Experimental Study On All Solid Waste Unburned Ceramsite

There is huge industrial solid waste production in China,reaching 3.787 billion tons in 2020 alone,but its comprehensive utilization rate is only about 57%.Among them,the utilization rate of gold tailings and red mud is 34.05%and 7.05%,respectively.In this paper,the preparation of all-solid-waste unburned ceramsite was studied and lightweight aggregate concrete was further prepared using three solid waste materials,including red mud,gold tailings,and mineral powder.The main research contents and results are as follows:（1）The mixture ratio of ternary solid waste cementitious system（red mud–gold tailings-slag powder）was studied,and based on this,the impact of gypsum content and varieties of alkali activators on the performance of the cementitious system was investigated.The results revealed that when m（red mud）:m（gold tailings）:m（slag）:m（gypsum）=2:8:9:1 and 2%Na₂Si O₃was used as alkali activator,the 28d compressive strength of the solid waste cementitious material was up to 45.9Mpa,and its flexural strength reached 8.8Mpa.Microscopic analysis（XRD,FT-IR,TG/DTG,SEM,and EDS）showed that the hydration products of solid waste cementitious materials mainly included AFt,C-S-H,and C-A-S-H.The heavy metal leaching test indicated that the leaching content of heavy metals in solid waste cementitious materials was lower than the requirements of relevant regulations.（2）The effects of the water-cement ratio,density reduction method,and curing method on the properties of unburned ceramsite were studied.The results showed that when the water-cement ratio was 0.3,there were no lightweight materials and foaming agent,and the ceramsite was maintained in water,its bulk density was962.3kg/m³,and the 28d cylinder compressive strength was up to 14.7Mpa,far greater than the requirement（3.5Mpa）of the ceramsite cylinder with a density grade of 1000in GB 17431.1-2010 of Lightweight Aggregate and Its Test Methods Part 1:Lightweight Aggregate;the water absorption was 23.56%at 1h and 24.5%at 48h.SEM analysis showed that the all-solid waste unburned ceramsite without lightweight materials and foaming agents had a porous structure,so its density could be reduced.However,EDS energy spectrum analysis revealed that the hydration products around the pores of the ceramsite were mainly C-S-H or C-A-S-H gel and AFt.The effective filling of the solid by the gel made the structure around the pores of the ceramsite dense.Therefore,although the all-solid waste unburned ceramsite had large porosity and high water absorption,its strength was still high.（3）The all-solid waste unburned ceramsite was used to prepare lightweight aggregate concrete,which was compared with the lightweight aggregate concrete prepared by the other two commercially available ceramsites（one is cement-based clay unburned ceramsite and the other is clay sintered ceramsite）.The results showed that the 28d compressive strength,splitting tensile strength,and dry apparent density of the lightweight aggregate concrete prepared by all-solid waste unburned ceramsite were 53.4MPa,6.6MPa,and 1781kg/m³,respectively.Compared with the concrete prepared by two commercially available ceramsites under the same conditions,the compressive strength was 15.6%and 81.4%higher,and the splitting tensile strength was 38.9%and 131.1%higher,respectively.SEM was used to observe the interface between ceramsite and cement mortar in three kinds of ceramsite concrete,and it was found that the interface area between all-solid waste unburned ceramsite and cement mortar was filled with dense hydration products,and its interface structure was better than that of the other two commercially available ceramsite concretes.