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This study prepared modified alkali-activated slag repair materials by incorporating an ethylene-vinyl acetate copolymer emulsion (EVA). Sulfate attack tests, shrinkage tests, scanning electron microscopy, and mercury intrusion porosimetry tests were conducted to examine the durability and microstructural features of the alkali-activated slag repair materials. The experimental results demonstrated that adding EVA can enhance the shrinkage and strength of alkali-activated slag mortar, but that the materials exhibit poor resistance to sulfate attack. Optimizing the ratio design can yield alkali-activated cementitious materials with high strength, good durability, high bonding strength, and low shrinkage. This can reduce brittleness and increase the shrinkage rate of the material's defects, which has significant implications for subsequent fracture repair. The image of the microstructure showed that the section of alkali-activated slag paste is smooth and exhibits polymer emulsion filling gaps in the amorphous cementitious material. A connection between fibrous filaments on the cross section of the matrix crack enhances the strength of the material. The proportion of microcracks is increased and material strength is decreased after sulfate attack. [ABSTRACT FROM AUTHOR]

The aim of this research is to investigate the sorptivity and capillary coefficient in unsaturated concrete using the capillary water absorption experiment. The effects of water-binder ratio, fly ash content, and aggregate content on the water absorption performance in concrete are compared. The decrease of water-binder ratio, aggregate content, and the increase of the initial degree of water saturation can lead to a decrease in the water absorption ability. With the increase of fly ash content, the water absorption ability first decreases and then increases; the 40% fly ash content had the worst water absorption ability. To forecast the water transport process, an unsaturated flow theory was used to predict the water content distribution in concrete during transport, this theory can well reveal the water distribution in concrete during water transport and the law of water content distribution is consistent with that of the water absorption experimental. [ABSTRACT FROM AUTHOR]

By combining the nearest surface distribution function and hydration kinetic equation, analytical equations are proposed to determine the pore phase and solid phase evolution in the interfacial transition zone (ITZ). In addition, the numerical models for concrete with a single flat aggregate are constructed based on the CEMHYD3D hydration model. The results show that the degree of hydration is the main factor affecting the ratio of the average porosity to the matrix porosity in the ITZ. With an increase in the aggregate volume fraction and interface thickness, the volume fraction of the ITZ first increases and then decreases. The degree of overlap increases linearly with the interface thickness and the aggregate volume fraction. As the distance from the aggregate surface increases, high-density C-S-H increases, while low-density C-S-H and calcium hydroxide phases decrease. Finally, the predicted results using the analytical equations and numerical simulation are verified by testing via back-scattered electron microscopy, which indicates that the experimental results are more consistent with the predicted results of the analytical model than with those of the numerical model. [ABSTRACT FROM AUTHOR]

This paper is aimed to study the corrosion resistance of Cr10Mo1 alloy corrosion-resistant steel (CR) in the seawater–sea sand concrete pore solution (SWSSCPS), compared with low-carbon steel (LC) and stainless steel (SS). X-ray photoelectron spectroscopy (XPS), SEM, atomic force microscope, and Mott–Schottky curve tests are applied to obtain information on the composition, structure, and morphology of the corrosion-resistant (CR) passive film. Finally, the difference between CR passive film and the other two kinds of steels under chloride attack is investigated, and the apparent morphology, microstructure, and chemical composition of the CR passive film during the attack are analyzed. With the exposure time increased, the passive film and interfacial integrity of CR are approximately equivalent to that of SS in terms of phase angle in the midband and low-frequency band modulus, indicating the anticorrosion performance of CR has a much better effect than that of LC and close to that of SS. The results reveal that the FeO in the passive film outer layer and a high amount of Cr2O3/Cr(OH)3 in the inner layer prevent CR from further corrosion by chloride ions. [ABSTRACT FROM AUTHOR]

• Using concrete with coarse aggregate for 3D printing concrete permanent formwork. • Interface splitting strength can be improved with the presence of coarse aggregate. • The reason for weakened interface bonding was investigated by stereomicroscope and X-CT. • The proportion of smaller stones in postcast concrete should be raised for better bonding. Using 3D concrete printing technology to produce permanent formwork for building components is a promising method that maximizes design freedom and material savings. In this study, 3D-printed permanent formwork made of concrete with coarse aggregate is manufactured and post cast with concrete containing different coarse aggregate particle size ratios. The results indicate that the splitting tensile strength of the concrete interface reaches 2.3 ∼ 4.4 MPa, of which the reduction rate range from 12.8%∼35.7% with higher bonding positions. Mesoscopic observation reveals the voids concentration and a lack of coarse aggregate phenomenon in the interface area. Increasing the proportion of small-sized coarse aggregates in the pouring concrete can better fill and improve the splitting strength of the interface area. [ABSTRACT FROM AUTHOR]

Concrete structures are prone to damage from various factors, particularly chloride ion penetration, which can lead to premature deterioration. Although self-repairing materials can mitigate damage and erosion, methods for evaluating their efficacy are lacking. This study explores concrete damage development, chloride and water transport in damaged concrete, and post-repair transport behavior. A comprehensive mechanical-transport-healing model for concrete was established to investigate the influence of damage and self-healing rates on chloride distribution. Results show that tensile loads under 5 μm have minimal impact on concrete transport, whereas larger displacements significantly accelerate water and chloride migration. This acceleration resulted in a 66 % increase in the chloride concentration at a depth of 15 mm with a displacement of 10 mm. Higher self-healing rates effectively reduced the chloride concentration within the 10–30 mm range. Increasing the healing rate from 70 % to 90 % led to 75 % and 35 % decreases in the chloride concentration at a depth of 30 mm after 100 years, respectively. These findings provide valuable insights into the relationship between the mechanical damage and chloride transport in concrete, which can inform the development of strategies for enhancing the durability of concrete structures exposed to chloride-rich environments. • A coupled mechanical-transport-healing numerical model is developed. • The relationship between damage on the acceleration of concrete erosion medium transport was quantified. • The effect of self-healing rate on the transport properties of damaged concrete was calculated, and the self-healing rate requirement for damaged concrete was proposed. [ABSTRACT FROM AUTHOR]

• Finite element model predicts HSR concrete fatigue life. • Model assesses impact of load frequency, stress ratio, and level. • Fatigue life of environmentally damaged concrete analyzed. High-speed railways have become a critical component of modern transportation, and ensuring the stability and durability of high-speed railway concrete under environmental and train fatigue loads is essential for ensuring project safety. This paper employs a numerical simulation method to predict the performance and lifespan of high-speed railroad concrete under fatigue loading with environmental damage. The study analyzes the effects of stress level (0.5–0.8), stress ratio (0.1–0.9), and load frequency (5 Hz–40 Hz) on the fatigue performance and lifespan of railway concrete during bending fatigue loading. A four-point bending numerical model of concrete is developed in this paper, which considers elastic modulus decay and surface cracking, in order to quantify the degradation of concrete properties in response to environmental and load-induced cracks. The numerical model is well-validated with experimental results, and the study establishes a correlation between concrete degradation and environmental and load-induced cracks, as well as the fatigue resistance of high-speed railroad concrete. The bending fatigue frequency of concrete should not exceed 25 Hz at high stress levels of 0.7. This study also shows that environment-induced initial damage will greatly reduce the fatigue resistance of concrete, and fatigue life degradation and elastic modulus decay have a nearly linear relationship. This research provides a crucial foundation for the fatigue design of concrete materials for high-speed railroads. [ABSTRACT FROM AUTHOR]

In the construction industry, it is imperative to replace natural sand with manufactured sand. The environment in northwest China is very complex and harsh. The application of manufactured sand concrete in such a harsh environment needs scientific and comprehensive research to meet the requirements. However, there is a gap in the study of sulfate freeze-thaw resistance of manufactured sand concrete in the complex environment of Northwest China. Therefore, this study investigated the northwest environment, designed an indoor sulfate freeze-thaw cycle experiment system close to the real environment, and designed a conductive titration method to test the sulfate ion content in hardened concrete. The influence of the freeze-thaw cycle on the diffusion depth of sulfate ions in manufactured sand concrete was studied. Finally, the following conclusions are obtained: In the process of conductometric titration, hydrochloric acid is used as the dissolution solution, Ag 2 O and CO 2 are used as neutralizers, and Ba(NO 3) 2 is used as the titration solution, which can perfectly eliminate the significant influence ions in the test solution, and can accurately test the content of sulfate ions in hardened concrete. The sulfate ion content of concrete at different depths was tested, and it was found that the two sides of sulfate erosion caused by freeze-thaw cycles were mainly reflected in about 100 freeze-thaw cycles. The limit number of freeze-thaw cycles N 0 and the limit diffusion depth X 0 are proposed, and the diffusion equation of manufactured sand concrete under the action of sulfate freeze-thaw cycles is derived. The proposed diffusion parameter v is unique to the concrete, which can well judge the sulfate freeze-thaw resistance of the concrete. When v is closer to 0, it shows that the resistance of concrete to sulfate freeze-thaw erosion is better. For the northwest environment of China, the manufactured sand concrete should ensure v < 6; the environment in Northwest China has a very complex multi-factor erosion environment. It is worth noting that this study is only applicable to laboratory conditions. To improve the accuracy and reference value of experimental research, future research needs to add more comprehensive environmental impact factors and collect actual data in the northwest environment of China for verification. • A detailed conductivity test method for sulfate ion content in hardened concrete was designed. • The diffusion equation of manufactured sand concrete under sulfate freeze-thaw cycles is derived by proposing the limit number of freeze-thaw cycles N 0 and the limit diffusion depth X 0. • The diffusion parameter v proposed by is a new concept, which can be used to judge the key index of sulfate freeze-thaw damage, and is of great significance for evaluating the frost resistance of manufactured sand concrete in the northwest environment of China. [ABSTRACT FROM AUTHOR]

To solve the problems of poor thermal insulation and heat preservation properties that exist in the walls made of small-size concrete hollow blocks, a new type of compound small-size concrete hollow blocks has been developed. As shown in tests and calculations, the compound blocks not only improve significantly the thermal insulation effect, heat preservation properties, and impermeability of the walls, but also show good decorative results. [Copyright &y& Elsevier]

Superhydrophobic technology in construction can effectively improve the barrier ability of the substrate to harmful water-based erosion media, among which the coating scheme is the most practical choice at present, but it may easily fail due to mechanical damage. Therefore, the current research focus has shifted to the development of internal superhydrophobic materials (ISMs) that maintain stable hydrophobicity even under harsh conditions of use and do not rely on expensive fluor-based surface modifications. In this study, the topological structure of waste denitrification fly ash (FA) was constructed using an innovative method, by precisely controlling the etching medium concentration and the form of FA, a one-step process was developed to create ISM with excellent matrix strength and strong waterproof properties. In this study, the alkaline environment generated by FA hydration was used to induce the silica-hydrogen bond dehydrogenation of polymethylhydrosiloxane (PMHS) and the free ammonium ion deamination to toughen the film; PMHS and liquid phase are used to produce the oil-water phase, and the oil film adheres to the surface of the generated NASH and sodium silicate crystals; The porous inner surface of ISM is formed with hydrogen- and ammonia-induced rough structure; The synthesized ISM retains superhydrophobicity and less compressive strength reduction value, and its superhydrophobicity even at damaged or friction interfaces. The material preparation method provides a good foundation and innovative design concept for the seepage prevention and maintenance of concrete structures, the construction of aerated FA bricks, the preparation of foam insulation materials, and the batch utilization of waste FA. • Denitrification fly ash is prepared into a masonry structure with internal hydrophobicity. • The mechanism of hydrophobic synergism between PMHS dehydrogenation film formation and fly ash etching deamination was revealed. • The internal and external wear resistance of the inner superhydrophobic material has been applied to actual engineering. [ABSTRACT FROM AUTHOR]

• 3DPC with 4.75–20 mm coarse aggregate size in continuous/discontinuous grading was designed. • The effect of coarse aggregate gradation on the fresh and hardened properties of 3DPC was investigated. • A correction coefficient for the existing compression stress–strain model was proposed to and fit 3DPC well. • Relationship between the coarse aggregate spacing and the correction coefficient was built and discussed. Coarse aggregate is an indispensable component of concrete, the gradation of which plays an important role in the properties of concrete due to its effect on particle distribution. The extrusion-based 3D concrete printing (3DCP) has become a promising technology while the influence of coarse aggregate gradation on the material design and performance of 3D printed concrete still lack understanding. This study experimentally investigates the fresh and hardened properties of 3D printed concrete with 4.75–20 mm continuous and discontinuous grading coarse aggregates, including flowability, buildability, axial compression, and drying shrinkage. The results reveal that 3D printed concrete with continuous grading performs better on flowability retaining and multilayer structure stacking than that with discontinuous grading. The evaluation coefficient of aggregate particle size is proposed to characterize the average particle size of coarse aggregates with different gradations, which shows linear relationship with coarse aggregate 3D spacing in 3D printed concrete. The current axial compressive stress–strain model for the conventional concrete prediction curve is modified to predict the effect of coarse aggregate gradation on constitutive relationship of 3D printed concrete. The increasing proportion of large-sized coarse aggregates can lead to a reduction in long-term drying shrinkage of 3D printed concrete. [ABSTRACT FROM AUTHOR]

A multiscale creep model of concrete is proposed from C–S–H gel scale to mesoscale considering the effects of ITZ and aggregates with irregular-shaped aggregates. A novel averaged Eshelby tensor-based homogenization method is devised to obtain the effective creep of concrete with realistic-shaped aggregates covering from ellipsoidal-like gravels, polyhedral-like crushed stones, to arbitrary concave aggregates. This method is generic that overcomes the constraints of the traditional Eshelby's solution. In addition, ITZ is regarded as a homogeneous viscoelastic layer, its volume fraction and viscoelasticity are derived. The proposed multiscale model is verified by comparing with finite element simulations and experimental data. The influences for a wide spectrum of aggregate and ITZ configurations on concrete creep are investigated. Moreover, the scale-transfer effect of microscale parameters on cement paste creep and on concrete creep is quantitatively characterized for the first time. • An averaged Eshelby tensor-based homogenization method is devised to deal with irregular-shaped inclusions. • A multiscale creep model for concrete is proposed considering from C–S–H gel scale to mesoscale. • The multiscale model is verified by comparing with finite element simulations and experimental data. • The parameter influences on concrete creep and their scale-transfer effects are investigated. [ABSTRACT FROM AUTHOR]

Highlights • The various regular- and irregular-shaped aggregates are constructed using a pixel-based method. • The effects of aggregate characteristics on elastic and diffusive properties of concrete are investigated. • The aggregate characteristics apart from the aggregate type, play a slight role in the elastic properties of concrete. • The aggregates characteristics have a significant influence on the diffusive properties of concrete. Abstract Concrete is a complex three-phase composite material at a mesoscale, thus its overall elastic and diffusive properties strongly depend on that of each component. However, the effects of aggregate characteristics are little considered, especially the aggregate shape effect. In this study, a set of numerical methods is employed to evaluate the effects of aggregate characteristics on the elastic and diffusive properties of concrete. Firstly, a concrete representative volume element (RVE) is constructed using a pixel-based method by packing aggregates surrounding a soft interlayer as ITZ in a homogeneous mortar matrix. The different aggregate characteristics including morphology, fineness and type, are respectively considered. Subsequently, a set of the finite element-based and finite difference-based numerical method that is designed for the pixel-based concrete structure, is applied to predict the elastic modulus and the diffusion coefficient of concrete. The simulated results indicate that aggregate characteristics apart from aggregate type play a negligible role in the elastic modulus of concrete, while the effects of aggregate characteristics on the diffusion coefficient of concrete are pronounced. The aggregates with less regularity or coarser size can decrease the diffusion coefficient of concrete. Furthermore, the property of ITZ is another pronounced factor for the elastic and diffusive properties of concrete in addition to aggregate area fraction. The weaker ITZ can significantly decrease the stiffness and increase diffusivity of concrete. The modelling results are expected to guide the design of concrete materials from the perspective of aggregate characteristics. [ABSTRACT FROM AUTHOR]

Aggregates with realistic non-convex morphologies and their surrounding interfacial transition zones (ITZs) significantly affect the diffusivity of concrete. Herein, we initially propose a mathematical-controllable parameterized method to devise three-dimensional (3D) non-convex aggregates. Then, we develop a GPU-based discrete element modelling (DEM) to generate random close packing of polydisperse non-convex aggregates. Next, we establish three-phase concrete mesostructures containing non-convex aggregates and ITZs and obtain the ITZ volume fraction by a Monte Carlo random point sampling method. Finally, we develop a dual-probability-Brownian motion (DP-BM) scheme to obtain the effective diffusivity of concrete. Moreover, the effects of volume fraction, size polydispersity and shape of aggregates as well as ITZ thickness on the ITZ volume fraction and concrete diffusivity are researched to probe rigorous component-structure-property relations for concrete. This work provides a comprehensive numerical framework for mesostructure characterization and diffusivity evaluation for concrete, which can be a valuable tool for durability assessment of concrete. [ABSTRACT FROM AUTHOR]

• A new avenue to prepare rubber aggregate with excellent interfacial adhesion and compatibility was developed by combining ultrasonic mechanochemistry and a modified slurry coating. • The interface between rubber particles and cement matrix was improved and the mechanical properties were vastly enhanced. • The modification of rubber powder significantly improved the abrasion resistance of crumb rubber concrete. • The abrasion mechanism of CRC was systematically analyzed and the abrasion mechanism models of the rigid and semi-rigid body were established. • The interface between rubber particles and cement matrix played an important role in controlling the abrasion resistance of CRC. The abrasion resistance of crumb rubber concrete (CRC) has always been a research hotspot. However, the large reduction in the mechanical properties of CRC limits the improvement of its abrasion resistance. In this study, a new method of modifying waste rubber powder (WRP) combining mechanochemical action, ultrasonic energy accumulation and the coating effect of the modified slurry was proposed. The mechanical properties of CRC with rubber volume fractions of 0%, 15%, 25% and 35% were determined. The abrasion resistance of CRC was studied by the ball bearing and ball milling methods. The abrasion mechanism of CRC was analysed, and abrasion mechanism models of the rigid and semirigid bodies were established. The results showed that the compressive and flexural strengths of modified CRC (MCRC) were increased by 74.2% and 45.7% respectively, compared with CRC. The abrasion resistance of concrete first increases and then decreases with increasing rubber content. Compared to the control concrete, the abrasion resistance of CRC and MCRC was increased by 14.9% and 24.8%, respectively. The mass loss rates of CRC and MCRC were 29.78% and 24.98% respectively, under the same volume replacement. The enhancement of abrasion resistance of the CRC is mainly due to the absorption of wear energy by rubber. The rubber-cement matrix (R-CM) interface played an important role in controlling the abrasion resistance of CRC. [ABSTRACT FROM AUTHOR]

• A novel method for three-dimensional modeling of end-hook steel fibers in UHPC was proposed. • The dynamic compression behavior of aeolian sand-based UHPC was studied via the split Hopkinson pressure bar technique and 3D mesoscale simulation, and the impact compression finite element model parameters suitable for aeolian sand UHPC were determined. • The effects of strain rate, fiber content and matrix strength on the dynamic mechanical properties of aeolian sand-based UHPC were determined, which have a profound significance for its application in protection engineering. The dynamic mechanical properties of ultra-high performance concrete (UHPC) containing aeolian sand was studied via the split Hopkinson pressure bar technique and three-dimensional mesoscopic numerical simulation. A novel method for three-dimensional modeling of end-hook steel fibers was proposed. Employing the 3D mesoscale model, the dynamic compressive responses of aeolian sand-based UHPC were simulated and analyzed. Simulation results exhibited constitutive relationships and failure patterns that agree well with the impact test results, which verified that the established three-dimensional mesoscopic model enables effective analysis of the dynamic mechanical properties of aeolian sand-based UHPC. Then the effects of strain rate, fiber content and matrix strength on the stress-strain relation and energy evolution process were quantitatively discussed, which provide a basis for the application of aeolian sand-based UHPC. [ABSTRACT FROM AUTHOR]

Abstract: The N-layered spherical inclusion theory is applied to develop a multi-scale model to predict the effective diffusion coefficient of chloride ion in concrete. The model treats concrete as four-phase composite materials consisting of matrix phase, aggregate phase, ITZ (interfacial transition zone) and their homogenization phase. With hardened cement pastes characterized by three parameters such as the porosity, tortuosity and constrictivity, the effect of the cement paste microstructures and ITZ on the chloride diffusivity in concrete is taken into account and the porosity distribution function and effective chloride diffusion coefficients of the ITZ are given in the model based on the cement particle distribution characteristics of the ITZ in concrete. To validate the proposed model, the diffusion coefficient of chloride ion by the steady-state migration test is measured on a series of mortar and concrete specimens and good agreement between the model and experiment is obtained. In addition, the model predicts that the chloride diffusivity of concrete composite materials depends on the chloride diffusion coefficient of the matrix and ITZ, volume fraction of the aggregate and ITZ, with the volume fraction of the ITZ influenced by aggregate size distribution, the volume fraction of aggregate and thickness of the ITZ. [Copyright &y& Elsevier]

• An extrusion-based 3D printer for concrete with the largest aggregate size of 20 mm was introduced. • The range of ratios of cement and aggregate of printable concrete with coarse aggregate was recommended. • The direction-dependent mechanical properties of 3D printed concrete were investigated. • The voids distribution and the microstructure of interlayer area in 3D printed concrete were studied through X-CT and SEM. Concrete with coarse aggregate in the 3D concrete printing (3DCP) has broad prospects for high strength, low cost and shrinkage. In this study, an extrusion-based 3D printer was designed and utilized to print concrete with the largest aggregate size of 20 mm. Printable concrete with coarse aggregate was designed by different volume ratios of cement to aggregate (C/A). Then the effect of C/A on the printability and direction-dependent mechanical performance was investigated. X-ray micro-computed tomography (X-CT) was used to detect and analyze the voids distribution characteristics of printed specimens. Scanning electron microscope (SEM) investigations of microstructure at the interlayer area were conducted. Results indicated that the initial flowability of printable concrete should be within 178–200 mm, and the recommended printable C/A was within 0.35–0.60. The decrease of C/A improved the maximum printing height and mechanical performance but weakened the shape-stability of the multi-layer structure. X-CT results indicated that reducing excess slurry content caused by the decline of C/A decreased the compactness of the printed structure. The compressive strength and flexural strength of 3D printed specimens showed a direction-dependent characteristic, mainly related to the non-uniform distribution of voids revealed by X-CT. SEM images revealed the "micro-bridging" morphology in the interlayer area and proved that there were carbonation and structural weakening problems at the surface and surrounding of this area. [ABSTRACT FROM AUTHOR]

Apparent gas-permeability (k a) of concrete highly depends on pore-structure and medium. However, the effects of gas-medium on permeability have yet been investigated in depth. In this work, concrete with various water-to-cement ratios and fly-ash/slag dosages is prepared for k a testing. Various gas-mediums (CO 2 and O 2) are applied for analyzing their effects on the k a. Meanwhile, pore-structure characteristic, inner gas-pressure, and gas-absorption in concrete are observed for exploring permeation mechanism. The results illustrate that the narrowing pore-scale effect and surface-diffusion contribution derived from gas-absorption of CO 2 and O 2 both have minor impacts on the k a. The k a of O 2 (k O2) is higher than that of CO 2 (k CO2) and their relative permeability (k O2 / k CO2) ranges from 1.18 to 2.29. These deviations are mainly caused by significantly different Knudson diffusion occurring in the area near the concrete outlet-gas side (approximately 5%). • Gas permeability of concrete is measured by various osmotic-mediums (CO 2 and O 2). • Inner gas-pressure distribution of concrete is obtained under steady-state flow. • The apparent gas-permeability of concrete tested by O 2 is higher than that by CO 2. • Gas absorption of CO 2 and O 2 has minor impacts on apparent gas-permeability. • The deviation of apparent permeability is mainly caused by Knudson diffusion. [ABSTRACT FROM AUTHOR]

• Gas permeability of concrete was measured considering on coarse aggregate settlement. • Concrete permeability was tested using various gas pressures and confining pressures. • Permeability curve can be observed with four zones following gas-pressure increasing. • Steady zone with 15.0–30.0 bar gas pressures was recommended for permeability test. • Confining pressure of 50 bar was suggested for concrete gas-permeability measurement. Permeability is an important characteristic associated with the durability of cementitious materials. Gas permeability testing could overcome some shortcomings of traditional methods but its key parameters have so far not been identified for long periods, reducing comparability of test results. In this study, coarse-aggregate settlement in concrete was taken into consideration by dividing concrete cores into smaller segments and the gas-permeability of concrete specimens was measured by the modified CemBureau method. Apparent gas-permeability (K a) values of the segments were determined under multiple inlet-gas pressures (1.0 bar–40.0 bar) and various confining-pressures (30 bar–90 bar), which then were applied to calculate the intrinsic permeability (K int) values and Klinkenberg coefficient (β k) to obtain optimal parameters of inlet-gas pressure and confining-pressure. Meanwhile, X-ray computed tomography (X-ray CT), mercury intrusion porosimetry method (MIP) and specific gravity method (SG) were used for auxiliary calibration of test parameters. The results showed that four zones with different inlet-gas pressures were observed for apparent gas-permeability: unstable zone, metastable zone, stable zone, and anamorphic zone. Combined with gas-permeability, pore characteristics were employed for auxiliary calibration of parameter optimization. In sum, 15.0 bar–30.0 bar inlet-gas pressure and 50 bar confining-pressure were determined as the best parameters for concrete gas-permeability testing. [ABSTRACT FROM AUTHOR]