Key technical issues in unidirectional carbon fiber reinforcement

Bonding performance and ductility

The overall composite effect of carbon fiber-reinforced concrete structure is mainly achieved by the good bonding between carbon fiber and concrete. The failure of the bonding zone may cause brittle failure of the structure, and the peeling failure of the bonding interface can be summarized into three types.

(1) The peeling failure caused by the stress concentration at the end of the carbon fiber that spreads toward the middle of the beam.

(2) At the point where the bending moment is the largest, the peeling failure caused by the mountain bending cracks spreads to both ends.

(3) The peeling failure caused by the shear cracks moving up and down.

Anti-fatigue problem

The fatigue resistance evaluation of carbon fiber reinforced concrete structures generally should be carried out for two failure modes: bending fatigue failure and shear fatigue failure. The research shows that the carbon fiber reinforced concrete has undergone a certain number of fatigue cyclic loadings, and its strength and ductility indexes have not decreased compared with the specimens that have not undergone fatigue cyclic loading during static load test and deflection test. This shows the excellent fatigue resistance of carbon fiber material itself.

Structure dynamic performance

Carbon fiber material is a kind of linear elastic brittle material. The brittle failure of carbon fiber reinforced concrete structure under impact load or dynamic load should be paid more attention. Through the impact load test of the reinforced bridge, it is proved that the impact resistance of the carbon fiber reinforced beam under the impact load is good. If the carbon fiber end adopts appropriate tracing measures, the impact resistance of the carbon fiber reinforced beam can be improved.

Durability

The reinforcement effect and durability of the reinforced concrete members after carbon fiber reinforcement are issues that the engineering community is more concerned about. Because carbon fiber reinforcement technology is an emerging reinforcement technology, and the factors that affect the durability of carbon fiber include environmental factors, temperature, ultraviolet radiation, freeze-thaw cycles, etc. Through indoor salt spray test, alkali resistance test, fatigue test of specimens and other accelerated aging tests and investigation of reinforced bridges, the conclusion is that carbon fiber has sufficient durability to ensure the repair and reinforcement of carbon fiber applications.