This research aims to develop a new composite deck system for strengthening of orthotropic steel bridge decks. In order to increase the fatigue strength of welded components and static strength of the bridge deck, the deck plate is strengthened with a number of layers of Glass Fiber Reinforced Polymer (GFRP) and a mixture of epoxy resin with fine aggregates. The number of layers and thickness of each layer is optimized after performing several experimental tests. This research indicated that the proposed deck strengthening solution reduces bending stresses of steel deck plate to 15 percent of steel stress without strengthening, which means for the fatigue load models as given in NEN-EN 1991 all stresses are below the cut-off limit 1σL. The static bending strength capacity and stiffness behavior is also investigated to evaluate the performance of the composite section in negative and positive bending moments.