Concrete recycling is gaining momentum as the construction industry adopts more sustainable solutions, with the Netherlands leading the way. However, reusing structural components rather than recycling them is even better, as it conserves energy and raw materials while further reducing CO₂ emissions. This is precisely what José Paredes Pineda accomplished by creating a testing protocol for the safe reuse of prestressed concrete bridge girders.
During his MSc in Civil Engineering at TU Delft, José Paredes Pineda attended a company speed dating event where he met a representative of Nebest. It turned out that their Closing the Loop consortium had just been commissioned by Rijkswaterstaat to pioneer in the high-quality reuse of prestressed concrete girders. The girders to be reused were from a decommissioned viaduct over the A9 highway, built in 1968. Their destination: a new viaduct near Nuth over the A76.
Many post-war bridges and viaducts in Europe and the USA need replacing, but their components still have several more decades of functionality.
“When designing a viaduct from scratch, you can freely choose the structural system, materials and geometries to ensure durability and safety,” Paredes says. “When reusing girders, it is essential to come up with the best possible prediction of the girders’ strength. However, no established or validated test protocol existed for that.” What started as an internship evolved into his Engineering Doctorate – a two-year programme combining scientific research with real-world industrial challenges. “Both the technical challenge and the sustainability aspect appealed to me.”
Shear force
Since construction of the old viaduct in 1968, the intensity of road traffic, in both frequency and weight, has changed a lot. The same is true for the design guidelines. For one, the girders were designed with little to no shear reinforcement, thereby failing to meet the current minimum amounts. Conventional methods, using hand calculations or a computer, could rule out the risk of all but one of the most critical failure modes of the girders.
“Shear failure in a girder without shear reinforcement is typically catastrophic, as it occurs with little to no warning,” Paredes says. “Despite over a century of research, existing models still cannot fully prevent this type of failure.” Proving the girders’ safety therefore required investigating the shear resistance experimentally under an externally applied load. “Most information would be obtained from destructive testing. But our goal was to reuse the girders.”
To destroy or not
The team decided on a probabilistic approach: rather than testing all the girders to the required resistance in their new use – which would be cumbersome – they would only test a small subset until failure.
Of the 33 girders they had at their disposal, they selected six girders that had suffered superficial damage during harvesting and transport to the test site. They then spent several months last summer developing and validating a testing protocol based on Paredes' research that would provide Rijkswaterstaat with the required certainty regarding the safety of the other girders being reused. “This included a detailed analytical and finite element study to predict what would be the behaviour of the girders under load testing. We also determined the critical loading position, which we later confirmed during load testing.”
Field testing
With the bureaucratic process taking time, Paredes had to frequently revise his planning. At times, it wasn’t even certain the testing and reuse would take place. “You must adapt, overcome, and be able to deal with these uncertainties. The most important part is to keep yourself motivated.” But last November, the six girders were load tested using a custom designed steel frame.
“Strukton took great care of site preparation and safety, while also ensuring efficient collaboration between all parties involved in testing.” Obviously, load testing girders until they fail is a spectacular sight, attracting not only the stakeholders but also many professionals and students from various universities. As the load increased, sensors recorded cracking before it became visible while cameras captured the forceful appearance of major cracks, confirming the expected failure mode. “We proved that the untested girders have more than twice the required resistance for reuse in the new bridge.”
As the load increased, the sensors recorded cracking before it became visible.
An even better testing method
The project has drawn interest from many parties. This is especially important as both Europe and the USA have experienced a boom in infrastructural development in the post-world war II period. “In the upcoming years, many bridges and viaducts will need to be replaced for functional reasons, but their components still have several more decades of technical service life.”
Part of Paredes’ engineering doctorate has been to plan ahead and optimise testing. Additional measurement equipment had therefore been installed to develop an improved testing protocol that allows all girders to be reused while still only testing a subset. “The protocol relies on sound waves. We listen for the first microcracks as they appear, to then stop load testing at a level where the girder's structural integrity remains unaffected.” Likewise, the team had designed their custom steel testing frame to be modular, fitting various sizes of girders. “I’m excited to put my specialised knowledge to good use at Nebest, and to be involved in more conventional projects as well.”
The Closing the Loop collaboration includes Nebest, Antea Group, Strukton Wegen & Beton, and GBN Groep.
Published: February 2025
Jose Paredes Pineda
Jose Paredes Pineda is doing a Engineering Doctorate at the department Engineering Structures.
![[Translate to English:]](https://filelist.tudelft.nl/_processed_/4/d/csm__AHK7694-%20portret_b54c5731c4.webp "[Translate to English:]")
![[Translate to English:]](https://filelist.tudelft.nl/_processed_/c/0/csm_Story-socialfoto%20en%20kaartje%20storyportal-AHK-0006_klein_1b74cd939b.webp "[Translate to English:]")
