Mechanism Effects Of Copper Tailings In Cement-based Materials

The mechanism effects of sole copper tailings and compounding copper tailings and graphene oxide on cement based materials were systematically studied in this paper.This study mainly consist of the grinding technology and particle characteristics of copper tailings,the hydration kinetics of cement-based materials containing sole copper tailings or compounding copper tailings and graphene oxide,and its effects on mechanical performance and microstructure properties of cement-based materials.The main research results are as follows:Based on the results of particle size distribtuion by laser particle size analysis,grinding kinetics simulation equation which could make a quantitative description of the copper tailings's grinding process were calculated.The grinding process of copper tailings is well conformed to the kinetic equation of Divas-Aliavden grinding,and the grinding efficiency of copper tailings is drawing near to zero after 90min.The particle size distribution of copper tailings well obeys the RRB and Swebrec equation.However,the RRB model is still superior to the Swebrec model in describing the particle size distribution of ball-mill copper tailings in the full size range.The initial packing density of cement-based materials containing 30%copper tailings ground for 60min is closest to the Full curve,which is helping to achieve a higher early strength of hardened paste.The particle size distribution of copper tailings has fractal features.Moreover,the longer the grinding time,the harder for the material to be ground.The study on hydration kinetics show that the addition of both copper tailings and graphene oxide in cement-based materials will lead to induction period be prolonged,the second exothermic peak time be delayed,and the exothermic rate and the hydration heat be lowered.While increasing grinding time of copper tailings will promote the hydration of composite cementitious system.The hydration mechanism and process were chronologically controlled by nucleation and crystal growth(NG),interactions at phase boundaries(I)and diffusion(D).The controlled effect of the NG,I and D mechanism was weakened with the increase of the amount of ground glass powder,but strengthened with increase of grinding time of copper tailings.Incorporating copper tailings in cement-based materials will strengthen the effect of NG mechanism,promoting early hydration.The addition content of copper tailings has little effect on the fluidity of cement paste,while increase the grinding time of copper tailings will decrease the fluidity of cement paste.The compressive strength of pastes increases with curing ages and decreases with the incorporation content of copper tailings.Either increasing its fineness or steam curing could be beneficial to strength development,and the promotion effect of steam curing is stronger than that of fineness increasing.Moreover,the promotion on strength increasing is even lager,at least 75%when in a combined fineness increasing and steam curing condition.Copper tailings exhibits minor hydration activity before 28d but showed certain hydration activity after that.The hydration activity is higher with finer copper tailings,lower W/C,and higher curing temperature.(2)The strength of paste containg both copper tailings and graphene oxide increase with curing ages.However,with increase of graphene oxide content,the results of strength are very distant,depending on the W/C ratio and the copper tailings content used.The results of mercury intrusion method(MIP)indicated that with the age increases,the distribution of pore structure tends to be optimized with the number of hazardous holes was decreased while the harmless holes was significantly improved.However,with the increase of copper tailings content,the law is reversed,leading to the strength weakening of specimens.The results of microcosmic test(XRD?TG-DTA SEM and EDS)showed that(1)Comparing with pure cement,the SiO2 was also be detected in cement-based materials incorporated with copper tailings besides crystal products including Ca(OH)2,CaC03,C2S,ettringite.dolomite ect.For specimens containing waste copper tailings,the amount of Ca(OH)2 decrease with time.As the amount of copper tailings content increased,the amount of Ca(OH)2 also decreased;(2)The addition of graphene oxide in both pure cement and copper tailings-cement composite materials had little effect on the kinds of hydration products as well as the amount of Ca(OH)2,inspite that hydrotalcite-like hydration products was detected at 90d;(3)The graphene oxide had a control effect on the morphology of hydrated products of low content(%)copper tailings-cement pastes at curing age of 3d,which makes the hydration products grow more fully,and the morphology is more unfolding and regularization,thus increasing the strength of the specimens.The innovation of this thesis are as follows:(1)The grinding dynamics and particle properties of copper tailings powder are studied,and a scientific method is provided for obtaining the optimum grinding time of copper tailings powder.(2)Our studies indicate that the regulating effect of graphene oxide on the hydration products is very limited.