Optimal Content and Lifespan Prediction of Nanomaterials in Nano-modified Concrete

With the advances in infrastructure construction in various countries around the world, extensive requirements have been promoted for the mechanical properties and durability of concrete. In this article, the effects of single and compound additions of nano-SiO₂ (NS) and nano-Fe₂O₃ (NF) on the mechanical properties and durability of concrete were evaluated through different experiments. Moreover, the optimal contents of these additions corresponding to their different properties were explored. The macroscopic test results indicated that the addition of nanomaterials had a perceptible effect on the mechanical properties and durability of concrete. The concrete mixed with 1.0% NS and 0.5% NF achieved optimal performance. With this composition, the compressive strength, flexural strength, water absorption rate, and chloride ion diffusion coefficient (corrosion resistance) of the 28 days concrete were 52.94 MPa, 7.27 MPa, 4.82%, and 4.52 × 10^–12 m²/s, respectively, which were 21.5%, 23.0%, 29.4%, and 37.2% higher than those of ordinary concrete at the same age. Microscopic observation and elemental analysis of the ITZ (interfacial transition zone) interface in concrete revealed that NS and NF contributed to nucleation. The two components reacted chemically with Ca (OH)₂ grains, resulting in the synergistic effect of the spatial morphology of the hydration products, thus increasing the density of the internal structure of the concrete. To facilitate the application of nanomaterials in engineering, functional relationships between the content of nanomaterials in concrete and the improvements in various properties of concrete were constructed with high accuracy. In addition, the time-dependent correlation coefficients of apparent chloride ion concentration and chloride ion diffusion were introduced based on Fick’s second law, and this model was applied to multiple long-term monitoring experiments to verify its accuracy under various exposure conditions, such as tidal zones, splash zones, and atmospheric zones. The improved Fick model was used to predict the service life of concrete. By taking the splash zone as an example, it was reported that under the same conditions, the expected lives of S2F0, S0F2, and S2F1 increased by 31.8%, 25.7%, and 50.2%, respectively, compared to that of OPC. The research results could provide a reference for the development of high-performance concrete.