Building Blocks for American Infrastructure
By Kate Kurtin
As a National Transportation Security Center of Excellence (NTSCOE), UConn’s School of Engineering engages in a range of research projects centered on securing our nation’s transportation infrastructure. NTSCOE was created by the Department of Homeland Security (DHS) in an effort to fund research and training on transportation security issues. With expertise in laboratory characterization of infrastructure materials, modeling and construction, Drs. Adam Zofka and Michael Accorsi (Civil & Environmental Engineering) and James Mahoney, Executive Director of the Connecticut Transportation Institute, have teamed up to study a material that is one of the primary building blocks of American infrastructure – concrete. “There has been a lot of work done recently that is completely changing the chemistry of concrete to make it radically different, which will have a big impact on structures,” Dr. Accorsi said.
The focus of this research is on characterization of ultra-high performance concretes (UHPC) and the development of predictive tools to enable the design of next generation transportation infrastructure. This work is prerequisite and complementary to other integrative technologies aimed at protecting our nation’s infrastructure. “Ultra-high performance concretes are a revolutionary class of cementitious materials that provide superior strength, ductility, blast and fire resistance, as well as durability and resistance to environmental degradation as compared to conventional concretes,” explained Dr. Zofka. UHPC has been completely redesigned at the micro-structural level. “Instead of using standard materials, UHPCs are very fine particles that include no coarse aggregates and are a much denser and stronger concrete,” explained Dr. Accorsi.
To date, the use of UHPC in structures has been limited, and basic research is needed to accelerate its widespread usage. Because of this, there are many questions about its performance. One specific question posed by DHS is how this new UHPC will stand up to extreme temperatures, such as may occur with an explosion or a fire. Because the microstructure of UHPC is so dense, when you heat it up the moisture cannot escape, allowing steam to build up and leading to potential disintegration and eventually structural failure. An example application is a tunnel fire. Dr. Accorsi explains, “Most tunnels are built of concrete. So if a vehicle full of gasoline explodes in a tunnel, temperatures of 1000ºC can result.” Under those conditions, he said, any concrete would lose its bearing capacity and integrity.
Knowing this, the researchers intend to conduct at-temperature mechanical testing of UHPC specimens in a 1000ºC furnace. The results of this testing will be used to advance the team’s abilities to analytically model the behavior of UHPC.. Furthermore, the team will conduct laboratory tests with digital image correlation to validate the modeling capability. All of this is in an effort to characterize the UHPC in order to be able to predict and model if and when a UHPC structure will fail. The final stage of this research will be to conduct large-scale benchmark simulations, such as building a tunnel in a computer program and to model how it will behave at different extreme temperatures.
When completed, this research will change the foundation of basic transportation and construction-based infrastructure. “This pioneering work will provide the necessary foundation for accelerated usage of UHPC in next generation infrastructure,” finished Dr. Zofka.