A short circuit in the electrical wiring caused an electrical spark that ignited debris piled up under the bridge, resulting in varying degrees of damage to the bridge girders and deck structure.

After the fire was extinguished, a professional testing agency conducted an on-site inspection and found that: 

a large area of the concrete at the bottom of the beam had peeled off, and the exposed steel bars showed signs of corrosion;

the waterproof layer on the bridge deck was burned, and the strength of the concrete in some areas dropped to 65% of the design value. If not repaired in time, it will seriously threaten traffic safety.

For structural damage caused by fire, a composite repair system of carbon fiber mesh and wet-applied polymer mortar was selected for the following key reasons: 

• The carbon fiber mesh has a tensile strength of 3400 MPa, which is 7-10 times that of ordinary steel, while its weight is only 1/4 that of steel. This allows for efficient restoration of structural load-bearing capacity without increasing the bridge's weight.

• The bidirectional carbon fiber mesh structure (2.0 cm spacing) simultaneously inhibits the propagation of longitudinal and transverse cracks. Combined with the polymer mortar, it forms a "sandwich" protective layer, significantly improving the structure's shear strength and seismic performance.

• Construction requires no complex heavy equipment, has low requirements for surface flatness, and is particularly suitable for repairing irregularly damaged surfaces after a fire, while also reducing traffic closure time.

Repair Construction Process

The entire repair project lasted 18 days, strictly following the process of "inspection and assessment → base surface treatment → core reinforcement → protective finishing":

• Base surface pretreatment: the damaged area was thoroughly excavated to remove loose concrete, rusted steel bars, and residual debris. exposed steel bars were treated for rust removal and corrosion prevention, and then a special interface agent was applied to enhance adhesion to subsequent materials.

• Carbon mesh fabric laying: based on structural stress analysis, carbon fiber mesh fabric was laid on the beams. a roller pressing process was used to ensure a tight fit between the mesh fabric and the base surface, achieving an impregnation rate of over 95% to avoid hollow defects.

• Wet-sprayed polymer mortar: two layers of special polymer mortar were sprayed to completely wrap the mesh fabric, forming a 15-20mm thick protective layer. the second layer was sprayed after the first layer had initially set, ensuring the continuity of the overall structure.

• Surface protection and curing: after the mortar had fully set, a fire-retardant and anti-corrosion coating was applied. during the curing period, ambient humidity was maintained, and direct sunlight was avoided. a strength test will be conducted 7 days later to ensure that the concrete strength of the repaired area has recovered to more than 95% of the design value.

Compared to the traditional construction cycle of over 30 days, this repair project was completed in just 18 days, significantly shortening the traffic closure time and reducing the impact on regional traffic. The carbon fiber mesh fabric has excellent corrosion resistance and aging resistance, and combined with a multi-layer protection system, it can effectively resist the erosion of the structure by rainwater and moisture, and is expected to extend the bridge's service life by 15-20 years.