Study on PVA-siloxane mixed emulsion coatings for hydrophobic cement mortar

Abstract

Efflorescence is widely regarded as a serious problem in cement-based exterior wall. This phenomenon can affect the appearance and long-term stability of the building. Based on the efflorescence mechanism, one of the causes of efflorescence is the existence of free water to dissolve soluble salts. Therefore, we propose a method for synthesizing hydrophobic cement mortar. The main challenge of the super-hydrophobic coating is its robust durability. To synthesize durable hydrophobic cement mortar, we use 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. Optical microscope and scanning electron microscope (SEM) and FT-IR spectroscopy were utilized to characterize the emulsions and coatings. Appearance analysis of the coatings was performed using a colorimeter and UV Spectrophotometer, and the durability of the coating was evaluated by abrasion resistance and water resistance. The measured water contact angles (CA) are between 120° to 140°, and the water absorption after 24 h and 48 h can be reduced by about 10 % and 15 % compared with the reference sample, including the water absorption coefficient is approximately lower than the untreated group 1.7–4 times. Finally, accelerated efflorescence test, image acquisition and analysis with Matlab software, determination of calcium ion leaching rate and TG-DSC analysis were performed. The results show that the cement mortar treated with hydrophobic emulsion has excellent water resistance and improved efflorescence resistance, and can be widely used in cement-based buildings.