| With the large-scale development of water resources and the continuous development of water environment control projects,the amount of dredged sludge is increasing.Dredged sludge has the characteristics of high clay content,poor mechanical property and contaminant.If it is not disposed reasonably,it will cause a great threat to the ecological environment.It has been the focus of scholars at home and abroad to treat and dispose the dredged sludge in terms of resources,harmlessness and reduction.Therefore,this paper takes the cement solidified dredged sludge as the research object,combines the fiber reinforcement and biochar modification technology,studies the influence of various modification methods and their coupling effects on the mechanical properties of the solidified dredged sludge,compares and analyzes the modification effect of the dredged sludge under different initial water content conditions,and uses the fiber Bragg grating technology(FBG)to explore the biochar modified solidification The law of shrinkage deformation and internal stress of dredged sludge with time in the process of curing and drying.In addition,scanning electron microscope(SEM)was used to analyze the mechanism of fly ash cement solidification and the coupling mechanism of biochar fiber solidification.The main results are as follows:(1)The ratio of cement and fly ash has a significant impact on the solidification effect of dredged sludge.The unconfined compressive strength(UCS)of the sample is the highest when the cement content is 5% and the fly ash content is 8%.This is because the strength of the sample is mainly affected by the following three factors when the dredged sludge is treated by cement and fly ash together,namely,the filling winding interlocking consolidation of hydrate generated by cement hydration reaction,the secondary filling caused by the pozzolanic reaction of fly ash,and the form filling effect of fly ash.These three factors promote each other and restrict each other,and are realized in the optimal ratio Maximum strength of the specimen.(2)Fiber reinforcement can significantly improve the mechanical properties of solidified dredged sludge.The influence of fiber on sludge solidification mainly depends on the content of fiber,the adhesion and friction between fiber and solidified dredged sludge particles.The strength of the sample increases first and then decreases with the increase of the fiber content,reaching the peak value when the fiber content is0.1%,and the fiber reinforcement can improve the toughness of the sample when it is damaged.(3)The initial water content is an important factor affecting the modification effect of dredged sludge.The UCS,residual strength and strain at failure decrease with the increase of initial moisture content.In the range of 50%-80% moisture content,the contribution of fly ash cement solidification to strength increases with the increase of moisture content.For the samples mixed with fiber and biochar,the reinforcement effect of fiber and the modification effect of biochar decrease with the increase of initial moisture content.(4)Biochar can promote the strength of dredged sludge solidified by cement.With the increase of the content of biochar,the strength of the sample increases exponentially.When the content of biochar increased from 0 to 20%,the UCS of the sample increased nearly 3.7 times.This is because biochar,as a porous material,increases the active surface of cement particles and promotes the hydration of cement.Based on SEM images,it is found that the strength of dredged sludge samples solidified by fiber reinforced biochar modified cement is improved,mainly because the hydration products of cement adhere to the interface of biochar fiber sludge and fill the soil pores.Through the formation of a hard network structure in the mixed system,the mechanical properties of the samples are improved.(5)Using fiber reinforced biochar to modify and solidify dredged sludge can achieve better results,mainly due to the benign coupling between various treatment technologies.The coupling mechanism of fly ash cement solidification technology and fiber reinforcement technology is: the hydrate produced by cement hydration reaction and fly ash pozzolanic reaction adheres to the fiber surface,increases the roughness of the fiber surface,improves the mechanical action mode of the fiber-soil particle interface,and improves the strength.The coupling mechanism of solidification technology,fiber reinforcement technology and biochar modification technology is as follows: biochar promotes the hydration reaction of cement,so that the cohesive force between fiber and solidified dredged sludge is enhanced,and the strength of sample is improved;although the addition of fiber can effectively improve the solidification effect of dredged sludge,the addition of excessive fiber is prone to fiber agglomeration,which will be in the trial The weak structural plane is formed in the sample,which reduces the strength of the sample.(6)Biochar can inhibit the shrinkage effect of cement solidified dredged sludge.In this paper,the strain time curves of the samples without biochar and the samples with10% biochar in the curing/drying process were compared through the restrained ring test.The strain time curves of the samples without biochar and with 10% biochar showed similar changes,but the shrinkage deformation of the samples with biochar was smaller than that of the samples without biochar.This is mainly due to the large specific surface area and rich porosity of biochar,which can stay in the free water in the sludge and supply water slowly in the cement hydration reaction stage,thus delaying the chemical shrinkage caused by cement hydration reaction. |
PDF Full Text Request