Study On The Properties Of 3D Printing Graphene-based Smart Cement Composites

Graphene,as a new two-dimensional carbon-based nanomaterial,has excellent mechanical,electrical,and thermal properties.The introduction of graphene in cementbased composites can improve its hydration and bonding effects,ameliorate the macroscopic properties of cement-based composites,and promote the sustainable development of the construction industry,but there are some key issues,for instance,poor dispersion and the existence of blended conductivity thresholds,has limited their application in cement-based materials.3D printing technology(Additive manufacturing)is a process based on digital model files that enables precise physical matter and rapid structural tailoring.Through the way of layer-by-layer printing to construct macroscopic objects,and has the advantages of large-scale preparation,controllable shape,and structured precise tailoring design.A large number of researchers have begun to apply it to the field of graphene functional materials.Therefore,the three-dimensional graphene carbon-based conductive phase constructed based on 3D printing "additive" technology has a rich pore structure,ultra-high conductivity,recoverable strain(>90%),a lightweight and stable conductive network in this paper.It improves the electrical conductivity of cement-based materials and enables them to obtain self-sensing ability and good alertness,and realizes the controllable structure and functional integration of threedimensional graphene conductive functional phases in cement-based materials.It provides scientific basis and technical support for the research of multifunctional and intelligent construction of cement-based composites.The main contents of this paper are as follows:(1)Using ultrasonic assist and adding polycarboxylic acid superplasticizer to improve the rheological properties of cement paste.Combined with 3D printing technology to achieve the controllable construction of conductive functional phasethree-dimensional graphene materials.The immersible rheological parameters of 3D printed graphene aerogel cement composites(3DGACC)were obtained according to self-extended flow test.The experimental results show that the cement paste has a infuse threshold value between 2~2.5mm in 3DGA design aperture when the water cement ratio is set to 0.45,which provides a parameter basis for 3DGACC controllable preparation.(2)3D printing technology can effectively reduce the quality of conductive phases(0.01%~0.18 wt%)of graphene nano-carbon-based materials in cement composite,and achieve high electrical conductivity(6.49~43.47S/m)of 3DGACC.The microscopic morphology of three-dimensional graphene and cement hydration products and the distribution of elements in the internal structure were observed by SEM and EDS characterization methods.The results show that the three-dimensional graphene network skeleton provides a certain template for crystal growth of cement hydration products Effect and make it distributed and grow.SEM and EDS characterization methods were used to observe the micro-morphology of three-dimensional graphene and cement hydration products and the distribution of elements in the internal structure.The results show that the three-dimensional graphene network skeleton provides a certain template for the crystal growth of the hydration products of cement and promotes its distributed growth.(3)The effects of 3DGA content,hydration process,water content,temperature,stress and strain on the electrical performance of 3DGACC have been systematically studied.The experimental indicates that the three-dimensional graphene conductive network has good structural stability and adaptability,does not participate in the hydration process,and with the increase of the water content,the resistivity of 3DGACC increases.It has good stability for the resistance sensitivity of the water content.Moreover,3DGACC shows a good range of 0 ~ 120? Negative temperature resistance effect,the negative temperature coefficient is about 8.8%/?.During the deformation and load failure process of 3DGACC,the resistance value of 3DGACC decreases first and then increases suddenly with the strain increases.3DGACC has a good force-electric segmented trigger response mechanism,in the range of small strain(0.3%~1.2%).The larger the strain,the better the response effect.The loading rate does not affect its pressure-sensitive characteristics,but as the number of fatigue times increases,the conductivity of 3DGACC will irreversibly occur slight reduction.'(4)Based on 3DGACC's good conductive properties and stable conductive network structure,this paper also studies its electrothermal and thermoelectric effects.Among the electrothermal effects,3DGACC has a good Joule heating effect and self-heating anti-fatigue characteristics in the range of 0 to 120 ? The temperature difference and the generated electromotive force for 3DGACC meet the linear dependence relationship in the normal temperature range of the building.3DGACC's seebeck coefficient reaches 19.64?V/k,and has good thermal-motor sensitivity and anti-fatigue characteristics.Both the preparation process at 80?water bath and high temperature thermal reduction will reduce the seebeck coefficient of 3DGACC,a and the high-temperature thermal reduction has a greater impact.