Research On Chloride Resistance Of Concrete With Nano-modified Waterborne Coating

The most common reason for the damage caused by the lack of durability of concrete structures is chloride erosion,which poses a serious threat to concrete structures.Coating on the surface of concrete is one of the effective means to improve the resistance to chlorine erosion of concrete engineering.Coatings can be divided into traditional coatings and waterborne coatings.Waterborne coatings have the advantages of low content of VOC,non-toxic and easy to clean,but there is still a certain gap compared with traditional coatings in corrosion resistance and aging resistance.With the continuous improvement of people’s awareness of environmental protection and the improvement of national environmental protection regulations,waterborne coatings will replace traditional coatings.Waterborne coatings are easy to be affected by aging,which lowers the life and abates its ability to upgrade the chloride resistance of concrete.In order to improve the chloride and aging resistance of waterborne coated concrete,waterborne polyurethane and waterborne epoxy resin coatings were modified by nano-SiO₂and nano-TiO₂,and then nano-modified waterborne coated concrete specimens were prepared.Then,the UV aging,electric flux and long-term chloride immersion experiments were carried out on the specimens,as well as scanning electron microscope and Fourier transform infrared spectroscopy on some of the waterborne coatings.The results show that the aging resistance and chloride resistance of waterborne coated concrete are improved to a certain extent after the waterborne coating is modified by nano-materials.The main results and conclusions are as follows:（1）There are great differences in the improvement of chloride resistance of concrete with different kinds of waterborne coatings,and the improvement effect of waterborne epoxy resin coating on chloride resistance of concrete is stronger than that of waterborne polyurethane coating.Compared with uncoated concrete,the chloride resistance of waterborne polyurethane and epoxy resin coated concrete increased by42.4%and 83.3%respectively,mainly due to different film forming methods.Waterborne polyurethane and waterborne epoxy resin coatings are one-component and two-component film-forming coatings,respectively.In the process of film formation,the volatilization of solvent in one-component coating will form pores on the surface and inside,while the two-component coating has two components.After mixing according to a certain proportion,a series of chemical reactions will take place in the process of film formation,resulting in fewer surface and internal pores,which makes its compactness better than that of one-component coating.（2）Nano-modified waterborne coating can further improve the chloride resistance of concrete,but different nanomaterials have slightly different improvement on chloride resistance of waterborne coated concrete,in which 2%nano-SiO₂ modified waterborne epoxy resin coated concrete has the best chloride resistance,which is 34.5%and 89.1%higher than waterborne epoxy resin coated concrete and uncoated concrete,respectively.The nanomaterials dispersed in the coating can fill the pores and micro-cracks,increase the compactness,improve the barrier performance and increase the chloride resistance to coated concrete.however,too much content will lead to the agglomeration of nanomaterials,resulting in uneven dispersion,thus reducing the increase of chloride resistance to coated concrete.（3）The waterborne coating is easy to be destroyed by UV radiation aging,and the UV radiation aging rate of waterborne epoxy resin coating is faster than that of waterborne polyurethane coating;the UV radiation aging resistance of nano-modified waterborne coating is enhanced,and the UV radiation aging resistance of nano-TiO₂modified waterborne coating is stronger than that of nano-SiO₂ modified waterborne coating.Nano-TiO₂ has the highest improvement on the ultraviolet radiation aging resistance of waterborne epoxy resin coating,with an increase of 37.7%.Nanomaterials not only play a filling role,but also play a role in shielding and absorbing UV light,thus reduce the effect of UV aging on waterborne coatings,among which nano-TiO₂has stronger ability to absorb and shield UV light.（4）Based on the functional relationship between chloride diffusion coefficient and UV aging time of coated concrete,a life prediction model of chloride resistance of waterborne coated concrete members considering UV aging and hydrolysis reaction in chloride environment is established.It is concluded that the waterborne coating can improve the chloride resistance life of concrete members,and the waterborne epoxy resin coating with the best effect increased by 26.74 years,that is,by 3.15 times.After nano-modification,the life of concrete members with nano-TiO₂ modified waterborne epoxy resin coating is the highest,reaching 49.51 years,which is 14.29 years higher than that of waterborne epoxy resin coated concrete members,and the increase is 40.6%.This thesis has 52 figures,29 tables and 120 references.