In order to improve the fire resistance of concrete beams and slabs strengthened with carbon fiber fabric, a thick coated fire retardant coating is selected as the protective layer.

Carbon fiber fabric under aerobic condition, its physical and mechanical properties do not decay before 1500 degrees Celsius. However, all the structural adhesives currently used are epoxy organic polymers, and their thermal stability and long-term chemical stability are poor, especially their upper temperature resistance limit is less than 80. The temperature of building fire can reach 1000 degrees Celsius. If the fire resistance of CFRP reinforced structure is not paid enough attention, the fire will easily cause the stripping of CFRP and concrete.

Suggestion on thickness of fire retardant coating for concrete beam and slab strengthened with carbon fiber fabric

The fire resistance limit of concrete beams and slabs strengthened with carbon fiber fabric under different section sizes, different resistance enhancement amplitudes, different resistance standard values and frequency combination effect standard values K is calculated. According to the fire-resistant grade stipulated in the fire-proof code for building design, the thickness of protective layer of fire-proof coating on concrete beams and slabs strengthened with carbon fiber fabric is suggested, as shown in Table .

Conclusion

1) Under standard fire, the resistance of concrete beams and slabs strengthened with carbon fiber fabric decreases approximately with the time of fire. The first stage is fire to paste softening. The second stage is that the adhesive softens until the yield strength of the tensile longitudinal bars begins to decrease under fire, and the resistance attenuation is not obvious in this stage. The third stage is that the yield strength of longitudinal reinforcement decreases further and the resistance decreases linearly with the fire time.

2) The fire-resistant limit of concrete beams and slabs strengthened with carbon fiber fabric can be met by coating the CFRP sheets with fire-resistant coatings of necessary thickness. At the same time of fire resistance, the greater the increase of resistance, the greater the thickness of the required fire retardant coating. The longer the resistance increases, the longer the fire resistance is, the greater the thickness of the required fire retardant coating is. Tabular form is given to recommend the thickness of fire retardant coating for concrete beam and slab strengthened with CFRP cloth.