applied pressure gradient because the measurement accuracy of the pressure is much higher of the extremely low flow. A pressure gradient of around 5 to 10 bar is applied by controlling the pressure at both sides of a saturated cement-based core embedded in a permeability cell. When the flow almost reaches steady state, the constant pressure mode is changed to the constant flow mode. The pressure and water flow are controlled by precise Syringe pumps. Tests were performed on hardened cement pastes with water/cement ratio ranging from 0.325 to 0.6 to verify the proposed method. The validity of Darcy's law was confirmed by the permeability measurements with various flow rates performing on very permeable cement paste sample. The results showed that the proposed method is giving reliable results within a reasonable experimental time (one week for permeability coefficient of 10-13 m/s).
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