| Alkali-activated cementitious materials are environmentally friendly building materials with good development prospects and are considered as the best substitute for ordinary portland cement.Since the macroscopic properties of materials depend on their microstructures,many scholars have tried to add nano-materials to alkali-activated materials to improve the mechanical properties and durability of the matrix by improving the internal structure,and achieved good results.Graphene is considered as the most excellent nano-material with excellent physical and electrical properties,such as large specific surface area,high mechanical strength,high thermal conductivity and conductivity.In recent years,graphene reinforced composites have aroused a worldwide research upsurge,among which the dispersion of graphene in the matrix is an important factor for its excellent performance in composites.NanoTi O2 has the properties of thermodynamic stability,high surface tension and good dispersion.It is an effective way to improve the dispersion of graphene by depositing nanoparticles on graphene sheet.In this paper,the preparation of titanium dioxide / graphene,the mechanical properties and impermeability of alkali activated slag composite were systematically studied,and the mechanism of graphene was comprehensively and deeply explored by a series of micro experiments.The main research contents are as follows:1.In order to prepare graphene with good dispersion,nano-titanium dioxide intercalation method was used to prepare titanium dioxide/graphene composite(Ti O2/RGO).The preparation methods and principles of Ti O2/graphene were systematically studied,and the dispersion and microstructure of modified graphene in water were characterized by means of dispersion stationary time method,infrared spectrum analysis,Raman and transmission electron microscopy.Results show that titanium dioxide between graphene layers can effectively overcome the van der Waals force between graphene layers and solve the agglomeration problem of graphene caused by van der Waals force between graphene layers.Compared with the control graphene,the suspension of graphene modified by titanium dioxide has good dispersion and no delamination occurs with the passage of time.2.The mechanical properties of graphene/alkali-activated slag composites and common alkali-activated slag were studied by flexural,compressive and four-point bending tests.The mechanism of graphene action was analyzed by XRD and SEM.The results show that the mechanical properties(flexural strength and compressive strength)of graphene/alkali activated slag mortar at different ages are significantly higher than that of control alkali activated slag mortar.When 0.03wt% graphene was added,the flexural toughness of alkali-activated slag composites increased by more than 80% compared with control samples.The abundant wrinkle texture on graphene surface can increase the contact area and mechanical biting force between graphene and matrix hydration products,resulting in strong interaction.The flexural toughness of composites can be significantly improved through toughening mechanisms such as crack deflection,branching and graphene pull-out.3.The permeation of water has a great influence on the durability of alkali-activated materials.The permeability of graphene/alkali activated slag mortar and control alkali activated slag mortar was studied by water absorption test,chloride ion permeability test and mercury intrusion test.The results show that the addition of graphene can obviously improve the pore structure of alkali-activated slag mortar,and the permeability and chloride ion corrosion resistance of the composites are significantly improved.The results are of great significance to the in-depth study of the durability of graphene/alkali-activated slag composites. |
