PROJECT 1 : Evaluating Concrete Bridge Decks Using Non-Destructive Evaluation (NDE) New Page

Reinforced Concrete (RC) is the most used construction material for various types of structures. The concrete cover above or below rebars play an important role in structural safety and durability. It may be necessary to find the actual covers in the field for checking construction errors and in cases of missing plans. Plastic fibers in RC can reduce shrinkage and thermal cracking. Ground Penetrating Radar (GPR) scanning can effectively find the rebar cover distances through non-destructive means. However, to date, the effectiveness of such scanning for fiber concrete is yet to be determined. This research focuses on evaluating RC bridge decks using GPR, which is important for ensuring safety and durability in existing infrastructure. The 2024 Research Experiences for Teachers (RET) Program on Sustainable and Resilient Infrastructure for Urban Communities at the University of Texas at Arlington (UTA) included STEM teachers from schools within the Dallas and Fort Worth Metroplex. The 6-week summer research project presented herein focused on the following goals: (1) locate embedded steel rebars in concrete specimens using GPR scanning; (2) investigate how fibers in concrete affect the compressive and bending capacities of specimens; (3) determine the effects of variables such as rebar cover depth and size, concrete type, concrete moisture content, and curing time on the aforementioned properties; and (4) analyze GPR signal variations with two-way travel time in light of various factors.  Following a background review, two small-scale RC beam samples were fabricated with plywood forms. The samples included steel rebars with variable sizes and cover depths. GPR scanning of cured concrete samples and data processing was done weekly for a month.  The samples were then tested in a 3-point bending set-up until failure. The results of the GPR scans showed significant changes during the first 3-weeks, after which the data remained constant.  This variation is attributed to the dielectric properties of concrete and ongoing cement hydration, which affected the radar waves. The addition of 1% fiber improved the average compression and bending strengths by approximately 10% and 45%, respectively. However, the cover determination was not affected by the presence of fibers. It may be concluded that proper curing and rebar placement are important for RC strength and durability. Non-destructive methods like GPR are effective for assessing concrete integrity. Classroom implementation begins with students casting and curing concrete cylinders to observe physical and chemical changes, exothermic hydration reactions, and the law of conservation of mass, comparing plain and fiber-reinforced concrete. In the second part, students use GPR to evaluate rebar health in the school parking lot and a hydraulic pump to test the compression strength of their concrete cylinders. Data analysis is conducted using RADAN 7 software to understand variations in GPR signals.