Surface protection of concrete by new protective coating Elsayed M. Elnaggar a , Tarek M. Elsokkary b , Mostafa A. Shohide b,⇑ , Basil A. El-Sabbagh b , Hamdy A. Abdel-Gawwad b a Chemistry Department, Faculty of Science, Al-Azhar University, Cairo, Egypt b Raw Building Materials Technology and Processing Research Institute, Housing and Building National Research Center (HBRC), Cairo, Egypt highlights  Asphaltic polyurethane coatings with different NCO/OH ratio were prepared.  Asphaltic polyurethane was applied as protective coating for concrete.  The coated concrete showed high performance in aggressive media. article info Article history: Received 10 March 2019 Received in revised form 13 May 2019 Accepted 3 June 2019 Keywords: Concrete protection Concrete surface treatment Protective coating Polyurethane coating Asphaltic coating and PU coating abstract This work aims at enhancing the concrete performance using a new protective coating named as asphal- tic polyurethane (As/PU) coating, which prepared at different NCO/OH molar ratios (1, 1.1, 1.2, 1.3 and 1.4). As/PU coating was prepared by the reaction of a fixed amount of methylene diphenyl diisocyanate (MDI) with the equivalent weight of mixed polyol (80% asphalt and 20% polyester). The performance of the prepared coatings was examined by the determination of curing time, dry film thickness (DFT), adhe- sion strength, and flexibility. The formulated coatings were applied on 28-days-cured concrete. The coated and uncoated concrete samples were evaluated regarding contact angle, water absorption, and chloride permeability. The resistivity of coated and uncoated concrete against sulfuric acid and sodium chloride solutions was evaluated. The preliminary results proved that the increase of NCO/OH molar ratio results in a remarkable increase in DFT, adhesion strength accompanied by decrease in curing time and flexibility of the prepared coatings. The concrete sample coated by As/PU with NCO/OH molar ratio of 1.4 demonstrates the highest contact angle associating with the lowest water absorption and chloride per- meability. In addition the increase in NCO/OH molar ratio of the applied coating has a positive impact on the mechanical properties of concrete. The coated concrete samples recorded higher resistivity against acid and salt attack compared to uncoated one. This proves the eco-efficient use of the prepared As/PU as an innovative protective coating for concrete. Ó 2019 Elsevier Ltd. All rights reserved. 1. Introduction Concrete is a composite material consisting of aggregates (fine and coarse) bonded together with a cement paste that hardens over time [1]. Durability is an important factor for quality of con- crete and it is defined as the capability of concrete structure to last a long time without remarkable deterioration [2]. The concrete structures can be damaged over time, resulting in deterioration of their elements due to the exposure to the different corrosive environments or chemicals. The aggressive salts can penetrate into the pore structure of concrete toward steel rebar and corroded it, causing in deterioration of concrete structures that exposed to aggressive environments. Concrete coatings are considered as one of the most suitable methods which mainly contribute to the mitigation of the detrimental impact on concrete structures origi- nated from aggressive media attack. Many types of organic coat- ings are applied to concrete surfaces to protect the porous structure of concrete and enhance the shelf life time [3,4]. Polyur- ethane coatings are a high-quality products have suitable curing time and good resistance to chemicals [5]. The protective perfor- mance of polyurethane coatings depends on the chemical and physical properties of the polyurethane raw materials. So, varying the nature of the polyols and the isocyanate components, a wide range of properties can be obtained [6]. The previous studies used the polyurethane by mixing it with asphalt at limited mixing ratios to produce modified asphaltic coating for different purposes https://doi.org/10.1016/j.conbuildmat.2019.06.026 0950-0618/Ó 2019 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail addresses: maxem505016@yahoo.com (M.A. Shohide), hamdyabdelgawwad@ yahoo.com (H.A. Abdel-Gawwad). Construction and Building Materials 220 (2019) 245–252 Contents lists available at ScienceDirect Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat