Research On Mechanical Properties Of Precast Recycled Concrete Sandwich Insulation Plug Wallboard

With the development of modern social architecture and urban renewal,the demolition of old buildings is also increasing.The treatment of construction waste generated by the demolition of these buildings has become an urgent social problem to be solved.In response to this problem,recycled concrete technologies such as recycled coarse aggregate(Recycled Coarse Aggregate,RCA),recycled fine aggregate(Recycled Fine Aggregate,RFA),and recycled fine powder(Recycled Concrete Powder,RCP)have been widely concerned.There have been a lot of studies on the technology of using single recycled aggregate to replace ordinary concrete to prepare recycled concrete.However,the research on using RCA,RFA,and RCP to replace natural coarse and fine aggregates and cement to make fully recycled concrete needs to be further carried out,which is of great significance for promoting the realization of the goal of ’ carbon peak and carbon neutralization ’.Prefabricated buildings also aim to improve building efficiency and reduce building carbon emissions,which plays an important role in promoting the standardization and industrialization of the construction industry.The thermal insulation external wall hanging board in the prefabricated building belongs to the external envelope structure,which plays the role of thermal insulation and barrier to the external environment.At the same time,the thermal insulation external wall hanging board bears the effects of transverse wind load and self-weight.It is necessary to study its structural form and mechanical properties.In this thesis,a new type of assembled thermal insulation exterior wall hanging board is proposed.Based on the orthogonal test method,the optimal mix ratio of fully recycled concrete suitable for this kind of wallboard is proposed.The optimal mix ratio is used to make the assembled thermal insulation exterior wall hanging board and carry out the mechanical performance test of the wallboard.The main work is as follows :(1)The mechanical properties,thermal properties of recycled concrete and the related research progress of fully recycled concrete are summarized,and the research status of assembled thermal insulation external wall hanging board is summarized.(2)The mechanical and thermal properties of fully recycled concrete considering RCA,RFA,RCP,water-binder ratio,and AOS air-entraining agent content were studied by orthogonal test.The results show that: The content of AOS air-entraining agent has the greatest influence on the mechanical properties of fully recycled concrete,and the replacement rate of RFA has the least influence.The optimal mix ratio obtained by comprehensive analysis of various factors is : water-binder ratio 0.43,RCA replacement rate 75 %,RFA replacement rate 50 %,RCP replacement rate 15 %,AOS air entraining agent content 0 %.This mix ratio not only ensures the basic performance of concrete but also maximizes the use of recycled materials,which has good environmental benefits.(3)A new type of(Fibreglass Reinforced Plastics,GFRP)four-legged stool connector is designed to connect the inner and outer wallboards of the assembled thermal insulation exterior wall hanging board.The wallboard material and the connector type are used as parameters to design the specimens,and the specimens are subjected to pull-out and shear tests.The uplift test results show that the failure mode of the specimens with Thermomass MS connectors is brittle failure after reaching the ultimate load,and the ductility of the specimens with GFRP4 footstool connectors is stronger,and the failure mode is ductile failure.The pull-out capacity of POG-R is 14.80 % higher than that of POT-R.The shear test results show that the failure of the specimen using Thermomass MS type connector occurs at the connector,which is the bending failure of the connector,while the specimen using GFRP4 foot stool type connector occurs in the concrete compression zone under the connector.The maximum shear ultimate bearing capacity is the specimen CG-C,followed by CG-R > CT-R > CT-C.(4)Four full-scale exterior wall panels were designed and fabricated.The out-of-plane bending test was carried out considering the parameters of wall panel material,connector form and insulation board position.The failure mode of the specimens was observed and the calculation formula of flexural bearing capacity was proposed.The bending test results showed that the cracks of the specimens with GFRP4 foot bench connectors are more dispersed and the stress range is wider.The flexural strength of the specimens using GFRP4 footstool connectors is significantly stronger than that of the specimens using Thermomass MS connectors.Based on the complete combination model,the reduction coefficient γ of GFRP4 footstool connector is calculated.At the same time,the specimen with the highest combination degree is determined as W-3 by calculation and analysis of combination degree.