Durability Study On Anchors For Prestressed CFRP Plate Strengthening Subjected To Chloride Corrosion

Reinforced concrete beams strengthened by Carbon Fiber Reinforced Polymer(CFRP)can effectively take advantages of high strength and light weight of composite materials,and also improve the utilization rate of materials.How to effectively pre-stress the carbon fiber plate and maintain the pre-stress level for a long time,the most important is to have a reliable reinforcement anchor.However,during the service process,the anchor is subjected to environmental corrosion and the anchoring restraint performance could be degraded,which would cause the carbon fiber slip inside anchor and cause a large prestress loss.The anchors commonly used in bridge reinforcement projects in China mainly include wedge-shaped clip anchors and flat anchors.The material used to make the anchors is steel.Under the combined action of the hot and humid environment and the chloride salt in the coastal areas of Guangdong,the anchors are prone to corrosion.The nature of steel corrosion is an electrochemical reaction process.Durability of anchors can be simulated and accelerated by Electrolysis Weight Loss Method in the laboratoryIn this paper,an anchor tensioning device was designed and six sets of anchor specimens(three sets of clip anchors and flat anchors separately)were tensioned.A pre-stressed anchor electrolysis weight loss test device was also designed based on the anchor tensioning device,which put specimens half-soaked in 3.5%NaCl solution and conducted constant current of 2.5A.Four sets of specimens were current conducted for 72h and 144h respectively.The fiber grating was used to monitor the prestress loss of the anchor specimen during the electrolysis weight loss.The variation of the anchor slip and the strain distribution of the CFRP plate were discussed.The main research contents and conclusions are as follows:(1)A set of flat anchor test pieces and a set of clip anchor test pieces were tensioned to damage by using an anchor tensioning device.The results show that the ultimate load,anchoring efficiency and ultimate slip of the flat anchor specimen are 141.105kN,77.53%,4.146mm,respectively.The ultimate load,anchoring efficiency and ultimate slip of the clip anchor specimen are 161.088kN,88.51%,4.319mm respectively.The anchoring efficiency of the clip anchor is higher,and the slip amount of the clip anchor is smaller at the same load level.(2)Based on the above-mentioned anchor tensioning platform,an electrolysis weight loss test device for prestressed anchors was designed.The strain variation and prestress loss of prestressed CFRP plates with accelerating corroded anchors were studied.The test results show that during the 72h energization period,the prestress loss of the flat anchor test piece and the clip anchor test piece at the first 8h have a large change,which is 5.7%and 7.16%respectively,and there is no obvious change during subsequent 64h.During the 144 hours of energization,the prestress loss of the flat anchor test piece and the clip anchor test piece at the first 8h was 87.5%and 7.85%,respectively.A significant prestress loss of the CFRP plate with flat anchor occurred after 122h power-on,and the pre-stress loss reached 20.86%;while the clip-on anchor test piece did not change significantly during the 144 h power-on.(3)Tensile tests were carried out on the four groups of corrosion specimens,and the anchoring efficiency after corrosion was analyzed.The results show that the anchoring efficiency of the specimens of the flat anchor specimens decreased significantly after the weight loss of electrolysis.The anchoring efficiency of the specimens after 72 h and 144 h decreased by 18.96%and 22.53%,respectively.While for the clip-on anchor,the anchoring efficiency all rose to 100%,mainly due to the increasing anchoring force caused by rust expansion.The failure mode of the three sets of flat anchor specimens is slip and split,while the failure mode for the clip anchor energized 72h is broken,and a certain degree of slip and splitting occurs when the current is applied for 144h.The chip anchor has excellent corrosion resistance to chloride salts,but the energization of 144h begins to adversely affect its anchoring properties.