Plain Ultra-high Performance Concrete Research Articles

Utilization of recycled fine aggregate in ultra-high performance concrete: Mechanical strength, microstructure and environment impacts

Recycled aggregate derived from construction and demolition (C&D) waste offers new opportunities for the construction industry due to the shortage of natural aggregate. This study presents the feasibility of utilizing recycled fine aggregate (RFA) in ultra-high performance concrete (UHPC) to alleviate autogenous shrinkage, mitigate environmental effects, and further improve mechanical strengths. Three types of RFA with different particle sizes (0–0.6 mm, 0.6–1.18 mm, and 1.18–2.36 mm) are pre-saturated and then used as substitutes for quartz sand in UHPC. The influences of pre-saturated RFA on the workability, internal relative humidity, autogenous shrinkage, compressive strength, resistance to chloride ion penetration, and microstructure of UHPC are investigated. Experimental results showed that, compared to the plain UHPC, incorporation of 20 % RFA with particle size of 1.18–2.36 mm provides efficient internal curing, maintaining a higher internal relative humidity, and thus reducing autogenous shrinkage by 78.5 % at the age of 7 days. The compressive strengths of the UHPC containing 20 % RFA with particle size of 1.18–2.36 mm shows 7.1 % increase at the ages of 28 days. While it has a negligible effect on the fluidity and resistance to chloride penetration. The underlying mechanisms for the enhancement of properties involve the improved hydration degree of UHPC due to internal curing, which optimizes the structure of the interface transition zone and reduces the number of large pores. Furthermore, the sustainability analysis indicated that the use of RFA in UHPC exhibits 7.0 % lower carbon emissions and 7.8 % lower energy consumption, respectively. This study successfully proposes an effective approach for mitigating the autogenous shrinkage of UHPC without sacrificing strengths.

Enhancing the dynamic splitting tensile performance of ultra-high performance concrete using waste tyre steel fibres

The application of waste fibres in ultra-high performance concrete (UHPC) would reduce the total material cost of UHPC, but it is still unclear whether industrial fibres can be replaced by waste tyre fibres in terms of the impact resistance. In the present work, a series of experiments were performed to figure out the influence of waste tyre steel fibre (WF) content (i.e., 1.0 %, 2.0 %, 3.0 % and 4.0 %) on the workability, compressive strength, elastic modulus, flexural strength and dynamic splitting performance of UHPC, in comparison with plain UHPC containing 2.0 % industrial straight steel fibre (IF). The results reveal that the slump of UHPC is reduced with the increasing WF fibre content, but the flexural and static splitting strengths of UHPC are improved by up to 31.0 % and 24.7 %, respectively, within the measured WF content. Moreover, the dynamic splitting strength and dissipation energy of UHPC are promoted when the WF content is lower than 3.0 %, while an opposite trend takes place as the content of WF reaches 4.0 %. Additionally, the dynamic increase factor of WF reinforced UHPC shows higher sensitivity to strain rate than UHPC containing 2.0 % IF throughout the strain rate range of 2.0 s−1–6.5 s−1. The optimal WF content of UHPC can be regarded as 3.0 % considering the overall static strengths, dynamic splitting behaviour, as well as economic and ecological impact.

Properties of local ultra-high-performance concrete with low dosage of polyvinyl alcohol and steel fibre

Ultra-high-performance concrete (UHPC) delivers better durability and mechanical properties than normal-strength concrete. However, conventional UHPC requires heat treatment and a high dosage of high tensile steel fibre to achieve a compressive strength of 120 MPa. The present study was conducted to test a local UHPC with low fibre dosage and without heat treatment by incorporating different polyvinyl alcohol (PVA) fibre and steel fibre. The fibres included in the experimental works were 30 mm PVA macro fibre, 8 mm PVA fibrin and hooked end steel fibre with 35 mm in length. Four series of UHPC were studied, which consist of plain UHPC mix and three fibre-reinforced UHPC mixes. 1% fibre volume was incorporated into all the fibre-reinforced mixes. The mixes were tested for compressive strength, modulus of rupture, drying shrinkage and porosity The UHPC had a compressive strength of more than 120 MPa and modulus of rupture from 8 to 11 MPa. The drying shrinkage of all the UHPCs was less than 255με when cured at 100% relative humidity. The porosity recorded for the UHPC was 2%. Current findings indicated that steel fibre reinforced UHPC performed better than UHPC with PVA fibre in terms of mechanical properties However, UHPC with PVA fibrin performed better in terms of the drying shrinkage. In conclusion, UHPC with more than 120 MPa can be achieved with normal synthetic and steel fibre without special treatment.

Strength Iso-Responses of Shear-Deficient Ultra-High Performance Fiber Reinforced Concrete Beams

The development of sustainable construction methods can be achieved by improving the performance of reinforced concrete elements, resulting in an increase in structural life expectancy. This paper presents a study of the structural performance of shear-deficient ultrahigh-performance concrete (UHPC) concrete beams to produce sustainable construction materials. In the first phase of the experimental campaign, performance-based optimizations were implemented for UHPC. The characteristic compressive strength of all mixes was kept at 130 ± 10 MPa. The elastic modulus of plain UHPC was obtained at 8 GPa, and for the fiber-reinforced one was 40 GPa. Additionally, 18 sets of reinforced UHPC beams were investigated for their structural behavior based on the overall depth, reinforcement ratio (ρ), and the shear-span-to-depth ratio (λ) as key variables. Here, λ was varied between 1 and 2 and ρ was varied between 0.56% and 3.15%. The experimental study determined the lowest shear strength as 4.56 MPa, and the highest shear strength was calculated as 11.34 MPa. The database of the current shear strength results and similar literature results were used to develop models for predicting shear capacity. This research focused on applying a statistical approach using neuro-fuzzy logic, the robust analytical model. The ratio of the experimentally calculated shear strength and the predicted shear strength for different values of λ and ρ was obtained between 0.75 and 1.25, which was in good agreement with the results of similar literature. The results of this study suggest that high-strength fiber may extend structural lifetimes in UHPC applications.

Hybrid effects of carbon nanotubes and steel fiber on dynamic mechanical properties of ultra-high performance concrete

This study aims to investigate the hybrid effects of carbon nanotubes (CNTs) and steel fiber (SF) on dynamic mechanical behavior of ultra-high performance concrete (UHPC) under the high-speed dynamic loading effects. The functionalized CNTs content varied from 0.0% to 0.20%, and SF volume content was added from 0.5% to 2.0%. The UHPC specimens were tested at strain rates ranging from about 60 s−1 to 240 s−1 using the split Hopkinson pressure bar. The dynamic behavior of specimens was evaluated in terms of stress–strain relationships, energy absorption capacity and failure patterns. Test results show that dynamic compressive properties of UHPC are strongly sensitive to strain rates. The individual addition of CNTs obviously improves the dynamic performance of plain UHPC, and there exists an optimal CNTs content of about 0.10% to achieve better improvement effects. The dynamic increase factor (DIF) is almost unrelated to CNTs content but closely correlated to strain rate variations, which can be well described by a modified empirical formula. Furthermore, it is found that the hybrid CNTs and SF display more significant reinforcing effects on dynamic properties of UHPC, as the UHPC specimen with 0.10% CNTs and 2.0% SF exhibits the highest dynamic compressive strength and toughness. Meanwhile, UHPC reinforced by hybrid fibers is less sensitive to high strain rates compared to plain UHPC. From microscopic observations, it is reasonably believed CNTs and SF exert synergistic reinforcing effects on UHPC matrix in view of their respective characteristics, which are more significant in improving the interfacial transition zone (ITZ) structure between SF and the surrounding matrix. This work promotes a fundamental understanding for the reinforcing effects of CNTs on UHPC, and provides an effective strategy to reinforce UHPC from multiscale perspectives.

Effect of nano-SiO2 on fiber–matrix bond in ultra-high-performance concrete as partial substitution of silica flour

This study investigated the effect of nano-SiO2, which partially substituted silica flour, on the rate-dependent bond behavior of straight steel fibers in ultra-high-performance concrete (UHPC). As much as 0%–50% by weight of the silica flour was replaced with the nano-SiO2. The packing density of the granular particles increased with the nano-SiO2 content up to 15%. However, upon increasing the nano-SiO2 content further, the packing density gradually decreased. A higher packing density was obtained at a replacement ratio of 15% than those of conventional UHPC. The static bond performance of steel fiber in UHPC was improved by adding up to 40% of nano-SiO2. Moreover, the best pullout resistance was observed in UHPC containing 10%–15% nano-SiO2 because of its filling effect and secondary pozzolanic reaction. The equivalent bond strength obtained on adding proper amounts of nano-SiO2 was thus nearly twice that of the plain UHPC. The impact pullout resistance for the UHPC matrix incorporating up to 30% of nano-SiO2 was higher than that for the plain UHPC; however, the best impact pullout resistance was observed at 10%–20% nano-SiO2 contents. A remarkable rate sensitivity of the bond strengths of straight steel fibers in the UHPC matrices was observed. The rate sensitivity of the average bond strength in the plain UHPC decreased on adding nano-SiO2. However, the rate sensitivity of the equivalent bond strength was insignificantly affected by the nano-SiO2 content. Overall, a 10%–15% nano-SiO2 content was considered to be the optimal in terms of the improved static and dynamic bond performances.

Roles of carbon black or carbon fibre on improving mechanical and electromagnetic properties of ultra-high performance concrete in K-band frequency range

To prevent electromagnetic wave pollution, the electromagnetic wave absorption capability and compressive strength of ultra-high performance concrete (UHPC) mixed carbon black (CB) and carbon fibre (CF) are methodically examined in K-band frequency range (i.e. 18–26.5 GHz). The mechanical properties, loss tangent, reflection loss, and microstructure of UHPC with the addition of CF and CB contents are determined via pressure tests, probe method, reflectivity tests, and scanning electron microscopy. The test results reveal that the compressive strength, dielectric loss tangent and reflection loss of UHPC are enhanced by the addition of CB and CF. When 0.5 vol.% CF is added, the reflection loss less than −10 dB in the K-band frequency range, and less than –15 dB in the frequency range of 21.68–23.38 GHz. By comparison, the reflection loss of UHPC with 0.5 vol.% CF is more than 1.8 times that of plain UHPC in the K-band frequency range.

Experimental Database on pullout bond performance of steel fiber embedded in ultra-high-strength concrete

The bond strength between the steel fiber and the ultra-high performance concrete (UHPC) matrix plays a significant role in improving the behavior of plain UHPC. This paper compiles the existing experimental research database on the pullout bond performance of steel fibers embedded in UHPC. The variations of key parameters in the database are the steel fiber type and geometry, fiber volume fractions, and fiber embedded length. The effects of these parameters are analyzed and discussed in detail. Based on the analysis of the results, it was found that the deformed steel fibers, i.e., the hooked-end, half-hooked-end, and twisted steel fibers clearly provided higher average bond strengths than that straight fibers. The average pullout bond strength was obtained by increasing of fiber volume fraction in the UHPC matrix up to 2% (11.21MPa) with an increment of 20.4%. When the steel fiber volume fractions increase beyond 2%, the average bond strength decreases. Additionally, it was also found that using smaller embedded lengths in deformed steel fibers could result in the improvement of bond strength. This could be due to the fact that the bond is controlled by the mechanical anchorage of the end-hook rather than the physio-chemical bond in the straight portion. Conversely, increasing the embedded length of steel fiber could greatly contribute to the enhancement of pullout resistance resulting in increased bond strength between the UHPC matrix and steel fibers.

Experimental and analytical investigation of UHPC confined concrete behavior

Ultra-High Performance Concrete (UHPC) is a self-levelling cementitious material with enhanced mechanical and durability properties when compared to normal strength concrete. Accelerated construction of concrete columns can be realized using a precast hollow UHPC shell as permanent formwork. Also, as a retrofit solution, UHPC can be placed around existing concrete columns with deficient confinement details. The continuous confinement provided by UHPC shell to both the concrete core and longitudinal reinforcement could be used to improve the seismic behavior of columns or reduce the amount of confining hoop reinforcement required in traditional column designs. An experimental and analytical study is performed with a main objective of quantifying the confinement effect provided by plain UHPC shell. The experimental investigation compressed of axial testing of 228 mm (9 in.) and 280 mm (11 in.) dia circular columns, 203 mm (8 in.) and 305 mm (12 in.) square columns confined with UHPC shell. Experimental investigation included a total of two normal strength concrete column specimens as control specimens and 11 column specimens confined with 1 in. and 2 in. thick UHPC shell. All the specimens were tested to failure under axial compression and were extensively instrumented. The confinement provided by the unreinforced UHPC shell improved the peak compressive stress and the crushing strain values of the core concrete by 15%–30% and 26%–46% respectively. The effectiveness of plain UHPC shell to provide confinement was found to considerable in circular columns compared square columns. A detailed 3D FEA models were developed in ATENA software and were validated using the experimental data. The FEA models captured observed responses accurately and provided insight into the observed experimental behavior. Based on the experimental and analytical study, it is recommended to include some transverse reinforcement in UHPC shells, especially for non-circular cross-section for improved confinement effect.

Effects of isothermal microwave heating on the strength and microstructure of ultra-high performance concrete embedded with steel fibers

This paper presents an investigation on the adoption of isothermal microwaving in curing ultra-high performance concrete (UHPC) embedded with steel fiber reinforcement. The plain UHPC and the one with varying levels of steel fiber reinforcement are developed by microwave heating at 80 °C for 30 min. The compressive and flexural strength, hydration products, microstructure and interfacial structure of the mixes are evaluated. The results show that, besides the common reactions of hydration, pozzolanic reaction, carbonation, a reaction consuming calcium carbonate is found to occur in the system; furthermore, a Hayne-like phase and a cancrinite-like phase are formed. The formation of them is reduced by increased reinforcement. The accelerated effects of microwave on reaction are found to vary with reinforcement. Accelerating hydration is beneficial from increased fiber contents. Steel fiber reinforcement is more effective in increasing the compressive and flexural strength of UHPC cured with microwaves than cured under standard conditions.

Influence of sisal fibers on the mechanical performance of ultra-high performance concretes

This paper investigated the utilization of natural sisal fibers in ultra-high performance concrete (UHPC). UHPC mixtures containing sisal fibers with different lengths (6, 12, and 18 mm) and volume contents (1.0%, 2.0%, and 3.0%) were prepared. Flowability, mechanical strength, and interfacial bond behavior between fiber and matrix were tested for every mixture. The distribution of sisal fibers in the UHPC matrix was evaluated using the ultraviolet (UV) light and fluorescent whitening agent (FWA). Finally, the microstructures of typical samples were observed by a scanning electron microscope (SEM). Experimental results indicated that the flowability of the fresh UHPC mixture decreased with the increase of length and volume fraction of sisal fibers. The content of 2.0% sisal fibers with a length of 18 mm increased flexural strength and toughness of UHPC by 16.7% and 540.0%, respectively, compared with plain UHPC specimens. The pull-out load and pull-out energy increased with the length of sisal fibers. Moreover, the sisal fibers can be uniformly distributed in the UHPC matrix. Therefore, the utilization of sisal fibers to manufacture a low-cost and low energy-consumption UHPC has great potential.

Axial Behavior of Reinforced UHPC-NSC Composite Column under Compression.

This paper proposes a novel reinforced ultra-high-performance concrete (UHPC)-normal strength concrete (NSC) composite column. The main feature of the reinforced UHPC-NSC composite column is the use of an exterior UHPC cover, which is helpful for improving the load-carrying capacity, deformability, and crack resistance. This study focused on the axial behavior of the reinforced UHPC-NSC composite column. A total of 12 specimens were designed to investigate the axial behavior of the composite column under compression. The thickness of the exterior UHPC cover, volumetric stirrup ratio, and construction method were considered as the main experimental parameters. The failure modes and strain–stress relationships are discussed in this paper. By introducing the exterior UHPC cover, the peak confined strength obviously improved. The compressive strain at the peak confined strength was mainly determined by the deformability of the plain UHPC material. The composite column resulted in a unique sudden drop immediately after the peak confined strength, owing to the rapid loss of the confining stress from the exterior UHPC cover. A trilinear model is proposed to describe the strain–stress relationship of the composite column. The results obtained by the modified model are in good agreement with the test results.

Test and simulation of circular steel tube confined concrete (STCC) columns made of plain UHPC

This study presents experimental and numerical investigations on circular steel tube confined ultra high performance concrete (UHPC) columns under axial compression. The plain UHPC without fibers was designed to achieve a compressive strength ranged between 150 MPa and 200 MPa. Test results revealed that loading on only the UHPC core can generate a significant confinement effect for the UHPC core, thus leading to an increase in both strength and ductility of columns, and restricting the inherent brittleness of unconfined UHPC. All tested columns failed by shear plane failure of the UHPC core, this causes a softening stage in the axial load versus axial strain curves. In addition, an increase in the steel tube thickness or the confinement index was found to increase the strength and ductility enhancement and to reduce the magnitude of the loss of load capacity. Besides, steel tube with higher yield strength can improve the post-peak behavior. Based on the test results, the load contribution of the steel tube and the concrete core to the total load was examined. It was found that no significant confinement effect can be developed before the peak load, while the ductility of post-peak stage is mainly affected by the degree of the confinement effect. A finite element model (FEM) was also constructed in ABAQUS software to validate the test results. The effect of bond strength between the steel tube and the UHPC core was also investigated through the change of friction coefficient in FEM. Furthermore, the mechanism of circular steel tube confined UHPC columns was examined using the established FEM. Based on the results of FEM, the confining pressures along the height of each modeled column were shown. Furthermore, the interaction between the steel tube and the UHPC core was displayed through the slip length and shear stresses between two surfaces of two materials.

Implication of calcium sulfoaluminate-based expansive agent on tensile behavior of ultra-high-performance fiber-reinforced concrete

This study aims to investigate the effects of a calcium sulfoaluminate (CSA) based expansive agent (EA) on the tensile behaviors of ultra-high-performance concrete (UHPC) reinforced with straight and twisted steel fibers. For this, five different CSA EA amounts ranging from 0% to 8% were considered. Because the major purpose of adding a CSA EA into a cementitious matrix is to reduce the amount of shrinkage, its implication on the free-shrinkage response of UHPC was also evaluated. The test results indicate that approximately 7% and 10% smaller shrinkage strains were obtained in UHPC matrices with 6% and 8% CSA EAs than that of plain UHPC, respectively. Most of the tensile parameters, including the tensile strength, strain capacity, and g-value, of UHPCs with straight and twisted steel fibers were deteriorated when including a CSA EA and increasing its amount, except for the tensile strength of straight fiber specimens. Thus, the CSA EA needs to be carefully applied for UHPC mixture, despite its positive effect on reducing the amount of shrinkage strains by greater than 6%. There was no clear trend regarding the effects of the amount of CSA EA on the number of fibers located near the localized crack of ultra-high-performance fiber-reinforced concrete (UHPFRC), and the unit number of fibers in UHPFRC specimens with 2% (by volume) of 0.3-mm diameter steel fibers ranged from 25 to 35 ea/cm2. The tensile strengths of UHPC reinforced with straight and twisted steel fibers were both improved when increasing the number of fibers, although the former showed a much higher rate of increase and degree of correlation than the latter. The strain capacity and g-value of UHPC with straight and twisted fibers showed only marginal correlations with the number of fibers regardless of the amount of CSA EA applied.

Virtual estimation of the Griffith’s modulus and cohesive strength of ultra-high performance concrete

This investigation presents a computational methodology to estimate the unit fracture energy (Griffith’s modulus) and the cohesive strength of ultra-high performance concrete (UHPC). The hydration of plain UHPC mixtures is simulated using the National Institute of Standards and Technology (NIST) Virtual Cement and Concrete Testing Laboratory (VCCTL) hydration simulator. The Young’s modulus of elasticity of the hardened concrete is obtained via finite-element analysis of a sample cube of its micro-structure. Applying the Extended Finite Element modeling capabilities of ABAQUS to previously grooved simple structural elements under gradually-increasing load, the results of computational simulations of the start of crack growth are linked to the corresponding predictions by regressions on experimental observations in classical linear elastic fracture mechanics physical tests. A procedure is developed to estimate both the Griffith’s modulus and the cohesive strength of the UHPC, which are difficult to assess experimentally. As an application, the effect on the horizontal thrust at the abutments of a two-hinged symmetric arch with a crown crack and uniformly loaded is analyzed using the data provided by the pure-bending test on a pre-grooved simply supported beam.

Study of Toughness and Macro/Micro-Crack Development of Fibre-Reinforced Ultra-High Performance Concrete After Exposure to Elevated Temperature.

This study has investigated the changes that might appear in post-peak flexural response. Before the flexural test, prismatic specimens were placed in a furnace chamber and exposed to elevated temperatures of 400, 600, and 800 °C. The flexural toughness test was carried out on two types of concrete: Plain ultra-high performance concrete (UHPC) and UHPC with different types of fibres (steel fibre (SF) and polypropylene fibre (PPF)) at 0.5%, 1%, 1.5%, and 2% volume fractions. During the flexural test in the macro-crack development analysis, the non-contact ARAMIS system was used to perform three-dimensional measurements of strain and displacement. The results of scanning electron microscope (SEM) observations of micro-crack development in UHPC without and with SF/PPF were also presented. The experimental results showed that in some cases, the load–deflection curve of fibre-reinforced UHPC displayed a double-peak response. The first peak signified the UHPC properties, while the second peak represented the properties of the fibres. Under flexural load, the toughness decreased as the temperature increased. Significant decrease in the load–deflection response and toughness were observed for the polypropylene fibre-reinforced UHPC when the temperature approached 800 °C. The SEM observation results showed that the thermal damage of fibre-reinforced UHPC depends on the pore pressure effect, the thermal mismatch, the decomposition of hydration products, and the formation of micro-cracks.

Experimental study on structural performance of UHPC and UHPFRC columns confined with steel tube

Structural performance of circular steel tube confined ultra high performance concrete (UHPC) columns under uniaxial compression was presented in this study. In addition to plain UHPC, steel fibers reinforced UHPC (UHPFRC) with 1% and 2% by volume were also investigated. A total of eighteen composite columns including short and intermediate columns were constructed and tested. Test results indicated that a substantial improvement in the strength and ductility was obtained by means of loading on only the concrete core. All specimens exhibited a shear plane failure of the UHPC and UHPFRC core which is normally associated with the softening behavior. The incorporation of steel fibers can enhance the ductility only for the intermediate columns and minimize the localized deformation of the columns. The influences of steel fibers and steel tube thickness on the axially compressive behavior were also identified. The analysis of test results demonstrated that the addition of steel fibers has negligible effect on the response of axial load versus axial strain. Furthermore, the impact of steel tube thickness and the confinement index on the strength and ductility was found to be more dominant than that of steel fibers.

Inclusion of nano metaclayed as additive in ultra high performance concrete (UHPC)

The utilisation of Ultra High Performance Concrete (UHPC) tailored with nano materials has growing an interest to the construction. In this research, nano metaclay UHPC mixes were used as additive range from 1, 3, 5, 7 and 9 percent from cement weight. The effect of nano metaclayed UHPC was evaluated in the forms of physical, workability, strength property and morphology of the microstructure in the UHPC and compared to the normal UHPC and metakaolin UHPC. For physical property, the nano metakaolined paste was confirmed using vicat apparatus and determination of fresh property was conducted using slump test. Meanwhile, compressive strength was conducted at 3, 7, 28 and 90, 180 and 365 days of age. The UHPC morphology was analysed using Scanning electron microscope (SEM). It can be concluded that the introduction of nano metaclay in UHPC increase the water demand in UHPC by increase the surface area. For compressive strength, introduction of nano metaclay shows no significant effect at early ages but gradually increase at later ages as compared to the plain UHPC.

Evaluation of axial strength in circular STCC columns using UHPC and UHPFRC

This study investigates the axial strength of circular steel tube confined concrete (STCC) columns with the employment of plain ultra high performance concrete (UHPC) and ultra high performance fiber reinforced concrete (UHPFRC) having compressive strengths of cylinders varying from 178.9 MPa and 198 MPa. UHPFRC used in this study had 1% and 2% volume fraction of steel fibers in the mixture. Eighteen specimens including both short and intermediate columns were cast and tested under concentric loading on the concrete core to generate the maximal confinement effect. Experimental results showed that the effect of steel fibers on the axial load versus axial strain responses, and on the enhancement of strength and ductility was insignificant, while the parameters of the steel tube and the concrete core length were found to play a major role. The ultimate loads of the tests presented herein were compared with those obtained from the predictions by seven analytical models and five existing design codes. The design expressions from these analytical models and codes were assessed. For the prediction of the ultimate loads of both short and intermediate column, the model by De Oliveira et al. [13] was the most suitable approach among seven selected models, whereas the ACI provision [1] was the best among five existing design codes. Furthermore, the experimental ultimate loads obtained from this study were combined with those from previous studies to examine the influence of different concrete strength ranges on the strength enhancement. Finally, unified formulae to predict the ultimate strength with a wide range of concrete strength up to 200 MPa were also proposed for both short and intermediate columns.

Numerical and Experimental Analysis of the Shear Behavior of Ultrahigh-Performance Concrete Construction Joints

Shear performance of plain UHPC (ultrahigh-performance concrete) construction joints is studied in both experimental and analytical ways. In push-off tests, three different contact surfaces of the construction joint were considered, while the case without any joint was provided for the reference. Test results indicate that the geometry of contact surfaces greatly affects shear performance of the construction joint. With simplifying structural behavior of contact surfaces and UHPC substrate, the finite-element analysis model is developed for every case studied by utilizing the ABAQUS software and validated against the test results. Agreement between experimental and numerical simulation results is excellent especially in terms of displacement, strength, and failure mechanism. It is expected that the present work provides a basis for further study on reinforced UHPC construction joints.