20 year anniversary of the Brugg railway bridge

The “new” railway bridge across the Aare near Brugg (Switzerland) was completed in 1996. It was built as a replacement for its predecessor of 1905 of which the natural stone piers were retained for the new build, rehabilitated with products from MC-Bauchemie.
On the occasion of the 20-year anniversary, MC Switzerland arranged an engineering conference at Technopark Brugg for 19 May 2016. This was attended by 40 structural planning engineers and client representatives. After the immaculate condition of the bridge had been confirmed during an inspection attended by all the participants, three speakers talked about the history and the construction of the bridge and related material technology issues.
New build on old piers

Bruno Kuhn, senior engineer from the company Gerber + Partner Bauingenieure AG Windisch, who was responsible for the overall management of the new bridge project crossing the Aare 20 years ago, provided a highly detailed description of the planning and implementation work involved. The dual-track steel railway bridge from 1905 had become unacceptable by the middle of the 1980s due to noise emission issues. From a number of possibilities examined, the decision was taken to replace it with a continuous prestressed concrete hollow-box construction with a ballast bed. For aesthetic and heritage reasons, the piers constructed from natural stone masonry were to be retained for the new structure.
Investigations carried out on the piers and the foundation soil revealed, however, that not only the 100-year-old masonry but also the foundations would not be able to withstand the high loads imposed by the new bridge. The foundation soil was therefore consolidated using a jet grouting process.

Repair of the natural stone masonry piers

The repair of the natural stone masonry piers involved the use of mortars and injection pastes from MC. The raked-out joints were initially filled with new joint mortar and subsequently sealed with a special weather-resistant waterproofing system. A matrix arrangement of bores was then drilled into the joint system to allow paste to be injected behind the new joint mortar. This measure increased the load-bearing capacity of the structure, while also retaining a degree of elasticity in the joints. Dr. Andreas Zahn, Head of the Masonry Field of Expertise at MC, took up the theme and discussed in some detail the methods and mechanisms by which masonry support structures operate. The natural stones are much too hard to be able to themselves absorb the deformations arising from loads or thermal effects, which means the joint material has to perform this function. Consequently, the joints have to be flexible enough while at the same time exhibiting sufficient strength in order to maintain a permanent and durable bond with the stones.
Moreover, the correct mineralogical composition of the masonry mortar and injection pastes is also essential if masonry structures are to be properly protected against aggressive chemical mechanisms. Professor Eugen Brühwiler, Chair of the Maintenance & Safety of Legacy Buildings Faculty at the École Polytechnique Fédérale de Lausanne, concluded the engineer-ing conference with a presentation on (bridge) construction materials of the future.