Ultra High Toughness Cementitious Composites Research Articles

Punching shear tests and design of UHTCC-enhanced RC slab-column joints with shear reinforcements

Reinforced concrete (RC) flat slab structure may suffer progressive collapse, which is usually caused by the punching shear failure of slab-column joints. Existing research has shown that the utilization of shear reinforcements or ultra-high toughness cementitious composite (UHTCC) in slab-column joints is efficient in improving their punching shear performance. In this study, shear reinforcement was introduced into UHTCC-enhanced RC slab-column joints. Specimens of UHTCC-enhanced slab-column joints considering the effect of shear reinforcements were tested. The cracking development process, bearing capacity, and ductility were analyzed. Yield line theory and critical shear crack theory were adopted to predict flexural and punching shear capacities, respectively. Finally, the failure patterns of the specimens were discriminated by comparing the predicted punching shear and flexural capacities, taking the ductile coefficient into account. The theoretical results combined with test results show the effect of shear reinforcement on the behavior of UHTCC-enhanced joints. Significant improvement in the bearing capacity and ductility of joints is achieved by applying shear reinforcement. The failure pattern of a joint varies from premature punching shear failure to flexural-triggered punching shear failure with the application of UHTCC, and this transform is more pronounced with shear reinforcement applied into the UHTCC-enhanced joint.

Study on the freezing resistance and repair technology of prestressed high-strength concrete pipe piles

This article takes a prestressed high-strength concrete tube pile (PHC tube pile) in Tianjin Port as the research object, considers the influence of the type of admixture, forming process, and maintenance method in the process of concrete fabrication, and carries out a rapid freeze-thaw test of PHC tube pile concrete. The changes in the mass loss rate, relative compressive strength, and relative dynamic modulus of elasticity with the number of freeze-thaw cycles, as well as the influence characteristics and mechanism of the admixture type, forming process, and curing method, were obtained. Based on this study, the repair and reinforcement of the base concrete were carried out using ultrahigh toughness cementitious composites and cementitious permeable crystalline composites, and a rapid freeze-thaw test was conducted on the repaired concrete specimens to verify the repair and reinforcement effects of the two materials. The study showed that the mass loss rate, relative strength, and relative dynamic elastic modulus can better characterize the freezing resistance of PHC piles, and it is safer to use the relative dynamic elastic modulus as the evaluation index of the freezing resistance of PHC pile concrete than the mass loss rate. The concrete admixture, forming process, and maintenance method have significant effects on the freezing resistance of the PHC pipe pile mix. The splitting damage surface of both ultrahigh-toughness cementitious composites (UHTTC) and cementitious capillary crystalline waterproofing (CCCW) repaired concrete is a reinforced surface, and both repair materials can improve the freezing resistance of PHC pipe piles through the crack arresting effect and reduction in initial porosity.

Fatigue behavior of short-headed studs embedded in Ultra-high Toughness Cementitious Composites (UHTCC)

The multi-cracking and strain-hardening capacities of Ultra-high Toughness Cementitious Composites (UHTCC) make it feasible for orthotropic steel bridge decks (OSBDs) applications to control crack width. In this composite bridge deck, shear connectors play an important role in providing good shear strength and ensuring structural service performance. To evaluate the shear resistance of short-headed studs embedded in ultra-thin UHTCC layer, three series of push-out tests were conducted in this study. The test results including shear strength, fatigue strength, failure modes, dynamic slip, stiffness degradation, plastic slip and residual mechanical properties were all considered and carefully discussed. In this study, the shear force of shear connectors was calculated and compared with current codes. The stress amplitude-fatigue life (S-N) relationship of studs was fitted by different codes. Then the empirical formulation was developed to predict the load-slip behavior and stiffness degradation of studs during fatigue loading. The relationship between plastic slip and fatigue life was established and normalized. Furthermore, based on post-fatigue static test results and test results in previous research, a new machine learning model was proposed to predict the residual shear strength of studs and contrasted with previous model. Then Analysis of Variance (ANOVA) with two parameters (i.e. load amplitude, maximum repeated force) was conducted and revealed that the peak load significantly impacted the residual shear strength of push-out specimens compared with load amplitude. Moreover, a parametric study was conducted to further investigate the degradation of studs under various working conditions. By experimental and theoretical analysis, UHTCC could fully develop the shear strength of studs embedded in ultra-thin cover thickness. And related models were established to predict the static and fatigue behavior of steel-UHTCC push-out specimen.

The investigation on mechanical properties of ultra-high toughness cementitious composite using orthogonal experiment

Ultra-high toughness cementitious composite (UHTCC) exhibits excellent deformability and multiple cracking properties under tensile loading, which are subjected to multiple compositional parameters. This paper simultaneously investigated the effects of water to binder ratio (W/B), cement and silica fume to fly ash ratio (CS/F), and amount of expanded perlite powder (EPP) on the mechanical properties of UHTCC using the orthogonal experiment, with compressive strength and tensile properties. The result of range analysis presented that the order of the influence of factors on mechanical indexes was CS/F > W/B > EPP. An increasing CS/F was conducive to the strength. Conversely, a lower CS/F had a beneficial effect on the tensile performance. In addition, the best level (within limited levels in this study) of each factor on indexes was carried out. The consequence of analysis of variance showed that W/B and CS/F had significance on the compressive strength and CS/F was a crucial factor in applications with lower crack width required, such as waterproof engineering. The comprehensive analysis indicated that the combination of W/B = 0.3, CS/F = 4:6, and EPP = 23.3 g/L was recommended for general mechanical properties of UHTCC.

Mesoscale numerical investigation of dynamic spalling fracture in toughness concrete

This study presents a two-phase mesoscale numerical model to investigate the dynamic spalling fracture behaviour of hybrid fibre ultra-high toughness cementitious composites (UHTCC). The model simulated the presence of random steel fibres and ductile UHTCC independently, and accurately incorporated the fibre-matrix bond-slip relationship, with carefully considering the influence of the inclination angle of the steel fibres on the pullout behaviour. Validation of the numerical model involved a meticulous comparison between numerical outcomes and results from spallation tests, encompassing strain-time and velocity-time histories, failure modes, and locations of cracking or fracture. Subsequently, the developed model was employed to analyse the impact of fibre inclination, stress wave amplitude, and waveform (based on the impulse equivalence principle) on the dynamic spalling fracture behaviour of hybrid fibre UHTCC. Evaluation of spalling fracture performance was based on both maximum velocity and pullback velocity of resulting fragments or free surfaces. Findings revealed that fibres parallel to the stress wave propagation direction exhibited optimum performance. It was also observed that stress waveforms with rectangular and sinusoidal shapes presented the highest risk of spalling fracture, while exponentially attenuated waves were comparatively safer. Additionally, stress waveforms with either rise time or duration at maximum pressure were deemed hazardous. Further, the hybrid fibre UHTCC demonstrated multiple spalling cracking/fracture behaviours under all stress waves except rectangular ones. This comprehensive exploration provided insights for the utilization of hybrid fibre UHTCC in impact engineering.

Numerical and analytical investigations on punching shear performance of UHTCC-enhanced RC slab-column joints

The excellent tensile strain-hardening behavior of ultra-high toughness cementitious composite (UHTCC) makes it applicable for enhancing the punching shear performance of reinforced concrete (RC) slab-column joints. However, construction of an entire slab-column structure employing UHTCC would inevitably lead to uneconomical designs. To balance the economic benefits with the punching performance, utilizing UHTCC in the core region of a slab-column joint is a promising approach. In this study, the impact of UHTCC application range (UAR) on the punching shear performance of UHTCC-enhanced RC slab-column joints (USCJs) was investigated, and an approach for determining the optimal UAR was also presented. Two USCJ specimens with different UAR were tested, and experimental results were compared with the counterpart numerical results to validate the finite element (FE) models. Twenty FE USCJ models with different UAR were established. Then the impact of UAR on development of critical cracks, ultimate resistance, and ductile behavior was examined. Analytical approaches based on the critical shear crack theory as well as on the combination of critical shear crack theory and yield line theory were adopted to predict the ultimate and flexural resistances, respectively. The failure mode was determined by comparing these two resistances and considering the ductile coefficient, based on which the effect of UAR on the failure mode was determined. The results show that the location of critical shear cracks and the appearance of flexural cracks vary with UAR. By increasing UAR, the ultimate resistance increases, but the ductile coefficient first increases and then slightly decreases. Provided that the UAR is increased to some extent, the growth rate of the ultimate resistance evidently slows down and the ductile coefficient peaks, indicating the optimal UAR considering both the economic efficiency and the punching performance. The presented approach shows promise for determining the optimal UAR in practical engineering designs.

Testing and Analysis of Ultra-High Toughness Cementitious Composite-Confined Recycled Aggregate Concrete under Axial Compression Loading.

In order to analyze the axial compressive properties of ultra-high-toughness cementitious composite (UHTCC)-confined recycled aggregate concrete (RAC), a batch of UHTCC-confined RAC components was designed and manufactured according to the requirements of GB/T50081-2002 specifications. After analyzing the surface failure phenomenon, load-displacement curves, scanning electron microscope (SEM), and parameter analysis of the specimen, the result shows that UHTCC-confined RAC is an effective confinement method, which can effectively improve the mechanical properties and control the degree of surface failure of RAC structures. Compared with the unconfined specimen, the maximum peak load of the UHTCC confinement layer with a thickness of 10 mm and 20 mm increased by 44.61% and 79.27%, respectively, meeting the requirements of engineering practice. Different fiber mixing amounts have different effects on improving the mechanical performance of RAC structural. The specific rule was steel fiber (SF) > polyvinyl alcohol fiber (PVAF) > polyvinyl alcohol fiber (PEF) > no fiber mixture, and the SF improves the axial compression properties of UHTCC most significantly. When there are strict requirements for improving the mechanical properties of the structure, SF should be added to UHTCC. On the contrary, PVAF should be added to UHTCC.

Flexural behavior of novel profiled steel-UHTCC assembled composite bridge decks

Ultra-high toughness cementitious composite (UHTCC) has been noticed in the application of composite bridge deck (CBD) structures to avoid tensile cracks, benefiting from its excellent crack resistance behavior and characteristic of tensile strain hardening. In this study, a novel profiled steel-UHTCC assembled CBDs was proposed by adopting duplicate profiled steel parts that integrated the Perfobond rib (PBL) shear connector onto their top flange plates, which will improve fabrication convenience and economic efficiency. The flexural behavior of the assembled CBDs was investigated. Four specimens assembled respectively with T-shaped, Z-shaped, B-shaped, and H-shaped profiled steel parts were designed and fabricated. The failure modes, load-deflection curves, strain distributions, and slippage situations of four specimens were monitored and discussed. Then, the theoretical analyses on the shear connection degrees and ultimate flexural capacities of the assembled CBDs were performed, and a theoretical formula was proposed for calculating the ultimate flexural capacity. Finite element (FE) models of the assembled CBDs were established via ABAQUS software and validated against the test results. Ten groups of FE examples were designed for the detailed study of several key design parameters including shear span length, PBL hole diameter, thickness of UHTCC slab, thickness of steel web, and normalized PBL hole numbers. Finally, the proposed theoretical formula was validated using experimental and simulated results, demonstrating the validity of the proposed formula.

Experimental and numerical investigations on the stress waves propagation in strain-hardening fiber-reinforced cementitious composites: Stochastic analysis using polynomial chaos expansions

The propagation of stress waves can result in spalling fractures in materials, which poses a threat to the safety of engineering structures. Hence, in-depth studies are necessary to mitigate such risks. Ultra-high toughness cementitious composites (UHTCC) with significant tensile strain-hardening properties are advanced engineering materials with great potential for impact engineering. The study used a combination of experimental and numerical methods to analyse the propagation and attenuation behaviour of stress waves in the UHTCC. The numerical model was developed using the Smooth Particle Galerkin (SPG) method and the Karagozian & Case concrete/cementitious (KCC) material constitutive model. Additionally, a quantitative global sensitivity analysis (GSA) using a polynomial chaos expansion (PCE) surrogate model and Sobol's method was conducted to analyse the stochastic input parameters of the numerical model. Results show that compressive stress waves undergo significant attenuation during propagation in UHTCC, and the developed numerical model accurately simulated the stress wave propagation process Furthermore, the PCE-Sobol GSA revealed that the selected stress wave propagation responses are most sensitive to the tensile strength of UHTCC. This study is expected to deepen the understanding of the propagation behaviour of stress waves in UHTCC and pave the way for promising applications of UHTCC in impact engineering.

Bending performance of RC slabs strengthened by CFRP sheets using sprayed UHTCC as bonding layer: Experimental study and theoretical analysis

Debonding failure is one of the main drawbacks of reinforced concrete (RC) structures strengthened with externally bonded (EB) fiber reinforced polymer (FRP) systems. Due to the huge application potential of sprayed ultra-high toughness cementitious composite (UHTCC) in strengthening and retrofit, this study, with the aim of delaying or preventing intermediate crack-induced debonding of EB FRP sheets, experimentally and analytically investigated the flexural behavior of RC slabs strengthened by EB CFRP sheets with sprayed UHTCC as bonding layers, which has been rarely reported in previous research works. For this purpose, five RC slabs with low strength concrete and low reinforcement ratio, including one control specimen and four strengthened specimens repaired by EB CFRP sheets with sprayed UHTCC as bonding layers, were manufactured and tested under four-point bending load. Variable parameters in the four strengthened specimens included the thickness (10 mm, 20 mm, and 30 mm) and length (600 mm and 900 mm) of the sprayed UHTCC bonding layer. The experimental results indicated that the specimens strengthened by EB FRP sheets with sprayed UHTCC as bonding layers experienced higher load-bearing capacity (24.43 %–120.92 %) and toughness (43.15 %–166.14 %), compared to the control specimen. The thickness of the UHTCC bonding layer had a significant effect on the structural performance. By increasing the thickness from 10 mm to 20 mm and from 20 mm to 30 mm, the ultimate load was enhanced by 32.69 % and 33.81 %, while the ultimate deflection was decreased by 14.99 % and 41 %, respectively. The test findings also showed that sprayed UHTCC had a strong cracking-control ability and that no debonding failure occurred between the UHTCC layer and the CFRP sheet, while interface slip was observed between the concrete substrate and the UHTCC layer. The sectional analysis method was then used to propose an analytical model for analyzing the composite action between the concrete substrate and the strengthening material, as well as a model for predicting the load-bearing capacity of strengthened specimens. Comparing the analytical results to the experimental ones revealed that the proposed models can properly predict the flexural behavior of RC slabs strengthened by EB CFRP sheets with sprayed UHTCC as bonding layers under four-point bending load.

A comprehensive study on the effect of reinforcing methods on the flexural behaviour of Concrete-RUHTCC composite beams

A systematic investigation on the effect of various reinforcing methods on the flexural behaviour of concrete-reinforced ultra-high toughness cementitious composites (RUHTCC) composite beams was conducted in this study, combining four-point bending tests, analytical modelling and numerical simulations. Seven specimens with steel reinforcement bars, steel wire mesh, basalt fibre fabrics, were tested, and it was found that the bending capacity of the beam increased with all these reinforcements (up to 152% comparing to that without reinforcement in this study), and various failure modes were captured including cracking in concrete and UHTCC, interfacial shear failure and interfacial peeling. An analytical model including solutions for the ultimate flexural capacity and critical strengths corresponding to interfacial shear failure and interfacial peeling was derived based on the plane-section and good material bonding assumptions. In addition, finite element models were built and used for carrying out parametric studies once they were successfully validated against experimental tests. In the end, the analytical model was further modified referring to the results of numerical parametric studies by integrating the effects of all the possible failure modes in a single expression. Thus, the proposed analytical model can be implemented and used in the design of concrete-RUHTCC composite beams.

Effect of moisture content on mechanical behavior of ultra-high toughness cementitious composites

This study presented an investigation into the basic mechanical properties of Ultra-high toughness cementitious composites (UHTCC) under varying moisture levels (0%, 56.5%, and 100%). UHTCC have been recognized for their excellent deformation and crack control abilities, making them ideal for repairing and reinforcing hydraulic structures. In this study, static compressive test and direct tensile test were conducted to determine the influence of free water on compressive strength, tensile stress and strain relationship, elastic modulus and energy absorption ability of UHTCC. Meanwhile, the notched beam fracture test and single fiber pull-out test were also performed to investigate the mechanism behind such phenomenon. The results of the study revealed that as the relative moisture content of UHTCC increased, the compressive and tensile strengths decreased to varying degrees. The softening effect of water on compressive strength of UHTCC was found to be more significant than that on its tensile strength. Furthermore, the direct tensile deformation capacity of UHTCC increased from 2.4% to 4.0% as the relative moisture content increased. Water infiltration into UHTCC was found to have a minimal effect on the number of tensile cracks but significantly increased their width. The results of notched beam fracture and fiber pull-out tests demonstrated that water infiltration led to a 30.4% decrease in matrix fracture toughness, a 37.3% decrease in chemical bonding strength, and a 23.4% decrease in frictional bonding strength between fibers and the matrix. The increased deformation ability of UHTCC in water environments was attributed to the increase in strain hardening energy index (Jb’/Jtip).

Investigation on triaxial compressive mechanical properties of ultra high toughness cementitious composites with high strain capacity

Ultra high toughness cementitious composites (UHTCC) with significant strain capacity and high toughness is expected and potentially utilized to improve the performance of engineering structures under complex loadings. This study discusses the triaxial compressive behavior of UHTCC tested under seven different confining pressures with the maximum normalized confining pressure reaching 0.51. The obtained results indicate that the deviatoric strength, peak axial strain and peak lateral strain of UHTCC increase substantially with increasing confining pressure. Among these, the peak axial strain-confining pressure curve exhibits a clear nonlinear increasing trend. For the stress-strain curves, almost no softening phenomenon was observed when the normalized confining pressure reached only 0.425. The William-Warnke and Power-Law failure criterion are found suitable for describing the triaxial characteristic. The toughness index well reflects the significant energy absorption capacity of UHTCC. Based on the experimental results, UHTCC is expected to perform well in important civil and military engineering application which is potential to resist multi-axial loadings.

Punching shear behavior and strength prediction of UHTCC-enhanced RC slab-column joints

RC flat slabs are widely employed in medium-height buildings due to their constructional and architectural advantages. However, due to the tensile brittleness of normal concrete, an RC slab-column structure may suffer progressive collapse induced by punching shear failure of slab-column joints. Considering the excellent tensile strain-hardening behavior of ultra-high toughness cementitious composite (UHTCC), the punching shear behavior of slab-column joints enhanced by UHTCC could be substantially improved. Three slab-column joint specimens with different UHTCC application ranges were tested under vertical monotonic loading. The cracking development process, peak bearing capacity, ductility, and post-punching capacity were recorded and analyzed. Yield line theory and critical shear crack theory were adopted to estimate the flexural capacity and punching shear capacity of the specimens, respectively, and the post-punching capacity was also calculated. Finally, the failure patterns of the specimens were determined by comparing the estimated flexural capacity with the estimated punching shear capacity and taking into account the ductile coefficient. The main conclusions are as follows: (1) applying UHTCC can considerably enhance the peak bearing capacity and ductility of a joint, and a more significant improvement effect is achieved by increasing the UHTCC application range; (2) adopting UHTCC affects the failure pattern of a slab-column joint from premature punching shear failure to flexural-triggered punching shear failure achieving better ductile performance, and flexural behavior becomes more evident with the increase of the UHTCC application range; (3) the post-punching capacity of a joint is improved when the UHTCC application range covers the entire punching shear region. Therefore, the progressive collapse resistance of the RC slab-column structures could be substantially improved by introducing the UHTCC-enhanced joints.

Effects of interval time and interfacial agents on the mechanical characteristics of ultra-high toughnessnn cementitious composites under 3D-printed technology

Anisotropic mechanical characteristics are crucial to the application of the printed structure. This study is aimed to investigate the effects of interval time and interfacial agents on the anisotropic mechanical strength of ultra-high toughness cementitious composite under 3D-printed technology. The bending capacity of ultra-high toughness cementitious composite under 3D-printed technology was compared with mould-casting ultra-high toughness cementitious composite. The compressive strength, flexural strength and splitting tensile strength were measured to represent mechanical properties in different directions and the microstructure of ultra-high toughness cementitious composite under 3D-printed technology with different interval time and interfacial agents were characterized using nanoindentation, scanning electron microscopy, and X-ray computed tomography. The experimental results indicated that the ultimate bending strength and bending toughness of ultra-high toughness cementitious composite under 3D-printed technology were 13.6% and 3.3% to 13.3% higher than those of mould-casting ultra-high toughness cementitious composite at 28 d, respectively. As the interval time increased, the mechanical properties showed differential development patterns. Specifically, compressive strength and splitting tensile strength had a higher rate of decline in the X direction (parallel to the printing path) than in the Y and Z directions but flexural strength was the opposite. A 3-h interval time reduced the 28-d compressive strength and splitting tensile strength in the X direction by 24.02% and 49.64% but the strength only decreased by 10.57% and 26.59% in the Z-direction. The addition of interfacial agents reduced anisotropy in compressive strength and splitting tensile strength but increased the anisotropy of flexural strength. When the interval time was 3 h, the increase rate of the 28-d flexural strength in the X direction, in which the flexural strength was weakest, was 22%–29% lower than that in the Y and Z directions under the effects of interfacial agents. A microstructure analysis showed that the filling effect and high moisture content of interfacial agents counteracted the negative impact of interval time on the width of the interface between layers and the porosity of ultra-high toughness cementitious composite under 3D-printed technology, which can enhance the interlayer bonding. These results can promote the application of ultra-high toughness cementitious composite under 3D-printed technology in additive manufacturing.

The effects of tensile strain rate on the dynamic tensile behavior of ultra high toughness cementitious composite

In this study, dogbone-shaped block specimens with cross section aspect ratio of 1.25 were prepared and tested at different strain rates ranging from 10−5 to 10−1 s−1 to investigate the dynamic tensile behavior of ultra high toughness cementitious composite (UHTCC) under different strain rates. The dynamic tensile responses were characterized in terms of the tensile strength, strain capacity, elastic modulus, specific energy absorption (SEA) and crack pattern. The results indicated that, with the increase of strain rate, the ultimate tensile strength increased by 160% but the strain capacity decreased by 80%. As the strain rate increased from 10−5 to 10−2 s−1, the elastic modulus and SEA increased by 40% and 50%, respectively. Reduction in the width of cracks in UHTCC was observed with the increase of strain rate while the number of cracks kept almost constant. Compared with thin planar specimens, the rate of increase in the ultimate tensile strength of UHTCC block specimens caused by strain rate increase was higher whereas that in the strain capacity was lower. Mesoscale numerical model with randomly distributed polyvinyl alcohol (PVA) fibers was built to analyze relationship between the cross section stress and displacement of specimens with different thicknesses. The results showed that the stress in the cross section and their corresponding relative displacement of block specimen were smaller than those of thin planar specimen under the same loading status. In addition, the cross section stress-displacement relationship of thin planar specimen was more sensitive to the strain rate than that of block specimen, which may be the reason for the weaker strain hardening behavior of thin planar specimens under dynamic tensile loading.

Experimental study on flexural performance of steel-UHTCC composite bridge decks considering different shear connection degrees

Traditional steel–concrete composite bridge deck (CBD) is prone to crack in the concrete layer, which reduces its flexural capacity and durability. Due to the excellent crack resistance behavior and characteristic of tensile strain hardening, ultra-high toughness cementitious composite (UHTCC) has become a promising material to solve this problem. In this study, the flexural performance of bridge decks composed of steel and UHTCC using shear studs is analyzed by means of experimental research and finite element (FE) analysis. Five steel-UHTCC CBDs with different shear connection degrees and rib dimensions were fabricated and tested. Then, FE models of steel-UHTCC CBDs were established by ABAQUS, involving FE examples for comparing with the tests and 10 groups of models to conduct a parametric study. The flexural resistant performance of steel-UHTCC CBDs was studied concerning the key design parameters, including stud number, span length, rib dimension, thickness of UHTCC and longitudinal reinforcement ratio. The effect of shear connection degree on the flexural resistance of CBDs was discussed in detail. Finally, a modified theoretical formula was proposed for predicting the flexural resistance of steel-UHTCC CBDs.

Investigation of continuous surface cap model (CSCM) for numerical simulation of strain-hardening fibre-reinforced cementitious composites against low-velocity impacts

This study calibrated the parameters of the continuous surface cap model (CSCM) for ultra-high toughness cementitious composites (UHTCC) with compressive strength from 25 MPa to 75 MPa, and the calibrated parameters could describe the mechanical behaviour of UHTCC, including the deviatoric response, volumetric response, tensile strain-hardening behaviour, strain rate effect, as well as the reduction of tensile strain-hardening behaviour at higher strain rate. The drop-weight impact tests on the reinforced concrete slab and reinforced UHTCC slab were proceeded to validate the soundness of the calibrated CSCM. The results show that the calibrated CSCM could accurately predict the impact response of reinforced UHTCC slab, and the most accurate simulation results were achieved in the model of the hexahedral elements with a mesh size of 10 mm. The calibrated CSCM parameters for UTHCC are expected to extend the application of UHTCC in the field of impact engineering.

The investigating on mechanical properties of engineered cementitious composites with high ductility and low cost

The engineering application of engineered cementitious composites(ECC) has always been limited by its cost, which mainly due to the high price of imported PVA fibers. In order to balance the mechanical properties and cost of ECC, this study presents an engineered cementitious composites with high ductility and low cost. The compressive strength, uniaxial tensile strain and uniaxial tensile strength of this ECC were 21.33 MPa, 5.10%, and 2.93 MPa, respectively. The high ductility and low cost of this ECC are mainly attribute to the reasonable combination of four materials, including PVA fibers, fly ash, CaCO3 whiskers(CW) and nano-CaCO3(NC). The optimal mixing ratio of the four materials is that the content of PVA fiber is 1.3%(vol%), the mass ratio of fly ash to cement is 3.0, 1% CW(vol%), and 1% NC(wt.%). The average crack width and the maximum crack width on the surface of the tensile specimen prepared according to the optimal mixing ratio can be controlled at about 42 μm and 100 μm, respectively. This excellent crack control ability mainly comes from the crack inhibition effect of PVA fibers and CW. Compared to classic ECC-M45, the total value coefficient and total cost of the specimens prepared according to the optimal mixing ratio were 112.59% and 36% of that of ECC-M45, respectively. And the designed ECC with high ductility and low cost has the applicability of engineering application, which has been proved by comparison with the mechanical properties of a sprayable ultra high toughness cementitious composites (UHTCC) that has been applied in practical engineering cases.

Study of the Durability Damage of Ultrahigh Toughness Fiber Concrete Based on Grayscale Prediction and the Weibull Model

The purpose of this research is to investigate the durability damage law for ultrahigh toughness cementitious composites (UHTCCs) under freeze–thaw environments and impact resistance. In this study, UHTCCs with fiber length-to-diameter ratios of 5/30, 8/30, 12/20, 12/30 and 12/48 were tested for impact resistance and freeze–thaw cycles. The freeze–thaw cycle process and impact resistance process for UHTCC are comprehensively analyzed and evaluated in terms of mass loss, compressive strength loss, relative dynamic elastic modulus loss and impact resistance number. The freeze–thaw damage prediction model for the relative dynamic elastic modulus of the UHTCC is established based on the regularity of the measured data for the relative dynamic elastic modulus of UHTCC and also on the GM(1,1) power model. The accuracy and reliability of the GM(1,1) power model is analyzed using the relative error, absolute correlation degree, mean variance and probability of small errors. According to the evolution law of the impact resistance number of the UHTCC, the impact damage prediction model for UHTCC is established based on the Weibull distribution model, and the accuracy of the model is analyzed by using the decision coefficient R2. The results show that UHTCC has high durability performance, and the durability performance of UHTCC at a length-diameter ratio of 12/48 is optimal. The freeze–thaw damage evolution model and impact damage evolution model established in this research are sufficiently realistic, the average relative error of the GM(1,1) power model is less than 5%, and the coefficient of determination R2 of the Weibull distribution model is greater than 0.93, which effectively reflects the damage development process for concrete under freeze–thaw and impact environment with high fitting accuracy.