The use of precast concrete superstructure elements can expedite project delivery, improve work-zone safety, and reduce overall project cost. To accelerate construction, the precast elements must be connected quickly on-site, ideally using as little additional material as possible. While the excellent tension and bond strengths of ultra-high performance concrete (UHPC) make it ideal for this purpose, the time at which UHPC achieves its design strength is directly proportional to the rate of hydration of the cementitious binder. While UHPC may provide the best solution in many instances, alternative joint materials that utilize polymer binders, instead of cementitious ones, may be more suitable if rapid strength gain is needed. This project explores a potential alternative closure joint material, fiber-reinforced polymer concrete (FRPC), which displays levels of the two critical characteristics (bond and tension strength) that are comparable to, or potentially better than, those of UHPC. FRPC has the advantage of requiring shorter closure windows (approximately 4 hours versus 72 hours of UHPC) due to the very rapid strength gain of the polymer, which could be ideal for overnight construction or rehabilitation projects, and provides an additional option to the engineer and contractor when choosing a closure joint material for a given circumstance.
The objectives of the research are to:
· Review the most promising FRPC materials,
· Assess the temperature dependent properties of FRPC behavior,
· Characterize the mechanical properties (tensile, flexural, and compressive strength) of FRPC, and
· Characterize the splice performance of deformed bars embedded in FRPC materials.
Based on the results of this experimental investigation, recommendations for the use of FRPC in ABC applications will be developed to maximize the benefit of this relatively new material for different ABC project applications.
The project includes five tasks to achieve these objectives:
Task 1 – Literature Review
A comprehensive review of past experimental research involving fiber reinforced polymer concrete will be completed, and a database will be established that compares the available polymer chemistries in terms of their mechanical and physical properties.
Task 2 – FRPC Material Characterization
The mechanical properties of FRPC materials (compressive strength, modulus of elasticity, flexural toughness, and tension strength) will be measured at several test temperatures and ages using standard test methods that would be part of a typical quality control program.
Task 3 – Testing of Splice Specimens
The tests will focus on a simplified, non-contact splice configuration that isolates the behavior of reinforcement in a closure joint to a specimen size that can be conditioned using conventional laboratory equipment and tested using a universal testing machine under precise displacement control. The variables that will be investigated include the temperature at time of testing, embedded length of the bar, overlap length between bars, bar spacing, side cover, and bar size.
Task 4 – Development of Design Recommendations
The results of the non-contact lap-splice tests and the measured mechanical properties will be used to develop design recommendations for precast concrete closure joints using FRPC. These design recommendations will be used to develop example joint configurations for connecting common precast concrete superstructure elements, such as decked girders or precast deck panels.
Task 5 – Interim and Final Reporting
The research team will submit timely quarterly reports, present annually at the Research Days meeting, and complete final report summarizing findings reached during the project.
Principal Investigator: Travis Thonstad, Assistant Professor
Research Assistant: Carolyn Donohoe, MSCE Student
Previous Progress Reports: