Impact resistance of world's hardest concrete tested for disaster prevention
Concrete is the most widely used building material in the world. Consequently, it is being continuously developed to fulfill modern-day requirements. Efforts to improve concrete strength have led to reports of porosity-free concrete (PFC), the hardest concrete tested to date.
Some of the basic properties of PFC have already been explored, so now a team including Kanazawa University in Japan has probed the impact response of this innovative material. Their findings are published in International Journal of Civil Engineering.
Ultra-high-strength concrete, with a strength at least equal to steel, offers significant advantages that include the potential to reduce the weight of large structures and protect them against natural disasters and accidental impacts. PFC is an ultra-high-strength concrete with properties that can be further enhanced by incorporating steel fibers.
The way in which PFC is prepared leads to very few voids in the final material, which gives it its high strength -- 400 MPa can be applied to PFC before it fails, compared with 20 to 30 MPa for standard concrete. Some of the basic material properties of steel fiber-reinforced PFC have already been reported; now the researchers have evaluated the impact response of a range of PFC preparations with different steel fiber contents and section heights.
Outline of degassing and water absorption treatment: The PFC specimens are then placed in a closed vessel that was depressurized using a vacuum pump, and water introduced from the outer surface to the inside. [Credit: Kanazawa University]
Curing process: After the water absorption treatment, the specimen was subjected to steam curing (heating rate: 15 C/h, max temp: 90 C, max temp holding time: 48 h, cooling rate: 15 C/h). Next, heat curing (heating rate: 60 C/h, max temp: 180 C, max temp holding time: 48 h, cooling rate: 60 C/h, 1 atm) was applied. [Credit: Kanazawa University]
"The continued development of building materials is particularly important in areas where frequent natural disasters threaten the integrity of structures," study lead author Yusuke Kurihashi explains. "We carried out impact tests on a variety of steel fiber-reinforced PFC samples to determine their reactions, and in so doing, accelerate the widespread application of PFC in building projects. Our testing is designed to simulate responses to events such as rock falls, blasts, and flying objects."
Failure condition after impact loading: The damage degree of the beams can be reduced by changing the steel fiber mixing rate in the PFC beam from 1 to 2 percent vol. [Credit: Kanazawa University]
The researchers made two key findings. First, they observed that increasing the steel fiber content from 1 to 2 percent in the PFC mix reduced the damage due to impact by 30 to 50 percent. This significant improvement in performance is expected to inform future material design decisions.
Second, they showed that it was possible to predict the behavior of the samples with approximately 80 percent accuracy by comparing calculated values with those that were measured, which will help to streamline development processes.
"We hope that PFC will contribute to enhanced building safety in the future," says Dr. Kurihashi. "Although additional experimental work and statistical processing is required to fully translate PFC into widespread practical applications, our findings make a significant contribution to understanding PFC's role in improving the safety of many large structures including high-rise buildings, bridges, and roads."
You can also learn more about PFC concrete, its special properties, and development on the Taiheiyo Cement website here. The site features descriptions and application examples with images.
Source: Kanazawa University, Taiheiyo Cement
Published May 2020
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