1 Project Overview

The No. 3 bridge of S201 line K111+825 Paihonggou managed and maintained by the Zhongchuan highway section is located in Lanzhou New District, Gansu Province. It is an important part of provincial highway S201 line. The bridge is a 1-10m hollow slab bridge, which was completed in 2003. In recent years, due to the large amount of building materials required for the construction of Lanzhou New Area, all of them have to arrive at the site via S201 line Yinglan Road. Heavy and overloaded vehicles are intensive, causing the hinge joints of the bridge to fall off and the 8# beam slab deck paving is damaged. Irregular fine cracks appear at the bottom of 1-6#, 1-7#, and 1-8# plates with a width of 0.1-0.2mm and serious water seepage between them. The technical status of the bridge is assessed as a third-class bridge, with serious safety hazards, and maintenance alone cannot solve the problem fundamentally. After the design of Highway Survey and Design Co., Ltd., the construction period and construction plan of the reinforcement and preventive maintenance project were finally determined.

2 Introduction to prestressed carbon fiber laminate and reinforcement technology

The modulus of elasticity of carbon fiber material is similar to that of steel, but the tensile strength is 10 times that of ordinary steel. The tensile strain when the steel bar yields is only 0.15%, while the tensile strain of 1.7% is required to exert the tensile strength of the carbon fiber material. After the carbon fiber is prestressed, the phenomenon of strain hysteresis of the carbon fiber sheet is avoided. The strength of the carbon fiber laminate is effectively exerted, the structural bearing capacity is improved, the bending rigidity of the bending member is improved, the deflection of the original member is reduced, and the deformation and crack propagation of the member are suppressed. It solves the contradiction between the high ratio of carbon fiber strength and elastic modulus, has very good economic and social benefits, and has the characteristics of high safety factor, high technical reliability index, economy, and high cost performance.

Compared with other reinforcement methods, the prestressed carbon fiber laminate reinforcement method has the advantages of high strength and efficiency, light weight, small space requirements, good durability, corrosion resistance, simple construction, no impact on traffic, and no need for regular maintenance.

3 Application example of prestressed carbon fiber laminate in No. 3 bridge of K111+825 Paihonggou of S201 line

3.1 Comparison and selection of reinforcement maintenance plans

Through comprehensive comparison and selection of structural forces, economics, etc., the main maintenance measures are finally determined as follows:

(1) Epoxy resin filled hinges;

(2) Reinforce the hollow slab with carbon fiber laminate;

(3) Repair the concrete spalling and cracks of the bridge abutment;

3.2 Main materials

1) Carbon fiber laminate: use anti-skid products with rough surface

2) Ordinary steel

3) Concrete: The strength of concrete used for reinforcement should be one level higher than that of the original structure and component concrete.

4) Adhesive glue: The performance of anchoring, bonding steel and crack repair structural glue should meet the requirements.

4 Construction process

4.1 Prestressed carbon fiber laminate construction steps

4.1.1 Drill holes and install anchor blocks

Install the carbon fiber half-tensioned end and the fixed end anchor block according to the design drawings to drill holes and implant supporting high-strength anchor bolts. The contact between the anchor block steel plate and the concrete beam is polished, cleaned, and other surface treatments are applied, then steel glue is applied, the anchor block is pasted on the bottom of the beam, and the anchor block is fixed with a nut.

4.1.2 Concrete surface treatment

After the anchoring block is installed, the concrete surface at these sticking positions is repaired, leveled, and cleaned.

4.1.3 Unloading and clamping of carbon fiber laminate on site

According to the position of the anchor block, the blanking length of the carbon fiber laminate is further compounded. The carbon fiber laminate is cut according to the blanking length, and the protective film in the clamping length at both ends of the carbon fiber laminate is removed. Special express adhesive glue is prepared and applied to the clamping length of the carbon fiber laminate. Put the inner surface into the wave-tooth fixture anchor and quickly tighten the upper and lower wave-tooth plates of the wave-tooth fixture anchor. Remove the protective film on the surface of the carbon fiber laminate and apply adhesive. At the same time, the same carbon fiber laminate adhesive was applied to the surface of the concrete at the bottom of the beam.

4.1.4 Anchorage and anchorage area protection

After the anchor is installed, epoxy-based protective material is used to smear and seal the abrasion of the anti-corrosion layer, and wire mesh is hung in the anchoring area, and the anchor is sprayed or coated with high-bonding waterproof mortar as the protective layer.

4.2 Corroded concrete repair

For the joint surface of the concrete components, first use a stiff brush dipped in acetone to remove oily dirt on the surface, rinse with cold water, and polish the adhesive surface, remove the 2~3mm thick surface layer, completely expose the new surface, blow off the powder, if the surface is uneven, use high-strength resin mortar to repair it.

4.3 Hinge reinforcement

The pressure infusion method is used to strengthen the hinge joints this time. The process flow is: remove the loose and inferior mortar in the hinge joints → clean the joint joints with a blower to keep them dry → erect temporary templates, bury grout nozzles and exhaust pipes →prepare grouting and grouting equipment → pressurized grouting → surface treatment → curing.

4.4 Crack sealing treatment

Cracks with a width less than 0.15mm are sealed with epoxy resin coating, and cracks with a width greater than 0.15mm are sealed with grouting. Seal the cracks with soapy water for leak testing, and clean the surface of the glue one day after the glue is injected.

4.5 Bridge deck paving and installation of drain holes

Re-lay steel bars, place drain holes at the preset drain holes, and redo the C40 waterproof concrete deck paving. The paving steel bars are Φ16 horizontally and Φ12 longitudinally, steel fiber concrete is used for the redo paving layer, and asphalt concrete is used for the surface layer.

5 concluding remarks

The design and construction technology of prestressed carbon fiber laminate bridge reinforcement proposed in this paper has good applicability and is more suitable for practical engineering operations than the commonly used methods in the past. It can improve the failure form of the beam, increase the yield load and the cracking load of the bearing capacity, reduce the deflection of the beam, and improve the deformation performance and crack form of the beam. The strength of carbon fiber laminate is also fully utilized, and it is suitable for the reinforcement and maintenance of diseased bridges. Engineering practice shows that the reinforcement effect of this method is good, and the construction period is only 45 days, which is convenient and fast. After reinforcement, the load-bearing capacity of the beam is significantly improved, the effects of deformation recovery and crack closure are obvious, the construction accuracy is high, and it has excellent structural performance.