The Strength And Microstructure Of Soda Residue Activated Slag Binding Materials

As a kind of industrial waste produced in the process of producing soda with ammonia alkali method,soda residue has caused serious environmental problems due to its discharge and stockpiling.The utilization of soda residue has become the focus of scholars at home and abroad.A kind of binding material based on soda residue and slag and a kind of binding material based on soda residue,slag and cement were developed in this paper.The flexural strength and compressive strength of 40 mm×40 mm×160 mm mortar specimens based on the two binding material systems were tested at different ages.The chemical bond rate of chloride ion of mortar curing for 28 days was tested.Meanwhile,microstructure and composition of hardened paste of soda residue-slag binding materials and soda residue-slag-cement binding materials curing for 28 days were analyzed by means of scanning electron microscope,energy dispersive X-ray spectroscopy,X-ray diffraction and thermogravimetric-differential scanning calorimetry.In the soda residue-slag binding material system,water-binder ratio was 0.5 and sand-binder ratio was 3:1,soda residue and slag were prepared according to the mass percentage of 1:4,the compressive strength of the specimen was 39.6 MPa and the flexural strength was 8.0 MPa;The chemical binding ratio of chloride ions was 84.4%.A large number of hydration products between 5μm and 10μm were observed by means of scanning electron microscope in the system,meanwhile,the water products were bonded to each other to form a dense three-dimensional network structure.The hydration products of binding materials after curing for 28 days were mainly C-S-H gel,C-A-C-H gel,C-A-S-H gel and 3CaO·Al₂O₃·CaCl₂·10H₂O crystal（Friedel′s salt）,which constitute the strength source of the whole binding materials based on soda residue and slag together.In the soda residue-slag-cement binding material system,water-binder ratio was 0.5 and sand-binder ratio was 3:1,soda residue,slag and cement were prepared according to the mass percentage of 2:6:2,the compressive strength of the mortar specimen was 45.1MPa and the flexural strength was 7.4 MPa;The hydration products of binding material system after curing for 28 days were mainly both C-S-H gel and 3CaO·Al₂O₃·CaCl₂·10H₂O crystal with a needle bar and irregular shape;The Ca/Si ratio of C-S-H gel in hydration products varied from 0.7 to 1.4,the ratio of n（Cx-S-Hy）/n（3CaO·Al₂O₃·CaCl₂·10H₂O）varied in the range of 1.8⁶.4,which constituted the main strength source of the whole binding material system together.The application of soda residue in the new binding material system not only alleviates the adverse impact of the discharge and accumulation of soda residue on the environment and reduces the consumption of cement in building materials,but also provides a new idea for the resource utilization of soda residue in the future and greatly reduces the cost of solid waste disposal of soda residue.