Reactive powder concrete (RPC) is a special type of concrete that possess ultra-high performance. RPC is prepared by replacing the ordinary aggregate of normal concrete with quartz powder, silica fume, steel fibers etc. As such, it has been gradually applied in the construction of bridges, high-rise buildings, nuclear power plants and in hydraulic engineering. However, RPC has been reported to develop a large number of cracks whether on the microscopic or macroscopic scale even when low water-to-cement ratio is used. These cracks make RPC brittle and subject to varying degrees of damage under external loads. Worse off, this brittle nature coupled with the existence of inertial stress (at high strain rates) has subjected RPC to tensile failure and seriously affected the safety of concrete structures. In order to reduce the initial defects of concrete materials and inhibit the formation and propagation of micro-cracks on the nanometer or micrometer scale, researchers have over the years diverted their focus to the field of nanotechnology. So being, it has been hypothesized that graphene; credit to its low density and small size that makes it easy to disperse in concrete matrix, coupled with its high stiffness and diameter-to-thickness ratio, could effectively offset the inertia stress, contributing to considerable improvement in the energy absorption of the concrete.
Unfortunately, this aspect of RPC combined with graphene has not been thoroughly investigated. In view of this, researchers from the Dalian University of Technology, Dalian, China: Jialiang Wang (PhD candidate), Dr. Sufen Dong and led by Professor Baoguo Han, in collaboration with Dr. Xun Yu at the New York Institute of Technology investigated the mechanical properties of graphene-reinforced reactive powder concrete at different strain rates. Typically, their approach entailed nano-modifying RPC by combining the characteristics of graphene and concrete. Their work is currently published in Journal of Material Science.
In their work, the mechanical properties of graphene reinforced RPC under different strain rates were systematically studied. The reinforcing mechanisms of graphene on RPC were analyzed by microscopic test results, and the dynamic compressive toughness of the concrete materials was characterized by using the dynamic impact toughness and impact dissipation. Finally, the reinforcing mechanisms of graphene on RPC were understood, and the dynamic constitutive model of graphene-reinforced RPC was established scientifically.
The authors highlighted that their experimental results revealed that under quasi-static loads, the incorporation of graphene significantly enhanced the compressive toughness of RPC. Additionally, under the high rate dynamic loads (strain rate of 200–800/s), the dynamic compressive strength, peak strain and ultimate strain of graphene-reinforced RPC were increased by 59.1 MPa/63.9%, 4300 με/66.0% and 12150 με /32.7%, respectively. Overall, the impact toughness of RPC was increased by 117%. It is these merits of graphene that significantly improve the impact performance of RPC at medium and high strain rates, which is of great significance for the safety of infrastructures, especially civil defense engineering, nuclear power protection structure and military defensive project.
In summary, the study demonstrated that RPC can be nano-modified using graphene to improve on its reinforcing mechanisms. In their work, the team attributed the reinforcing mechanisms of graphene on RPC to their nucleation and bridging effect. In a statement to Advances in Engineering, Professor Baoguo Han, the lead author highlighted that the interlaminar slip and structural fracture of graphene further absorbed strain energy released by cracking and therefore improved the mechanical properties of the RPC.
Jialiang Wang, Sufen Dong, Xun Yu, Baoguo Han. Mechanical properties of graphene-reinforced reactive powder concrete at different strain rates. Journal of Material Science (2020) volume 55: page 3369–3387.