# Experiment on the Tensile Strength of Concrete Joint Surface at Early Ages  
[PERSON]  
1 College of Water Conservancy and Hydropower Engineering, Hohai University, Nanjing 210003, China; [EMAIL_ADDRESS]  
[PERSON]  
2 Changiang River Scientific Research Institute, Wuhan 430010, China; [EMAIL_ADDRESS]  
[PERSON]  
3 Huai'an Water Conservancy Survey & Design Inst Co., Ltd., Shenzhen Rd., Huai'an 223005, China; [EMAIL_ADDRESS] (Y.C. ); [EMAIL_ADDRESS] (M.W. ); [EMAIL_ADDRESS] (F.W.) [PERSON]  
3 Huai'an Water Conservancy Survey & Design Inst Co.  
such as air bubbles within the post-cast concrete may lead to a weak bond between the old and new concrete interfaces; coupled with the difference between the shrinkage characteristics of the newly poured part and the mature concrete, the strength of the two bonding surfaces is thus weakened, making it easy for cracks to be formed, and thus becoming a weak point in the overall structure. Therefore, it is of great significance to study the strength of the interface between new and old concrete. Currently, the investigation into the bonding strength between new and old concrete interfaces is primarily conducted through experimental research and analysis [1; 2; 3; 4]. The bond strength tests are categorized into the following three types according to the stress state generated in the bond surface: tensile, shear, and (tensile) compressive shear tests. [PERSON] et al. [5; 6] conducted bond strength tests on 164 specimens using each of the three types of test methods above. After analyzing the test results, it was found that the results of the bond strength test on the bonding surfaces were significantly affected by the type of test. In the order of oblique shear test, double-sided shear or pure shear test, split test, and pull-off test, the bond strength decreases sequentially with the test methods. Increasing the roughness of the bonding interface can significantly improve the bonding properties of old and new concrete [7; 8; 9; 10; 11] and enhance the strength of the concrete bonding interface. For example, applying surface treatment methods to the existing base concrete layer before adding a new concrete layer can be effective. Typical surface treatment methods include using a wire brush [12], sandblasting [13; 14; 15], water spraying [16], manual chiseling [17], and grooving [18; 19]. In some cases, different types of adhesives can be added to the base layer to enhance bonding strength. Additionally, the research on aging mainly focuses on the following two aspects: first, altering the age of the old concrete substrate, and second, changing the age of the new and old concrete specimens after the pouring is completed. Based on the consideration of roughness factors, [PERSON] et al. [20] designed an experiment using the chiseling method. The test results showed that increasing the roughness of the interface between new and old concrete can significantly improve the bond strength. [PERSON]'s research team [21] chose to chisel the surface of the old concrete two weeks after pouring, and then pour the repair material. Tensile strength measurements were conducted on the samples on the 2 nd, 7 th, 14 th, and 28 th days after pouring. The experimental results indicated that the test age had a certain impact on the tensile strength; as the age increased, the tensile strength of the interface between the new and old concrete slightly increased. In summary, the study of the tensile strength of the bond surface of old and new concrete plays an important role in guiding the correct modeling of the mechanical properties of the joint surface during simulation calculations. In this paper, in order to investigate the tensile strength of a concrete joint surface at an early age, the split tension test method is adopted, and the innovative use of no-chiseling stopping tape to produce a uniform rough surface of concrete and expand the cross-section area of concrete specimen blocks is used to enhance the accuracy of the test results.