This state-of-the-art review summarizes key findings on the use of carbon nanotubes (CNTs) as nano reinforcements in cement-based materials, focusing on their effects on hydration, mechanical performance, and durability. Conventional reinforcements, such as steel bars and fibers, function at the millimeter or microscale, providing tensile strength but failing to address nanoscale flaws. In contrast, CNTs have been shown to improve flexural strength and elastic modulus, refine microstructure, bridge cracks, reduce shrinkage, and modify pore structure, benefits partly attributed to their extraordinary modulus of elasticity, which can reach up to 1 TPa. Despite these promising results, the literature remains mixed, limiting broader adoption and commercial application. While some studies report improvements in strength and stiffness, others note potential weakening of the cement nanostructure or early deterioration. Key challenges, including workability loss, dispersion quality, and corrosion risks, are also emphasized. Research on compressive stress and strain behavior and long-term durability remains limited. The review concludes with practical perspectives and recommendations to facilitate the future use of CNTs in sustainable, high performance concrete systems, providing a clear pathway toward practical implementation. This study adopts a structured state of the art review approach. Peer reviewed literature published over approximately the past one and a half decades is synthesized, with emphasis on CNT dispersion, hydration, mechanical, and durability related performance of cementitious materials.