Language: English
Bridge Rpair and Reinforcement
Horse CFRP Carbon Fiber
The bonded part of the carbon FRP used in the bridge did not appear to slip, crack, loose and peel. The quality of the bridge has been steadily improved without cracks. Moreover, the capital cost required to bonding carbon FRP to strengthen and repair the bridge is small.
1 Project Overview
Reconstruction and reinforcement of a section of the old bridge, which was built in 2012. However, four years after it was put into use, the entire bridge suffered varying degrees of damage due to the burning of waste combustibles under the bridge. In particular, the damage to the bridge piers, bearings and other parts closer to the scene is particularly serious. In most of these locations, the bottom concrete fell off, leaving the steel bars exposed. It was identified that the bridge was classified as Category 3, so it needed treatment. Taking into account the requirements of the bridge for the bearing capacity and durability of the pier columns, it was decided to use Carbon FRP to reinforce the technology. The carbon FRP with a maximum diameter of up to 10 cm and polymer cement mortar are used for reinforcement. The selection reference data of specific carbon FRP is shown in Table 1.
2 Carbon FRP reinforcement principle
2.1 Carbon FRP materials
From the point of view of composition, the components of this material are matrix and fiber. This material has several obvious advantages:
①Excellent elasticity, and the stress-strain variable is an important reference index.
②Corrosion resistance, light texture and good performance.
③Convenient operation and easy construction.
Therefore, construction materials of this material are often used in the construction of sticking carbon FRP. Compared with steel, the weight of this material is only 0.25 times that of it, but it has a tensile strength that is more than 10 times higher than that of steel. It is expressed by a specific value, that is, the tensile strength of this carbon fiber composite material can be Reach 43000MPa.
2.2 Bonding material
Only bonding materials that meet the standards of strength, stiffness and flexibility can ensure that the combination of concrete and carbon FRP has sufficient strength. Moreover, the bonding material of this material can be used after the concrete has broken, so that the two sides of the split can be integrated into a whole. In addition, the bonding material does not have harsh requirements for curing conditions, and can be cured even under normal conditions. Generally speaking, for reinforcement construction in the field, the best bonding curing time should not exceed 3h. Taking into account the performance requirements of the construction bridge, the bonded material also needs to have a certain fluidity and viscosity index. Leveling materials, primers, and impregnating resins are currently popular bonding materials.
3 Construction process
The specific construction process of sticking carbon FRP reinforcement technology is:
Construction preparation-construction lofting-concrete surface treatment-preparation and painting of the bottom layer resin a pair of unevenness for leveling-application of impregnated resin or paste of resin-pasting of carbon FRP and quality inspection-surface maintenance
4 On-site inspection method of carbon FRP reinforcement quality
4.1 Selection of equipment and samples
Use bond strength tester. After the reinforcement of the carbon fiber sheet is completed, the quality is checked on the surface of the structure. Regarding the selection of the sampling method, full consideration should be given to the area where the carbon FRP is pasted. If the number of samples is within 500m2, one set should be taken. If it is 500~1000m2, take two sets of quantities. For those exceeding 1000m2, take 2 groups per 1000m2, and the distance between each sample should be at least 500mm.
4.2 Test procedure
This test uses a bond strength tester. The orderly organization test is based on the corresponding instruction manual. The loading speed is controlled at 1500~2000N/min. The load when the sample is damaged is detected in time and accurately recorded.
4.3 Test results
4.3.1 Forms of destruction
(1) The damage of the concrete is expressed by Ar.
(2) Interlayer failure, represented by Br, occurs between resin and concrete.
(3) The damage of the carbon FRP, represented by Cr, is generally concentrated inside the carbon FRP.
(4) Bond failure, expressed as Dr, occurred between the fiber sheet and the steel standard block.
4.3.2 Arrangement of test results The number of samples in each group is set to 3, and the arithmetic average is obtained after calculation based on the obtained test data, and this result is regarded as the positive tensile bond strength. In addition, the test results include the specific failure mode and the average value of the positive tensile bond strength.
4.3.3 Judgment of construction quality
(1) When the damage form is Ar, it indicates that the construction quality meets the requirements.
(2). When the failure mode is Br, Cr, Dr, analyze the average value of the positive tensile bond strength of each group first, and the value is required to be >2.5MPa. After analyzing the internal samples, the minimum value of the positive tensile bond strength is considered, which is required to be greater than 2.25MPa. At the same time, meeting the above conditions indicates that the construction quality meets the requirements.
(3) When the failure mode is Br or Cr, the analysis is carried out in the same way as above. Consider the average value of the positive tensile bond strength of each group. If the value is within 2.5MPa and the minimum value of the positive tensile bond strength of each sample does not reach 2.25MPa, the quality requirements are not met at this time, and the number of samples must be expanded and tested again in the same way.
(4) The failure form is Dr, considering the average value of the positive tensile bond strength of each group. If the value is within 2.5MPa and the minimum value of the positive tensile bond strength of each sample does not reach 2.25MPa, the quality requirements are not met at this time, and the sample must be prepared again and tested in the same way.
5 reinforcement effect
After the above construction is completed, in order to confirm that the reinforced bridge meets the standard requirements, it must be verified. After inspection, the resin glue of the bottom brushing resin glue part and the upper brushing part have penetrated into the carbon fiber cloth, and produced a good bonding effect. The carbon FRP bonded part used in the project did not appear slip, crack, Loose peeling and other phenomena. In addition, the bonding position of the project is accurate and the bonding length also meets the requirements. After two years of use after the completion of the construction, the quality of the bridge has been steadily improved without cracks.
6 Conclusion
To sum up, the carbon FRP reinforcement technology mentioned in the text is simple to operate and convenient to construct, and it is favored in bridge reconstruction and reinforcement projects.
In addition to the above advantages, the capital cost required for the bonding carbon FRP reinforcement technology is relatively small, and it has been proved that the bridge reinforcement effect achieved by this technology is very good, so it has a good promotion and application prospect.
