Study on the Evaluation of Bonding Shear Performance of 200MPa Ultra-High Performance Concrete in Joints

Abstract

Recently, UHPC(Ultra-High Performance Concrete) has been developed based on the theory of high-density filling. When UHPC is applied to the on-site, the concrete joint is inevitably generated on the unexpected places due to the amount of casting at 1 day, the casting plan, the workers, the defect of the construction equipment and the delay in transportation. it may cause cracks and leaks, further corrosion of the reinforcing steel, which may degrade the durability of the concrete. Thus, the purpose of this study is to investigate the influence of UHPC joints in terms of materials and to propose a shear bond strength evaluation equation as a part of UHPC structure and member design. This paper is composed of 6 chapters in total. The contents of each chapter are as follows. Chapter 1, the background and necessity of the study and the purpose of the study are described. Chapter 2, the limitations of the definitions of domestic and external joints, attachment mechanisms, regulations and research trends, and existing shear bond strength evaluation equations are presented. Chapter 3, direct shear test was carried out to investigate the effect of cold joint according to the delay time on UHPC shear bond performance. Chapter 4, the influence of construction joints on the shear bond performance of UHPC using Push-off test classifying Series I (Reinforced) and Series II (Unreinforced). Chapter 5, the shear bond strength evaluation equation which reflects the UHPC strength zone and the bond performance factor is presented. Chapter 6, concludes the following conclusions considering the each chapter. 1. The optimum condition and the cause of the deterioration of the shear bond due to the occurrence of the cold joint were identified. (In the case of NC, the performance can be secured up to 120 minutes. In the case of UHPC, the optimum condition is 15 minutes. Approximately 7 % of bond performance is improved when compaction is carried out) 2. For optimal interface treatment of construction joint, it is preferable to use a waterjet (about 19 % reduction compared to the monolith specimen) to induce the interlocking of the aggregate in the NC. it is preferable to use a uneveness (about 21 % reduction compared to the monolith specimen) to induce the mechanical interlocking for improving the shear bond performance in the UHPC. 3. When the unevenness was applied on the construction joint, the shear bond performance of NC and UHPC increased about 1.5 times and 7.1 times respectively every time the unevenness increased by 10 mm. 4. We proposed the final shear bond strength evaluation equation (Vn) considering the proposed ACI 318-14 evaluation equation (Vs) and the proposed concrete shear bond strength evaluation equation (Vc).