| In recent years,with the acceleration of urbanization in China,a large number of old buildings have been demolished,resulting in a sharp increase in the total amount of construction solid waste in China.It has been clearly stated in the report of the 20th National Congress of the Communist Party of China that promoting the source reduction of solid waste and the utilization of construction waste is an important link to achieve the low-carbon emission reduction and high-quality development in China,while recycled aggregate is a key focus area for the recycling and reuse of construction solid waste.Recycled sand powder is an accompanying product during the process of preparing recycled coarse aggregate or directly processed into a mixture of recycled sand and fine powder with a particle size of less than 5mm from construction waste.At present,the research on recycled coarse aggregate in concrete production has made great progress and has been applied in practical projects,but there are few reports on the research on the resource utilization of recycled sand powder.Therefore,under the support of the National Natural Science Foundation of China（52078261）and（51978353）,this paper uses the preparation process of recycled sand powder to treat brick-concrete construction waste and waste concrete,the brick-concrete recycled sand powder（RMSP）and concrete recycled sand powder（RCSP）are obtained.The basic properties of recycled sand powder,recycled concrete powder（RCP）and recycled brick-concrete powder（RMP）are systematically studied.The effects of RMSP and RCSP as recycled fine aggregate,fly ash（FA）and RMP as mineral admixtures on the properties of recycled sand powder based cement mortar are explored.The feasibility of preparing recycled sand powder based foamed concrete by recycled sand powder is verified.The main results based on the above research are shown as follows:（1）Compared to RMSP,RCSP has a lower micro-powder content and water demand ratio of mortar,and higher apparent density,crushing index and mortar strength ratio.According to the technical requirements of recycled fine aggregate for concrete and mortar,the recycled sand powder belongs to II-zone medium sand,and its main performance indexes meet the requirements of III-class recycled fine aggregate.Compared to RMP,the particles of RCP are finer,resulting in an increase in the water requirement ratio.The main chemical components in RMP and RCP are both similar to FA,which have certain potential pozzolanic activity,and the activity index of 28d strength of RMP is higher than that of RCP.（2）When the cement-sand ratio is 1:5 and 1:6,the main properties of recycled mortar prepared by RMSP and RCSP both meet the requirements of relevant specifications.Through comprehensive comparison,it is found that the workability and mechanical properties of RCSP mortar are both better than those of RMSP mortar.In addition,with the increase of FA and RMP content,the 2h consistency loss rate(Sp2h)of mortar is improved,but the mechanical properties of mortar are deteriorated,and the main properties of FA mortar are better than those of RMP mortar.（3）RMSP was used as recycled fine aggregate to explore the preparation of recycled sand powder-based foamed concrete（RSPFC）with a density grade of A10.On this basis,the effects of RMSP content,water-material ratio,foam volume and water reducer content on the dry density,compressive strength and thermal conductivity of A10 RSPFC were systematically studied by orthogonal test.The range analysis result shows that the foam volume is the main factor affecting the performance of RSPFC,and the optimum mixing ratio of RSPFC is found to be:RMSP content of 15%,water-to-material ratio of 0.37,foam volume of 0.72m3,water reducer content of 0.27%.The performance indexes of RSPFC prepared by this mixing proportion are:dry density of 1011.3kg/m3,compressive strength of 3.6MPa,thermal conductivity of 0.1996W/（m·K）and water absorption of 19.8%.The main performance meets the requirement of《FC A10-C3-W20-P-JG/T 266-2011》. |
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