Research On The Strength Experiment And Solidification Mechanism Of Cement Solidified Sandy Silt

A large number of abandoned soil are produced during the process of engineering construction,stacking is the most common method to treat the abandoned soil,and occupies a lot of valuable land resources.For the reasons of its huge quantity,low strength,small stiffness,poor stability,sandy silt cannot be used directly in embankment filling and other projects.It is necessary to carry out the research on its resource utilization,for example,solidifying sandy silt as subgrade filler.This can not only bring huge economic benefits,but also produce better social benefits.To carry out the study of resource utilization of sandy silt,cement is used as curing agent,and four kinds of admixture,those are gypsum,lime,clay particle and fly ash are also selected.According to "Technical Guidelines for Construction of Highway Roadbases" and based on related experiment result,the cement content is selected to be 11%.The contents of admixture are selected as 2%,3% and 4%,respectively.The preparation and maintenance of experimental samples are carried out according to the method specified in the "Material test methods of materials stabilized with inorganic Highway Engineering".In order to study the influence of the admixture on the strength of cement stabilized sandy silt with different content,unconfined compression strength test,indirect tensile strength test,compression rebound test and flexural tensile strength test were carried out.In order to reveal the solidification mechanism,thermal field scanning electron microscopy and X ray diffraction experiments are carried out.Based on the study,following conclusions are drawn:(1)The strength and stiffness of the solidified sandy silt increase with the increase of curing age.The growth rate in the early stage is faster and the growth rate is slow when the curing age is more than 28 days.The intensity and stiffness of the solidified soil with different admixture and content are not the same with the age,and tends to be stable when the curing age is more than 60 days.(2)Lime is not suitable for the admixture of cement solidified sandy silt.Clay particle with 4%content can increase the early strength,and is suitable for the engineering with high early strength requirements.Gypsum with 2% content and fly ash with 4% content can greatly increase the strength of cement stabilized sandy silt.(3)The particle of the original sandy silt has a smooth surface,has no cementitious material,the particles of sandy silt cannot be well connected together.Macroscopically,the sandy silt has low cohesive force,poor stability,low strength and rigidity.When fly ash is added,two hydration reactions have occurred,more gridding hydrated calcium silicate(C-S-H)appears,and the C-S-H peak in the X ray diffraction pattern is more obvious,which promotes the increase of strength.When gypsum is added,ettringite(AFt)is produce due to the hydration reaction between gypsum and three calcium aluminate,and AFt peak is shown in the X ray diffraction pattern,the needle like AFt become more dense than that without any gypsum,and AFt can better fill the gap during the later period;When clay particle is added,there is no obvious difference between the peak of X ray diffraction pattern with clay particle and that without clay particle,which indicate that the main function of the clay particle is not to involve the chemical reaction,but to improve the composition of gradation.The conclusions obtained in present thesis can provide reference for the solidification of sandy silt as subgrade filler,and also provide a reference for better utilization of sandy silt and other abandoned soil.