As one of the most obvious manifestations of tangible footprint of human civilization on Earth, concrete is largely and widely applied, and has become the largest amount of man-made engineering material in the world. Compared with other engineering materials, concrete consumes less production resource and energy, has fewer harmful by-products, and causes less environmental impact. Additionally, due to its excellent mechanical properties, such as compressive strength and fatigue resistance, along with its water and fire resistance, the infrastructure constructed by applying concrete has the advantages of high safety, durability, and low maintenance. Consequently, concrete remains a reliable choice for sustainable development of the field of human construction and engineering and remains indispensable in the future. However, inherent shortcomings and current performance limitations of concrete do not meet the requirements for the construction and expansion of human living spaces in the future. Moreover, the production and use of large quantities of concrete have a significant impact on resources, energy, and environment. Nanoscience and nanotechnology can be used to understand and control concrete at its fundamental level, enabling the realization of (ultra) high-performance and multifunctional/smart concrete, which in turn can give impetus to addressing the aforementioned challenges and achieving sustainable development. This article focuses on three core research advancements related to enhancement/modification mechanisms, preparation and performance control, and performance and functionality characterization for engineering applications of nanoengineered concrete. It mainly introduces the explanation/principle investigation of scientific phenomena including nano-core effect, nano-core effect zone, nano-core effect-induced enrichment effect for interface enhancement, nano-core effect-induced ultrahigh-density calcium silicate gel, and nanoscale pore structure characteristics, the exploration of advanced technologies for performance modulation and large-scale preparation of nano-engineered concrete (e. g. , surface treatment, self-assembly, and in-situ growth techniques, etc. ) , as well as the understanding gained from the expansion of the properties of nanoengineered concrete and the validation of engineering applications in the fields of civil engineering, transportation, municipal, marine, energy, and military.
Ultra-high performance cementitious composites (UHPCC) are the most innovative and promising new generation of cementitious composites over the past three decades. However, while low porosity and high density contribute to the extremely high strength of UHPCC, they also lead to issues such as high capillary suction, severe autogenous shrinkage, rapid hydration rate, and large temperature stresses within the material. Nanofillers with small size and nano effects are helpful to improve the continuity of cementitious raw materials at the nanoscale across multiple scales. They make up for the nanostructure defects of cementitious composites, thereby modifying their mechanical and durability properties from the bottom up, and at the same time endowing cement-based composite materials with functional properties. Carbon nanotubes ( CNTs) not only have the inherent characteristics of carbon fiber materials, but also have high electrical conductivity, thermal conductivity, heat resistance, and corrosion resistance, which is an excellent type of nanofillers and an ideal reinforcing filler for composites. Based on this, this paper summarizes the relevant properties and research status of UHPCC, nanofillers reinforced cementitious composites, particularly CNTs reinforced cementitious composites, and analyzes the optimization methods for achieving the ultrahigh performance of UHPCC. Nano-modification of UHPCC holds promise for fundamentally designing the structure and properties of cementitious composites, achieving complementary strengths and synergistic effects in performance. It is one of the innovative approaches in the development of UHPCC.
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