Technical University, Trondheim, Norway

Re-alkalisation of a 13 story building.

A 13 story building at the Technical University of Trondheim, Norway, suffered from rebar corrosion. The re-inforcement on the main facades, which consist of rows of slender columns filled out with windows and concrete plate elements, was in jeopardy due to a carbonation of about 20 mm in depth. Thanks to thicker cover, the re-inforcement in the end walls was not in immediate danger, except along architectural grooves, where rebar corrosion leading to cracks and spalls was evident.

The building, see photograph, houses offices, lecture and study rooms, hence, a low noise level was, of vital importance when choosing repair methods. Re-alkalisation was chosen for the main facades, since these had a general carbonation problem.

The rehabilitation was performed in the summer of 1989 by our sub-licensee, Malermester Jacob Opdal Overflateteknikk A/S, under the supervision of NOTE-BY, a consulting company, and of employees, in particular Geir Lunde, from The Building Department at the university. Two students did their diploma work on this project. Their report will be available after contesting.

Re-alkalisation was performed at 12 V DC and was complete in 3 to 5 days. The current density was approx. 0.3 to 0.5 A/m².

Afterwards, the building was coated with a CO2, protective coating, partly for cosmetic purposes, and partly to stop further carbonation of the end walls, which were not re-alkalised To verify the quality of the rehabilitation, 12 N.O.T. reference electrodes have been installed for future corrosion monitoring.

NTH: Part I and Part II

Re-alkalisation of two 13 storeyed buildings at the Norwegian Institute of Technology, University of Trondheim.

The two 13 storeyed buildings suffered from rebar corrosion due to carbonated cover. A survey revealed that the main facades which consist of rows of slender columns filled out with windows and concrete plate elements had a general carbonation problem, while along the gables, thanks to thicker cover, rebar corrosion was limited to architectural grooves.

Since the building houses offices, and lecture and study rooms a low noise level was of vital importance when choosing repair methods. The building in the foreground was rehabilitated in 1989. Here, the main facades were re-alkalised while the gables were patch repaired. During this rehabilitation it became evident that the extent of rebar corrosion along the gables was larger-than anticipated.

The second building, in the background, was rehabilitated last summer (1993). Here, both the main facades and the gables were re-alkalised.

About 2000 m² were re-alkalised in 1989, while the treated area in 1993 was about 3000 m². The re-alkalisation treatment time was generally between 3 and 5 days. Both contracts, including necessary patch repair and painting for cosmetic purposes after treatment were completed within approx. 2 months.

The works were supervised by the clients as well as the consultant. The client, the Norwegian institute of Technology, University of Trondheim, used the works as thesis material for civil engineering students. The students' work last summer included an inspection to evaluate the durability of the 1989 re-alkalisation. The thesis will not be available until after contesting, but we have been told that no reduction in alkalinity, nor any corrosion, has been discovered in the re-alkalised areas. We therefore expect that the thesis will provide further evidence which will re-confirm that re-alkalisation is technically, practically and commercially a sound technique.

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