# Safety Performance Evaluation of Ultra-High-Performance Concrete Semi-Assembled Barrier
## 2 Structural Characteristics of Barrier  
The newly developed semi-assembled UHPC barrier comprised several prefabricated UHPC shell segments, internally filled concrete, dowel bars, connecting rods, and supporting blocks. It is a separate barrier (Figure 1). The geometric shape of the barrier refers to the general diagram of 'Design Rules for Highway Traffic Safety Facilities' (JTG D81-2017) [26], which is an F-shaped slope. The UHPC shell segment is 4 m long and the shell thickness is 30 mm. The top is reserved with an internal concrete filling hole, the reserved port spacing is 2 m, and the size is 100 mm \(\times\) 300 mm. The barrier segments are connected longitudinally by steel bars. The segments are connected by dowel bars at the expansion joints. The barrier segments other than the expansion joints are connected by connecting rods. Both ends of the connecting rods are poured into the segments. The size of the connecting rods is \(\Phi\)22 \(\times\) 600 (mm). The supporting block is set at the center of the segment and the connection of adjacent segments is every 2 m on the back of the barrier. The size of the supporting block is 400 \(\times\) 400 \(\times\) 100 (mm), and it is prefabricated with ordinary concrete. The cement used in UHPC was Ordinary Portland Cement Type (PO. 52.5), produced by Jidong Cement Factory in Tangshan, China. Silica fume (SF) was produced by Henan Borun Casting Materials Co. (Zhengzhou, China), with a particle size range of 0.10-0.15 \(\upmu\)m, a specific surface area of 21 m\({}^{2}\)/g, and a SiO\({}_{2}\) content of 98.1%. Limestone powder (LP) was produced by Lingshou Dehang Mineral Products Co. (Shijiazhuang, China). The quartz powder (QP) had a particle size of 2000 mesh and a density of 2.65 (g/cm\({}^{3}\)). In this study, sand (S) was used at three levels, 20-40 mesh, 40-70 mesh, and 70-120 mesh, with a ratio of 5:2:3. A polycarboxylate superplasticizer (SP) with a water reduction rate of 26% was used in the test, which was produced by Suzhou Fuke Technology Co., Ltd. (Suzhou, China). The steel fiber was copper-plated straight steel fiber with a length of 12 mm and a diameter of 0.2 mm. The test water was laboratory tap water. The water-cement ratio was 0.165. To reduce the auto shrinkage of UHPC and improve its crack resistance and durability, expansive additives (EA) and antifoaming admixtures (AFA) were added in this study. The cement used in NC was Ordinary Portland Cement Type (PO. 42.5). The coarse aggregate (C) was crushed stone with a particle size of 5-10 mm. The mix proportion of concrete is provided in Table 1.  
Figure 1: Schematic of semi-assembled barrier sections. The compressive strength of NC and UHPC used in the barrier was tested, yielding a 28 d strength of 30.9 MPa and 142.48 MPa. The tensile strength test of the UHPC and NC was conducted using a universal testing machine. The average values of the three test blocks were obtained. The tensile strengths of UHPC and NC were 9.81 MPa and 300 MPa. To provide reliable material parameters for the finite element simulations of barrier collisions, a conventional triaxial test of the UHPC was conducted using a rock thermal-hydraulic-mechanical (THM)-coupled microcomputer servo triaxial test system (Figure 2). The radial pressure \(\sigma_{3}\) was set to 0, 5, 10, 15, and 20 MPa, respectively. Three specimens for each \(\sigma_{3}\) were utilized for the test, and the average results of the three specimens were taken for analysis. Uniaxial compression tests were conducted at a radial pressure of 0 MPa, with only axial loading to determine the uniaxial mechanical properties of UHPC. The test results are presented in Table 2.