Superhydrophobic rice husk ash coating on concrete

[Display omitted] •Silica particles in rice husk ash was modified using fluoroalkyl silane.•The hydrophobic silica particles were spray coated on concrete coated with adhesive.•Water contact angle of 152.3±0.5° on the coated concrete was observed.•The cumulative water uptake was reduced as much as 40.38%.•The water sorptivity was reduced up to 44.44%. The silica particles in rice husk ash are useful to create the roughness required by the superhydrophobic coating on concrete. The superhydrophobic coating was prepared using rice husk ash dispersed in the ethanolic solution containing fluoroalkyl silane, 1H,1H,2H,2H-perfluorodecyl triethoxy silane (2vol.%). The ash solution was sprayed on a layer of commercial adhesive coated on the concrete. The water contact angle of 152.3±0.5° on the coated concrete was observed. The cumulative water uptake was reduced as much as 40.38% while the water sorptivity was reduced up to 44.44%. The penetration of water into the coated concrete under the water pressure of 500kPa was successfully reduced after 72h, but not fully prevented. The ash coating did not affect the surface hardness or the compressive strength significantly, but the ash coating resulted in a higher ultrasonic velocity due to the reduction of surface porosity.