Contaminated Sediment Solidification Improvement Technology And Road Performance Research

The water system in my country is widely distributed,and a large amount of sediment is deposited at the bottom.With the massive excavation of sediment,the problem of its disposal is becoming more and more serious.After solidifying and improving the bottom mud,it can be used in the field of road construction,which can not only make reasonable use of the bottom mud but also solve the problems of insufficient supply of roadbed fillers in the process of road construction.The commonly used solidifying material for polluted sediment is cement,but the cement production process consumes a lot of resources and emits a large amount of CO₂,which will cause serious pollution to the environment.Activated MgO is a more sustainable cementitious material than cement due to its low firing temperature and low CO₂ emissions.Based on this,this thesis relies on the project"Solid Waste and Polluted Sediment Treatment Technology Engineering Demonstration and Equipment Research and Development",using active MgO,desulfurized gypsum,and steel slag as curing agents to solidify and improve the contaminated sediment,and to improve the road mechanics of the solidified sediment.A series of experimental studies on performance,durability and microscopic properties have been carried out to provide a theoretical basis for the application of low-carbon and environmentally friendly sediment solidification technology in the field of road construction.First,through physical and mechanical tests,the basic physical and mechanical properties of the Xiaoqing River polluted sediment were mastered.Secondly,through the single mixing test of the three curing agents,the effect of each curing agent dosage on the strength of the polluted sediment was clarified.Combined with the response surface method,the optimal dosage of the three curing agents was obtained.Thirdly,through the X-ray diffraction test and scanning electron microscope test,the material composition and microstructure of solidified sediment with different curing agent dosages were analyzed.Finally,the road mechanical properties of the cured sediment were obtained through the unconfined compressive strength test,splitting test,and compressive resilience modulus test under the optimal dosage of curing agent;meanwhile,the dry shrinkage test was carried out.,dry-wetting cycle test,freeze-thaw cycle test,analyzed the impact of environmental changes on the durability of the solidified sediment;combined with the leaching test,evaluated the environmental safety of the solidified sediment.The main research conclusions are as follows:(1)The natural water content of the contaminated sediment is 17.9%,the content of the gravel group is 13.7%,the content of the sand group is 62.7%,the content of the fine group is23.6%,the liquid limit is 29.30%,the plastic limit is 22.90%,and the index is 6.40,which is silty sand;the main component of polluted sediment is quartz;the optimum water content of polluted sediment is 14.4%,the maximum dry density is 1.93g/cm~3,the CBR value is 16.84%,and the compressive resilience modulus is 38MPa,the unconfined compressive strength is392.39k Pa.When the contaminated bottom mud is used as subgrade filler,its compressive resilience modulus and compressive strength cannot meet the requirements of the specification.(2)When the curing agent has been added alone,the strength of magnesium oxide and desulfurized gypsum solidified polluted sediment increases with the increase of the curing agent content,while the strength of the steel slag solidified sediment first increases and then decreases with the increase of the steel slag content.Based on the results of the single-mixing test of the curing agent,the content of the three curing agents was used as the variable,and the unconfined compressive strength of the specimen after curing for 7d and 28d was used as the response value optimization.Through variance analysis and factor effect analysis,the optimum dosages of magnesium oxide(MgO),detached gypsum(DG)and steel slag(SS)were found to be 7.62%,11.31%and 5.80%when they were mixed to solidify the contaminated sediment.(3)Under the optimal dosage of the curing agent,MgO will undergo a hydration reaction to form Mg(OH)₂ and M-S-H,and the Ca O in the desulfurized gypsum will be hydrated to form Ca(OH)₂.It reacts with steel slag to form calcium silicate hydrate gel(C-S-H)and calcium aluminate hydrate gel(C-A-H),C-A-H is further converted into ettringite(AFt).And the resulting gel and substance will make the microstructure of the sample more compact and the strength improved.(4)The mechanical properties of the solidified bottom mud under the optimal mixing amount meet the requirements of road performance;the cumulative water loss rate and cumulative dry shrinkage of the solidified bottom mud show a trend of rapid growth in the early stage and gradually stable in the later stage;The increase in the number of thawing cycles will reduce the unconfined compressive strength of the solidified sediment;the first 9wet-dry cycles have a greater impact on the strength of the specimen,but the appearance of the specimen is basically not damaged;the first freeze-thaw cycle The effect has the greatest impact on the strength of the specimen,and the strength loss rate exceeds 30%.When the number of freeze-thaw cycles reaches 6,the surface of the test piece will appear with fine cracks,and the soil blocks will fall off at the edges and corners.The pores with a pore diameter of 0.01?0.1?m inside the piece will decrease,and the pores with a pore size of0.1?1?m will increase,and the effect of freeze-thaw cycles on the pore structure of solidified contaminated sediment samples is greater than that of drying-wetting cycles.