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Adjacent concrete box-beam bridges are widely used in short and medium span bridges. However, this bridge system has long term durability issues caused by shear key failure and reflective cracking in the upper. This paper investigates a new maintenance method of shear key joint. High performance grouting material with good fluidity, low water-cement ratios, slight expansion, little bleeding and excellent wear ability was used in the repairing process. An adjacent box-beam bridge with 3box-beams was designed and constructed to verify this strengthen approach in the laboratory. A concentrate load was imposed in the mid-span to simulate the vehicle loading. The deformation of box-beam, concrete strain and cracks were tested, then the load-deformation curve and the relative deformation difference were obtained . It was indicated that the mechanical property of the shear key repaired by the high performance grouting material can satisfy the design requirement, and have a greater strength. Introduction Precast prestressed concrete box beams are widely used in short and medium span bridges. The reasons for their popularity include ease of construction, fast installation, shallow superstructures yielding hither clearance when replacing old bridges. Although the structure performance of such bridges has been successful, this bridge system has long term durability issues caused by shear key failure and reflective cracking in the topping [1]. In many cases this cracking has resulted in water leakge, which could lead to lose the integrity of the bridge [2,3]. In order to solve this problem, a series of strengthening and maintenance technology have been developed, such as bonding transverse steel plate[4] or Π-shaped plate[5,6] in the bottom flange, prestressing transverse tendons[7] etc. By the application of these technologies, the mechanical performance of shear key can be promoted, and the integral behavior of the adjacent bridge would be great improved. However, these approaches still has a few disadvantages, such as breaking prestressed strand during rebar implanting, and not easy to operate in field[8]. High performance grouting material which is composed with of special additive, macromole polymer material and low alkali ordinary portl and cement, has many advantages such as high fluidity, low water-cement ratios, slight expansion, little bleeding and good wearability etc. As the repairing work can be carried out under the bridge, this method has a smaller communication impact, and lower construction expense with short timelines. Especially for small defects in the pavement deck, this reinforce approach has a more obvious advantage, and the maintenance costs can be greatly reduced in the life cycle of the adjacent concrete box-beam bridge. 0239 4th Annual International Conference on Material Science and Engineering (ICMSE 2016) © 2016. The authors – Published by Atlantis Press Maintenance Procedure of Shear Key The maintenance technology of shear keys with high performance grouting material can be summarized as follow: (1) Checking the actual quantity of the defects in shear keys, then marking them in the bridge. (2) Picking out the gravel and debris from the joints with special brush, then cleaning with powerful water cannon. (3) Sealing the ends of hinge joints by polyurethane foaming agent. (4) Setting the injection tube in the joints every 5 meters. The size of the injection tube is selected according to the width of hinge joints, a measuring tube need to be installed in the other end of the box beam joint. (5) Sealing joints under the box-beam: plug hinge joints from one end to the other end along the bottom of the box-beam by polyurethane foaming agent, and the plugging height is controlled from 3 to 5cm. prepare some wedge-shaped strips with length of 5cm wide, width of 3~5mm before grouting, height of 3cm,drive the wedge wood into slurry leakage gently to compact the crack when there is leaking under the box-beam. (6) Checking the sealing quality after sealing operation completed, and carry out pressurized air experiment or close water experiment, If the sealing property does not meet the requirements, it is necessary to repair the leakage again. (7) Pressure grouting: press continuous, slow and uniform speed into the grouting material through the crack with the pressure of 0.3-0.5MPa by the grouting machine, stop grouting when the paste is at the same level as the plate and there is no air bubbles. The storage time from mixing the grouting material shall not exceed 30 minutes, time out or liquidity does not meet the requirements of the grouting material shall not continue to be used, the schematic diagram of the construction is as shown in Fig. 1. Foam polyurethane High performance grouting material Fig. 1 Schematic diagram of the construction of high performance grouting material Layout of text Design of the Test The test box-beam was dismantled from a service bridge in highway road which has been in service for 10 years, as is shown in Fig. 2. The concrete’s design strength is C50, and the measured strength is 54MPa. In both ends of the beam, a few of diagonal cracks have been found, and the width is no less than 0.05mm. Before the test, all the visible cracks were repaired with epoxy pouring sealant. 0240 4th Annual International Conference on Material Science and Engineering (ICMSE 2016) © 2016. The authors – Published by Atlantis Press Fig. 2 The test void-box beam The loading system employed for the test box-beam is shown in Fig.3, consisted of a loading sensors, a hydraulic jack, a steel I-beam, an anti-force frame, some buttress and concrete weights etc.. The loading force was applied to the cross-sectional center of the adjacent bridge through the hydraulic jack hydraulic equipped with an out-of-plane frame as well as a force transducer to record the actual vertical force. I-beam Concrete weight Anchor rod

Strengthen Method of the Shear Keys in Adjacent Concrete Box-beam Bridges Using High Performance Grouting Material