Research On Preparation And Properties Of Tailings-Hybrid Fiber Reinforced ECC Materials On Cement Pavement

Engineered cementitious composite(ECC)can effectively solve the problems that concrete is brittleness and easy cracking,whereas its widely application are limited by its high price.At the same time,the utilization rate of tailings is seriously insufficient,and the problem of tailings management needs to be solved urgently.With the combined tailings with the concept of hybrid fibers,tailings-hybrid fiber reinforced engineered cementitious composite(T-HFRECC)materials with a low-priced,high ductility,low-carbon and environment friendly were prepared by combining tailings and hybrid fibers.The optimal mixing process for T-HFRECC was determined by pre-experiment.Based on the results of the pre-experiments,the influence of different tailings content,gradation and particle size on T-HFRECC pavement material was determined by workability and mechanical properties tests.Then,on this basis,the various performances of the T-HFRECC prepared with different content of tailings powder instead of cement were comprehensively analyzed by workability and mechanical properties tests.And by means of micro-experiment such as SEM and MIP,the mechanism of the effect of tailings powders on T-HFRECC was analysized.Finally,the effect of volume fraction of differnet fiber on the workability and mechanical properties were investigated by orthogonal tests.The results of this study were as follows:(1)Through fluidity,3d and 7d compression and flexural strength tests,the best mixing instrument was determined to be the Detong vibrating mixer,and the best mixing sequence was determined as follows:1.all powder+calcium carbonate whiskers,dry mixing for 4 min;2.the part of water+additional solution were added(water-to-binder ratio is controlled at about 0.28),wet stirring for 5 min;3.PVA fiber and PP fiber were added,mixing for 5 min;4.the remaining water was added,mixing for 5 min.(2)The fluidity of the T-HFRECC reduced as the tailings increased,but the folding ratio,compressive strength and flexural strength first increased and then decreased.And the replacement of the same size of quartz sand by same size of tailings could not affect its performance.(3)Through comparative analysis of the 7d and 28d splitting tensile strength and flexural strength,it is found that the tailings powder content should not exceed 10%of the cement quality.In the microscopic test,the incorporation of fine tailings powder reduced the heat of hydration,aand it could optimized the matrix but affect the bonding of the fiber and the matrix to a certain extent.(4)The results of orthogonal experiment based on content of PVA fibers,modified PP fibers and calcium carbonate whiskers shown that the optimal mix ratio was 0.9%PVA fibers content,0.8%calcium carbonate whisker and 0.3%modified PP fibers.(5)Compared to the benchmark ECC,the workability of the T-HFRECC increased by 19%,28d compressive strength,flexural strength,splitting tensile strength and folding ratio increased by 6%,52%,19%and 44%,respectively.And the price was reduced by 4.8 times,the carbon emission was reduced by 258kg in per cubic meter production of T-HFRECCC.The mechanical properties and workability of T-HFRECC had improved to a certain content,and it has better toughness and impact resistance.