Superhydrophobic rice husk ash coating on concrete H. Husni a , M.R. Nazari a , H.M. Yee a,⇑ , R. Rohim a , A. Yusuff a , Mohd Azahar Mohd Ariff b , N.N.R. Ahmad c , C.P. Leo c,⇑ , M.U.M. Junaidi d a Faculty of Civil Engineering, Universiti Teknologi MARA, 13500 Permatang Pauh, Penang, Malaysia b Faculty of Chemical Engineering, Universiti Teknologi MARA, 13500 Permatang Pauh, Penang, Malaysia c School of Chemical Engineering, Engineering Campus, Universiti Sains Malaysia, 14300 Nibong Tebal, Penang, Malaysia d Department of Chemical Engineering, Faculty of Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia highlights  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%. graphical abstract S par ilanation on ticles in rice silica husk ash Spray coating coated with on concrete adhesive Sup su erhydrophob rface 152.3 ic ° article info Article history: Received 11 January 2017 Received in revised form 9 March 2017 Accepted 10 March 2017 Keywords: Rice husk ash Superhydrophobic coating Concrete abstract 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 (2 vol.%). The ash solution was sprayed on a layer of commercial adhesive coated on the concrete. The water con- tact 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 500 kPa was successfully reduced after 72 h, 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. Ó 2017 Elsevier Ltd. All rights reserved. 1. Introduction Concrete is a very strong and durable material in construction industry, but it can suffer from the loss of strength due to water penetration. Water can penetrate easily into the porous and hydro- philic concrete. The water penetration not only generates the dis- tress in concrete, the water also carries other aggressive substances that can cause the corrosion of reinforcement steels. Furthermore, the rust occupies a great volume in concrete, result- ing expansion and tensile stress. The cracking, spalling and delam- ination of concrete are the subsequent effects of expansion and tensile stress formed in the concrete. http://dx.doi.org/10.1016/j.conbuildmat.2017.03.078 0950-0618/Ó 2017 Elsevier Ltd. All rights reserved. ⇑ Corresponding authors. E-mail addresses: minyh@ppinang.uitm.edu.my (H.M. Yee), chcpleo@usm.my (C. P. Leo). Construction and Building Materials 144 (2017) 385–391 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat