Effect Of Graphene On Carbonation Depth Of Concrete Under Climate Change

In recent years,global warming,continuous growth of carbon dioxide concentration and significant climate change have made the service conditions of reinforced concrete structures more harsh.With the development of new materials,researchers try to introduce nano-materials into cement-based materials to improve their mechanical properties and durability.In this paper,a new type of two-dimensional nano-materia-graphene nanoplatelet,is added into concrete.The main climatic conditions affecting the depth of concrete carbonization are carbon dioxide concentration,humidity and temperature.The variation of carbonization depth of ordinary concrete and graphene nanoplatelet concrete under climate change is studied through experiments.The main research contents are as follows:（1）Carbonation experiments were conducted with CO₂ concentration as a variable,and the effect of carbon dioxide concentration on the carbonation depth of graphene concrete was discussed.By means of scanning electron microscopy（SEM）and X-ray diffraction（XRD）,the change characteristics of surface morphology and microstructure of ordinary concrete and graphene concrete after carbonization were obtained,and the action mechanism of graphene on concrete carbonization products was discussed.The least square method was used to fit the experimental data,and the effect of CO₂ concentration on the carbonation depth of graphene concrete and ordinary concrete was obtained.（2）Carbonation experiments were carried out with temperature as a variable to study the effect of temperature on the carbonization depth of graphene concrete.Scanning electron microscopy and X-ray diffraction were used to characterize concrete with different carbonization ages.The characteristics of surface morphology and the similarities and differences of carbonization products of ordinary concrete and graphene concrete after carbonization were obtained.The influence factors of temperature on carbonization depth of graphene concrete and ordinary concrete were obtained by fitting the temperature influence coefficient with experimental data.（3）Carbonation experiments were carried out with humidity as variable,and the effect of humidity on the depth of carbonization of graphene nanoplateletconcrete was analyzed.The surface morphology and microstructure of ordinary concrete and graphene nanoplatelet concrete with different humidity were characterized by scanning electron microscopy（SEM）and X-ray diffraction（XRD）.The action mechanism of graphene nanoplatelet on concrete carbides was discussed.The experimental results were fitted and the influence factors of humidity on graphene nanoplatelet concrete carbonization were obtained.The results show that: When the CO₂ concentration ranges from 6% to 10% and the temperature and humidity are constant,graphene reduces the depth of concrete carbonization.Graphene accelerates the increase of concrete carbonization depth when the temperature ranges from 29℃ to 41℃ and the CO₂ concentration and humidity are fixed.Graphene decreases the increase of carbonation depth of concrete in the range of 50% to 85% humidity,when the concentration of CO₂ and humidity are fixed.By scanning electron microscope,it is found that after the carbonization of concrete,fibrous,short rod like hydrated calcium silicate gel and square CH crystal are gradually formed into calcium carbonate crystals,filling the concrete internal pores and making the concrete more dense inside.XRD analysis shows that under the action of climate change,the existence of graphene does not change the carbonation products of concrete.When the concentration of carbon dioxide and humidity are taken into account,the amount of calcium carbonate crystal decreases with the addition of graphene.When temperature is taken into account,the degree of crystallization of graphene concrete carbonization products is better and the depth of carbonization increases rapidly.