Preparation And Properties Of Supplementary Cementitious Materials Based On Recycled Construction Waste Powder

With the continuous improvement of the level of urbanization in China,there were more and more demolition and renewal projects of buildings/structures,and the production of construction and demolition waste（CDW）increased greatly year by year.The traditional landfill treatment could no longer fit the requirements of environmental protection and social sustainable development.Compared with the preparation of recycled aggregate,using recycled powder（RP）to prepare supplementary cementitious material（SCM）for cement,mortar and concrete was expected to further improve the value of CDW.And the partial replacement of cement would also indirectly reduce CO₂emissions from the building materials industry,especially the cement industry.In this paper,the SCM based on RP of CDW was prepared,and the composition,structure and properties of RP was studied systematically.Then RP was modified by high titanium slag,steel slag and siliconmanganese slag with regional characteristics,and the compound supplementary cementitious material（CM）based on RP was prepared.The effect of SCM based on RP of CDW on the performance of concrete was studied.The results show that:（1）RP particles were loose and had high porosity.The water requirement ratio and 28d strength activity index of recycled brick powder were 109-112%and 74.8-79.8%,respectively.Increasing fineness could reduce water requirement ratio and increase activity,and the pozzolanic activity of recycled brick powder developed slowly.The water requirement ratio and 28d strength activity index of recycled concrete powder were113-115%and 75.3-76.3%,respectively.The increase of fineness would increase the water requirement ratio,and the increase of fineness had little effect on the activity.Recycled concrete powder had high activity in the early stage but did not develop in the later stage.（2）RP was modified with steel slag,high titanium slag-steel slag and siliconmanganese slag,and the fluidity ratio of mortar prepared by CM was more than 95%.The strength activity index of CM modified by high titanium slag-steel slag was low in the early stage,but the strength increased in the later stage,and the activity index reached 83.9%in 28d.The activity index of CM modified by siliconmanganese slag increased at each age,and the 28d activity index reached 98.1%.（3）RP had a great negative effect on the workability,mechanical properties and durability of concrete.Compared with RP,the CM based on RP of CDW could improve the workability,mechanical properties and durability of concrete to a certain extent.