CBDG 28^th Annual Conference

VENUE
Institution of Structural Engineers, London, EC1V 3PS

DATE
Wednesday 18th June 2025

Maximising Value from Concrete Bridges

Returning again to the Institution of Structural Engineers in London, 60 delegates and speakers took part in the 28th annual conference of the Concrete Bridge Development Group in June.

Opening the proceedings was CBDG Chairman, Steve Cook (Arup), with warm words of welcome and the value of collaboration. “We deliver better as a community”, he said: “your willingness to share is appreciated”. We've got the message about CO₂, he added, and turning to the theme of the day, argued for keeping our infrastructure in service for as long as practicable.

Morning session: Design & Materials

The first presentation was the keynote address by Chris Hendy (AtkinsRéalis) entitled Designing concrete bridges for 100% utilization to codes. It was a presentation based on thoughts arising from meetings of the Net Zero Bridges Group. We can do little with the material itself, he suggested, but we can use less of it and reduce embodied carbon. Most utilisation is around 80%; that leaves 20% potentially to cut. But why so reticent to design from 100% utilisation? He looked options for optimising design. In one example cited, the exercise of non-linear analysis made a 25% saving in rebar. Trials cost, it’s true, but can save a lot of money and trouble in the long term. He suggested it was worth looking for the origin of code provisions, and not just accepting them blindly. Using more material will not resolve matters if there is an underlying problem. Emphasising a key point, he stressed being objective and not just pushing for a percentage. Improving utilization rates was a theme returned to throughout the day.

The morning session was headed Design and Materials and the next two speakers focussed on the latter aspect.

‘Potential Benefits of Steel Fibre Reinforced Concrete to EN1992-1-1(2023) for bridges’, by Craig Giaccio (Hewson Consulting) was first. Craig introduced the basics of SFRC and the implications for design, discussing relevant provisions in the secondgeneration BS EN 1992-1-1:2023, in which the Bridges part is now an annex. He noted that SFRC is not otherwise codified to any extent. He ended with some examples of SFRC's use in a single-span integral bridge to reduce congested reinforcement.

‘Exploring Value from Novel Lower Carbon Materials in Modular Bridge Abutment Shells’, was presented by a triumvirate of speakers: Dr Mohammad Dakhel and Dr Ana Pavlovic (Laing O'Rourke), and Sarah Pedley (Ramboll/University of SheIield). Each took a diIerent aspect: Mohammad introduced Laing O'Rourke and its development of modular bridge abutment shells, with testing at BRE; Ana considered the selection and testing of various means of reducing the embodied carbon of the materials used (including Wagner's Earth Friendly Concrete and reinforcement from recycled steel or basalt fibre); and Sarah addressed measures to build confidence in novel solutions: international examples and both current and future standards. Sarah sought the valuable and achievable in new technology, ending with an exhortation to incremental improvement: “Don't let best be the enemy of better.”

Breaking for coIee, the opportunity was taken to introduce representatives of the two sponsoring organisations - Construction Repairs Ltd and Balvac - both of which had literature and exhibition stands in the refreshment area.

The next two presentation were case studies, drawing on the experience of particular projects. Lee Hardwell (Arup) described the design and build of a highly constrained railway bridge in Huddersfield. Span 29 was a bridge reconstruction involving two prestressed concrete beam decks on new concrete abutments as part of strengthening the historic Huddersfield Viaduct for the TRU project. Originally the bridge was designed to carry five railway tracks, reduced to two in the 1960s, and the project was to reinstate two additional tracks to four in total. Dating from the 1840s, the original bridge was built of brick, at a skew of 52o. Options for the widening were to use steel or, as chosen, prestressed concrete beams on new abutments with diaphragms. Lee explained how the design evolved from integral to simply supported beams, and finally to Y-beams, including a special edge beam. Patterned concrete was used for the parapets to tie in with the aesthetic requirements of the Grade II listing.

This was followed by Graham Webb (WSP) speaking about the Fehmarn Belt Fixed Link between Denmark and Germany. He admitted he was very conscious (at a bridge conference), that his subject was a tunnel, rather than bridge, but he needn't have worried - there were many aspects of applicability and it was all very interesting! The scheme is being built for the Danish government, enabling a 150 km detour to be replaced by a much shorter direct link to Germany. The tunnel itself is to be an immersed tube, floated out and sunk into a sea-bed trench, the geology and other considerations not being suitable for a bored tunnel. The assembly site is 1m square metres in area, with direct links to the precast factory. There are five production lines, with elements that elevate to enable the exit of the 24m-long tubes, nine segments together at a time, and 79 of them in total. There are also two special units that carry the facility for services. Otherwise there is a standard design, varied only to accommodate diIerences in depth. The geology is a consideration that introduces uncertainty and so requires modelling and analysis. WSP's role is as a third-party checker, using highly automated processes - very necessary when there are 15,000 calculation sheets!

Afternoon Session: Repair & Monitoring

First up after lunch was a short introduction to the Group's next publication, TG19: Precast Superstructures by lead author Matthew Baxman (Hewson Consulting). He offered preliminary comments, explaining that TG19 was conceived as a sister document to TG17, offering high level treatment of its subject, signposting to more detail elsewhere. It aimed to reflect the current state of technology, and not include innovations or predictions of future practice. He hoped the guide might be used as a decision-making tool for early-stage planning. He then went on to describe the core sections, 3-7. He said there were lots of precedents and hoped the guide would unlock the benefits of precasting.

The afternoon was otherwise designated Repair and Monitoring, and the first of four presentations was entitled ‘Rehabilitation of Haulbowline Bridges, Cork Harbour’, by Michael Minehane (RPS), visiting from the Republic of Ireland. He introduced Cork Harbour as the headquarters of the Irish Naval Service, but also the principal production site of Irish Steel during its years of operation: 1939-2001. In 1966, the current bridge was commissioned by Irish Steel, a rocky island dividing it into two sections over the north and south channels: 140m of eight spans and 217m of nine spans respectively. On the island, East Tip had been used for spoil from iron processing and was now considered hazardous. It was to be remediated before Ireland's presidency of the European Union, and the scale of task is indicated by the 20,000 lorry movements needed to convey the capping material. In view of this exceptional demand, the bridge was checked. Numerous defects were observed, perhaps more conspicuously, cracking at the featured half-joints, with a 45o shear. There had been little maintenance since the 1960s, so lots of testing was undertaken. The results showed high levels of chlorides (unsurprisingly for a maritime location), but also (surprisingly) very high cube strengths. However, the half-joints were subjected to a 26t load restriction until a 12-month programme of strengthening could be undertaken - to remediate half-joints or replace with X braces - and otherwise repair and refurbish the bridge.

In a thought-provoking discourse, Dr David Collings (Arcadis) considered the concept of asset lifetime and explored the availability of useful data. Lifetime is an important parameter for assessing economic viability and sustainability. However, there is little information available, as David found, certainly for the UK (though more for the USA). David introduced his concept of ‘Useful lifetime’ - as opposed to design life (ie without major repair or adaptation) or age (ie years to date) - noting it was influenced by factors such as design quality, form, material, construction, usage intensity, and maintenance practice. He sought to provide data. E.J. Walbank surveyed a sample of bridges in 1989, for which the average age was 19 years, now 50 years; Pugsley (1968) oIered 120 years and Caprani & De Maria (2020), 773 bridges aged 33 years. For the USA, F. Hughes found 45/46 years for steel/concrete bridges by average age, whereas for railway bridges, the average age was 103 years, not the 120 years now assumed in the UK (The Code provides for 100 years, while the British national annex stipulates 120 years). Finally, David tested the published figures against database derived from his own survey of bridges over the River Thames, and shared his findings.

Next was Dr Wayne Dodds (Amey) on ‘Monitoring of Impressed Current Cathodic Protection Systems - Achieving Best Value’. Outlining the three main types, including galvanic anode and hybrid, he described the impressed current technique as “the Rolls Royce option”, most likely to oIer the greatest savings when whole life costs are considered. He acknowledged the system's shortcomings and reviewed selection criteria before describing the requirements for regular monitoring if the adequate protection of assets is to be achieved.

Concluding was unexpectedly a double bill. The subject, Muon Tomography: Unlocking the Interior Secrets of Reinforced Concrete Structures to Prolong Infrastructure Lifespan', was initially addressed by the advertised speaker Graham Kneller (GScan), who explained something of the science behind the use of muons for testing and the role of AI for its evaluation. But he was joined on the day by Chris Mundell (AtkinsRéalis) fresh from having spoken at a ‘Moonshot’ event the day before. Chris, Technical Director, was introduced as the delivery lead for Structures Moonshot, the NDT project for National Highways, and was thus able to add an enthusiastic client endorsement which left the session on a pleasingly positive note. He explained that the A14 Huntingdon Viaduct had been hydro-demolished and three sections were used as a sample, one of which was assigned to GScan to test. The first scans were carried out in late 2023. These were passive scan that needed weeks to be interpreted eIectively. But the pace of technological development in this field was described as “absolutely phenomenal” and GScan “nothing if not persevering”. By 2024 they were using AI and colour coding diIerent defects. 3D images were developed in ways that were “incredibly exciting” and National Highway is now to invest. The second phase of the programme took place at Torvand, Tartu, using diIerent materials and including deliberate defects. The results came out in Feb 2025 and Phase 3 will take place over the next 9-12 months, using Muon testing on real structures. It was accepted by the speakers that the equipment is large and heavy (90kg), so, with logistics a challenge, this does suggest selective use. But when needed, Chris aIirmed, it is very useful.

Wrapping up the programme, Saeed Ziaie (WSP), chairman of the CBDG Technical Comment summarised the day, oIering some concluding words on the underlying themes and giving thanks to the speakers and other contributors to the success of the event.

Once the conference proceedings had drawn to a close, those delegates who hadn't had to get away assembled for an informal drinks reception in the Institution's members' area. The evening concluded with a dinner at Cote Barbican nearby, for speakers and those delegates who had booked ahead. It was a jolly way to wind down after a long day.

Feedback was generally very positive, with several participants indicating they had enjoyed the variety of interesting presentations, perhaps best encapsulated by this comment: “I found the day very enjoyable and interesting, there was a good mix of topics covered and plenty of opportunities for conversations, both during the day and at the meal afterwards”.

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