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The contribution of ethylene vinyl acetate (EVA) to enhancing cement properties, especially in terms of thermal stability and microstructural changes under elevated temperatures, has not been fully clarified. This research conducted comprehensive experiments to determine the heat-induced damage of EVA mortar and contrasted it with the control group subjected to high temperatures. The results indicate that EVA improves mortar's resistance to heat-induced degradation through gasification and decomposition processes. Notably, a strong correlation between compressive strength and ultrasonic pulse velocity (UPV) is observed. Moreover, the new phase existence of calcium acetate (CA) further reveals EVA's active participation in the cement hydration, increasing the content of ettringite (AFt) and calcium hydroxide (CH). Finally, microscopic analysis reveals voids formation due to calcium silicate hydrate (C-S-H) dehydrates after high thermal treatment. This research offers valuable insights for the utilization of EVA in construction projects subjected to elevated temperatures. [ABSTRACT FROM AUTHOR]

Hail presents a significant threat to the structural integrity of aircraft, particularly with the extensive use of foam sandwich structures in aerospace applications. Therefore, it is crucial to consider the effects of hail impact on foam sandwich structures. This paper aims to investigate the impact of ice projectiles on carbon Fiber/PMI foam sandwich structures, using both experimental and numerical simulation approaches. The gas cannon was employed to launch ice projectiles, which were then directed towards the carbon Fiber/PMI foam sandwich structures. Additionally, a numerical simulation model was developed using ANSYS/LS-DYNA software to analyse the impact of these ice projectiles. Moreover, the validity of the finite element model was confirmed through experimental verification. The study involves simulations of single-point continuous impacts of ice projectiles and multi-point simultaneous impacts on carbon Fiber/PMI foam sandwich structures, while maintaining the same total impact energy. By varying the distribution of ice projectiles, the dynamic response and damage characteristics of the target plate are analysed. Specifically, the research aims to investigative the deformation characteristics of the target plate and the energy absorption of the structure. The research results underscore the importance of considering the distribution of ice projectiles in mitigating structural damage caused by hail impact. [ABSTRACT FROM AUTHOR]

Fiber reinforced polymer (FRP) bars have received extensive promotion and application in the structural engineering. However, due to the limitations inherent in using single material, FRP reinforced concrete structures often encounter issues, such as brittle failure and inadequate energy dissipation, particularly in complex natural environments and under various loading conditions. In this study, the preparation of nano‐SiO2‐modified carbon/basalt hybrid FRP bars was carried out using the pultrusion‐winding process and ultrasonic treatment. The objective was to investigate the influence of the fiber volume ratio and mass fraction of nano‐SiO2 on the mechanical properties of FRP bars under drying and alkaline conditions. Molecular dynamics simulations were performed to construct interface models between fibers and epoxy resin in order to elucidate the toughening mechanism of nano‐SiO2 and the degradation mechanism in alkaline conditions. The research results show that elevating the substitution rate of carbon fibers and incorporating nano‐SiO2 doping bring about alterations in the brittle fracture characteristics of BFRP bars and enhance the post‐yield performance and interlaminar shear properties of hybrid FRP bars, concurrently mitigating the degradation of mechanical properties induced by exposure to alkaline solutions. MD simulations indicate that the addition of nano‐SiO2 improves the binding rate of hydrogen bonds between BF and epoxy resin, resulting in a higher interfacial energy between BF/epoxy resin compared to CF/epoxy resin. Moreover, nano‐SiO2 effectively mitigates the impact of alkaline solutions on the formation of interfacial hydrogen bonds. The findings of this study serve as a valuable reference for the design and application of FRP reinforced concrete structures. Highlights: Nano‐SiO2 modified B/CFRP bars made via extrusion‐winding & ultrasonic treatment.Improved mechanical properties and plastic deformation in Nano‐SiO2 modified B/C FRP bars.Nano‐SiO2 inhibits B/CFRP bars degradation in alkaline solution.Nano‐SiO2 bind more at BF/epoxy than CF/epoxy interface.Nano‐SiO2 reduces alkaline solution effect on interfacial H‐bonding. [ABSTRACT FROM AUTHOR]

To confirm the effect of confining pressure on the dynamic mechanical behavior of ultrahigh-performance concrete (UHPC), this study used a true triaxial split Hopkinson pressure bar test system to perform dynamic compression tests on UHPC under triaxial constraints. The confining pressure range considered was 5~10 MPa, the strain rate range was 35~80 s−1, and the steel fiber contents were 0.5%, 1% and 2%. The three-dimensional dynamic engineering stress-strain relationship and equivalent stress-strain relationship of UHPC under different confining pressures and different strain rates were obtained and analyzed in detail. The results show that under the confinement condition, the dynamic peak axial stress–strain and dynamic peak lateral stress–strain of UHPC have strong sensitivity to the strain rate. In addition, the dynamic peak lateral stress–strain is more sensitive to the confining pressure than the dynamic axial stress. An empirical strength enhancement factor (DIFc) that considers the strain rate effect and confining pressure was derived, and the impact of the coupling between the enhancement caused by the confining pressure and the strain rate effect on the dynamic strength of the UHPC under triaxial confinement was discussed. A dynamic strength failure criterion for UHPC under triaxial constraint conditions was established. [ABSTRACT FROM AUTHOR]

When compared with normal concrete, ultrahigh‐performance fiber‐reinforced concrete (UHPFRC) could signally enhance the bond with reinforcing bars. Accordingly, incorporating UHPFRC to connect precast concrete columns allows smaller bar splice lengths and provides ease of construction. In this article, a two‐stage research program was presented. First, the behavior of double‐row spliced rebars in UHPFRC was tested under direct tension, and the bars adopted internal strain measurement to characterize the bond stress distribution along the splice length. The failure of specimens was governed by UHPFRC splitting, and the bond stress of spliced rebars in UHPFRC presented a two‐local peaks profile. Second, the hysteretic performance of precast concrete columns with spliced connections based on UHPFRC was determined by full‐scaled cyclic tests and numerical simulations. Precast columns with UHPFRC connections at the column base exhibited similar ductility, energy dissipation capacity, and higher bearing capacity to the monolithic concrete columns. Finally, some practical considerations and recommendations were proposed. [ABSTRACT FROM AUTHOR]

The re-centring ability and durability of important bridges have been the main objectives in recent provisions of seismic design codes. To achieve better recoverability and durability for piers, this article presents a double-reinforced pier configuration, in which the outer layer is reinforced with fibre-reinforced polymer (FRP) rebar and the inner layer is reinforced with steel rebar. An equal flexural capacity design method was used to determine the double-reinforced configurations. The effects of the potentially influential design parameters on the seismic response of piers were studied and compared to those of conventional RC piers. The results show that the proposed design method can satisfy the ultimate capacity and durability demands. The double-reinforced piers had a better performance than conventional piers in terms of the ductility, post-yield stiffness and residual deformation. The maximum deformation and energy dissipation capacity of the double-reinforced piers were comparable to those of the conventional RC piers. The results also demonstrated that the proportion of steel reinforcement had a clear effect on the performance of double-reinforced piers. However, FRP reinforcement with a high modulus of elasticity should be avoided due to the adverse effect on ductility. [ABSTRACT FROM AUTHOR]

The bond behavior of CFRP-concrete interface is the analysis foundation for concrete structures with external strengthening CFRP. In the paper, the influences of the thickness of CFRP plate and adhesive layer on interfacial adhesive properties are investigated through the finite element program. The influence rules of the thickness on the interfacial ultimate bearing capacity and the effective bond length are performed. The results show that the thickness of adhesive layer and CFRP plate has a significant effect on the interfacial performance of CFRP-concrete.

In this study, freezing and thawing tests were conducted on lightweight concrete and aggregate at different freezing rates (one cycle per day and six cycles per day) in order to investigate their freeze--thaw resistance and clarify the effects of various lightweight aggregate properties (density, water content, crushing strength, and pore structure) and freezing rates on their freeze--thaw resistance. The results indicate a high and direct correlation between the freeze-thaw resistance of lightweight concrete and aggregate. The higher density lightweight aggregate concrete showed superior freeze-- thaw resistance at each freezing rate, while concrete made with the lower density aggregate achieved freeze--thaw resistance only at the low freezing rate. The aggregate tests showed similar results, too. The freeze--thaw resistance can be influenced by the properties of lightweight aggregate and the freezing rate, but the most fundamental factor is the pore structure of the aggregate. Lightweight aggregate, which has lower pore volume and more small pores, can have good resistance to freezing and thawing. DOI: 10.106l/(ASCE)0899-1561(2008)20:1(78) CE Database subject headings: Concrete; Aggregates; Freeze-thaw; Pore size distribution.

The improved properties of ethylene-vinyl acetate (EVA)-modified cement-based materials have not been fully clarified, especially crack resistance and pore structure. The purpose of this research was to investigate the influence of EVA copolymer on the mechanical performances and microstructural properties of cement paste. Strengths, autogenous and drying shrinkage, and water absorption expansion were investigated to evaluate the mechanical properties and volume stability. The ring restrained shrinkage and chloride permeability tests revealed the crack resistance and enhancement of impermeability. The microstructures of EVA-modified cement-based materials were characterized by scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP) techniques. The experimental results indicated that mixing EVA into cement-based materials increased the flexural strength, reduced the crack propagation and chloride ion penetration, and reduced the negative capillary pressure by improving the water retention. The addition of EVA resulted the remarkable reduction of harmful pores. The optimal mass fraction of EVA powder was approximately 4%. [ABSTRACT FROM AUTHOR]

The dynamic mechanical properties of materials under high strain rate are generally measured by the split Hopkinson pressure bar (SHPB). However, due to the high risk of operation of this kind of equipment and the mutual influence of test parameter settings, experimental experience has great influence on the test results, which makes it difficult for students to learn and operate. The virtual simulation experiment teaching project developed in this paper can get different experimental results and test precision, even failure test by setting different test parameters, so as to help students to master and analyze the rules of measurement parameter setting, and cultivate their practical operation ability. [ABSTRACT FROM AUTHOR]

Lack of post-yield stiffness and corrosion resistance could inevitably result in a considerable loss of seismic performance for steel reinforced concrete (RC) piers. Fibre reinforced polymer (FRP) reinforcement can provide high tensile strength and protection from corrosion. To achieve a better post-yield stiffness and durability for piers, FRP/steel double-reinforced configurations were designed by the proposed flexural-capacity design method. A seismic fragility assessment was also conducted to investigate the effectiveness of design parameters, namely the ultimate tensile strength of FRP reinforcement, elastic modulus of FRP reinforcement, and ratio of steel reinforcement for a double-reinforced configuration to that for a steel RC configuration ( ρ steel / ρ prototype ). The results demonstrated that the FRP/steel double-reinforced piers satisfied the mentioned objectives, while the fragility of these piers was a 30.2% less than that of conventional steel RC piers. A 79.9% higher median PGA at the collapse damage state was achieved, when the elastic modulus of FRP reinforcement changed from 164 to 80.7 GPa. An increase in the median PGA of 34.8% can be achieved along with the increase of the ultimate tensile strength of FRP reinforcement. When ρ steel / ρ prototype was approximately 66%, FRP reinforcement exhibited the highest effectiveness on the seismic performance of piers. [ABSTRACT FROM AUTHOR]

Lack of corrosion resistance and post-earthquake resilience will inevitably result in a considerable loss of function for concrete bridge piers with conventional steel reinforcement. As an alternative to steel reinforcement, shape memory alloy (SMA)-based reinforcing bars are emerging for improving the seismic performance of concrete bridge piers. This paper presents an assessment of concrete bridge piers with different reinforcement alternatives, namely steel reinforcement, steel-SMA hybrid reinforcement and SMA reinforcement. The bridge piers with different reinforcements are designed having a same lateral resistance, or in other words, the flexural capacities of plastic hinges are designed equal. Based on this, numerical studies are conducted to investigate the relative performance of different bridge piers under seismic loadings. Seismic responses in terms of the maximum drift, residual drift as well as dissipated energy are obtained and compared. The results show that all the three cases with different reinforcements exhibit similar maximum drifts for different earthquake magnitudes. The SMA-reinforced bridge pier has the smallest post-earthquake residual displacement and dissipated energy, whereas the steel-reinforced pier shows the opposite responses. The steel-SMA hybrid reinforcement can achieve a reasonable balance between the residual deformation and energy dissipation. [ABSTRACT FROM AUTHOR]

Determining the rheological properties of cement-based materials and selecting the types and amounts of superplasticisers (SPs) that are appropriate for actual projects are important and topical issues. In this study, the rheological properties of cement pastes with different types of SP were investigated using an AR2000ex rheometer. A colour function method (CFM), in combination with the experimental data, was used to calculate and determine the rheological properties. This paper presents a new selection method (rapid determination system (RDS)) for determining the most suitable SPs. The results show that shear stress, plastic viscosity, normal stress and other mechanical properties are influenced by different volumes and types of SPs. Based on the CFM and RDS, 0·38% HW (a polycarboxylate-type SP) was determined to be the most appropriate. [ABSTRACT FROM AUTHOR]

Concrete exposed to the tidal zone of the Yellow Sea and bearingCrassostrea gigas(CG) with differing areal coverages was investigated for evidence of biologically induced corrosion prevention. The experimental results indicated that both the chloride ion profile and the neutralization depth of the concrete decreased with increasing CG coverage. Moreover, the water absorption rate and the chloride ion permeability of concrete with the original surface intact also declined with increasing degrees of CG coverage. However, the water absorption rates of three concrete samples with 2 mm of the surface layer removed were similar, as was their chloride ion permeability. Mercury intrusion porosimetry tests indicated that CG significantly reduced the pore structure of the concrete surface layer. SEM observation revealed that the CG cementation membrane and left valve were tightly glued to the concrete surface and had a dense structure. Concrete durability indices showed that high CG coverage greatly improved concrete durability. [ABSTRACT FROM AUTHOR]

• CFRP/PMI sandwich panels were experimentally studied under ice projectile impact with different incident angles and impact velocities. • The impact force of the ice projectile and the peak deformation of the target plate correlate with the ice projectile's normal velocity. • The energy absorption of the foam layer shows a quadratic positive correlation with the normal velocity of the ice projectile. The integration of composite sandwich structures in aircraft design necessitates consideration of hail impacts within aerospace applications. This investigates the dynamic response and damage characteristics of a carbon fibre/PMI foam sandwich structure under hail impact through both experimental and numerical simulation methods. These methods analyse the impact velocity, fibre panel thickness, and angle of incidence of the ice projectiles. The study establishes relationships among various parameters such as ice projectile impact force, foam absorption energy, and target plate deformation in relation to the impact velocity and angle of incidence. The damage sustained by the carbon fibre/PMI foam sandwich (CPS) structure due to ice projectile impact was systematically categorized and examined. Additionally, the effects of normal and tangential impact velocities on the target plate's dynamic response during oblique impacts were investigated. This research serves as a valuable reference for understanding the dynamic response and damage characteristics of composite foam sandwich structures subjected to ice projectile impacts, With a focus on the carbon fibre/PMI foam sandwich structure. [ABSTRACT FROM AUTHOR]

This paper aims to investigate the effect of the polypropylene fibre (PP) and basalt fibre (BF), singly or in hybridization, on the workability, mechanical, chloride resistance and pore structure characteristics of concrete. Sixteen mixtures consisting of PP and BF, both at volume content of 0.0, 0.1, 0.2 and 0.3%, were fabricated, and the slump, compressive, splitting tensile, flexural and charge passed were tested. The results show the hybridization of the PP and BF can improve three types of strength of concrete in comparison to their single fibre. Nevertheless, the hybridization is not always conducive, and the synergy of fibres is proposed and divided into positive and negative effects. The combination of the PP and BF both at content of 0.1% achieves the best mechanical performance, and is recommended for practical usage. Incorporating fibres reduces the chloride resistance of concrete, and the hybridization is helpless to this phenomenon; even the reduction is intensified at a highly hybrid fibre volume. However, increasing the curing age can mitigate this adverse effect caused by fibres. Furthermore, the microstructures were explored to elucidate the macro-properties of concrete in terms of interface and pore structure. [ABSTRACT FROM AUTHOR]