Waterproof and self-healing concrete for Paleis Het Loo

The large-scale renovation and rebuilding of Paleis Het Loo in Apeldoorn poses considerable challenges. Also when it comes to the concrete work. For example, how can the watertightness of the more than eight-meter-high underground extension be guaranteed? How should the limited available space be dealt with? And how can the enormous loads on the formwork best be absorbed? This was right up Budobouw BV from Zwolle, which was commissioned by and worked closely with BAM Bouw en Techniek - Regio Oost to provide all the concrete work for Plot 2. From the construction of the new, underground foyer and pavilions to the concrete works for the renovated East and West wings and including the concrete floor and concrete roof for the office and energy building.

For the expansion under the Bassecour (the forecourt), BudoBouw BV was able to use a temporary building pit made of underwater concrete and grout walls. "In this cofferdam a levelling and insulation layer of cellular concrete was applied, on which we poured the concrete floor," director Denis van Wijk and company manager Jeroen van Ostaijen of BudoBouw BV tell us. "On this concrete floor, both walls with double-sided formwork (concrete-setting box and closing box) and single-sided walls were applied, after which the concrete was also poured here." A Self-Healing Agent additive was added to the concrete for the basement floor and basement walls. "This additive consists of pellets that contain spores, an activator and nutrients. When groundwater enters the concrete structure due to unexpected (hair) cracking, these spores autonomously develop into bacteria that eat the nutrients present. This releases limestone and seals the crack, preventing leaks. When no more water enters, the bacteria automatically convert back into spores after which - in case of any new crack formation - the healing process repeats itself."

Large forces

A fantastic solution, but one that also poses challenges. "This is because this waterproof and self-healing concrete puts different, larger forces on the 8-meter-high formwork," said Van Ostaijen. "This is why we were involved by BAM Bouw en Techniek - Region East as early as the design phase to determine the best suited formwork, correct working methods and most suitable pouring sequence for this work." In consultation with formwork specialist Doka, BudoBouw BV decided to place more braces and large, steel yokes, which would transfer the additional forces toward the floor. For the first floor of the extension, a combination of wide slabs and hollow-core slabs with steel beams was chosen, allowing for large spans. "In the deck of the underground extension there will be a special, curved construction of masonry. To make this so-called vault possible, we had a plastic mold made to size that is set on site. Then the concrete floor will be poured over this."

Renewal and aggravation

For the renovation of the Oostvleugel, BudoBouw BV partly renewed and reinforced the existing construction to enable higher user loads. The concrete specialist from Zwolle is realizing here, among other things, the concrete piles, elevator wells and floors and is replacing the existing masonry. The contract for the West Wing is expected to be awarded soon.