This paper utilizes the advanced potential of pseudodynamic three-dimensional finite-element modeling to study the axial mechanical behavior of square and rectangular reinforced concrete columns, confined with fiber reinforced polymer (FRP) jackets and continuous composite ropes in seismic applications. The rigorous and versatile Riedel-Hiermaier-Thoma (RHT) material model for concrete is suitably calibrated/modified to reproduce the variable behavior of characteristic retrofitted columns with deficient internal steel reinforcement detailing, suffering nonuniform local concrete cracking and crushing or bulging and bar buckling. Similarly, the 3D FRP jacket or rope confinement models may account for damage distribution, local fracture initiation and different interfacial bonding conditions. The satisfactory accuracy of the reproduced experimental stress-strain envelope behavior enables the analytical investigation of several critical design parameters that are difficult to measure reliably during experiments. Additional parametric analyses are conducted to assess the effects of steel quality. The significant variation of the field of developed strains on the FRP jacket at the ultimate and of the developed strains and deformations on steel cages among different columns are thoroughly investigated. This advanced analytical insight may be directly utilized to address missing critical parameters and allow for more reliable FRP retrofit design of seismic resistant reinforced concrete (RC) columns. Further, it allows for arbitrary 3D seismic analysis of columns  or addresses predamages. Advanced fiber reinforced polymer (FRP) materials made of carbon, glass or aramid fibers, and structural fiber ropes, are widely used in several structural retrofit applications worldwide or as an internal reinforcement ,16,17,18All these experimental investigations have led to the proposal of a large amount of semi empirical models trying to predict with accuracy the ultimate stress and strain behavior of concrete columns when subjected to monotonic axial loading ,56,57,58Yu et al.  made a cThe extensive investigation of the recent experimental and analytical databases by Fanaradelli et al. ,71 suggeThe approach followed herein is the utilization of several characteristic existing experimental efforts of columns under axial concentric loading-unloading-reloading cycles of increasing compressive displacement cc) and the corresponding axial strain (εcc) and the ultimate axial stress (fcu) and strain (εcu) of confined concrete at the failure of the column. These characteristic values are depicted in cu = fcc. For columns with descending second branches, based on the loading control (and loading rate) followed during the tests, very low axial stress values may be recorded at failure. However, based on the existing design recommendations [cc . Therefore, the failure (ultimate) stress may be fcu = 0.85 × fcc if there is a gradual load drop  or higher than 0.85 × fcc and lower than fcc if there is an abrupt FRP fracture. Based on this approach the corresponding εcc and εcu are defined at the same points, see also [The final database by Fanaradelli and Rousakis  gathers ndations ,73, the see also ,53,58,63cu for all the columns of the corresponding database presents AAE higher than 50%. This paper suggests that the gathered characteristics and experimental results are not adequate in order to accurately predict the strain at failure. Therefore, 3-dimensional FE models of characteristic columns were developed and analyzed pseudodynamically, aiming at addressing unidentified design parameters through thorough assessment of the analytical results at regions that the corresponding experimental results were not available or impossible to measure . RC squroach in , Ilki etroach in  and Isleroach in . All theThe rigorous and versatile 3-dimensional pseudodynamic finite-element modeling was used for the first time to study the axial mechanical behavior of square and rectangular RC columns, confined with FRP jackets and continuous composite ropes for seismic resistant applications. Advanced material models for concrete, composites and steel are suitably calibrated to conduct numerous analyses. ANSYS Explicit Dynamics  was usedThe Riedel-Hiermaier-Thoma (RHT) model ,77,78 waThis failure surface can be used to represent the following aspects of the response of geological materials: pressure hardening, strain hardening, strain rate hardening in tension and compression, third invariant dependence for compressive and tensile meridians, strain softening (shear induced damage) and coupling of damage due to porous collapse. It enables the reproduction of monotonic, repeated or cyclic imposed displacements  highly inelastic behaviors, damage redistribution effects and highly local degrading behavior. The RHT model was suitably calibrated through extensive and comprehensive investigations to eliminate the effect of the rate of axial loading and to provide satisfactory hardening or softening or crashing behavior of concrete under triaxial loading and the effects of predamaged concrete core and damage redistribution. In these pseudodynamic analyses, plastic deformation is computed by reference to the Von Mises yield criterion. Therefore, the local yield condition isp0 is the yield strength and A the tangent modulus.The onset of yielding (plastic flow) is purely a function of the deviatoric stresses (distortion). A bilinear isotropic hardening model was used to define the yield stress (Y) as a linear function of plastic strain, εThe model for structural reinforced polymer composites was suitably calibrated taking into consideration the common properties of epoxy resins used for fiber sheet impregnation and bonding on concrete. Therefore, the analyses may reproduce local damage initiation of the jacket  and thus consider the effects of the corner radius of the section. Full bonding of the jacket on concrete was considered in all cases . As the fibers in the FRP jackets, considered in the present study, were all oriented in the hoop direction, the stiffness (both tensile and compressive) in the axial direction  was negligibly small. Therefore, the elastic lamina option was used to model an orthotropic elastic material. A local coordinate system was assigned to the FRP jacket, and the hoop direction and the axial direction were adopted as the first principal and second principal material orientations, respectively.The modulus of elasticity in the axial direction and the shear modulus were both assumed to have lower values than the ones provided by the manufactures for the net fiber sheet, because they take into account the impregnation with the epoxy resin. For example, for the carbon fibers for specimen series BS1C/BS2C of FE analysis includes the following steps: (1) the geometric characteristics of the members of the model were determined, (2) the properties of the materials were defined, (3) the connections and contacts among members were assigned and (4) the type of discretization of the model and the density of discretization was determined depending on the number of seeds in each surface and the suitable meshing technique . Seeds are constant nodes, placed along the perimeter of the cross sections. They control the precise location of the meshing nodes. Thus, special care was taken for the seed distribution, in order to take into account, the curvature of the edges and crucial detailing of the specimens. The main target of meshing is the compatibility of the nodes between the concrete core and the FRP jacket in order to avoid convergence problems during analysis, (5) the mode of imposed displacement over time was defined to simulate pseudodynamic application. Monotonic axial displacement was forced at the top of the column, directly on the concrete core and not on the FRP jacket and (6) the boundary conditions of the model were determined. “Fixed Support” was chosen at the base of the column. The monotonic mode can provide the envelope analytical load-displacement curve and thus avoid the extremely time-consuming cyclic mode, as the experimental response between identical columns subjected to monotonic or cyclic loading was fairly close to each other.Two body interactions were created. All the elements adopted the “Frictionless” type. This type simulated friction conditions between all the elements. For the second “Body Interaction”, only the elements that made up the longitudinal and transverse reinforcement were selected and for the integration of the reinforcement within the concrete core. When an element consists of several parts, it is necessary to determine the connections between the elements. Based on numerous investigations with five available contact options, the interaction surface between the FRP and the concrete that is in contact was considered fully “bonded” for all specimens. All the nodes of bodies included in bonded interactions were tied to faces of involved bodies.Explicit mesh was followed to form accurate 3D grid. Six-node elements  and present satisfactory convergence with the experimental results up to the ultimate conditions of the column series BS1C, as shown in The performance of the FE analytical models for the columns with steel stirrups spaced at 95 mm (BS2C series) was similar, as presented in The performance of the FE models against the experimental behavior of RC columns of the square concrete section of very low concrete strength and with a different corner radius with steel reinforcements of intermediate quality are presented in The comparisons for the RC columns of rectangular section with steel reinforcements of lower quality and sparse stirrups are presented in Based on the advanced and reliable FE analyses, several aspects of the behavior of the retrofitted RC columns may be further investigated. The RHT model for concrete may provide quantification of the local damage initiation, extent and development within the concrete core through the index named after the damage coefficient  at different levels of imposed displacements. The FE analyses suggest that the first local damage for BS1C1C initiated at the concrete located at the middle-side regions of the specimen at its middle-height, between the two steel stirrups and the FRP jacket a at 0.00Similarly, specimen BS1C3C shows first local damage in the concrete at the center of the specimen, between the two steel stirrups and the FRP jacket e at the These analyses suggest that in experiments the effects of slender bars could be more pronounced (for the FRP jacket to reach its capacity) as the bars are in reality self-anchored inside the column and not fixed on the bottom and top boundaries as in the FE models. However, no unstable behavior of the bars under compression was recorded in the FE analyses up to the ultimate axial strain. It seems that there might be an interaction between the local damage of the concrete and the FRP fracture that needs further experimental and numerical investigation.The analytical elaboration for the specimens BS2C1C and BS2C3C with stirrups at 95 mm spacing (BS2C series) shows that the concrete failed locally and the FRP also reached its local failure. For BS2C1C, for axial strain of 0.009375, the concrete local failure started at the corner region of the mid-height stirrup a–c. At tThe FE results for BS2C3C were similar with the initiation of local failure within the concrete but without simultaneous local FRP failure. However, at the ultimate condition, the damage spread further within the concrete and FRP strain at the ultimate condition was again higher than its capacity a–c.Specimen BS2C5C behaved differently than the other two specimens of this series. Specimen BS2C5C had 5 layers of CFRP and the concrete did not exhibit local damage. It is observed that in the last step of the loading, there was severe damage at the corners of the middle stirrup, but the concrete did not fail locally e,f. The The ratio of strain at the corner of the middle stirrup to strain of the corner in-between the two stirrups in the BS2C1C specimen was close to 3, while in the other two specimens the same ratio was about 2. This is a consequence of the first development of concrete cracks at the corner, at the level of the middle stirrup as is shown in the corresponding figures. The ratio of the maximum strain at the corner, at the level of the middle stirrup to the minimum strain of the mid-side at the same level for all these specimens, was close to 1. It seems there was more uniform strain distribution along this axis for the three specimens. It seems that there was a more pronounced interaction between the local damage of the concrete and the FRP fracture at the corners that needs further experimental and numerical investigation.The FE analyses for specimen LSR-R-1-3-10b, with a very low corner radius of 10 mm, suggest that the first local damage initiates at the concrete located at the four corners of the specimen at the level of the stirrup and it is extended to more than the half height of it. The first local damage was shown for an axial strain of 0.045 a. It is The FE analytical behavior of column LSR-R-1-3-20b was similar. The concrete local failure initiated at the 0.033 axial strain and it was located at the same concrete area d. The coSpecimen LSR-R-1-3-40b shows similar damage development inside the concrete core f–h. Thercu < 0.85 × fcc < fcc) and the ultimate stress fcu was less than 15% of the maximum bearing stress. So, there was a revision of the ultimate value to the 0.85 × fcc and of the corresponding value for εcu compared to the experimental stress-strain curves of the test results. The analytical results were evaluated for the ultimate axial strain equal to 0.005.The FE analysis shows that local damage initiated at the concrete located at the area around the longitudinal steel bars at the level of the stirrup a,b in spSpecimen R2.0H2CL4 exhibited similar behavior to the previous column. The concrete area located around the longitudinal steel bars at the level of the stirrup was crucial a,b. The cc). The maximum tensile strains on the FRP were similarly low around 0.004–0.0064.It seems that in both cases, due to the high side ratio , the effectiveness of the confinement provided by the steel stirrups and the FRP jacket was too low to enhance the deformability and strength of the plain concrete or to restrict the unstable behavior of slender steel bars. Therefore, there was a degrading post-peak stress-strain behavior and the bearing stress was more or less stabilized at very low levels for structural applications (lower than (0.80–0.85) × fBS2C3C .BS2C3C_360 .BS2C3C_450 .The presented FE analyses did not deal with the effect of the quality of steel reinforcement on the effectiveness of the external FRP confinement. Additional FE analyses were performed for conventional longitudinal bars of 14 mm diameter with nominal yield strengths: 360 MPa, 450 MPa and 560 MPa. All different analyses were terminated for the same ultimate tensile strain of the FRP at the corner, at the level between two stirrups, as assessed for specimen BS2C3C (0.009179). For specimen BS2C3C_360, the ultimate stress from the FE analysis was 46.5 MPa at a strain of 0.01125 and specimen BS2C3C_450 provided analytical stress of 48.71 MPa at a strain of 0.01195.The analytical elaboration for the specimens BS2C3C_360 and BS2C3C_450 show that the material that finally fails was again the concrete, as in specimen BS2C3C. For BS2C3C_360, the tensile FRP strain at the ultimate condition, at the corner region of the mid-height stirrup was 0.01308 and at the corner of this stirrup it was 0.01398 b. For spIt is also observed that the differences in the characteristic values for the strain of the FRP and longitudinal and transverse steel reinforcements among these specimens were marginal. Comparing the FE results of these three RC columns, it seems that the axial stress-strain capacity of the columns was marginally decreased due to the lower yield stress of the steel bars. The bars of lower yield stress marginally affected the axial deformability levels of the columns, exhibiting a decrease of axial strain ductility.Analyses were performed on cylindrical columns confined with Ropes of Polypropylene by Rousakis  Figure a. These VFR = 738 MPa and a tensile elongation at a failure of 4.6%. The first column had one layer with 5.83 mm spiral spacing , the second one had one layer with 13.18 mm spiral spacing  and the third had one layer with 20.06 mm spiral spacing . The columns of the v1 group had stopped early for safety reasons before the fracture of the confining means.The vinylon fiber ropes (VFRs) of the study consisted of three Z-twisted fiber strands . They had a low E-modulus of 15,900 MPa, a tensile strength of ft/fc was 0.1 (where ft is the tensile strength and fc is the compressive strength [The concrete was modeled using the RHT concrete model. The compressive strength for specimen VinL1v1R1 was 17.9 MPa and the tensile strength ratio fstrength ). The coThe analytical stress-strain curve for specimens of the VinL1v1 group subjected to axial compression is depicted in Finally, analyses were carried out on square RC columns confined with ropes of polypropylene by ,47 Figub,c. Thesy,long = 500 MPa and fy,stirrup = 220 MPa, respectively. The modulus elasticity of steel was Es = 200,000 MPa and the Poisson’s ratio ν = 0.3.For the simulation of PPFR, which is a Z-twisted two-strand rope, the ultimate stress was 405.3 MPa, the tensile modulus of elasticity was 2.0 GPa and 20.36% elongation at failure. The yield strength of the longitudinal steel and stirrups was fThree-dimensional finite-element modeling was used herein to study the axial mechanical behavior of square and rectangular RC columns, confined with FRP jackets and continuous composite ropes. The pseudodynamic approach was utilized for the first time to enable for the reproduction of monotonic, repeated or cyclic imposed displacements . It may capture demanding inelastic behaviors, damage redistribution effects and local degrading behavior. The analytical models of the small and real scale columns under investigation were developed based on suitably calibrated material models, realistic representation of all the internal steel detailing and the external FRP jacketing, suitably designed FE meshing and interactions among different materials and interfaces and proper body interactions (necessary for the pseudodynamic process). The analytical results of RC columns confined with composites compared well with the experimental stress-strain curves of several characteristic RC columns of the square or rectangular concrete section with varying concrete strength, corner radius, FRP jacket mechanical properties or non-bonded composite rope confinement. In particular, the FE analyses follow closely the experimental curves for specimen series BS1C/BS2C and LSR-R-1-3 with ascending curves and for specimen series R2.0H2CL with descending second branches. All the analyses were stopped at the experimental ultimate axial displacement while the corresponding ultimate axial stress in all cases exhibited an AAE of 13%. Therefore, the proposed validated pseudodynamic modeling approach enabled for the first time to investigate analytically several critical design parameters and conduct parametric analyses.The advanced FE models considered the effects of the slenderness of bars, deficient stirrups or local crushing of the concrete and therefore were used as a basis to investigate the effects of steel reinforcement quality on the stress-strain behavior of the columns. Several parametric analyses were investigating the influence of different yield stress of longitudinal steel and stirrups . It is observed that the bars of lower yield stress affected marginally the axial deformability levels of the columns, exhibiting a decrease of axial strain ductility.FRP jacket fracture is widely accepted as the failure criterion for most of the experimentally investigated cases and for the proposed design models. Further, the contribution of steel bars and stirrups may be variable. This study focused on the significant variation of the field of developed strains on the FRP jacket at the ultimate condition and on the developed strains and deformations on steel cages among different columns. Eventually, all steel bars under compression exhibited and maintained strains higher than the yield one with high variation along the axis. All stirrups under tension exceeded their yield strain or achieved strains very close to it. The measured deformations suggest nonuniform bulging of the retrofitted column both axially and transversely. The critical position to place strain gauges in order to measure the representative axial strain of the steel reinforcement under axial compression in experiments (close to the average one for the column), may be in the middle-height of the area of interest (far from end boundaries) and at the mid-distance between successive stirrups  and not at the area close to the stirrups. The investigated variable field of FRP strains suggest that there was, in some cases, local fracture of the jacket at the corner region  while the global behavior of the column did not reach the ultimate failure. This aspect was captured due to the suitable composite jacket modeling among others. The measured FRP tensile strains were higher at the corner region at the height of the stirrups for most of the specimens. For lower FRP confinement and for lower corner radius there was a high local damage development in the concrete and local bulging in both the concrete and FRP. It seems there was an interaction between the local damage of the concrete and the FRP fracture that needs further investigation. Finally, the advanced parametric FE analyses confirm previous investigations ,67,68 anAll these investigated critical parameters will significantly enrich the extensive experimental databases for such retrofitted columns gathered in ,71. The


High-performance pumping concrete has been widely used in high-rise building construction because of its superior qualities. However, early cracking problems can occur in cast-in-place pumping concrete, which is due to the excessive use of cement. In this paper, an innovative concrete mixing procedure called “post-filling coarse aggregate concrete” (PFCC) was adopted and applied to large slump concrete. The influence of the post-filling coarse aggregate (PFA) ratio on the mechanical properties of large slump concrete were investigated. Three different concrete strength grades  and five different PFA ratios  were considered. The designed slump for the reference concrete was 180–200 mm. Experimental tests on the compressive strength of cubic specimens, axial compressive strength of prism specimens, splitting tensile strength, modulus of rupture and modulus of elasticity were performed. All tests were conducted in room conditions. Results showed that the slump of the PFCC decreases as the PFA ratio increases. It also indicated that, in general, the mechanical properties of PFCC are not linearly increasing as the PFA ratio rises, and there exists a turning point. Based on the experimental investigation and analysis in this study, the optimum post-filling coarse aggregate ratio is recommended to be 20%. Coarse aggregate interlocking concrete is a new type of concrete mixing process, designed to replace a portion of cementitious materials with low cost coarse aggregate to maximize the ratio of aggregate to binder (coarse aggregate to cement binder ratio). The conventional concrete with the same water-cement ratio as coarse aggregate interlocking concrete is made usually as reference concrete (RC). Compared with reference concrete, the coarse aggregate interlocking concrete increases the amount of coarse aggregate and reduces the amount of cementitious materials. It not only improves the concrete properties such as strength, modulus of elasticity, shrinkage reduction and durability, but also exerts a positive impact on energy conservation and carbon dioxide emission reduction. Recycled coarse aggregate concrete also presents its potential for economic and environmental sustainability and has been studied by researchers extensively ,2,3,4,5.Concrete is a multi-phase material composed of coarse aggregate, mortar and an interfacial transition zone between the two. As the skeleton of concrete strength, coarse aggregate is usually the strongest element in concrete with the best volume stability and durability ,17. MeddPost-filling coarse aggregate concrete is one kind of coarse aggregate interlocking concrete. The coarse aggregate at different gradations is evenly added to premade concrete before the pumping and casting. The strength of the coarse aggregate itself is much higher than that of the mortar, and the strength of the concrete can be enhanced within a certain volume content range of coarse aggregate. Shen et al. ,24 studiShen et al.  investigIt is well known that the interfacial transition zone between the coarse aggregate and cement paste is very critical and could determine the failure of concrete. Normally, the following measures were adopted to improve the strength and mechanical performance in the interfacial transition zone (ITZ): (1) decrease water/cement ratio; (2) use supplementary cementitious materials or high performance admixture; (3) select the high quality aggregate to improve the ITZ performance; (4) improve the concrete fabrication process technology, i.e., mixing, placement and curing technology. Among all the measures mentioned above, the investigation of the effect of the mixing procedures on the mechanical performance of concrete is the objective in this study, by using post-filling coarse aggregate concrete. The post-filling coarse aggregate concrete technology not only realizes the green high-performance of concrete, but also significantly reduces the cost of concrete and reduces carbon-dioxide emissions, which is one of the effective ways to achieve low-carbon emissions in the cement concrete industry. Although Shen et al. ,23,24,25The study of the basic mechanical properties of post-filling coarse aggregate is crucial to understanding its structural behavior in order to facilitate its application in engineering. Hence, the post-filling coarse aggregate concrete (PFCC) with different post-filling ratios and different concrete strengths are studied in this paper. In this study, the mixture design and optimization for post-filling coarse aggregate large slump concrete will be performed for different concrete strength grades. The slump loss, compressive strength of cubic specimen and prism specimen, splitting tensile strength, modulus of elasticity as well as modulus of rupture are studied. Through the experimental study, the relationship between the post-filling coarse aggregate (PFA) ratio and the above properties of large slump concrete are obtained, and the optimized PFA ratio is recommended. The percentage of the volume of the coarse aggregate to the total volume of the concrete is defined as post-filling coarse aggregate ratio. Five PFA ratios  and three different concrete grades  are studied as parameters in this study. The PFA ratio of 0% indicates the reference concrete without post filled coarse aggregate. It aims to provide research data and design guidelines for the application of post-filling coarse aggregate concrete in the building engineering as well as civil infrastructure.3, as shown in P·II32.5R cement and P·II42.5R ordinary Portland cement were used. Fly ash was used to replace part of the cement. The coarse aggregate for reference concrete was continuous graded gravel with a particle size of 5–10 mm, as shown in The design of the mixture proportions of concrete is to meet the workability and strength requirements. Three different compressive strength  of concrete were designed in this study, which is denoted as C30, C40, and C50. The required slump of concrete in this study is 180–200mm. The mixture proportions are shown in Before mixing the concrete, the inside of the mixer was prewetted. Then the pre-weighed materials including coarse aggregate, fine aggregate, cementitious materials and water were poured into the mixer in turn. The polycarboxylic acid superplasticizer was dissolved into the water and added into the mixture. All mixture components were mixed in a self-falling mixer for 3 to 5 min. After that, the coarse aggregate was filled into the concrete mixture and then was stirred for 10 to 15 s. Finally, a slump test was performed for the fresh concrete and specimen’s mechanical properties. After the specimens were cured for 48 h in the room environment , specimens were demolded and immediately moved to the standard curing room for 28 days before testing. The steps of post-filling coarse aggregate are shown in cuf), splitting tensile strength (tsf), modulus of rupture (rf), modulus of elasticity (cE), compressive strength of prism specimen (cf) were prepared according to the Chinese standard GB/T50081-2002 )tsf of concrete.In general, the brittle failure at the splitting tensile strength was observed for all concrete specimens, as shown in The splitting tensile strength test for the cubic specimen was conducted to obtain the tensile strength of the concrete. The experimental results are shown in The modulus of ruptures (MORs) of tested specimens with variations of PFA ratios are shown in The modulus of elasticity of the concrete specimens with variations of the PFA ratio are shown in 4, 3.63 × 104 and 3.59 × 104 MPa, respectively. The increase of the moduli of elasticity compared with the reference concrete are 0.65 × 104 (22.4%), 0.56 × 104 (18.2%) and 0.03 × 104 MPa (0.84%). Generally, the modulus of elasticity of the PFCC is greater than that of the reference concrete. It is worthy to mention that, unexpectedly, the modulus of elasticity of the reference concrete is higher than that of the C50 PFCC at the 10% and 15% PFA ratio. This inconsistency is speculated to be caused by test errors and discreteness of concrete specimens. It can be seen from The axial compressive strength of prism specimen with dimension of 150 mm × 150 mm × 300 mm was also tested. It was observed that the vertical cracks  of the prism specimen appeared until the peak load was reached. Then, the load carrying capacity dropped immediately and the vertical cracks continued to develop toward the top and bottom of the specimen in width and in depth. Finally, the specimen was failed by the crushing of concrete and a penetrating diagonal crack was formed accompanied by the cracking sound.In the axial compression test, the failure mode of the PFCC specimen is primarily the same as that of the reference concrete specimen, which are both brittle failure modes along the longitudinal direction. It exhibits that, as seen in The test results of the axial compressive strength of PFCC are shown in As shown in Therefore, it can be inferred that the axial compressive strength for the prism specimen increases and then decreases with the increase of the PFA ratio generally. The highest compressive strength occurs at the approximate PFA ratio of 10–20%. Compared with the reference concrete, the axial compressive strength of the PFCC is approximately increased by 10% overall. A 15–20% post-filling aggregate ratio is suggested for axial compressive strength.A cost analysis was conducted for the reference concrete and post-filling aggregate concrete at various post-filling ratio according to the current market price. The results are shown in It can be seen from The objective of this research is to elucidate the relationship between the post-filling coarse aggregate technology, particular the post-filling ratios, and the mechanical properties of large slump PFCC associated with different concrete strength grades. It aims to provide a promising concrete production technology on the premise of its cost-saving as well as environmental benefits. The workability, compressive strength, elastic modulus, splitting tensile strength and modulus of rupture were experimentally tested and analyzed. Based on the experimental study and analysis of mechanical properties of the post-filling coarse aggregate concrete (PFCC), a few specific conclusions can be drawn.(1) With the increase of the post-filling coarse aggregate (PFA) ratio, the slump of concrete decreases. Experimental results indicate that the slump of PFCC could meet the designed requirement of larger than 140 mm when the PFA ratio is no more than 15%.(2) Results show that the failure mode of PFCC is similar as that of reference concrete. For C30 and C40 concrete, the failure of PFCC is basically the bond failure between the coarse aggregate and the cement paste. While the splitting cracking failure of the coarse aggregate was observed primarily for the C50 concrete. Moreover, the brittleness of the PFCC specimen is higher than that of the reference concrete specimen.(3) The compressive strength test results of the cubic specimen show that the compressive strength of the PFCC at 7 d and 28 d increases first and then decreases as the PFA ratio increases for three concrete grades, which are all higher than those of reference concrete. For cubic compressive strength, the optimized PFA ratio in volume is 20%.(4) The splitting tensile strength, modulus of rupture, axial compressive strength as well as the modulus of elasticity of PFCC are improved compared with those of reference concrete. The recommended PFA ratio is 15% for above properties. It was also found that, as the concrete strength grade increases, the enhancement of splitting tensile strength, modulus of rupture, axial compressive strength and modulus of elasticity in absolute value are increased.(5) Generally, it does not indicate significant differences on the failure modes between the post-filling coarse aggregate concrete specimens and the reference concrete specimens.


The deformation and cracking of concrete will lead to various deterioration processes, which will greatly reduce the durability and service life of the concrete pavement. The relating previous studies and analysis revealed that the coupling action of environmental temperature, moisture, and wheel load will cause cracking and seriously affect the normal service and durability of pavement concrete. This paper presents theoretical and numerical state-of-the-art information in the field of deformation and failure of pavement concrete under coupling action of moisture, temperature, and wheel load and draws some conclusions. (a) Concrete is a typical porous material, moisture and heat transfer theory has obtained enough data to simulate the hygro-thermo properties of concrete, and the relationship between moisture and heat is very clear. (b) There are few studies on concrete pavement or airport pavement considering the coupling action of moisture, temperature, and wheel load. (c) Concrete pavement is subjected to hygro-thermal-mechanical coupling action in service, which has the characteristics of a similar period and its possible fatigue effect. (d) COMSOL software has certain advantages for solving the coupled hygro-thermal-mechanical of concrete. Cement concrete pavement is widely used in the construction of the airport runway and high-grade highway in China. More than 80% of the airport pavement in China adopts cement concrete . For pavThis paper will start from the coupling action of moisture, temperature, and wheel load that affects the deformation and failure of concrete pavement in the service life. The basic model of the multi-physical fields of concrete, research on the fatigue effect of concrete pavement, research on the deformation and failure of concrete pavement or airport pavement (except for concrete pavement or airport pavement), and the numerical simulation method of hygro-thermal-mechanical coupling deformation of concrete are discussed. This paper will provide new research ideas for the study of concrete deformation and failure of the pavement.Concrete is a typical porous medium material ,6, and iGenerally, it is assumed that the moisture transfer in porous cement-based materials is in the form of diffusion, and the humidity gradient is the driving force of humidity (liquid water and steam). According to Fick’s law and mass conservation equation, the one-dimensional transmission formula is as follows :(1)∂∂x is as follows :(2). The rheological model is shown in In the formula, the For the pavement in the area with significant temperature and humidity changes, frequent takeoff and landing of aircraft or airport runway of large military multi-wheel aircraft, heavy load and frequent traffic, the pavement is more prone to deformation and damage. The problem of deformation and cracking of airport runway, highway, and urban road pavement has not been well solved because the influence factors of pavement concrete deformation and failure are not fully considered in the design stage. The above factors include temperature change, dry and wet change, and dynamic and static action of wheel load and its coupling effect. The research on the fatigue effect of airport concrete is mainly as follows: large scale airfield concrete slabs were tested by Jeffery R. Roesler  in the lIn the related research on deformation and failure of airport pavement or cement concrete pavement, many researchers mainly focus on the influence of temperature, fatigue load and freeze-thaw, temperature and humidity changes on the shrinkage, and cracking of pavement concrete ,30,31,32Seongcheol. Choi  et al. sMany Chinese researchers have carried out research on warpage stress. In recent years, there have been studies considering the joint effect of temperature effect and wheel load stress. Tan Zhiming et al.  earlier A 3D finite element model was established for analyzing the mechanical responses of cement concrete airport pavement to multiple-gear military aircraft loadings. The test results showed that the maximum tensile stress in the pavement occurred at the bottom of the slab, the tensile stress and the deformation of the pavement under two 8-wheeled gears were smaller than that under one 8-wheeled gear. The elasticity modulus of the slab, the resilience modulus of the base and the reaction modulus of the subgrade all had significant effects on the mechanical responses of the pavement.Zheng Fei and Weng Xingzhong  analyzedThe research on the hygro-thermal-mechanical coupling action analysis was previously in the field of rock engineering and had always been a research hotspot ,54. The In the research of the numerical simulation method of hygro-thermal-mechanical coupling deformation of concrete, there are four main numerical simulation methods:This method does not involve the internal heat and mass transfer mechanism and specific processes of the porous media, but only considers the relationship and cross effect between various flows and forces of heat and mass transfer. A phenomenological equation can be obtained to describe various flows. Phenomenological methods are difficult to apply in practice due to the influence of test conditions and many material parameters. Due to the lack of effective means and methods for testing moisture distribution, the moisture migration rate is slower than the thermal migration rate. In the process of solving various models, the values of some coefficients are basically based on experimental or empirical data, which affects the versatility of this method.This method considers the heat absorption or exotherm in the process of heat and mass transfer, and establishes a partial differential equation system based on the principles of mass conservation and energy conservation in the process of moisture migration. The method of numerical analysis is used to solve the equations to obtain the analytical solutions of the heat, humidity fields, and their dynamic changes ,73,74,75The finite element method is the most widely used numerical calculation method in scientific research and has become the main tool for solving scientific and technological problems. At present, many commercial finite element softwares have been developed, such as ANSYS, MSC, ADINA, ABAQUS, etc. In the finite element analysis method, the model should be established first, and then solved by self-programming ,58,63,81The analysis method of COMSOL multi-physical field coupling calculation software ,70,86 waThe studies of the coupled hygro-thermo-mechanical behavior of concrete pavement have been reviewed in this paper. The various aspects on the deformation and failure of concrete pavement under coupling action of moisture, temperature and wheel load presented in this paper could be summarized and concluded as:1. Concrete is a typical porous material, moisture and heat transfer theory had been obtained enough data to simulate the hygro-thermo-mechanical properties of concrete, and the relationship between moisture and heat is very clear.2. There has been some research on the moisture-heat-mechanical coupling of concrete materials, but most of the research focused on the performance of concrete in fire or high temperature. There are few studies on the moisture-heat-mechanical coupling deformation of concrete under normal service conditions.3. In the related research on deformation and failure of airport pavement or cement concrete pavement, many researchers mainly focused on the influence of temperature, fatigue load and freeze-thaw, and temperature and humidity changes, which lead to the shrinkage and cracking of pavement concrete. There are few kinds of literature considering the coupling action of moisture, temperature, and wheel load at the same time.4. Concrete pavement is subjected to hygro-thermal-mechanical coupled action in service, which has the characteristics of a similar period and its possible fatigue effect. In the existing moisture-heat-mechanical coupling research, the research on “force” is mostly the load of a certain stress level continuously applied, but not enough attention is paid to the periodicity of wheel load and the change of temperature and humidity.5. COMSOL software has certain advantages for solving the coupled hygro-thermal-mechanical of concrete.In the later research, the deformation and failure mechanism of pavement concrete under the coupling action of moisture, temperature, and wheel load need to be studied.


To study the permeability of superabsorbent polymer (SAP) modified concrete and the effect of internal pore characteristics on the permeability of concrete specimens, the results of the water penetration under pressure test, the mercury intrusion porosimetry (MIP) test, and scanning electron microscopy (SEM) of SAP concrete were obtained and analyzed. The research shows that the addition of an appropriate amount of SAP can effectively improve the anti-permeability performance of concrete. After adding 0.2~0.6% SAP of cement quality to concrete, the penetration height value was reduced by 35~45%, the porosity was increased by 21–95%, and the tortuosity is increased by 14–15%, and all indicators show regular changes with the increase in SAP usage. Adding SAP to concrete changes the internal connection state of concrete, thereby further improving its impermeability by reducing the capillary pressure and changing the shape of the pores. The liquid permeation resistance is increased by the “threshold effect” inside concrete; this “threshold effect” is caused by the addition of SAP. With the improvement of the aesthetic and functional requirements of building structures, high-strength concrete is increasingly used in modern civil engineering structures. However, high-strength concrete also faces the problem of poor permeability due to its extremely high density, which in turn is difficult for conventional external curing methods to effectively maintain. Using a certain method or additive to achieve and improve the internal curing efficiency of concrete is a feasible solution. Shideler and A. Bentur studied the mechanical properties and volume stability of concrete mixed with pre-wet light aggregate and found that this method helps to reduce the self-shrinkage and cracking of concrete ,2. JenseSuperabsorbent polymers (SAPs) are multi-functional polymer materials. SAP has been widely used in industry, agriculture, forestry, medical and health supplies, and other fields. In the field of civil engineering, the performance of concrete can be improved by a variety of methods that involve the use of SAP as a new type of concrete admixture. SAP can be used as an internal curing material for low water cement ratio concrete. After absorbing water, the SAP particles become distributed uniformly in concrete, thus effectively providing the hydration water in the course of concrete hydration as well as effectively reducing the autogenous shrinkage of concrete and preventing concrete cracking ,6,7. SAPConcrete is a porous, heterogeneous composite material at various scales. The external media, such as water and gas, are transported in various forms within the material, mainly through its own connected pores and fractures. The permeability depends mainly on the connectivity of the internal pores and the tortuous nature of the infiltration path.After different stages of the hydration reaction, the internal pore radius of the pores inside concrete is uneven. The difference in capillary pore diameter makes the transport mechanism of gas and liquid through concrete different. In general, when there is a pressure difference, the transport of gas and liquid can be analyzed according to the laws of gas or hydrodynamics . When there is a difference in concentration, the liquid and the substance dissolved in the liquid will move under the action of diffusion. When there is a potential difference, a phenomenon related to electroosmosis and electrodeposition occurs. When there is a temperature difference, the liquid moving through the concrete is subjected to the thermal mass transfer law.− and SO42− resulting in corrosion of concrete reinforcement, alkali aggregate reaction, and, eventually, the destruction of concrete; thus, to some extent, the permeability of ions determines the rate of deterioration of concrete. Therefore, the study of the permeability of concrete is of great significance. The Rose study found that the main factors that affect the speed and scope of water penetration in concrete materials are the pore structure and the fracture morphology of concrete materials [Water is the element that most commonly and easily comes into contact with the concrete medium. Water molecules can easily enter the concrete through its pores to reduce the pH value of concrete pore fluid. In addition, the water carries harmful ions, such as CLaterials . To studAt present, there are two types of concrete curing methods: external curing and internal curing. Traditional curing methods include wet curing , chemical curing, and the cementing of plastic film on the surface of cement materials. However, these external curing methods are labor-intensive and time-consuming, and because water in external curing has difficulty entering the interior of the concrete, the water required for the subsequent hydration of the cement cannot be continuously replenished, so the final curing effect is poor ,16. InteAccording to 2010 ACI Concrete Terminology (American Concrete Institute), internal curing refers to the following: in a fresh cementitious material, the internal water source is provided by a pre-wetted lightweight aggregate (LWA) or a superabsorbent polymer (SAP); the released moisture can be supplied to the hydrating cement . The useAccording to the different mechanisms of water absorption and storage, the curing materials are divided into two categories. One is a porous structure of light aggregate, mainly including clay or shale quality materials, which can use their own pores to absorb and preserve water; however, its water absorption capacity is low. The other is a superabsorbent polymer, which is a typical functional polymer material with high water absorption; it uses the chemical bond between polymer molecules and water molecules to absorb and retain moisture. The two types of internal curing materials have different structural characteristics, and their mechanisms of interaction with water are quite different; thus, the curing effect of concrete is also different. In this paper, the effect of the latter (SAP) on the impermeability of concrete is studied.A superabsorbent polymer is a type of polymer material with a strong water absorption capacity and water holding capacity ,19. In vSAP can react with water via the carboxyl group and hydroxyl group and absorb liquid water, which is several thousand times its own weight. SAP exhibits a gelatinous form after absorbing water, as shown in After SAP water swelling, it will release the corresponding water with an increase in pH value or ionic concentration. In the process of cement hydration, the hydration products of cement produce a large number of cations dissolved into the water, thereby increasing the pH value of the system rapidly; then, the water-containing SAP is continuously released to provide water for the cement to further generate water splash reactions. SAP in the fresh concrete will undergo swelling and form spherical pores in the concrete after drying, as shown in 2=CH–CONH2) as the main monomer, acrylic acid (CH2=CH–COOH), methacrylic acid (CH2=C(CH3)COOH), methyl acrylate (CH2=CH-COOCH3), ethyl acrylate (CH2=CH–COOCH2 CH3) and methacrylate (CH2=C(CH3)COOR) as comonomers, and then binary polymerization. The particle sizes of the SAP were 50 mesh and 100 mesh, the performance index of which is shown in The SAP used in this test was acrylic superabsorbent resin , which is based on acrylamide , Dm represents the average water penetration height (unit: cm), H represents the water column height (unit: cm), T represents the testing time (unit: h), and ϕ represents the porosity of concrete, which can be obtained using an MIP experiment.The osmotic coefficient is calculated according to Formula (2):Permeation experiments were conducted on each group of samples to obtain the penetration height and calculate the corresponding osmotic coefficient; the calculated results are shown in The permeation heights of the P-50 and P-100 samples are normalized by the penetration height of the P-0 samples; the normalized infiltration heights of the samples are shown in Based on the results of the MIP experiment, the porosity of SAP concrete was statistically analyzed to study the effect of porosity on the permeability of SAP concrete, as shown in After adding SAP, the porosity of the concrete increased, whereas the penetration height decreased—that is, the impermeability increased. In the case of the addition of the same SAP concentration, the improvements in the porosity and anti-permeability of the small-diameter SAP concrete sample is more is more obvious.The average pore size, which is an important parameter of the concrete pore structure, characterizes the pore structure of the overall situation. Han Yong Moon  studied The average pore size comparison figure is drawn from the MIP experimental data, as shown in From the average pore size data, the permeability of SAP concrete does not decrease with the increase in the average pore size; rather, it shows a growing trend, which represents the unique performance of SAP in terms of its effect on the permeability of concrete.Based on the water penetration under pressure test, SAP is found to have some influence on the permeability of concrete; however, its influence mechanism cannot be obtained and explained directly from the water penetration under pressure test. It is necessary to further analyze the pore structure of SAP concrete by means of scanning electron microscopy (SEM); the mechanism underlying the effect of SAP on the permeability of concrete will be discussed based on the microscopic pore structure characteristics.The characteristics of the pore structure of concrete determine the permeability of concrete, and the change in pores has a significant influence on the permeability of concrete, from both macroscopic and microscopic perspectives. There is a certain relationship between the permeability and the connectivity of the internal pores. Only when the pore size is greater than the critical diameter will infiltration further proceed . With the continuous improvement of pore measurement technology, the combination of computers and electron microscopes resulted in the development of a quantitative stereo micrography technique based on the optical microscopy image analysis method. Using this method, a series of parameters, including pore diameter, stomatal gradation, and stomatal distribution, can be obtained. In this paper, a large number of SEM photographs of concrete was obtained using scanning electron microscopy (SEM); the stomatal structure parameters of the samples were obtained by analyzing the micrographs with Image-Pro software. A TDCL-SU1510 scanning electron microscope was used to obtain the SEM micrographs of the microstructures. Finally, the micro-images were analyzed and processed with Image-Pro software to obtain the required pore parameters.ρ (units: Pa), surface tension γ (units: N/m), wet angle θ (units: °), and pore radius r (units: m) have the following relationship:According to the Cantor equation , the capSAP particles can also be considered as a group of air bubbles in concrete, which can not only block the connectivity of the pores but also increase the average concrete pore size, as shown in ρ) can reduce the permeability of concrete. Thus, we can preliminarily explain the phenomenon previously reported in In fact, as long as the concrete is in contact with water, even if there is no water pressure difference, the phenomenon of infiltration will occur because of the role of capillary pressure. The increase in the average pore size causes the capillary pressure to decrease, which results in a shallow suction of the liquid and an increase in the impermeability. A decrease in capillary pressure (q/dt represents the penetration rate (units: cm3/h), K’ represents the real permeability (units: cm/h), A represents the cross-section area of the specimen (units: cm2), , ρ represents the capillary pressure (units: cm), fh represents the capillary resistance (units: cm), and L’ represents the actual penetration depth (units: cm).When the concrete is submerged in water, it will be affected by the combined effect of water pressure difference, capillary pressure, and capillary resistance. The following formula can fully reflect the relationship between the penetration rate and the water pressure, capillary pressure, and capillary resistance .(4)dqdtWith the increase of the actual penetration depth, the capillary resistance will change. When the penetration depth reaches the opposite side of the concrete specimen, the direction of the capillary pressure will also change—that is, from positive to negative (opposite to the water pressure). The capillary pressure, which originally promotes the penetration of the liquid, will hinder the penetration of the liquid in this case. Therefore, the real permeability coefficient calculated using Equation (4) varies nonlinearly with the actual penetration depth. The permeability and capillary permeability of concrete also have such a close relationship through the change in the relatively high capillary resistance. When the capillary penetration is poor, the capillary resistance is relatively high. Microscopic pore structure observation of each sample is conducted using SEM, and a typical internal cavity communicating state is obtained  of the seepage medium—that is, the true length of the trajectory of the seepage fluid particles passing through the medium unit distance in the channel. The tortuosity of the channel is a dimensionless unit. The larger the value, the greater the number of mesopores and small pores or the better the connectivity of the pores, which can be calculated by mercury withdrawal in the MIP experiment ,31,32.The analysis results of the porosity of the sample are shown in The normalized values of the tortuosity of the P-50 and P-100 samples are obtained by using the P-0 samples as the reference values; the normalized diagram of the tortuosity value of each sample is shown in fh in Equation (4)—thereby effectively reducing the permeability of concrete.From the above analysis, it can be seen that SAP particles effectively improve the capillary resistance—that is, the value of Rose  categoriSAP concrete is different from ordinary porous concrete, which is formed by filling gas and foam; after the completion of hydration, each cavity will still contain SAP particle residues. Since the SAP particles have the characteristic of repeated water absorption, after permeating water re-enters, the SAP particles gradually absorb water and swell and then move toward the neck of the cavity under the action of water pressure until they finally block the cavity. This process will increase the resistance of liquid seepage to a certain extent and further promote the increase in capillary resistance, forming a “threshold effect” inside the concrete and reducing the capillary liquid surface tension; as a result, the impermeability of concrete is improved, as shown in From the above analysis, it is known that the addition of SAP reduces the capillary pressure and increases the resistance of the pores. In addition, SAP also has a unique “threshold effect” in the cavity, which leads to the permeability of the SAP concrete still being good under the condition of increasing porosity and average pore diameter.(1) After adding SAP of 0.2%~0.6% cement in concrete, its penetration height value will be reduced by 35%~45%. The penetration height of concrete specimens with the same SAP particle size will increase with the increase in SAP addition, and the penetration height of concrete specimens with the same SAP amount will decrease with the decrease in SAP particle size. This shows that, after adding SAP to concrete, its impermeability performance is improved to a certain extent, and the smaller SAP particle size and smaller addition amount have the best effect on improving the impermeability of concrete.(2) Quantities of 0.2%~0.6% of SAP can increase the porosity of concrete from 0.056 to 0.069~0.111. The porosity and average pore diameter of concrete both increase greatly with the increase in SAP addition, and under the same SAP addition amount, the porosity and average pore diameter of SAP concrete with small particle diameters are higher.(3) The addition of 0.2%~0.6% of SAP can increase the tortuosity of concrete by 1.14~1.5 times, and the tortuosity of concrete increases with the increase in SAP. Among them, the larger SAP particle size concrete specimens increased slightly.(4) The addition of SAP decreases the internal capillary pressure of concrete; moreover, a large number of closed or semi-closed cavities, which are formed by the SAP particles in the concrete, cut off the connectivity of the pores, thereby increasing the impermeability of concrete. This explains the inherent mechanism of improvement of the impermeability of concrete in the case of SAP concrete with increasing porosity and average pore size. SAP has a unique “threshold effect” in the cavity, indicating that the permeability of the SAP concrete is still good under the condition of increasing porosity and average pore diameter.


The tensile properties of plain concrete are very important for the concrete structural design, and the complete tensile stress-strain curve is essential for creating accurate and reliable designs, especially when considering special load cases such as earthquakes and impacts. To study the complete tensile stress-deformation response of plain concrete, the direct tension tests were conducted on a novel thermal tensile testing machine (TTTM), which was reformed from a hydraulic universal testing machine (UTM). Acoustic emission (AE) technology was applied to monitor the damage process of plain concrete in tests. The TTTM was powered by the thermal expansion of loading columns, and had a stiffness similar to the specimen, thus eliminating the potential AE noises in the UTM, and simulating the rapid fracture process in real concrete structures. A static-dynamic acquisition system was established to obtain the complete tensile stress-strain curves, of which the data before and at the fracture moment were respectively acquired by the static acquisition system and the dynamic acquisition system. The AE technology is a useful approach to analyze the damage process of concrete, and makes it feasible to determine the damage state and the fracture location of the specimen in real time. The tensile properties of concrete materials are indispensable for the assessment and design of concrete structures. The complete tensile stress-strain curve of plain concrete, especially the softening response, is necessary when accessing the structural safety of concrete buildings subjected to various load cases. Meanwhile, the concrete materials bear the main load in the low reinforced or plain concrete structures, and the structural stiffness and stability may vary greatly once the concrete materials crack due to tension. Consequently, studying the complete tensile stress-deformation response of concrete is of significance in concrete structural engineering.The tensile softening response of concrete is the most difficult part to acquire in the complete tensile stress-strain curve. The reason for this is that the concrete, as a quasi-brittle material, is easy to fall into an unstable cracking state when the energy released by concrete structures or test machines is greater than the energy material needed to crack stably. The extremely short time of the unstable cracking process make it difficult to record the relevant data. At present, the common test methods to study the tensile softening response of concrete can be mainly classified into three categories: direct tension tests (DTTs) ,2,3,4,5;Since Evans and Marathe  observedIn addition, due to the inhomogeneity of concrete, the damage process of the concrete material in DTTs is complex and unpredictable. Consequently, the real-time damage monitoring can facilitate the analysis of the cracking process, and guide the adjustment of the instruments during the tests. Acoustic emission (AE) technology , as a useful method to analyze the damage evolution inside the concrete material in real time , was comIn the research for this paper, a novel thermal tensile testing machine (TTTM) was constructed. The AE technology was applied to monitor the damage process of plain concrete in the DDTs conducted on the TTTM. The TTTM was powered by the thermal expansion of loading columns, and had a stiffness similar to the specimen, thus avoiding the influence of potential AE noises and simulating the rapid fracture process in real concrete structures. Meanwhile, due to the sudden change of deformation and load at the rapid fracture process, a static-dynamic acquisition system was developed, which could switch the acquisition mode from the static mode to the dynamic mode automatically. Some complete tensile stress-strain curves were obtained with the developed system, and the damage evolution of plain concrete in DTTs was analyzed.The mix proportion of concrete is given in .The dimension of specimens was 100 mm × 100 mm × 300 mm. After the casting and hardening of the concrete, the specimens were covered with a plastic membrane to prevent moisture from evaporating. The specimens were demolded 24 h later, and then cured by being sprayed with water daily and covered with the plastic membrane until the end of a 28-day period. These specimens were stored in an indoor dry environment after the curing, and tested a year later. Before testing, the specimens were processed, which will be elaborated upon in Section 2.5The direct tension test was conducted on the TTTM, which was reformed from a conventional hydraulic UTM . The schematic diagram of the TTTM is drawn as The loading process on the original UTM was realized by the hydraulic system before reforming. However, the hydraulic system might generate mechanical and electric noises during the AE monitoring, and even some important AE signals could be flooded by the AE noises. For this reason, the UTM was reformed to achieve silent operation by the thermal loading system. The reformed UTM, i.e., the TTTM, had four columns and two beams. Two threaded columns could be controlled to rotate clockwise or anticlockwise to move the lower beam up or down, and the other two columns would be heated by electric heating elements during the loading process. The two heated columns elongated under thermal expansion, so that the upper beam would be elevated and the specimen could be in tension through the load-transferring device.The original holding device of the UTM was replaced with a load-transferring device, as shown in −5/°C, therefore the max elongation of the heated columns is just 1.4 mm. Even though the value exceeds the max deformation of specimens at the tensile failure moment , the max elongation would still be insufficient if too much clearance existed among the components on the load transfer path. For this reason, the clearance among the components was reduced as much as possible before the heating process. The thread clearance between the thread columns and lower beam was reduced by elevating the lower beam with the screw jack below, and other clearance was reduced by the preloading of nuts and bolts. The nut on the load transducer was the last one to preload, and the last preloading process should be carried out under load monitoring, as the process would put the specimen under certain tension.The process of heating columns was realized by connecting the electrically-heated coils winded around the columns with current. Accordingly, the deformation rate of the specimen could be controlled roughly through adjusting the current in the electrically-heated coils. The diameter and the length of the heated columns are 70 mm and 1000 mm, respectively. In view of the heating range of the electrically-heated coils and the actual efficiency of heat transference, the max amplitude of the temperature rise on the columns could only be 120 °C. The material of columns is steel and its thermal expansion coefficient is 1.2 × 10In view that the stiffness of the test machine has a certain influence on the test result of the post-peak part, the stiffness comparison between the TTTM and the original UTM is presented in this section. The main difference between the two test machines is the load power system, which can change the load transfer path and determine whether to consider the stiffness of the oil cylinder in the stiffness calculation. Without regard to the influences of some components  on the stiffness calculation, the stiffness schematic of components can be depicted as The whole test process can be simplified as seven steps, which are presented and elaborated below.1.Processing the specimen. To ensure uniform stress distribution at the ends of the specimen, the sticky steel glue with high strength  was used to stick the specimen on the blind flanges. Meanwhile, to avoid fractures near the ends of the specimen or at the interfaces between the specimen and the blind flanges, the specimen was reinforced with steel plates inside and around the ends of the specimen shown as , and the2.Preloading bolts and nuts. Before the specimen was stuck on the blind flanges, the blots on the blind flanges and the nuts on the thread rods were preloaded. The step could make the load-transferring device and beams become an entirety, thus weakening the influence of the load-transferring device on the stiffness of the TTTM and minimizing the disturbance of the specimen during and after the sticking process.3.Sticking the specimen. After the glue applied at the processing step became solidified, the specimen was placed on the TTTM with adequate glue on the ends of the specimen. Furthermore, the surfaces of the specimen and blind flanges were wiped with alcohol before sticking. Then, the power of the test machine was turned on and the lower beam was elevated by the rotation of thread columns until the redundant glue on the ends of the specimen came out, thus minimizing the thickness of the glue layer and clearance among components.4.Installing sensors. The sticky steel glue needs at least three days to reach the designed strength, so the installation of sensors shown in  could be5.Reducing the clearance. The nut on the load transducer was first released, and then the lower beam was lowered about 1 cm for the space needed in the next steps. After that, the lower beam was elevated by the screw jack to reduce the thread clearance between the thread columns and the lower beam. Finally, the nut on the load transducer was preloaded to reduce the clearance among the upper subplate, the load transducer and the upper threaded rod. Meanwhile, there is the last preloading which needs to be done under load monitoring, in which the load should be below 2 kN (about 10% of peak load).6.Heating the columns. The electrically-heated coils wound around the columns were connected with the current after the previous steps, and instruments started to record data at the same time. To adjust the deformation rate, a transformer was connected with electrically-heated coils in series.7.Switching acquisition mode. To avoid missing the deformation and load data at the instantaneous fracture process, two methods were set to switch the acquisition mode from the static mode to the dynamic mode. The first method was to switch the acquisition mode automatically according to the abrupt fall of the load rate, and the second one was to switch when abundant AE signals were generated around the peak stress level. Additionally, the latter could only be done manually, as the AE acquisition system was independent with the acquisition system of deformation and load in the tests.The performance of the TTTM can be observed from the diagram of deformation vs. time before the fracture moment shown as , in whicOwing to the sudden change of load and deformation at the instantaneous fracture, the data at this stage were obtained by the dynamic acquisition system, but the data redundancy would emerge if the dynamic acquisition lasted too long. Meanwhile, the condition of specimens is not stable around the peak stress level, and they may fracture at any moment. For these reasons, the acquisition system needs to be switched automatically from the static mode to the dynamic mode near the fracture moment. The switching moment should be less than 30 s and more than 5 s before the fracture moment, so that the stored data would not be too large and the data during the fracture process could also be acquired. After the test, the data at the fracture process could be extracted from the acquired data.−5/s to 100/s. According to the variations of the deformation rate, the curves at this stage can be divided into four phases, which may correspond to the generation of numerous micro-cracks, the growth of macro-cracks, the rapid development of macro-cracks and the final fracture of the specimen. As shown in Compared with load signals, deformation signals might not be sensitive enough to determine the switching moment timely, and the trends of deformation on two sides of the specimen might not be consistent around the peak stress level . According to the test data, the switching moment was set as the moment when the load rate was less than −2 N/s and the load was larger than 20 kN at the same time . The boundary conditions of specimens under direct tension can affect the crack propagation around and after the stress peak ,25,35. TThe stress distribution inside the specimen is nonuniform for the inhomogeneity of concrete material, which includes initial micro-cracks, voids and randomly distributed coarse aggregates. The cracks would occur and propagate at the weakest region of the specimen, so eccentric loading could hardly be avoided during the test, and the final fracture might occur randomly on the unreinforced area. The fracture location of most specimens was near the ends of the specimens shown as , and thel is the length of the measurement area, The complete load vs. deformation curve can be obtained through splicing the data recorded by the static acquisition system and the dynamic acquisition system, respectively, which is depicted in 0/s, which are closed to the strain rates of tests on the TTTM at the post-peak stage. It is obvious in To compare the test results of the DTTs conducted on different test machines, the complete stress-strain curves were extracted from the relevant literatures ,36,37. ATo further verify the validity of TTTM, the normalized stress vs. crack width curve of tests on the TTTM is compared with that in available literatures ,36 as sb. To makIn addition, the rapidly changing deformation and load at the post-peak phase are susceptible to the experimental conditions. The filter cutoff frequency of acquisition instruments and the performances of sensors at high sampling frequency would both affect the accuracy of data at the post-peak phase.Due to the extremely short duration of the fracture process, the AE data at this process was very limited. Fortunately, the AE data before the fracture moment was plenty, and numerous signals increased with the loading time.The signal strength (SS) is the area inside the envelope curve of the AE waveform packet . The cumulative signal strength (CSS) is the accumulated value of the SS with the testing time, and is a useful indicator to analyze the concrete damage evolution. In addition, one important reason for designing the TTTM is to avoid the potential background noises emerging in the DTTs conducted on the conventional UTM. Among the AE parameters, the peak frequency is an important reflection on the frequency characteristics of signals, which is the corresponding frequency of the highest Fourier transform value of a signal waveform. The scatter diagram of peak frequency vs. strain is depicted in As mentioned above, the number of AE signals at the fracture process is very limited, so it is almost impossible to analyze the fracture process of the specimen through AE parameters; the waveform analysis shown in The complete tensile stress-strain curve was obtained from the direct tension test conducted on the TTTM, of which the data at the rapid fracture process was acquired by the dynamic acquisition instrument and laser displacement sensors. The performance of the TTTM and corresponding test procedures were introduced in detail.−5/s to 100/s.With the developed TTTM, the mechanical response of concrete at the fracture process was studied. During the fracture process of the concrete in direct tension, the released elastic energy stored in the experimental machine system before fracture could cause a large variation of the strain rate, which varies from 10A static-dynamic acquisition system was established to deal with the sharp variations of the deformation and load at the post-peak stage. The acquisition mode of the acquisition instrument could be switched from the static mode to the dynamic mode automatically before the fracture moment. The phenomenon of the AE data explosion could also trigger the switching of the acquisition mode during tests.The developed TTTM could avoid the potential AE noises emerged in tests conducted on the conventional UTM, and AE results of plain concrete tested on the TTTM show that large amounts of information at the low frequency band (<100 kHz) exist.The AE technology is a useful approach to determine the fracture locations in real time, and provides an efficient method to study the damage evolution of plain concrete. With the measured AE data, it could be concluded that some micro cracks initiate at the linear elastic stage of concrete in direct tension and propagate at the nonlinear stage, and then more micro-cracks occur intensively in concrete around the peak stress level.To study the complete tensile stress-strain response of plain concrete, a TTTM for the direct tension test was developed by reforming a conventional hydraulic UTM, and its stiffness was close to the specimen. AE technology and a static-dynamic acquisition system were also applied in the tests. The main conclusions could be drawn as follows:


Gypsum was the final product of the sulfuration reaction, and the mass percentage of gypsum in the powdery precipitated substances at different water–cement ratios was more than 50%. When the water–cement ratios was 0.37, 0.47, and 0.57, the highest Ca(OH)2 content was found for the lowest water–cement ratio. As the water–cement ratios increased, the amount of powdery precipitated substances decreased and the CaCO3 content and pH increased.This paper presents an experimental investigation of the sulfuration mechanism of concrete. The microstructure, mineral phase composition, substance content, and pH of the concrete were determined using scanning electron microscopy, X-ray diffraction, comprehensive thermal analysis, and pore-solution pH test. It was observed that light-grey spots appeared on the surface of the specimen, and a large amount of powdery precipitated substances appeared. At the initial stage of sulfuration reaction, the formation of ettringite blocked the concrete pores and densified its cracks and voids. Subsequently, ettringite reacted with H The global coal consumption in 2017 was 3731 Mtoe, which accounted for 28% of the total energy consumption [oduction ,5. From ion tons . Accordi2 concentration in industrial environment is much higher than that in general atmospheric environment. The SO2 concentration in Wuhan Iron and Steel Plant was monitored. The SO2 concentration of the crystallization-tank section in the coking ammonium sulfate workshop was 6.65 mg/m3 [2 concentration in Wuhan No. 2 steelmaking plant was 1.29 mg/m3 [Because of the special production process, the SO65 mg/m3 , and the2 diffuses into concrete and reacts with calcium-containing substances, which reduces the alkalinity of pore solution and expands the solid-phase volume, that is, concrete sulfuration [SOfuration . On the 2 environment. Furthermore, the research is beneficial to put forward the evaluation method of concrete durability in SO2 environment.Developing technologies and strategies for sulfur resistance of concrete is imperative in industrial construction. To achieve this target, understanding the sulfuration mechanism of concrete is necessary. The study on sulfuration mechanism of the concrete is the foundation for the prediction model of corrosion depth in SO2 corrosion. Tang [2 concentration. When the relative humidity was in the range of 40–90%, the sulfuration rate of the concrete was maximum at the relative humidity of 80% [2 and CO2. The results show that the sulfuration depth of the mortar was 0.5 mm at the age of 90 days, and the carbonation depth was 6 mm. Only a few investigations have been carried out through theoretical research , in situon. Tang  found thy of 80% . Scholl y of 80%  carried However, there are few studies on the sulfuration mechanism of concrete at present. The study on sulfated products of concrete is the basis step for studying the sulfuration mechanism. Sulfur oxides can react with all the calcium compounds of hydrated cement, and convert them into sulfur-bearing compounds, which mainly come under consideration includes calcium sulfite, calcium sulfate and calcium sulfoaluminate .2O3·3CaSO4·32H2O, AFt) are affected by ambient temperature [2O3·CaSO4·12H2O (AFm) at 20 °C were at pH ≤10.7 and ≤11.6, respectively [The types of sulfur-bearing compounds are different under different conditions and situations. The formation and the stability of ettringite  to explore the crack-development pattern and sulfated product-type changes at different ages. The mass, X-ray diffraction (XRD), comprehensive thermal analysis (TG-DSC), and pH of the powdery precipitated substances were tested to investigate the damage degree and final sulfated products in the concrete. The effects of water–cement ratio on the mass, substance content, and pH in the powdery precipitated substances were discussed.The diffusion and reaction of SO2 diffuses into concrete through micro-pores and micro-cracks, and continuously dissolves in water to form H2SO3. On the one hand, H2SO3 ionizes into H+ and 2SO3 reacts with O2 in the air to form H2SO4, which ionizes into H+ and SOnd SO42− .(1)SO2++, 2 ionizes into Ca2+ and OH−, which react with H+, 3, CaSO4, and H2O. Subsequently, H+, 3, CaSO4, and H2O.H3 is an intermediate product, and it can combine with O2 to form CaSO4. CaSO4 can combine with water to form hemihydrate gypsum and gypsum.CaSOGypsum reacts with calcium aluminate in concrete to form calcium sulfoaluminate. When the gypsum content is low, gypsum and calcium aluminate first form AFm.With the continuous formation of gypsum, AFm is transformed into AFt.When the temperature exceeds a certain temperature, AFt decomposes into AFm, and calcium sulfate. When the temperature dropped to a room temperature, AFm could transform to AFt again in moist environment .(14)3CaBecause of the decrease of pH, AFm and AFt decompose, and the products are gypsum and an aluminum-containing gel .(15)3CaP.O. 42.5 Ordinary Portland cement, in compliance with Chinese Standard GB 175-2007 , was useThe experimental specimens with dimension of 100 mm × 100 mm × 100 mm were prepared using three mixture proportions. The specimens were prepared in three mixtures, namely C40, C30, and C20, with three water–cement ratios of 0.37, 0.47, and 0.57, respectively. The specimens were moisture-cured at 20 ± 2 °C and 95% relative humidity for 28 days and then dry-cured until 90 days. The mixture proportion of concrete are listed in 2 is mainly generated by combustion, and it is emitted after desulfurization treatment through the chimney. The wet-desulfurization technology without Gas Gas Heater (GGH) is usually adopted in China. The SO2 concentration and temperature of the flue gas decreased, and the humidity increased. The average temperature of the flue gas was approximately 50 °C, and the humidity at the tail device reached saturation. Therefore, the temperature in this experiment was 50 °C, and the relative humidity was 98%.SO2 in the concrete is one-dimensional.The specimens were taken out and dried at 60 °C for 48 h. When the specimen temperature dropped to room temperature, the specimen surface was sealed with epoxy resin except for the two opposite sides. The purpose is to ensure that the transmission and reaction of SOThe specimens were placed on a bracket in the concrete sulfuration test chamber. The distance between adjacent specimens was not less than 50 mm.2 concentration was 9000 ppm.The ambient temperature in the sulfuration test chamber was 50 °C, the relative humidity was 98%, and the SOThe experiments were performed for four different test ages, including 2, 5, 10, and 20 days, and the specimens were taken out from the sulfuration test chamber. The powdery precipitated substances on the specimens surface were collected for 20 days.There is no generic standard of concrete sulfuration test method. According to the concrete accelerated carbonation test method in accordance with Chinese Standard GB/T 50082-2009 , the accSEM  test was employed to observe the morphology of concrete after the sulfuration reaction. Single specimen was used at one test age for each water–cement ratio. The specimen was cut into slices of 1–2 mm thickness from the surface, and then the samples with the diameter about 5 mm were obtained by pliers and tweezers. A few samples were taken out at different test ages and were immersed in ethanol to terminate all the reactions, including the hydration reaction and carbonation reaction. Before the test, the samples were removed from ethanol, air dried at room temperature for 10 min, and dried at 50 °C for 24 h. A platinum coating was subsequently applied onto the surface of the specimens for enhanced electrical conductivity. The measurements were carried out with the secondary electron detector. The accelerating voltage was 20 kV and the working distance was 10 mm.Three specimens were used for each water–cement ratio. The powdery precipitated substances were gathered from the exposed surface of specimens at the age of 20 days. The powdery precipitated substances of three specimens were crushed and mixed evenly.The powdery precipitated substances of sulfated concrete were crushed and mixed, and the powder was then passed through a 0.16-mm sieve.The powder was placed in a weighing bottle and dried at 50 °C for 24 h. Then, the weighing bottle was sealed and transferred in a drying and cooled down to room temperature.Three grams of dried powder were placed in a triangular flask. A pipette was used to accurately measure 60 mL of distilled water. Next, the distilled water was poured into the triangular flask. The triangular flask was shaken in an oscillator  for 10 min. After standing for 24 h, the solution in the triangular flask was filtered using a fast quantitative filter paper.The filtrate was tested using a pH meter .Pore-solution pH test was performed to determine the pH of the powdery precipitated substances, and it was conducted three times for each water–cement ratio. The experimental method was performed as follows:XRD  analysis was used to examine the mineral-phase composition of the surface powdery precipitated substances. The powdery precipitated substances were first pulverized using an agate mortar, and then passed through an 80-μm sieve. The powder was dried at 50 Rigaku for 24 h. The diffraction used a Cu-Kα source. Scanning was performed from 5° to 45° at a step of 0.02°.The TG-DSC  method was used for qualitative and quantitative investigation of the surface powdery precipitated substances. The preparation method of the powder was the same as that of the powder used in the XRD method. The samples were heated in air atmosphere from 30 to 900 °C at a heating rate of 10 °C/min.The appearance of the C30 specimens for sulfuration ages of 0, 2, 5, 10, and 20 days is shown in The appearance of light-grey spots on the concrete surface was due to the formation of sulfated products. These products gradually increased as the sulfuration progressed, and, therefore, the light-grey area on the concrete surface increased. Because the sulfated products blocked the pores in the concrete, the surface initially became denser. When the sulfated products exceeded the pore capacity, cracks formed on the concrete surface. Subsequently, powdery precipitated substances appeared.The appearance of concrete at water–cement ratios of 0.37, 0.47, and 0.57 in the 20 days sulfuration is shown in After cleaning the powdery precipitated substances, the appearance of sulfated concrete for 20 days is shown in 2 increased. Increasing the alkali content can accelerate the reaction rate of concrete [The cement content per unit volume of concrete increased with the decrease in the water–cement ratio, thus the content of the hydration products Ca(OH)concrete . TherefoThe crack development trend of the C30 specimen at different sulfuration ages is shown in After sulfuration for 10 and 20 days, a circle of white substances appeared around the cracks, indicating that the cracks were caused by the formation of a large amount of solid sulfated products, which exceeded the capacity of the pore structures. Sulfated products were generated inside the concrete; thus, the solid-phase volume in the cracks and voids continuously increased. The cracks and voids were significantly reduced. Finally, a large amount of sulfated products blocked the pores, resulting in excessive internal stress . Therefo2 into the concrete, H+, The mineral-phase composition of the C30 specimen at different ages is shown in ubstance b. The maubstance c, and AF+ dissolved in water to form non-gelling silica gels, which were stacked with one another  are 26.62°, 36.54°, and 39.44°. Therefore, the sulfated product of the powdery precipitated substances was mainly gypsum.The composition of the powdery precipitated substances was analyzed by XRD, as shown in 2, and CaCO3, respectively.4·0.5H2O) at 150 °C, and hemihydrate gypsum becomes anhydrous gypsum (CaSO4) at 170 °C. The content of gypsum was obtained by chemical reaction, i.e., Equation (17).The endothermic peak of gypsum was the most obvious, indicating that the content of gypsum in the powdery precipitated substances was the highest. Gypsum dehydrates and decomposes into hemihydrate gypsum 2 was the highest. Ca(OH)2 dehydrates and decomposes into CaO, as shown in Equation (19). The contents of Ca(OH)2 in the C20, C30 and C40 specimens were 9.85%, 8.81%, and 11.42%, respectively.The endothermic peak of Ca(OH)2 content was found for the lowest water–cement ratio. The cement content per unit volume decreased with the increase of the water–cement ratios. Therefore, the content of Ca(OH)2 per unit concrete decreased. However, fine aggregate of the C20 specimen was less than that of C30 specimen. Therefore, the Ca(OH)2 content of C20 specimen was slightly larger.According to the research results, the highest Ca(OH)3 was observed in the C20 and C30 specimens, and the endothermic peak of CaCO3 could not be obviously detected in the C40 specimens. CaCO3 decomposes into CaO and CO2, as shown in Equation (20). The content of CaCO3 in the C20 and C30 specimens was 16.68% and 8.25%, respectively. The carbonation of concrete occurred in air, and the larger was the water–cement ratio, the easier was the carbonation reaction. Therefore, the content of CaCO3 increased with the increase of water–cement ratios.CaCO2, Ca(OH)2, and CaCO3. SiO2 is the main component of sand and granite, and Ca(OH)2 is the hydration product of concrete. CaCO3 is the carbonation product formed by the reaction of Ca(OH)2 with CO2. Therefore, the final sulfated product was gypsum.The main components of the powdery precipitated substances were gypsum, SiO+ [2 were the most in C40 specimens. Therefore, the pH of C20 specimen was much higher than that of C30 and C40 specimens. The pH of C40 specimen was just a little lower than that of C30 specimen.+ . TherefoThe pH of the powdery precipitated substances at different water–cement ratios was acidic; thus, it was difficult for calcium sulfoaluminate to exist. Therefore, obtaining AFt and AFm in the powdery precipitated substances was impossible.In this study, the variations in the appearance, development trend of a micro-crack, product-type changes, and powdery precipitated substances of sulfated concrete were evaluated. The main conclusions are as follows:(1) The surface of hardened concrete was dark grey and smooth, and light-grey spots appeared on the surface at the initial stage of sulfuration reaction. Then, the light-grey area increased, and the surface increasingly became denser. Next, all areas on the specimen surface became light grey, and the corners of the concrete began to fall off. Finally, a large amount of powdery precipitated substances appeared. The content of the powdery precipitated substances decreased with the increase in the water–cement ratio.(2) The initial cracks in the hardened concrete were obviously reduced because of the formation of sulfated products. The number of cracks initially decreased with the sulfuration age. Following the sulfuration-reaction process, the products exceeded the capacity of the pores in the concrete; thus, new cracks appeared. In the later stage of sulfuration reaction, the continuous increase in solid products in the pores increased the number of cracks and broadened their width.+. C–S–H was decomposed into a non-gelling silica gel. Ca(OH)2 constantly dissolved and reacted; thus, the alkalinity of the concrete decreased. Finally, AFt decomposed into gypsum.(3) AFt was formed at the initial stage of sulfuration reaction. The hydration products in the concrete decomposed by H2 content was found for the lowest water–cement ratio, and the CaCO3 content increased with the increase in the water–cement ratios.(4) The average mass of powdery precipitated substances in the C20, C30, and C40 specimens was 3.67, 15.40, and 41.03 g, respectively. The pH increased with the increase in the water–cement ratio, and the pH were between 3.19 and 4.20. The final product of the powdery precipitated substances was gypsum, and the mass percentages of gypsum at different water–cement ratios were more than 50%. The highest Ca(OH)


Antibiotic resistance is a public health problem of growing concern. Animal manure application to soil is considered to be a main cause of the propagation and dissemination of antibiotic residues, antibiotic-resistant bacteria (ARB), and antibiotic resistance genes (ARGs) in the soil-water system. In recent decades, studies on the impact of antibiotic-contaminated manure on soil microbiomes have increased exponentially, in particular for taxonomical diversity and ARGs’ diffusion. Antibiotic resistance genes are often located on mobile genetic elements (MGEs). Horizontal transfer of MGEs toward a broad range of bacteria  has been identified as the main cause for their persistence and dissemination. Chemical and bio-sanitizing treatments reduce the antibiotic load and ARB. Nevertheless, effects of these treatments on the persistence of resistance genes must be carefully considered. This review analyzed the most recent research on antibiotic and ARG environmental dissemination conveyed by livestock waste. Strategies to control ARG dissemination and antibiotic persistence were reviewed with the aim to identify methods for monitoring DNA transferability and environmental conditions promoting such diffusion. In recent decades, the overuse and misuse of antibiotics in human and veterinary medicine has become a serious public health issue . The incAntibiotics are used worldwide in livestock production, thus increasing the risk of antimicrobial resistance (AMR) spread. When administered for prophylactic treatments, antibiotics can directly increase selective pressure, thus favoring the generation of antibiotic-resistant bacteria ARB; . For theAntimicrobial resistant genes can enter and persist in ecosystem through multiple pathways. They spread across soil , crops , and gutIn this review, the effect of antibiotic occurrence in animal manure on the dissemination of AMR and ARGs in agricultural fields are discussed in a critical way. The main strategies to mitigate ARGs’ dissemination and to control antibiotic persistence are also reported. Methods monitoring changes in microbial communities and transferability and environmental diffusion of DNA were addressed as well.Escherichia coli and other Enterobacteriaceae  is the most frequently identified as responsible for spreading antibiotic resistance determinants amongst commensals and pathogens of humans and domesticated animals. Moreover, int1 cassette was found in different environments, such as fresh water, sediments, and sludge  (sul genes were found in IncQ plasmid group (dfr), which confer resistance to antimicrobial trimethoprim, have been identified in both class 1 and class 2 integrons  are widely diffused in different pathogenic and environmental bacteria   are partsul) . In surfid group . Similarntegrons . Similare waters , wastewae waters . Tetracybacteria  and are bacteria . In the Essentially, ARGs’ diffusion is associated with a stress response activated by exposure to antibiotics as well as with the mobilization of several integrative and conjugative elements. ARGs’ maintenance depends on their considerably low fitness cost. In fact, once a specific ARG has been acquired by a bacterial cell, it must evolve to produce more benefits than costs in order for multiple copies of the same gene to be kept and to maintain the expression control of genes in MGEs . FurtherIn veterinary medicine, antimicrobials can be used as therapeutics and/or growth promoters. Antibiotic growth promoters (AGPs) are antimicrobial substances administered at a sub-therapeutic dose for a prolonged time with the main purpose being to improve the feed conversion rate, especially in young animals, raising the economical profit of farmers. Since 2006, both the European Union and Australia have forbidden the use of AGPs. Nevertheless, in most other countries the use of AGPs is still permitted .Among breeding farms, poultry and pig livestock have received the majority of antibiotics for therapeutic or prophylactic use , resultiBesides direct collection into aerobic or anaerobic lagoons, animal manure can undergo drying and liquid-solid phase separation. Manure solid phase, as well as whole manure if shovellable, is traditionally composted to produce biofertilizer. Currently, anaerobic digestion and biological treatments of animal manure are often adopted on intensive animal farms .Composting can substantially reduce the antibiotic load, especially during the thermophilic phase , but recBiological treatments of animal manure and wastewater, which are adopted to reduce the environmental input of nitrates, slightly decreases the levels of antibiotic residues and pathogenic bacteria . AntimicAnerobic digestion (AD) is adopted to stabilize manure with a final production of methane , 2017. AConstructed wetlands are vegetated aquatic systems that can be adopted for the treatment of wastewater and agricultural drainage water . Their aOxidizing post-treatments, as ozonation or Fenton conditions, can be used on animal or treated wastewaters to degrade antibiotics and bacteria thanks to the activity of reactive oxygen species . Among aEven though AMRs introduced in the environment with animal manure have been largely explored , contradBoth 16S rRNA amplicon and untargeted sequencing can be considered exhaustive methods for the exploration of microbial community structure in manure-fertilized soil and farm waste. Several studies on resistome diffusion in wastewater treatment plants , sewage 10 and 1012 copies per gram, respectively  and ARGs have been markedly increasing. The quantification of ARGs in soils amended with livestock and swine manure  was perfectively . Here, tith ARGs , 2019.Pseudomonas putida UWC1, Acinetobacter sp., Ralstonia eutropha, Agrobacterium tumefaciens, and E. coli. The plasmid transferability in E. coli strains was not efficient, underlying a broad but highly specific host range  and metagenomic data.AC: original draft preparation, figure and table conceptualization, review, and editing. PT, MM, and SB: review. DL: original draft preparation and table preparation. IB and PM: original draft preparation and review. All authors contributed to critically revising the manuscript and gave final approval for publication.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.