Multi-Modal Nondestructive Evaluation Approach to Assess the Condition of the Grout in Bonded Post-Tensioned Ducts
Presented By: Arezoo Imani
Affiliation: BDI
Description: Post-tensioned (PT) girders have been widely used in bridge construction due to their performance, cost, and durability advantages. If constructed adequately, PT systems are generally more durable than conventional reinforced bridges and can span longer lengths. The grout system in bonded PT ducts provides continuous load transfer between concrete and tendons as well as protection against corrosion of the steel strands. In the decades after WWII, the technology for post-tensioning had initial design and constructability challenges but continued to evolve and improve. Many older post-tensioned structures suffered from some grout deficiencies. Excessive water or substandard construction practices during the grouting can result in ungrouted areas or voids within the duct. Additionally, any exposure to chlorides, sulfates, and moisture in the grout system can lead to the degradation of the steel tendons or the formation of soft grout. Due to the embedment of the post-tensioning in concrete, the strands cannot be readily inspected. Therefore, novel ways to examine the grout condition for PT structures have been explored by bridge owners and agencies. A comprehensive multi-technology nondestructive evaluation approach to assess the condition of the grout in bonded post-tensioned ducts using Ground penetrating radar (GPR), ultrasonic tomography (UT), impact echo (IE), high-resolution imaging (HRI) is presented in this work.
Evaluation and Mitigation of Bonded Post-Tensioning Corrosion in Minneapolis Bridges
Presented By: Natallia Shanahan
Affiliation: Vector Corrosion Services
Description: Corrosion of bonded post-tensioning (PT) can occur along the strands within the ducts with no externally visible signs of concrete deterioration until significant section-loss has occurred. This can significantly affect the structural capacity of the element without any visual indications. PT corrosion is typically caused by grouting defects, such as voids and soft grout. Grouting defects cannot be detected through normal bridge inspection methods like visual or tactile inspection methods because the PT strands are encased within plastic or metal ducts and are often embedded within slabs or walls. VCS has effectively used impact echo/pulse velocity (IE/PV) testing to locate grouting defects in internal PT tendons on structures throughout the world. This presentation will discuss IE/PV testing performed on the internal PT of 3 bridges in Minneapolis, Minnesota: a pedestrian bridge and two vehicle bridges. While the pedestrian bridge has minor grouting defects, the vehicular bridges had significant voiding and soft grout issues. The presentation will detail effective methods for the inspection of bonded PT to find these issues prior to significant damage occurs. In addition, the presentation will discuss effective preservation techniques that are used on bonded PT to mitigate the identified damage. This includes tendon drying, impregnation with a corrosion inhibitor, and regrouting.
State-of-the-Art and Novel Trends in Ultrasonic Imaging of Concrete Structures
Presented By: Roman Pinchuk
Affiliation: Acoustic Control Systems
Description: Full Matrix Capture (FMC) is an advanced ultrasonic testing technique that has significant potential for inspecting concrete structures due to several key advantages: comprehensive data collection, high-resolution imaging, improved defect detection, versatility and flexibility, better characterization of flaws, and robust post-processing capabilities.
In ultrasonic testing, FMC is utilized in two main configurations: matrix FMC and linear FMC. These configurations refer to the arrangement of the transducer elements and how they capture and process data.
Linear FMC is commonly used in applications where the inspection area is relatively flat and one-dimensional scanning is sufficient. The widespread use of linear FMC is due to its simplicity, speed, and cost-effectiveness. However, linear FMC has certain disadvantages, such as limited coverage and lower resolution, particularly affecting the near-surface area.
In matrix FMC, the transducer elements are arranged in a two-dimensional grid (matrix array). This configuration captures ultrasonic data in both axes (x and y), providing a more comprehensive three-dimensional view of the inspected area. The Dry-Point-Contact (DPC) transducers are matrix FMC-ready by design. However, the application of matrix FMC faces several challenges, primarily due to the complexity of the electronics, algorithmic complexity, and consequently, the high computational resources required.
This contribution reveals the latest advancements in matrix FMC, which include techniques for the elimination of long and shear surface waves, data collection, pre-processing, filtering, and real-time image synthesis on graphical shaders. Additionally, it discusses the assembly of multiple measurement positions into a solid 3D volume with joint layer processing. We also discuss practical examples of FMC applications, highlighting the effectiveness and potential of this technique in various real-world scenarios.
Digital Twin to Simulate the Propagation of Acoustic Waves in Prestressed Concrete Elements
Presented By: Horst Trattnig
Affiliation: Vallen Systeme GmbH
Description: According to the German Federal Highway Research Institute (BASt), approximately 69% of bridges in Germany are currently constructed using prestressed concrete. Over 1200 of these bridges were built before 1965, during which time the prestressed steel used was potentially susceptible to stress corrosion cracking (SCC). Currently, Acoustic Emission Testing (AT) is the only reliable and economically viable technique for monitoring prestressed wire breaks.
In Germany, AT is almost routinely used to monitor prestressed concrete bridges suspected of SCC. Notable examples include the Elsen Bridge in Berlin and the Altstadt Bridge in Brandenburg/Havel. However, the acoustic analysis of prestressed concrete structures required to plan a monitoring system, and the analysis of acoustic emission signals to diagnose wire breaks, are both complex and time-consuming.
Simulating sound propagation in prestressed concrete structures could significantly reduce the effort for the acoustic analysis needed to plan a monitoring system and increase the accuracy and reliability of the results. A digital twin is intended to enable the user to put together a virtual prestressed concrete structure from a modular set of geometric elements and to determine positions of virtual prestressed wire breaks in the structure. With the subsequent simulation, both the preparatory acoustic analyzes and the arrangement of the sensors in monitoring can be optimized. By comparing simulated signals and signals detected in monitoring, the identification of tension wire breaks and thus the reliability of monitoring can be significantly improved.
Monitoring of Prestressed and Post-Tensioned Reinforcement Systems
Presented By: Mohamed ElBatanouny
Affiliation: Wiss, Janney, Elstner Associates, Inc.
Description: Prestressed and post-tensioned (PT) reinforcement is widely used in many components in both buildings and bridges due to their beneficial properties. These systems, however, are susceptible to corrosion damage, which could lead to cross-section loss and ultimately breakage of the wires that forms the tendons. When a wire break occurs, it emits a stress wave that sensors could detect and locate. This presentation will discuss case studies that demonstrates monitoring applications to detect wire breaks in prestressed and PT systems.