PSI - Issue 64

Tom Argyle et al. / Procedia Structural Integrity 64 (2024) 1376–1385 Argyle et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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of this paper) and concluded on the following: Replace all existing strengthening plates in sequence with embedded Carbon Fibre Reinforced Polymer (CFRP) plates or rods. 5. Design development and Early Contractor Involvement Due to the innovative nature of the chosen design solution and approach taken by the M25 DBFO Contract, an extensive Early Contractor Involvement (ECI) by Octavius and design development process was undertaken to understand the materials, methods and programme times and demonstrate the installation quality of the system. 5.1. Initial offsite and laboratory trials (Plate installation / Accelerated curing) The off-site trial undertaken by the contractor reviewed different methods of substrate preparation for recessing the plates into the top of the existing deck slab to provide a flat finished upper surface to the concrete for waterproofing. Plates being initially preferred due to the smaller number of installations required. Different methods including milling, grinding and saw cutting were all trialled but found to be more time intensive and less reliable than chasing out for rods. Based on the off-site trial outcomes, the CFRP rod was preferred due to better consistency in installation quality and reduced overall programme durations. With a key requirement of the design solution being minimal impact on the use of the Junction 3 roundabout, an innovative accelerated curing methodology was trialled, to limit the duration the structure may need to be closed to traffic as initial engagement had identified blockers to curing the resin under the single lane of traffic operation. The technique passes current through the CFRP plate, which acts as a resistor and so generates heat to cure the resin and is typically used in countries with low ambient temperature. Whilst the technique was demonstrated successfully to accelerate the curing time over a limited length it could not be achieved over the length of plate required due to the high electrical resistance present. The solution would also not have been as practical for the rod installation due to the higher number of rods that would have needed to be cured in parallel.

Fig. 4. ECI Trials of installation of CFRP plates. Cutting methodologies trialled including milling (far left) and saw cutting (left). Curing techniques including passing electricity through the plate to induce heat for accelerated cure times (right / far right).

Therefore, following the outcome of the laboratory trials and subsequent engagement with specialist suppliers, an approach to using rapid curing resin products that were suitable for installation and curing under the small strains from adjacent open lane operation was identified as most viable. 5.2. Rapid Curing / Rod Installation Procedural Trials A second round of ECI procedural trials were undertaken to verify the viability and quality of installation of Near Surface Mounted Rods. This trial also included trials on varying slot width and waterproofing system compatibility. Following engagement between contractor and specialist suppliers of the CFRP and waterproofing systems a layer of kiln dried sand was applied to the fresh surface of the resin, with excess removed once cured. The waterproofing system was then applied to this roughed substrate.