Study On The Activation Process And Mechanism Of Iron Tailings Powder And Its Influence On The Performance Of Concrete

Although the rapid growth of the number of iron ore tailings,the utilization rate of iron ore tailings is very low and the environmental pollution has become increasingly serious.In order to realize sustainable development of building materials industry,it is an effective way of resource utilization of solid waste to prepare large building material concrete with iron tailings resources.The development of iron ore tailings as concrete mineral admixture can be applied to the large amount of concrete to increase the added value.The iron tailings must be activated.Mechanical activation can induce and produce chemical activity which is difficult or unable to be induced by heat energy.It is one of the effective methods to carry out active excitation in simple process without high temperature calcination.Based on the mechanical activation method and theory,this paper makes systematic research of the mechanical activation effect and the chemical-mechanical coupling effect which has revealed the mechanochemical effect and its relationship with hydration activity.According to the research of the mechanism of hydration and hardening of activated iron ore tailings,the work performance,mechanical properties and durability of concrete incorporated by activated iron ore tailings are analyzed and studied comprehensively.?1?The research of mechanical activation on the activation of iron ore tailings:During the process of mechanical activation,the particles of iron ore tailings experience three different deformation stages,namely,brittle deformation stage,the stage of brittle and plastic deformation,plastic deformation stage.When it is 2.0h of the mechanical activation,the particle density of iron ore tailings reaches a minimum value of 2.75g/cm³.The specific surface area reaches the maximum value of 770m²/kg.The distribution of particle size becomes narrower.The cumulative content of the particles which size are less than 5 ?m reaches the maximum value of 77.70%.The average particle size of D50 and D90 has dropped to a minimum of 3.20 ?m and 7.54 ?m.The water requirement of mechanically activated iron ore tailings is equivalent to that of the secondgrade fly ash.With the dosage of 30% iron ore tailings by mechanical grinding for 2 hours,the activity index of the 28 d compressive strength reaches 81%.The pozzolanicity of MIT is qualified,which can be judged as active mixed material.Under the action of mechanical activation,the peak intensity of X-ray diffraction of iron ore tailings particles is weakened.The internal crystal structure is destroyed.The amorphous degree is deepened.The crystallinity?K?of zeolite crystal surface of the iron ore tailings after grinding for 2.0h is the smallest.The M value of amorphous matter is close to 20%.Based on the analysis of the surface binding energy of XPS,the lattice distortion of iron ore tailings under mechanical activation occurred.The binding energy of each element is gradually reduced to form a phase with high activity and low binding energy.The Si2p,Al2p,O1s binding energy of iron ore tailings after mechanical grinding for 2.0h is lowest,respectively,102.54 eV,74.31 eV,531.32 eV.The infrared spectrum IR test shows that disordered material on the surface of powder by mechanical grinding increases.The deformation and dislocation of the crystal lattice,the formation of unstable crystal structure,the vibration energy can be improved.It increased the activity of iron tailings.Under the action of mechanical activation,the iron tailings particles have happened obvious mechanochemical effects.?2?The effect of chemical-mechanical activity on the iron ore tailings:The optimal scheme of chemical-mechanical activation was obtained by orthogonal test: t=2.0h,d=0.5%;CaSO₄?2H₂O as the optimal activator.Under the chemicalmechanical action,the iron ore tailings have experienced three different failure and deformation processes.When the dosage of CaSO₄?2H₂O is 0.5% and the coupling activation time is 2h,the particle density of iron ore tailings reaches a minimum value of 2.74g/cm³.The maximum value of specific surface area reaches 813m²/kg.With the increase of CaSO₄?2H₂O content,the density of iron ore tailings first decreased and then increased.The specific surface area shows first increasing and then decreasing trend.Compared with mechanical activation,the particle size distribution of chemicalmechanical activated iron ore tailings is narrow.And the degree of particle refinement is increased.When the dosage of CaSO₄?2H₂O is 0.5%,the accumulation content of particle in less than 5?m can reach 81.25%.The accumulation of the particle which less than 3 ?m reached the highest content of 59.48%.When the proportion of iron ore tailings with 0.5% CaSO₄?2H₂O by coupling activation?CMIT?for 2h is 30%,the flexural strength ratio and activity index of 28 d are 103% and 85% respectively.Its strength is greater than MIT.The pozzolanicity of the CMIT is qualified,which can be judged as active mixture.XRD researches show that the degree of amorphous CMIT is greater than MIT.Its amorphous amount reaches 22.29%.The surface binding energy of CMIT is lower than MIT.The binding energies of Si2 p,Al2p and O1 s are 102.50 eV,74.25 eV,531.25 eV,respectively.The chemical-mechanical activation is more conducive to the formation of the phase with high activity and low binding energy.Through the infrared spectrum IR,the chemical-mechanical activation makes the iron ore tailings to produce more deformation and the dislocation.Disordered substances will increase,and own higher reactivity.Compared with the mechanical activation,the chemical-mechanical activation has a better effect on the potential activity of iron ore tailings and has obvious chemicalmechanical effect.?3?The study on the mechanism of hydration and hardening of activated cement by iron ore tailings:With the increase of MIT and CMIT,t_a?t_c?t_d are gradually shortened.And dQ_a/dt,dQ_c/dt,dQ_d/dt and Q_a?Q_c?Q_d are gradually reduced.Under the same dosage,the hydration induction time of MIT?ta?is shorter than CMIT.The heat release rate of dQ_a/dt is less than MIT.And the total heat flux?Q_a?of MIT is greater than that of MIT.During the acceleration period of hydration,the nucleation rate K of hydration products of CMIT is greater than that of MIT.In the period of hydration deceleration,the total amount of CMIT is larger than that of MIT.The hydration rate(Q_a-c)of CMIT was greater than that of MIT at the maximum hydration rate.CMIT promote the second hydration of aluminum phase.The Q_d of composite cement system of CMIT is higher than that of MIT.The influence of CaSO₄?2H₂O of MIT on the hydration of cement is different from that of CMIT.The existence of chemical mechanical coupling effect is confirmed.Through the XRD analysis of hydration products,it is confirmed that the hydration degree of the composite system with iron ore tailings is lower than that of the reference cement at the early stage of hydration.However,in the later hydration period,the peak of Ca?OH_?2 has a certain decrease due to the occurrence of the second hydration.And the peak value of AFt is stabilizing.The result of thermal analysis shows that there are 4 endothermic peaks in the composite system of activated by iron ore tailings.The heat loss occurs for three times.The micro-morphology analysis of the hydrated products of CMIT shows that with the increase of hydration age,a dense structure is formed between the gel and the particles.This significantly reduces the porosity of cementitious materials.The results of MIP test of hardened cement paste show that the total porosity of cement paste mixed with mineral admixture is higher than that of blank cement in the early hydration age.In the later stage of hydration,the second hydration reaction and micro aggregate effect occur.The total porosity was lower than the blank sample.The total porosity is the lowest in 28 d hydration age of CMIT.Gel pores of hardened paste slightly increase and small capillary pores decrease.The minimum pore size can be minimized,which reduces the connectivity of pores.Through the characterization of different detection methods,it is proved that CMIT is more hydrated than that of MIT.?4?The research on the performance of concrete activated by iron ore tailings:Compared with the pure concrete,the fluidity of the concrete is improved by adding the activated iron ore tailings.But the fluidity is lower than that of the concrete with fly ash.The improvement and workability of high-strength concrete are better.The ratio of MIT to CMIT should not exceed 40%.The fluidity of the concrete with double-mixed iron ore tailings is obviously higher than that of the concrete with single-mixed iron ore tailings.This is close to the fluidity of the concrete with double-dosaged fly ash.Under the condition of low ratio water to binder,it is more favorable to improve the fluidity of concrete.The appropriate amount of concrete to improve the fluidity of concrete increased to 60%.With the increase of the amount of activated iron ore tailings,the compressive strength of concrete at different ages decreases.The strength of highstrength concrete with single activated iron ore tailings increases more obviously.When the dosage of CMIT is 40%,the compressive strength of 28 d and 60 d of high strength concrete is about 67.9MPa and 73.5MPa,respectively.It is beyond pure concrete.The compressive strength of concrete with double-mixed iron ore tailings at 3d is lower than that of single-mixed iron ore tailings.But the later compressive strength is higher than that of concrete with single activated iron ore tailings.At the same dosage,the compressive strength of MIT and CMIT is higher than that of the concrete with fly ash at the early stage.However,the growth rate of later strength is less than that of fly ash concrete.The contribution of iron ore tailings in CMIT to the strength is better than that of MIT.The chloride ion permeability of activated iron tailings concrete is higher than that of pure cement and fly ash concrete.And the resistance to chloride ion penetration of CMIT concrete is higher than that of MIT concrete.The carbonation resistance of activated iron tailings concrete is lower than that of pure cement concrete.But this is higher than that of fly ash concrete.And the carbonation resistance of MIT concrete is slightly better than that of CMIT concrete.The frost resistance of concrete mixed with mineral admixture is better than that of pure cement concrete.The frost resistance grade of blank sample is F75.And the frost resistance grade of concrete mixed with mineral admixture reaches F125.MIT and CMIT have the same effect on the frost resistance of concrete.Through the comprehensive analysis of the mechanism of the reaction activity of iron ore tailings under the action of mechanical-chemical coupling activation,a new way of environmental protection and high efficiency can be found.