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In this study, micro-grooves were fabricated on a chemical vapour deposition (CVD) diamond coating using spray-mist-assisted laser machining. In this paper, the advantages and characteristics of spray-mist-assisted laser machining are analysed through comparison with other forms of laser machining based on morphology and composition. Meanwhile, the effects of process parameters (laser power, scanning speed, defocusing quantity, air pressure, spray angle, and offset distance) on the machining characteristics were investigated using the Taguchi method, and the optimal parameter range of spray-mist-assisted laser-machined CVD diamond coating was obtained. The results indicate that spray-mist-assisted laser machining can effectively remove the recast layer and ensure the precision and continuity of laser machining. The most significant factor affecting the cross-sectional area of the grooves is laser power, while laser power and scanning speed significantly affect depth-to-width (D/W) ratio of grooves. The spray parameters had no significant effect on the characteristics of ablative grooves because the thickness of the water film formed by spray-wall impingement was relatively thin and stabilised.

In this research, a strategy to design structured grinding wheels to machine designed structured surfaces in micro-scale through the grinding process is investigated. Firstly, the geometry of the microstructured surface is defined. A mathematical model to describe the geometry of the structured grinding wheel and the grinding parameters is presented according to the geometry of the designed microstructures on the workpiece surface. And then, several operating conditions for the grinding operation are mathematically determined and kinematically simulated using a proper programming language to produce the designed geometry of the microstructured surface. The errors in the simulated geometries of the machined microstructures are calculated and analyzed. Finally, the reasons for deviation and ability to minimize error sources are investigated.

Solid solution powders of Ti-22Al-25Nb (at.%) were successfully prepared with Ti, Al, and Nb elemental powders via mechanical alloying (MA). The effects of milling time, stearic acid process control agent and Al2O3 reinforced particles on the morphology evolution, average particle size, crystallite size, solid solution and phase of mixed powders were studied. The solid solution mechanism and strengthening mechanism of Ti, Al and Nb mixed powders during MA were revealed. In addition, the strengthening effect of Al2O3 reinforced particles was clarified. The mixed powders at different milling times were characterized by X-ray diffraction and scanning electron microscopy. The microhardness of the solid solution powders was investigated, and the solid solubility of Al and Nb atoms in the Ti matrix was quantitatively calculated. The results revealed that the crystallite size of mixed powders without the addition of Al2O3 reinforced particles decreased with the increase of MA time, and was 18 nm after MA for 60 h. The solid solubility values of Al and Nb in the Ti matrix were 22.68 at.% and 9.49 at.%, respectively. The addition of Al2O3 reinforced particles could effectively refine the mixed powder particles, but had no obvious effect on the evolution of particle morphology; the values of load-bearing effects ( Δ σ Load ) and orowan strengthening ( Δ σ Orowan ) were determined to be 27.5 MPa and 88.4 MPa, respectively. The microhardness values of the Ti-22Al-25Nb solid solution powders and Ti2AlNb-5 wt% Al2O3 nanocomposite powders were 435 HV and 465.8 HV, respectively. Compared to Al2O3 reinforced particles, stearic acid process control agent could significantly inhibit the welding between Ti, Al and Nb powders, making the powders more prone to disperse and break into small flakes with a smaller average particle size of 10 µm at 60 h. With the addition of stearic acid, the mechanical alloying process of Ti, Al and Nb element powders was inhibited, and the solid solubility of Al in the Ti matrix and the microhardness of the mixed powders after MA for 60 h were reduced to 16.31 at.% and 330 HV, respectively.

A stimulation technology of multi-stage fractured horizontal well is commonly used for enhancing the productivity in the development of low-permeable oil reservoirs. However, it is well known that the fluid flow in low-permeable oil reservoirs doesn't obey conventional Darcy's law, and the threshold pressure gradient exists; as a result, in fact, the model of multi-stage fractured horizontal well in low-permeable oil reservoirs belongs to a nonlinear moving boundary problem. And realization of the numerical simulation for the model is very complicated and difficult. It is significant to figure out the threshold pressure gradient effect on the numerical simulation results for the solution of actual engineering problems. In view of the concerns, based on the subsurface Darcy's flow module in COMSOL Multiphysics, an effective numerical simulation method is presented here: The non-Darcy kinematic equation at the full pressure gradient range is expressed at the interface of the gravitational acceleration vector in Darcy's law. Furthermore, the simulation method is strictly verified through the comparison with two analytical solutions for a one-dimensional case and a two-dimensional case (radial flow) respectively. Consequently, according to a constructed model, which can cover non-Darcy flow in the unstimulated reservoir area with threshold pressure gradient, Darcy's flow in the stimulated reservoir area and Darcy's flow in the main hydraulic fractures, the two-dimensional numerical simulation of the multi-stage fractured horizontal well in the low-permeable oil reservoir is realized just through the subsurface Darcy's flow module. Finally, through analyses and discussions on the numerical results for several designed simulation scenarios, some significant conclusions are obtained such as due to the threshold pressure gradient effect, there exists large undeveloped areas in low-permeable oil reservoirs, which don't change with the production time for the constant well production pressure condition; SRV fracturing can largely improve the utilization degree of the low-permeable reservoir area between the adjacent main hydraulic fractures at the early production period; it is very necessary to incorporate the threshold pressure gradient effect in the simulation for the optimal well spacing design in the development of low-permeable oil reservoirs.

Many engineering technologies involve the moving boundary problems for the radial seepage flow with a threshold pressure gradient, such as the well testing in the development of low-permeability reservoirs, heavy oil reservoirs and groundwater resources. However, as a result of the strong nonlinearity, an exact analytical solution of the moving boundary problems for the radial seepage flow with a threshold pressure gradient has not been obtained yet. Here, a dimensionless moving boundary mathematical model for the radial fluid flow in an infinite low-permeability reservoir with a threshold pressure gradient is developed first. The setting of a variable well production rate for an inner boundary condition can make the mathematical model exhibit a full self-similarity property. Second, by introducing some similarity transformations, the nonlinear system of PDEs of the model can be equivalently transformed into a closed pseudo-linear system of ODEs, whose exact analytical solution can be easily obtained. What's more, the existence and the uniqueness of the exact analytical solution to the moving boundary model are also proved strictly through the mathematical analysis. Third, it is also strictly proved that the exact analytical solution can be degenerated to that of the model of the Darcy's radial fluid flow as the threshold pressure gradient approaches to zero. Finally, by a comparison of model analytical solutions, it is demonstrated that the moving boundary conditions must be incorporated in the modeling of the radial seepage flow with a threshold pressure gradient; otherwise, the effect of the threshold pressure gradient on the radial seepage flow can be overestimated largely.

GNSS based Bistatic Forward Looking Synthetic Aperture Radar (GNSS-BFLSAR) system is particular kind of passive bistatic SAR system. In the system, GNSS is used as the transmitter, while the receiver is mounted on the airplane. The airplane travels along a straight line and the imaging target is in the front. GNSS-BFLSAR is benefited from low cost and good safety. It is widely used in self-landing, self-navigating and battle field information acquiring, etc. This paper is focusing on the investigation of point target 2-D spectrum of GNSS-BFLSAR and Point Spread Function (PSF) generation method. First, a geometric model of such system is built, followed by the generation of echo signal. Then, the analytical formula of 2-D spectrum is obtained. Next, the PSF generation is provided. In the end, the whole procedure is simulated with Matlab. The simulation result verifies the validity of theoretical analysis of this paper and makes a foundation for imaging formation research of such system in the future.

A powder metallurgy (P/M) Ti-22Al-25Nb (at%) alloy was prepared by spark plasma sintering of pre-alloyed powders at 1000 °C/80 MPa/10 min. The solution treatments of the P/M Ti-22Al-25Nb alloy were conducted at a temperature range of 940–1030 °C at 30 °C intervals and holding times of 10 min, 30 min, 60 min, and 120 min. The effects of the solution temperature and the holding time on the microstructure evolution, B2 grain growth behavior, phase transition, tensile mechanical properties, and fracture behavior of the P/M Ti-22Al-25Nb alloy were systematically evaluated using optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction, and tensile tests. The results indicated that the microstructure and mechanical properties were closely linked to the solution temperature and the holding time. The effect of the holding time and the solution temperature on the B2 grain growth is well described by Beck's equation and Hillert's equation, respectively. The tensile tests showed that the tensile properties of the solution-treated P/M Ti-22Al-25Nb alloy were mainly affected by the number of O phases in the interior of the B2 grains and the phase transition degree of the α2 phase at the grain boundary. The P/M Ti-22Al-25Nb alloy solution-treated at 940 °C/10 min exhibited the best mechanical properties at room temperature with a yield strength, tensile strength, and elongation of 867.8 MPa, 949.5 MPa, and 7.4%, respectively. A phase transition model of the α2 phase was established. In addition, a tensile fracture model of the P/M Ti-22Al-25Nb alloy solution-treated under different conditions was established.

Grain growth behavior of a powder metallurgy (P/M) Ti-22Al-25Nb alloy was investigated by applying a series of isothermal treatment tests over a wide range of temperatures and holding times. An isothermal treatment scheme was conducted in the B2 phase region (1070-1110 °C) and α2 + B2 phase region (1010-1050 °C) at holding times of 10, 30 min, 1, 2, and 3 h, respectively. The effects of temperature and holding time on the microstructure evolution and microhardness of the P/M Ti-22Al-25Nb alloy at elevated temperatures were evaluated using optical microscope, scanning electron microscope, x-ray diffraction, and Vickers hardness test techniques. The results revealed that the alloy’s treated microstructure was closely linked to temperature and holding time, respectively. The change law of B2 grain growth with holding time and temperature can be well interpreted by the Beck equation and Hillert equation, respectively. The B2 grain growth exponent n and activation energy Q were acquired based on experimental data in the α2 + B2 and B2 phase regions. In addition, the grain growth contour map for the P/M Ti-22Al-25Nb alloy was constructed to depict variations in B2 grain size based on holding time and temperature.

In the present study, repetitive upsetting-extrusion (RUE) process was employed to induce severe plastic deformation (SPD) for an AZ91D magnesium alloy at temperatures ranging from 285 °C to 380 °C. Finite element method (FEM) and technical experiment were performed to reveal the non-uniform behavior during the RUE process. The results from the finite element analysis showed that effective strain was unevenly distributed in one-cycle strained sample and the non-uniformity would exist permanently with increasing deformation cycles. The microstructure evolution of the RUE processed alloys was characterized by optical microscopy, which clarified the microstructural development from heterogeneous and coarse as-cast structure, heterogeneous and refined structure to final homogeneous and fine-grained structure of the 340 °C and eight-cycle processed sample. In addition, a critical strain was suggested from the metallographic observation results. It was proposed that α -Mg grain structure was sufficiently refined by imposing accumulated strain beyond the critical value and the invariability of grain sizes was illustrated. A homogeneous structure with mean grain size of ∼3.04 μm was obtained after 285 °C and three-cycle RUE process, corresponding to an accumulated true strain of about 3.75. Furthermore, the fragmentation and dispersed distribution of the β -Mg 17 Al 12 phase induced by shearing was confirmed by referring to scanning electron microscope (SEM) examination. Moreover, refining mechanisms responsible for grain structure were discussed in detail with reference to the transmission electron microscope (TEM) analysis results.

Mesophase carbon microbeads (MCMBs) were synthesized by thermal polycondensation with fluidized catalytic cracking residue oil (FRO) as the feedstock. The evolution features of functional groups of the residual oils and the residual solid products from thermal polymerization were analyzed, and the effect of olefinic compounds on the coalescence between mesophase spheres was investigated in depth. The results showed that the olefin contents of residual oil, heptane-soluble, and heptane-insoluble/toluene-soluble decreased simultaneously as the reaction proceeded while that of toluene-insoluble increased, indicating that the olefins in the solvent phase could not only provide molecule sources for the development of carbonaceous mesophase but also directly assemble into the insoluble mesogens. More importantly, the involvement of olefins caused a sharp increase of the system viscosity, making it difficult for the mesophase spheres to completely coalesce into regular large ones after cohering, leading to the apparent deformation. In contrast, catalytic hydrotreatment can saturate olefinic species and enhance the hydrogen transfer ability of FRO to further avoid the induction effect of olefins, slow down the mesophase development, reduce the system viscosity, and consequently avoid the deformation of mesophase spheres.

LiNi0.8Co0.1Mn0.1O2 (NCM811) often suffers from the poor cycle stability as the cathode material for the lithium-ion battery (LIB), while Al2O3 or MgO coating is the most common method to resolve such problem. However, the reported techniques often produced Al2O3 or MgO particles with the large size or zero dimensional (0 D) spheres, which resulted in ununiform or thick layer coating on the surface of NCM811. Herein, Mg-Al layered double oxide (Mg-Al-LDO) nanosheets derived from Mg-Al layered double hydroxide (Mg-Al-LDH) were firstly studied as a potential coating material because of their two dimensions (2D) and few-layer structures (less than 10 nm). The Mg-Al-LDO nanosheets were coated on NCM811 microspheres via the intercalation-exfoliation-calcination strategy. The Mg-Al-LDO nanosheets modified NCM811 samples exhibited enhanced cycle performances. The capacity retention improvements of this work (11–18%) were higher than those of the reports (0.7–15.6%). Typical sample showed the capacity retention of 95.5% after 50 cycles, and it increased by 18% compared with that of pristine NCM811 after 100 cycles within 2.75–4.3 V at 0.5 C rate. This improved cycle performance can be attributed to the unique thin and continuous Mg-Al-LDO nanosheets coated on NCM811, which not only inhibits HF corrosion and the residual alkali salt formation, but also reduces Ni2+/Li+ cation mixing. This method provides a new strategy for the surface modification of nickel-rich layered cathode materials.

Saline water is an alternative resource that could be used to meet agriculture irrigation demands. Fouling, particularly that caused by calcium carbonate (CaCO3), often occurs in saline irrigation water distribution systems, and severely restricts the utilization of saline irrigation water. So far, water acidification is the common practice for avoiding CaCO3 fouling. However, this approach is often ineffective and regularly contributes to environmental pollution. This study investigated an effective practice to overcome CaCO3 fouling issues by regulating shear stress, temperature and ions in saline irrigation water irrigation systems. The effects of different near-wall shear stress at 0.05, 0.20, 0.40 and 0.60 Pa, coupling with temperature of 10, 20 30 and 40 oC and cations Mg2+ and Fe3+ were analyzed. Results demonstrated that the CaCO3 fouling rate was linearly increased at initial shear stress, while decreased at higher shear stress, and the highest fouling rate was observed at 0.40 Pa, ranging between 21.4%−80.3%. The coupling of temperature and cations with shear stress significantly (p 1) among different shear stress get larger with increasing temperature, while they decreased and increased with the addition of Mg2+ and Fe3+, respectively, when compared with pure solution of CaCO3. Refinement analysis showed the largest unit-cell volume and lattice parameter of calcite at shear stress of 0.40 Pa, resulting in a significant effect on distribution of fouling particle sizes and morphologies. Moreover, some anti-fouling measures were further proposed based on the formation behavior of CaCO3 fouling. These findings might provide a new perspective to control CaCO3 with potential implications for sustainable saline water management for irrigation.

In the present study, semi-solid billets of AZ91D magnesium alloy were prepared by employing the repetitive upsetting-extrusion (RUE) based strain induced melt activation (SIMA) process. Thixoforming experiments were performed using semi-solid alloys experiencing various RUE temperatures and semi-solid reheating temperatures. The microstructure characterization and microhardness of the thixoformed products were investigated. Microstructure examination results indicated that semi-solid globular microstructure ensuring good thixotropic filling performance was prepared by applying the RUE-based SIMA method. Thixoformed components with good surface quality were obtained. Compared with the original as-cast alloy, significant grain refinement and microhardness improvement occurred in the thixoformed components. And the mean grain sizes and microhardness values were measured to be in the ranges of 11.81–23.84 μm and Hv80.67–Hv90.65, respectively. By means of further comparison of microstructure and microhardness, the grain coarsening and microhardness reduction of the thixoformed components were verified by elevating the RUE deformation temperature and semi-solid remelting temperature. Furthermore, strengthening mechanisms during thixoforming involving the application of the RUE-based SIMA route were discussed in detail. The results showed that the comprehensive effect of fine grain strengthening, dispersion strengthening, and solid solubility strengthening should be responsible for microhardness improvement.

In this paper, numerical simulations of fractured vertical well in low-permeable oil reservoir are carried out and two issues: threshold pressure gradient (TPG) in reservoir matrix and proppant distribution in hydraulic fractures are focused on. A physical definition of effective fracture length (EFL) is presented to evaluate the fracture effectiveness due to uneven proppant distribution. In terms of numerical processing for TPG, based on the subsurface Darcy's flow module in COMSOL Multiphysics, an effective numerical simulation method is adopted by substituting the gravitational acceleration vector in Darcy's law (Liu et al., 2019b). The simulation results show that, proppant distribution has great influence on fracture effectiveness. Unappealing proppant distribution can reduce effective fracture length by 49.6%, which is negative for low-permeable oil reservoir development. TPG in reservoir matrix mainly affects the moving boundary and pressure-disturbed area in reservoir. When TPG in matrix reduces from 0.02 MPa/m to 0 MPa/m, the distance of moving boundary at 300 days could increase for almost double and pressure-disturbed area enlarged drastically for around 74%. Furthermore, a heterogenous low-permeable oil with secondary fracture networks is designed to study the joint effect of TPG and proppant distribution. If we neglect these two factors, cumulative oil rate will be greatly overestimated by 38.6% at 1000 days. At the same time, the existence of natural fractures could also affect the streamline distribution in low-permeable oil reservoir and contribute to fluid flow in reservoir.

The transport and deposition of particulate materials through fractures is widely involved in environmental engineering and resource development engineering. A 3D Computational Fluid Dynamics-Discrete Element Method (CFD-DEM) coupling method was used to investigate the particle and fluid flow. The Gauss Model was applied to construct the rough surfaces. First, the numerical results were compared with the previous results and reasonable agreements were obtained. Second, the results indicated a novel flow pattern of particles in rough fractures. Then, a comprehensive particle sedimentary analysis indicated that the deposition distance of particles was inversely proportional to the particle size and density ratio. In addition, the particle deposition rates were increased by the mean roughness and there was an uneven sediment distribution impacted by roughness. Reasons for this uneven sediment distribution were analyzed in detail. Moreover, the bridge plugs of particles considering the closure of fractures were simulated as well. A part of particulate materials would be filtered at the inlet due to size effect and the transport distance of entered particles decreased significantly when the particle was large. A critical particle radius (R

In the paper, the study on the exact analytical solution of the moving boundary problem of one-dimensional Bingham fluid seepage flow is extended from the infinite long porous media (Liu et al., 2012) to the finite long porous media. Two exact analytical solutions are presented by appropriately relying on some methods of mathematical physics and mathematical techniques. One is for the model with finite closed outer boundary condition; the other is for the model with finite constant pressure outer boundary condition. The existence and the uniqueness of the exact analytical solutions are also strictly proved theoretically. In addition, the numerical solutions of the two models by the finite difference method are also provided. Through the comparison, it is found that these exact analytical solutions have very excellent agreement with the numerical solutions although few terms of the infinite function series existent in the exact analytical solutions have to be retained for the calculation. Furthermore, for the two models, the effect of the threshold pressure gradient on the transient pressure and the transient pressure derivative at the inner boundary for the whole flow process is analyzed through the analytical solutions. Finally, through the comparison of the relevant model solutions, it is concluded that it is very necessary to incorporate the process of moving boundary for the modeling of non-Darcy Bingham fluid flow in finite long porous media with threshold pressure gradient; otherwise, large errors can be introduced in predicting the transient pressure and the transient pressure derivative in the porous media. The presented work can support solid theoretical foundations for the experiment design of measuring the threshold pressure gradient and the pressure transient analysis in the field of inverse problems in the petroleum engineering, which have been widely involved in the development of low-permeable oil reservoirs and heavy oil reservoirs.

Recycle Aggregate Concrete (RAC) is a common “green” product used for a variety of purposes, although the durability and strength of the material still need more research to adequately determine influences on these parameters. The failure pattern, punching bearing capacity, and deflection variation of wallboard of both ordinary concrete and RAC with various rebar reinforcement diameters and spacing were analyzed. Based on experimental data, the ABAQUS finite element analysis of the thin wallboard was performed, and the calculated results are in good agreement with the experimental results. The results show that the failure characteristics of ordinary concrete wallboards and RAC wallboards are similar, but the brittleness of the RAC specimens is more significant. Under the same reinforcement ratio, concrete material, whether new or recycled, had little effect on the punching bearing capacity of the specimens. In the case of a low reinforcement ratio, increasing the reinforcement ratio (decreasing the spacing of steel bars) can effectively improve the bearing capacity of the wallboard. Under the same reinforcement ratio, the wallboard with larger diameter and larger spacing has a higher bearing capacity and less deformation after failure.

In this study, the cyclic behaviors of low rise concrete shear walls using recycled coarse or fine aggregates were investigated. Eight low rise Recycled Aggregates Concrete (RAC) shear wall specimens were designed and tested under a cyclic loading. The following parameters were varied: replacement percentages of recycled coarse or fine aggregates, reinforcement ratio, axial force ratio and X-shaped rebars brace. The failure characteristics, hysteretic behavior, strength and deformation capacity, strain characteristics and stiffness were studied. Test results showed that the using of the Recycled Coarse Aggregates (RCA) and its replacement ratio had almost no influence on the mechanical behavior of the shear wall; however, the using of Recycled Fine Aggregates (RFA) had a certain influence on the ductility of the shear wall. When the reinforcement ratio increased, the strength and ductility also increased. By increasing the axial force ratio, the strength increased but the ductility decreased significantly. The encased brace had a significant effect on enhancing the RAC shear walls. The experimental maximum strengths were evaluated with existing design codes, it was indicated that the strength evaluation of the low rise RAC shear walls can follow the existing design codes of the conventional concrete shear walls.

In order to quantitatively evaluate the shear-bearing capacity of shear connectors of square concrete filled steel tube (CFST), push-out tests on 14 square CFSTs with shear connectors have been carried out. Among the 14 CFSTs, there are 13 specimens with steel plate connectors and one specimen with steel bar connectors. The following factors are investigated to figure out their influences on the performance of CFSTs, which are the width to thickness ratio of steel tube, thickness of steel plate, length of steel plate, strength of concrete, welding condition of steel plate, number of steel plate layer and interlayer spacing. The test results show that the ultimate bearing capacity and the elastic stiffness increase with decreasing width to thickness ratio of the steel tube, and increasing thickness and length of the steel plate. With increasing concrete strength, the ultimate bearing capacity also increases. However, the welding condition has no effect on the ultimate bearing capacity. The ultimate bearing capacity of the CFST with double-layer steel plate is greater than that with single-layer steel plate. The ultimate bearing capacity of steel bar type shear connector is 87% greater than that of the steel plate type shear connector, and the steel bar specimen shows good ductility. A formula for calculating the shear-bearing capacity of shear connectors has been developed, and the calculated shear-bearing capacities are in good agreement with the test data.

This paper summarizes an engineering experience of solving the problem of thermal cracking in mass concrete by using a large project, Zhongguancun No.1 (Beijing, China), as an example. A new method is presented for controlling temperature cracks in the mass concrete of a foundation. The method involves controlled cycles of water circulating between the surface of mass concrete foundation and the atmospheric environment. The temperature gradient between the surface and the core of the mass concrete is controlled at a relatively stable state. Water collected from the well-points used for dewatering and from rainfall is used as the source for circulating water. Mass concrete of a foundation slab is experimentally investigated through field temperature monitoring. Numerical analyses are performed by developing a finite element model of the foundation with and without water circulation. The calculation parameters are proposed based on the experiment, and finite element analysis software MIDAS/CIVIL is used to calculate the 3D temperature field of the mass concrete during the entire process of heat of hydration. The numerical results are in good agreement with the measured results. The proposed method provides an alternative practical basis for preventing thermal cracks in mass concrete.

The seismic performance of recycled aggregate concrete (RAC) composite shear walls with different expandable polystyrene (EPS) configurations was investigated. Six concrete shear walls were designed and tested under cyclic loading to evaluate the effect of fine RAC in designing earthquake-resistant structures. Three of the six specimens were used to construct mid-rise walls with a shear-span ratio of 1.5, and the other three specimens were used to construct low-rise walls with a shear-span ratio of 0.8. The mid-rise and low-rise shear walls consisted of an ordinary recycled concrete shear wall, a composite wall with fine aggregate concrete (FAC) protective layer (EPS modules as the external insulation layer), and a composite wall with sandwiched EPS modules as the insulation layer. Several parameters obtained from the experimental results were compared and analyzed, including the load-bearing capacity, stiffness, ductility, energy dissipation, and failure characteristics of the specimens. The calculation formula of load-bearing capacity was obtained by considering the effect of FAC on composite shear walls as the protective layer. The damage process of the specimen was simulated using the ABAQUS Software, and the results agreed quite well with those obtained from the experiments. The results show that the seismic resistance behavior of the EPS module composite for shear walls performed better than ordinary recycled concrete for shear walls. Shear walls with sandwiched EPS modules had a better seismic performance than those with EPS modules lying outside. Although the FAC protective layer slightly improved the seismic performance of the structure, it undoubtedly slowed down the speed of crack formation and the stiffness degradation of the walls.

Recycled aggregate concrete (RAC) is an environmentally friendly building material. This paper investigates the mechanical behavior of recycled aggregate concrete filled steel tube (RACFST) columns exposed to fire. Two groups of 12 columns were designed and tested, under axial compression, before and after fire, to evaluate the degradation of bearing capacity due to fire exposure. Six specimens were subjected to axial compression tests at room temperature and the other six specimens were subjected to axial compression tests after a fire exposure. The main parameters of the specimens include the wall thickness of the steel tube (steel content) and the type of concrete materials. Several parameters as obtained from the experimental results were compared and analyzed, including the load-bearing capacity, deformation capacity, and failure characteristics of the specimens. Meanwhile, rate of loss of bearing capacity of specimens exposed to fire were calculated based on the standards EC4 and CECS28:90. The results show that concrete material has a large influence on the rate of loss of bearing capacity in the case of a relatively lower steel ratio. While steel content has little effect on the rate of loss of bearing capacity of concrete-filled steel tube (CFST) columns after fire, it has a relatively large influence on the loss rate of bearing capacity of the RACFST columns. The loss of bearing capacity of the specimens from the experiment is more serious than that from the calculation. As the calculated values are less conservative, particular attention should be given to the application of recycled aggregate concrete in actual structures.