An innovative normal concrete (NC) with partial use of ultrahigh-performance concrete (UHPC) composite structure is proposed in this paper to reduce the long-term creep-induced deflection in continuous box-girder bridges. The creep properties of NC-UHPC composite columns were experimentally investigated, and test results showed that the creep coefficients in NC-UHPC composite columns decreased considerably compared with NC columns. A creep computational model of the NC-UHPC composite was further developed to describe long-term creep behaviors of the composite columns in good agreement with the test results. Based on the proposed creep model, the long-term behaviors of a long-span box-girder bridge, made of the NC-UHPC composite, were evaluated by finite-element analysis (FEA), and the influences of the UHPC area fraction and the length of embedded precast UHPC columns were also discussed. Compared with the traditional prestressed concrete (PC) box girder, the long-term creep-induced deflection at the midspan of the NC-UHPC composite bridge reduced by 54.5%. The NC-UHPC composite is, therefore, conceived to be one of effective solutions for long-term creep-induced deflection control of long-span continuous PC box-girder bridges.

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.

The crack pattern of steel reinforced ultrahigh performance concrete (UHPC) beam is usually characterized by many densely distributed fine cracks (i.e., multiple microcracks) along with localized macrocrack, and the crack width development rate along the beam height is smaller than that of normal concrete since steel fibers and steel reinforcement bars are supposed to be effective in controlling crack width propagation of the UHPC beam. However, an effective crack width prediction formula is still underdeveloped for steel reinforced UHPC beam. The present study aims to formulate a crack width prediction equation based on the equations in Chinese code GB50010 where the parameters can be regressed and calibrated. Ten UHPC beams with different steel fiber volumes and reinforcing ratios are experimentally tested to collect crack width and spacing data for comparison and validation purposes. Nonuniformity distribution coefficient of rebar strain and average crack spacing are calibrated by the test data. Also, rebar stress is calculated with considering residual tensile strength of UHPC based on a sectional analysis. The modified crack width equation is validated with the test results, showing the best prediction accuracy of 0.97 and standard deviation of 0.11 for the test beams in this study compared to those predicted by JTG 3362, CECS 38, MC and AFGC. This study is emphasizing crack width prediction and control in designing UHPC structures.

Precast concrete bridge structures have been extensively used because of the mature construction techniques, fast construction, and their economy. Considerable practical applications, however, present certain disadvantages, such as cracking and water infiltration in their normal strength concrete (NSC, compressive strength 40 MPa) joints connecting prefabricated deck panels. Ultra-high performance fiber reinforced concrete (UHPFRC, compressive strength 143 MPa) has been proven highly effective in replacing the conventional cementitious grout materials in precast bridge structures. In the present study, three types of UHPFRC connections, rectangular, zigzag-shaped, and diamond-shaped, were experimentally evaluated on their flexural capacities, interface bonding performances, and failure modes through four-point bending tests (loading rate 0.1 kN/s). The results showed that all the UHPFRC connections exhibited apparently higher flexural capacities than an intact precast NSC member and had such strong UHPFRC-NSC interfacial bonding that the interfacial first-crack strengths were not less than the NSC member. Having the capability of modeling the UHPFRC connections and their interface properties, the developed finite element (FE) models of the precast slabs with UHPFRC connections produce numerical results in good agreement with the flexural tests. By means of the FE models, parametric investigations were carried out to make suggestions on optimizing the UHPFRC connection designs for practical use.

In this investigation, the effects of different fabrics with 0.20% carbon fiber textile (CFT), 0.21% glass fiber textile (GFT), and 0.25% basalt fiber textile (BFT) on the properties of TR-UHPC were investigated by axial tensile tests. A bending test of the BFT-UHPC pavement slab was carried out. In terms of axial tensile performance, the fiber textiles ranked in the following sequence: CFT, BFT, and GFT. Additionally, the corresponding increases in the initial cracking strength and ultimate tensile strength were 18.0% and 21.9% for the CFT, 12.0% and 16.0% for the BFT, and only 9.1% and 8.0% for the GFT, respectively. Increasing the textile reinforcement ratio of the BFT from 0.25% to 0.50% improved the cracking stress and peak stress of the specimen by 12.0% and 15.9%, respectively. Moreover, the ultimate strain of the 0.50%-BFT reinforcing case was 1.4 times that of the 0.25%-BFT reinforcing case and 2.6 times that of the unreinforced specimen in terms of ductility. The results of the stacking test on the BFT reinforced UHPC pedestrian slab indicate that the mid-span deflection of the test slab under normal use load is 0.775 mm, which is only 19.8% of the deflection limit. Additionally, the test slab remained in the elastic stage without any cracking. The BFT effectively enhanced the toughness of the UHPC thin slab after cracking. It is expected to be applied as a novel structure to bridge pedestrian slabs, bridge decks, and other thin UHPC members, thereby improving the durability and mechanical properties of bridge structures.

This study develops a new type of decorative bridge panel by ultra-high-performance concrete (UHPC) based on the project of the Guangyangwan Bridge. First, the numerical analysis was carried out using MIDAS and ABAQUS to find the critical position of the bridge and decorative panels. The numerical results showed that the last concrete cantilever segment had the greatest vertical deflection, and the corresponding panel had the greatest stress response. Based on the numerical results, this study conducted a series of full-scale, self-balanced bending tests to examine the crack resistance of six UHPC panels and six glass fiber-reinforced concrete (GRC) panels with varying curved section thicknesses (from 25 to 40 mm). The experimental results indicate that, due to the high strength of the UHPC matrix and the wall effect of steel fiber distribution, the crack resistance of UHPC panels is significantly superior to that of GRC panels. UHPC panels possessed superior stiffness and ductility, while GRC panels showed brittle fracture when the curved section thickness reached 34 mm. The uniaxial tensile cracking strength of UHPC with a steel fiber volume fraction of 1.6% was 14.7% greater than that of GRC with a glass fiber volume fraction of 5%. At the same curved section thicknesses, UHPC decorative panels exhibit cracking loads and ultimate loads that are 64.3% to 123.0% and 29.2% to 115.0% greater than GRC panels, respectively. Hence, UHPC is more suitable to produce ultra-thin decorative panels for bridges that are subjected to severe environmental action and external forces.