Production & Placement

Which parties have been involved in the development of the shape of the mould?

The mould has been developed utilising expertise of concrete specialists as well as mould specialists. Based on their advice different types of Xbloc® moulds have been developed. The choice of a particular mould option can be made by the contractor depending on his preferences. The four Xbloc® prototypes, each 4 m3 in size, were cast using a horizontal mould. With this type of mould, the upper nose of the Xbloc® is cast on top of the X approximately one hour after the rest is cast. The prototype drop tests indicated that this had no affect whatsoever on the strength of that particular nose. In a later stage in the Xbloc® development vertical formwork was constructed and used for Xbloc® unit production.

For the Xbloc project on Guam 8 m3 Xblocs are cast using the horizontal mould. The Xblocs are lifted from the mould with lifting anchors. Photos can be found here

How can we get the Xbloc® mould for our preferred sizes?

Depending on the required Xbloc® unit size, ready-for-use Xbloc® moulds may be available for the contractor. Please contact Delta Marine Consultants to check mould availability. If no existing moulds are available, steel moulds can be ordered through DMC. Alternatively it would be possible to have the moulds manufactured locally using the mould drawings provided by DMC.

How do you compact the concrete?

The concrete may be compacted using vibration pokers as used in standard concrete works. The nose of the Xbloc® can readily be compacted by providing an opening in the nose of the mould.

What is the production rate of the Xbloc®?

Under normal circumstances it should be possible to attain a 1-day production cycle. In cold weather conditions additional measures may have to be taken to achieve this production rate. Using adjusted formwork (Bar Beach, Nigeria)  and under good circumstances even 2 Xbloc® units can be made per mould per day.

After how many days can the block be transported?

The unit can be lifted as soon as a compressive strength of 15 MPa is reached. This value may be typically reached after 3 depending on the conditions. Feel free to contact us to provide you with indications for your specific project. In some projects it has been possible to move the Xbloc units with a shovel equiped with a modified fork after 1 day.

What other specifications are applicable?

The complete specifications and recommendations are included in a document that can be obtained by Delta Marine Consultants.

What are the requirements regarding placement?

The recommended placement density depends on the size of the unit and may be found in the design table. The required placement density must lie between 98 % and 105 % of the recommended packing density. Furthermore each Xbloc® must be secured by two other units and must be in contact with the under layer.

Are the Xbloc® units easy to place compared to other units?

Yes, this is one main advantage of the Xbloc® unit compared to other single layer units. Due to its shape the unit can readily find a stable position on the slope. In contrast to other single layer armour units no orientation of the unit is specified which further increases the placement speed.

If Xbloc® are so easy to place, why does Delta Marine Consultants have to provide assistance?

DMC experience with Xbloc® placement is invaluable and is essential to ensure swift unit placement together with good packing density. Assistance from Delta Marine Consultants during unit placement is included in the royalty fee.

Is the assistance of divers required for placement under water?

Due to its shape the Xbloc® units are easier to place than other single layer units. This decreases the need for assistance from divers, but it is normally advisable.

How fast can Xbloc® be placed?

From experience with unit placement in the Xbloc® projects that have have been completed and that are under construction, and in scale models (including slope construction for the model tests) it was found that the Xbloc® armour units are more straightforward and faster to place than other single layer armour units. This is due to the symmetry and the number of interlocking faces of the Xbloc® unit: the unit can easily find an interlocking position. However, the exact placement rate is dependent on the project specific conditions. Placement rates of up to 40 Xblocs per hour have been achieved with an excavator placing 2 m3 Xblocs above water. Typically Xbloc placement rates ly between 8 and 25 blocks per hour, depending on the location, above/below water and use of excavator or wire crane. Please contact us for more information.

What equipment is required for unit placement?

The units may be placed using a crane equiped with a sling, a hook or a clamp. The optimal position of the units during placement is with a leg of the unit pointing downwards, ensuring easy placement. A clamp may also be used in combination with notches in one of the legs of the unit.

How do you deal with loose Xbloc®?

Loose blocks should simply be replaced to enhance interlocking capacity.

What is meant by random unit placement? Does it mean that the units are thrown onto a slope?

Random placement means that the orientation of the units may vary. This does not mean that the units are thrown upon the slope. The units are placed individually, one by one upon a slope, just as with heavy rock and other armour units.

Do the sharp edges of the unit, suffer damage during handling and placement?

Some minor damage may occur, but this does not affect the strength or stability of the unit.

How do you realise the required packing density in practice?

When the advised horizontal distance between the units is achieved, this will result in a placement density within the required range of the specified placement density. A properly placed bottom row of units will specially contribute to achieve this density. Furthermore, in each project the placement should normally start with a trial placement of the units during which the crane driver and other supervisors will be guided by an experienced Delta Marine Consultants specialist.