Study On The Effect Of Super-hydrophobic Coating On The Anti-efflorescence Of Cement-based Decorative Mortar

Cement-based decorative mortar as a decorative green material,surface efflorescence will affect the appearance and long-term stability of buildings.Based on the efflorescence mechanism,one of the causes of efflorescence is the existence of free water to dissolve soluble salts.The current waterproof methods mainly include coating technology and water-repellent treatment,but there are problems with poor bonding and stability.Taking into account the characteristics of superhydrophobic coatings that are breathable and strong in chemical bonding,we propose a method for synthesizing superhydrophobic cement mortar.The study uses PVA as an adhesive to enhance the durability of the coating,and use siloxane material as a hydrophobic agent,through high-speed mixing,to obtain a PVA-coated siloxane material hydrophobic coating.And adding inorganic nanoparticles or using the cement mortar’s microstructure to construct a rough structure,superhydrophobic cement mortar is obtained under the dual effects of low surface energy and rough structure.To explore the preparation method of cement mortar superhydrophobic coating,this paper designed hydrophobic emulsions of different proportions,conducted in-depth research on the influence of hydrophobic emulsions on surface morphology.Moreover,starting from the structural mechanism of superhydrophobic materials,the method of using nylon mesh and cement coating to build a rough layered structure on the surface of the mortar.The results show that different types of hydrophobic emulsions have different effects on the surface roughness of the mortar.The closer the droplets of the hydrophobic emulsion are arranged,the rougher the surface of the mortar and the more hydrophobic.In the surface roughness DHM test,the average distance of the surface roughness peaks of a single PDMS-type siloxane hydrophobic coating is the smallest,the height is the highest,and the contact angle is also the largest.This further illustrates that the static contact angle is influenced by both the average spacing and height of the surface roughness peaks.Finally,the rough structure of the cement mortar surface is prepared with micron-scale sand and micro-nano cement particles and hydration products cement particles and hydration products,and air gaps are formed between the micro-nano structures.Under the modification of the hydrophobic emulsion,the liquid comes into point contact with the surface of the mortar,so that the droplets fall on the surface of the mortar and roll off naturally.The surface contact angle of the obtained superhydrophobic cement mortar is 150±0.5°.Further explore the water resistance and durability of superhydrophobic coating cement mortar coating,this paper uses a colorimeter and ultraviolet spectrophotometer to analyze the appearance of the coating,and evaluate the durability of the coating through abrasion resistance,water resistance,and aging resistance measure.The results show that the hydrophobic emulsion used in the facing mortar has no impact on the appearance of the mortar.Because the hydrophobic emulsion penetrates into the mortar and contains a large number of spiral Si-O bonds,it gets a good high-temperature resistance and aging resistance.The surface hydrophobicity remains stable under extreme conditions.The water absorption coefficient of the prepared hydrophobic mortar is about 1.7-5 times lower than that of the reference sample.Finally,to evaluate the impact of the hydrophobic coating on the efflorescence resistance of the cement mortar,image acquisition analysis,and ion leaching rate determination,XRD and TG-DSC were performed after the accelerated efflorescence measure.The results show that the presence of the hydrophobic coating inhibits the infiltration of external moisture,thereby reducing the dissolution of Ca（OH）₂and the generation of CaCO₃.The leaching concentration of Ca²⁺and Na⁺of the cement mortar coated with the hydrophobic coating is reduced by three orders of magnitude,and K⁺is reduced by one order of magnitude,and its anti-efflorescence ability is improved.