Study On Modification And Mechanism Of Red Mud Used In Base Pavement

Red mud is a solid industrial waste produced in the process of alumina.As a big country in aluminum production,China has produced a huge amount of red mud.Due to the low utilization rate of red mud,the surplus of red mud has become increasingly large,and the problems of storage and pollution of red mud have become increasingly serious.Based on the study of traditional lime-stabilized red mud,this paper introduced coal-measure metakaolin(CMK)and cement as modifiers to modify lime-stabilized red mud in order to better consume red mud on a large scale.The unconfined compressive strength,impermeability and resistivity of the modified red mud were studied by using different amounts of metakaolin and cement from coal measures.The microstructure and products of the modified red mud were analyzed by XRD and SEM,which provided experimental and theoretical reference for the large-scale use of red mud.The main research contents of this paper are as follows:(1)Under the condition of traditional two-lime stabilized red mud(red mud: fly ash:lime =80:10:10),coal measure metakaolinite and cement were introduced to replace 1%,2%,3%,4% and 5% of lime with equal amounts,respectively.Unconfined compressive strength at 7d,28 d and 90 d ages was tested to explore the strength development law of modifier with different dosage at different ages.The results show that the strength of modified red mud increases first and then decreases with the increase of CMK content,and the optimal CMK content is 2%.With the increase of cement content,the strength of modified red mud increases rapidly at first and then tends to be stable,and the optimal cement content is 3%.With the increase of CMK content,the unconfined compressive strength of the modified red mud increased significantly from 7 days to 28 days,with an average growth rate of 2.39%/d.Unconfined compressive strength increased slowly from 28 d to 90 d,with an average growth rate of 0.50%/d.With the increase of cement content,the variation trend of unconfined compressive strength of the modified red mud with age is roughly the same as that of CMK.The unconfined compressive strength of the modified red mud increases significantly from 7days to 28 days,with an average growth rate of 1.84%/d.Unconfined compressive strength from 28 d to 90 d increased slowly,with an average growth rate of 0.10%/d.(2)Permeability meter was used to test the change of permeability coefficient of each ratio at the age of 28 d,and the change of permeability coefficient with the change of CMK and cement content,so as to explore the influence of permeability pressure and modifier content on the anti-permeability performance of modified red mud.The results show that with the increase of permeability pressure,the increase of permeability coefficient is small when the content of CMK is 2%-3%,and the permeability coefficient of modified red mud with cement is only slightly increased.The permeability coefficient of modified red mud decreases first and then increases with the increase of the content of CMK.When the content of CMK is 2%,the permeability coefficient reaches the minimum value.With the increase of the content of cement,the permeability coefficient decreases rapidly at first and then slows down gradually.When the cement content is more than 3%,the permeability coefficient drops less and tends to be stable.(3)LCR digital electric bridge was used to test the resistivity of each ratio at curing ages of 7d,28 d and 90 d,to study the influence of CMK and cement content on the resistivity of the modified red mud,and to explore the feasibility of using resistivity to characterize the unconfined compressive strength of the modified red mud.The results show that the influence of current frequency on the resistivity of the modified red mud samples is roughly equal.With the constant increase of the current frequency,the resistivity on the whole presents a rapid decline and then a gradual gradual trend.The subsequent studies of this paper will use the corresponding resistivity value at 50 k Hz for analysis and research.With the increase of CMK content,the resistivity increases first and then decreases,and reaches the peak value when the content is 2%.With the increase of cement content,the resistivity of modified red mud showed a slight decrease and then an upward trend.At different ages,the resistivity of CMK modified red mud increases as the age increases.When the content of CMK is less than 2%,the resistivity increases slowly in the early curing age(7d～28d),and greatly in the later curing age(28d～90d).When the CMK content is 3%～5%,the resistivity increases in a consistent range.Modified cement red mud also belong to the whole of resistivity along with age growth trend,the cement content is 0% ～ 2%,the modified red mud resistivity present all over the whole curing age is relatively steady growth,the cement content is 3% ～ 5%,the modified red mud green resistance has a larger increase in the early curing age,the late growth rate is small,stable in the end.(4)The composition of pure red mud,lime stabilized red mud,modified red mud with 2%cement content and modified red mud with 2%CMK content was detected by X-ray diffraction,and the hydration product composition of modified red mud was studied.The results showed that the main products of modified red mud,such as silica,calcium carbonate and ferric oxide,remained unchanged with the difference of modifiers,but ettringite appeared when CMK was added.When cement is added,calcium hydroxide and ettringite are found in the products.The formation of these substances significantly improves the structure and properties of red mud.(5)Scaning electron microscopy was used to observe the morphology of red mud stabilized by lime,red mud modified by 2% cement content and red mud modified by2%CMK content,and to study the influence of modifiers on the internal structure of modified red mud.The results show that the structure of the lime stabilized red mud is loose.With the addition of CMK,the porosity decreases,the soil particles are uniform and the structure is compact.With the addition of cement,gels and blocky materials appeared in the generated species,which further filled the pores and greatly improved the physical and mechanical properties of the lime-stabilized red mud base material.