| With the rapid development of urbanization in China,the production of construction waste is increasing year by year,and the accumulation of large amounts of construction waste is causing great pollution to the environment.Waste concrete is crushed,screened and ground to produce recycled coarse and fine aggregates and recycled powder and applied to concrete structure is one of the effective measures to solve the above problems.Currently,there are a lot of studies on the application of recycled coarse and fine aggregates,but there are fewer studies on recycled powder.Compared with ordinary concrete,the mechanical properties of recycled concrete are slightly deficient.In this thesis,the recycled powder is used as raw material to partially replace cement make up for its defects by incorporating fibers to prepare High Ductility Recycled Powder Concrete(HDRPC)and investigate the fracture properties and tri-axial compressive properties of HDRPC materials.The Carbon Summit and Carbon Neutral policies not only promote the development of assembled buildings but are also crucial to the green retrofitting and seismic strengthening of existing buildings.Reinforcement of seismically damaged buildings can not only restore their seismic performance but also reduce the large amount of waste concrete generated by the demolition of seismically damaged buildings,which is one of the effective measures for carbon reduction and emission reduction.In this thesis,we use HDRPC to strengthen the seismic damaged parts of nodes and study the seismic performance of nodes under different construction methods and strengthening methods.The main work and results of the thesis are as follows:(1)To sort out and summarize the application of recycled concrete and recycled powder in Engineered Cementitious Composites,the current research status of fracture performance and tri-axial compressive performance of recycled concrete,and the research progress of seismic performance of assembled nodes and reinforced assembled nodes.(2)Based on the three-point bending test,the effects of water-binder ratio,recycled powder content,fiber type on the fracture performance of HDRPC were investigated,and the toughening effect and improvement mechanism of each factor on HDRPC were analyzed according to the double-K fracture parameters and combined with microscopic morphology.(3)Through tri-axial compression tests,the parameters of the enclosing pressure and the above variables are used and normalized to study the influence of each parameter on the stress-strain curve,peak stress,and peak strain of HDRPC,and establish the peak stress-encircling pressure principal structure equation.(4)One cast-in-place node and two assembled nodes were rated for damage and designed for reinforcement,the seismic performance of each node was studied by low circumferential reciprocal load tests using different construction methods and different reinforcement methods as parameters.The results show that:(1)HDRPC material has excellent flexural and compressive properties,and its application in node reinforcement can effectively improve the seismic performance of nodes.(2)The increase of water-binder ratio,recycled powder content,and PVA fiber proportion showed a trend of increasing and then decreasing with HDRPC fracture performance;when the water-binder ratio was 0.28,recycled powder content was 45%,compounded with 0.2% BF and1.7% PVA fiber,HDRPC has the best fracture toughness.(3)The increase in the value of the surrounding pressure makes the HDRPC peak stress and peak strain tend to increase,and BP45-0.28 has the best performance.(4)Using HDRPC to reinforce nodes can effectively restore their bearing capacity and improve their energy dissipation capacity.HDRPC materials work better with the prefabricated node,the energy dissipation capacity of the prefabricated node is better than that of the cast-in-place node,and the shear deformation of the core area is small,the seismic performance of the reinforced PHDJ1 nodes is optimal. |
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