Experimental study of durable, hydrophobic, and self-cleaning mortar coating enhanced with SiO2 nanoparticles and stearic acid on concrete

Concrete is a common material that is widely used in various construction industries. Due to the porous structure of concrete, water and other factors enter and cause it to deteriorate. Applying hydrophobic mortar can be introduced as an effective way to prevent water entry into concrete. In this research, the nanostructured hydrophobic cementitious mortars containing stearic acid and SiO 2 nanoparticles were fabricated. The effects of different amounts of stearic acid (0.38, 0.75, 1.5, 2.25, and 3 wt.%) and SiO 2 nanoparticles with a ratio of 3:1 on the wettability, water absorption, morphology, compressive strength, and required shear stress of hydrophobic cementitious mortar were evaluated. Also, the abrasion’s effects on hydrophobicity, self-cleaning performance, and resistance of coating against atmospheric condition were considered. The results showed that the coated samples with 0.38, 0.75, 1.5, 2.25, and 3 wt.% stearic acid have water contact angles (WCA) 121.5, 122.5, 134.25, 137, and 136.55 ° , respectively. Moreover, the samples containing 2.25 and 3 wt.% stearic acid had the lowest water absorption rate among all samples. After 24 hours, the water absorption of uncoated concrete was 4.938 kg/m 2 , whereas the sample containing 3 wt.% stearic acid showed 300 times more impermeability. The SEM images of the coating containing 2.25 wt.% stearic acid revealed a denser structure compared to other stearic acid samples. The sample containing 2.25 wt.% stearic acid exhibits the highest compressive strength, showing an increase of 3.5% compared to the uncoated sample. Even after 50 scratch cycles, the sample kept a high WCA, proving its excellent resistance to wear. Its hydrophobic surface also demonstrated impressive self-cleaning ability. The sample also showed a remarkable 90% reduction in the shear stress needed to seperate ice, and had 10% reduction in WCA term after UV exposing.