Research On The Influence Law Of Doped Carbon Nanotubes On The Mechanical Properties,Deformation Properties And Durabilities Of Concretes

Improving the mechanical properties,deformation properties and durability of cement-based materials are the focus in the field of building materials.At present,carbon nanotubes（CNTs）are favored by scholars due to their excellent microscopic fiber toughening and nano-filling characteristics.The incorporation of CNTs to improve the macro performance of cement-based materials has become a research hotspot,which is of great significance in the context of limited building materials resources,environmental protection and sustainable development.Therefore,in this study,the mechanical properties,deformation properties and durability of CNTs modified concrete were evaluated after reasonable ultrasonic treatment of a carboxylated CNTs.The microscopic improvement mechanism of CNTs on the macroscopic properties of concrete was revealed through a series of microscopic tests.（1）The effects of ultrasonic time and standing time on the dispersion of CNTs were studied by using ultrasonic dispersion method to treat CNTs suspension.The results showed that with the increase of ultrasonic treatment time from 0 to 75min,the absorbance peak first increased and then decreased,and the absorbance peak reached the peak of dispersion effect at 45min.In addition,after the ultrasonic treatment of CNTs suspension for 45min,the peak absorbance tended to decrease with the increase of the standing time.（2）The effect of of CNTs on the mechanical properties of mortar was studied.The results showed that with the increase of the content of CNTs,the change trend of mortar’s compressive strength was first slightly decreased,then significantly increased and finally decreased,while the change trend of flexural strength was first increased and finally decreased.When the content of CNTs was 0.10%,the mortar’s compressive and flexural strength reached the maximum.When the content of CNTs was 0.10%,the compressive and flexural strength of mortar at 28 days increased by 34.17%and 15.30%,respectively.（3）The effect of CNTs on the deformation performance of mortar was studied.The results showed that the drying shrinkage of mortar first decreased and then increased with the increase of the content of CNTs.When the content of CNTs was 0.10%,the drying shrinkage rate of mortar was the lowest,which was reduced by 21.26%at 60d compared with the blank group.（4）The effect of of CNTs on the durability of concrete was studied.The results showed that with the increase of the content of CNTs,the chloride diffusion coefficient of mortar increased slightly at first,then decreased significantly,and finally increased,with the greatest decrease at 0.10%compared with the blank group.With the increase of the content of CNTs,the carbonization depth and carbonization coefficient of mortar first increased slightly,then decreased significantly,and finally increased,with the greatest decrease at 0.10%.With the increase of the content of CNTs,the mass loss rate and the dynamic elastic modulus loss rate of concrete after 50 and 75 freez-thaw cycles decreased first and then increased,and the mass loss rate and dynamic elastic modulus loss rate of C10 were the lowest.（5）The effects of CNTs on the micro-morphology,hydration characteristics and pore characteristic structure of concrete were studied.The results showed that the incorporation of an appropriate amount of CNTs（0.10%）was conducive to the formation of a dense matrix.CNTs could bridge the micro-pores and micro-cracks of the matrix,strengthen the weak area of the matrix,and fill the pores with a network structure to form finer pore diameter.The addition of CNTs could promote the hydration of cement.With the increase of the content of CNTs,both the content of Ca（OH）₂ in the matrix and the adiabatic temperature rise showed a trend of first increasing and then decreasing,reaching the maximum at 0.10%.The addition of proper CNTs（0.10%）could optimize the pore structure of the matrix.Compared with C0,the porosity of C10decreased the most,reaching 18.73%.The total pore area,median pore diameter and average pore diameter of C10 were the lowest in all groups.