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Smart condition monitoring and prompt NDT assessment of large concrete bridge structures

Final Report Summary - CROSS-IT (Smart condition monitoring and prompt NDT assessment of large concrete bridge structures)

Executive Summary:
Over the last 20 years half of all bridges built worldwide have been of a pre-stressed concrete design, with 25% being reinforced concrete and the remainder being made of steel construction. In the European Union (EU) there are approximately 300,000 concrete bridges with a reported replacement value of over €300 billion.

When concrete is used in bridges, tunnels and buildings, its load bearing capacity has to be increased by reinforcing it with steel bars and tendons. The failure of these large structures is normally due to corrosion of the internal steel reinforcement and tendons. This can be caused by normal age related degradation that can be triggered by water ingress into surface cracks resulting in corrosion.

The deterioration in bridges is exacerbated by the fact that axle loads have risen above those in operation when the bridges were designed, and this exposes these structures to stresses beyond their limits. Early signs of deterioration are often not seen and a high level of skill is required to distinguish signals from noise. At present there is no single non-destructive testing (NDT) technique capable of practical inspection of pre-stressed tendons throughout their length and existing NDT techniques such as visual inspection have major limitations. Bridge owners and operators therefore have a real need for improvements to present maintenance and Non-Destructive Testing (NDT) inspection practices for these structures.

Project Context and Objectives:
The CROSS-IT project aims to develop a new technology to inspect concrete bridge structures for dangerous levels of age-related degradation, which could consist of cracks due to water ingress and corrosion of internal steel reinforcement. The technology is based on a hybrid system of Ground Penetrating Radar (GPR) and Ultrasonic Guided Waves (UGW), using the positioning advantages of GPR to locate the internal steel reinforcements, and UGW, to detect flaws and corrosion on those. The system will display the results as a visual 3D map on a dedicated laptop running a purpose designed program.

To accomplish the project objectives, the work activities have been organised into a number of
discrete Work Packages. Those were divided into research (WPs 1 to 5), demonstration (WP6),
dissemination and exploitation (WP7) and management (WP8).
The description for those work packages are shown below:
WP1 – Project Specifications and Industrial requirements
WP2 – Modelling and Theoretical Studies
WP3 – Ultrasonic Transducer Design
WP4 – System software design
WP5 – System design, integration and testing
WP6 – Laboratory and field trials on concrete samples
WP7 – Exploitation and dissemination
WP8 – Project Management

At the beginning of the project, with the advice of Atkins, the consortium has identified the test cases where the CROSS-IT project would be most beneficial to resolve the most critical problems within the concrete structures. Briefly, the following major tasks have been carried out throughout the development:

• Modelling of UGW in concrete and tendons and the discovery of the optimum propagation mode(s)
• Selection of UGW transducers to propagate the optimum mode(s) as determined from the modelling and experiments
• Training of a Neural Network for data analysis
• Software and hardware to combine the GPR and UGW signals and to display the results to the operator (advanced signal processing)

Project Results:
The details of technical and scientific results for each work package are presented as follows:
WP1 – Project Specifications and Industrial requirements is 100% complete at the end of the Project and D1.1 – Report on project specifications and samples design was submitted. The deliverable was prepared with the collaboration of consortium - specifically the end users and SMEs. The overall objective of this Work Package (WP) was to arrive at detailed specifications in the light of standards, literature, industrial feedback and discussion between the consortium members. It was essential that the project met the needs of SMEs and end-user for successful exploitation of the technology at the end. A range of samples that were used for the laboratory trials and in WP6 were identified and purchased. Some of the samples were manufactured by the end of this work package based on the parameters specified in Deliverable D1.1. The ultrasonic properties and the combination of the two technologies, GPR and UGW, together were investigated in defect free samples first. Later in the project suitable defects have also been introduced and more samples were procured and manufactured in accordance with the needs.

WP2 – Modelling and Theoretical Studies is 100% complete at the end of the Project and D2.1 - Report on the Modelling of ultrasonic guided waves and defect detection was successfully submitted.
The overall objective of this Work Package was to carry out theoretical modelling of Ultrasonic Guided Waves (UGW) in the steel reinforcement and tendons and to select the best propagation modes through the interfaces between the concrete, steel reinforcement and tendons. A major part of this study examined how the presence of ribs on the steel bar affected the propagation of axisymmetric wave modes. The final conclusion from the modelling work package was that, in general, the results are consistent with what was expected based on other papers and research work studied during this project. The theoretical work in this work package was used as a tool to assist in defining the detailed experimental plan covering practical ultrasonic tests on the bars and cables.

WP3 – Ultrasonic Transducer Design is 100% complete at the end of the Project and D3.1 - Transducer Design and D3.2 - Transducers array system for use on concrete and buried tendons were submitted. The work covered the array design, including consideration of the transducers to be used, the ultrasound propagation characteristics across the bars and concrete, coupling and the imaging of the responses from the bar and concrete. Various ultrasonic transducers have been obtained and tested including variable angle beams designs. The transducer arrays have been designed to propagate the optimum mode or modes as determined from the modelling and experiments in WP2. Once the ultrasonic testing of the concrete samples was completed, the level of ultrasonic wave energy was fully understood and the power level that was required for the ultrasonic transducers and arrays were then tuned accordingly using the power electronic amplifiers that were also being developed.

WP4 – System software design is 100% complete at the end of the Project and D4.1 - Integrated system software for the condition monitoring was submitted. The aim of this work package was to design an integrated software system with an interactive Human-Computer Interface able to oversee the processing of GPR data, generate a 3D map of the location of the tendon and predict the best location for the ultrasonic guided wave transducer array placement. The general location of the duct, its orientation and its depth in the concrete were determined and depicted in 3D volume with high accuracy and resolution. Furthermore, the implementation of the required algorithms was integrated to the complete condition monitoring program. Software routines for automated LRU signal pre-conditioning were proposed and the developed algorithms for signal optimization and feature extraction were presented. In addition, the basic features for the Neural Network development, that would be the core of the condition monitoring system and would automate the defect detection process, were defined.

WP5 – System design, integration and testing is 100% complete at the end of the Project and D5.1 - Fully integrated working hardware system was submitted to summarise the work carried out under this work package. Within Work Package 5, the CROSS-IT Human Compute Interface (HCI) was designed and implemented according to the requirements defined among the CROSS-IT consortium, and the GPR and UGW systems were both integrated to the CROSS-IT laptop running the GUI. The integrated system software (Neural Network) for the atomization of the defect detection process was developed. The defect detection rate for pitch-catch for both 25 mm and 20 mm re-bars was 100% and more than 94% respectively, and for concrete-to-concrete around 55%. The fully integrated system was tested and validated and the GUI was also tested, debugged and used to display both the GPR and UGW signals.

WP6 – Laboratory and field trials on concrete samples is 100% complete at the end of the Project and D6.1 - Laboratory and Field trials on concrete samples was submitted to summarise the work carried under this WP. The completed CROSS-IT system was demonstrated to the SMEs at the final meeting and together with validation tests it has been shown to detect defects that were added to the sample concrete blocks at TWI. The experiments have shown that when the CROSS-IT system is used as a long term permanently installed monitoring system, the Neural Network neural network can be trained to see much smaller defects.

Potential Impact:
The successful implementation of the CROSS-IT system aims significant reduction in inspection time when compared with existing state of the art inspection techniques and due to the use of guided waves allow a much greater range of inspection from one single location than has ever been achieved. It also aims to minimise the need for corrective maintenance (back filling inspection holes) thus leading to a substantial decrease of the overall operational costs. This will revolutionise bridge inspection and maintenance procedures.

List of Websites:
CROSS-IT is collaboration between the following organisations: TWI Ltd, National Technical University of Athens, Technology Assistance BCNA 2010 SL, INETEC-Institut za nuklearnu tehnologiju, ACUTECH Ltd, ATKINS. The project has received funding from the European Union’s Seventh Framework Programme for research, technological development and demonstration under grant agreement no 286981.

The project website, presents introductions to all CROSS-IT consortium members with links to their respective websites.

This website will be kept as the main platform for any communications related to the CROSS-IT project beyond the project term.
Project Co-ordinator
Kamer Tuncbilek –
Granta Park, Great Abington
Cambridge CB21 6AL, UK