Analysis Of Mechanical Properties And Microstructure Of Nano-MgO-fiber Modified Cement Expansive Soil

Because of the cycle of water absorption,expansion,loss of water and shrinkage of expansive soil,the cracks on the surface of expansive soil are staggered,which is very harmful to the project.Cement is a common chemical curing agent of modified expansive soil,but it can not meet the demand of bearing capacity and crack resistance in engineering more and more.Nano MgO and polypropylene fiber(referred to as fiber)as new materials have a wide range of value in the improvement of cement modified expansive soil.In this paper,the above two materials are studied respectively to get the improvement effect of the two materials on cement modified expansive soil.This article selects the expansive soil in nanyang,henan region,based on the different nanometer MgO style(0.5%,1%,1.5%,2%),and different fiber(0.2%,0.4%,0.6%,0.8%)than modified cement expansive soil in the age of 7 days and 28 days separately the unconfined compressive strength test,direct shear,conventional triaxial shear,such as indoor test,studied under the different factors of cement expansive soil mechanics,strength characteristics and deformation law of destruction.The main work and results of the study are as follows:(1)In the unconfined compressive strength test,when the age is 7days and28 days,the stress-strain curves of the modified cement expansive soil with different nano-mgo and fiber incorporation ratio are all softening curves with obvious peaks.The compressive strength of cement expansive soil increased first and then decreased with the increase of nano MgO and fiber incorporation ratio.When the incorporation ratio of nano MgO was 1%,the unconfined compressive strength was the largest at the ages of 7days and 28 days,which was 17% and 33% higher than the unconfined compressive strength of cement expansive soil.When the fiber incorporation ratio was 0.6%,the unconfined compressive strength was the largest at the age of 7days and 28 days,and the unconfined compressive strength was 13% and 17% higher than that of cement expansive soil,respectively.The unconfined compressive strength of expanded soils with nano-mgo and fiber modified cement increases with the growthof age.(2)through direct shear test,the shear strength of cement expansive soil with different nano MgO and fiber incorporation ratio increased linearly with the increase of load at various ages.With the increase of nano MgO and fiber incorporation ratio,the cohesion increased first and then decreased.When the incorporation ratio of nano MgO is 1.5%,the cohesion of cement expansive soil increases by 93% and 65%,respectively.When the fiber incorporation ratio is 0.6%,the cohesion of cement expansive soil increases by 34% and 58%,respectively.In general,the effect of MgO modified cement expansive soil is better than that of fiber modified cement expansive soil at different ages.(3)combined with triaxial shear test,after curing for 7days and 28 days,the deviatoric stress of modified cement expansive soil increases with the increase of confining pressure,and the stress-strain curves are all softening curves.When the incorporation ratio of nano MgO was 1.5%,the strengthening effect was the best,and the cohesion was improved by 94% and 72%,respectively,compared with that of cement expansive soil.When the fiber incorporation ratio was 0.6%,the cohesion was the highest,which was 58% and 47% higher than that of cement expansive soil.With the increase of confining pressure,the brittleness index and ductility of modified cement expansive soil decreased.(4)SEM and EDS microscopic tests were carried out on nano MgO and fiber modified cement expansive soil with curing age of 7days to analyze their microscopic mechanism.Micro-test results show that proper amount of nano MgO and fiber can make the overall structure of expansive soil become more compact and reach the effect of strengthening cement expansive soil.Macroscopic mechanical properties are explained by microscopic mechanism.