Preparation Of Green Low-carbon Composite Cementitious Materials From Multi-source Solid Waste

Aiming at the problems of large stock of industrial solid waste and low utilization rate of recycling,green low-carbon composite cementitious materials were prepared to improve the utilization rate of waste aerated concrete（WAC）and steel slag（SS）in building materials by taking WAC and SS as the research objects.Firstly,the physical and chemical properties of WAC and SS are studied,and then the activation of WAC and SS is studied by means of mechanical-chemical coupling activation.Secondly,the preparation and properties of composite cementitious material containing WAC,SS,and cement（ASCM）were studied by single factor control variable method.On the basis of ASCM,the preparation and properties of composite cementitious material containing WAC,SS,slag,and cement（ASSCM）were studied by orthogonal test.Finally,the phase composition,structure and hydration hardening mechanism of ASSCM were investigated by hydration thermal analysis,X-Ray diffraction（XRD）,scanning electron microscope（SEM）and energy dispersive spectrometry（EDS）.The following conclusions are drawn:（1）With the increase of grinding time,the particles below 10μm in WAC increase significantly,forming a new main peak between 1μm and 10μm,and the overall distribution range is"bimodal".When the grinding time of WAC was 40 min,28d activity index was 81.43%,which can meet the requirement of 28d activity index≥65%for GB/T2847-2005 Pozzolanic materials used for cement production.The correlation between specific surface area and grinding time of WAC can be expressed by the simulation equation S=427.49lgt-26.96.The excitation effect of each basic activator on WAC is Na₂SiO₃·9H₂O>Na₂SO₄>Na₂CO₃>Na OH.（2）When the specific surface area of WAC and SS were 655 m²/kg and 461 m²/kg respectively,WAC:SS:C:desulfurization gypsum=20:20:54:6,2%Na₂SiO₃·9H₂O（the composite cementitious material mass percentage）,water-binder ratio of 0.56,cement-sand ratio of 1:3,the 28d flexural and compressive strength of ASCM are 5.6MPa and25.8MPa respectively,and the flow elongation is 233mm.（3）On the basis of ASCM research to study ASSCM,it is concluded that when WAC:SS:S:C=16:10:32:42,the 28d flexural and compressive strength of ASSCM are 7.1MPa and 34.5MPa,respectively.The physical performance specifications of ASSCM meet the requirements of P.C 32.5 in GB175-2020 General Portland Cement.（4）The hydration process of ASSCM is similar to that of cement,but ASSCM can shorten the induction period and reach the second heat release peak in 11.2h,reducing the hydration heat release rate by 46.95%and the total heat release by 58.86%.The hydration products of ASSCM mainly include C-S-H gel,Friedel salt,Thaumasite,AFt,Ca（OH）₂,some slag and inert substances that did not participate in the reaction（quartz,calcium carbonate and Tobermolite in WAC and RO phase and Fe₃O₄ in SS,etc.）.（5）In the early stage of hydration of ASSCM,it is mainly manifested as the hydration reaction of cement,and the synergistic hydration reaction of slag and SS under the excitation of Ca²⁺and Na²⁺.In the later stage of hydration,ASSCM has the dual effects of volcanic ash effect and microaggregate filling.The active particles in the system continue to hydrate,and the hydration products generated can still produce sufficient gelling capacity.The inert particles that do not participate in the hydration reaction and a large number of active particles that have been hydrated on the surface of the system fill the pores of the slurry,improve the microstructure of the slurry,and improve the mechanical properties.