| Concrete as a building material is widely used in the field of engineering in the world,among which the cementitious material in concrete-cement is an important part of concrete.China,a major cement producer,produces hundreds of millions of tons of cement every year,an energy-intensive and highly polluting process.In order to save energy and protect the environment,it is very important to use industrial solid waste processing active materials to replace part of the cement in practical engineering to reduce the cement consumption.At present,concrete admixtures are mainly active materials such as fly ash and slag.However,due to the influence of region and transportation radius,it cannot meet the application demand in remote areas.Therefore,it is more practical to develop tailings with potential activity,wide area and large quantity for concrete admixtures.Tailings is the industrial solid waste with the largest discharge,and iron tailings have the largest discharge.A large amount of iron tailings not only occupies a large amount of land,but also causes serious pollution to the surrounding land resources and environment,and even endangers the lives and health of surrounding residents.In this paper,iron tailings are taken as the research object.The element composition,mineral phase composition,particle size distribution and mineral phase transformation of iron tailings during calcination are analyzed by means of XRF,XRD,laser particle size analyzer,FT-IR and TG-DSC,and the influence rule of iron tailings in concrete is studied by colloid-sand test.Finally,concrete admixtures meeting market requirements are prepared and the results and conclusions are as follows:(1)By mechanical activation of iron tailings,iron tailings with different specific surface area are replaced by 30%cement.When the specific surface area is 453 m~2/kg,the mechanical strength of iron tailings based concrete is the best,and the activity index is 77.82%.The research shows that iron tailings powder has a certain role as filler in concrete.(2)When exploring the influence of different surfactants on the mechanical properties of iron tailings based concrete,it is found that citric acid has the best adsorption effect on the particles in concrete(cement particles and iron tailings particles).During concrete mixing,iron tailings powder can be better dispersed in the slurry to fill its internal pores and improve the mechanical strength of iron tailings based concrete.When the content of citric acid was 0.6‰,the mechanical strength of iron tailings concrete was improved the best,and the activity index was increased by 7.94%compared with the control group.(3)The influence of different reinforcers on mechanical strength performance of iron tailings replacing 30%cement was explored,and the optimal dosage of different activators to improve mechanical strength of iron tailings based concrete was obtained:sodium sulfate content 1%,silicon slag content 1.5%and oxalic acid content 3%.Compared with control group,the activity index increased by 2.87%,4.27%and 7.55%,respectively.(4)The effect of citric acid,sodium sulfate,silicon slag and oxalic acid on mechanical strength of 30%cement replaced by iron tailings was designed by orthogonal experiment.After calculating the activity index and range of the specimen at the age of 7d and 28d,the optimal dosage of each admixture in the composite activator in iron tailings based concrete and the excitation effect of each phase of the activator were analyzed and determined.The optimal compound activator ingredients were 2%oxalic acid,0.2‰citric acid,1.5%silicon residue and 1%sodium sulfate.The activity index of 7d and 28d reached 87.8%and 92.6%,respectively.Compared with the blank control group,the activity index of 7d and 28d increased by 16.3%and16.5%,respectively.It was found that the compound admixture was not suitable for replacing 50%cement with iron tailings.(5)The mineral phases in iron tailings during thermal activation were analyzed by XRD,TG-DSC and Fourier infrared.It is found that the amorphous silicon and aluminum are separated from the Muscovite in the iron tailings by the form of broken bond when the activation temperature is less than 1000℃.The strength and activity test verified that the optimal decomposition temperature was 800℃,and the iron tailings at different activation temperatures were replaced with 50%cement.It was verified that the mechanical properties of iron tailings at 800℃were the best,and the activity index of iron tailings increased by about 11%compared with the original iron tailings.(6)Iron tailings were replaced by granulated blast furnace slag and metakaolin in turn.The test shows that the best replacement amount of granulated blast furnace slag is 30%,and the activity index is increased by about 26%.The optimum replacement amount of metakaolin was 15%,and the activity index increased by 27.6%.(7)When the compound admixture was added into PS concrete and PSM concrete for the same trial,the mechanical properties and mobility were enhanced,the activity index increased by 14.7%and 6.8%,and the mobility increased by 9.0%and 16.7.The technical indexes of S85 powder and S105powder admixture are achieved respectively. |
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