The poor structural condition of the Valkenburg monument, built in 1906, was well known. Major maintenance had been planned ever since concrete decay was identified in 2002, but it had never been carried out – something Professor Nijsse says is not uncommon.
Monument preservation
His impression is backed up by the Cultural Heritage Agency of the Netherlands (RCE) which states that 14% of the monuments registered with them are in poor structural condition. “That doesn’t necessarily mean they are on the verge of collapse,” the RCE adds. Out of 63,000 listed monuments, nearly 9,000 are in a bad state. “So we can very likely expect more of these collapses in the future,” Nijsse concludes.
This poor state of maintenance is no coincidence – it is, unfortunately, typical for monuments. Before major maintenance work can be carried out, the owner must first obtain permission. The costs are usually extremely high due to the use of outdated techniques and inferior materials. On top of that, subsidies for such restorations are limited, meaning that owners have to invest a significant amount themselves. And not everyone can – or wants to – do that.
Concrete crown
The concrete decay mentioned in the media, was limited to the concrete crown added in 1930 on top of the original marlstone tower, says Nijsse. The concrete crown, featuring an illuminated cross, replaced a wooden roof which had been blown off multiple times. Concrete decay involves water infiltration, rusting reinforcement bars, and flaking concrete fragments.
“But underneath that, you have the original marlstone tower from 1906. The masonry was probably never of particularly high quality, and after more than 100 years, it had likely reached the end of its lifespan.”
Nijsse recalls factory chimneys collapsing in the 1970s due to the behaviour of poorly constructed masonry under pressure. In his view, it is no coincidence that the tower gave way on a cold night following one of the first warm days of the year. What happens in such conditions?
“By mid-March, the sun is already quite strong during the day, heating up the tower’s south side, causing it to expand. Meanwhile, the north side remains in the shade and stays cold. This results in an uneven expansion, creating tensile stress that pulls apart the mortar joints. At night, everything contracts again. The off-centre concrete crown, with its uneven weight distribution, likely delivered the final push that caused the tower to collapse.”
Reconstruction
The Dutch broadcaster NOS reports that Valkenburg’s mayor, Daan Prevoo, is working with the Cultural Heritage Agency to assess what can still be salvaged of the tower. He hopes to fund its reconstruction through crowdfunding.
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