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The eccentric load behaviour of circular reinforced concrete columns strengthened with a novel engineered cementitious composite jackets reinforced with synthetic macro-fibres and polypropylene was investigated. Furthermore, an innovative method of interface treatment known as longitudinal grooving was used. Twelve test columns were cast, six of which were strengthened with 15 mm thick composite jackets, while three were strengthened with ultra-high-performance fibre-reinforced concrete jackets. In addition, three of the six columns strengthened with the composite jackets were confined with glass-fibre-reinforced polymer warps. The experimental results showed that both methods enhanced load-carrying capacity and energy dissipation with increasing load eccentricity. For example, the specimens strengthened with the composite jackets exhibited increases of 167% and 194% in load-carrying capacity, and enhancements of 92% and 53% at eccentricities of 30 and 60 mm, respectively. Finally, the previously reported model and different codes were used to validate the results, from which interaction diagrams were drawn. This showed a good agreement between experimental and predicted results. [ABSTRACT FROM AUTHOR]

This paper presents the comparative fire performance of reinforced concrete (RC) beams made of concretes with different strengths by undertaking fire resistance tests. Four RC beams made of normal strength concrete (NSC), high strength concrete (HSC), and ultra-high performance concrete (UHPC) with different fiber combinations, were subjected to structural loading and tested under fire conditions. Results from the fire resistance tests show that UHPC beams undergo severe fire-induced spalling and exhibit lower fire resistance as compared to HSC and NSC beams. Additionally, the inclusion of polypropylene (PP) fibers in UHPC beams aids in reducing spalling and increasing fire resistance in UHPC beams. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study that investigates the effect of fiber dimension on preventing spalling of ultra-high-performance concrete (UHPC). UHPCs with different dimensions of polypropylene (PP) fibers were prepared for permeability test at different temperatures and spalling test under ISO834 fire curve. Scanning electron microscope (SEM) observation was also conducted focusing on the fiber of a UHPC sample at the same location after it was subjected to elevated temperatures. The results of permeability tests and spalling tests showed that longer fibers of 12 mm and 18 mm and finer fibers of 28 μm and 33 μm were more beneficial for increasing the permeability of UHPC at high temperature, resulting in higher effectiveness on spalling prevention. Permeability measurements indicated a significant increase occurred at 150°C regardless of fiber dimensions; this increase plays an important role in spalling prevention. SEM results further testify that this increase can be attributed to the formation of microcracks caused by expansion of PP fibers. An aspect ratio of 300 is recommend for spalling prevention of UHPC, when 3 kg/m3 of PP fibers are used. [ABSTRACT FROM AUTHOR]

This study explores the effect of nanosilica (NS) and ground granulated blast furnace slag (GGBFS) in varied quantities (0%–5% NS and 0%–25% GGBFS) on the postfire mechanical and endurance characteristics of concrete at temperatures ranging from 200°C to 1,000°C. To examine bonding performance and structural endurance, a full range of experimental evaluations was methodically carried out, including bond strength evaluations, rapid chloride permeability, chloride attack tests, and water penetration testing. Advanced methods like scanning electron microscopy and X-ray diffraction were used to examine the postfire internal structure. The combination of NS and GGBFS in concrete compositions resulted in noticeable improvements in mechanical resilience and endurance. This was evident by increased bond strength (a notable 12% rise with 4% NS and 20% GGBFS), decreased chloride permeation (a significant 26% drop), and decreased water penetration (about 20% reduction). Interestingly, this optimum concrete mix performed well even at high temperatures, with modest performance improvements at 200°C–400°C but apparent structural deterioration at greater temperature levels. Nonetheless, the composite concrete was demonstrated to perform well at higher temperatures in contrast with control samples. Further, this research develops a reliable correlation for forecasting concrete performance under high heat circumstances as well as providing essential insights critical for the precise design of concrete buildings in extreme situations. [ABSTRACT FROM AUTHOR]

To improve shear capacity, as well as reduce on-site casting and steel consumption, a novel Y-shaped perfobond rib (Y-PBL) shear connector with ultra-high-performance concrete (UHPC) grout was proposed. The shear behavior of the Y-PBL shear connector was investigated by six groups of pushout specimens. Their failure modes, load–slip curves, load–separation curves, strain analysis, and shear transfer mechanisms were discussed. Subsequently, finite-element analysis (FEA) models were established to study the effect of parameters on the shear behavior of the Y-PBL shear connector, as well as to compare the shear capacity contributions with straight-shaped PBL (S-PBL) shear connectors. Analytical models were proposed to predict the shear capacity of the Y-PBL shear connector. The results reveal that the proposed Y-PBL shear connector has superior shear capacity and stiffness. The contribution of the perforating rebar is minor compared with the end-bearing effect of UHPC. The analytical predictions agree well with the experimental and FEA results. This study can be used to guide the design and application of the Y-PBL shear connector in steel-concrete composite bridges. [ABSTRACT FROM AUTHOR]

This paper presents the results of the experimental evaluation of four nonproprietary ultra-high-performance concrete (UHPC) mixture proportions currently being used for industrial applications by various precast concrete producers across the United States and Canada. The main objective of this research was to acquire data about the effects that creep and shrinkage phenomena produced with UHPC materials. Shrinkage was assessed by the ASTM C157 testing method modified by ASTM C1865 and ASTM C1698. Creep was evaluated by the ASTM C512 testing method modified by ASTM C1856. Results for creep and shrinkage strains and creep coefficient are presented and discussed. Comparisons with conventional concrete are also made. This detailed characterization of creep and shrinkage properties of the nonproprietary UHPC mixture proportions advances the understanding of UHPC materials and phenomena and offers useful information for further research on applications of UHPC for prestressed concrete structural components. [ABSTRACT FROM AUTHOR]

Amorphous alloy fiber has the advantages of high tensile strength and high corrosion resistance compared with steel fiber, but its interfacial bonding with cement matrix is poor and requires surface modification treatment. In this study, the surface modification of amorphous alloy fiber was carried out by using silane coupling agent KH-550 solution, and its effect on the mechanical properties of ultra-high-performance concrete was investigated. The results showed that the amorphous alloy fibers modified with 15% concentration silane coupling agent KH-550 solution can effectively improve the mechanical properties of the ultra-high-performance concrete, where the interfacial bond strength with the cement matrix reached 3.29 MPa and the roughness reached 3.85. The compressive strength, flexural strength, tensile strength, and peak stress of the ultra-high-performance concrete mixed with modified amorphous alloy fibers could reach up to 133.6 MPa, 25.5 MPa, 8.32 MPa, and 114.26 MPa, respectively, which were 2.9%, 6.3%, 10.9%, and 4.3% higher than those of the ultra-high-performance concrete with unmodified amorphous alloy fibers. As the surface of the fiber was modified, its properties changed and the bonding effect with the cement matrix was better, which in turn improved the mechanical properties of the ultra-high-performance concrete. [ABSTRACT FROM AUTHOR]

Ultra-high-performance concrete with coarse aggregates (UHPC-CA) has the advantages of high strength, strong shrinkage resistance and a lower production cost, presenting a broad application prospect in civil engineering construction. In view of the difficulty in establishing a mathematical model to accurately predict the mechanical properties of UHPC-CA, the back-propagation artificial neural network (BP-ANN) method is used to fully consider the various influential factors of the compressive strength (CS) and flexural strength (FS) of UHPC-CA in this paper. By taking the content of cement (C), silica fume (SF), slag, fly ash (FA), coarse aggregate (CA), steel fiber, the water–binder ratio (w/b), the sand rate (SR), the cement type (CT), and the curing method (CM) as input variables, and the CS and FS of UHPC-CA as output objectives, the BP-ANN model with three layers has been well-trained, validated and tested with 220 experimental data in the studies published in the literature. Four evaluating indicators including the determination coefficient (R2), the root mean square error (RMSE), the mean absolute percentage error (MAPE), and the integral absolute error (IAE) were used to evaluate the prediction accuracy of the BP-ANN model. A parametric study for the various influential factors on the CS and FS of UHPC-CA was conducted using the BP-ANN model and the corresponding influential mechanisms were analyzed. Finally, the inclusion levels for the CA, steel fiber, and the dimensionless parameters of the W/B and sand rate were recommended to obtain the optimal strength of UHPC-CA. [ABSTRACT FROM AUTHOR]

Novel ultra-high-performance concretes (UHPCs) made with calcium-oxide-activated materials (CAM), modified synthetic macro (MSM) fibres, glass fibres and steel fibres were developed. The mechanical and durability properties of UHPC-CAM specimens made with the different fibre types were tested and compared. The microstructure of the samples was examined using scanning electron microscopy (SEM). The environmental impacts of the mix designs were assessed using the Impact 2002+ method, a life cycle assessment tool. The results showed that the UHPC-CAM made with glass or MSM fibres had a high compressive strength (>110 MPa) and improved ductility. These specimens also had low water absorption and high electrical resistance, indicating low corrosion risk. SEM analyses showed that the MSM fibres created a denser geopolymer matrix than the glass fibres. The UHPC-CAM was found to have a lower environmental impact than conventional UHPC in terms of human health, ecosystem quality, carbon dioxide footprint and use of resources. MSM fibres were determined to be the most eco-friendly fibres for UHPC-CAM production. [ABSTRACT FROM AUTHOR]

The aim of this research was to develop cost-effective and environmentally friendly ultra-high-performance concrete (UHPC) using fly ash (FA) and quartz powder (QP) as sustainable cement replacements. The performance of the various constituents was examined and their influence on fresh and hardened properties was investigated in order to determine the optimum trial mix design. A cube compressive strength of 144 MPa was achieved with 20% FA and 10% QP and other ingredients without any special heat treatment. Advanced characterisation studies, such as the heat of hydration and X-ray diffraction analysis, were performed to gain understanding of the performance of FA-blended UHPC. Various fracture properties (fracture toughness, fracture energy, brittleness etc.) were investigated considering geometrically similar notched beam specimens for UHPC mixes with steel fibre contents of 1.5% and 2.5%. The optimum UHPC mix achieved good scores in terms of the strength index and the embodied carbon dioxide emissions index, indicating that the concrete is eco-friendly and sustainable. [ABSTRACT FROM AUTHOR]

It is the purpose of this study to evaluate, through combined experimental and numerical research, the performance of ultra-high-performance concrete (UHPC) jackets as a means of seismic retrofitting of columns with brittle detailing under cyclic loading. A series of conventionally designed RC column elements were constructed based on detailing methodologies of pre-1980s standards. After imparting preliminary damage to the columns, simulating the aftereffects of seismic excitation, the plastic hinge zone was repaired using cover replacement by a commercial-grade tension-hardening UHPC jacket and tested under cyclic displacement reversals to obtain quantified evidence regarding the performance of this retrofit methodology. Significant improvements in strength and ductility were observed in both the UHPC-repaired and -strengthened specimens, while failure modes associated with the limitations of lap-spliced connections at the column–footing interface were eliminated. Parallel finite-element analysis (FEA) simulations were used to evaluate the broader distributions of the longitudinal strains in the flexural reinforcement, illustrating the contribution of the UHPC jackets in prolonging the seismic response of retrofitted members. [ABSTRACT FROM AUTHOR]

The fineness modulus (FM) denotes the average particle size of fine aggregates. The FM of the sand, and other constituent qualities, have a major effect on the strength and durability of geopolymer mortar. Finer particle size increases the surface area, influencing heat absorption and emission, impacting the mechanical strength of geopolymer concrete. Heat energy notably accelerates reaction kinetics, accelerate geopolymerization processes. The purpose of this study is to ascertain how the compressive strength (CS) of fly ash (FA) and Ground granulated blast-furnace slag (Slag) based geopolymer material (GPM) is affected by the fineness modulus (FM) of sand that has been heated to 100°C±5°C. To make the paste for the geopolymer material, natural river sands with FM of 1.85, 2.41, 2.79, and 3.32 were used. For the investigation, 36 samples of a 50×50×50 mm3 cube were hot cured at 50°C for 3 h to determine the CS of GPM paste after 3 h, 1 day, and 7 days. The study's conclusions show that sand FM has a large effect on the flow rate (%) of GPM. In particular, a greater flow rate (%) of GPM paste was connected to a higher sand FM. Notably, the most pronounced improvements in CS growth rate (%) were seen in GPM paste made with heated sand that had FM values of 1.85 (fine sand) and 2.79 (medium sand). Furthermore, when heated sand was utilized, the FM had a substantial impact on the CS of GPM matrix. The mineral composition, including unreacted FA and Slag components, underwent assessment using energy dispersive X-Ray analysis (EDX) and scanning electron microscopy (SEM). These analyses revealed that fine aggregates, with increased surface area content, contributed to higher concrete strength compared with those with a higher concentration of coarse aggregates. It follows that when attempting to create geopolymer material with strong early-strength qualities, fine sand, well graded sand ideal match to the ASTM upper and lower bound limits are the best options for fine aggregates. [ABSTRACT FROM AUTHOR]

Due to the severe environment, damages often occur early on hydraulic structures, even in parts submerged in water. This paper presents a study on how the load-bearing capacity of the hydraulic structure is enhanced, once it has been rehabilitated by underwater concreting. A column has been considered as the hydraulic structure. The damaged part of the column was submerged in water, hence, it was repaired by the underwater concrete. For this, the tremie casting method was taken into account. The compression test results pointed out that the damaged column after rehabilitation had a similar loadbearing capacity to the undamaged column, while the not rehabilitated column had reduced load-bearing capacity by 20%. The failure mode of the damaged column after the rehabilitation presented longitudinal cracks along the body of the column, which is similar to that occurred in the undamaged column. Besides, there was no sign of delamination between the protective layer and the existing concrete of the damaged column, proving the feasibility of the selected casting method and concrete mixture for rehabilitation. [ABSTRACT FROM AUTHOR]

Vibration mixing, characterized by the high-frequency vibrations of the mixing shaft, can enhance the mechanical properties of ultra-high-performance concrete (UHPC). However, the effects of vibration mixing on carbon nanotube (CNT)-reinforced UHPC have not been previously reported. To investigate the impact of vibration mixing on the properties of CNT-reinforced UHPC, a comparative study was conducted using different vibration mixing durations and twin-shaft mixing. The results indicate that for CNT-reinforced UHPC, vibration mixing achieves better flowability, higher wet apparent density, and superior mechanical properties in shorter mixing times compared to twin-shaft mixing, making it a more favorable method. Considering vibration mixing times ranging from 3 to 7 min, the optimal time was found to be 3 min, during which the axial compressive strength increased by 3.3%, the elastic limit tensile strength and tensile strength improved by 14.6% and 15.8%, respectively, and the initial cracking strength and flexural strength increased by 12.6% and 13.4%, respectively, compared to values after 10 min of twin-shaft mixing. [ABSTRACT FROM AUTHOR]

Ultra-high-performance concrete (UHPC) is widely used in precast concrete-steel composite beams because of its beneficial properties, including reduced structural weight, higher flexural rigidity, and reduced tensile crack formation. In comparison to conventional steel-concrete composite beams, steel-UHPC composite beams exhibit superior characteristics, including reduced structural deadweight, enhanced flexural stiffness, and the capacity to withstand tensile cracking. One successful attempt at meeting the current demands for expedited girder engineering is the development of steel-UHPC composite beams with full-depth precast slabs as key components affecting the overall structural performance using dismountable single embedded nut bolts (SENBs) and widely used studs as competitive alternatives. In contrast, shear connectors are exposed to a combined tensile and shear stress in service life rather than shear only. The corresponding scientific problem is the problem of combined effects under stress in practical applications, but there is currently no relevant research. The shear performance of SENBs in precast steel-UHPC composite beams under tension and shear loads remains unclear. For this purpose, ten push-out specimens and theoretical analyses were performed in this paper, considering the influence of the connector's type and tensile-to-shear ratio. However, ten specimens were conducted to investigate the tensile-to-shear ratio, and the connector's type on shear performance is limited. In the future, an increasing number of specimens and test parameters should be considered to investigate the shear performance of precast steel-UHPC composite beams. An increase in the tension-to-shear ratio resulted in a substantial reduction in the ultimate shear capacity, initial shear stiffness, and ductility of the studs. The increase in the tensile-shear ratio from 0 to 0.47 resulted in a 16.9% decline in the ultimate shear capacity, a 30.4% reduction in the initial shear stiffness, and a 21.7% decrease in the ductility of the Series I samples. However, an increase in the tensile-to-shear ratio of the Series II samples from 0 to 0.47 resulted in a 31.3% decline in ultimate shear strength, a 33.2% decline in initial shear stiffness, and a 41.9% decline in ductility. The SENBs demonstrated minimal deviations in ultimate shear capacity compared to their stud counterparts, despite exhibiting notable differences in shear stiffness, and ductility. A lower tensile-to-shear ratio was recommended in practical engineering, which might achieve a larger ultimate shear capacity, stiffness, and ductility. The design-oriented models with enhanced applicability were developed to predict the tension-shear relationship and the load-slip curve of SENBs in prefabricated steel-UHPC composite beams subjected to combined tensile and shear loads. For a tensile-shear relationship model, the point error range was 0 to 0.08, with an average error of 0.03. The square coefficient (R2) was 0.99 for a load-slip curve model. The study findings could offer a credible reference for the shear mechanism of such economical and environmentally friendly precast steel-UHPC composite beams in accelerated bridge construction. [ABSTRACT FROM AUTHOR]

This study investigates the torsional performance of reinforced concrete beams with transverse circular openings and examines methods to mitigate the detrimental effects of these openings using Ultra-High-Performance Concrete (UHPC) and diagonal reinforcement. The experimental component involved casting and evaluating eight beams with dimensions of 150 × 200 × 1200 mm under pure torsion. Among these, two beams were solid (without openings), one was made from normal-strength concrete (NSC), and the rest were cast with UHPC. The beams with openings were categorized into two groups based on the size of the openings—small and large. Each group comprised three beams: the first was cast from NSC and included diagonal reinforcement, the second from UHPC with diagonal reinforcement, and the third from UHPC but without diagonal reinforcement. Results indicated that all beams with openings cast from UHPC exhibited a substantial increase in ultimate torque compared to the control NSC solid beam. NSC beams with small openings showed a marginal decrease in ultimate load capacity by 1.47%, whereas those with large openings experienced a significant reduction of 17.65%. UHPC effectively compensated for the strength lost due to the absence of diagonal reinforcement in both small and large openings. Initial stiffness in NSC beams decreased by 19.4% and 70.1% for small and large openings, respectively. Conversely, UHPC beams demonstrated improved initial stiffness, with increases of approximately 64% for small and 34% for large openings. This study proposes ultimate torsional equations for UHPC beams with various opening sizes. These equations are validated by comparing them with results from previous experimental research, examining the performance of UHPC beams with and without openings. [ABSTRACT FROM AUTHOR]

Manufactured sand (MS), due to its wide availability and cost-effectiveness, is used as an alternative aggregate for quartz sand (QS) in ultra-high-performance concrete (UHPC) to prepare ultra-high-performance manufactured sand concrete (UHPMC). This study aims to assess the bond behavior of 600 MPa-grade, high-strength, hot-rolled ribbed bars (HRB 600) in UHPMC. Thirty specimens were designed for the pull-out tests, taking into account several feature parameters, including MS replacement ratio (0%, 50%, 100%), water–binder ratio (0.17, 0.19, 0.21), steel fiber content (0%, 1%, 2%), and anchorage length (2d, 3d, 4d, 5d). The effects of the feature parameters on the failure mode, bond stress–slip curves, bond strength, bond-slip mechanism, and constitutive model were analyzed and illustrated. The results reveal that the pull-out specimen of UHPMC exhibits three distinct failure modes: rebar pull-out failure, UHPMC splitting failure, and splitting-pull-out failure. The bond strength increases from 46.57 MPa to 56.92 MPa when the steel fiber content increases from 0% to 2%. Additionally, a decrease in anchoring length is beneficial for improving the bond strength; as the anchoring length increases from 2d to 5d, the bonding strength decreases by 35.84%. The bond strength increases with an increase in the MS replacement ratio. As for the water–binder ratio, the bond strength presents the highest value when the water–binder ratio is 0.17. In addition, a new bond-slip constitutive model applicable to UHPMC and HRB 600 rebar, considering the MS replacement ratio, the water–binder ratio, etc., is proposed, which presents favorable prediction accuracy. [ABSTRACT FROM AUTHOR]

High-Performance Concrete (HPC) and Ultra-High-Performance Concrete (UHPC) have many applications in civil engineering industries. These two types of concrete have as many similarities as they have differences with each other, such as the mix design and additive powders like silica fume, metakaolin, and various fibers, however, the optimal percentages of the mixture design properties of each element of these concretes are completely different. This study investigated the differences and similarities between these two types of concrete to find better mechanical behavior through mixture design and parameters of each concrete. In addition, this paper studied the correlation matrix through the machine learning method to predict the mechanical properties and find the relationship between the concrete mix design elements and the mechanical properties. In this way, Linear, Ridge, Lasso, Random Forest, K-Nearest Neighbors (KNN), Decision tree, and Partial least squares (PLS) regressions have been chosen to find the best regression types. To find the accuracy, the coefficient of determination (R2), mean absolute error (MAE), and root-mean-square error (RMSE) were selected. Finally, PLS, Linear, and Lasso regressions had better results than other regressions, with R2 greater than 93%, 92%, and 92%, respectively. In general, the present study shows that HPC and UHPC have different mix designs and mechanical properties. In addition, PLS, Linear, and Lasso regressions are the best regressions for predicting mechanical properties. [ABSTRACT FROM AUTHOR]

Lightweight aggregate concrete, known for its light weight, thermal insulation, and excellent durability, has garnered significant attention and is considered an ideal material for lightweight ultra-high-performance concrete. Previous research has discovered that prewetting lightweight aggregates can continuously release water during the setting and hardening process of concrete, providing internal curing. However, the moisture release behavior of prewetted lightweight aggregates under different temperature and humidity conditions, as well as their internal curing mechanisms in low water–cement ratio mixtures, remains unclear and requires further investigation. In response to environmental sustainability, this study utilizes industrial waste γ-C2S to produce a high-strength carbonized γ-C2S lightweight aggregate (CC) and primarily compares the water absorption and release characteristics of three different types of lightweight aggregates, focusing on the influence of curing temperature and humidity on the water release behavior of the prewetted CC and establishing a water release model for the prewetted CC in cement-based materials. The experimental results indicate that the water absorption rates of the self-made high-performance lightweight aggregate (CC), magnesian lightweight aggregate (MC), and shale lightweight aggregate (SC) conform to the typical Boxlucas equation. In an air environment, the CC has the longest water release duration, followed by the MC, with the SC being the fastest. The water storage performance of the prewetted SC was poor, while the 100% prewetted CC exhibited better water storage during the mixing stage. When the CC is 100% prewetted, it can significantly increase the free water content in the interfacial transition zone, aiding in the hydration of the interfacial transition zone and enhancing the efficiency of shrinkage compensation by the expansive agent. This improvement contributes to the mechanical strength and volumetric stability of cement-based materials. [ABSTRACT FROM AUTHOR]

Progress in building construction requires more durable concrete with higher strength. Polymer and water reducer liquids can improve concrete strength and durability. This research aims to improve the mechanical properties of polymer-modified concrete by using anti-slip sand and silica fume to achieve more durable concrete against sulfate attack and higher mechanical properties. The study shows an increase in compressive strength from 25.7 MPa for reference mix to 45.5 MPa using 15% silica fume and 30% Anti-slip sand; tensile strength increased from 2.72 to 4.4 MPa. Flexural strength also increased, and durability to sulfate attack also increased. The study includes the increment of durability against freezing-thawing cycles for different mixes. [ABSTRACT FROM AUTHOR]

Water permeability of reinforced concrete is essential for transportation of ingress ions inside concrete structures. The coupling effect of permeability and loading presents a challenge for the experimental simulation of water-permeate reinforced concrete subjected to tension. This renders the development of the model based on dimensionless analysis, using a series of experimental tests from an innovative experimental system that allows simultaneous measurement of permeability and crack width. The experiments focused on both ordinary concrete and high strength concrete under tension. The relationship between permeability and variables such as deformation, diameter of rebars, tensile load, and crack width under tension was formulated through multiple regression analysis using the testing data. The load to deformation characteristics determines the permeability of the concrete under tension. The proposed model accounts for the influence of continuous loading on permeability, as demonstrated by the robust analysis and proposed yield effective point. The robust analysis demonstrates that the diameter of the rebar, load, and crack width exert minimal influence on the permeability of concrete at lower significance levels. However, permeability variations become pronounced from 0.5 threshold, with significant changes observed between 0.5 and 0.9 thresholds. The findings indicate a differential impact of the variables on the permeability of concrete under tension. The yield-effective points delineate the relationship between the rebar diameter, load, and crack-width on the permeability of concrete with a threshold of 0.5, 0.5, and 0.58, respectively. At a threshold of 0.78, higher permeability will occur in the concrete, attributed to the prevalence of deformation. This deformation highlights the parameters with the most significant influence on the permeability of concrete under tension. The robust analysis and yield effective point derivative are useful parameters to measure concrete permeability and evaluate the behavior of the permeability model under tension. [ABSTRACT FROM AUTHOR]

The present article aims to study the behavior of RC columns under blast loading. A nonlinear dynamic Three‐Dimensional (3D) Finite Element FE model‐based explicit solver available in ABAQUS Software is used. A parametric study is investigated to enhance the blast resistance of RC columns under three different scaled distances z of an explosion, that is, 0.23, 0.5, and 1.07 m/kg1/3 for close, intermediate, and Far in‐distance. In addition, three levels of concrete grades are used, which are Normal Strength Concrete (NSC), High Strength Concrete (HSC), and Ultra High‐Performance Concrete (UHPC). The study also considers Three reinforcement ratios for longitudinal and transverse reinforcement ratios of (ρL = 1.28%, 2.4%, and 3.1%) and (ρs = 0.6%, 0.9%, and 1.35%), respectively. Further, three different Axial Load Ratios, ALR = 0.01, 0.2, and 0.4, are considered to examine the effect of increasing ALR on the RC column under close explosion. For more investigation, the parametric analysis considers two geometrical shapes of RC columns (square and circular). The material behaviors of concrete and reinforcing steel bars are represented using Concrete Damage Plasticity (CDP) and Johnson–Cook (J–C) models, respectively, available in ABAQUS Software. The FE model has been initially validated against experimental study. The FE‐predicted deflection and damage were observed and agreed with the practical cases. In addition, the parametric study's results demonstrate that the RC column's blast deflection is significantly reduced with increasing reinforcement ratios. However, increasing concrete grade could efficiently reduce blast damage and deflection. Furthermore, compared with NSC, UHPC significantly reduced maximum damage and deflection by around 60% for square and 55% for circular columns, respectively. [ABSTRACT FROM AUTHOR]

High performance concrete (HPC) has the characteristics of high strength, high brittleness and low toughness, so it can not be widely used in engineering field. The rubber particles themselves have good elasticity and excellent wear resistance. To this end, rubber particles were used to prepare high performance rubber concrete (HPRC) instead of fine aggregate, and compressive strength and splitting tensile strength tests were carried out according to standard test methods. These data were evaluated, and it was found that adding different mesh number (10 mesh, 20 mesh, 30 mesh) and different content (10%, 20%, 30%) of rubber particles reduced the compressive and tensile properties of highperformance rubber concrete to different degrees. The rubber particles with l size of 30 mesh and content of 10% have the least influence on the mechanical properties of high-performance rubber concrete, and the compressive strength and tensile strength of HPC 28 days only decrease by 18.19% and 5.56%, respectively. From the damage form, the addition of rubber particles makes the high performance concrete change from brittle to ductile. The research shows that recycling rubber from waste tires into concrete manufacturing is an environmentally friendly and feasible waste management strategy. These results have the potential to replace concrete in construction and promote sustainable growth. [ABSTRACT FROM AUTHOR]

The influence of the volume fraction (VF) of steel fibres, polyvinyl alcohol (PVA) fibres and their combination on the mechanical and fracture mechanical properties of ultra-high-performance concrete (UHPC) was studied. To analyse the synergistic effect of steel fibres and PVA fibres on the deformation properties of UHPC, the gain ratios (the ratios of the mechanical properties of UHPC reinforced with hybrid fibres (HUHPC) with those of UHPC reinforced with steel fibres (SUHPC)) were obtained for equal total fibre VFs and equal steel fibre VFs. The steel and PVA fibres reduced the compressive strength of the UHPC to some extent and, with increasing VF, the ratios of flexural strength/compressive strength and tensile strength/compressive strength increased gradually. The fracture mechanical properties of the UHPC were significantly improved with the addition of steel fibres and PVA fibres; the latter were superior in improving the deformation properties of the UHPC. Except for compressive strength, the gain ratios of mechanical parameters of HUHPC to SUHPC calculated with equal steel fibre VF were higher than for equal total fibre VF; 0.25% PVA fibres mixed with SUHPC further improved the bending tensile and fracture mechanical properties. [ABSTRACT FROM AUTHOR]

Due to its high strength, the use of ultra-high-performance concrete (UHPC) is particularly suitable for components subjected to compressive loads. Combined with its excellent durability, UHPC can be used to produce highly resource-efficient components that represent a sustainable alternative to conventional load-bearing structures. Since UHPC fails in a brittle manner without the addition of fibers, it is typically used in conjunction with micro steel fibers. The production of these steel fibers is both expensive and energy-intensive. Natural plant fibers, due to their good mechanical properties, cost-effective availability, and inherent CO2 neutrality, can provide a sustainable alternative to conventional steel fibers. Thanks to the low alkaline environment and dense matrix of UHPC, the use of natural plant fibers in terms of durability and bond is possible in principle. For the application of natural plant fibers in UHPC, however, knowledge of the load-bearing and post-cracking behavior or the performance of UHPC reinforced with natural plant fibers is essential. Currently, there are no tests available on the influence of different types of natural plant fibers on the load-bearing behavior of UHPC. Therefore, five series of compression and bending tensile tests were conducted. Three series were reinforced with natural plant fibers (bamboo, coir, and flax), one series without fibers, and one series with steel fibers as a reference. Under compression loads, the test specimens reinforced with natural plant fibers did not fail abruptly and exhibited a comparable post-failure behavior and damage pattern to the reference specimens reinforced with steel fibers. In contrast, the natural plant fibers did not perform as well as the steel fibers under bending tensile stress but did show a certain post-cracking bending tensile strength. A final life cycle assessment demonstrates the superiority of natural plant fibers and shows their positive impact on the environment. [ABSTRACT FROM AUTHOR]

Three-dimensional printing technology (3D printing) is becoming a more and more popular technology for aerospace, biology, medicine, mechanics, civil and other engineering fields. In civil engineering, researchers and engineers attempt to print construction materials such as concrete using 3D-printing technology. This study aims to investigate the reinforcement of concrete beams with 3D printing. To achieve this, fused deposition modeling (FDM) technology as a printing method and polylactic acid (PLA) as a material were selected. Two types of geometries were chosen to find the optimal mechanical behavior of concrete: high-performance concrete (HPC) reinforced with four types of trusses (Pratt, Howe, Warren, and Warren with vertical) and ultra-high-performance concrete (UHPC) reinforced with a hyperboloid shell structure. The compressive and tensile strengths of reinforced UHPC were examined by a three-point bending test, and reinforced HPC was examined by a four-point bending test. The results of the experiments show that hyperboloid shell structures can absorb energy, although the strength of reinforced UHPC is reduced. For example, there was a decrease of over 20% in the compressive strength and 41% in the flexural strength, but the ductility was raised. Adding the hyperboloid shell structure improved the deformability of the UHPC. When Warren and Howe trusses were added to the HPC as reinforcements, the flexural strength improved by over 26% and 4.3%, respectively. The overall results of this study show that the concrete reinforced with 3D-printed trusses was better than that with a hyperboloid shell structure. [ABSTRACT FROM AUTHOR]

The strengthening of existing columns using additional reinforced concrete (RC) jackets is one of the most popular techniques for the enhancement of a column's stiffness, load-bearing capacity and ductility. Important parameters affecting the effectiveness of this method are the strength of the additional concrete, concrete shrinkage and the connection between the old and the new concrete. In this study, the application of Ultra-High-Performance Fiber-Reinforced Concrete (UHPFRC) jackets for the structural upgrade of RC columns has been examined. Extensive numerical studies have been conducted to evaluate the effect of parameters such as the thickness of the jacket, concrete shrinkage and the addition of steel bars, and comparisons have been made with conventional RC jackets. The results of this study indicate that the use of UHPFRC can considerably improve the strength and the stiffness of existing reinforced concrete columns. The combination of UHPFRC and steel bars in the jacket leads to the most effective strengthening technique as a significant enhancement in the stiffness and the ultimate load capacity has been achieved. [ABSTRACT FROM AUTHOR]

Utilizing the high strengths, toughness, and durability of ultra-high-performance concrete (UHPC), a segmentally prefabricated orthotropic steel–UHPC composite deck (POSUCD) system has been developed for long-span cable-stayed bridges. The deck system combines an orthotropic steel deck (OSD) with a reinforced UHPC layer using notched perfobond strips (NPBLs). The UHPC layer is prefabricated onto the OSD of the girder segment in the factory to form the POSUCD. After the precast UHPC layer is cured, the girder segments are transported to the bridge site and assembled. The precast UHPC layers are then connected via transverse wet joints before tensioning stay cables. Against the background of the Danjiangkou Reservoir Bridge with a main span of 760 m, finite element (FE) analysis was conducted to examine the stress state and flexural tests were carried out on local full-scale models to verify the feasibility of POSUCD. The results show that the prefabricated UHPC layer reduces the maximum static compressive stress of the steel deck in the girder system by 21%, and the stress ranges at fatigue-prone details of the steel deck are decreased by 28%–90% compared to traditional OSDs with asphalt overlay. Since the prefabricated UHPC layer helps withstand dead axial load in the main girder, the high compressive strengths of UHPC can be utilized more effectively than in deck systems with UHPC only used as a cast-in-situ overlay to resist vehicular wheel loads. The transverse wet joint interfaces were identified as the weakest aspect of the POSUCD, whether under tension or compression; however, their nominal flexural strengths along the longitudinal direction meet the required design standards. The shear resistance of NPBLs was also well confirmed by the minimal interfacial slip on the specimen when it reached the ultimate capacity under positive bending moment. [ABSTRACT FROM AUTHOR]

With the addition of electrically conductive steel or carbon fibers, Ultra-High-Performance Concrete (UHPC) possesses an intrinsic self-sensing capability. This opens up the possibility of combining the resilience and sustainability of UHPC with the development of self-sensing solutions for structural applications. In this study, the self-sensing behaviour of a proprietary nano-engineered UHPC material subjected to tension was investigated. To assess the self-sensing performance of the material, bulk resistivity measurements were used on direct tension and pure flexure tests, while a novel wireless approach that operates on was used on out-of-plane bending tests. The wireless approach used alternate current (AC) measurements while the bulk resistivity methods were performed through direct current (DC) and the four-probe method. In both methods, the fractional change in resistance was correlated to the state of deformation. The disposition of the actual strain field was evaluated using Digital Image Correlation (DIC). It was found that in the case of direct tension and pure flexure, the fractional change of resistance was initially decreased up to the onset of strain localization, while it gradually increased in the post-peak range, where the separation of the localized crack gradually increased. In the case of the wireless approach using AC, the onset of cracking was successfully predicted with an abrupt increase in resistivity. The wireless strain-sensing approach also captured the Poisson's effect due to the loading. [ABSTRACT FROM AUTHOR]

The use of ultra-high-performance concrete (UHPC) allows for much smaller cross-sections compared to conventional reinforced concrete columns, which may make reinforced UHPC (R-UHPC) columns more susceptible to slenderness effects. Currently, there is no guideline in design standards for the slenderness limit of R-UHPC columns. This paper, therefore, attempts to develop a design provision for determining the slenderness limit of R-UHPC columns. Firstly, a numerical analytical model was proposed for predicting the load-deflection of R-UHPC columns under eccentric loading, which was validated by comparing its predictions with available experimental results from the available literature. Based on the validated model, a parametric study was then conducted to determine the key parameters affecting the slenderness limit of R-UHPC columns. It was found that the slenderness limit corresponding to the 5% strength reduction was sensitive to the ultimate compressive strain of UHPC, the tensile strength of UHPC, and the reinforcement ratio. On this basis, a design equation for the slenderness limit of R-UHPC columns in single curvature was statistically derived. Additionally, the slenderness limit for R-UHPC columns in non-sway frames was also proposed in a convenient form for design procedures. [ABSTRACT FROM AUTHOR]

This study investigates the response of small-scale, reinforced ultra high performance concrete beams. Seven specimens were cast and experimentally tested. Steel fiber volume fraction, amount of longitudinal and transverse steel reinforcement, and casting direction varied between specimens. High longitudinal reinforcement ratios of 4.1% and 9.5% were expected to drive relatively large shear demands and low steel fiber volume fractions of 0.5% and 1% were expected to decrease the UHPC's ability to resist tension, shear, and compression. Specimens were either cast at one end or mid-span. All specimens failed in shear, as expected. R/UHPC beams with only 0.5% fibers and a stirrup spacing equal to half the beam's depth carried more ultimate load than beams with 1% fibers and twice the stirrup spacing. At a 0.5% fiber volume fraction, UHPC performed well, exhibiting fiber bridging in tension and resisting spalling in compression. As longitudinal reinforcement ratio increased from 4.1% to 9.5%, load carrying capacity generally increased, but not proportional to the increase in steel. Placement method did not influence fiber orientation in the R/UHPC beams when measured in 2D planes transverse or longitudinal to the specimens' major axis. The longitudinal and transverse reinforcement interrupted fiber flow and prevented significant fiber alignment; combined with the short span of the beams, these factors mitigated the influence of placement method. [ABSTRACT FROM AUTHOR]

Developments in concrete technologies have allowed engineers to design lightweight, slender, and aesthetically attractive structures. The application of new concrete types in real projects, however, is uncommon. The lack of regulation, uncertainty in material performance, and the absence of successfully implemented projects hinders the use of modern concretes in everyday design projects. The present paper examines the application of two specific concrete types in a prototype footbridge: ultra-high-performance concrete (UHPC), and biological self-healing concrete (BSHC). The material properties of UHPC were selected and tailored specifically for the prototype structure, applying the principles of performance-based design. To evaluate the efficiency of self-healing under real environmental conditions, BSHC beams were designed as a structural part of the bridge. The step-by step presentation of the bridge development demonstrates the specifics in material design and a structural analysis of the prototype structure. The prototype structure serves as demonstrative example of the use of BSH and UHP concretes, encouraging engineers towards the wider application of advanced materials in construction projects. [ABSTRACT FROM AUTHOR]

The design of end zones to prevent severe cracking is a key requirement toward durable prestressed girders. Traditional approaches employ large amounts of steel reinforcement to attain this requirement, which may result in steel congestion. This paper investigates a hybrid girder concept that uses Ultra-High-Performance Concrete (UHPC) and Carbon Fiber Reinforced Polymer (CFRP) bars to enhance crack control and long-term durability in the end zones of prestressed girders. The objectives of this study are to quantify the UHPC zone lengths needed to restrain end zone cracks, eliminate or reduce the required amount of steel reinforcement, and investigate its replacement with CFRP bars. A finite element modeling (FEM) approach was developed for this purpose and its fidelity was validated with experimental data. The FEM results showed that UHPC zones with lengths below or equal to half of the girder depth can significantly reduce end zone cracking. CFRP bars can be added in the UHPC zones as a conservative measure to crack control, to ensure the long-term corrosion resistance of the girders. [ABSTRACT FROM AUTHOR]

Precast segmental ultra‐high‐performance concrete bridge presents broad application prospects. UHPC keyed joints play significant roles in the structural performance of such bridges, which require systematic investigation to comprehend their shear behavior and mechanism thoroughly. This study aimed to explore the shear mechanism of UHPC epoxied‐keyed joints. Experimental and numerical investigations were conducted to investigate the influence of key size, key number, key angle, and reinforcement form on the shear performance. The test results showed that the failure mode was primarily affected by the key number and reinforcement form, which can be divided into three categories: direct shear, segmental shear, and stepwise shear failure. The large‐keyed joints exhibited superior shear performance compared to the three‐keyed joints. The initial shear stiffness, ultimate bearing capacity, and normalized shear stress were 15%, 5.3%, and 5.6% higher, respectively. Furthermore, the mechanism of the two reinforcement forms was clarified. The key rebars mainly improve the ductility of the specimens, while the dowel action of the embedded rebars can enhance the shear efficiency and synergistic force ability of the joints. The numerical simulation results indicated that 2.7% was the best ratio of key rebar, and embedded rebars with larger diameters can strengthen the shear capacity and post‐peak performance of the joints. [ABSTRACT FROM AUTHOR]

To address the issue of easy shearing damage of Carbon Fiber Reinforced Polymer (CFRP) in enhancing the axial compressive performance of CFRP and Ultra‐High‐Performance Concrete (UHPC) strengthened concrete columns, two methods, prestressed CFRP and UHPC with spiral stirrups, were employed for composite strengthening of reinforced concrete (RC) columns. A total of one unstrengthened column and eight strengthened columns were designed and fabricated to validate the effectiveness of the proposed methods. The axial compressive performance and bearing capacity of each specimen were analyzed by considering parameters such as single or composite strengthening method, presence of spiral stirrups in UHPC, and application of pre‐stressed CFRP. The results show that, compared with any single strengthened specimen, the ultimate bearing capacity of the composite strengthened specimen is greater than the sum of the corresponding single strengthened specimens, and the bearing capacity of the prestressed CFRP with spiral stirrup UHPC composite strengthened specimen is the most significant, reaching 235.63%. By incorporating spiral stirrups in the UHPC jacket, the phenomenon of uneven fragmentation during the failure of the strengthened column is improved. This helps prevent premature shearing damage of CFRP and enhances the fracture strain and effective utilization of CFRP. Additionally, prestressed CFRP effectively restrains the lateral deformation and crack development of the core concrete in the UHPC jacket, fully utilizing the high compressive strength of UHPC. This further enhances the ultimate bearing capacity and ductility of the specimens. Based on the experimental phenomena and strain of each material, the failure mechanism of prestressed CFRP‐spiral reinforced UHPC composite‐strengthened columns is proposed. Finally, a unified bearing capacity calculation formula for single and composite strengthened columns is established, based on the theory of confined concrete strength and the assumption of strength increment superposition. The formula is validated with experimental results from relevant literature, showing small errors in the calculated results and indicating good applicability of the formula. [ABSTRACT FROM AUTHOR]

The use of carbon nanomaterials in ultra-high-performance concrete (UHPC) to improve its mechanical properties and durability is growing. Graphene oxide (GO) has emerged as one of the most promising nanomaterials in recent years for enhancing the properties of UHPC. The majority of research so far has been on the properties of UHPC enhanced with GO, but its high cost has limited its application in engineering. This work suggests a machine learning (ML)-based approach to optimize the mix ratio in order to lower the cost of graphene oxide-modified UHPC. To do this, an artificial neural network (ANN) is used to create the prediction model for the 28-day compressive strength and slump flow of UHPC. The performance of this model is then compared using nine different ML techniques. Subsequently, considering the restrictions of the UHPC component content, component proportion, and absolute volume, a genetic algorithm (GA) is adopted to lower the UHPC cost. The sensitivity analysis is carried out in the end. This study's findings indicate that there is a decent degree of prediction accuracy since the difference between the ANN model's predictions and the experimental outcomes is just 10%. The cost of UHPC optimized by GA is reduced to 776 $/m3, significantly lower than the average cost of UHPC. [ABSTRACT FROM AUTHOR]

Ultra-High-Performance Concrete (UHPC) was renowned for its exceptional mechanical strength and durability. While contemporary UHPC is made using high-quality materials and equipment, its enormous use of natural resources in construction has had global ecological impacts. Employing materials that are accessible locally without specialized procedures. This study concentrates on UHPC mixtures, formulated with indigenous materials, aiming to develop an economical product without the need for high-speed mixers or special fibers. The mixtures are designed with optimal proportions of various supplementary cementitious materials (SCM's). The study begins with an analysis of flow behaviour, followed by an evaluation of mechanical properties using non-destructive techniques (NDT) under different curing conditions. The UHPC mixtures demonstrate compressive strengths from 70–85 MPa to 110–144 MPa under standard and hot water curing. Relationships between destructive and NDT test outcomes are also determined. The hot water curing process leads to the formation of calcium-silicate-hydrate(C – S – H) gel, with calcium-hydroxide (CH) crystals observed within the amorphous C – S – H gel. The use of high-temperature curing improves mechanical characteristics by (35–40%) and densifies the microstructure. Consequently, producing UHPC using widely accessible materials without further processing and common technologies like conventional casting and standard curing would increase its cost-effectiveness and environmental sustainability. [ABSTRACT FROM AUTHOR]

Ultra-high-performance fibre-reinforced concrete (UHPFRC) specimens with and without longitudinal reinforcement were experimentally tested under direct tensile loading. The variables considered were the volume fraction of fibres (1.0% and 2.0%), the type of steel fibres (straight and hooked end) and the longitudinal steel reinforcement ratio (none and 1.2%). All of the specimens were tested using a servo-controlled fatigue testing machine in displacement control mode. The changes in displacement were monitored using linear variable displacement transducers and the digital image correlation technique. The strain profiles at different loading stages were used to identify the crack evolution process. The average localised strain was found to be 0.2–0.36%, with corresponding crack widths of 0.3–0.6 mm. A uniaxial tensile stress–strain model was developed based on the test results and data from the literature. Longitudinally steel-reinforced specimens showed both stiffening and strengthening effects. Tension-stiffened specimens with 1.0% fibres failed at a higher strain due to the formation of multiple macrocracks. In the specimens with 2.0% fibres, the rebar fractured in a brittle manner due to crack localisation. It is concluded that a higher longitudinal reinforcement ratio is needed to utilise UHPFRC effectively under tension-dominant loads. [ABSTRACT FROM AUTHOR]

The use of advanced materials, such as ultra-high-performance concrete (UHPC), and slender cross-sectional shapes in bridge girders can result in high susceptibility to shear failure during fire exposure. Shear limit state is usually not considered in fire design, which can be a major risk for I-shaped girders with slender webs. This paper presents the development of an approach to evaluate the shear capacity of UHPC bridge girders during fire through extension of room temperature capacity equations to elevated temperatures. Four types of standard AASHTO concrete bridge girders are analyzed under both standard and hydrocarbon fire scenarios. The output results are utilized to evaluate the progression of temperatures and deflections throughout fire exposure, as well as estimate degradation in flexural and shear capacities. Results show that the fire resistance of UHPC bridge girders are significantly affected by fire severity and concrete mass and that these factors should be taken into consideration in fire design of UHPC bridge girders. [ABSTRACT FROM AUTHOR]

The effects of different flyash content, steel fibre content and water-binder ratio on the dynamic compressive strength of alkali-activated slag high performance concrete (ASHPC) were studied. When flyash and water-binder ratio rose, the dynamic compressive strength of ASHPC fell by 27.3% and 23.5%, respectively, and increased by 81.6% when steel fibre content increased. The dynamic elastic modulus rises by 35.0% with an increase in steel fibre content and falls by 48.0% and 65.6%, respectively, with an increase in flyash content and water-binder ratio. The toughness conversion ratio and pre-peak toughness ratio dropped by 34.1% and 9.5%, respectively, whereas the post-peak toughness ratio rose by 36.4% with an increase in flyash content. The test block's pre-peak toughness ratio and toughness conversion ratio increased by 12.7% and 60.0%, respectively, with an increase in steel fibre , whereas the post-peak toughness ratio declined by 31.0%. With the increase of water-binder ratio, the pre-peak toughness ratio and toughness conversion rate of the test block increased by 31.0 % and 132 %, respectively, and the post-peak toughness ratio decreased by 42.8 %. The energy absorption and reflection rise while the energy transmission falls as flyash concentration and the water-binder ratio rise. The transmission energy rises as the amount of steel fibre grows, while the energy absorption and reflection fall. [ABSTRACT FROM AUTHOR]

A novel composite column was introduced by integrating a concrete-filled steel tube column encasing a Fiber Reinforced Polymer (FRP) confined ultra high performance concrete (UHPC) core. In this paper, the seismic performance of four SCF-UHPC composite column-to-steel beam connections using external diaphragm joints was experimentally investigated under the quasi-static test. All specimens failed due to the formation of plastic hinges at the beams and the tearing failure on the beam flanges at the plastic hinge zone. The local buckling at the column end and the panel zone was observed for the specimens receiving the higher axial compression ratio. The increase of FRP tube thickness is more effective in improving the ductility and energy dissipation capacity of the joints than increasing the UHPC core diameter. On the contrary, increasing the UHPC core diameter led to better resistance to the shear deformation of the panel zone. The proportion of shear deformation to the total deformation of the panel zone and the strain distributions were investigated to determine the effect of each component. The composite column in the panel zone mainly carried the compression-bending effort, and the external diaphragm mainly took the shear effort. All joints were eventually classified as semi-rigid type joints, according to the initial rotational stiffness. [ABSTRACT FROM AUTHOR]

This article discusses a numerical study on predicting the bond-slip relationship of reinforced concrete using surface-based cohesive behavior. The study aims to develop a finite element modeling strategy to accurately predict the bond-slip behavior in reinforced concrete. The article provides a comprehensive review of previous research on bond-slip behavior and includes a table of maximum bond stress equations from different literature sources. The document discusses the testing procedure and finite element modeling strategy for studying the bond behavior between concrete and reinforcement in pullout tests. The document also explains the loading and boundary conditions applied in the finite element model and the interaction between reinforcement and concrete. The text discusses the different contact models available in ABAQUS for simulating contact between surfaces. It concludes by discussing the finite element mesh size and solution procedure used in the study. The text discusses the results of finite element analysis (FEM) conducted on reference specimens to predict their failure modes and bond stress-slip behavior. The analysis used different mesh sizes and analytical models to simulate the behavior of the specimens. The results showed that a finer mesh size of 10 mm provided more accurate predictions of failure patterns, while a mesh size of 10 mm or larger could be used to estimate specimen strength. The FEM developed using the analytical model by Strum and Visintin showed the most accurate prediction of maximum bond stress. The failure modes observed in the analysis included pullout failure, splitting followed by pullout failure, and splitting or splitting-pullout failure. The FEM models generally performed [Extracted from the article]

Ensuring resilience through rapid buildings recovery in seismic zones has been placed at the forefront of recent studies. However, studies that compare the relative resilience of buildings constructed with different materials are lacking. This paper focuses on a comparative resilience analysis of concrete moment frames where beam-column connections are made with varying types of concrete mixtures. The connections are made with normal strength concrete (NSC), rubberized concrete (RbC), steel fiber rubberized concrete (STFRC), synthetic fiber rubberized concrete (SYFRC), and high strength concrete (HSC). Nonlinear static pushover and incremental dynamic analysis (IDA) are utilized to understand system response and the level of damage sustained following an earthquake. Subsequently, seismic fragility functions are constructed for the five considered frame types. The frames are subjected to different seismic scenarios, and the corresponding losses, recovery time, and resilience are quantified. A comparison between the five frame types is carried out to examine the optimal concrete mixture to be used to reduce damage probabilities, total direct losses, and recovery time and subsequently enhance resilience. The results show that rubberized concrete strengthened with steel and synthetic fibers can reduce economic losses by up to 19% and increase building resilience by up to 37% compared with the frames constructed with normal strength concrete. [ABSTRACT FROM AUTHOR]

Composite pressure tanks have received increased attention across a number of civilian applications due to their lightweight and high strength. Traditionally, the design of composite vessels is based on deterministic analysis. However, the design of these structures is challenging and involves several kinds of uncertainties. In fact, different computational investigations have been carried out but no studies provide a resolution for small failure probability evaluation of composite pressure tanks. The aim of this study is to establish a computational framework to investigate small failure probability levels of composite tanks using the Subset Simulation method (SS). The model was developed in two steps, first, the development of limit state functions for hoop and helical layers using netting analysis, and afterwards, a probabilistic computation with six random variables. To quantify the effect of the randomness of different parameters on the structural reliability of composite tanks, a sensitivity analysis was performed using different values of coefficients of variation (COV). It was observed from the results that SS has the ability and the accuracy required to evaluate small failure probabilities which are commonly encountered in composite tank applications. In addition, the hoop strength, the internal pressure, and the thickness of the composite are the major design variables that have a great impact on the structural reliability of the axially symmetric composite tank whereas the fiber winding angle has little effect. Moreover, high COV values drastically reduce the safety zone, which could eventually lead to the burst failure of the composite pressure tank. Furthermore, this study implements a reliability-based design from the perspective of hoop and helical composite layer thicknesses, thus providing a rational assessment of the risk of structural failure. [ABSTRACT FROM AUTHOR]

This paper investigates the efficacy of ultra-high-performance concrete (UHPC) jacketing as an option for seismic retrofit (repair or strengthening) of structural components that have been damaged by reinforcement corrosion. Previous work has illustrated that UHPC cover fully mitigates corrosion in the absence of service cracks and significantly reduces the corrosion rate in the case of preexisting cracks. In the present experimental study, cover replacement by UHPC is used to repair and strengthen corroded columns. Six lap-spliced columns designed based on pre-1970s design standards were constructed and subjected to artificial corrosion. Parameters of the investigation were: a) the aspect ratio of the specimens; b) the bar size (to account for the effect of bar diameter loss on bond); and c) the condition of the specimen (repair or strengthening after damage due to application of simulated seismic load to assess the effectiveness of retrofitting corroded components, even after having endured earthquake damage). The results show that thin UHPC jackets replacing conventional concrete cover suffice to impart a significant increase in strength and ductility of the columns. The jackets also endow the corroded and unconfined lap splices with significant force and deformation development capacity, thus alleviating a source of excessive column flexibility in existing construction. [ABSTRACT FROM AUTHOR]

The performance of concrete materials deteriorates under load fluctuation and long-term erosion from the external environment, leading to damage. In order to solve the problems of concrete materials needing repair, poor working performance and the low mechanical strength of ordinary concrete repair materials, this paper explores a series of experimental studies on the preparation of ultra-high performance concrete repair materials and solves the two technical problems of the low early strength and poor fluidity of ultra-high-performance concrete. The effects of different steel fibers and dosages of early strength agents on the working properties, mechanical properties and microstructure of fast-hardening UHPC are discussed. Finally, the mix ratio of fast-hardening UHPC with a 2 h compressive strength of up to 47 MPa and fluidity of up to 300 mm is obtained through the test, which is in line with practical applications in engineering and provides a reference for the design and analysis of fast-hardening UHPC repair materials. [ABSTRACT FROM AUTHOR]

The creep behavior of Ultra-High-Performance Concrete (UHPC) was investigated by machine learning (ML) and SHapley Additive exPlanations (SHAP). Important features were selected by feature importance analysis, including water-to-binder ratio, aggregate-to-cement ratio, compressive strength at loading age, elastic modulus at loading age, loading duration, steel fiber volume content, and curing temperature. Four typical ML models—Random Forest (RF), Artificial Neural Network (ANN), Extreme Gradient Boosting Machine (XGBoost), and Light Gradient Boosting Machine (LGBM)—were studied to predict the creep behavior of UHPC. Via Bayesian optimization and 5-fold cross-validation, the ML models were tuned to achieve high accuracy (R2 = 0.9847, 0.9627, 0.9898, and 0.9933 for RF, ANN, XGBoost, and LGBM, respectively). The contribution of different features to the creep behavior was ranked. Additionally, SHAP was utilized to interpret the predictions by the ML models, and four parameters stood out as the most influential for the creep coefficient: loading duration, curing temperature, compressive strength at loading age, and water-to-binder ratio. The SHAP results were consistent with theoretical understanding. Finally, the UHPC creep curves for three different cases were plotted based on the ML model developed, and the prediction by the ML model was more accurate than that by fib Model Code 2010. [ABSTRACT FROM AUTHOR]

In structures manufactured using 3D concrete printing, cracks can easily propagate along the interface between printed layers. Therefore, it was necessary to determine the interlayer bond strength. In this study, direct shear and tensile tests were performed to determine the interlayer bond stability of the 3DCP members. To confirm the appropriateness of the mix proportion used to fabricate the specimens, the open time available for printing was identified via a mixing test, and the extrudability and buildability were verified via a printing test. In addition, direct shear and tensile tests were performed using the specimen manufacturing method (i.e., mold casting and 3D printing) and printing time gap (PTG) between the laminated layers as key test variables. The interlayer bond strengths of the specimens, according to the variables obtained from the test results, were compared and analyzed based on the interfacial shear strength standards presented in the current structural codes. In the direct shear test, failure occurred at the interlayers of all the specimens, and the interlayer bond strength tended to decrease with increasing PTG. In addition, the interlayer bond strength of the direct shear specimens exceeded the interfacial shear strength suggested by current structural codes. In contrast, in the direct tensile test, interlayer surface failure occurred only in some specimens, and there was no distinct change in the interlayer bond strength owing to PTG. [ABSTRACT FROM AUTHOR]

This research employs response surface methodology (RSM) to optimize and model ultra-high-performance concrete (UHPC) formulations, integrating desert sand and varying proportions of supplementary cementitious materials (SCMs), specifically fly ash (FA) and ground granulated blast furnace slag (GGBS). By investigating the influence of desert sand and SCM contents, the study aims to discern their impact on the workability and 7-day compressive strength of UHPC. Employing a central composite design (CCD), thirteen separate mixes were formulated. Key responses, namely workability and compressive strength, were evaluated. The developed models underscore the enhancement in UHPC performance through the partial replacement of cement with SCMs. Notably, an optimal combination of 75% desert sand and 30% SCMs resulted in a workability of 69.4 mm and a 7-day compressive strength of 46.01 MPa. The findings emphasize the potential for eco-friendly concrete in the construction industry, also prompting further exploration into long-term strength and higher SCM concentrations. [ABSTRACT FROM AUTHOR]

Box beams constructed earlier were prone to inadequate bending capacity owing to low construction standards, overloading, and environmental degradation. To resolve the challenge, three full-scale box slab beams in service for 15 years were strengthened with a high-strength mortar layer and an ultra-high-performance concrete (UHPC) layer in this paper. The flexural performances of unstrengthened beams (control beam) and strengthened beams (mortar beam, UHPC beam) were investigated by in situ four-point bending tests and numerical simulations. The experimental results showed that the cracking of box beams, strengthened with high-strength mortar and UHPC layers, was effectively mitigated. In comparison to the control beam, the cracking load of the mortar beam and the UHPC beam increased by 20%, and the ultimate load increased by 23.5% and 35.3%, respectively. The high-strength mortar layer had little influence on the elastic-phase stiffness of box beams. In contrast, the stiffness of the elastic phase of the box beam, strengthened by the UHPC layer, increased by 32.9%. In the numerical simulations, the load-deflection curves obtained from finite elements and tests coincided well. The characteristic loads showed relatively good agreement with the test results, with errors below 10%. Combined with the tests and numerical analyses, the proposed equations for predicting the ultimate bearing capacities of the control beam, mortar beam, and UHPC beam were presented with a better prediction accuracy. [ABSTRACT FROM AUTHOR]