While modern weapon makers churn out more powerful artillery creating concern about infrastructure security, civil engineers are working to construct safer and more durably designed buildings to protect society. To that end, one such development is a new form of concrete known as high-performance fiber reinforced concrete (HP-FRC). It is believed that this adaptation of concrete could be critical in the field of protective design specifically regarding ballistic impact. However, as this material is still new to the industry there is little understanding about just how it can withstand high impact blast loads.
The lack of data regarding how HP-FRC stands up to blasts got Mason’s Associate Professor Girum Urgessa thinking. Urgessa, teaching in the Sid and Reva Dewberry Department of Civil, Environmental, and Infrastructure Engineering (CEIE) explains, “Here at Mason, we’ve studied the modeling aspect of the penetration mechanics, but our verification capability is limited because of the scarcity of experimental data.” However, Urgessa saw a perfect match for research collaboration with Eric Jacques, Assistant Professor in the Structural Engineering & Materials Group at Virginia Tech. There, Jacques can access the Thomas Murray Structures Laboratory, equipped with a large-scale gas-detonation blast simulator.
The collaboration came to fruition via Urgessa’s 4-VA@Mason grant Scaled-testing of Projectile Penetration in Conventional and High-Strength Concrete Targets. In addition to Urgessa and Jacques on the project, Mason faculty member Dhafer Marzougui and graduate student Geoffrey Dilg volunteered their time assisting with post-test computational modeling. Undergraduate student Shima Abdel Monem Awwad also worked on the project. The project team got started, building 15 small-scale fiber-reinforced concrete targets of varying thicknesses. These were built at Tech for ballistic experiments using a light gas gun.
Four HP-FRC specimens were subjected to ballistic projectile impact loading, which provided the ability to model/predict projectile penetration depths across a variety of concrete strengths and types. Says Urgessa, “Three out of four initial trials provided us with complete projectile perforation, while the third trial resulted in spalling, penetration, and radial cracking.” Although they were able to conclude that the Cem-FIL glass fibers helped reduce the effects of the cracking by holding the sections together, they did not stop the projectile from perforating. In the cases where the projectile perforated through the specimen, the fibers had either pulled out of the concrete or ruptured at most crack locations.
“Overall, this experiment proved to be very successful and has given us the opportunity to shed light on a relatively new material and that has a variety of real-world applications,” concluded Urgessa.
