Polymer composites in cement and concrete refer to the incorporation of polymer materials, such as fibers, resins, or latexes, into concrete mixtures to enhance specific properties and performance characteristics. These composites improve the mechanical properties, durability, and chemical resistance of concrete, making it suitable for various applications, particularly in severe environmental conditions. The mechanism behind polymer composites involves the bonding between the polymer components and the cement matrix, which alters the microstructure and enhances the interface transition zone between the aggregates and the cement paste. This integration can significantly reduce the permeability of concrete, enhance its tensile strength, and improve its resistance to environmental factors such as freeze-thaw cycles, chemical attacks, and UV exposure. However, these benefits come at the cost of potential effects such as the variability in long-term performance depending on the type of polymer used and the environmental conditions to which the concrete is exposed.