Preparation of Lightweight Aggregate Use by Ferrochrone Slag Based on the Interfacial Zone Optimization and the Performance of Concrete

Author:Zhang Li Hua

Supervisor:zhang yun sheng


Degree Year:2018





Development of high strength lightweight aggregate concrete provides a new key material using for the precast element,super large-span bridge and so on.The characteristics of light weight and high strength are not only beneficial for reducing structure self weight,structure’s sectional area,and construction price,but also beneficial for improving anti earthquake ability and increasing the service life.Thus,its technological and economic values are obvious.However,in our country,the lightweight aggregate industry faces difficulties of shortage of natural resource,environmental damage and lack of theoretical guidance of preparation of high strength and performance lightweight aggregate.From this,this article uses ferrochrome slag as main raw material,the cordierite ceramic porous lightweight aggregate covered with belite with nucleus-shell structure was successfully designed and prepared.The design method of high performance lightweight aggregate was based on the inner nucleus strengthening and outer shell improvement.The preparative technique,mechanical properties and durability of the lightweight concrete were studied.The interfacial zone properties and micro structural evolution process as well as the regular pattern of failure were discussed.All those efforts lay scientific foundation for future study of high performance lightweight aggregate and the concrete.The obtained achievements and innovations are given following.The constitute design and sintering technology as well as chemical reaction mechanism of the normal lightweight aggregate were studied.Based on the Reilly phase diagram,the preparing chemical principle of the lightweight aggregate with large dosage ferrochrome slag(50%70%)was studied.Through the experimental research on constitute,microstructure,and properties,the calcining parameters of stable and reproducible lightweight ferrochrome slag aggregate were obtained.That is,after the idiosome was pre-dried at a temperature of 600℃for 10 min,it was heated to 1210℃1250℃and kept this temperature for 10 min.After cooled to 1000℃,the specimens were rapidly air cooled to room temperature.Its appearance density is in the range of400kg/m31500kg/m3 and its compressive strength is in the range of 0.5MPa6.5MPa。The design,performance and reaction mechanics of cordierite ceramic porous lightweight ferrochrome slag aggregate covered with belite in a form of nucleus-shell structure were studied.A new design approach of the high performance lightweight ferrochrome slag aggregate was proposed.The main phase of inner nucleus is porous ceramic consisting mainly of cordierite(more than 85%).The chemical composition meets the MgO-SiO2-A12O3 ternary phase diagrams.The dosage of ferrochrome slag in the aggregate is about 40%50%.The shell consists mainly of reactive mineralsβ-C2S and C4A3-S.From the exploring suitable solid reaction temperature and calcining assistant agent,the calcining system of the complex structure was adjusted to the nucleus and shells being mate.That is,after the complex structural idiosome was pre-dried at a temperature of 600℃for 20 min,it was calcined at temperatures of 1260℃1280℃and kept this temperature for 30min,then it was cooled to 800℃and then rapid air cooled to room temperature.In this way,the inner nucleus and shells were successfully calcined synchronous,and the inert high strength cordierite was covered with reactive belite mineral,which was beneficial for the improvement of transition zone between aggregate and main matrix.The appearance density of the prepared aggregate is about 1300kg/m3.The compressive strength of this aggregate particle reaches up to7MPa and its water absorption is less than 2%.Besides,this thesis reveals the formation mechanism of microstructure by means of SEM,XRD,and energy spectrum analysis.The mix proportions,performances,and environmental coordination of lightweight concrete made with this aggregate were studied.According to the strength requirement of lightweight aggregate,for long span structural engineering,the concretes with uncovered normal lightweight aggregate and nucleus-shell structure lightweight aggregate with bulk density of 1800kg/m3 were prepared in this study,there compressive strengths can reach to 48MPa and 52MPa respectively,the later shows better workability,better mechanical properties,and better durability such as anti chemical corrosion,anti carbonation,and freeze-thaw resistance than the former.Compared with uncovered lightweight aggregate,the prepared complex structure aggregate presents multi-characteristic damage,and the brittleness property was improved.In order to ensure the environment safety of lightweight ferrochrome slag aggregate concrete,this paper has taken Cr leaching tests which reveal the fact that Cr3+element was solidly dissolve in coordination and spinel lattice and certify conforming to the environment requirements.In order to analyze the effects of the prepared complex structural lightweight aggregate on the transition zone characteristics and its concrete,a test method was invented to measure the transition zone characteristics.The test results show that the transition zone of uncovered aggregate,the CH orientated growth and AFt in a form of cluster shape,the crystal size is thick and big,causing a more porous transition zone.In contrast,in transition zone of the nucleus-shell structural lightweight aggregate,the CH and AFt present disorder distribution.They cover with C-S-H gel and result in a dense microstructure.The measured thickness of interfacial transition zone by means of back scattering electron image analysis are 40μm,25μm,and 15μm respectively at ages of 28d,90d,and 180d.