Uniaxial Compressive Stress-strain Curves Research Articles

Unified uniaxial compressive constitutive model for C20–C120 concrete based on stochastic damage theory

The concrete uniaxial compressive stress-strain model is essential for analyzing reinforced concrete members and structures. However, models applicable to C20–C120 concrete are still relatively rare. Moreover, the previous empirical model construction methods may not reflect the physical mechanisms and randomness of concrete failure well. To this end, the database was constructed by collecting and analyzing uniaxial compressive stress-strain curve test results from different scholars. The cubic compressive strength in the database ranges from 9.9 MPa to 137.3 MPa. The adaptability of the stochastic damage model was validated using the database of test curves. Subsequently, stochastic damage models for C20–C120 concrete were calibrated based on concrete compressive strength grouping curves, and practical analysis models were suggested. The results indicate that the calculated curves closely match the test curves when the plastic strain evolution parameters η1,c and η2,c in the stochastic models are taken as 0.001–0.30 and 0.19–0.25, respectively. The adaptability of the stochastic damage model is satisfactory, but the plastic strain evolution laws vary for different concrete compressive strengths, influenced by mix proportions and the probability of failure of each component on the meso-scale. When η1,c is calculated by the empirical formula proposed in this paper and η2,c is approximated as 0.22, the calculated curves for C20–C120 concrete are consistent with the mean values of the test curves. The proposed practical analysis models provide comparable accuracy to stochastic damage models, eliminating the need for iterative calculations, making them convenient for engineering applications.

Constitutive modeling and extended performance evaluation of concrete reinforced with non-hybrid waste tire steel fibers

This paper investigates the extended performance and constitutive modeling of waste tire steel fiber reinforced concrete (WFRC), making notable contributions to civil engineering materials. The study assesses constitutive modeling, reinforcement indices, and the long-term performance of concrete reinforced with varying percentages of waste tire steel fiber (WSF) ranging from 0.30 % to 1.75 %. A modified analytical model for predicting compressive stress-strain curves of WFRC is introduced and compared with previous analytical models for fiber-reinforced concrete. Additionally, a novel waste tire steel fiber reinforcing index, based on WSF properties, is proposed. Empirical relationships between strength properties and reinforcement indices are established. Experimental strength properties at the standard age, as well as water absorption, carbonation depth, and split-tensile strength of specimens aged beyond the standard age at 600 days and fiber-matrix interaction obtained by SEM analysis, are reported. Prediction models are proposed for estimating the mechanical properties of WFRC at the standard age, with results compared against existing codes. The proposed modified analytical model for the uniaxial compressive stress-strain curve demonstrates better coherence with experimental curves than existing models. Furthermore, empirical equations developed in terms of the waste tire steel fiber reinforcing index demonstrate satisfactory alignment between predicted and experimental strength properties. Significant improvements are observed in specimens aged 600 days, indicating the promising role of WSF in enhancing the long-term performance and serviceability of structures. Further studies are recommended to explore the performance of WFRC in aggressive environmental conditions.

Experimental Study on the Mechanical Properties of Steel Fiber Ferronickel Slag Powder Concrete

The use of ferronickel slag powder (FNSP) as a cementitious additional material has been supported by numerous reports. FNSP concrete has the same shortcomings as ordinary concrete, including low hardness. In this study, in order to make FNSP concrete more durable, end-hooked type steel fibers were incorporated. To understand how various elements affect the mechanical properties of steel fibers, an experiment was carried out on the mechanical properties of steel FNSP concrete (SFNSPC). FNSP’s principal ingredients, with a particle size distribution ranging from 0.5 to 100 μm and a sheet-like powder shape, are CaO, SiO2, Al2O3, MgO, and others, according to tests conducted on the material’s microstructure and composition. Then, eighteen mix proportions were developed, comprising six distinct FNSP replacement rate types and three distinct steel fiber content types. Crucial metrics were evaluated and analyzed, including the relationship among the toughness, tensile strength, and compressive strength as well as slump, splitting tensile strength, compressive strength, and uniaxial compressive stress–strain curve of SFNSPC. The results showed that the slump of SFNSPC under different FNSP replacement rates decreased with increasing steel fiber volume. Steel fibers have a small but positive effect on SFNSPC’s compressive strength; nonetheless, as FNSP replacement rates increased, SFNSPC’s slump gradually decreased, though not by much. These results show that FNSP is a viable alternative cementitious material in terms of strength. Specifically, the splitting tensile strength of SFNSPC improves with an increase in steel fiber content, and the pace at which SFNSPC strength drops with an increase in the FNSP replacement rate. With varying mix proportions, the stress–strain curve trend of SFNSPC remains mostly constant, and steel fibers improve the compressive toughness of SFNSPC. After adding 0.5% and 1.0% steel fibers, the toughness index of concrete with different FNSP replacement rates increased by 8–30% and 12–43%, respectively.

Study on mechanical properties and meso-damage mechanism of carbon-polyvinyl alcohol hybrid fiber reinforced recycled coarse aggregate concrete under the coupling action of sodium sulfate and dry-wet cycles

In order to investigate the influence of the coupling effect of sodium sulfate dry-wet (DW) cycles on the mechanical properties of carbon-polyvinyl alcohol hybrid fiber reinforced recycled coarse aggregate concrete (HFRAC), HFRAC specimens were subjected to uniaxial compression tests. The total volume fraction of fibers was kept constant at 0.4%, and various volume fractions of carbon fibers (CF) were added to the recycled coarse aggregate concrete (RAC), namely 0%, 0.1%, 0.2%, 0.3%, and 0.4%, with polyvinyl alcohol (PVA) fibers replacing a portion of CF in equivalent volume. Uniaxial compressive stress–strain curves were obtained for HFRAC specimens subjected to different numbers of DW cycles (0, 30, 60, and 120 cycles). Microscopic testing methods including acoustic emission (AE), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and nuclear magnetic resonance (NMR) were employed to analyze the microstructure, erosion product composition, and pore structure changes of the specimens. The results revealed that, for RAC specimens, the peak stress (σp) and elastic modulus (E) initially increased and then decreased, whereas the peak strain (εp) initially decreased and then increased with an increase in the number of DW cycles. After adding hybrid fibers, the σp values of CF, Hybrid 3:1, Hybrid 1:1, Hybrid 1:3, and PVA specimens increased (or decreased) by 12.0%, 11.43%, 0.9%, −9.5%, and −8.5%, respectively, compared to RAC. The Hybrid 1:3 specimen exhibited a negative hybrid effect. With an increase in the erosion age, the Hybrid 3:1 specimen demonstrated enhanced resistance to sulfate attack and achieved the highest σp value after 120 cycles. The influence of sulfate DW cycles coupling on the microscopic damage mechanism of HFRAC was analyzed using a statistical damage constitutive model. The microscopic damage evolution process was characterized by five characteristic parameters: E0, εa, εh, εb, and H. The analysis results indicated a clear correlation between the variation of these characteristic parameters and the number of DW cycles. An effective connection was established between the microscopic damage mechanism and the macroscopic nonlinear constitutive behavior. The phenomenon of relative lagging of acoustic emission signals during the uniaxial compression process was explained from the perspective of effective stress. This study provides a theoretical basis for the promotion and application of RAC under sulfate DW cycle environments.

Research on axial compressive performance of ceramic concrete reinforced with HTPP fibers

This study investigates the influence of High-Toughness Polypropylene (HTPP) fiber content (0 %, 0.3 %, 0.6 %, 0.9 %) on the axial compressive performance of ceramsite concrete. Four sets of ceramsite concrete cube and prism specimens were prepared, and the cube compressive strength and full stress-strain curves for each set were tested. Based on the experimental results, it analyzed the variation characteristics of HTPP fibers on the stress-strain curve of ceramic concrete at different stages, studied the peak stress, peak strain, elastic modulus, toughness, and energy absorption capacity of ceramic concrete. Finally, the stress-strain curve has been fitted. The results indicate that: HTPP fibers can significantly enhance the strength and toughness of ceramic concrete, the compressive strength of the cube increased by 23.8 %, the axial compressive strength increased by 19.0 %, the residual stress increased by 143.0 %, the absolute modulus increased by 164.1 %, the toughness increased by 51.5 %, and the energy dissipation coefficient increased by 9.4 %. By fitting the experimental curve, the mathematical expression for the uniaxial compressive stress-strain curve of ceramic concrete reinforced with high tenacity polypropylene (HTPP) fibers has been proposed. The model matches well with the experimental results, which provides a theoretical basis for the structural analysis and design of this type of concrete.

A nonlinear elastic-strain hardening model for frozen improved sandy soil under uniaxial compression loading condition

Artificial freezing is one of the most effective methods in the excavation of water-rich soils. This work aims at investigating the influence of cement‑sodium silicate grout (C-S grout) and organic polymer stabilizer (OPS) on the uniaxial compressive strength (UCS), stress-strain curve, and unfrozen water content of frozen sandy soil. A series of uniaxial compression tests and nuclear magnetic resonance (NMR) tests were conducted on the saturated frozen sandy soils improved by C-S grout and OPS (“C-S grout-improved soil” and “OPS-improved soil”) under different negative temperatures (i.e., −5 °C, −10 °C, −15 °C, and −20 °C). Based upon the experiment results and existing stress-strain models, including improved Duncan-Chang model and elastic-strain hardening model, a nonlinear elastic-strain hardening constitutive model for improved soils was proposed, in which each parameter has well-defined physical meaning. The results showed that, as the temperature decreases, the strengths of frozen improved soils gradually increase. The strength of OPS-improved soil first increases and then decreases with the increase of OPS dosage. Contrary to the UCS, the unfrozen water content of two improved soils was observed to gradually decrease with the decrease of temperature. As the OPS dosage increases, the unfrozen water content of improved soils decreases first and then increases. When the strain is <0.2, the stress-strain curves of frozen C-S grout-improved soil exhibits a behavior of yielding first and then hardening after the nonlinear elastic stage, while OPS-improved soil exhibits continuous strain hardening behavior. With temperature and unfrozen water content given, the new nonlinear elastic-strain hardening model can accurately predict the stress-strain behavior of frozen improved soils. This study is helpful to the stability analysis of artificial frozen walls and pre-control of environmental deformation during the excavation of water-rich sandy soils.

Experimental study on the basic properties of new biomass bamboo aggregate concrete

Gravel aggregate is an important part of concrete, but the resources of natural aggregate, such as gravel, are increasingly scarce and may have adverse effects on the environment. Therefore, a new biomass bamboo aggregate concrete was proposed in this study, which bamboo aggregate was used to replace gravel aggregate to alleviate the shortage of gravel resources. To study the basic properties of bamboo aggregate concrete and explore its feasibility, tests for compressive strength, splitting tensile strength, flexural strength, and uniaxial compressive stress-strain curve were conducted. The microstructure was also observed. The research parameters included the concrete curing age and different bamboo aggregate volume replacement ratios. The results presented that the mechanical properties of bamboo aggregate concrete were enhanced with increasing age. Compared with the normal concrete, the mechanical properties of bamboo aggregate concrete decreased as the replacement ratio of modified bamboo aggregate increased, but the 28-d compressive strength of modified bamboo aggregate concrete could still reach 74% of that of normal concrete. The mechanical performance of bamboo aggregate concrete was significantly influenced by whether bamboo aggregates were modified. The uniaxial compressive stress-strain model proposed by GB50010-2010 was suitable for bamboo aggregate concrete. The interfacial bonding effect between modified bamboo aggregate and cement matrix was improved.

Study on the Self–Bearing Mechanism and Mechanical Properties of Gangue Slurry under Overburden Loading

The mining of coal resources is accompanied by a large amount of solid waste such as gangue, which seriously affects the ecological environment. The gangue grouting backfilling technique can achieve the dual goals of gangue disposal and surface deformation control by injecting gangue slurry into the underground. The bearing mechanical characteristics of gangue slurry directly affect the surface deformation control effect of the grouting backfilling technique. In this study, a loading simulation system of grouting backfilling materials was designed, uniaxial confined compression tests were conducted, and the self–bearing mechanism of large particle–sized gangue slurry with different fluidities under instantaneous and creep loading modes was investigated. Additionally, the mechanical characteristics of the compacted body (i.e., the gangue slurry after creep loading) were analyzed. The results indicate that the self–bearing process of gangue slurry can be divided into three stages: the rapid compression and drainage stage, the pore compaction and water bleeding stage, and the particle crushing and elastic–plastic deformation stage. The uniaxial compressive stress–strain curve of a compacted body can be classified into four stages: elastic stage, yield stage, reinforcement stage, and crushing stage, and the strength of the compacted body is affected by the loading time and fluidity of the slurry. When the slurry with a fluidity of 240 mm is subjected to constant pressure for 3 h, the compressive strength of the slurry reaches the maximum value of 4.98 MPa, and 13.1% stress damage occurs when the constant pressure reaches 4 h. This research provides a theoretical basis for the improvement of the proportion and bearing characteristics of gangue grouting materials.

Rapid inverse design of metamaterials based on prescribed mechanical behavior through machine learning

Designing and printing metamaterials with customizable architectures enables the realization of unprecedented mechanical behaviors that transcend those of their constituent materials. These behaviors are recorded in the form of response curves, with stress-strain curves describing their quasi-static footprint. However, existing inverse design approaches are yet matured to capture the full desired behaviors due to challenges stemmed from multiple design objectives, nonlinear behavior, and process-dependent manufacturing errors. Here, we report a rapid inverse design methodology, leveraging generative machine learning and desktop additive manufacturing, which enables the creation of nearly all possible uniaxial compressive stress‒strain curve cases while accounting for process-dependent errors from printing. Results show that mechanical behavior with full tailorability can be achieved with nearly 90% fidelity between target and experimentally measured results. Our approach represents a starting point to inverse design materials that meet prescribed yet complex behaviors and potentially bypasses iterative design-manufacturing cycles.

Study on dynamic mechanical properties and meso-damage mechanism of carbon fibers recycled aggregate concrete under freeze-thaw environment

The uniaxial compression mechanical properties tests of carbon fibers recycled aggregate concrete (CFRAC) were carried out in order to investigate the effect law of coupling freeze-thaw cycles (FTCs) and dynamic strain rates on the mechanical properties of CFRAC. Two cases of carbon fibers (CFs) doping of 0% and 0.3% were considered. The full CFRAC uniaxial compressive stress-strain curves at different strain rates (10−5/s, 10−4/s, 10−3/s, 10−2/s) after different FTCs (0, 50, 100) were obtained. The microscopic characteristics and microcrack propagation process of the specimens were analyzed by means of nuclear magnetic resonance (NMR), scanning electron microscope (SEM) and acoustic emission (AE). The results showed that the specimens still had significant strain rate sensitivity after FTCs. With the same amount of CFs doping and strain rate, the strength and elastic mode (E) of the specimens kept decreasing as the number of freeze-thaw cycles (N) increased. With the same N, the strength and E of the specimens increased and the deformation capacity decreased as strain rate increased. With the addition of 0.3% CFs, the frost resistance and crack resistance of the specimens were significantly enhanced. Combined with the statistical damage constitutive model, the influence of FTCs and dynamic strain rates coupling on the meso-damage mechanism of CFRAC was analyzed. The meso damage evolution process was characterized by five characteristic parameters E0, εa, εh, εb and H. The results showed that there was an obvious regularity between the change of characteristic parameters and CFs content, dynamic strain rate and the N. An effective link between the fine-scale damage mechanism and the macroscopic nonlinear intrinsic behavior was established. The phenomenon of AE signal lag in uniaxial compression was explained from the perspective of effective stress.

Uniaxial Compressive Stress-Strain Model of Jujube Nucleus Concrete following Exposure to Elevated Temperatures.

Aiming to provide a solution for natural resource consumption and agricultural waste pollution, jujube nucleus is utilized as a substitute for coarse aggregate in the preparation of lightweight aggregate concrete. The effect of the jujube nucleus (JN) replacement ratio and the elevated temperature on the uniaxial compressive stress-strain curves of jujube nucleus concrete (JNC) are experimentally studied. The results show that the failure of the JNC prisms became more serious with the increase in the JN replacement ratio. The linear proportion in ascending branch and the descending slope of the stress-strain curves for JNC increased gradually with the increase in the JN replacement ratio and elevated temperature, which is probably owing to the higher porosity and lower stiffness of the jujube nucleus, compared to natural aggregate. Moreover, as the JN replacement ratio and the elevated temperature increase, the peak stress and elastic modulus in the stress-strain curves of JNC decrease gradually, whilst an increase in the peak strain shows up, which is possibly due to the growth of hydrate calcium silicate and calcium hydroxide hampered by sucrose molecules. Based on the test results, a series of theoretical formulas are proposed to predict the compressive performance of JNC. A material constitutive model is developed for describing the stress-strain relationship of JNC by considering the JN replacement ratio and elevated temperature.

Synthetic salt rock prepared by molten salt crystallization and its physical and mechanical properties

Physical simulation is an important research method for salt cavern energy storage construction technology. However, its progress is constrained by lack of effective model salt. Exploratory experiments were conducted to prepare salt rock by molten salt crystallization. A well-made synthetic salt rock was obtained from repeated adjustment of staged cooling conditions and controlled crystal growth procedures. Samples were taken for microscopic, physical, and mechanical tests, and compared with natural salt rock. SEM, CT and p-wave velocity results show that synthetic salt rock achieved crystallization. Its crystal structure, grain size and intercrystalline relationship are consistent with those of natural salt rock. Its density distribution is uniform and compaction is good. X-ray results prove a high crystallinity and stable mineral composition. Porosity of synthetic specimens ranges from 2.3% to 5.9%, permeability is in the range of E−13 to E−16 m2. Uniaxial compression stress-strain curves, strengths, deformation modulus and poisson's ratios are close to those of natural salt rock. It has obvious ductility and damage occurs after dilation deformation. We initially illustrate energy storage and heat storage-transfer principles of molten salt. The mechanism of layered growth in molten salt crystallization is revealed. The findings provide new insight on salt rock preparation, crystallography, molten salt and salt cavern study.

Carbonation Resistance and Pore Structure of Mixed-Fiber-Reinforced Concrete Containing Fine Aggregates of Iron Ore Tailings

The disposal of industrial by-product tailings has become an important issue in solving environmental pollution. In this study, 15%, 30%, 50%, and 70% iron tailings were used to replace the natural sand in concrete, and 1.5% steel fiber and 0-0.75% PVA fibers were added to the iron tailings concrete. The effects of the iron tailings replacement rate and the fiber content on the mechanical properties, carbonization depth, and concrete porosity were studied in a carbonization environment. The results demonstrated that the compressive and splitting tensile strengths of concrete first increased and subsequently decreased with an increase in the iron tailings replacement rate, while the carbonation depth and porosity initially decreased and subsequently increased. When the replacement rate of iron tailings was 30%, the compressive strength and split tensile strength were increased by 7.6% and 17.7%, respectively, and the porosity was reduced by 8.9%. The compressive strength, carbonation depth and porosity of single-doped steel-fiber concrete were superior to those of ordinary iron tailings concrete. However, compared with single-doped steel fiber, the performance of steel-PVA fiber was further improved. Based on the mechanical properties, the carbonation depth test results of the three aforementioned types of concrete, the mathematical expression of the uniaxial compression stress-strain curve of iron tailings concrete, and the prediction equation of the carbonation depth of mixed-fiber iron tailings concrete were proposed. This study provides a reference for the application and popularization of fiber-reinforced iron tailings concrete in carbonization environments.

Full uniaxial compressive stress–strain curve of high-performance concrete with ASR inhibition measures exposed to lye solution at 38 °C for 10 years

This study focuses on the long-term stress–strain relationship of high-performance concrete (HPC) containing alkali active aggregate using Alkali-Silicate reaction (ASR) inhibition measures. The experimental study is carried out on specimens under the action of standard alkaline solution (1 mol/L) at 38 °C for 10 years. HPC with strength class C40 to C60 in the range of 0.5 % to 1.9 % equivalent alkali content using alkali-activated aggregates and large dose mineral admixture suppression measures were used in the test. The basic mechanical properties and the full uniaxial compressive stress–strain curve were measured, and the correlation between the stress–strain curve and the equivalent alkali content of long-aged HPC with potential ASR hazard was discussed. The results show that HPC has certain ASR swelling characteristics when soaked in standard alkaline solution at 38 °C for 10 years. A mathematical model of the HPC uniaxial compressive stress–strain constitutive relation considering ASR damage is established.

Experimental Study on Strength Weakening of Gypsum Rock with Effect of Long-Term Overlying Strata Pressure

A long time lag is the main characteristic of gypsum mined gob collapse disasters. With the coring of a gypsum rock specimen from the supporting pillars in gob, which formed over several years, the strength weakening effect of the gypsum rock with long-term overlying strata pressure is revealed by experimentation. The results show that: uniaxial compression stress–strain curves represent major differences in different lateral depths of the same supporting pillar. With the increase in lateral depth, peak strength increases and the corresponding strain decreases, which becomes more obvious as the age increases. As a function of time, peak strength decreases and the corresponding strain increases in the shallow part of the pillar as the age increases. Peak strength fluctuates in the middle part and increases in the deep part; the corresponding strain fluctuates in the middle and deep parts, but demonstrates the opposite changing law. Finally, the reason for the above law was comprehensively and thoroughly researched and demonstrated. The maximum strength weakening rate of gypsum rock in the shallow part of a supporting pillar of 0.5 m depth was 21.06% in the year 1996. The slow strength weakening effect of gypsum rock with long-term overlying strata pressure is the essential reason why gypsum mined gob collapses occur in subsequent years or even decades.

Mechanical Properties and Uniaxial Failure Behavior of Concrete with Different Solid Waste Coarse Aggregates.

To reveal the differences between the mechanical properties of solid waste coarse aggregate concrete and natural coarse aggregate concrete (NCAC) under equal strength, the basic mechanical properties of coarse aggregate concrete with seven different solid wastes (i.e., self-combusted coal gangue, uncombusted coal gangue, marble sheet waste, granite sheet waste, iron waste rock, recycled concrete, and self-combusted coal gangue ceramicite) were tested, and the trends in failure morphology, elastic modulus, and the stress–strain full curves of the different solid waste coarse aggregate concretes were analyzed and compared with NCAC. Finally, the interfacial structure of the concrete was characterized by SEM. The results showed that C30 strength grade concrete was prepared with different solid waste coarse aggregates; however, the 28 d compressive strength, split tensile strength, axial compression strength, flexural strength, and elastic modulus of the concrete was 35.26–47.35, 2.13–3.35, 26.43–42.70, 2.83–3.94, and 17.3–31.2, respectively. The modulus of elasticity of the solid waste coarse aggregate concrete was smaller than the NCAC under equal strength, with a maximum difference of 45%. The peak compressive strain and ultimate compressive strain were larger than the NCAC, with a maximum difference of 43%. The crushing value of the solid waste coarse aggregate affected the splitting tensile strength, flexural strength, and modulus of elasticity of the concrete to a greater extent than the compressive strength. The transition zone at the concrete interface of the coarse aggregates with different solid wastes varied widely. The porous micro-pumping effect of the self-combusted gangue and self-combusted gangue vitrified reinforced the concrete interface transition zone, and the polished surface of sheet waste, uncombusted gangue, and recycled concrete aggregate surface adhesion weakened the interface transition zone; Finally, the uniaxial compressive stress–strain curve model for concrete with different solid waste coarse aggregates was established based on the Guo Zhenhai model.

Uniaxial Compressive Stress-Strain Relation of Recycled Coarse Aggregate Concrete with Different Carbonation Depths.

Highlights Uniaxial compressive stress–strain curves of recycled aggregate concrete (RAC) with different carbonation depth were investigated.The effect of carbonation depth on peak stress, strain, elastic modulus, and the relative toughness of RAC was studied.Stress–strain models of recycled aggregate concrete with different carbonation depths were established. The stress–strain relation of recycled aggregate concrete (RAC) after carbonation is very important to the assessment of the durability of RAC. The objective of this study is to investigate the uniaxial compressive stress–strain curves of RAC after carbonation. In this study, the specimens were prepared with 70-mm diameter and 140-mm height cylinders, and the carbonation of the specimens was accelerated after curing 28 days. Then a uniaxial compressive loading test on the specimens was performed by using a mechanical testing machine. The results show that the peak stress () and elastic modulus () of all specimens increase with the increase of carbonation depth. The ratio of ultimate strain to peak strain () and relative toughness of the specimens decrease with the increase of carbonation depth. Furthermore, carbonation has a stronger effect on natural coarse aggregate concrete (NAC) than the 50% replacement rate of RAC with similar compressive strength. Stress–strain models of recycled aggregate concrete with different carbonation depths were established according to experimental results.

Prediction of Concrete Meso-Model Stress-Strain Curve Based on GoogLeNet

Generally, the macro-scopic mechanical properties of heterogeneous composites depend on meso-components’ distribution and mechanical properties, but it is extremely difficult to establish a clear macro-meso relationship expression. To cope with this challenge, for concrete, a strategy based on deep learning was proposed to obtain the stress-strain curves through meso-model image information. First, the GoogLeNet model based on convolutional neural networks was used for image information recognition and extraction. According to the complexity of the stress-strain curve, data preprocessing operations were performed and the corresponding multi-task loss function was designed. The meso-model images in the data set were generated with the random aggregate model based on the Monte Carlo method, and numerical simulation experiments were conducted to obtain the uniaxial compressive stress-strain curve of the corresponding meso-model. Finally, the feasibility of the proposed method was evaluated through training and testing. The training efficiency and prediction accuracy of the GoogLeNet model are better than the AlexNet and ResNet models, and have good generalization ability and robustness.

Experimental Study on Mechanical Properties of Steel-Polyvinyl Alcohol Fibre-Reinforced Recycled Concrete

Research on the utilization of recycled concrete in civil engineering applications is gaining popularity world-wide due to the increased efforts to promote preservation of the environment and sustainable development. Recycled concrete is, however, presently still limited to nonstructural applications. This is due to the poor mechanical properties of recycled concrete, which make it difficult to cope with complex mechanical environments. Therefore, an experimental work is presented to investigate the mechanical behaviour of recycled concrete, focusing on the cube, flexural, and uniaxial compressive mechanical properties of steel-polyvinyl alcohol fibre-doped specimens. The test results showed that the compressive strength and the flexural strength of the recycled concrete increased by 6.0% and 55.2%, respectively, when steel fibre was single-incorporated. The cubic compressive strength of the recycled concrete decreased by 14.1% when polyvinyl alcohol fibre was single-incorporated, but there was a 47.9% increase in the flexural strength of recycled concrete. Based on these tests, the elastic modulus, the Poisson’s ratio, and the uniaxial compression toughness were digitised to derive mathematical expressions that provided a theoretical understanding of the mechanical properties of steel-polyvinyl alcohol fibre-reinforced recycled concrete. Moreover, combining the characteristics of the uniaxial compressive stress–strain curve of fibre-reinforced recycled concrete, an equation for the uniaxial compressive stress–strain curve of recycled concrete associated with the fibre characteristic value was established, which agreed well with the test results.

Acoustic Emission Features of Anthracite under the Influence of Loading Rate

Loading rate is an important impactor of the mechanical properties, as well as the deformation and failure mode of coal and rock. Using an RMT-301 rock mechanics tester and a Soft Island acoustic emitter, uniaxial compression and acoustic emission (AE) tests were carried out on coal samples under different loading rates. The results show that uniaxial compressive stress-strain curves of the rock samples each consist of four segments: compaction, elasticity, yield, and failure. As the loading rate increased from 0.01mm/s to 0.02mm/s, the peak strength rose, the post-peak deformability dropped, the brittle failure features of anthracite became more obvious, more AE events took place, and AE frequency increased. Energy analysis shows that, the faster the loading rate, the larger the AE count, the faster the energy accumulation, but the fewer the total energy accumulation.