Study On High Quality Recycled Aggregate Preparation Technology And Activating Cement Powder

The mass production and low recycling and utilization rate of waste concrete result in a large number of demands of lands for these discarded waste concrete, which causes occupancy and squander of natural resources and lands. In China, annually newly-built concrete buildings require a great number of recycled aggregate and excavation of mountains, digging of river sand, and these all do harm to the ecosystem. Researching the recycling and utilization technology that improves the recycling and utilization efficiency makes significant contribution to protection of the natural environment and resource.Regarding to the recycling and utilization of waste concrete, temporarily focusing on the production of high quality recycled aggregate and the activation of cement powder; Since the recycling and utilization rate increases with the improving of recycled aggregate; The activated cement powder can replace part of the gel material; These could raise the efficiency of recycling and utilization of waste concrete. This thesis aims at research and study on the production technology of high quality recycled aggregate and the activation of cement powder.The heat treatment of materials in interfacial transition zone of the waste concrete was processed by changing heating rate. It provided theoretical basis for separation of aggregate experience by using DSC, SEM and XRD which researched the changing of substances, structure and crystallinity in interfacial transition zone materials from the beginning of heat treatment to the end. The coarse aggregate of the waste concrete were separated by transferring heat treatment temperature and vibration time which took delamination rate, crush index and energy consumption as the standard. It took detection to property of obtained recycled coarse aggregate depended on national standard. Fine aggregates of waste concrete were separated by transferring vibration time and winnowing wind force which took separation efficiency as the standard. It took detection to property of obtained recycled fine aggregate depended on national standard. Corse aggregates of waste concrete were separated by transferring heat treatment temperature and vibration time which took delamination rate, crush index and energy consumption as the standard. Cement Powder generated by separation process, was mechanical activated with utilizing ultra-air grinding machine by changing grinding time and taking strength of cement paste which is used for detecting activity of powder as the standard. Come to the conclusions that:1. There are cracks that the number and size increased with the temperature increase in interfacial transition zone of waste concrete by heating treatment. The crystallinity of interfacial transition zone materials decreases with the temperature of heat treatment increase. The destruction are obvious in interfacial transition zone of concrete waste by Heating rate of lOK/min and the heating temperature of 500℃.2. The method of separating the coarse aggregate in waste concrete is:With the heating rate of 10K/min, the waste concrete blocks are heated to 500℃, keeping 30min, natural air cooled, vibration milled 30min, washed, dried, maked. The resulting high water absorption of recycled coarse aggregate in addition, the particle size distribution, clay content, flakiness content are in line with the relevant provisions of the two GB gravel, well-prepared physical properties of recycled coarse aggregate.3. The method of separating the fine aggregate in waste concrete is:the particle size is less than 4.75mm material in vibration mill vibration mill 15min, using 16m/s wind speed, the cement powder is separated to obtain recycled fine aggregate. Made of recycled fine aggregate particle size distribution and clay content was in line with the Second District Building sand standard, sturdiness mass loss than the standard, a bulk density of below standard.4. Use air mill grinding after 45min, the particle size is 5um-20um, the degree of crystallinity increases with grinding time of decline. Paste strength experimentally measured activation compressive strength slurry block is 20.6MPa, than the non-activated sample improved 160.7%. Obtained cement powder mechanical force activation time of 45min.The quality of recycled coarse aggregate and recycled fine aggregate by researching was better than common production, there was practical significance in enhancing the activation of cement powder by mechanical-chemical method.