Reserach On Volume Stability Of Nano-graphene Oxide Cement-based Composites

Cement-based materials are currently the most widely used and largest building materials in the world.However,traditional cement-based materials often produce a large number of cracks during service because of the low tensile strength and poor toughness,which seriously affects the safety and durability of the structure.Graphene(GE)is known as the "King of New Materials" in the 21 st century.It has many excellent physical properties in existing nanomaterials,such as the thinnest sheet? the highest mechanical strength and the best thermal conductivity.The nanostructures make it widely used in materials science.Graphene oxide(GO)is a derivative prepared from graphene.It possesses excellent physical properties of graphene,it is rich in oxygen-containing groups(such as-OH?-COOH?-O-)and other reactive groups make it have good hydrophilicity and have broad application prospects in advanced civil engineering materials.At present,the research on the mechanical properties of graphene oxide cement-based composites has been deepening,but the study on the volume stability of cement-based composites by graphene oxide has not been studied,and the regulation and mechanism of graphene oxide on cement-based materials is still unclear.Therefore,the research on the volume stability of graphene oxide cement-based materials in time is not only of high theoretical value for graphene oxide cement-based composites,but also has a strong guiding significance for the development of high-performance concrete cracking risk prediction.In this paper,Vosviewer is used to scientifically analyze the current research field of graphene oxide,and through the comparative test of commercially available small layer graphene oxide and multilayer graphene oxide and different dosages,the hydration of graphene oxide to cement-based materials is studied.The effect of rate and hydration process;study the chemical shrinkage and self-shrinkage of graphene oxide-based materials at early age;further microscopic characterization by microscopic testing methods such as SEM,XRD and SAP,and propose corresponding graphene oxide to cement-based materials The regulation and mechanism explanation;and the interface model of graphene oxide and calcium hydroxide was established by molecular dynamics software to optimize the kinetics and carry out correlation analysis.Research indicates:(1)The incorporation of a small amount of graphene oxide and multilayer graphene oxide does not change the overall hydration process of the cement.Because of the nano-effect of graphene oxide and the surface rich in a large number of oxygen groups,it can provide sufficient chemical reaction nucleus and simultaneously react the nucleus.It can adsorb water molecules and cement particles,increase the chance of contact between cement and water,and promote the reaction rate in the initial stage of the reaction.(2)The incorporation of graphene oxide can adjust the hydration product well.It can be clearly found by scanning electron microscopy that the hexagonal plate crystals in the cement product increase after the addition of graphene oxide,and the regular arrangement is arranged,indicating that the calcium hydroxide crystal is adjusted.The microscopic morphology forms a flower-like hydration product;the phase analysis by XRD can further confirm that no new product is found,indicating that this regulation template does not utilize chemical reaction between GO and hydration products,but utilizes The activity of the oxygen-containing group of graphene oxide plays a role in template regulation;further measuring the average particle size of calcium hydroxide crystals,it can be found that the incorporation of graphene oxide can refine the crystal size of calcium hydroxide,with age The increase also has a certain inhibitory effect on the growth of calcium hydroxide crystals,which eventually leads to the incorporation of graphene oxide,which will generally reduce the chemical shrinkage of cement.(3)The incorporation of graphene oxide increases the self-shrinkage.With the increase of the amount of self-contraction,the self-shrinkage is more obvious.Due to the hydrophilicity of graphene oxide,graphene oxide adsorbs more free water in the capillary,with water.Further deepening of the process,the water in the capillary pores is continuously consumed,forming a capillary pore static pressure,compressing the capillary wall,and increasing the self-shrinkage.Characterization by nitrogen adsorption shows that the incorporation of graphene oxide mainly causes the internal pores to be slit-shaped.After the incorporation of graphene oxide,the internal large pores can be transformed toward small pores,which contributes to the oxidation nano-effect.Refine the internal aperture.(4)Incorporation of graphene oxide will increase self-shrinkage,and self-shrinkage will be more obvious as the amount of graphene oxide increases.Due to the hydrophilicity of graphene oxide,graphene oxide adsorbs more free water in capillary pores.As the hydration process deepens,the water in the capillary pores is continuously consumed,forming a capillary pore static pressure,compressing the capillary wall,and increasing the self-shrinkage.Characterization by nitrogen adsorption shows that the incorporation of graphene oxide mainly causes the internal pores to be slit-shaped.After the incorporation of graphene oxide,the internal large pores can be transformed toward small pores,which contributes to the oxidation nano-effect.Refine the internal aperture.(4)The interface layer between graphene oxide and calcium hydroxide was established,and the interface layer was further optimized by molecular dynamics.The simulation results showed that calcium ions in the calcium hydroxide crystals moved toward the surface of graphene oxide,indicating that graphene oxide to calcium hydroxide The regulation is mainly reflected in the adsorption of calcium ions.It can be further confirmed by the radial distribution function that the attraction is dependent on the hydrogen bond.