Study On Preparation And Properties Of Concrete By Utilizing Unburned High-strength Aggregate From Dredged Sediment

With the progress of industrialization and dredging engineering,volume of dredging project has exceeded 1 billion cube meters annual in China recent years.Dredged silt is fluid plastic with low carrying capacity,and it would be difficult to use directly without further dehydration and drying.Moreover,secondary environmental pollution will be cause by accumulating sediment because of inability to dispose.In another sense,demanding for building materials grows with each passing day in China,but the mineral resources,such as gravel,are being excessive consumed,which will cut the mountain into cliffs,thus seriously affect the ecological environment.Considering the above issues,dredged sediment can be chosen as the raw material to prepare new green building materials,in order to replace the natural gravel aggregate in concrete,hence to solve the above two aspects of the dredging sediment placement and the consumption of mineral resources.Based on above problem,this study focuses on the interface mechanism,practical application and cyclic performance of the dredged sediment unburned aggregate concrete,in order to verify the feasibility of its application in concrete.On the one hand,the high water absorption ratio of unburned aggregates,which is prepared by mixing dredged sediment with cementitious material in pellet granulation,would leads to the fuller hydration of surrounding the aggregate in the later maintenance of the concrete specimen.On the other hand,the composition of the shell of aggregates is in same phase with cement matrix,and bonding between aggregate and cement matrix is more compact.These two above aspects can make the aggregate surface form an interface area with higher strength and denser structure.In this paper,effects of water to cement ratio,sand ratio,aggregate gradation,aggregate volume fraction,aggregate replacement rate and other factors on concrete performance are investigated by using the method of datum mix ratio inquiry,orthogonal experiment,single factor experiment and recycling experiment,respectively.The experimental results show that the strength of concrete specimen can be as high as 20.707 MPa(14#),which is beyond the requirement of design standard C20,in the case of replacing gravel with high strength aggregate in ratio of 100%.It is possible to preliminarily speculate that the unburned high strength aggregate of dredged sediment is feasible in the application of replacing natural aggregate in concrete.Besides,some of the samples meet the requirements of frost resistance D25 grade and sulphate resistant KS15 grade standard.The optimum ratio of concrete is that the aggregate volume fraction is 0.40,5～16 mm is continuously graded,the sand ratio is 0.41,and the water cement ratio is 0.55.The residual material of damaged or broken dredged sediment unburned high strength aggregate can still be reused as certain extent,that is,the recycling of high strength aggregate is feasible.In addition,the difference between the interfacial zone property of the "high strength aggregate-cement matrix" and "gravel-cement matrix" is comparative study and mechanism analysis.The results show that the reasons for the high strength of the unburned aggregate concrete include the characteristics of the reflux,the structure of the aggregate shell and the operation of the granulation shell,and the modification of the interface relationship.When the cementitious material mixed with the filler to prepare the building materials,filler would not participate in the volcanic ash reaction but easy to be hydrated,thus reducing"concrete-sediment" interface can effectively improve the strength of the building materials.The preparation of aggregates from dredged sediment is the best way to reduce the interfacial area of "concrete-sediment",and thus has the ideal strength performance.Finally,through the results of the preliminary market research in the actual application and the process flow,equipment selection,economic benefit and social benefit in the preliminary design of industrialization,it can be found that the dredged sediment unburned high strength aggregate has a certain feasibility in practical application in replaying crushed stone aggregate in concrete.