Experimental Study On Mechanical Properties And Mechanism Of Cement Soil Improved By Nano Materials

Cement soil refers to the building materials formed by mixing and setting a certain proportion of soil,water and other cement materials.It is widely used in engineering practice.In this paper,the relevant experimental research is carried out on the muddy soft soil encountered in the foundation treatment project of cement soil mixing pile of regulating gate C001 of the Yangtze River to the Huaihe River.Based on the laboratory test,the influence laws of relevant parameters,including cement content and curing age,on its strength are analyzed,and nano materials are added to cement soil on the basis of these parameters.By means of nuclear magnetic resonance（NMR）and thermal field scanning electron microscope（SEM）,this paper explores the improvement effect of nano materials on the strength of cement soil,and analyzes the mechanism of nano materials improving the strength characteristics of cement soil.The main conclusions are as follows:（1）In each curing cycle of the experimental study,the strength of cement soil samples increases with the increase of cement content.In the early stage of sample curing（7d-28d）,the strength of cement soil samples increases most significantly,but in the late stage of curing（60d-90d）,the strength growth trend of cement soil samples with each content slows down significantly,indicating that the influence of cement content and curing age on the strength of cement soil samples is mainly reflected in the early stage,and the potential is insufficient in the later stage.Based on the laboratory test and considering the economy and practicability,it is verified that the cement mixing pile project of water diversion from the Yangtze River to Huaihe River adopts 18%cement content,which can not only meet the actual construction needs of the project,but also save the construction cost to the greatest extent.（2）The strength of cement soil samples mixed with Nano-Si O₂（NS cement soil）increases with the increase of Nano-Si O₂ content within the variation range of experimental research content,and shows a linear upward trend as a whole.Different from nano-Si O₂,the strength of cement soil mixed with Nano-Fe₃O₄（NF cement soil）increases first and then decreases with the increase of Nano-Fe₃O₄ content,it reaches the maximum under the condition of 3%,indicating that the addition of nano materials can enhance the strength of cement soil to a certain extent.（3）The NMR test results show that with the increase of curing age,the porosity of the sample gradually decreases,the proportion of small pores increases,and the proportion of medium and large pores decreases,indicating that the pores in the cement soil sample are continuously refined and compacted with the growth of curing age.At the same time,the research shows that the porosity of NS cement soil sample decreases exponentially with the increase of Nano-Si O₂ content,while for NF cement soil sample,the porosity reaches the minimum under the condition of 3%content,which corresponds to the macro mechanical strength.（4）SEM and XRD test results show that the two nano materials can fill the pores of cement soil,promote the early hydration reaction of cement and increase the strength of cement soil samples because of their strong activity and small size.However,different from Nano-Fe₃O₄,after adding Nano-Si O₂,the contents of hydration products such as C-S-H and C-A-H increase significantly,accompanied by the decrease of cement clinker mineral content,indicating that Nano-Si O₂ can participate in the secondary hydration reaction of cement and significantly improve the compactness and uniformity of matrix structure.