Saturated Concrete Research Articles

Electrical characterization of freeze-thaw damage in saturated concrete and its interfacial transition zones

Determining the freeze-thaw (F-T) damage of the interfacial transition zone (ITZ) is crucial to understanding the mechanism of F-T in concrete and improving its frost resistance. In this paper, the F-T damage of saturated concrete/mortar and ITZ is characterized using AC impedance spectroscopy, and the micro-mechanisms of F-T damage in cement-based materials (CBMs) are summarized. Firstly, the damage factor was defined by the effective resistivity of the CBMs, and a correlation between the damage factor and the compressive strength loss was established. The F-T damage process was divided into a damage development stage and a damage stabilization stage based on the damage factor and fractal dimension. Then, the effective resistivity separation formula was proposed to calculate the ITZ effective resistivity, and the ITZ damage factor was calculated for non-destructive quantitative characterization of the F-T damage in the ITZ. Finally, the microscopic mechanism of F-T damage in CBMs and their ITZs was summarized based on damage factor, fractal dimension, super depth of field microscopy, and nanoindentation. The results showed a linear relationship between the damage factor and compressive strength loss (Lc = 0.176Er+0.030); the ITZ had damage factors of 80 % and 70 %, which were 1.6 and 1.4 times higher than those of the matrix, respectively; F-T cycles produce micro-damage, part of which connects with the disconnected pores to form connected pores, the micro-damage extends and accumulates along the surface of the aggregates, leading to ITZ debonding from aggregate and deterioration of the mechanical properties.

Continuous damage of concrete structures due to reinforcement corrosion: A micromechanical and multi-physics based analysis

Deterioration of concrete and composite structures due to the corrosion of embedded steel components (rebar, structural steel components, and steel fiber, etc.) is a self-accelerating process involving multiple chemophysical processes that occur concurrently in the heterogeneous structure of concrete. The multiple-inclusion matrix of concrete and the multi-chemophysics nature of steel corrosion synergistically challenge an accurate analysis and evaluation of the deterioration process using homogeneity-based continuum mechanics. This study presents a three-dimensional micromechanical model developed for quantifying the continuous deterioration of concrete by steel corrosion. Continuous damage theory of solid-state materials was applied to a steel-concrete sample that consists of mortar, aggregate, and steel phases as were reconstructed from high-resolution X-ray CT images. With due consideration of the variations in environmental temperature and moisture, the complex chemophysical processes involved in corrosion-induced deterioration of concrete were solved concurrently using finite element analysis. Results of the study indicate that capillary suction in a variably saturated concrete plays an important role in steel corrosion and that removal of chloride by an externally applied electrical field can effectively mitigate steel corrosion and the incurred concrete deterioration.

An implicit consideration of fluid flow in the calculation of drying shrinkage of porous materials: Case of saturated concrete in low humidity environment

AbstractThe drying shrinkage of porous materials is significantly dependent on external relative humidity (). The perspective of temperature increase due to the climate change will accentuate the drying phenomenon in structures in lands and cities. The evolution of shrinkage can be determined by equivalent pore pressure consisting of capillary pressure , disjoining pressure and pressure caused by interfacial energy. For concrete structures, up to condition, standard models can reproduce the drying shrinkage experiments accurately. However, as the decreases to 30%, these models seem to be limited because the measured relationship () differs from the corresponding static equilibrium relationship as the drying occurs rapidly and the dynamic fluid flow effects on capillary pressure have been neglected. In this paper, the standard shrinkage model has been improved to take into account the dynamic flow effect and the viscoelastic behaviour of the solid skeleton. The dynamic and standard models have been compared with experimental results of drying shrinkage of concrete with two different relative humidity conditions. The standard model clearly showed its limitations at low external relative humidity . However, the dynamic model showed good prediction of mass loss and shrinkage strains at high and low humidity conditions. Furthermore, the numerical and experimental investigations indicate that not only the dynamic effects but also the additional pressure induced by surface energy should be taken into account to quantify the drying shrinkage of cement‐based materials at low condition.

Experimental and numerical investigation on saturated concrete subjected to underwater contact explosion

The hydraulic concrete structures were partially or fully in direct contact with water during the service life. The mechanical properties of saturated concrete are different from dry concrete because of the presence of water. To investigate the underwater blast resistance mechanism of saturated concrete, saturated concrete slabs were first tested in underwater explosion experiments with different TNT masses of 2.5 g, 5 g, and 10 g. The experimental results showed that the crater on the front of the concrete slab was smaller than those on the back and the size of the crater increased with increasing mass of TNT. Numerical simulations were conducted and material parameters were determined based on additional tests: The damage model under different stress states was proposed by repeated loading and unloading tests in tension and compression under different confining pressures. The damage model was then embedded into the Holmquist-Johnson-Cook (HJC) model. Quasi-static and dynamic compression experiments were conducted to determine the material parameters of the saturated concrete. A three-dimensional fluid-solid coupling numerical model in ABAQUS was proposed for simulating the underwater explosion and its interaction with the saturated concrete slab. Finally, the mechanisms that produce differences in the damage pattern of concrete slabs at different explosive masses are revealed.

Coupled Effect of Chloride Corrosion and Repeated Uniaxial Compressive Loading on Unsaturated Concrete.

Concrete structure performance continuously deteriorates during operation, and the performance is simultaneously affected by chloride corrosion and repeated traffic loading. Repeated-loading-induced cracks have an impact on the rate of chloride corrosion. Chloride-induced concrete corrosion also affect the stress level of the structure under loading. Therefore, the coupled effect of repeated loading and chloride corrosion on the structural performance needs to be investigated. An upgraded test device was developed for chloride corrosion testing of unsaturated concrete structures under repeated loading. Based on the experimental results, considering the influence of repeated loading on the moisture diffusion coefficient and the chloride diffusion coefficient, a chloride transport model for unsaturated concrete under the coupled effect of repeated uniaxial compressive loading and corrosion was established. The chloride concentration under coupled loading was determined by the Crank-Nicolson finite difference method and the Thomas algorithm, and then chloride transport under the coupled effect of repeated loading and corrosion was analyzed. The results showed that the stress level and the repeated loading cycles directly affect the relative volumetric water content and chloride concentration in unsaturated concrete. The effect of chloride corrosion is more severe in unsaturated concrete compared to saturated concrete.

Relationship Between Dynamic Tensile Strength and Pore Structure of Saturated Concrete under Lateral Pressure

The dynamic properties of concrete in two states (saturated and dry) were compared and analyzed through a series of dynamic biaxial tensile-compressive (T-C) experimentals. All specimens were subjected to constant biaxial T-C stress ratios (0.5:−1, 0.25:−1, 0.1:−1, 0.05:−1 and 1:0 respectively) at different strain rates (10−5s−1 to 10−2s−1). It was found that the biaxial T-C ultimate strengths of both kinds concrete closely relate to the lateral pressure of the specimen, and the independent tensile and compressive strength increases with the increase of strain rate. In the case of exerting lateral pressure, the failure states of specimens show same manner as that of the uniaxial tensile specimens, which indicates that the specimens were completely fractured under tensile loading. The test results show that the biaxial T-C strength of saturated concrete is lower at strain rates of 10−5s−1, whereas it is higher at the other three strain rates (10−4s−1, 10−3s−1 and 10−2 s−1). This distinct difference indicates that saturated concrete is more rate sensitive under lateral pressure. Through mechanical analysis the article explains the reason of this phenomenon is mainly dued to the beneficial tensile stress of the pore water surface and the Stefan effect. Meanwhile, the strength prediction expression of saturated concrete was established under the condition of stress ratio and strain rate are considered simultaneously.

Influence of Inertia on the Dynamic Compressive Strength of Concrete.

The rate sensitivity of concrete material is closely related to the inertia and viscous effects. However, the effect of inertia on the dynamic strength of concrete remains unclear. In this paper, digital image correlation technology was applied to study the strain variation of dry and saturated concrete with different loading rates. The test results indicated that the strain gradually decreased with the distance from the load end, and the strain gradient around the load region increased with the strain rate, especially for saturated concrete. Then, a single degree of freedom model was established to evaluate the dynamic compressive strength of elastic concrete. The calculated results indicated that the influence of inertia on the dynamic increase factor (DIF) was negligible for concrete within a low strain rate. When the strain rate is larger than 100/s, the inertial effect on the strength of concrete should be considered. After that, a quasi-static concrete damaged plasticity (CDP) model was employed to simulate the influence of inertia on the stress distribution and axial reaction force at the loaded end of concrete under different rates of compressive loading and verified with experimental results. The results obtained in this study indicated that the dynamic nominal strength of concrete obtained from the tests could not be directly used for structural analysis which may overestimate the effect of inertia on the dynamic response of the structure.

An Experimental Study on Mechanical Properties and Fracture Characteristics of Saturated Concrete under Coupling Effect of Low Temperature and Dynamic Load

Concrete is widely used in bridge foundation, water supply, and drainage engineering. On the one hand, the saturated concrete is always in the saturated state. In the cold winter, northeast China and the alpine region suffer from freezing disaster. On the other hand, it has to continue to bear the dynamic load action of vehicles and running water, which makes the stress state of saturated concrete more complicated under the coupling action of low temperature and dynamic load. In order to study the mechanical properties and fracture characteristics of saturated concrete under the coupling effect of low temperature and dynamic load, the impact compression tests of concrete under normal temperature 20°C, -5°C, -10°C, and -15°C were carried out with a diameter of 74 mm split Hopkinson pressure bar (SHPB). The stress-strain characteristics, energy dissipation, and failure modes of specimens under different low temperatures were studied. From a detailed point of view, the failure mechanism of low-temperature water-saturated concrete is expounded. The results show that under the same dynamic load, the dynamic stress-strain curve of saturated concrete changes obviously with the change of low temperature. The dynamic compressive strength of the natural specimen at room temperature is high while that of the water-saturated specimen is low, and the dynamic compressive strength is opposite at low temperature. At the same temperature, the energy time-history curves of concrete in the saturated state are different from those in the natural state, mainly in the plastic section. The energy time-history curves of saturated concrete are different at different temperatures, and the energy dissipation rate of saturated concrete increases linearly with the decrease of temperature. Under the experimental conditions, the dynamic strength of saturated concrete increases linearly with the decrease of temperature, and the peak strain of saturated concrete decreases linearly with the increase of temperature. With the decrease of temperature, the fragmentation of saturated concrete under the impact of the same air pressure gradually increases, and the integrity of the specimen gradually improves. Low temperature can improve the impact resistance of saturated concrete, which is consistent with the failure law of natural state concrete. The water-saturated low-temperature state of the concrete void is filled with ice crystal particles; for low-temperature water-saturated concrete in the impact of the dynamic load, the microstructure is affected by the ice crystal structure which is not easy to change; the specimen along the axial force direction microdefect development produces a crack, the crack along the parallel to the pressure direction of cracking, through the two ends of the specimen, and finally produces axial splitting tensile damage. The research results have important theoretical significance for the safety design of low temperature saturated concrete structures.

Monitoring chloride diffusion in BFS concrete using an Electrical Resistivity Tomography device

Corrosion of steel bars in Reinforced Concrete (RC) due to the penetration of chlorides coming from seawater is one of the main pathologies leading to degradation of marine structures. Destructive Evaluation (DE) methods like coring from concrete in such marine environment are difficult and expensive for the survey of marine RC structures. Whereas, Non-Destructive Evaluation (NDE) methods based on the wave propagation (electric and electromagnetic) can reduce the number of cores necessary to evaluate the health of the studied structures. The aim of this work is to study the chloride ingress into saturated concrete by using the NDE methods and especially the Electrical Resistivity Tomography device. Accordingly, chlorides diffusion campaign with two different chloride concentration ([NaCl] = 35 and 90 g/L) was carried out on two slab of concrete contains slag addition. Apparent resistivities are then inverted in order to obtain a resistivity profile versus depth with two different software: Res1D and Ceris. Moreover, resistivity measurements were performed regularly on the slabs to obtain the resistivity profiles. On the other hand, a calibration method was realized to relate the resistivity to the chloride content for each type of concrete. The chloride profiles evaluated by NDT are then compared to those obtained by a destructive method (potentiometric titration) at three different exposure periods. The long-term goal is to use directly the NDE results in the model of chloride ingress into saturated concrete

Comparative study of the effects of different nanomaterials on the failure process of saturated concrete in an underground reservoir of a coal mine

The macroscopic failure of concrete used to form an artificial dam in an underground coal mine reservoir is the final manifestation of crack propagation and penetration: the mode of crack propagation is key to the safety evaluation of concrete structures. To improve the performance of concrete in such an artificial dam forming an underground coal mine reservoir, many scholars have investigated nano-modified concrete, but the effects of nanomaterials on the crack propagation mode and failure mode of saturated concrete are not yet fully understood. In the present research, uniaxial compression and acoustic emission (AE) experiments were conducted on saturated concrete specimens containing different types and amounts of nanomaterials, and the crack propagation mode, failure mode, and bearing capacity of different saturated concrete specimens were compared and studied. The results show that: the failure mode, crack propagation mode, and bearing capacity of saturated concrete can be modified by adding nanomaterials, and the type and content thereof can affect the modification effect provided. Considering the strength, bearing capacity, and crack-propagation mode, saturated concrete specimens containing 3 wt% nano-Al2O3 exhibit the best performance, with characteristics of high strength, high bearing capacity, steady crack propagation, and small-scale cracking. The results have guiding significance for damage-warning and safety assessment of hydraulic structures.

Effect of free water on fatigue performance of concrete subjected to compressive cyclic load

To clarify the effect of free water on the fatigue behaviour of concrete, dry, saturated, and water-submerged concretes were subjected to different stress levels of cyclic loads. The failure modes and S–N curves were determined. The evolution of fatigue deformation, the energy dissipation characteristics, and the impact mechanism were discussed. Water content was observed to affect the fatigue life of concrete. Owing to the interaction of free water, the fatigue life of concrete in saturated and water-submerged conditions reduced significantly compared to that of dry concrete. The compressive fatigue failure mode shifted from splitting failure in dry concrete to combined splitting and shearing failure in saturated concrete and shear failure in water-submerged concrete. The strain rate and dissipated energy of concrete in fatigue stage II increased with the water content and maximum stress level. The strain rate in stage II and the dissipated energy were logarithmically and linearly correlated with the fatigue life of concrete.

Performance Degradation of Subsea Shield Tunnel Segment Accounting for Concrete Strength Loss and Steel Bar Corrosion

Subsea shield tunnels usually serve in a typical corrosive marine environment. Under the action of chloride penetration and carbonization, tunnel lining segments are often damaged because of concrete strength loss and steel bar corrosion induced concrete cracking during their service life, which seriously degrades the service performance of the tunnels. A systematical experimental and numerical investigation into the performance degradation of subsea shield tunnel segments accounting for concrete strength loss and steel bar corrosion is presented in this paper. The study demonstrates that chloride penetration decreases the peak strength and elastic modulus of the segment concrete by 42% and 46.1%, respectively. The average of the ratio of dissipated energy to the total energy of dry concrete is much smaller than that of water saturated concrete and chlorine solution saturated concrete, and chloride penetration reduces the energy storage capacity of concrete, and the ability to resist damage is weakened. When steel bars corrode for 120 days, the outer cracks continue to extend, and the concrete around the inner steel bars just begin to crack initiation; when corrode for 20 years, the length of the inner cracks gradually exceeds that of the outer cracks, and the inner cracks initiating from different steel bars coalesce with each other and form a continuous failure surface, causing great serious damage to the segment. Due to the difference in concrete strength, for the outer layer, the evolution processes of steel bar corrosion-induced cracks show the characteristics of early initiation, slow propagation, and late coalescence, and those for the inner layer have the characteristics of late initiation, rapid propagation, and early coalescence. During the whole process the propagation speed of the inner and outer cracks appears to be fast first and then slow. Moreover, the study also illustrates that the final state of segment performance degradation after crack coalescence presents the characteristics of whole lamellar exfoliation of the concrete cover.

Using a geochemical model for predicting chloride ingress into saturated concrete

Chloride ingress into concrete was simulated based on a geochemical model that includes Fick's second law for transport phenomena and thermodynamic equilibrium, kinetics treatment and surface complexation for chemical phenomena. The geochemical model was validated by comparing the numerical results and experimental data (extracted from the literature) for CEM II concrete exposed to sodium chloride, potassium chloride, magnesium chloride and calcium chloride solutions. The geochemical model was then applied to investigate the influences of different chloride solutions. The results showed that exposure to magnesium chloride solution led to the greatest amount of Ca2+ leaching. Relationships between the total chloride content (TCC) and the free chloride content (FCC) of concrete were established. Increasing the exposure time of the concrete was found to lead to a decrease in chloride binding capacity. The proposed correlations allow determination of the FCC or the TCC of concrete when one of the two is known. The geochemical model was also verified by predicting the chloride content of a CEM III concrete bridge submerged in seawater after 17 and 34 years. With numerous applications, the geochemical model seems a reliable tool for the durability design of concrete structures exposed to chloride environments.

Study on Calculation Model for Compressive Strength of Water Saturated Recycled Aggregate Concrete

It has been proved that the compressive strength of water saturated concrete is lower than that of air dry concrete. Due to the water absorption of recycled aggregate (RA) is noticeably higher than that of natural aggregate (NA), the mechanical properties of water saturated recycled aggregate concrete (RAC) are quite different from those of water saturated natural aggregate concrete (NAC). At the same time, the calculation of concrete compressive strength is the first step of concrete mix proportion design. Therefore, it is essential to investigate the compressive strength of RAC in water saturated state. In this study, firstly, the water content and effective water absorption of NA, recycled brick aggregate (RBA) and recycled concrete aggregate (RCA), as well as the water content and effective water absorption of concrete specimen were tested; secondly, the effects of water/cement ratio, water saturation and coarse aggregate types on the compressive strength of water saturated concrete were studied; finally, the calculation model for compressive strength of water saturated concrete was proposed. The test results show that: Within 120 hours, the maximum effective water absorption of NA, RCA and RBA is 0.32%, 0.61% and 8.18%, respectively. Within 240 hour, the maximum effective water absorption of NAC, recycled concrete aggregate concrete (RCAC) and recycled brick aggregate concrete (RBAC) is 0.73%, 0.81% and 1.89%, respectively. In air dry and water saturated state, the descending order of compressive strength of concrete is: NAC > RCAC > RBAC. The average relative error of the calculation model for compressive strength of water saturated concrete is 7.1%. In the calculation model, water/cement ratio, effective water absorption, water saturation and coarse aggregate types are considered. The results of this study have great significance for the mix proportion design of water saturated concrete.

Mechanical Modification of Nanomaterials on Fully Saturated Concrete in Groundwater Reservoir Under Long-Term Water Immersion

With the increasing number of hydraulic structures in service, many scholars have investigated the performance of saturated concrete, however, there are few studies on the influences of different contents and types of nanomaterials on the performance of fully saturated concrete. In this paper, a series of experiments on concrete with different contents of nano SiO2, nano Al2O3 and nano TiO2 are performed, such as electron mirror scanning, uniaxial compression, acoustic emission, etc., and the microstructure, mechanical properties of samples are compared and analyzed. The results show that: 1) By the addition of various kinds of nanomaterials to saturated concrete, the microstructure of saturated concrete is significantly improved, and the compactness and integrity of the slurry are improved 2) The mechanical properties of saturated concrete are significantly improved by the addition of 3 wt% nanomaterials. And the compressive strength of the saturated concrete sample containing 3 wt% nano-Al2O3 is the largest and the deformation modulus of the saturated concrete sample containing 6 wt% nano-Al2O3 is the largest. 3) Compared with dry concrete, when the concrete is saturated, the modifying effect of nanomaterials on the mechanical properties of concrete is weakened. The results of this study have important guiding significance for the study of the nano-modification and the safe operation of hydraulic structures.

A Research About One-dimensional Chloride Ion Erosion In Concrete Under Drying-wetting Cycles

Reinforced concrete structures are now widely used in China, and with the exploitation of marine resources, many concrete structures are in a relatively harsh service environment. Concrete in wave and tidal stream areas is in a dry and wet cycle state. When unsaturated concrete is in a dry and wet cycle state, chloride ions will invade the concrete by diffusion and convection, which accelerates the erosion of the reinforcement within the concrete and degrades the concrete performance. Therefore, the study of chloride ion erosion in concrete under dry and wet cycles is particularly important. Fick’s law is a good predictor of the diffusion of chloride ions in saturated concrete with stable boundaries, but it is difficult to obtain satisfactory results for concrete under dry and wet cycles. There are many difficult parameters in the microscopic model that make programming the calculations more difficult. In this paper, we propose to use the radial basis function matching point method to solve the problem. It is found that the error is within acceptable limits and can be used to calculate the one-dimensional erosion of chloride ions under dry and wet cycles through solving the validation algorithm.

Effect of non-isothermal flow on chloride ion transport in saturated concrete

The presence of a temperature difference changes the mode of motion of the fluid. The macroscopic motion of the fluid causes the relative displacement between the various parts of the fluid, which in turn affects the transfer of temperature in the medium. To investigate the effect of temperature transfer coupled fluid motion on chloride ion transport in concrete, a mesoscopic model of chloride ion transport in non-isothermal flow of concrete was established and compared with experimental data. Based on the finite element software, the influence of temperature transfer on the internal fluid motion and chloride ion transport of concrete was analyzed. And the effect of convective motion of fluid on the temperature transfer in concrete was studied. It is found that when the heating time is the same, the dynamic viscosity of the fluid in the concrete decreases with the increase of temperature; the chloride ion concentration increases with the increase of temperature at the same depth of concrete; when considering the influence of laminar flow, the temperature is transmitted faster in the concrete and exhibits uneven diffusion from high temperature to low temperature; non-isothermal flow promotes the diffusion of chloride ions in concrete, and the higher the temperature.

Effects of Saturation Levels on the Ultrasonic Pulse Velocities and Mechanical Properties of Concrete.

The main objective of this research is to investigate the effect of water content in concrete on the velocities of ultrasonic waves (P- and S-waves) and mechanical properties (elastic modulus and compressive strength) of concrete. For this study, concrete specimens (100 mm × 200 mm cylinders) were fabricated with three different water-to-binder ratios (0.52, 0.35, and 0.26). These cylinders were then submerged in water to be saturated in different degrees from 25% to 100% with an interval of 25% saturation. Another set of cylinders was also oven-dried to represent the dry condition. The dynamic properties of concrete were then assessed using a measurement of elastic wave accordance with ASTM C597-16 and using resonance tests following ASTM C215-19, before and after immersion in water. The static properties of saturated concrete were also assessed by the uniaxial compressive testing according to ASTM C39/C39M-20 and ASTM C469/C469M-14. It was observed that the saturation level of concrete affected the two ultrasonic wave velocities and the two static mechanical properties of concrete in various ways. The relationship between P-wave velocity and compressive strength of concrete was highly sensitive to saturation condition of concrete. In contrast, S-wave velocity of concrete was closely correlated with compressive strength of concrete, which was much less sensitive to water saturation level compared to P-wave velocity of concrete. Finally, it was noticed that water saturation condition only little affects the relationship between the dynamic and elastic moduli of elasticity of concrete studies in this study.

Influence of Humidity on the Elastic Modulus and Axis Compressive Strength of Concrete in a Water Environment.

Concrete structures are often in different humidity conditions that have a significant impact on the elastic modulus of concrete, therefore, systematic research on the evolution of the law of concrete elastic modulus under different humidity conditions is needed. In this study, the variation laws of the water saturation of concrete specimens with strength grades C15, C20, and C30 were obtained, and then the influence laws of the water saturation on the concrete axial compressive strength were carried out, and the prediction model of elastic modulus of concrete with respect to water saturation was constructed. The results showed that the water saturation of concrete with strength grades C15, C20, and C30 increased with an extension of immersion time, and the water saturation showed an approximately linear rapid growth within three soaking hours, reaching 47.56%, 71.63%, and 47.29%, respectively. Note, the concrete reached saturation state when the soaking time was 240 h. The axial compressive strength with strength grades C15, C20, and C30 decreased with increased water saturation, and the axial compressive strength of saturated concrete decreased by 27.25%, 21.14%, and 20.76%, respectively, as compared with the dry state concrete. The elastic modulus of concrete with strength grades C15, C20, and C30 increased with increased water saturation, and the elastic modulus of saturated concrete was 1.18, 1.19, and 1.24 times higher than those of dry concrete, respectively.

Equation of state for saturated concrete: A mesoscopic study

The equation of state (EoS) plays an important role in accurately predicting the damage and failure of underwater concrete structures with impact and blast loadings. In underwater situations, the capillary pores of concrete are filled with free water, which is known to strongly influence the EoS, with much higher volumetric stiffness for saturated concrete than for dry concrete. In this context, appropriate consideration of the free water effect on the EoS of saturated concrete is essential, which is, however, a complex and expensive task when explored experimentally. In this study, the free water effect is investigated by numerical shock simulations performed on a 3D mesoscopic concrete model comprising mortar and coarse aggregate. Two widely used methods are employed to introduce the free water effect on the EoS of the mortar: the Hugoniot mixing rule and the effective stress law. With the Hugoniot mixing rule, the EoS of the mortar depends on the material properties of its different components and their volume fractions. With the effective stress law, the pressure consists of two parts, one supplied by the dry solid skeleton and the other by the free water. Numerical results reveal that both methods can well reproduce the experiment-supported phenomenon of saturated concrete exhibiting much higher volumetric stiffness than dry concrete. Additionally, the EoS of saturated concrete predicted by the two methods agree well and are mutually verified. Furthermore, it is found that the volume fraction of the coarse aggregate strongly affects the EoS of concrete, while its shape and size gradation have no discernible influences.