Preparation And Modification Of 0-3 Cement-based Piezoelectric Composites

Cement-based piezoelectric composite(CPC)has both sensing and actuating functions,of which the preparation process is simple and the production cost is inexpensive.It has a similar physical and chemical properties with concrete,which can overcome the problem of bad compatibility,as well as low impedance matching,between traditional piezoelectric materials and concrete.It is expected to achieve a better precision in health monitoring of concrete structures using this kind of material as a sensor.Therefore,it is of great academic value to research the piezoelectric materials in the intelligent development of civil engineering.In this paper,the effects of composition,forming process and polarization on the properties of CPC were studied,and the effects of carbon nanotubes(CNTs)and polyvinyl alcohol(PVA)on the properties of CPC were investigated.It was characterized by XRD,FTIR,SEM and TEM.The results show that the piezoelectric strain constants(d33),piezoelectric voltage constant(g33)and electromechanical coupling coefficient(Kt)of CPC with Sulphoaluminate Cement as matrix,are better than those of White Cement and Portland Cement.At the initial stage of hydration,the piezoelectric properties of CPC increased continuously,which is tend to be stable after 10d hydration.SEM analysis shows the larger the particle size is,the easier they contact.As a result,CPC with larger particle size has better d33,g33 and dielectric constant(?r),but the piezoelectric properties tend to be stable when particle size is larger than 126?m,and CPC with large particle size is close to parallel model.But that are not conducive to electromechanical coupling performance and the mechanical quality factor.With the increase of functional phase,d33,g33 and ?r are increasing,SEM analysis shows that the larger the content of functional phase,the easier they contact.When the functional phase volume content exceeds 60%,both electromechanical coupling performance and mechanical quality factor are reduced.The effects of forming process and polarization on the properties of CPC were studied.It shows that the higher the forming pressure is,the better d33 and ?r of CPC are.SEM analysis shows too much pressure could lead to more layers' crack in composites,so that the composite performance declines.In this paper,the best forming pressure is about 90MPa.In addition,the best polarization process parameters in this paper are as follows:polarization temperature:40?;poling time:15min;polarization voltage:4kV/mm.The effects of modifiers on the properties of CPC were studied.It shows that the dispersion of CNTs is not the same treated by different methods,TEM analysis shows the size of CNTs treated by OP-10 is larger than the other two,of which the distribution is more uniform,and the performance is the best.FTIR analysis shows the existence of chemical bonding between CNTs and cement,and the introduction of CNTs will not affect the hydration of cement.With the increase of CNTs,d33,?r and Kt are increasing.When the volume content of CNTs is 0.7%,d33 reachs the the best value of 42.3pC/N.The addition of CNTs can reduce the polarization temperature of CPC to room temperature.With appropriate volume content of PVA,the polymer can be well bonded with the cement matrix,thereby reducing the porosity of composites.The value of d33,g33 and Kt are increasing with the increase of the content.Porosity analysis shows that incorporation of PVA can reduce the CPC porosity and increase its density.In addition,the performance of composite is getting worse when the volume content is more than 3%.This is due to excessive PVA could form a lamellar organic film on the surface of cement and functional phase particles,which hinder the hydration of the cement matrix and the later polarization.The modification of cement-based piezoelectric composites can improve the accuracy of the internal structure health monitoring of concrete,and increase the feasibility of the application.It is of great significance to reduce the accident rate,casualties and the loss of state and social property.