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In order to study the dynamic damage evolution law of tunnel‐lining concrete with non‐through crack under single‐side sulfate attack, a 420‐day sulfate attack concrete test was conducted and the uniaxial compression and acoustic emission (AE) tests were carried out on each corrosion time. The test results showed that the compressive strength of each group can be divided into rising stage and falling stage, and the existence of non‐through crack reduced the compressive strength of concrete specimens and accelerated the corrosion of concrete specimens by sulfate. AE ringing count can be divided into compaction stage, elastic stage, yield stage, and post‐peak stage; the variation patterns of AE varied at different stages. Sulfate attack caused the yield point of concrete to advance. With the increase of corrosion time, microcracks increased gradually, cement mortar was consumed continuously, concrete spalling occurred, the proportion of AE cumulative ringing count Stage II decreased gradually, and the proportion of Stage III increased. Non‐through crack changed the energy storage of Stages II and III and reduced the AE activity of concrete after corrosion. The deeper the crack was, the smaller the average cumulative ringing count was and the lower the AE activity was. AE cumulative ringing counts can be used to characterize the damage evolution of corroded concrete. [ABSTRACT FROM AUTHOR]

This paper significantly extends investigations into internal damping ratios in both undamaged and damaged conditions for normal-strength concretes (NSCs) and high-strength concretes (HSCs). This study examines concretes with compressive strengths ranging from 42 to 83 MPa. Cyclic loads were applied using a servo-controlled hydraulic testing machine, and for each cyclic step, the dynamic elastic modulus ( E d ) and internal damping ratio (ξ) were determined through acoustic tests. The results show that the normal-strength concretes ( f c = 42 MPa) exhibited an undamaged internal damping ratio of ξ = 0.5 % , reaching a maximum of ξ = 2.5 % at a damage index of 0.8. Conversely, the high-strength concrete mixtures ( f c = 83 MPa) showed an undamaged internal damping ratio of ξ = 0.29 % , with a peak value of ξ = 0.93 % at a damage index of 0.32. The initial internal damping values are influenced by porosity and transition zones, which affect the material behavior under cyclic loads. Progressive damage leads to increased Coulomb damping due the cracking process. Few studies have quantified and comprehended the internal damping ratio under cyclic loading-induced damage, and this research advances our understanding of NSC and HSC behavior under dynamic excitation and damage evolution, especially in impact scenarios. [ABSTRACT FROM AUTHOR]

In this work, a novel method for damage evolution analysis of concrete under uniaxial compression is proposed based on the multi-feature acoustic emission (AE) and the Gaussian mixture model (GMM) clustering. The hierarchical clustering algorithm is adopted to select optimal AE parameters, while multiple features of these parameters are generated through the principal component analysis (PCA). Then the concrete damage signals are separated by using the GMM clustering with multiple features. Meanwhile, the waveform signals associated with concrete damage in each cluster are validated using the Fast Fourier transform (FFT) and the continuous wavelet transform (CWT). Finally, the damage evolution process of concrete under uniaxial compression is divided based on the variation of AE characteristics. The results show that the frequency ranges of signals for micro-cracks, mixed cracks and friction of concrete under uniaxial compression are 20–30 kHz, 20–65 kHz, and 100–120 kHz, respectively. The damage process of concrete under uniaxial compression is divided into three stages according to the inflection points of the cumulative energy curve, namely the initial compaction stage, the crack formation stage and the failure stage. [ABSTRACT FROM AUTHOR]

The mechanical properties of interfacial transition zones (ITZs) have traditionally been simplified by reducing the stiffness of cement in previous simulation methods. A novel approach based on the discrete element method (DEM) has been developed for modeling concrete. This new approach efficiently simulates the meso-structure of ITZs, accurately capturing their heterogeneous properties. Validation against established uniaxial compression experiments confirms the precision of thismodel. The proposed model can model the process of damage evolution containing cracks initiation, propagation and penetration. Under increasing loads, cracks within ITZs progressively accumulate, culminating in macroscopic fractures that traverse themortarmatrix, forming the complex, serpentine path of cracks. This study reveals four distinct displacement patterns: tensile compliant, tensile opposite, mixed tensile-shear, and shear opposite patterns, each indicative of different stages in concrete's damage evolution. The widening angle of these patterns delineates the progression of cracks, with the tensile compliant pattern signaling the initial crack appearance and the shear opposite pattern indicating the concrete model's ultimate failure. [ABSTRACT FROM AUTHOR]

The current constitutive model and damage evolution law of crumb rubber concrete (CRC) were obtained by fitting and changing parameters based on the normal concrete model. However, this model does not accurately reflect the characteristics of the material. In this paper, we studied the energy dissipation in the failure process of CRC to derive the constitutive model and damage evolution law of CRC based on the energy method. Four substitution rates of 5%, 10%, 15%, and 20% were selected, and the rubber concrete prism was prepared by replacing the natural fine aggregate with the same volume of crumb rubber aggregate. After that, uniaxial compressive tests were conducted. The energy lost due to the damage was calculated and analyzed, and the energy method was used to establish the damage evolution law and damage model of the crumb rubber concrete. The results demonstrated that the Guo Zhenhai damage model, which is based on the energy method, can more effectively explain the crumb rubber concrete stress–strain full curve, and the energy consumed as a result of the damage exhibits a growing and then reducing pattern with the increase in rubber doses. When the energy-based method is used, the Guo Zhenhai damage evolution model is similar to the damage evolution law calculated using the SIR damage evolution model. During uniaxial compression damage, rubber concrete with various rubber dosages demonstrated varying energy absorption in different deformation phases. When the rubber particle content was 10%, the energy absorption capacity of the specimen was 6.9% higher than that of normal concrete. [ABSTRACT FROM AUTHOR]

Cyclic disturbance loading affects the continuous operation of concrete structures. This study aims to better understand the failure behavior of concrete structures under cyclic disturbance loading. This study combined acoustic emission (AE) and digital image correlation (DIC) technologies to study mechanical failure behavior and damage evolution of concrete materials under cyclic disturbance loading and unloading. The AE event time-frequency characteristics, surface principal strain program, and damage parameters of samples with different cyclic disturbance amplitudes were obtained by theoretical calculation. The results reveal that when minor disturbance amplitudes are applied, the elastic modulus of concrete specimens tends to increase. When the disturbance amplitude is too large, the elastic modulus of the specimens drops, leading to faster specimen failure. The AE characteristic parameters exhibit a Felicity effect after the sample is subjected to a cyclic disturbance loading. Moreover, the larger the amplitude of the disturbance load, the more frequent the low-frequency and high-amplitude events generated during the final rupture, the higher the concentration of the principal strain on the sample's surface, and the wider the crack band distribution. AE energy and Effective crack are consistent in characterizing damage, and the changing trend of these two damage parameters can better reflect the deterioration process of concrete. The research results will provide practical and theoretical insights for safely operating and maintaining concrete structures.

To reveal the dynamic response characteristic and damage-fracture evolution laws of concrete under pulse water jet impact, the numerical simulations on pulse water jets impinging concrete for different operating parameters were established based on SPH-FEM coupling algorithm and verified in this paper. The concrete-breaking effects of pulse water jet and continuous water jet were compared, and the effects of key jet parameters and concrete strength on the damage-fracture characteristics of concrete were investigated. And the damage and stress evolution laws inner concrete were revealed. The results show that there is a better concrete-breaking effect for pulse water jet by repeatedly utilizing the extremely high water-hammer pressure and effectively weakening the water-cushion effect, compared with continuous water jet. The broken pit area and the total length of main cracks decrease with the increase of pulse length, and there is an optimal pulse spacing for pulse water jet to improve the concrete-breaking effect. The broken pit area and the total length of main cracks both linearly increase with the increasing jet velocity and exponentially increase with the increasing jet diameter. As the concrete strength increases, the broken pit area shows an S-shaped curve decreasing trend and the total length of main cracks exponentially decreases. The broken pit width first rapidly increases and tends to stabilize with the increase of jet velocity and concrete strength, and changes linearly with jet diameter and is less affected by pulse length and spacing. The farther away from the jet impact center, the longer the damage cumulative period of concrete due to the jet impact energy attenuation. In horizontal direction, concrete breakage range is approximately 4–5 times of jet diameter; in vertical direction, the previous pulses will cause concrete to be destroyed or damaged, and the subsequent pulses will make the damaged concrete suffer greater stress, causing more serve damage. And the induced stress peak decreases in form of Power function with the increasing distance. The research results could provide theoretical guidance for the parameters selection of pulse water jet efficiently breaking concrete.

In light of the limited research on latent damages during the construction of large-span suspension arches, this study introduced a method to simulate structural damage utilizing random porosity. Initially, based on data from real-world engineering projects, the most susceptible areas within the arch structure were pinpointed. Subsequently, multiple test arch simulation models were constructed. Employing Python, commands for random porosity were implemented within ABAQUS and distinct mesh modules were devised to depict structures under varying degrees of damage. The current investigation delved into the structural responses of these susceptible areas under different damage rates, shedding light on damage progression patterns. Notably, our findings demonstrated that concealed damages on the top plate of the arch foot profoundly influenced structural integrity, whereas damages at the arch hance were comparatively minimal and predominantly manifest at the arch base. The pronounced localized damage at both the arch base and hance initiated and intensified at sectional corners, necessitating enhanced anti-crack measures in these regions. Moreover, depending on the stresses of the arch structure, diverse reinforcement strategies could be employed, optimizing the balance between load-bearing efficiency and cost considerations. [ABSTRACT FROM AUTHOR]

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In seasonally frozen areas, the bearing capacity and durability of the concrete could be deteriorated with irreversible damage of the meso-structure under the periodic freeze-thaw cycles. The freeze-thaw damage of concrete is essentially the accumulation of fatigue damage caused by initial defects including internal pores and cracks under the action of periodic frost heave force. Therefore, it is of great significance to evaluate the safety of in-service concrete structures in cold regions by studying the damage evolution characteristics of the meso-structure of concrete under freeze-thaw cycles. The meso-structure evolution and mechanical damage characteristics of concrete under freeze-thaw cycle were main concerns. The research status of meso-structure acquisition and characterization technologies, laboratory physical test and numerical simulation approaches of concrete under freeze-thaw cycles, and mechanical damage characteristics and durability evaluation were systematically summarized and analyzed. Previous studies mainly focused on the local damage evolution of concrete at the macro-scale. The meso-structure evolution and damage characteristics of concrete under freeze-thaw cycles were studied from the meso-scale. In this way, the freeze-thaw failure mechanism behind the macro-mechanical properties and durability deterioration could be deeply analyzed, as well as the development law of the propagation, coalescence and penetration of the initial defects of pores and cracks. Furthermore, the inherent relationships between the meso-structure evolution and the macroscopic damage characteristics considering the different freeze-thaw cycle parameters could be established. Finally, the accurate analysis and prediction of the macroscopic physical and mechanical characteristics of concrete materials under the freeze-thaw environment could be achieved. A reference of the identification of damage characteristics, stability and durability analysis of engineering structures in cold regions during service could be provided by the correlational research. [ABSTRACT FROM AUTHOR]

In practical engineering, concrete is often under continuous stress conditions and there are limitations in considering the effect of wet–dry cycles alone on the strength deterioration of concrete. In order to study the deterioration of concrete strength under the coupling of load and wet-dry cycles, concrete specimens were loaded with 0%, 10%, 20%, and 35% stress levels and coupled to undergo one, three, and seven wet–dry cycles. The strength deterioration of the concrete was obtained by uniaxial compression and the regression equation was established. The strength deterioration mechanism of the concrete under the coupled conditions was analyzed and revealed through an AE acoustic emission technique and nuclear magnetic resonance technique. The results of the study show that, with the same number of wet–dry cycles, there are two thresholds of a and b for the uniaxial compressive strength of concrete with the stress level, and with the progression of wet–dry cycles, the length of the interval from a to b gradually shortens until it reaches 0. The cumulative AE energy of concrete decreases with the progression of wet–dry cycles; using the initiating crack stress as the threshold, the calm phase of concrete acoustic emission, the fluctuating phase, and the NMR T2 spectral peak area show different patterns of variation with the increase in the number of wet–dry cycles. [ABSTRACT FROM AUTHOR]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The back-filling body in the gob-side entry retaining is subject to continuous disturbance due to repeated mining. In this study, uniaxial and cyclical loading tests of back-filling concrete samples were carried out under laboratory conditions to study damage evolution characteristics with respect to microscopic hydration, deformation properties, and energy evolution. The results showed that, due to the difference in the gradation of coarse and fine aggregates, the cemented structure was relatively loose, and the primary failure modes under cyclical loading were tensile and shearing failure, which significantly decreased its strength. With an increasing number of loadings, a hysteresis loop appeared for the axial strain, and the area showed a pattern of decrease–stabilization–increase. This trend, to a certain extent, reflected the evolution of the cracks in the back-filling concrete samples. The axial, radial, and volumetric plastic strain curves of the back-filling concrete samples showed a "U" shape. The plastic strain changed in three stages, i.e., a rapid decrease, stabilization, and a rapid increase. A damage parameter was defined according to the plastic strain increment to accurately characterize the staged failure of the samples. The plastic strain and energy dissipation of the samples were precursors to sample failure. Prior to the failure of the back-filling samples, the amount and speed of change of both the plastic strain and energy parameters increased significantly. Understanding the characteristics of plastic strain, damage evolution, and energy dissipation rate of the back-filling samples are of great reference value for realizing real-time monitoring of back-filling concrete in the gob-side entry retaining and providing early warning of failure. [ABSTRACT FROM AUTHOR]

Copyright of Bulletin of the Chinese Ceramic Society is the property of Bulletin of the Chinese Ceramic Society Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Although rubberized concrete is widely accepted as an eco-friendly building material, its engineering applications are far limited due to its relatively low strength. To address this deficiency, the current study examines the effect of enhancing the strength of rubberized concrete through incorporating basalt fibers (BF) and water-based epoxy resin (ER) at varying proportions. In this study, both experimental testing and numerical simulations were conducted to investigate the mechanical, impact, and abrasion resistance properties of BF-ER composite enhanced rubberized concrete (BERC) using 12 different mix ratios. The evolution of damage in BERC was investigated, and the reinforcing mechanism of the fiber-polymer composite was elucidated through micro-morphology and pore structure analysis. The results indicate that the compressive strength and impact resistance of rubberized concrete are significantly improved due to inclusion of BF-ER, with the former achieving up to 60 % higher than normal rubberized concrete, while the latter attains improvement of 100 %. Due to the energy-absorbing behavior of rubber particles and the enhanced bonding effect provided by fiber-polymer, BERC exhibited a ductile failure mode, characterized by development of more complex cracks. Inclusion of fiber polymer resin has strengthened the weak interfacial transition zone (ITZ) between rubber particles and cement paste, albeit at the cost of increased porosity caused by the multiple interfaces of BF. From the current study, the optimal dosages of BF and ER are determined to be 2 kg/m3 and 4 kg/m3, respectively. The research results have provided useful insights on the application of rubberized concrete in critical engineering structures that require impact and abrasion resistance. • Mechanical properties and microstructures of BF and ER reinforced rubberized concrete were studied. • The influences of epoxy resin content on abrasion resistance of the BERC. • Effects of basalt fiber on compressive behavior and failure mode of rubberized concrete. • The basalt fiber and epoxy resin could be used in rubberized concrete to improve impact resistance. [ABSTRACT FROM AUTHOR]

Damage evolution in concrete is a complex phenomenon involving micro-cracks that originate from different material phases (mortar matrix, ITZ and aggregate), and culminate into a major crack. The information about the individual damaged material phases can provide major insights into the global failure behaviour, cracking path, and fracture processes. The evolution of damage, damage mechanisms and the material phase of origin of micro-cracks is highly influenced by the type of concrete (Normal and high strength). In order to investigate the evolution of damage in concrete of varying strength, notched beam specimens with different water-to-cement ratios have been prepared and tested under C M O D control. The evolution and growth of damage have been continuously monitored during testing through acoustic emission techniques. Based on acoustic emission results, it has been demonstrated that the damage progression in concrete can be better described as a function of the wavelet entropy of the AE events occurring during the entire loading duration, and therefore, an analytical model for the damage evolution has been proposed. The study reveals that, under the high-strength category, the level of deterioration reduces as the w / c ratio rises, while in normal-strength concrete, a reverse trend is observed. Furthermore, a novel approach has been proposed that utilizes wavelet entropy and amplitude to differentiate amongst various damaged material phases with the help of an unsupervised clustering algorithm. Normal-strength concrete with a w / c ratio of 0.4 has been used to demonstrate the proposed methodology and has been validated with the help of experiments performed on the mortar and the parent stone of aggregate. A higher occurrence of mode-I cracks compared to mode-II cracks across all material phases has been observed for the specimen. Additionally, ITZ and aggregate exhibit a greater proportion of tensile and shear cracking events than the matrix phase. In the end, a deep learning convolutional neural network (CNN) model is devised utilizing labelled scalogram images of the AE waveforms to discriminate between the various damaged material phases. A 10-fold training cross-validation of the dataset has been carried out to achieve a stable performance. The deep learning model performs well in discriminating the damaged material phases with high training, validation, and testing accuracy. • A damage variable based on wavelet entropy to evaluate the amount of deterioration in concrete has been proposed. • The damaged material phase identification with the help of acoustic emission event has been performed. • A convolutional neural network has been developed to discriminate between the AE events pertaining to different material phases. [ABSTRACT FROM AUTHOR]

To investigate the applicability of recycled sand concrete in high-speed railway ballastless track bed, in this study, the fatigue life, strain evolution curve and calculated stiffness of C40 concrete incorporating 0, 50 % and 100 % recycled sand were explored. Digital image correlation (DIC) and the nanoindentation test were used to explore the influence of recycled sand on the performance of concrete. The results show that the flexural fatigue life of recycled sand concrete conforms to a two-parameter Weibull distribution. The fatigue strain progression and calculated stiffness demonstrate a distinct three-stage trend. Compared to natural aggregate concrete, the first-stage strain contribution of recycled sand concrete decreases by approximately 10 %. With the increase of fatigue cycles, the calculated stiffness decreased significantly, the dissipated energy increases gradually. Compared with recycled sand-free concrete and full recycled sand concrete, the concrete containing 50 % recycled sand possesses the highest elastic modulus and lowest thickness of the interfacial transition zone (ITZ), thus the average fatigue life of recycled sand concrete increased by 4.9 and 10.2 times. • Flexural fatigue performance of concrete is optimal when the replacement ratio of recycled sand is 50 %. • Flexural fatigue strain evolution of recycled sand concrete was monitored by DIC technique. • Flexural fatigue damage evolution mechanism was analyzed by nanoindentation technique. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Zhejiang University: Science A is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• Characterizing quantitatively the physical characteristics of aggregate-cement interface. • Effects of casting and material composition factors on the microstructural and mechanical properties of ITZ are discussed systematically. • Developing correlations between microstructures and essential mechanical properties. • Seeking approaches to enhance the adhesion of paste to aggregates and fill micropores. Interfacial Transition Zones (ITZ) with high porosity are easier pathways for damage initiation and propagation. However, their mechanical performance has hardly been examined owing to the length scale of the microregions, as well as the heterogeneous and opaque constituent properties, which have been increasingly studied in recent years. This study presents a comprehensive review of the ITZ, determining strategies at the meso -micro level, quantitative characterization, and physical features. It focuses on the effects of various casting and material composition factors on the microstructural and mechanical properties of the ITZ, including porosity, thickness, volume, and elastic modulus. The correlations between the microstructures and the essential mechanical properties are discussed in detail. The weak bonding properties of the ITZ can be tailored by the material composition, which changes its internal microstructure, enhances the adhesion of the paste to aggregates, and fills micropores in cement. Several approaches can be employed to achieve this, such as adding minerals, increasing the curing age, and adjusting the water-cement ratio and sand fineness. The content of the weak ITZ can be reduced by optimizing the size distribution and volume fraction of the aggregates. Furthermore, modelling the gradient distribution of the ITZ thickness and elastic modulus is crucial in numerical simulations to enable an accurate investigation of the damage accumulation process in concrete. This study also identifies the challenges in the mechanical behavior of ITZ and serves as an engineering design guide for more advanced fracture-resistant concrete structures. [ABSTRACT FROM AUTHOR]

• FD is used to quantify crack distribution and track the concrete cracking process. • A novel calculation method for damage identification based on crack FD is proposed. • FD-based damage accumulates with crack development throughout the tensile process. • It varies with the aggregate gradation, specimen size, and aggregate distribution. • It suggests the damage value of 0.8 for concrete entering the local failure stage. The randomness and irregularity of concrete cracking present a challenge of quantitatively identifying the developing of damage degree of concrete subjected to complex external conditions. In this study, a concrete meso -mechanical model is established to quantitatively analyze crack propagation and damage evolution under uniaxial tension. Fractal dimension (FD) is used to quantify the crack distribution and track the entire process of concrete cracking. A novel calculation method for the damage identification based on crack FD is proposed, so that the quantitative correlation among the three curves of stress–strain, crack fractal dimension-strain, and damage variable-strain for concrete is obtained. During the hardening stage, the micro-cracks initiate at interface transition zone between aggregates and mortar, causing an increase in crack FD. As the load reaches its maximum, some micro-cracks tend to localize and form a crack aggregation zone. At the subsequent softening stage, the micro-cracks in other regions undergo a rebound phenomenon, resulting in a decrease in crack FD. Once the crack aggregation zone is formed, the macro-crack concentrates and continues to propagate, leading to an increase in crack FD again. This FD-based damage degree accumulates with crack development throughout the tensile process and varies with the aggregate gradation, specimen size, and aggregate distribution. This study suggests that the mutation point of the crack FD-strain curve after the peak stress point is the critical point at which concrete enters the local failure stage, and the corresponding damage value approximates 0.8. [ABSTRACT FROM AUTHOR]

• A coupled thermo-mechanical constitutive model for concrete is developed. • The model is formed based on thermodynamics framework and internal variable theory. • The model is upgraded for fiber reinforced concrete with fiber influence coefficient. • An orthotropic triaxial compression model was developed for concrete under fire. • Good effectiveness and accuracy of the model have been validated with tests data. In the current study, a coupled thermo-mechanical constitutive model of concrete was newly developed to characterize the mechanical responses of concrete at different temperatures within thermodynamics framework. The coupling thermo-mechanical contributions among thermal effect (up to 800°C), damage evolution and thermo-plastic hardening were creatively taken into account in energy potential function. The thermal damage evolution law and load induced plastic mechanical damage evolution law was developed respectively and were coupled in the dissipation function. The thermo-mechanical hardening rule was considered through adopting back stress and hardening parameters. A particular advantage of the proposed model is that fiber influence coefficients can be employed in potential functions to upgrade for modeling fiber reinforced concrete. The impact of types and volume fractions of fibers on the reinforcement mechanism was calculated in the fiber influence coefficients. Besides, an orthotropic triaxial compression model was developed for concrete and fiber reinforced concrete to predict multiaxial stress behavior at high temperature. The proposed model was coded and implemented into the Fortran program and the nonlinear behaviors of concrete and fiber reinforced concrete were predicted. Good effectiveness and accuracy have been validated through comparing the modelling results and six groups experimental results in literatures, which illustrates that the proposed model is robust and reliable. Finally, a discussed study was conducted to investigate the effect of hardening parameters and thermal effect on the yield surface. [Display omitted] [ABSTRACT FROM AUTHOR]

The fatigue process of concrete under compressive cyclic loading is still not completely explored. The corresponding damage processes within the material structure are especially not entirely investigated. The application of acoustic measurement methods enables a better insight into the processes of the fatigue in concrete. Normal strength concrete was investigated under compressive cyclic loading with regard to the fatigue process by using acoustic methods in combination with other nondestructive measurement methods. Acoustic emission and ultrasonic signal measurements were applied together with measurements of strains, elastic modulus, and static strength. It was possible to determine the anisotropic character of the fatigue damage caused by uniaxial loading based on the ultrasonic measurements. Furthermore, it was observed that the fatigue damage seems to consist not exclusively of load parallel oriented crack structures. Rather, crack structures perpendicular to the load as well as local compacting are likely components of the fatigue damage. Additionally, the ultrasonic velocity appears to be a good indicator for fatigue damage beside the elastic modulus. It can be concluded that acoustic methods allow an observation of the fatigue process in concrete and a better understanding, especially in combination with further measurement methods.

• X-ray CT scanning tests were conducted to obtain the research data. • The initial damage distribution of the concrete was identified. • Study the relationship between the statistical features and damage evolution. Concrete CT test is an effective method used to analyze micro-structural damage evolution of concrete under loading condition. In the CT images of different stress states in the same section, gray value changes in the original number matrix of CT image are the key to investigate microscopic damage evolution of concrete. However, the slight changes in the gray value of CT images before peak stress cannot be intuitively observed with the naked eye. This study mainly aims to develop a coupled method based on statistical method and X-ray CT to extract indicators of such subtle changes. Different cross-sectional CT images of concrete at different stress stages were obtained by uniaxial static compression CT test. The theory of the grey level co-occurrence matrices (GLCM) was then adopted to analyze micro-damage evolution and crack properties. That is, the GLCM of the CT images were calculated, and four statistical features including contrast, energy, correlation, and homogeneity were extracted, which can be extended into quantitative analysis of micro-damage hidden in the CT images of concrete. Results exhibited that the damage growth area, concentrating between the 45th and 225th concrete cross-section, could be predicted by the distribution of four statistical features (i.e., contrast, energy, correlation and homogeneity) at the fourth scan, and it is consistent with the crack location in the fifth scan. The contrast, energy and homogeneity follow the Gaussian distribution under five scan stages, and the correlation follows the Laplace distribution. In addition, the changes of bandwidth in color heat map illustrating the GLCM before and after specimen failure show that the bandwidth is positively correlated with micro-structural damage of concrete specimen. [ABSTRACT FROM AUTHOR]

The variation of properties of concrete with initial damage under sulfate and wet-dry-cycle environments was experimentally investigated. With increased corrosion time, changes in the parameters of concrete with initial damage were analyzed, including mass, ultrasonic velocity, compressive strength, stress-strain curves, and the activities of acoustic emission under uniaxial compression. A quantitative evaluation and parameter fitting for corrosion damage was made based on damage mechanical theory. Based on the acoustic emission characteristics, a damage model of corroded concrete with initial damage was established and its damage evolution was analyzed. Using environmental scanning electron microscopy (ESEM) and energy-dispersive X-ray analysis (EDX), the damage mechanisms were revealed in observations of the microstructures and element compositions of concretes with initial damage induced by sulfate corrosion. The research results show that with increased erosion time, the mass, ultrasonic velocity, and compressive strength of concrete with different degrees of initial damage first increase and then decrease. Increases in the degree of initial damage may accelerate the degradation of physical and mechanical properties, but a threshold effect exists. Compressive strength and ultrasonic velocity can be regarded as damage variables, and corrosion damage evolution equations and the functional relationship between different damage formulas were established. With increased erosion time, the stress-strain curve of concrete with initial damage is obviously concave-upward and the elastic-stage time period can be comparatively shorter whereas the yield-stage time period increases. An increase in the degree of initial damage results in an obvious attenuation of the acoustic emission activity, which lags behind the time of the obvious acoustic emission response. Based on the acoustic emission characteristics, the damage evolution process of concrete with initial damage can be divided into three stages, including the compaction, stable damage evolution and development, and accelerating damage development stages. With an increase in the degree of initial damage, stronger corrosion reactions and composition changes occur inside the concrete. Compared to undamaged concrete, the expansion and extension of denser and deeper micro-cracks occur in concrete with initial damage under sulfate attack, which accelerates the degradation of the physical and mechanical properties of corroded concrete.

A nonlinear parallel-bonded stress corrosion (NPSC) model is proposed to simulate the fatigue characteristics of artificial rock (concrete) during cyclic loading. Numerical simulations of fatigue tests replicate the main mechanical features of concrete specimens subjected to cyclic loading observed in the laboratory. A nonlinear reduction speed of the bond diameter between two bonded particles represents the damage rate induced by the fatigue load. The damage rate is proportional to the maximum cyclic load level when the minimum cyclic load level is fixed. Compared with laboratory data, a logarithmic function of bond diameter in the NPSC model resulted in the best fit to simulate the fatigue behaviour of concrete. The simulation includes acoustic emission (AE) monitoring during fatigue tests. The axial strain of the assembly is governed by the evolution of bond breakages. The sum of released bond strain energy is documented as value proportional to cumulative AE energy. The simulation results show very similar evolution compared with laboratory data, which verifies the effectiveness of AE energy simulation. [ABSTRACT FROM AUTHOR]

Graphical abstract Typical photos of crack propagation in a sample of w / c = 0.65 at different corrosion times of 120, (b) 140, (c) 180, (d) 210, (e) 230, and (f) 250 days. Highlights • Information entropy is selected to describe the randomness of cracks evolution in concrete under sulfate attack. • Equation of entropy evolution is derived by means of the chemical reaction rate for the formation of delayed ettringite. • The normalized entropy exponentially increases with the non-dimensional time. Abstract In this paper, the corrosion experiment of concrete showed that the length and orientation of cracks, as well as their propagation direction are randomly distributed. By virtue of SEM and XRD techniques, the growth of delayed ettringite was detected, which leads to expansion stress and then induces the nucleation and propagation of cracks. To investigate the statistical characteristics of cracks, the concept of information entropy was adopted. Furthermore, based on the entropy evolution at different corrosion times and the chemical reaction rate of delayed ettringite, a model for entropy evolution was proposed. It is shown that the normalized entropy exponentially increases with the non-dimensional corrosion time. [ABSTRACT FROM AUTHOR]

• ES-UHPC exhibits significant tensile strain-hardening behavior at early age. • ES-UHPC obtain high ductility and bonding between steel fiber and matrix at 1 d. • Damage evolution was monitored by acoustic emission method. • AE analysis proves that the ES-UHPC exhibits multiple cracking behavior at 28 d. • Ettringite is the main hydrates and the content increases rapidly from 4 h to 1 d. The properties of early age strength ultra-high performance concrete (ES-UHPC) made with calcium sulfoaluminate (CSA) cement, including tensile performance, damage evolution monitored by acoustic emission (AE) and microstructure were evaluated in this work. Results show that the ultimate tensile strain ε Utu of ES-UHPC can reach to 0.199% at 1 d, which is 4.23 times larger than that of normal UHPC (N-UHPC) at the same testing age. AE testing results indicate that both types of UHPCs exhibit multiple cracking behavior at 28 d. With the tensile strain developing, the two UHPCs show a similar damage evolution trend and multiple microcracks with crack-width smaller than 0.01 mm generated after 0.046% strain reached. Microstructure tests demonstrate that ettringite presented after 4 h and the content increased significantly from 4 h to 3 d, which contributed to the early mechanical properties for ES-UHPCs. [ABSTRACT FROM AUTHOR]

High-strength concrete is commonly used in tall buildings. Due to the poor high-temperature resistance of concrete, the fire safety of tall buildings has always been a huge concern. The application of tall building refractories might slow down structural damage, reduce economic loss and protect personal safety. In this paper, the rock wool fibre was taken as an example of tall building refractories. On this basis, the author probed into the mechanical properties and damage evolution of the tall building refractory, and set up a meso-damage mechanics model for the material. The research results show that the rock wool fibre refractory (RWFR) witnessed a reduction in elastic modulus after being damaged under the growing stress; when the temperature was below 600 °C, the RWFR enjoyed good properties with only a slight decline in strength, which could satisfy the requirement on the bearing capacity; the results simulated by the constitutive model agree well with the test results. The research lays solid experimental and theoretical bases for the promotion of RWFR in tall buildings. [ABSTRACT FROM AUTHOR]

This study focused on the rate-dependent relaxation time of concrete using the split Hopkinson pressure bar test and the ultrasonic technique. Based on the experimental results, and considering the viscous effect in concrete, the viscoelastic stress-strain relationship was established in terms of the principles of irreversible thermodynamics and the generalized Onsager's principle, providing the convergence of an iterative scheme in terms of the Lipschitz's condition. It was found that the relaxation time of concrete depends on the strain rate. Furthermore, considering the state equations and damage evolution, a nonlinear viscoelastic constitutive model of concrete coupling damage was proposed. Compared with the experimental results, this model could better characterize the strengthening and softening characteristics of concrete prior to and beyond the strength limit. Further analysis indicated that the viscous effect is dominantly caused by the C-S-H in concrete. [ABSTRACT FROM AUTHOR]

This paper conducts a quantitative analysis of microstructural damage evolution of concrete materials under freeze-thaw action using three-dimensional X-ray computed tomography. The study employs two resolution-scales to evaluate concrete samples under various cycles of freeze-thaw action. The three-dimensional microstructural damage characterization, pore network (porosity, pore size, and pore distribution) as well as the defects in the aggregates are specifically investigated. The microstructures of concrete under different freeze-thaw action show that the interfacial transition zone is most likely to be damaged first under frost attack. Furthermore, the freeze-thaw action deteriorates not only the interfacial transition zone but also cement matrix and aggregates. The impact of freeze-thaw cycles is notable on the internal micro-pores and micro-cracks of the concrete. More pores and cracks can be nucleated during the freeze-thaw action, and further accumulate and grow in the paste and aggregates, eventually leading to final failure of concrete materials. As demonstrated in this study, three-dimensional X-ray computed tomography is capable of acquiring microstructures of concrete and revealing existence of internal pores and cracks in different phases of concrete, and more effective to characterize accumulated damage of concrete due to freeze-thaw action. [ABSTRACT FROM AUTHOR]

To study the dynamic mechanical characteristics and constitutive relation of concrete materials under freeze–thaw (FT) cycle conditions, C35 concrete was taken as the research object in this paper, and FT tests were carried out with a freeze–thaw range of −20–20 °C and a freeze–thaw frequency up to 50 times. By using the separated Hopkinson pressure bar (SHPB) system, impact compression tests of concrete specimens under different FT cycle actions were developed, then the dynamic fracture morphology, fracture block distribution, stress–strain curve, peak stress and other dynamic mechanical properties of concrete were analyzed, and the influence law of FT action and strain rate was obtained. Through introducing the freeze–thaw deterioration damage factor and the stress damage variable, the dynamic visco-elastic damage constitutive equation of freeze–thawed concrete was constructed based on component combination theory. Furthermore, the damage evolution process and mechanism of freeze–thawed concrete materials were revealed. The research results show that the dynamic mechanical properties of concrete under a freeze–thaw environment are the combined results of the freeze–thaw deterioration effect and the strain rate strengthening effect. The dynamic visco-elastic damage constitutive model established in this paper can effectively describe the dynamic mechanical properties of freeze–thawed concrete, and has the characteristics of few parameters and good effect. The stress damage evolution path of concrete goes backward with the increase of FT cycles and the development speed gradually slows down. The greater the difference in FT cycles, the greater the difference in stress damage path.

Highlights • Full-field evolution of strain distribution of test specimen is obtained using the DIC technique. • Cohesive zone model for describing the interface stress-displacement relationship is proposed. • Interface fatigue S-N curve of a ballastless track in high-speed railways is acquired. • Interface damage evolution of ballastless track under cyclic temperature loads are investigated. Abstract The interface damage of ballastless tracks in high-speed railway is considered as one of the most critical damage problems, however, the mechanical property and damage evolution of the concrete interface of ballastless tracks are rarely ascertained, and maintenance of the interface damage has been a heavy burden on the modern railway networks. This work aims to reveal the damage constitutive relationship and fatigue performance of the concrete interface of double-clock ballastless track based on experimental tests and simulation analysis. Firstly, by making the composite specimen composed of half track-slab concrete and half supporting-layer concrete and by designing experiment programs for the interface cracking test, the full-field evolution of strain distribution of the specimen under monotonic splitting loading is obtained based on the digital image correlation (DIC) technique, and the key parameters of a cohesive zone model for describing the interface stress-displacement relationship is determined. Subsequently, the interface damage evolution is investigated by applying cyclic splitting loads, and the interface fatigue S-N curve is acquired and validated by comparing with relevant references. It is found that the fatigue life of the concrete interface can be easily predicted with only knowing its secondary growth rate of the opening displacement amplitude. Furthermore, to elucidate the practical application of the experiment data and proposed models, the interface damage evolution of the double-block ballastless track under monotonic and cyclic temperature gradient loads are investigated, respectively. Simulation results show that much attentions should be paid to the negative temperature gradient load (below −60 °C/m) that could cause initiation of interface cracks. The proposed fatigue S-N curve enable a convenient and effective prediction for the interface fatigue damage of ballastless track with different service state under random loading cycles. [ABSTRACT FROM AUTHOR]

Meso-scale modeling approach is helpful for understanding the mechanism of both global nonlinear behavior and local failure pattern of concrete materials and structures. As a typical multiphase composite material, concrete is composed of randomly-distributed coarse and fine aggregates, mortar, interfacial transition zone (ITZ) together with initial pores or defects. The meso-scale mechanical behavior of concrete usually exhibits nonlinear and stochastic characteristics. In this paper, the influence of both distribution and geometrical shape of aggregates, the existence of ITZ, and meshing approach on macro stress-strain relationship, damage evolution and the final failure pattern of concrete are studied systematically. The results indicate that the effect of meso-scale structure of concrete on the nonlinear and stochastic characteristics of macro stress-strain curves and failure patterns is different when the concrete specimen is under tension and compression loadings. Comparatively, the geometrical parameters of coarse and fine aggregates have limited effect on the macroscopic tensile strength, but obvious effect on the post-tension segment and the compressive macro stress-strain curve. Moreover, the damage evolution and failure pattern of concrete under uniaxial tensile and compression are sensitive to the meshing approach. The existence of ITZ affects the tensile and compressive strength of concrete significantly. The statistic characteristics of macro stress-strain curves under both tension and compression loadings from the multi-scale simulation is compared with that from experimental studies and the rationality of the meso-scale simulation approach is validated. [ABSTRACT FROM AUTHOR]

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Concrete is typically treated as a homogeneous material at the continuum scale. However, the randomness in micro-structures has profound influence on its mechanical behavior. In this work, the relationship of the statistical variation of macro-scale concrete properties and micro-scale statistical variations is investigated. Micro-structures from CT scans are used to quantify the stochastic properties of a high strength concrete at the micro-scale. Crack propagation is then simulated in representative micro-structures subjected to tensile and shear tractions, and damage evolution functions in the homogenized continuum are extracted using a Helmholtz free energy correlation. A generalized density evolution equation is employed to represent the statistical variations in the concrete micro-structures as well as in the associated damage evolution functions of the continuum. This study quantifies how the statistical variations in void size and distribution in the concrete microstructure affect the statistical variation of material parameters representing tensile and shear damage evolutions at the continuum scale. The simulation results show (1) the random variation decreases from micro-scale to macro-scale, and (2) the coefficient of variation in shear damage is larger than that in the tensile damage. [ABSTRACT FROM AUTHOR]

The critical microcracks make durability of the concrete seriously weakened, and the water-cement ( w/ c) ratio plays a key role in the durability of concrete, acoustic emission (AE) rate ' a' value is an effective parameter to evaluate the amount of critical microcracks quantitatively, so the study on the influence factors and the distribution of w/ c ratio on the value ' a' can provide a promising reference value for the practical engineering. A total of 90 specimens in different w/ c ratio are tested under axial compression in the experiment. The whole damage evolution processes are monitored by fulldigital AE acquisition system. The differences of the amount of critical microcracks in different w/ c ratio are explored based on the AE rate process theory, and the rule of the effects of w/ c ratio on the rate ' a' value is revealed through the analysis of fracture energy and cumulative AE energy in the failure process. The results show that a linear relationship was observed between cumulative AE energy and rate ' a' value, the amount of critical microcracks and the rate ' a' value increase with the increase of w/ c ratio, while the cumulative AE energy and cumulative AE hits are on the contrary. [ABSTRACT FROM AUTHOR]

This article presents an anisotropic damage model for concrete that couples between elasticity and continuum damage mechanics. The formulation of constitutive model is based on the elastic strain energy in the framework of irreversible thermodynamics. The thermodynamic free energy is represented as a scalar function of elastic strain and damage tensors and used to derive the constitutive law and thermodynamic conjugate force of damage that is used to derive the dissipation potential. The damage evolution law is governed by the normality rule. The formulation of elastic strain energy of damaged material is capable of modeling the concrete anisotropic behavior under different loadings without decoupling the stress or damage release rate. A series of unknown parameters in the model formulation was used to control the constitutive behavior and damage surface. A Genetic algorithm FORTRAN subroutine is used to estimate these parameters based on the coupling between the constitutive and damage evolution equations. The performance of the damage model is verified with the experimental data from the literature. The model has shown a good agreement with the experimental results. It describes the anisotropy induced by the crack development within the concrete. [ABSTRACT FROM AUTHOR]

The mechanical properties of concrete under cyclic tensile loading using square waveform, sine waveform and ramp waveform are studied. The experiments are performed on a closed-loop electro-hydraulic servo-controlled material testing system (MTS). The axial strain, dissipated energy per loading cycle, the damage evolution law and deformation modulus are mainly studied. The results show that the three-stage evolution law of axial strain and damage variable of concrete under ramp waveform and sine waveform are more obvious than those under the square waveform. The dissipated energy changes at different stages of fatigue life. At the beginning and end of the fatigue life, the rate of dissipated energy is higher than that at the medium stage of the fatigue time, which is attributed to the formation of cracks. The evolution of deformation modulus of concrete subjected to cyclic tensile loading using three loading waveforms also shows three stages: fast increase in the damage-increase at a slow constant rate-and accelerated increase in damage until failure. [ABSTRACT FROM AUTHOR]

Alkali-activated concrete (AAC) is recognised as a novel sustainable construction material to substitute Portland cement concrete with superior thermal and mechanical performance. However, AAC would suffer significant deterioration when subjected to elevated temperatures due to different damage mechanisms, including thermal incompatibility caused by different thermal coefficients between matrix and aggregates, pore pressure build-up and phase transformation. This paper presents a systematic and comprehensive review on the behaviour of different types of AAC such as alkali-activated fly ash, alkali-activated slag, alkali-activated metakaolin and alkali-activated fly ash-slag systems at elevated temperatures in terms of phase stability and microstructural evolution as well as thermal and mechanical performance. The effective strategies for improving the high-temperature resistance of AAC are reviewed and discussed from the perspectives of AAC matrix, aggregates and fibre incorporation, with special focus on how these strategies can tackle different damage mechanisms. This paper summarises the recent advances in the field and identifies the remaining challenges and opportunities for future research. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to develop a confinement enhanced damage-plasticity model for concrete that can characterize the improvement of strength and ductility under high confining stress. The influence mechanisms of confinement in damage and plasticity sub-space are discussed separately. In the damage subspace, a confinement influence function considering the difference between uniaxial and multiaxial damage evolution is suggested based on the strain energy equivalence confinement. A confinement enhanced damage evolution model is established, which can capture the strength increase under high confining stress. In the plasticity subspace, a confinement enhanced phenomenological plasticity model, which includes equation of state of the spherical space, is provided to reproduce the high ductility at the principal stress direction under lateral confining stress. The simulated strength and stress–strain curves under active confinement agree well with the experimental results. Furthermore, the predicted three-dimensional ultimate stress points are consistent with the classic strength surface, validating good performance of the proposed model. • A confinement enhanced damage-plasticity model for concrete is developed. • A confinement influence function is introduced in the damage sub-space. • A confinement enhanced phenomenological model is built in the plasticity sub-space. • The model is validated to reproduce hardening and ductility under confinement. [ABSTRACT FROM AUTHOR]

A coupled viscosity-damage model of concrete under high strain rate is proposed based on the bi-scalar plastic-damage model. A rheological model is provided to explain the time delay mechanism of the damage under dynamic loading. A rate-dependent damage evolution is established by introducing the Duvaut–Lions type of the damage driving stress rate, and damage and viscosity are coupled. The operator splitting method is used to design an explicit calculation procedure. It is illustrated how the damage evolution predicted by the model differs for dynamic loading and quasi-static loading. Excellent comparisons between the simulated and experimental results show that the model can be used to reflect the strain rate effect of concrete under impact. • A coupled viscosity-damage model with dynamic effect is developed for concrete. • A rheological model is presented to explain relationship of damage and viscosity. • The Duvaut–Lions type of rate dependent damage driving stress is constructed. • The viscosity-damage coupling is established, and dynamic damage evolution is built. • A series of simulations of concrete dynamic tests validate the proposed model. [ABSTRACT FROM AUTHOR]

In order to study the size effect on the AE rate ' a' value, three kinds of mix ratios were set up by different particle sizes and water cement ratios, 45 cement mortar specimens with five different heights were tested under axial compression. And the whole damage processes were monitored by full-digital acoustic emission acquisition system, followed by an analysis of mechanical behavior and AE activity. The experimental results show that the height of the cement specimen has significant effects on the compressive strength and the acoustic emission rate ' a' value, but a slight effect on the accumulated AE hits number, which is analyzed from aspects of failure process of cement mortar specimens. [ABSTRACT FROM AUTHOR]

Damage evolution is detected via the degradation of modulus of concrete immersed in sulfate solution. The mechanism of the damage is investigated by using SEM method, and it is proved that the internal expansion stress induced by delayed ettringite leads to the nucleation of micro-cracks. The criterion of damage nucleation is proposed in terms of the tension strength of concrete. The differential equation with respect to the internal expansion stress is derived by virtue of chemical reaction rate on delayed ettringite formation, and a new chemo-mechanical model of corrosion damage in concrete under sulfate attack is then proposed. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study on cuboid stirrup-confined concrete specimens under uniaxial monotonic loading and cyclic loading. The effects of stirrup volume ratio, stirrup yield strength, and concrete strength on damage evolution of the stirrup-confined concrete were investigated. The experimental results showed that the strength and ductility of concrete are improved by appropriate arrangement of the stirrup confinement. Firstly, with the increase of the stirrup volume ratio, the damage evolution of concrete can be relatively restrained. Secondly, higher stirrup yield strength usually leads to larger confining pressures and slower damage evolution. In contrast, higher concrete strength leads to higher brittleness, which accelerates damage evolution. Based on the experimental data, a plastic strain expression is obtained through curve fitting, and a damage evolution equation for stirrup-confined concrete is proposed by introducing a confinement factor ( C). The comparisons results demonstrated that the proposed damage evolution curve can accurately describe the experimental results. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study on circular stirrup-confined concrete specimens under uniaxial and monotonic load. The effects of stirrup volume ratio, stirrup yield strength and concrete strength on damage evolution of stirrup-confined concrete were investigated. The experimental results showed that the strength and ductility of concrete are improved by appropriate arrangement of the stirrup confinement. Firstly, the concrete damage evolution can be relatively restrained with the increase of the stirrup volume ratio. Secondly, higher stirrup yield strength usually causes larger confining pressures and slower concrete damage evolution. In contrast, higher concrete strength leads to higher brittleness, which accelerates the concrete damage evolution. A plastic strain expression is obtained through curve fitting, and a damage evolution equation for circular stirrup-confined concrete is proposed by introducing a confinement factor (C) based on the experimental data. The comparison results demonstrate that the proposed damage evolution model can accurately describe the experimental results. [ABSTRACT FROM AUTHOR]

Ultra-high performance concrete (UHPC) is vulnerable to high temperature-induced damage due to its dense microstructure. To mitigate thermal damage of UHPC, this study develops synergistic flame-retardant polymer (SFRP) fibres by introducing organic-metallic fillers and experimentally investigates the thermal properties, compressive behaviour, and microstructural evolution of SFRP fibre reinforced UHPC subjected to elevated temperatures up to 800 °C. Results indicated that the addition of SFRP fibres can effectively prevent the explosive spalling and significantly reduce the strength loss of UHPC at high temperatures due to the thermal mismatch between fibres and concrete. SFRP fibres were also proved to help greatly enhance the fire resistance and mitigate the thermal damage of UHPC, which can be attributed to the increased connectivity of pore structure, filling effect of flame-retardant polymers, and delayed degradation of micromechanical properties. The SFRP fibre content of 2.0 vol% is recommended considering the residual strength and damage mitigation efficiency. [ABSTRACT FROM AUTHOR]

Theoretical and experimental studies on the nonlinear mechanical properties of lightweight foamed concrete under uniaxial compression are conducted over the temperature range of 223–343 K and the strain rate range of 0.001–118/s in this paper. The experimental results show that the mechanical properties of the materials under uniaxial compression are strongly dependent on the density and temperature, but are weaker on strain rate. Based on the experimental results, the characteristics of density effect and temperature effect are analyzed and a calculation model is developed to describe the nonlinear mechanical behavior of lightweight foamed concrete. The model takes into account the effect of material damage, density and temperature. The experimental verification and the error analysis show that the model is shown to be able to predict the nonlinear deformation behavior of lightweight foamed concrete over a wide range of temperatures and densities. [ABSTRACT FROM AUTHOR]