Moisture Transport In Concrete Research Articles

Does ITZ Influence Moisture Transport in Concrete?

Does ITZ Influence Moisture Transport in Concrete?

Boundary conditions for the problem of moisture transport in concrete

When calculating of the moisture transport in concrete of such geotechnical structures as a pile or diaphragm wall, contact with soil is forming the special boundary conditions. If the soil is in the full saturated state, then the Darcy’s law should be used to solve the problem, the boundary condition for which is the water pressure. Otherwise, the Bažant- Najjar model is used, for which the boundary condition is the relative humidity of soil environment at a certain temperature. The soil environment temperature is unique characteristic for each construction area. For Moscow region, the weighted arithmetic mean temperature to the depth of 60 m is 7.3°C. It is proposed to calculate the relative humidity of the soil environment according to the Kelvin capillary condensation equation, in which the suction is calculated using the Mualem-van Genuchten hydraulic model from the degree of saturation. Two well- known sets of hydraulic parameters of the Mualem-van Genuchten model, compiled on the HYPRES and the HYDRUS-1D database from the European soil map texture classes and the USDA textural soil classification respectively, were compared with the measurement results for soil samples classified according to Russian the GOST 25100. The experimental data showed a good approximation to the calculation with a set of parameters obtained on the basis of the HYPRES database. At the same time, the solution with the HYDRUS-1D parameter set showed a poor correlation.

Influence of Temperature on the Moisture Transport in Concrete

Moisture with harmful ions penetrates into the interior of concrete, which causes deterioration of the concrete structure. In this study, a moisture saturation equilibrium relationship of concrete was tested under different temperatures and relative humidity conditions to develop moisture absorption and desorption curves. Based on experimental data and numerical simulation, a model of moisture transport in concrete was established. The results from the model indicate that the moisture absorption rate was lower at higher temperatures and largely dependent on the saturation gradient, while the desorption was increased at higher temperatures and mostly affected by the saturation gradient. The proposed model was highly in agreement with the experimental data.

Drying and shrinkage of massive concrete wall segments—3 years experiment and analytical observations

This paper presents 3 years lasting large scale experiment focusing on simultaneous measurements of drying profiles and shrinkage on massive concrete wall segments considering size effect. Three large specimens with thickness 20, 40 and 80 were accompanied by group of small specimens in order to measure additional parameters. Specimens were made from the same concrete mixture and placed in the same environment in the laboratory. Typical concrete mixture was used having water cement ratio 0.5 and average 28-days compressive strength 55 MPa. Pore relative humidity was measured in different depths using embedded plastic tubes and moisture meter, shrinkage (or swelling) strain was measured by embedded vibrating wire strain gauges. Special attention is paid and comments are stated to initial swelling up to 80 μm/m and to observed size effects in drying and shrinkage. Extensive data collected during this experiment were compared with results of various numerical models for shrinkage of concrete and with results of models for moisture transport in concrete. Discussion on the predictive capability of these models is provided. Calculation of apparent shrinkage from measured drying profiles of the wall segments using shrinkage point model is carried out and compared with measured shrinkage as well.

Spalling and cracking modelling of high-performance concrete exposed to elevated temperatures

Concrete spalling and cracking play an important role in the mechanical behaviour of concrete structures subjected to thermal loading. However, the spalling and cracking of concrete has still not been sufficiently modelled. Based on the theory of poroelasticity, an anisotropic fixed smeared crack model is proposed for modelling the spalling and cracking of heated high-performance concrete. In the model, the permeability and Young's modulus of cement paste are estimated as a function of heating history based on the thermal decomposition analysis. The vapour pressure build-up and moisture transport in concrete are modelled in a numerical manner. The constitutive relation with the effects of thermal stress and vapour pressure is derived for the non-linear mechanical analysis. Finally, the proposed model is verified with experimental results obtained from the literature.

The Effect of Temperature on Moisture Transport in Concrete.

Most concrete structures and buildings are under temperature and moisture variations simultaneously. Thus, the moisture transport in concrete is driven by the moisture gradient as well as the temperature gradient. This paper presents an experimental approach for determining the effect of different temperature gradients on moisture distribution profiles in concrete. The effect of elevated temperatures under isothermal conditions on the moisture transport was also evaluated, and found not to be significant. The non-isothermal tests show that the temperature gradient accelerates the moisture transport in concrete. The part of increased moisture transfer due to the temperature gradient can be quantified by a coupling parameter DHT, which can be determined by the present test data. The test results indicated that DHT is not a constant but increases linearly with the temperature variation. A material model was developed for DHT based on the experimental results obtained in this study.

Time-dependent buckling analysis of SiO2 nanoparticles reinforced concrete columns exposed to fire

Time-dependent buckling of embedded straight concrete columns armed with Silicon dioxide(SiO2) nano-particles exposed to fire is investigated in the present study for the fire time. The column is simulated mathematically with Timoshenko beam model. The governing mass conservation equations to describe heat and moisture transport in concrete containing free water, water vapor, and dry air in conjunction with the conversion of energy are considered. The characteristics of the equivalent composite are determined using Mori-Tanaka approach. The foundation around the column is simulated with spring and shear layer. Employing nonlinear strains-displacements, energy methods and Hamilton\'s principal, the governing equations are derived. Differential quadrature method (DQM) is used in order to obtain the critical buckling load and critical buckling time of structure. The influences of volume percent of SiO2nano-particles, geometrical parameters, elastic foundation and concrete porosity are investigated on the time-dependent buckling behaviours of structure. Numerical results indicate that reinforcing the concrete column with SiO2nano-particles, the structure becomes stiffer and the critical buckling load and time increase.

Coupled heat and moisture transport in damaged concrete under an atmospheric environment

This paper presents thermogradient and hygrogradient coefficients as indicators for evaluation of coupled effects of heat and moisture transport in concrete. A numerical model for coupled heat and moisture transport was established and solved as well as a method to determine thermogradient and hygrogradient coefficients. Effects of temperature and humidity gradients were investigated through experiments, which covered also the effects of damage on moisture transport, temperature and humidity distributions along with coupled transport. The experimental results showed that temperature and humidity gradients accelerated moisture transport along with increased damage. In addition, the effect of temperature gradient on temperature distributions was significant, while the effect of humidity gradient was small. However, both temperature and humidity gradients had significant effects on relative humidity distributions. Hence, coupled heat and moisture transport in concrete had a significant effect on moisture transport, and the effect of damage on moisture transport must be considered when determining humidity field in damaged concrete.

Effect of mechanical damage on moisture transport in concrete

This paper is devoted to the influence of mechanical damage on moisture transport in quasi-brittle materials, such as concrete. The mechanical analysis is based on the isotropic damage model with the equivalent strain suitable for concrete. The mechanical model is formulated in the rate form in order to connect it with the nonstationary moisture transport which is modeled by a simple diffusion model derived from convection approach. The moisture transport is based on the volumetric moisture content. Three different formulas are used for description of the change of permeability with respect to growing damage parameter. Numerical approach is tested on an example of four-point shear test.

Effect of Damage on Moisture Transport in Concrete

AbstractThis paper presents the results of an experimental and analytical study on the effect of distributed cracks (damage) on moisture transport in concrete. Specifically, the writers investigate the following: (1) how damage affects the saturated and unsaturated transport and electrical resistivity, (2) whether one-dimensional (1D) analysis based on the sharp front (SF) theory can explain the relation between the saturated and unsaturated transport in damaged concrete, and (3) which transport mechanism is more sensitive to damage. Conceptual models are developed based on damage mechanics and fluid transport to explain the experimental data. Material constants are also provided for numerical modeling of unsaturated transport in damaged concrete. The results show that damage differently affects each of the transport mechanisms, and saturated hydraulic conductivity is more sensitive to damage as compared to sorptivity and electrical resistivity. The simplified 1D analysis, based on the sharp front theory,...

Aspects of Permeability in Modelling of Concrete Exposed to High Temperatures

The development of heat and moisture transport in concrete is critical to the development of pore pressures, which are thought to be a primary driver of damage and thermal spalling in concrete exposed to elevated temperatures. In the light of uncertainty and variation in the value of certain material properties and constitutive or parametric descriptions found in the literature, various sets of numerical experiments were conducted to investigate the significance of the intrinsic permeability, the evolution of permeability related to temperature and the relative permeability of the fluid phases as functions of saturation in predicting and analysing the behaviour of concrete drying under normal, low temperature, isothermal conditions and under exposure to very high temperature conditions as might be encountered during a fire. A fully coupled hygro-thermo-mechanical finite element model for concrete was employed with the permeability values and parametric functions altered in the model as required. Results of mass loss and the development of gas pressures with time were considered in relation to the potential for the occurrence of damage and thermal spalling, which is thought to be variously related to these processes. The analyses showed that permeability, and its variation with temperature, are very important in controlling the predicted behaviour at both low and high temperatures. Most significant of all were the relationships chosen to define the relative permeabilities. These were shown to strongly control the results of analyses of both low and high temperature problems and to potentially imply apparently different permeability values for the same concrete.

Coupled Heat and Moisture Transport in Concrete at Elevated Temperatures—Effects of Capillary Pressure and Adsorbed Water

ABSTRACT The importance of capillary pressure and adsorbed water in the behavior of heat and moisture transport in concrete exposed to high temperatures is explored by incorporating their behavior explicitly into a computational model. The inclusion of these two phenomena is realized with a formulation of a modified model, which represents an extension to the significant work of Tenchev et al. Comparative studies were carried out, using a benchmark problem, and it was determined that while the Tenchev formulation underestimated the capacity for fluid transport in the concrete, resulting in an overprediction of pore pressures (which may affect the prediction of mechanical damage and spalling), the inclusion of capillary pressure had little effect on the results. More important was the accurate representation of the free water flux, which has a significant effect on the prediction of vapor content and subsequently pore pressure. It was furthermore found that, while the adsorbed water flux may be minimal when concrete is exposed to high temperature, its presence has a significant effect on the fluid transport behavior and the prediction of pore pressures.