Ultra-high Performance Concrete Layer Research Articles

Bonding performance between ultra-high performance concrete and asphalt pavement layer

The bonding performance between the ultra-high performance concrete (UHPC) and asphalt pavement layers is crucial to prevent the interface of asphalt pavement and bridge deck from falling off. In order to improve the bonding performance between UHPC and asphalt pavement layers, the surfaces of UHPC specimens were treated using four different techniques: spreading gravels, spreading steel balls, pickings and grooving. Through the pull-out and shear tests, the bonding performance between UHPC and asphalt pavement layers was evaluated. The pull-out strength and shear strength were used to evaluate the influence of different surface patterns on the bonding performance between UHPC and asphalt mixture layers. Additionally, the MATLAB software was employed to extract the digital image characteristic parameters of UHPC surfaces, and the neural network was constructed using the characteristic parameters to predict the bonding performance between UHPC and asphalt pavement layers. Results show that the spreading gravels, spreading steel balls, broom picking, cutting machine picking and grooving can all improve the bonding performance. Among the techniques, the cutting machine picking has the most obvious improvement on the pull-out strength and shear strength. The accuracy of neural network prediction model is reliable, and the correlation between the predicted value and the measured value is high. The result is of great significance to enhance the bonding performance between UHPC bridge deck and asphalt pavement layer, thus improving the durability of UHPC bridge structures.

Impact resistance of ultra-high performance concrete strengthened reinforced concrete beams

To improve the impact resisting performance of reinforced concrete (RC) components, three strengthening designs based on ultra-high performance concrete (UHPC) are proposed in this study. Drop hammer impact test was conducted to evaluate the dynamic response and failure modes of RC beams and UHPC strengthened RC-UHPC beams. Test specimens included two control RC beams, a RC beam with UHPC layer retrofitted on the tension surface, a RC beam with UHPC layers retrofitted on both the compression and tension sides, two RC beams with UHPC layer that was not directly attached to the tension surface, but with 5 mm gap between the interfaces. Test results showed UHPC strengthened beams had a good impact resistance. Under the impact from 641 kg weight dropping from 0.5 m, with a 15 mm UHPC layer directly attached to the tension surface of the RC beam, the crack pattern shifted from concrete spalling to diagonal shear failure, and the maximum and residual displacements decreased by 9.1% and 25.3%, respectively. RC-UHPC beams with non-attached interfaces exhibited even better impact resistance, the UHPC layer was able to develop multiple energy dissipating tensile cracks prior to failure, and the gap ensured a larger moment resistance leading to reduced beam deflections. The repeated impacts were performed on RC-UHPC beams. With the same total impact energy, the single impact was found to be more hazardous than the repeated impacts. Nonlinear finite element modelling was developed to further interpret the experimental results. With the validated numerical model, energy absorption curves, dynamic shear force and bending moment distribution diagrams were derived. Based on the experimental and numerical data, the shear mechanisms of RC beams and RC-UHPC beams were studied. The effects of non-attached spacing length, spacing depth and UHPC layer thickness were investigated in the parametric study.

3D-Printing of Ultra-High-Performance Concrete for Robotic Bridge Construction

Automation and robotics are integral parts of many industries but their potential for field implementation has not been significantly recognized by the construction industry. This is mainly attributed to conventional construction and design practices which undermine the benefits offered by these new technologies such as repetitions, precision, time savings, and increased safety. There is a need for advanced materials and 3D-printing systems which are capable of constructing structural elements with performance that emulates conventionally cast elements. This study presents a detailed framework and performance metrics for materials and 3D-printing systems for bridge applications. In addition, a study was carried out on ultra-high-performance concrete (UHPC) which showed sufficient extrudability and workability for 3D-printing applications. A 3D-printing system was developed for 3D-printing of continuous additive layers of UHPC with accelerated heat curing. Accelerated heat curing was used to enhance buildability, expedite the printing of the UHPC layers, and maximize the number of printed layers within the material open time. The effect of heat curing on material properties was also evaluated to obtain the optimal temperature to satisfy compressive strength requirements. This research effort aims to augment automated construction techniques and develop solutions to extend the applications of accelerated bridge construction.

Static and fatigue test on lightweight UHPC-OSD composite bridge deck system subjected to hogging moment

A cost-effective Lightweight Composite Bridge Deck (LCBD) system, including Orthotropic Steel Deck (OSD) and lightweight Ultra-High Performance Concrete (UHPC) layer is proposed to increase the stiffness and fatigue performance of conventional OSD. Static and fatigue tests on two full-scale strip models subjected to four-point bending were carried out. The static nominal cracking stress of the UHPC layer with reinforcement spacing of 80 mm is 24.59 MPa, while it increases to 35.68 MPa when the reinforcement spacing is reduced to half (40 mm); both values are far greater than the nominal stress of 12.7 MPa obtained in the prototype bridge. Increasing the reinforcement ratio can increase the bending stiffness of LCBD and decrease the tensile strain of the UHPC layer, while the change in range is relative slight. Furthermore, the flexural strength of UHPC and the reinforcement ratio are important factors affecting the fatigue life of the UHPC layer. When the reinforcement spacing increases from 40 mm to 80 mm, the fatigue life of the UHPC layer still satisfies related code requirements. Thus, for reduction in the engineering cost and construction complexity, the reinforcement spacing can be set as 80 mm. However, the application of the UHPC as the steel deck pavement, the rib-to-diaphragm welded joint is still prone to fatigue cracks. In addition, the existing S-N curves are hard to directly use for fatigue life prediction of the UHPC layer because of the great differences in the definition of stress level and evaluation index of failure in the fatigue test, which need to be modified in further studies.

Experimental and numerical study on the tensile behaviours of wet joints in steel-UHPC composite decks using a novel tensile test setup

A composite deck system composed of ultrahigh performance concrete (UHPC) and an orthotropic steel deck has been proposed to solve fatigue cracking and corrosion problems in traditional orthotropic steel deck systems. In a prefabricated steel-UHPC composite deck system, a wet joint is usually formed between two adjacent prefabricated UHPC layers. The interface between the prefabricated UHPC layer and cast-in situ UHPC is defined as a wet joint. To investigate the tensile behaviours of the wet joint, a novel tensile specimen configuration simulating the wet joint was initially proposed. The effects of reinforcement diameter and embedment length were experimentally investigated. The test results revealed that increasing the embedment length could enhance the crack resistance at the wet joint, but the influence could be neglected when the embedment length is greater than 10 db (db = diameter of reinforcement). Based on tensile tests, three-dimensional FE models were developed to simulate the tensile behaviours of the wet joint, and their accuracy was confirmed by the test results. With the validated FE model, the effect of UHPC thickness on the tensile behaviours of wet joints was investigated. Finally, specific design parameters were recommended according to the test and numerical results.

A preliminary study on the development of the normal concrete-UHPC composite beam via wet casting

Ultra-high-performance concrete (UHPC) is an innovative cementitious composite containing steel fiber reinforcement that can improve the behavior of structural elements thanks to its high strength and improved ductility properties. The mix design that provides these superior properties of UHPC also makes it a high-cost material. For this reason, the use of UHPC in parts where it contributes more significantly to the performance of the structural elements will lower down the costs and reduce the negative environmental effects caused by high cement content. In this preliminary study, the production of normal concrete (NC)-UHPC reinforced concrete (RC) composite beams by wet-on-wet casting was investigated by producing mini-RC beams. In the production of mini-RC beams, normal mortar (NM) and self-compacting mortar (SCM) mixtures were used to represent an NC. The results showed that in the production of NC-UHPC composite beams, the mixtures should have different rheological properties depending on the order of the layers. Increasing the total thickness of the UHPC layer enhanced the initial and yield stiffnesses as well as the peak loads. UHPC layer with thicknesses of 15 mm in tension zone, 30 mm in tension zone, and 15+15 mm in tension+compression zone led to the load-carrying capacity increment ratios of 20%, 34.6%, and 24.3%, respectively. However, increasing the thickness of the UHPC layer in the composite beams, especially more than 15 mm, reduced the ductility ratio and energy absorption capacity. Optimizing the tensile reinforcement ratio in UHPC layers can overcome the drawbacks in the ductility.

Structural Response of Steel Jacket-UHPC Retrofitted Reinforced Concrete Columns under Blast Loading.

The lateral capacity of exterior concrete columns subjected to a blast load is the key factor in the building collapse probability. Due to potentially severe consequences of the collapse, efforts have been made to improve the blast resistance of existing structures. One of the successful approaches is the use of ultra-high-performance-concrete (UHPC) jacketing for retrofitting a building’s columns. The columns on the first floor of a building normally have higher slenderness due to the higher first story. Since an explosion is more likely to take place at the ground level, retrofitting the columns of the lower floors is crucial to improve a building’s blast resistance. Casting a UHPC tube around a circular RC column can increase the moment of inertia of the column and improve the flexural strength. In this study, a retrofitting system consisting of a UHPC layer enclosed by a thin steel jacket is proposed to improve the blast resistance of buildings in service. Most of the previous research is focused on design aspects of blast-resistant columns and retrofitting systems are mostly based on fiber reinforced polymers or steel jackets. A validated FE model is used to investigate the effectiveness of this method. The results showed significant improvement both at the component and building system levels against combined gravity and blast loading.

Finite element model to predict structural response of predamaged RC beams reinforced by toughness-improved UHPC under unloading status

This paper simulates the structural response of strengthened predamaged reinforced concrete (RC) beams with reinforced ultrahigh performance concrete (UHPC) layer using finite element (FE) analysis. The FE models simulate the whole strengthening procedures for the predamaged RC beams by using UHPC to replicate the actual test conditions. A ‘tracking and positioning elements and nodes’ technology is applied for UHPC elements when the strengthening UHPC layer is activated. Concrete damaged plasticity (CDP) model is used for normal strength concrete and UHPC. The nonlinear behavior of reinforcing bars is taken into account. A newly developed interfacial model for the UHPC-RC interface is included in the FE model. The FE models are calibrated and validated by comparison with the experimental results. Load-deflection curves, characteristic loads, and damage patterns extracted from the FE simulation agree well with the experimental results. Finally, a parametric study is conducted to investigate the effect of height of the UHPC layer, height of the RC layer (size effect), and reinforcement ratio inside the UHPC layer on the flexural response of the strengthened beam with pre-damage in the RC beam. This study might provide a reference for future design and construction of predamaged RC beams reinforced by UHPC layer, to extend their service life and reduce maintenance costs.

Flexural strengthening of large-scale damaged reinforced concrete bridge slab using UHPC layer with different interface techniques

This paper investigated the flexural behavior of large-scale damaged reinforced concrete (RC) bridge slab strengthened with the ultra-high performance concrete (UHPC) layer at the tensile side. The RC slabs were preloaded under flexure to introduce cracks. The pre-damage degree was evaluated using the crack width at the highest load. Then, two types of interface technique of the RC substrate were conducted before strengthening of the UHPC layer. The first technique was a combination of embedded studs and rough surface (S-R) on the RC substrate. The second technique was rough surface (R) only. Experimental results indicated that the UHPC layer enhanced the flexural capacity and stiffness of the damaged RC slab. The UHPC layer also restrained and delayed the crack development in the RC and UHPC layers. It should be highlighted that the strengthened slab with the S-R interface technique exhibited significant mechanical performance compared with the interface treated using the R technique only. Therefore, the enhanced flexural performance of the UHPC-RC slab using the S-R technique may have an impact on the analysis and design of strengthening large-scale damaged RC bridge slab.

Characteristic analysis of acoustic emission monitoring parameters for crack propagation in UHPC-NC composite beam under bending test

Ultra high performance concrete (UHPC) has more outstanding mechanical properties and durability than normal concrete (NC) materials. Currently, analysis methods for the mechanical properties of UHPC structures and UHPC composite structures, such as measuring structural deflection, strain, and observing crack propagation, are relatively single. Acoustic emission (AE) technique is a non-destructive testing method that evaluates the damage state of structures effectively. The variation characteristics of AE parameters can be used to analyze the damage process and the failure precursor information of the structures. On this basis, AE technique was used to monitor the crack propagation of the UHPC-NC composite beam under four-point bending test in this study. Results showed that the U-shape UHPC layer gave full play to its high strength and ductility characteristics under bending, which was mainly manifested in reducing the number and width of cracks of the UHPC-NC composite beam, reducing the mid-span deflection and increasing the cracking load (Pcr) and ultimate load (Pu). AE ringing counts, energy, and b-value showed different and easily distinguishable variation characteristics at each failure stage of UHPC-NC composite beam and can be considered the optimal AE monitoring parameters. RA-AF association analysis can be used to further analyze the failure mode of UHPC-NC composite beam. AE monitoring method can be considered an alternative to traditional monitoring methods for the real-time monitoring of crack propagation in UHPC-NC composite beams.

Hot spot stress investigation on rib-to-deck-to-floor beam connections in UHPC reinforced OSDs

Orthotropic Steel Decks (OSDs) are widely used in various steel bridge types and however, their fatigue performances remain a prominent issue. In this paper, experimental work was conducted to investigate the hot spot stresses at various details of rib-to-deck-to-floor beam (RDF) welded connection in OSDs reinforced by ultra-high-performance concrete (UHPC). Quadratic extrapolation approach was applied to determine the hot spot stresses at weld toes of different fatigue prone details according to IIW specifications. Parametric studies were performed using finite element analysis to examine the effect of structural key parameters on the hot spot stresses including UHPC layer thickness and UHPC elastic modulus. Experimental results indicated that longitudinal flexural increased the out-of-plane distortions of the U-rib walls, therefore the hot spot stresses at locations on the U-rib were remarkably higher than that around floor beam cut-out. It is observed that hot spot stresses at region A on the U-rib wall directly under the acting load were controlled by tensile stresses, while region B on the other side of the acting load had compression stresses. The application of 60 mm UHPC layer significantly reduced the hot spot stresses at critical location on the U-rib and around floor beam cut-out by 57.8% and 36.5%, respectively. Parametric study results demonstrated that increasing UHPC layer thickness significantly reduced the hot spot stresses at all considered locations, while increasing the elastic modulus of UHPC layer slightly influenced the hot spot stresses and its effect can be neglected.

Full‐Scale Model Experimental Study of the Flexural Behavior of Hollow Slabs Strengthened by UHPC

The hollow slabs strengthened by ultrahigh performance concrete (UHPC) composite beam show many advantages over traditional reinforcement methods. In this paper, full‐scale model load tests were carried out on an nonstrengthened prestressed concrete hollow slab and an UHPC‐strengthened prestressed concrete hollow slab, comparing the load deflection, crack width, bearing capacity, deformation resistance, and self‐vibration frequency of the two. Static loading experimental results indicate that UHPC enhances the overall performance of prestressed concrete hollow slabs by decreasing deflection and crack width and improving bearing capacity. The strengthening effects of UHPC on a prestressed concrete hollow slab’s flexural behavior are also discussed, such as deflection, crack width, bearing capacity, deformation resistance, self‐vibration frequency, flexural behavior, and cracking load. Deflection and crack width under a load of 800 kN decreased by 45.8% and 56.3%, respectively, and the initial self‐vibration frequency, ultimate bearing capacity, and cracking load increased 19.2%, 21.4%, and 50%, respectively. The plane assumption can be made generally throughout the overall test process while using UHPC strengthening, which significantly constrains crack width and improves stiffness and deformation capacity. The UHPC layer and the prestressed concrete hollow slab were connected by shear studs to produce a good composite action between them, and the bending performance and bearing capacity of the whole structure were clearly improved. In addition to experiments, a validated numerical model is developed to verify the flexural performance of hollow slab strengthened by UHPC.

UHPC-based strengthening technique for orthotropic steel decks with significant fatigue cracking issues

Fatigue cracking is a common drawback of orthotropic steel decks (OSDs), especially for long-span steel bridge decks, and it is difficult to repair such decks effectively. This paper proposes an ultrahigh performance concrete (UHPC)-based strengthening technique for OSDs with significant fatigue cracking issues. A multiscale finite element (FE) model based on the Wuhan Junshan Yangtze River Bridge is established. Analysis results show that the vehicle-induced stress values in the OSD are significantly reduced. However, the maximum tensile stress at the bottom of the UHPC layer is 12.9 MPa under the vehicle load, indicating that the UHPC layer is at risk of cracking. Two alternative retrofitting schemes for the UHPC layer are presented. One involves reinforcement by adding one-story transverse steel bars, and the other involves adding steel strips to strengthen the bottom of the UHPC layer. Transverse bending tests were conducted to compare these two schemes. The results show that the tensile strength of the UHPC layer strengthened with 80-mm-wide steel strips could reach 43.2 MPa, and that this was the superior scheme. A test involving 10 million fatigue-loading cycles was conducted to evaluate this steel strip strengthening scheme. The results indicate that the UHPC layer has a fatigue life of 8 million cycles. Thus, the fatigue life of OSDs with significant fatigue cracks can be improved using this strengthening technique.

Reduce hot spot stresses in welded connections of orthotropic steel bridge decks by using UHPC layer: Experimental and numerical investigation

Orthotropic steel decks (OSDs) are widely used in long span steel bridges owing to their outstanding structural characteristics and lightweight; however, the fatigue resistance of OSDs is still a prominent problem of such deck structures. Ultra-High-Performance Concrete (UHPC) has been recently employed in orthotropic steel decks to enhance their structural behavior and extend their fatigue life. In this paper, experimental work has been carried out to investigate the effect of employing UHPC overlay on the hot spot stresses at fatigue prone details of OSDs. Three full scale rib-to-deck-to-floor beam (RDF) welded connections were fabricated and tested. One centric wheel load was applied; so that, the effect of in-plane and out-of-plane distortions of floor beam web can be considered. In parallel with the experimental program, a finite element (FE) analysis was also performed. Upon validation of FE models against experimental results, a parametric study was carried out to study the effect of key structural parameters that primarily influence the hot spot stresses. Experimental results indicated that, the stresses around floor beam cut-out were slightly higher than the hot spot stresses at considered locations on U-rib due to in-plane and out-of-plane distortions of the floor beam web under centric loading. The application of 60 mm UHPC layer effectively reduced the hot spot stresses by 26–83% at the considered locations of the test specimens. Results of parametric study indicated that, increasing UHPC layer thickness significantly enhanced the stiffness of the bridge deck and therefore effectively reduced the hot spot stresses at considered spots. On the other hand, the effect of increasing UHPC elastic modulus slightly influenced the hot spot stresses at considered locations and its effect is deemed neglectable.

Dynamic properties of a steel–UHPC composite deck with large U-ribs: Experimental measurement and numerical analysis

Steel–ultra-high-performance concrete (UHPC) composite decks, which are composed of thin steel– UHPC layers and large U-ribs, are an innovative bridge deck system. In this study, experimental and numerical approaches were combined to investigate the dynamic properties of a steel–UHPC composite deck. A large-scale steel–UHPC composite deck specimen was fabricated and tested under hammer impacting. The effects of the impact force characteristics on structural vibrations and noise were evaluated, and the vibration transmission characteristics in the deck were explored. The experimental results revealed that the steel–UHPC composite deck with large U-ribs exhibited complicated dynamic properties in different frequency bands. A finite element (FE) model was built and validated through comparison with the experimental natural frequencies and frequency responses. FE analysis was then used to compare the steel–UHPC composite deck with two other bridge deck systems (a conventional orthotropic steel deck and a steel–concrete composite deck). The numerical results indicated that the thin UHPC layer guaranteed the stiffness of the steel deck plate in the low-frequency range. At frequencies above 200 Hz, the vibration energy of the conventional orthotropic steel deck was approximately 0.45 times that of the steel–UHPC composite deck. Two countermeasures for reducing vibration (i.e., adjusting the crossbeam spacing and filling the large U-ribs with plain concrete) were found to be effective. Based on the simulation results, filling the U-ribs with plain concrete was the most effective approach and reduced the vibration energy by an average of 285% in the center frequency range of 63–1600 Hz.

Experimental study and theoretical prediction on shrinkage-induced restrained stresses in UHPC-RC composites under normal curing and steam curing

Ultra-high performance concrete (UHPC) has been recently developed as an innovative cementitious-based material, which exhibits excellent tensile and compressive strengths, as well as long-term durability. However, information regarding shrinkage-induced stress development in a composite system of UHPC-reinforced concrete (RC) is limited. The objective of the present research is to identify the restrained shrinkage of reinforced UHPC layer restrained by the RC substrate in UHPC-RC composites for 150 days. Free shrinkage of the UHPC layer was also measured for comparison. The UHPC layers were cured under normal laboratory (NC) temperature (5°C–35°C) and high-temperature steam (HC) at a temperature of 100°C for 48 h. Shrinkage-induced restrained stresses composite members have been evaluated based on a preexisting model used for conventional concrete. As UHPC shows different properties such as strength, shrinkage, and viscous behavior compared to conventional concrete, the development of elastic modulus of UHPC was included in the model for verification of cracking potential. A parametric study was conducted to investigate the influence of creep coefficients of UHPC and NSC on the restrained stresses. Results showed that restrained shrinkage in UHPC overlay was decreased by 57% and 80% compared to free shrinkage under NC and HC, respectively. The five stages of UHPC shrinkage development under NC during the first three days were observed while UHPC shrinkage under HC continually and rapidly increased during the curing period. On the other hand, the same shrinkage value was obtained for both NC and HC of UHPC at the age of 150 days. The preexisting model could calculate the restrained stresses, which was compared with tensile strengths of the different ages. The parametric study indicated that increasing creep coefficients of UHPC and NSC decreased the magnitude of shrinkage-induced restrained stresses in UHPC-RC composite structures.

Experimental study on flexural behavior of damaged reinforced concrete (RC) beam strengthened by toughness-improved ultra-high performance concrete (UHPC) layer

The flexural test was conducted to investigate crack resistance, loading bearing capacity, deformation characteristics and failure modes of damaged reinforced concrete (RC) beams strengthened by reinforced ultra-high performance concrete (UHPC) layer (Abbreviated as UC). Also, their mechanical properties were compared with those of the unstrengthened RC beam (Abbreviated as I–C). Additionally, the effects of pre-damage degrees in the RC beams and three strategies for the improvement of toughness of the reinforced UHPC layer on the cracking and flexural performance of UC were discussed. The results showed that UC acted monolithically under flexure without interfacial debonding before typically flexural failure. Compared with I–C, cracking and ultimate loads of UC increased by 1.57–3.32 times and 1.72–2.21 times, respectively. The reinforced UHPC layer effectively suppressed the cracking of the RC beam, making crack width in the RC beam propagate slowly with the load. Moreover, the severer the pre-damage degree of the RC beam, the smaller improvement of the flexural performance of UC. The addition of steel wire mesh, orientation of steel fibers and moderate-temperature steam curing further improved the cracking and flexural performance of UC with the most evident improvement in the addition of steel wire mesh. Finally, the theoretical model and formula were proposed for the calculation of load bearing capacity of UC with consideration of the influence of the pre-damage degrees in the RC beams, and the experimental results verified that the theoretical formula can accurately predict the load bearing capacity of UC.

In Situ Experimental Study on the Behavior of UHPC Composite Orthotropic Steel Bridge Deck.

A novel ultra high performance concrete (UHPC) layer composite orthotropic steel deck was adopted in the construction of a new bridge in China to improve the fatigue performance of the orthotropic steel deck plate and reduce the disease of surface wearing layer. In situ experiments were conducted to study the UHPC layer’s impact on the behavior of the orthotropic steel deck. The test vehicle loads were applied on the deck plate before and after UHPC layer paving, the stresses where fatigue cracks usually occur and the deflections of critical sections were measured. The test results verified that the UHPC composite steel deck system could significantly reduce the stress of the rib-to-deck connection region and the stress at the bottom toe of rib-to-diaphragm weld. In addition, it slightly influenced the performance of U shape rib, girder web-to-deck and diaphragm cutout.

Flexural capacity prediction of composite RC members strengthened with UHPC based on existing design models

Ultra-high-performance concrete (UHPC), a new generation of cementitious materials with very high strength, ductility, and durability, has been used for enhancing reinforced concrete (RC) structures as a strengthening material. The structural performance of RC members strengthened by UHPC or UHPC-concrete composite members is significantly improved. However, there are few methods for predicting the capacity of UHPC-concrete composite members. The present study proposes a simple method based on existing design models for the prediction of the flexural strength of composite RC members strengthened with UHPC at the tension zone. Rectangular stress block diagrams are used for the compression and tension zones of the conventional concrete and UHPC layers, respectively, in a composite section. The prediction results show good agreement with experimental results. The failure modes are predicted and compared with those observed in an actual test. Furthermore, a parametric study is carried out by varying some parameters, including the thickness of the UHPC layer and the compressive strength of UHPC. The results show that the proposed method can predict the flexural strength of UHPC-concrete composite members.

Interfacial bond properties between normal strength concrete substrate and ultra-high performance concrete as a repair material

Ultra-high performance concrete (UHPC) is suitable for the durable rehabilitation and strengthening of deteriorated normal strength concrete (NSC) structures due to its excellent characteristics, such as superior compressive strength, high tensile capacity, and extremely low permeability. However, a successful repair depends on whether the UHPC-NSC interface can provide good bonding performance under various applied loads and working conditions throughout its service life. In this study, the bond characteristics between the NSC substrate and UHPC layer were investigated by applying slant shear, splitting tensile, and direct tensile tests, and the interfacial bond strength and corresponding failure modes were observed. Seven studied factors, the roughness of substrate surface, UHPC age, moisture degree of substrate, curing condition of UHPC, strength of NSC substrate, bonding agent and expansive agent were included to explore their influences on the bond strengths, and the UHPC-NSC interfacial bonding enhancement mechanism. Results indicated that the UHPC overlay achieved superior interfacial bond performance for the rehabilitation of concrete structures, with the appropriate surface roughness and substrate wetness. The UHPC-NSC composite samples met the minimum requirements of the interfacial bond strengths specified in ACI 546-06 and achieved an “excellent” bonding quality. Furthermore, the friction coefficient for calculating interfacial bond strength was back-calculated according to the results obtained from the corresponding direct tensile and slant shear tests.