Through efficient concrete moisture control, cracked and fractured balcony accesses at Denmark’s oldest hospital were successfully renovated.

It is not often that the hospital itself is the patient, but that was precisely the case with Esbønderup Hospital, which underwent extensive renovation between 2000 and 2005 to remedy serious cracking of the concrete in the hospital’s balcony accesses.

The concrete structure had suffered from various types of damage caused by alkali silica reactions and freeze/thaw action: comprehensive cracking to the bottoms of balcony access plates and to some of the protruding cantilever beams, and also, importantly, to the concrete flooring of the access balconies. Moreover, consequential damage in the form of leaching with the formation of stalactites, stalagmites and curtains was also found.

And to top it all, the patient – i.e. the balconies – were suffering from rust flaking on the reinforcement bars of the balcony parapets caused by the thinness of the concrete cover. If the balconies were to survive, action had to be taken against the moisture that was slowly but surely destroying the concrete.

No clear solution

The County of Frederiksborg, which is responsible for the maintenance of Esbønderup Hospital, had been watching the deterioration in the condition of the balconies with some anxiety for a number of years. The technicians and engineers agreed that the damage was accelerating, but that there was no clear solution as to how it could be remedied.

"The visual inspection of the concrete balcony accesses at the hospital were showing clear signs of water ingress into the concrete caused by the cracks. Sporadic repairs involving the surface treatment of the balcony floors had been attempted, but this failed to stop the formation of cracks. It was concluded that comprehensive renovation was required if the balconies were to be saved - that was if they were repairable at all", as architect Kai Clemmensen from the Property Department of the County of Frederiksborg put it.

The cause of the trouble were alkali silica reactions

The fatal cracking was the result of alkali silica reactions, which had created tensile stresses in excess of what the concrete floor could withstand. Esbønderup Hospital was designed in 1970 when the 1949 concrete standard was still applied. This standard is not considering alkali silica reactions and therefore there were no requirements intended to prevent this damage.

Moreover, the joint sealing intended to absorb the temperature deformations in the balcony accesses was not tight, and rainwater had leached in dissolving some of the calcium hydroxide in the concrete.

Renovation strategy

Whilst it is not difficult to stop leaching in the concrete and corrosion to the reinforcement, repairing cracks in the concrete caused by alkali silica reactions is a different matter. Normally such repairs will not last long, as it is not possible to return the concrete to its original condition. On the other hand, it is possible to stop alkali silica reactions so new cracks are avoided and old cracks do not get bigger, as engineer Ervin Poulsen, who was consultant to the County of Frederiksborg for the renovation of Esbønderup Hospital, knew, and he had a remediation strategy ready.

"Water causes problems, and therefore the water must be led off", says Ervin Poulsen. He continues, "In this case it was a question of removing the moisture and inserting an efficient seal, which could keep water out in future. We decided to cover the balcony accesses with plastic film to protect against further water intake. In addition, we replaced the floor and a watertight membrane was laid on the 50-metre long balcony tops and a water repellent, diffusion-open protection on the lower sides. The renovation of the balconies at Esbønderup Hospital gave us here an opportunity to demonstrate new methods and technologies, in that the method for the drying out of the concrete was not unknown in Denmark at that time, but it had never been used consistently", explains Ervin Poulsen.

Measurements document damp value

The salient point in Ervin Poulsen’s renovation strategy was whether the moisture in the concrete could be removed to the extent needed for alkali silica reactions to “hibernate”, and consequently it was crucial to obtain valid data which could document the drying-out process.

Specialist Brian Kofoed from FORCE Technology was the man behind the many measurements made prior to, during and after renovation of the balcony accesses at the hospital in the North of Sealand. 

"FORCE Technology carried out the current condition analysis of the damaged concrete structures and thus contributed to identifying the causes of the whole problem. We were well acquainted with the extent of the damage and the renovation strategy, so we started on moisture measurements three months prior to the actual renovation work. Using six different moisture measurement probes, we were always up-to-date with the degree of water saturation. The measurements were made both with portable and permanently mounted probes and gave both a detailed and varied picture of the drying-out process", explains Brian Kofoed.

After some three months of measurements the moisture content of the concrete had stabilised at a level where renovation work could begin, but in order to completely document the process, measurements were performed over a 4-year period. 

"The detailed measurements were the determining factor for the entire process. No steps were ever taken until measurements documented that moisture level was within the acceptable range. One could say that the measurements gave the go-ahead for the subsequent step in the process", says Ervin Poulsen.

FORCE Technology ensures knowledge transfer

Renovating hospital buildings presents many challenges because many factors must be considered - not the least of them being the hospital’s patients. The damaged balconies were part of a ward at Esbønderup Hospital and the County had made it a requirement that it should remain in full operation throughout the renovation work. And it did.

"This has been a successful process and the comprehensive documentation has confirmed that we made the right choice of renovation method. Our own engineers were in close communication with FORCE Technology and the consultants, and knowledge has been transferred to us on an ongoing basis. We believe that the method sets a precedent and can be used on other county buildings ready for renovation", says Kai Clemmensen.