Study On The Groutability Of Carbon Nanotubes Reinforced Cement Based Grouting Materials

With the rapid development of national economy,higher quality requirements have been put forward for roads,bridges and real estate industries.Concrete structures are widely used in these fields.In order to solve the problems of the generation and development of cracks in largescale projects,grouting materials are usually used to repair the cracks.Cement based grouting material has the advantages of low price,non-toxic,high strength and good application prospects,but it also has the disadvantages of low tensile strength and poor toughness.To solve these problems,domestic and foreign scholars put forward the view that nano materials composite cement-based materials can improve the toughness of materials,and the addition of carbon nanotubes can inhibit the shrinkage deformation of cement-based specimens,In this paper,the influence of carbon nanotubes on the groutability of cement-based grouting material is systematically studied,and the carbon nanotubes grouting material is poured into the concrete cracks to evaluate the crack filling and the bonding effect between the two.The main research contents are as follows:(1)In this paper,ultra-fine cement,quartz powder,silica fume,expansive agent and other raw materials and admixtures are selected,and the amount of carbon nanotubes in the references(0.02wt%,0.05wt%,0.1wt%,0.2wt% and 0.3wt%)with better mechanical properties is used to prepare the carbon nanotubes reinforced ultra-fine cement grouting material.The rheological properties,fluidity and expansibility were tested,and it was found that the rheological curve of ultra-fine cement grouting material conformed to modified Bingham model,after adding carbon nanotubes,still conforms to the model;carbon nanotubes can inhibit the early shrinkage of cement-based grouting material;when adding 0.1wt% carbon nanotubes,the fluidity of grouting material is the best,the plastic viscosity and yield stress are the minimum;and at this time,it is the best amount of carbon nanotubes for compressive strength.(2)Grouting materials with different amount of carbon nanotubes are poured into concrete cracks through grouting device,and the grouting pressure reflects the difficulty of grouting.Group A3 grouting materials(with 0.1wt% MWCNTs)have low viscosity,good flow performance,low grouting pressure,low grouting difficulty and strong ability of grout to penetrate into small cracks.After grouting,the test block has three different kinds of damage after secondary splitting Form.Therefore,three different failure models are established in this paper,which are local splitting failure of grouting material,bond failure of grouting material and concrete and overall splitting failure of concrete.Among them,the first failure occurs when the splitting tensile strength of grouting material is small(Group A0),the second failure occurs when the bonding strength between grouting material and concrete is small(group A1),the third failure occurs when the splitting tensile strength of grouting material itself and the bonding strength between grouting material and concrete are strong,and the third failure occurs when the a2-a5 grouting material grouting test block is damaged.(3)Through CT scanning of concrete samples with six different MWCNTs grouting materials,the filling effect picture of carbon nanotube grouting materials in concrete blocks and the internal structure information of samples are obtained.The pore parameters are extracted and three-dimensional reconstruction is carried out by using the data analysis quantization and visualization module of avizo software,and the optimal content of carbon nanotube is 0.1wt%,At this time,the porosity of grouting material is the smallest,and the grouting material with more pores is 0.2wt% and 0.3wt%(Group A4 and group A5);based on all the above tests,the best CNT content is 0.05wt% and 0.1wt%(group A2 and group A3).(4)By observing the interface between concrete and grouting material with electron microscope,it is found that there are a lot of hydration products ettringite and hydrated calcium silicate at the interface,and carbon nanotubes with crisscross structure are observed on the hydration products.On the one hand,carbon nanotubes fill the pores,on the other hand,they can coordinate the shrinkage of grouting material and expansion of ettringite,restrain the deformation and offset the external load,Delay the development of cracks.(5)Based on the lattice Boltzmann method,the flow process of grouting materials is simulated.The grouting materials with different viscosities flow into the narrow channel at the same initial velocity.When the fluid with higher fluidity(lower viscosity)passes through the narrow channel,the resistance is small,and the diffusion range to both sides increases after passing through the narrow channel.When it passes through the narrow channel,the velocity first decreases and then increases;When the fluid with low fluidity(high viscosity)passes through the narrow channel,the resistance is large,and the diffusion range to both sides after passing through the narrow channel is small,resulting in fluid retention.When passing through the narrow channel,the velocity decreases,and then continues to decrease.