The old Årsta Bridge
Projektengagemang Anläggningsunderhåll has since 2007 contributed with technical expertise, knowledge of materials, quality inspections, measurement, monitoring and planning the renovation of the Old Årsta Bridge. The project is conducted within an expanded collaborative contract with NCC, the Swedish Transport Administration and Projektengagemang in accordance with FIA (Renewal in the Construction Industry). The renovation is carried out with full train traffic on the bridge at normal speed. The bridge was designed as an arch with 20 pieces of concrete vaults. The bridge is 750 m long and was built in the late 1920s. A renovation was necessary after almost 90 years of operation in order to keep the bridge in operation for at least another 50 years. Computational work has been intense and a Ph.D project on the bridge design will be finalized at Royal Institute of Technology (KTH), Stockholm shortly.
In order to carry out the renovation, an introduction of a new material via concrete injection processes, and an extensive clean-up is carried out by Projektengagemang. In principle, concrete injection is performed using a mold filled with ballast, after which a cement-based grout is injected into the mold. It was noted that the material used to perform the injection shrinks considerably less than conventional concrete and cement content, and in many cases can be halved with full strength. This in turn means that the carbon load can be split with the new material, which creates the possibilities for a range of promising projects with similar environmental profile. The total cost of the material is in the same range as conventional concrete.