Marine concrete structures, due to proper mechanical behavior and high durability for the world population, which are directly or indirectly related to marine infrastructure and various industries seem essential. On the other hand, concrete production and other related industries in marine environments are the main agents of production of pollution and waste and excessive consumption of the earth's natural resources and energy. Therefore, it seems that the simultaneous use of cement replacements to reduce the generation of greenhouse gases derived from cement production and plastic waste as fiber can decrease environmental pollution and improve concrete mechanical behavior. This study investigates the impact of incorporating 0.5 and 1% strip disposable glass fibers (GF) and strip garbage bag fibers (BF) on the flexural and cracking characteristics of reinforced concrete (RC) beams containing 10% metakaolin/zeolite. The investigation is conducted over 28 and 180 days in the tidal environment of the Oman Sea. Considering the results, by adding GF and BF to the green RC beams the flexural toughness (T) increased up to 47 and 27%, respectively. Furthermore, the cracking load (Pcr) of glass fibers RC (GC) and bags fibers RC (BC) beams was lower than RC up to 32 and 21%, respectively. Moreover, the incorporation of GF and BF resulted in an increase of up to 28% and 16% in the maximum load capacity (Pmax) of RC beams, respectively. In addition, the Pmax and T of GC beams were higher than BC. Besides, it was observed that metakaolin GC and BC beams exhibited a greater value of Pmax and T compared with zeolite beams.).