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This paper focuses on behaviors of moisture dispersed in nano‐macro scale pores under various temperature and relative humidity conditions. The authors formulated an equilibrium relationship between liquid and vapor phases and a moisture flux driven by pore pressure, vapor pressure and temperature gradients. In addition, liquid and interlayer water...
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... i : viscosity of liquid water under ideal conditions, and G e : additional Gibbs energy required for liquid flow under non ‐ ideal conditions. Because the viscosity η i of liquid water, like density and surface tension, is dependent on temperature, the following regression formula based on measured values [4] is used (Fig. ...
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... Water transport in mortar matrix is based on previous studies (Maekawa et al. 2003, Ishida et al. 2007, Maekawa et al. 2009). The equation is described as ...
... where ϕ cr is crack volume fraction in cracked matrix, S cr is the saturation degree of crack, q cr is water flux vector in the crack (m/s), and l cr is the local coordinate defined by the crack direction. The flow of numerical simulation is shown in Fig. 2. It is based on a multi-scale computational system DuCOM for simulating the properties of cement-based materials (Maekawa et al. 2003, Ishida et al. 2007, Maekawa et al. 2009). Initial conditions are input, including materials and mix proportion, specimen shape and size, and environment conditions. ...
... Water pressure and saturation degree of mortar matrix are simulated based on the models in DuCOM (Maekawa et al. 2003, Ishida et al. 2007, Maekawa et al. 2009). As aforementioned in Eq. (1), water transport in mortar matrix takes into account the pore structure of mortar matrix, which are the porosity and pore size distribution of capillary, gel, and interlayer pores. ...
Strain-hardening cement-based composites (SHCC) under cracked condition exhibits remarkable capillary absorption due to water ingress from multiple cracks. Surface treatment using water repellent agents is an effective way for improving water resistance of SHCC, but the water resistance may remarkably decrease when cracks penetrate impregnation depth. Another way is to add water repellent agents directly into the mixture, offering SHCC integral water repellency even if cracks form later. However, although integral water repellent treatment has been proved feasible by previous studies, there is still lack of simulation work on the treated SHCC for evaluating its durability. This study presents a simulation method for capillary absorption of cracked SHCC with integral treatment based on a multi-scale approach proposed in the authors' previous work. The approach deals with water flows in bulk matrix and multiple cracks using two individual transport equations, respectively, whereas water absorbed from a crack to its adjacent matrix is treated as the mass exchange of the two equations. In this study, the approach is enhanced for the treated SHCC by integrating the influencing of water repellency into the two transport equations as well as the mass exchange term. Using the enhanced approach, capillary absorption of water repellent SHCC under cracked condition is simulated, showing much more reduced water ingress than the untreated concrete, which is consistent with total absorption data from previous tests. This approach is also capable of simulating water spatial distribution with time in treated SHCC reasonably.
... The carbonation model of concrete materials developed by Papadakis [23,24] has been cited by many researchers [25] and has been verified in the actual use of concrete. The hydration model developed by takes the hydration exotherm of the mineral composition of cement and the hydration exotherm of mineral admixtures into account and predicts the changes in the mechanical properties and shrinkage of concrete under different mix ratios and different curing conditions [28]. It also predicts the drying shrinkage and various durability properties, such as carbonation [26], chloride ion erosion, and steel corrosion [26]. ...
Although quartz powder is a common concrete filling material, the importance and originality of this study lies in the development of a hydration model for quartz powder–cement binary mixtures and the adoption of this model to predict the development of concrete material properties. The purpose of this study is to use this model to promote the material design of environmentally friendly concrete and to elucidate the relationships in the development of the various properties of quartz powder concrete. The method used in this study was as follows: The parameters of the hydration model were obtained through seven days of hydration heat experiments. The hydration heat up to 28 days was also calculated, and the various properties of the concrete were predicted from the heat of hydration. The main findings of this study were as follows: (1) The ultimate hydration heat released per gram of cement for the different quartz powder substitution rates and quartz powder particle fineness was the same, at 390.145 J/g cement, as was the shape index of the hydration model at −1.003. (2) Moreover, through the model calculations, we found that, at the twenty-eighth day of the curing period for the quartz powder specimens with different quartz powder substitution amounts and different fineness, the reaction level of the cement was similar, at 0.963, as were the values of the cumulative heat of hydration, with both at 375.5 J/g cement. (3) The model showed that, in the late stage (28 days) of hydration for quartz powders of different fineness and when the substitution amount was the same, the cumulative heat of hydration over 28 days was similar. (4) The properties of concrete were evaluated using the calculated hydration heat. Overall, the predictive performance of the power and linear functions was similar, with no significant differences being found.
... Therefore, ρ (kg/m 3 ) and μ (kg.m -1 .s -1 ) were calculated according to the specified temperatures (T in o C) by [20]: ...
This study performed a sensitivity analysis to correlate the frictional head loss calculated by the Darcy-Weisbach (D-W) and the Hazen-Williams (H-W) formulas. For a broad variety of fluid temperatures, velocities, and pipeline diameters, this study considered an extensive discussion and analysis to determine friction loss within pressurized pipelines using Microsoft Excel. Regression analysis and statistical tools were applied to improve the relationship between the two equations. A more accurate expression was developed to calculate the friction loss in terms of the H-W equation. The estimated values were compared with previous experimental and numerical studies, and a good agreement was observed. The proposed model was evaluated using WaterGEMS software in an application example of a water supply system against the D-W and H-W equations. Good agreements were recorded between predicted values and previous studies, with an error of less than 1%. These findings can be used to improve the hydraulic design of engineering applications.
... used a single parameter model, shown in Equation (3b), with p as the fitting parameter to describe moisture distribution in prisms of cementitious stabilised binders for the determination of D(θ n ) using Boltzmann-Matano's method. Specimens of three different lengths (40,80, and 120 mm) were allowed to dry from two opposite sides (75 × 75 mm) following the procedure given in Sakata (1981) [12] for 50 days. The duration of drying in this study also appears to be well short of what would have been needed to equilibrate the mass loss. ...
... temperature without a temperature gradient does not have a significant influence on moisture transfer in concrete [39] . Another study on the impact of drying temperature on moisture transport in cementitious materials has reported that diffusion of trapped moisture in the ink bottle pores comes into picture as the temperature rises to 40°C [40] . Thus, the D(θ n ) obtained using Equation (5b), which follows from the 2-parameter θ n (ϕ) model, offers a better representation of the moisture transport processes underlying the drying phenomena. ...
This study utilises moisture distribution profiles harvested from literature and gravimetric observations made in the laboratory to analyse the robustness of three Boltzmann-profile, θn(ϕ) models which were previously adopted by various researchers for the modelling of non-linear hydraulic diffusivity, D(θn) of drying mortar and concrete. Such an analysis is necessary to ensure that the D(θn) data is reliable and free from modelling artefacts. A 2-parameter θn(ϕ) model is found to be better suited for the inverse estimation of D(θn) in comparison to a widely used 3-parameter model. The 2-parameter model captures the effects of water-to-cement ratio and temperature on D(θn) in accordance to the physics of the drying phenomenon. Also, it does not cause a sudden drop in the diffusivity curve near high saturation levels as is noted with the 3-parameter model. It is further noted that the 3-parameter θn(ϕ) model fails to fit low θn - low ϕ data which is typically obtained using non-destructive imaging techniques. The 2-parameter model can fit low θn - low ϕ data and is also suitable for high θn - low ϕ data, obtained through gravimetric experiments, within the limit of θn < 0.80.
... The equilibrium moisture content, θ eq (m 3 /m 3 ), can be calculated using the models given in the following equations (Espinosa and Franke 2006;Ishida et al. 2007;Patil and Bhattacharjee 2008;Kondraivendhan 2010;Kondraivendhan 2010;Espinosa and Franke 2006;Hall and Hoff 2002;Lyklema 2000;Espinosa and Franke 2006): (15) r eq = f * (r k + t a ) (16) r k = −2 × 10 9 × V m × σ R(T + 273.15)log(RH/100) ...
Assessing the probability of failure of typically adopted cover depths to resist the onset of carbonation-induced corrosion under the influence of seasonal rains is important for the durability design of reinforced concrete elements. The exposure scenario commonly manifests in the tropics, wherein the majority of monsoonal rainfall remains confined to location-specific annual wet-spells. The study aimed to develop an improved methodology for the identification of annual wet-spell and proposed an index based on the judicious combination of wet-spell characteristics to enable the mapping of its severity over a region of interest and facilitate the selection of Moisture Reference Years (MRYs). The developed paradigm was implemented using gridded meteorological data sets to map the severity of annual wet-spell at 1° resolution for India. The map provides an improved severity classification compared to rainfall amount over regions of scanty rain but considerable wet-spell duration. The estimates of time conducive for carbonation over a period of 100 successive MRYs, as deduced from the simulated moisture distribution data for the five climatic zones of India, were also found to correlate well with the corresponding index values. Finally, the √t modeling of the carbonation depth using the derived estimates of conducive duration and assessment of failure probabilities of typical cover depths suggested that a nominal depth of 45 mm is able to resist carbonation at a safety level of 90% for all the five climatic zones.
... To comply with the true properties of a fluid, user-defined properties were utilized in the model, including density, viscosity, heat capacity, and thermal conductivity for both pure water and nanofluid. In order to account for the temperature-dependent properties of the nanofluid, the ANN models from Section 2.1 were employed by transferring the MATLAB code to the C language, while the water properties were incorporated with temperature dependency using the equations from Ishida et al. (2007) and Ishida et al. (2007) and Kays et al. (2005) as described in Eqs. (10)-(12). ...
... To comply with the true properties of a fluid, user-defined properties were utilized in the model, including density, viscosity, heat capacity, and thermal conductivity for both pure water and nanofluid. In order to account for the temperature-dependent properties of the nanofluid, the ANN models from Section 2.1 were employed by transferring the MATLAB code to the C language, while the water properties were incorporated with temperature dependency using the equations from Ishida et al. (2007) and Ishida et al. (2007) and Kays et al. (2005) as described in Eqs. (10)-(12). ...
... The average deviations were collected as 8.95 % for the Nusselt number and 7.45 % for the pressure drop from Fig. 5. This section also verifies that the model can adapt the temperature-dependent equations from Ishida et al. (2007) and Ishida et al. (2007) and Kays et al. (2005). The agreement between the simulation results and the experimental results in validation can also serve as a verification of the applied equations. ...
... The saturation is assumed to be 0.80, based on water transport analyses using a thermal dynamic multi-scale water transport model[47]. The corrosion rates of the experimental specimens and the model predictions are summarised inFig. 5. ...
Most of the existing infrastructures (e.g., oversea bridges) are made of reinforced concrete (RC); therefore, their safety is of high priority for our society. RC structures undergo continuous deterioration due to a combination of chloride ingress and loading actions. Chloride-induced corrosion is thus one of the most serious threats. In this work a stochastic model is presented which couples degradation effects of crack development and corrosion progression based on physicochemical and mechanical models to estimate the probability of failure of a RC structure over time. To enable an efficient probabilistic assessment, a novel rapid numerical approach (RNA) is implemented for modeling the chloride diffusion. Numerical experiments show that the probability of corrosion failure is significantly underestimated if the coupled degradation effect of cracks and corrosion is not considered. Finally, parameter analyses are used to identify the effects of individual parameters, including external load level, supplementary cementitious materials and environmental temperature, on the probability of corrosion failure of RC beams over time.
... The multiscale integrated simulation scheme used in this study has been summarized in Fig. 1. Starting with nanoscale hydration kinetics, chemo-physical reactions of the cement phase are simulated [26]. Then, hydration products, along with cement particles, form complex micropore structures, within which moisture transport and thermodynamic equilibrium can be formulated [27]. ...
A coupling model reflecting the interaction between freeze–thaw cycles (FTCs) and alkali–silica reactions (ASRs) is established from the microscale to the macroscale under the consideration of non-uniform environmental and mechanical conditions. At both material and structural levels with/without reinforcement, the deformation and damage patterns of specimens under single and coupled FTCs and ASRs were simulated by multiscale finite element analysis and partially verified by experiments. Furthermore, following different sources of damage actions, the remaining fatigue life of reinforced concentrate (RC) slabs under traffic loads was investigated. The results show that ASR-driven expansion is mainly governed by the arrangement of reinforcing bars, whereas FTC damage is mainly initiated from corners, edges, and surfaces of RC slab parts and closely relies on water supply. In addition, the severity of coupled damage (FTC and ASR) can be significantly greater than that of the sum of single ASR and FTC damage due to the gel-filling of pores and entrained air. Finally, in terms of the remaining fatigue life, the ASR could be occasionally beneficial for bridge decks under moving traffic loads due to gel-filled cracks and chemical prestressing. However, if cracks are empty or filled by condensed liquid water, the overall fatigue life will be significantly reduced.
... The multiscale integrated simulation scheme used in this study has been summarized in Fig. 1. Starting with nanoscale hydration kinetics, chemo-physical reactions of the cement phase are simulated [26]. Then, hydration products, along with cement particles, form complex micropore structures, within which moisture transport and thermodynamic equilibrium can be formulated [27]. ...
Keywords frost damage alkali-silica reaction (ASR) bridge deck combined effect fatigue life A coupling model reflecting the interaction between freeze-thaw cycles (FTCs) and alkali-silica reactions (ASRs) is established from the microscale to the macroscale under the consideration of non-uniform environmental and mechanical conditions. At both material and structural levels with/without reinforcement, the deformation and damage patterns of specimens under single and coupled FTCs and ASRs were simulated by multiscale finite element analysis and partially verified by experiments. Furthermore, following different sources of damage actions, the remaining fatigue life of reinforced concentrate (RC) slabs under traffic loads was investigated. The results show that ASR-driven expansion is mainly governed by the arrangement of reinforcing bars, whereas FTC damage is mainly initiated from corners, edges, and surfaces of RC slab parts and closely relies on water supply. In addition, the severity of coupled damage (FTC and ASR) can be significantly greater than that of the sum of single ASR and FTC damage due to the gel-filling of pores and entrained air. Finally, in terms of the remaining fatigue life, the ASR could be occasionally beneficial for bridge decks under moving traffic loads due to gel-filled cracks and chemical prestressing. However, if cracks are empty or filled by condensed liquid water, the overall fatigue life will be significantly reduced.
... Moreover, the ascending scanning curves with different starting points exhibit different scanning behaviors, indicating that different physical phenomena are at play. When the RH remains above 40%RH, the main contributing factors are the release and filling of liquid water, which can be described by the "ink-bottle" effect (Ishida et al., 2007) arising from the geometrical confinement posed on water in pore cavities by water in narrow pore necks as RH decreases, and multilayer adsorption and capillary condensation in previously emptied pores as RH increases. When the RH is below 30%RH, no liquid water may persist in pore structures due to the cavitation phenomenon as the negative pressure exerted on the stretched water in pore cavities exceeds the limit of stability, the overlapping of ascending curves with starting points in 10-30%RH suggests that the pure physisorption is probably reversible. ...
