Initial Elastic Modulus Research Articles

Experimental Study on Uniaxial Compression Behavior of Fissured Loess Before and After Vibration

Fissured loess is one of the sources of geological hazards such as landslides and collapse under dynamic load. In this study, acrylic pipes with an inner diameter of 62 mm were processed into molds with different inclination angles (α = 0°, 15°, 30°, 45°, 60°, and 90°), and soil samples with preset fissure angles were prepared in two parts, i.e., loess block and weak interlayer. The sample was first vibrated by a test bench with sinusoidal waveform output, followed by uniaxial compression tests to investigate the mechanical properties of fissured loess before and after vibration. Results indicate that the failure mode of fissured loess is independent of the vibration disturbance; four types of failure modes were found after vibration, i.e., compressive fracture failure at α = 0° and 15°, slip failure at α = 60°, slip-fracture coupled failure at α = 45°, and compressive shear failure at α = 30° and 90°. The effect of vibration parameters on the stress–strain curve of fissured loess is mainly reflected in the decrease of both peak strength and initial elastic modulus. U-shaped changes of uniaxial compressive strength were observed in the ranges of 0°–45° and 45°–90°, respectively.

IMPROVEMENT OF MECHANICAL PROPERTIES OF WOOD AT THE ACCOUNT OF THEIR ADHESIVE

High-quality solid wood of deciduous and coniferous species in Ukraine is becoming less and less every year. Therefore it is necessary to use that wood which is available. Various methods and techniques are used to improve the mechanical properties of wood. One of them is gluing wood boards of different thickness. In this article we present the following studies taking into account the actual work of the material.
 The method of researches of glued wood of different breeds by axial compression along fibers by short-term loading at standard humidity (by increase of displacements) is given. Complete deformation diagrams “stress σc - deformations uc” are constructed and the main parameters are established: maximum disturbances, critical deformations, initial modulus of elasticity. The strength of glued wood increases in comparison with the indicators of continuous humidity of 12% at the age of 60 by 13-25%; critical deformations slightly increase or decrease in one direction or another; the initial modulus of elasticity increases by 13–31%.
 This improvement is due to the ingress of glue into the body of wood, ie due to gluing is the modification of wood and the formation of composite material. The strength of such a composition is directly affected by the thickness of the board. The smaller the thickness of the board, the stronger the product.
 It is established that the deformation diagrams of glued wood have two branches: ascending and descending. That is, the work of such composite materials is observed, both in the subcritical stage and in the supercritical stage. Therefore, the samples have a certain residual strength after passing the maximum stress values.
 It has been established that gluing wood increases the strength and initial modulus of elasticity of the composite material and depends on the thickness of the board.

Experimental Study on Dynamic Mechanical Characteristics and Energy Evolution of Sandstone under Cyclic Impact Loading

In order to study the dynamic mechanical properties of the surrounding rock of roadway in deep mines with rock burst, cyclic impact compression tests of sandstone under different impact velocities were carried out by using the split Hopkinson pressure bar (SHPB) test system, and the dynamic stress-strain curves of the samples under cyclic impact loads and the relationship between energy dissipation and impact numbers were analyzed. The results show that, as the impact loading times increase, the initial elastic modulus of sandstone samples decreases, the peak stress decreases, and the peak strain increases; the average strain rate increases. The cumulative damage of sandstone samples under impact load is significantly affected by impact velocity and times. During the cyclic impact test, the reflected energy of sandstone increases with the increase of impact numbers, while the transmitted energy decreases and the absorbed energy increases; the cumulative specific energy absorption variable is introduced, and the cumulative specific energy absorption value of the samples increases with the increase of impact numbers, which can better characterize the variation of energy accumulation and dissipation of sandstone samples under cyclic impact.

Nonlinear models to predict stress versus strain of early age strength of flowable ordinary Portland cement

In this study, the impact of two types of polymers on the stress-strain (σ − ε) behaviour, elastic modulus and toughness of cement-based cementitious material. Cement paste modified with two types of polymer up to 0.06% (% wt) with an interval of 0.02% were tested. The σ − ε behaviour of modified cement with polymeric admixtures was examined for curing periods up to 28 days. Adding polymers improved the flowability of cement by 7% to 26%, but it decreased the water/cement ratio () by 12% to 43%, depending on the polymeric structure and its content. The nonlinear Vipulanandan p-q model was tested to predict the σ − ε relationship of the modified cement with polymers and was compared with the β model. The Vipulanandan p-q model and β model performance were evaluated by comparing with several functional models using residual error and root mean square error. The compression strength of cement increased by 107% to 257% when 0.06% of polymers were added to the cement. Modifying the cement with polymeric admixtures enhances cement's initial elastic modulus (Ei) by 23% to 240% according to polymeric admixture types, curing age (t), and polymeric admixture percent. During the early curing time, the cement modified with polymeric admixture was able to withstand large deformations that mean increase the samples' ductility, but with increasing curing, the cement modified polymers become brittle and the strain at failure reduced. The modulus of elasticity and total toughness of the cement paste were correlated well with compressive strength.

Method of determination the initial elasticity modulus and timber deformation modulus under the influence of acid environment

The technique of experimental researches of timber by axial compression along fibers by short-term loading for operation in various acid environments (hydrochloric, acetic and lactic acids) during displacements increase is developed. The results of researches of the initial elasticity modulus and the deformations modulus taking into account the factor of environment aggressiveness are given. It is found that the effect of acids on wood with different impregnation periods significantly reduces the initial elasticity modulus and deformation modulus and depends on the impregnation period.

СИЛОВЫЕ ИСПЫТАНИЯ ПЛЕНКИ ЭТФЭ

Studies of mechanical properties of ethylene-tetrafluoroethylene (ETFE) film they are relevant for wide application in the construction of translucent coatings in the climatic conditions of Russia, especially in the Arctic zone. Power tests were performed for a film with a thickness of 250 microns on an INSTRON bursting machine, as well as with a uniformly distributed load at positive and negative temperatures. The initial modulus of elasticity according to GOST 34370-2017 was established, which was 1090 MPa. Three loading stages have been identified for the calculations of translucent coatings. In the elastic stage of operation of the ETFE film, the average modulus of elasticity was 35.8 MPa, in the elastic-plastic stage – 1.78...2.71 MPa and in the plastic stage of operation – 0.06...0.086 MPa. Force tests of a membrane made of ETFE film with a thickness of 250 microns on a power triangular frame with a uniformly distributed load of up to 8,577 kPa did not lead to rupture of the membrane at any positive (+15 ...+18 оС) not at subzero temperatures (-23...-29 оС). Repeated mechanical damage (cuts) of the membrane under a load of 8.50 kPa at a temperature of -26 оС also did not lead to its rupture. The deflections of the membrane at positive temperatures reached 84 mm, at negative temperatures – 58.2 mm. Power tests of the ETFE film have shown its ultra-high strength characteristics, which makes it possible to widely use it to create a comfortable environment in structures erected in the Arctic and other territories of Russia when localizing production in Russia.

Strength properties of chemically modified solid woods

A new composite material based on solid wood and polymer composition ‘silor’ under surface modification was obtained. A method of experimental studies of the compressed polymer composition ‘silor’ of solid hardwood by compression along the fibers has been developed. Experimental studies of such composite materials under a rigid test regime have been carried out. Complete diagrams of deformation such materials from the beginning of loading to destruction are constructed (ascending and descending branches). The main mechanical properties of new composite materials based on solid wood are determined. The method of determining the initial modulus of elasticity and modulus of deformation on the basis of graphs "E-η". It is established that the modification of the polymer composition ‘silor’ significantly improves the strength and deformability of hardwood (birch, alder, ash). With surface modification of solid hardwood, the maximum stresses increase by 12–22% in comparison with solid 60 year old wood with a moisture content of 12%. Deformability decreases within 17–25%. The initial modulus of elasticity of the studied samples is higher by 21–38%.

A tension stiffening model for FRCM reinforcements calibrated by means of an extended database

In the context of the mechanical behavior of the FRCM (Fiber Reinforced Cementitious Matrix) composites as structural retrofitting technique, an accurate analysis of its tensile performance by collecting an extended database of experimental results is presented. The experimental data concern the results of more than 750 tensile tests carried out on FRCM coupons, made with different types of constituent materials (mortar and fiber grid), different geometrical properties and tested with different test set-ups. The data are subdivided into uniform classes and some exclusion criteria are adopted. The influence of the mechanical and geometrical parameters of the constituents on the tensile response of the FRCM reinforcement is assessed. Thus, the relations between the peculiar points of the experimentally-obtained stress–strain law (cracking stress, failure stress, initial elastic modulus, stiffness of the specimens at failure) and the mechanical properties of the constituents are defined. Those relations are the basis to derive an analytical provisional formulation able to reproduce the stress–strain law of the FRCMs, starting from geometrical and mechanical features of the constituents. The proposed tension stiffening model is validated through comparisons with experimental results of FRCM made with different grid types and different mortar nature.

Novel rechargeable calcium fluoride dental nanocomposites

ObjectivesComposite restorations with calcium fluoride nanoparticles (nCaF2) can remineralize tooth structure through F and Ca ion release. However, the persistence of ion release is limited. The objectives for this study were to achieve long-term remineralization by developing a rechargeable nCaF2 nanocomposite and investigating the F and Ca recharge and re-release capabilities. MethodsThree nCaF2 nanocomposites were formulated: (1) BT-nCaF2:Bisphenol A glycidyl dimethacrylate (BisGMA) and triethylene glycol dimethacrylate (TEGDMA); (2) PE-nCaF2:Pyromellitic glycerol dimethacrylate (PMGDM) and ethoxylated bisphenol A dimethacrylate (EBPADMA); (3) BTM-nCaF2:BisGMA, TEGDMA, and Bis[2-(methacryloyloxy)ethyl] phosphate (Bis-MEP). All formulations contained 15% nCaF2 and 55% glass particles. Initial flexural strength and elastic modulus, F and Ca ion release, recharge and re-release were tested and compared to three commercial fluoride-containing materials. ResultsBT and BTM nCaF2 composites were 3–4 times stronger and had elastic modulus 2 times that of resin-modified glass ionomer controls. PE-nCaF2 had comparable strength to RMGIs. All nCaF2 composites had significant F and Ca ion release and ion rechargeability. In F and Ca recharging cycles, PE-nCaF2 had the highest ion recharging capability among nCaF2 groups, followed by BT-nCaF2 and BTM-nCaF2 (p < 0.05). For all recharge cycles, ion release maintained similar levels, demonstrating long-term ion release was possible. Furthermore, after the final recharge cycle, nCaF2 nanocomposites provided continuous ion release for 42 days without further recharge. SignificanceNovel nCaF2 rechargeable nanocomposites exhibited significant F and Ca ion release over multiple recharge cycles, demonstrating continuous long-term ion release. These nanocomposites are promising restorations with lasting remineralization potential.

Nonlinear characteristics and a new fractional constitutive model for warp-knitted NCF composites under normal loading conditions

This paper presents a new fractional constitutive model to reveal the nonlinear and viscoelastic properties of fabric composites under normal loading conditions. The uniaxial tensile tests for warp-knitted non-crimp fabric (NCF) composites under different strain rates were carried out, and their nonlinear characteristics and quasi-yield behaviors under normal loading conditions were investigated. A new nonlinear constitutive model was then proposed by employing the fractional calculus operator theory, and the proposed models were verified by the experimental results and implemented in the simulations based on UMAT subroutine in FEA code ABAQUS. Results show that the warp-knitted NCF composites' filling yarns would produce greater yarn geometric deformation than the warp yarns due to their yarn waviness. The variations of initial elastic modulus under increasing strain rate show rising tendencies, which uncovers the materials’ strain-rate effect. Owing to the expressiveness of deformation mechanisms offered by model parameters, the proposed model could effectively present the nonlinear and viscoelastic characteristics of the fabric materials under normal loading conditions. In addition, The UMAT subroutine shows a good applicability, and the FE model with the Equation Constraint could simulate the uniform stress states accurately.

The effect of overconsolidation on monotonic and cyclic behaviours of frozen subgrade soil

This paper presents an experimental investigation on the monotonic and cyclic behaviours of the overconsolidated subgrade soil used in the Lanzhou-Urumchi high-speed railway at the temperature of -3°C. The important mechanical parameters of the overconsolidated soil, i.e., failure strength, initial elastic modulus, accumulative permanent strain and resilientmodulus were experimentally studied by using triaxial tests. Testing results indicate that the failure strength, initial elastic modulus, dilatancy and stress–strain relationship of frozen sample are all dependent to the overconsolidation ratio (OCR). The failure strength is slightly more susceptible to the overconsolidation ratio than the initial elastic modulus. The anisotropically consolidated path (k0=0.5-1) has a negligibleimpact on the stress–strain-strength behaviors. The development characteristics of accumulative permanent strain and resilient modulus are collectively dominated by the overconsolidation ratio and shear stress amplitude. Axial permanent strain acceleratedly accumulates with the decrease of the overconsolidation ratio at the same shear stress amplitude. According to the shakedown theory, allowable cyclic stress ratio was introduced to analyze accumulative deformation characteristics of frozen sample. The overconsolidation ratio and loading cycle number have negligible influences on the allowable cyclic stress ratio of frozen subgrade soil. Four cyclic stress-paths with the same shear stress amplitude were adopted in triaxial cyclic tests with aim to investigate the path-dependent deformation behaviors of frozen subgrade soil. The relationships of axial permanent strain under different cyclic stress-paths are roughly proportional, regardless of the cyclic stress ratio (CRS) and loading cycle number. Those quantitativerelationships can be completely determined by the overconsolidation ratio and cyclic stress-path parameter. The effect of cyclic stress-path on resilient modulus is more than the effect of overconsolidation ratio and less than the effect of shear stress amplitude. Several empiricalmodelswere proposed for the overconsolidated subgrade soil at the negative temperature to characterize the evolution laws of the above-mentioned engineering properties. Those empiricalmodels are capable of giving well descriptions of the development of those engineering parameters for frozen subgrade soil over a wide range of the oveconsolidation ratio.

Deformation Characteristic of a Supported Deep Excavation System: A Case Study in Red Sandstone Stratum

A complete case record of a deep foundation pit with pile-anchor retaining structure excavated in red sandstone stratum is presented in this study. The horizontal displacement of pile top, the horizontal displacement at various depths, the axial force of anchor cable, and ground settlement during construction are measured. A three-dimensional numerical model is established to analyze the additional stress and deformation induced by the excavation and the accuracy of the FEM model is verified by comparing with field measured results. Both the measured and numerical simulation results show that the deformation of the pile-anchor supported deep excavation is significantly affected by the spatial effect. The results show that the deformation in the middle of the foundation pit is greater than the pit angle and that the deformation of the long side is greater than that of the short side and gradually decreases from the middle to the pit angle. The deformation and stress in the middle of the long side of the foundation pit are the largest, which is the most unfavorable part. With the increase of vertical excavation depth, the spatial effects tend to increase, and the influence scope of spatial effects is about five times the vertical excavation depth in the red sandstone stratum. The ground settlement outside the pit is mainly distributed in a groove shape, and the maximum settlement occurs about 8.5 m away from the pit edge. Finally, parametric studies of reinforcement parameters indicated that 1.5–2.0 times the initial elastic modulus and cohesive force of soil should be used for reinforcement. It is recommended that the ranges for pile diameter, pile spacing, anchor cable prestressing and inclination angle should be selected as 0.8–1.2 m, 1.4–2.0 m, 100–150 kN, and 10°–20°, respectively.

Numerical study of ground deformation during underground coal gasification through coupled flow-geomechanical modelling

This paper presents a coupled flow-geomechanical model to study the ground deformation due to geoenergy applications involving complex thermo-hydraulic-chemical–mechanical coupled processes, such as underground coal gasification (UCG). The model is developed by coupling two sub-models, that is, the chemical reactions associated flow model that can predict temperature development and cavity growth and the geomechanical model that considers the temperature-dependent thermo-mechanical properties of geologic materials and the conversion of coal to the cavity. Numerical simulations of a field-scale UCG project with the linked vertical wells (LVW) were conducted through coupled flow-geomechanical modelling. The effects of the thermo-mechanical properties of the strata adjacent to the coal seam and the UCG operational conditions on the temperature distribution, cavity formation, and ground deformation in the operating stage of UCG were studied. Simulated results showed that temperature of over 1200 K would be obtained between the injection well and the production well in the coal seam while the 400 K isotherm only moved less than 2 m vertically in the strata near the UCG reactor. Cavity with long forward length and short backward length was formed between the injection well and the production well. Ground deformation during UCG was caused due to the combined effects of temperature and cavity evolution. The parametric sensitivity study showed that when the initial elastic modulus of the surrounding strata decreased from 4 GPa to 1 GPa, its effect on the ground deformation beyond the right side of the production well was not of significance. The ground deformation was not sensitive when the initial thermal expansion coefficient of the surrounding strata was reduced to the order of magnitude of 1.0-6 (K−1). In addition, adjusting the supply rate of O2 and modifying the location of the horizontal gasification channel can control the ground deformation during UCG. The coupled flow-geomechanical model presented in this paper can be helpful in the safety control of UCG.

Study on sliding friction characteristics of magnetorheological elastomer—copper pair affected by magnetic-controlled surface roughness and elastic modulus

To optimize the online friction coefficient adjustment, it is necessary to study the parameter change features of the magneto-sensitive polymer and its influence on the friction characteristics under magnetic field. A series of magnetorheological elastomers (MREs) with different initial surface roughness were prepared, and a sliding friction platform with MRE—copper block pair was built to carry out magnetic-controlled friction characteristic experiment. Results show that the sliding friction coefficient of MRE decreases with the increase of the magnetic field, but the degree of reduction is quite different under different initial surface roughness and elastic modulus. When the initial surface roughness of MRE is between 0.5 and 2.5 μm and the carbonyl iron particles volume fraction is between 10% and 15%, its magnetic-controlled friction coefficient has the largest reduced value of 22.75%. Moreover, features of elastic modulus and surface topography under magnetic field were tested and analyzed. By combining with the single peak contact model and the friction binomial law, the relationship between the surface roughness and elastic modulus of MREs and the sliding friction force is deduced, and it is proved that the friction coefficient is affected by the coupling effect of surface roughness and elastic modulus. The magnetic-controlled elastic modulus is the key factor, which determines the overall downward trend of the friction coefficient of MREs. Magnetic-controlled surface roughness also plays an important role in the adjustable range of friction coefficient, and reducing the initial surface roughness can increase the magnetic-controlled friction coefficient adjustable range.

Curcumin-loaded composite hydrogel based on scallop (Patinopecten yessoensis) male gonad hydrolysates and κ-carrageenan: Characterization and in vitro digestibility

A composite hydrogel composed of scallop (Patinopecten yessoensis) male gonad hydrolysates (SMGHs) and κ-carrageenan (KC) was fabricated with a designed microstructure to preserve curcumin (Cur) during the upper gastrointestinal tract (GIT). The presence of KC obviously increased the initial elastic moduli (8.2–761.8 Pa), shortened the relaxation time T23 (517.37–420.10 ms) as well as caused the blue shift of the emission peak and quenched the intrinsic fluorescence of Cur in SMGHs/KC-Cur system, signifying the solid combination within SMGHs and KC. In addition, the red shift in O–H stretching bands and blue shift in amide I bands in SMGHs/KC-Cur further accentuated the involvement of hydrogen bonds and electrostatic interactions within SMGHs, KC and Cur. The disappearance of crystalline structures suggested the successful embedment of Cur in the hydrophobic core of SMGHs. Moreover, the microstructure of the hydrogels varied from heterogeneous with tattered large pore cavities and scattered patches to homogeneous distribution with dense mesh and solid network wall. These scenarios caused a more compact network of SMGHs/KC-Cur than SMGHs-Cur to protect Cur from releasing in simulated intestinal and simulated colonic phases with slower released rate, both of which had the final extent of Cur release exceeding 90%. Furthermore, cryo-SEM showed that the significant release of Cur from hydrogels in the simulated intestinal phase was due to SMGHs matrix erosion with even larger pore sizes, tattered network and thinner network wall. Therefore, it is suggested that SMGHs/KC hydrogels with biocompatibility and good tolerance to acid environment could be reliable and desirable soft materials to embed and deliver Cur to the colon, having potential applications in functional foods and biological therapeutic purposes.

Effects of hydro-mechanical material parameters on the capillary barrier of reinforced embankments

This paper presents a numerical analysis of the water infiltration process in embankments reinforced with permeable geosynthetics. An emphasis is given to the study of the capillary barrier permanence at the soil-geotextile interface. For the analysis, an infiltration-deformation coupled model is used, and the numerical results are validated with experimental data. The proposed model properly describes the main characteristics of the capillary barrier phenomenon observed experimentally. A parametric analysis is performed to investigate the effects of the initial void ratio (e0), overconsolidation ratio (OCR), initial shear elastic modulus (G0), coefficient of compressibility (λ), anisotropy of the hydraulic conductivity (kr), initial suction (ψi), and water retention curve parameters (α and n′) on the performance of the capillary barrier during a rain infiltration process. Finally, a statistical analysis is carried out to evaluate the parameters that have influence on the development of pore water pressure (PW). The implemented infiltration-deformation coupled model shows the effect of the hydraulic parameters on the development of the capillary barrier -as commonly considered in conventional analysis- as well as the effect of the mechanical parameters of the soil and geotextile. The overall results highlighted the capability of the model, in combination with statistical analyses, to capture the complexity of the capillary barrier development in reinforced soil structures.

Redox-Responsive Hydrogels with Decoupled Initial Stiffness and Degradation.

Disulfide-cross-linked hydrogels have been widely used for biological applications because of their degradability in response to redox stimuli. However, degradability often depends on polymer concentration, which also influences the hydrogel mechanical properties such as the initial stiffness. Here, we describe a one-pot cross-linking approach utilizing both a thiol-ene reaction through a Michael pathway with divinyl sulfone (DVS) to form non-reducible thioether bonds and thiol oxidation promoted by ferric ethylenediaminetetraacetic acid (Fe-EDTA) to form reducible disulfide bonds. The ratio between these two bonds was modulated by varying the DVS concentration used, and the initial shear or elastic modulus and degradation rate of the hydrogels were decoupled. These gels had tunable release rates of encapsulated dextran when exposed to 10 μM glutathione. Fibroblast encapsulation results suggested good cytocompatibility of the cross-linking reactions. This work shows the potential of combining DVS and Fe-EDTA to create thiol-cross-linked hydrogels as redox-responsive drug delivery vehicles and tissue engineering scaffolds with variable degradability.

Experimental investigation and prediction model for UCS loss of unsaturated sandstones under freeze-thaw action

Sandstone is widely distributed in cold regions and the freeze-thaw deterioration of them has caused many geological engineering disasters. As an important and direct index of frost resistance, the strength loss of sandstones under freeze-thaw actions should be investigated to provide a guidance for the stability assessment of geological engineering. In this research, the UCS (Uniaxial compressive strength) loss of six typical sandstones with different water contents after 0, 20, 40 and 60 freeze-thaw cycles was measured in the laboratory. The experimental results indicated that the freeze-thaw damage was more serious in sandstones containing high water contents, and the critical saturations for causing a significant loss of UCS under freeze-thaw were 60%-80% for these sandstones. Below this critical saturation, the UCS loss of the sandstones was mainly caused by water weakening rather than freeze-thaw damage. Besides, a developed strength prediction model was proposed by combining the exponential decay function and multiple linear regression method. The initial porosity, elastic modulus and tensile strength of fresh sandstones were a good parameter combination to accurately determine the decay constant in this developed model. The main novelty of this model is that it can accurately and easily estimate the UCS loss of sandstones after any freeze-thaw cycle only using the initial parameters of fresh sandstones, but it does not need to perform freeze-thaw and mechanical strength experiments. This study not only provides an accurate prediction model of UCS under freeze-thaw, but also makes a contribution to better understanding the frost resistance mechanism of sandstones.

Triaxial tests on the overconsolidated methane hydrate-bearing clayey-silty sediments

Significant experimental efforts have been made to understand the mechanical behaviors of hydrate-bearing sediment; however, studies on the influence of over consolidation conditions on hydrate-bearing sediment are quite rare, while a series of exploratory drilling surveys for hydrate in hydrate-bearing sediment has reported that the phenomenon of over consolidation or apparent over consolidation is widespread. In this study, we present triaxial test results of influence of the over consolidation on hydrate-bearing clayey-silty sediment. The results reveal that both the tested normally consolidated and overconsolidated hydrate-bearing sediment appear to undergo strain-hardening and volumetric contraction, although the increasing over consolidation ratio would weaken the strain-hardening phenomenon and enhance the initial elastic modulus and failure strength. In addition, the increasing hydrate saturation would also increase the initial elastic modulus and failure strength and decrease the volumetric strain of the overconsolidated hydrate-bearing sediment. The mechanism controlling the influence of over consolidation on the hydrate-bearing sediment has been further investigated and discussed by scanning electron microscopy, and it is found that the over consolidation could damage a certain proportion of the cementation structure formed by the hydrate, while increasing the particle occlusion and strengthening the sediment. Under low over consolidation condition, these two mechanisms may almost counteract each other, while under high over consolidation condition, the strengthening mechanism caused by over consolidation is dominant.

Uniaxial compression performance and stress–strain constitutive model of the aluminate cement-based UHPC after high temperature

In this study, a total of 72 prism specimens were manufactured to investigate the steel fiber volume fraction and exposure temperature on the uniaxial compression performance of the aluminate cement-based ultra-high performance concrete (A-UHPC). The main uniaxial compression performances of the A-UHPC after high temperature were examined, including the apparent characteristic, mass loss, failure mode, compressive strength, peak strain, initial elastic modulus and compressive stress–strain curve. As the exposure temperature increased, the failure mode of the non-fiber specimen showed a trend of transition from brittleness to ductility, the uniaxial compressive strength first increased and then decreased and the peak strain gradually increased. However, the initial elastic modulus continued to decrease. Subsequently, the calculation formulas of the uniaxial compressive strength, peak strain and elastic modulus considering the influence of temperature were proposed through regression analysis, and the uniaxial compression stress–strain constitutive model of the A-UHPC with 3% volume steel fiber was established and verified. Finally, the deterioration mechanism of the A-UHPC after high temperature was revealed by SEM for microscopic phase tests.