The main motivation within this thesis is to explore the possibility of increasing the service life of box-beam bridge girders to aid the ambition of the Dutch government to become a circular economy. The construction industry still follows a more or less linear economy system. Many bridges in the Netherlands are approaching the end of their service lives, and efforts are being made to extend the lives of these bridges. This is but a temporary solution, and these bridges will require replacement within 20-30 years. This provides an opportunity to incorporate circularity within new and upcoming structures from the design phase onward rather than only as an end-of-life practice. Therefore this thesis explores the possibilities of incorporating the strategy of lifespan extension, in the form of a cover increase against chloride-induced corrosion. The exact increase was calculated through the use of a relevant service life design model (DuraCrete) and compared with the Eurocodes. The reliability of the model was checked using a Monte Carlo simulation. Subsequently, the circular aspects of future adaptability were also investigated considering a fictitious scenario of increased traffic load. Hence, it was concluded that a marginal increase in concrete volume and prestressing steel per beam would allow for a more durable and adaptable beam for the future.

Adopt the concept of demountable and rebuildable brides to an existing idea of an integral bridge. An understanding of the different forces and moments that the bridge will have to take up and how the critical connections (deck-abutment) can be realized. Applying the understanding of how integral and demountable bridges behave and try to integrate the characteristics of both to achieve rebuildable/demountable construction. In this additional thesis, the first steps to make an integral bridge demountable is looked at in detail. The concepts of vertical prestressing with unbonded bars are explored to achieve the demountable abutment, and abutment- deck connection. The different forces that arise due to this method of prestressing have been accounted for to ensure the basic safety of this design is met.