Maintenance of historic concrete structures requires specific approach

Restoration of historic concrete is not yet a mature field. Where it still sometimes goes wrong is that companies that specialize in concrete restoration focus purely on the technical aspect of these types of objects. The uniqueness of the object does not always get sufficient attention. The National Cultural Heritage Agency makes a case for maintenance, repair and renovation of historic concrete objects while preserving their cultural-historical values.

"As the National Cultural Heritage Agency, we actually fulfill two roles," begins Michiel van Hunen, senior specialist in conservation and restoration. "We have the legal task of advising municipalities (competent authority) on any intervention in monuments, including work on historic concrete. Based on that advice, the municipality decides whether to grant the permit. On the other hand, we also present ourselves primarily as a knowledge organization. With publications, books, (knowledge base) articles and brochures we spread our message as widely as possible and reach property owners, restoration architects, contractors, engineering firms, etc."

The National Heritage Agency itself does not own any built monuments. "Those are vested in other organizations, such as the State Property Agency. So we do not develop plans ourselves, but respond to plans from the formal route," Van Hunen emphasizes. "Preferably, as a knowledge and expertise center, we are already involved in the preliminary process." For maximum "clout," the Cultural Heritage Agency also has local representation. "In each region there is a construction advisor working, among others, as well as an architectural historian, an archaeologist and a landscape architect. They are the first-line contact, so to speak, and can call on the constituency for more specialized issues, like the Monuments Department of which I am a part. I myself am a specialist in historic concrete, historic steel structures and historic masonry, among other things. Our department also employs specialists with knowledge of natural stone, bells, organs, mills, colors, wood, preservation, etc."

With concrete maintenance on historic structures, Van Hunen says it is important to pay attention to the guidelines of the foundation ERM, Erkende Restauratiekwaliteit Monumentenzorg. "They have drawn up two implementation guidelines (Concrete Restoration Advice (URL 2003) and Concrete Restoration Realization (URL 4005)) for the restoration of historic concrete. Because, as mentioned, unfortunately, the historical aspects of an object are not always taken into account by specialized concrete restorers. Suppose an object is subject to chloride degradation, in nine out of ten cases, modern structures will have the concrete replaced. With historic properties, it is important to surface a little more detail. What exactly is the chloride content? How high is the risk? Is there an alternative repair method that assumes (more) material preservation? When working on a historic property, we advocate a building history or value assessment. Historical value is layered. Before the intervention, it is important to know whether the value is in the history of use or, for example, in the architectural concept." 

A good example of such "layered value" can be seen at the famous Kazemats at Kornwerderzand, which suffer from a material problem. "They have both original paintings and bullet impacts from the war. So the value is clearly on the surface," Van Hunen emphasizes. "The trick here is to find a technical solution to stop the carbonation and ASR (alkali-silica reaction) to prevent further damage, but while maintaining the historical value. As the National Cultural Heritage Agency, we are closely involved in this along with colleagues from the region. And so we are active in many areas to endorse the importance of the historical aspects when maintaining historic concrete structures. We therefore advise to respect the guidelines of the ERM foundation when carrying out work and refer to them in subsidy decisions. We also assist owners and managers in dealing with historic concrete through articles on our knowledge base (kennis.cultureelerfgoed.nl). All with a view to maximum quality and preservation of cultural history."