Mechanical Properties Of CFRP Reinforced Expansive Concrete Beams With Eccentric Self-Prestress

Due to shrinkage, concrete usually cracks under restrained conditions. This phenomenon often leads to the corrosion of the steel inside, and it severely influences the servicability and duability of concrete structures. Prestressed concrete structure has prominent advantages on cracking resistance. However, the complexity of streching-technique and strictness of anchorage have limited the application and development of prestressed concrete structure in the engineering field. Using expansive concrete brings a solution to this problem. Carbon-fiber-reinforced polymer (CFRP) can replace steel as protection from corrosion. It also serves as formwork for casting concrete as well as provides restrained condition better than steel reinforcement. For this concern, a hybrid CFRP-wrapping expansive concrete beam structure is proposed. This hybrid CFRP wrapping expansive concrete structure has good potential on delaying cracking and eliminating the corrosion. This thesis focuses on the mechanical properties of hybrid beams with eccentric prestress under short-term and long-term, respectively. Researches conducted are summarized in detail as below:(1) Mechanical properties of hybrid beams in short-termMaterial tests on concrete and CFRP were conducted first. In this section, different reinforcements of CFRP were designed by changing the layers of CFRP sheets. Static strain of seven CFRP-reinforced expansive concrete beams and seven CFRP-reinforced conventional concrete beams was monitored for one month. And beam specimens were tested to investigate their flexural behavior under four-point bending test. The main parameters studied were types of concrete, layers and layout of CFRP sheets. It was designed to explore the effect of self-prestressing on beams bending performance. In the mean time, it was a key point to see the influence of the eccentric self-prestressing generated from concrete expansion and eccentric restraint of CFRP on flexural performance of beams. Based on the tests result, SHCC specimens showed a prominent advantage on delaying cracking and the control of crack width compared to PCC specimens. In terms of ultimate load capacity, SHCC specimens showed better performance than PCC specimens. Eccentric layout of CFRP sheets gave a certain enhancement to the flexural properties of the hybrid structure, compared to the symmetrical layout.(2) Mechanical properties of hybrid beams in long-termFourteen composite beam specimens and four control specimens were designed. A series of tests were conducted including material test, long-term static strain monitoring of beam specimens (five months) and four-point bending test. It focused on prestress loss in long-term and improvement of the hybrid beams caused by the camber. The long-term mechanical properties of hybrid beams were tested by four-point bending test. Test results indicated that at the same layout of CFRP, SHCC specimens had better performance than PCC on delaying cracking, the control of crack width and the ultimate load capacity. The flexural capacity of the beam specimens increased with the increase of reinforcement ratio of CFRP. However, excessive reinforcement ratio caused change of the failure mode from bending failure to shear failure. Under the condition of same reinforcement ratio, beam specimens with eccentric layout beam specimens showed superior flexural performance than those of symmetric layout.(3) Theoretical calculation and comparison with test resultsThe theoretical calculations of cracking and ultimate loads of specimens were carried out. Besides, load-deflection curves of specimens were calculated. According to the failure modes, different calculation equations of ultimate loads were presented. The calculation results agreed well with the test results. It can provide valuable references for further research and engineering application.