against corrosion damages in the long term. The optimal shape of a single layer armour unit combines the robustness of a compact concrete body with the slenderness required for interlocking. The structural integrity is normally confirmed by finite element calculations (FEM) and prototype drop tests. Although both wooden and steel moulds can be used to construct the Xbloc formwork, steel moulds are preferred as they can be used repetitively to produce large numbers of armour units. Various mould designs, consisting of 2 sections, are applied. The moulds are either vertically or horizontally assembled. Pouring and compaction of concrete is done simultaneously. An appropriate formwork design is facilitating the stripping of the moulds at an early stage and prevents to large extent from honey combing, surface bubbles and striking damages. Due to the shape of the Xbloc unit, a relatively simple formwork can be used which is made of a limited number of different steel plates. Since a single Xbloc unit can weigh up to 45 tons, the construction is done as close as possible to the area of application. Placement In contrast to the placement of other interlocking concrete blocks, the Xbloc unit does not require very stringent specifications about the orientation of each unit on a breakwater slope. Because of the shape of the Xbloc, each of the 6 sides of the unit is efficiently interlocking. Therefore, the blocks easily find a position that fully activates the interlocking mechanism. This increases the efficiency of placing armour units on a slope. Due to the random structure and high porosity of an Xbloc breakwater, an artificial reef habitat is created for marine fauna and flora. XblocPlus DMC came to the market in 2018 with the XblocPlus. The name suggests an improved version of the Xbloc, but that is not the case. It is a block that works in a different way, and therefore also has its own advantages and disadvantages. The XblocPlus is a block that needs to be placed regularly and therefore has characteristics that one also finds in placed blocks such as natural basaltic columns or concrete placed blocks like Basalton. The development of this block started in particular because DMC saw opportunities for the Afsluitdijk improvement that started in 2018. Here this block is used in the wave impact zone, the block in this context is called the ‘Levvel-block’, after the joint-venture that improves the Afsluitdijk. The Basalton