Why Carbon Fiber-Reinforced Polymers (CFRP) Strengthening Material Needs To Be Fire-Proofed?

Following reinforcement, the buildings’ required fire protection grades should be achieved using fire-resistant materials and associated treatment techniques. When reinforced structures are placed in other special environments, efficient protection materials should be chosen based on the specific situation. Currently, thick fire-retardant coating, ultra-thin fire- retardant coating, fire prevention board, and ordinary cement mortar are the main fire protection materials utilised in CFRP-strengthened reinforced concrete structures.

1. Thick fire-retardant coating – Thick fire-retardant coatings work by using the good thermal insulation of high-efficiency insulation materials that are already present in the coatings and the heat absorption effect of additives to prevent and consume fire heat from reaching the surface of the substrate, thereby reducing the substrate’s critical temperature. In addition to its apparent benefits in terms of fire resistance, thick fire retardant coatings also have the advantages of being water-borne, inexpensive, and weather resistant.
2. Ultra-thin fire-retardant coating – A light porous carbonised foam layer is created when the coating expands and foams during firing, effectively preventing heat from transferring to the substrate. In an experiment, it was discovered that reinforced beams with ultra-thin fire-retardant coatings for fire protection initially had wider cracks in the coating, which slowly filled as the foaming thickness increased. In comparison to thick fireproof coating, ultra-thin fireproof coating exhibits lower fire resistance. In addition to the wire mesh between coatings and CFRP, a small amount of quartz sand should be sprayed outside to improve the adhesion between coatings and CFRP.
3. Fire prevention board – It is made mostly of inorganic materials, to which different modified materials are then added following a certain process. This type of board exhibits good dimensional stability and fire insulation performance while retaining some strength in a fire.
4. Cement mortar – The surface of the reinforcement components will be coated or sprayed with cement mortar. Mortar made of cement is not fire-resistant. Under the circumstance of a low fire-proof limit, it is suggested that regular cement mortar can also be employed as a fire-proof protective method for strengthening concrete beams. CFRP should be protected against early shedding by being set between cement mortar and U-shaped steel wire mesh. To reinforce the steel wire mesh, expansion screws should be installed at the top of the beam on both sides.