| Recycled concrete refers to the concrete made of waste concrete,waste clay bricks and other construction wastes after crushing,cleaning and grading,partially or completely replacing natural coarse and fine aggregates.Recycled concrete can not only reduce the construction cost,solve the problems of urban construction waste stacking,land occupation and environmental pollution,but also realize the recycling of resources and sustainable development.However,compared with the natural aggregate,the recycled aggregate has the defects of high water absorption,large apparent density,large crushing index,etc.,so its mixing amount is often small and the utilization rate is low when it is used,and the quality of the recycled aggregate made of construction waste from different sources and with different service life is discrete,so it is difficult to follow the unified specifications and standards when it is actually used.Therefore,on the basis of the overall replacement rate of recycled aggregate being 60%,this paper develops a new type of recycled concrete composite self insulating block,and explores the influence of different types and dosage of recycled aggregate on the physical and mechanical properties,durability and thermal performance of recycled concrete block.The results are as follows:(1)The mechanical and thermal properties of recycled concrete were studied by taking the types of recycled aggregate(waste concrete aggregate,waste red brick aggregate)and recycled aggregate content(the replacement rate of coarse aggregate was 100%,and the replacement rate of recycled fine aggregate was 40%,50%,60%,respectively)as variables.The research shows that with the increase of recycled aggregate replacement rate,the mechanical properties of recycled concrete are gradually reduced,but the thermal performance is gradually improved.The mechanical properties of recycled concrete mixed with red brick aggregate are worse than that of recycled concrete mixed with waste concrete aggregate,but its thermal performance is better.(2)Through observing the micro morphology and hydration products of interface transition zone of different types of recycled concrete,it is found that there are many complex interface transition zones in recycled concrete,and many cracks and holes have been produced by recycled aggregate after years of service use and crushing treatment process.The performance of interface transition zone is weak,which is the fundamental reason that the mechanical properties of recycled concrete are inferior to ordinary concrete.(3)Based on the mixture ratio of recycled concrete,a new type of recycled concrete composite self insulating hollow block was developed.The physical properties,mechanical properties,frost resistance,thermal insulation and fire resistance of the block were tested and studied.The research shows that with the increase of the replacement rate of recycled aggregate,the block is lighter,the water absorption rate is increased,and the thermal insulation performance is gradually enhanced,but the mechanical properties and frost resistance are gradually weakened.The mechanical properties and frost resistance of the block mixed with discarded red brick aggregate are worse than those of the block mixed with discarded concrete aggregate,but the thermal insulation performance and fire resistance are better.(4)Using ABAQUS finite element analysis software,a model of recycled concrete block masonry is es Tablelished,and the influence of recycled aggregate type on the thermal performance and fire resistance of the masonry is studied through simulation analysis.The results show that the heat transfer coefficient of the four walls is about 0.37 W/(m~2·K),and the fire resistance limit is more than 1 hour,which conforms to the requirements of relevant specifications.The simulation results are in good agreement with the test results,and the error is within the interpre Tablele range. |
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