The effect of compressive loading on the residual gas permeability of concrete (original) (raw)
Impact of reinforcement-concrete interfaces and cracking on gas transfer in concrete
Construction and Building Materials
The durability of reinforced concrete structures is largely impacted by their transfer properties, which can be evaluated through, for example, permeability measurement. Usually, concrete permeability is studied on plain specimens and the effect of the presence of steel bars on permeability in reinforced concrete has been little studied in the literature. The steel-concrete interface presents a larger porosity than plain concrete, which can be the cause of preferential percolation paths for fluids. Such percolation paths could create a lower resistance to fluid transfer and modify transfer kinetics. For reinforced and prestressed structures with large reinforcement contents, such as found in nuclear power plants, the impact of the reinforcement on gas transfer should be identified to obtain a better assessment of the flow within the structure. The aim of this experimental study is to characterize the effect of the presence of reinforcement on such flows by measuring leakage rates, permeability, and time to reach the steady state. Measurements were performed with a Cembureau constant head permeameter on cylindrical concrete specimens with or without steel bars. Since gas transfer into concrete depends on the rate of saturation of the material, the specimens were tested at different degrees of saturation: 0%, 6%, 30%, 60%, 80%, 90% and 100%. The analysis quantifies the impact of the defects created by the steel bar for each state. The results show that material composed of concrete and reinforcement can be divided into two distinct permeability zones: the plain concrete and the steel-concrete interface with or without cracking. These two zones can be associated in series and/or in parallel according to the configuration. The consequences on permeability measurement in reinforced structures are discussed.
1999
This paper describes the main results obtained jointly by a number of French laboratories within the framework of a group under AFREM (Association Francaise de Recherches et Essais sur les Materiaux et les Constructions). The objectives of this group were to define a preconditionin g process which would result in a better distinction between the various types of concrete with an acceptable test length, and to draft a recommendation for measuring the gas permeability of concrete. The procedure for measuring the gas permeability of concrete provides good reproducibility. However, the equipment used does not allow the measurement of permeability values greater than 10 -19 m². A conditioning procedure for predrying a test sample before measurement was defined. This conditioning procedure is the result of a compromise among the necessary attributes of a test, which should be easy to apply and as rapid as possible, while not degrading the test sample excessively. A drying temperature of 8...
Gas and water permeability of concrete
Geological Society, London, Special Publications, 2014
Concrete is used as a barrier on surface or near-surface facilities for the final disposal of low- and intermediate-level radioactive waste, where gas can be generated and affect the hydraulic properties and the processes taking place in concrete. In this framework, gas-transport properties of concrete samples were investigated using two different laboratory test set-ups: a non-steady-state equipment working under low injection pressures; and a newly fine-tuned steady-state set-up working under different pressures.Permeability decreased with water content increase but was also greatly affected by the hydraulic history of concrete (i.e. if it had been previously dried or wetted). The intrinsic permeability determined with gas flow was about two orders of magnitude higher than that determined with liquid water (10−16 v. 10−18 m2), probably due to the chemical reactions taking place during saturation (carbonation). The relative gas permeability of concrete increased sharply for water d...
Permeability of a Macro-Cracked Concrete Effect of Confining Pressure and Modelling
Materials, 2021
The effects of confining pressure are investigated for two samples of a macro-cracked concrete. Samples are first macro-cracked with a splitting tensile strength test (Brazilian) technique. Gas permeability is continually measured under increasing (or decreasing) confining pressure, whereas crack closure (or opening) is recorded with an LVDT (Linear Variable Differential Transformer) device. Despite a mechanical closure of the macro-crack, identified at around 20 MPa confining pressure, gas permeability continues to decrease as confinement is increased. This means that a model of the macro-crack by two parallel planes (using Poiseuille law) cannot be used to represent permeability variations during closure (or opening) of cracks. As a consequence, a physical model is designed in order to simulate with a better consistency the real behaviour of the macro-crack. This simple modelling allows both behaviours, mechanical and hydraulic, under confining pressure, to be simulated with the s...
The effect of mechanical stress on permeability of concrete: A review
Cement & Concrete Composites, 2009
The presence of aggressive fluids and their transport is by far the most important factor controlling the durability of cement based composites. In structural concrete, the application of mechanical stress leads to cracking, which in turn affects the transport properties adversely, but very little is known of this influence. The paper highlights the vast discrepancy between experimentally determined permeability data, which appear to be largely artifacts of disparate test procedures. In particular, it is not clear if an equilibrium was attained in the fluid flow and further, whether the flow measurements were made in the presence of the applied stress, which together make it very difficult to compare experimental data. Nevertheless it is clear that stress induced cracking leads to a surge in fluid flow and there exists a threshold value for both the applied stress and the resultant crack width associated with fluid permeability in concrete.
Water retention and gas relative permeability of two industrial concretes
Cement and Concrete Research, 2012
This experimental study aims at identifying the water retention properties of two industrial concretes to be used for long term underground nuclear waste storage structures. Together with water retention, gas transfer properties are identified at varying water saturation level, i.e. relative gas permeability is assessed directly as a function of water saturation level Sw. The influence of the initial de-sorption path and of the subsequent re-saturation are analysed both in terms of water retention and gas transfer properties. Also, the influence of concrete microstructure upon water retention and relative gas permeability is assessed, using porosity measurements, analysis of the BET theory from water retention properties, and MIP. Finally, a single relative gas permeability curve is proposed for each concrete, based on Van Genuchten-Mualem's statistical model, to be used for continuous modelling approaches of concrete structures, both during drying and imbibition.
Gaz permeability of mechanical damaged concrete
Permeability is used to evaluate durability characteristics of concrete, but it is commonly estimated by measuring the gas permeability of never stressed nor damaged specimens. The purpose of this study is to investigate experimentally the effect of axial compressive loading on the permeability of concrete. Three types of concrete were used: Ordinary Concrete, High Performance Concrete, and High Performance Steel Fiber Reinforced Concrete. Monotonic and cyclic loads were applied on 220 x 110 mm diameter specimens. Stress levels ranged from 60% to 90% of the ultimate strength. After loading, three 50 mm thick slices were cut from each cylinder and dried in a ventilated oven. Two gas permeability tests were performed during the drying procedure, the first after one month at 60°C and the second after an additional month at 80°C or 105°C. Permeability was measured using a constant head permeameter with nitrogen as the neutral percolating gas. To assess the level of mechanical damage for concrete cylinders, compressive force and longitudinal strains were recorded during and after loading, and dynamic moduli were measured just before and after loading. A relationship between mechanical damage indicators and permeability is presented and discussed.
About Gas Permeability and Diffusion through Concrete
10th MATBUD’2023 Scientific-Technical Conference
Gas production is expected in radioactive-waste storage structures. This will induce a slow increase in gas pressure, which necessitates the study of gas transfer at a low pressure. In this special case, calculations of the flow through storing materials while solely using permeability and Darcy's law are likely to be inadequate, as diffusion may play a crucial role in the process. The gas permeability and gas diffusion coefficient of industrial concrete have then been measured on the dry material. Diffusion tests were performed with a new device, specially designed for this study. The diffusion coefficient was directly measured with the use of the first Fick's law, as the test was analyzed under a steady state. Using some simplified hypotheses, it was then possible to compare the proportion of flow occurring due to diffusion with the one occurring due to permeation. The tendency is very clear and unambiguously shows that diffusion is predominant at a very low injection pressure but becomes negligible as soon as the gas pressure exceeds a moderate value.