Surface treatments on concrete: an overview on organic, inorganic and nano-based coatings and an outlook about surface modification by rare-earth oxides

Cementitious construction materials like concrete stand as pivotal constituents in the respective industry owing to their wide-ranging benefits in terms of abundant raw material sources, ease of processing, versatile usability, exceptional material properties, durability, and cost-effectiveness. Nonetheless, the production of cement is associated with substantial carbon dioxide (CO₂) emissions, thereby contributing significantly to global greenhouse gas levels. This conundrum underscores the pressing need for innovative solutions that can mitigate the environmental impact while preserving the indispensable attributes of cementitious construction materials. This review article delves into the realm of surface treatments as a promising avenue to augment the service life and sustainability of concrete structures. The primary objective of using coating technologies is to curtail the overconsumption of cement and natural resources – such as water, sand, and gravel – by extending the longevity of cementitious construction materials, which contributes to an alleviation in the environmental footprint of cement production and, subsequently, to a reduction in global anthropogenic CO₂ emissions. In this comprehensive study, we discuss three distinct types of established surface coating: (1) organic coatings, (2) coatings based on nanomaterials like graphene, and (3) inorganic coatings. Through a systematic examination of these approaches, we elucidate their mechanisms of protection, highlighting their potential to enhance the durability, resistance to environmental stressors, and overall performance of cementitious construction materials. Based on a comprehensive literature review, we compare the performance of these surface treatments in terms of protecting different cementitious surfaces against different degradation scenarios. Finally, we give an outlook on new innovative approaches for the protection of cementitious surfaces, including the presentation of the concept of incorporating rare earth metal ions into the surface of cementitious construction materials. This could potentially combine the advantages of organic and inorganic surface treatments as well as integral waterproofing.