Research On Road Performance Of Magnesium Oxychloride Cement-based Multiphase Cementitious Material Modified And Solidified Sludge

The solidification treatment technology is widely favored by domestic and foreign silt treatment projects due to its advantages of simple process,high efficiency,reduced sludge pollution,and solidified soil can be used as a fill resource.However,there are relatively few studies on the road performance of dewatered sludge modified by green magnesium oxychloride/magnesium phosphate cement combined with industrial by-products.In this paper,a series of physical and mechanical tests were carried out to explore the effect of magnesia cement-based multiphase cementitious materials to modify dewatered sludge and its performance as a roadbed filler.The main research contents and results are as follows:（1）Through the liquid-plastic limit test,the California Bearing Ratio（CBR）test,the compression test and the water stability test,it was analyzed whether the dewatered silt from Wuhan East Lake could be directly used as subgrade fill.The test results show that the liquid limit and plasticity index of the dehydrated sludge in East Lake meet the relevant specification requirements,but the CBR value is small,the compressibility index is large,and the water stability is poor,which does not meet the specification requirements.Therefore,East Lake dewatered sludge cannot be directly used as subgrade filler.（2）The composite modifier（called"magnesium oxychloride cement-based multiphase cementitious material"）is composed of different high calcium fly ash and granulated blast furnace slag powder mixing ratios under a certain amount of magnesium oxychloride cement is used to dewater East Lake.The silt was modified（called"modified silt"）,and considering the influence of 4 kinds of curing age,the mechanical properties of the modified silt were studied by carrying out the limit water content,CBR,compression,and water stability tests of the modified silt.At the same time,the microscopic mechanism of magnesium oxychloride cement-based multiphase cementitious materials to improve the characteristics of dewatered sludge was explored by scanning electron microscopy and nuclear magnetic resonance experiments.The results show that the addition of a modifier effectively reduces the porosity of dewatered sludge,improves its structural compactness and mechanical properties,and with the extension of curing age,the modification effect becomes more significant.Based on the test results,the optimal ratio of modifiers and the optimal curing age of the samples were determined.（3）The soil-water characteristic curve test,dynamic triaxial test,and unconfined compressive strength test were carried out after the modified solidified sludge samples made according to the above optimal ratio and optimal curing age were subjected to different drying and wetting cycles.The effects of wetting and drying cycles on the water-holding properties,dynamic parameters（modulus of resilience（M_R）and cumulative plastic strain（ε_p））,and static strength（unconfined compressive strength（q_u））of the modified sludge were investigated.The results show that with the increase of the number of drying and wetting cycles:（i）in the range of 0～10⁴k Pa,the water holding capacity of the sample decreases;in the range of 10⁴k Pa～10⁵k Pa,the water holding capacity of the sample tends to be consistent;（ii）the modified solidified sludge The elastic modulus,cumulative plastic strain,unconfined compressive strength,elastic modulus at 1%strain(E_1%),and strength(S_u1%)of the specimens all decreased with the increase in the number of wetting and drying cycles,and The drop caused by the first three wet-dry cycles was more pronounced.The attenuations of M_R,q_u,E_1%,and S_u1%are mainly closely related to the generation of cracks during the first wet-dry cycle.A prediction model of the dynamic and static parameters of the modified solidified sludge was established to reflect the influence of the number of drying and wetting cycles.（4）After the drying and wetting cycle,the sensitivity of M_R to the change of confining pressureσ_c increases;the deviatoric stressσ_d has two opposite effects on the stiffness of the specimen:（i）Repeated shearing causes damage to the structure of the specimen,which in turn causes The stiffness decreases;（ii）the sample produces cumulative plastic strain during the repeated shearing process,the sample is gradually compacted,and the stiffness is improved.（5）The plastic cumulative strainε_p of the specimen is mainly concentrated in the initial stage of loading（namely N≤1000）,and the growth rate ofε_p caused by subsequent repeated loading is relatively slow.In the initial state,ε_p of the modified solidified sludge is plastically stable,and after drying and wetting cycles,ε_p of the sample will transform into a plastic transitional type at highσ_d and lowσ_c levels.The dry-wetting cycle has a great influence on the relationship betweenε_p-average stress p of the modified solidified sludge.The relationship between the forces p has a greater impact.