Mechanical Properties And Constitutive Relationship Of Low Carbon Concrete Activated By Soda Residue-carbide Slag

Soda residue（SR）,calcium carbide slag（CS）and iron tailings are bulk industrial solid wastes that need to be treated urgently.At present,the development and preparation of new alkali activated binder and concrete according to the physical and chemical characteristics of various solid wastes is an important green,low-carbon and sustainable development direction of the building materials industry.The mechanical properties and strength formation mechanism of solid waste-based binder,the development law of mechanical properties and constitutive relationship of solid waste-based concrete are the key scientific issues that need to be solved urgently for further engineering application of solid wastes.In this study,the synergistic activation of SR and CS was formed through component optimization design,and a new type of binder was prepared by replacing strong alkali to activate ground blast furnace slag（GBS）-fly ash（FA）.The microstructure was actively adjusted from the optimization of curing method,so as to greatly improve the early mechanical properties.Furthermore,two types of low-carbon concretes were prepared by combining ordinary aggregate and iron tailings solid waste aggregate,and their mechanical properties and constitutive relationship were systematically studied.The multi-strength binder system was developed using SR-CS synergistically asctivated GBS-FA.Through macroscopic physical and mechanical properties testing and microscopic analysis,the micro hydration model was constructed,revealing the strength formation mechanism.The results show that the new binder system had a 28d strength of17.5-43.2 MPa.The alkaline environment created by the SR and CS synergistically promoted the decomposition of active components such as calcium,silicon,and aluminum in the precursor,and combined with the additional Cl^-,CO₃^2-,and Ca²⁺provided by the SR and CS to synergistically promote the formation of hydration products C-（A）-S-H gel,hydrated calcium chloroaluminate,and Hydrotalcite crystal.The gel and the crystalline products were mixed with each other to form a hardened structural skeleton,which constituted the source of strength.The effects of preparation process and curing method on the mechanical properties of the new binder system were studied,and the influence mechanism was revealed combined with micro analysis.The results show that the use of wet basis could significantly promote the hydration reaction and improve the mechanical properties,while the use of powder could cause the carbonization of OH^-in the process of drying and grinding,resulting in the weakening of the activation effect.The optimal curing method was 60-75℃@12h,which could accelerate the early hydration reaction,form a dense microstructure,and greatly improve the early mechanical properties.Too high curing temperature or too long heat curing time would cause microstructure deterioration,increase the number of macropores and pores in the matrix,and reduce the strength in the later stage.Combined with two types of aggregates,normal aggregate and iron tailings,two types of concrete were prepared.Considering multiple factors,the basic mechanical properties such as uniaxial compression,tensile and flexural properties and constitutive relationship were systematically studied.The results show that the two types of new concrete have greater tensile compression ratio and flexural compression ratio than the PCC with the same grade,that is,the tensile and flexural properties are better.Based on statistical analysis methods,prediction models for standard compressive,axial compressive,tensile and flexural strengths were established.Under uniaxial compression,the new concrete had lower elastic modulus,longer plastic segment and larger peak strain than PCC.The descending section after peak stress was steeper han PCC,indicating greater brittleness.Based on the classical constitutive model of Guo Zhenhai,the compression constitutive relationship suitable for the new concrete was established through statistical analysis.Considering multi-level confining pressure,the failure characteristics and stress-strain relationship of the two types of concrete under triaxial compression were studied.The results show that the confining pressure could significantly improve the mechanical properties,but the improvement was lower than that of PCC of the same grade.At the same time,the confining pressure could significantly increase the plastic deformation capacity and improve the brittleness after the peak stress.Based on statistical analysis,the qualitative and quantitative relationships between key parameters such as peak stress,peak strain,elastic modulus and confining pressure were established.Based on the two-parameter Mohr-Coulomb failure criterion and multi-parameter failure criterion,an improved Mohr-Coulomb failure criterion expression with a power function form and a parabolic compression meridian failure criterion equation were proposed respectively.Based on the classical constitutive model of Guo Zhenhai,the quantitative relationships between the parameters of the rising section,the falling section and the relative confining pressure were established respectively through statistical regression,and then the constitutive relationship under triaxial compression was established.