Is the Core-loc the "best" unit for all applications?   

The Core-loc presently represents  an efficient  use of concrete for breakwater armour units.  This is due to an optimised packing density and in this sense it is the best unit.  Some applications might require very large units (like cubes in excess of 100 t required at Sines, Portugal) or be prone to unsuitable or inappropriate construction conditions which would present practical limitations to the application of Core-loc.  If you are unsure about the practicality of Core-loc for a specific application contact us with the project details for an assessment.

It is more important to achieve the correct armour unit placement for single layers compared to double layers?

Yes.  While the concepts behind rubble mound breakwaters have essentially stayed the same over many years, advances in positioning and measurement instrumentation now enables much more effective control of placement and the recording of placed positions.    It should also be borne in  mind that fewer units need to be placed in a single layer compared to a double layer.  More time can therefore be spent on ensuring the correct position of Core-locs without increasing the total construction time.

What are the advantages of using Core-loc?

  • A highly robust near zero maintenace armour layer with potential cost savings over other units.
  • Typically, a cost saving of between 20 and 40 percent in general compared to double layer units. 
  • Fewer units to be manufactured and stored (fewer moulds, less storage space required).
  • Technical assistence from licensee  (CLA).
  • Assistance with  quality assurance and control.


How many breakwaters have been built with Core Loc units?

Approximately 19 breakwaters worldwide.

Does a single layer represent a higher risk of failure than double layers?

No.  If the same volume of concrete is used for a single layer than that proposed for a double layer, the single layer would be typically  much more stable than the units in the double layer.

What are typical royalty charges?

Approximately 10 percent of the armour placement cost.  If you want to compare the cost of Core-locs with other units, increase the volume of concrete by 10 percent to obtain an estimate of Core-loc costs that include the royalty.

What quality assurance measures are provided?

The established practical technical specifications provide the necessary backup for quality assurance.  Experience with application of the Core-loc is shared between Core-loc projects and provides constant input into practical solutions to some of the challenges facing the application of single armour layer construction.  The value of "having been there" goes a long way to ensure that quality can be achieved in a practical way.

What references are available on Core Loc units?

A number of projects are listed at

Who holds the Core-loc patent?

The patent is held by the U.S. Army Corps of Engineers.  Core-loc Africa holds the license for territories in Africa which means that CLA is the only point of contact with regard to the application in these territories.  However, practical experience and research is shared with other license holders and the Corps of Engineers.

What are the steps to be taken should I wish to use Core Loc?

Contact CLA with the following information:

Location and purpose of structure
Water depth at toe of structure
Expected wave climate

CLA will assist you with a preliminary unit sizing which can be used for costing purposes.  If a decision is made to go ahead with a Core-loc structure a detailed design by a competent professional  designer will be required.  Scale hydraulic models are recommended as part of the detailed design.

Where can I obtain Core Loc model units?   

A range of model units are retained by the Core-loc Licensor and Licensees of the various territories.  Available units can generally be rented at a cost of US$ 1.4/kg/week (excluding shipping and handling costs). New units can also be manufactured to exact standards within a relatively short time.  Further information both for renting and manufacturing units can be provided on request.

What are typical construction costs?

It is difficult to give a general indication of costs.  The size of the project, location and purpose can affect unit costs significantly.  For new breakwaters, the cost of quarry rock is likely to be more than the cost of concrete armour units.  Typical construction costs based on previous projects can be provided where possible  for new projects.     

What support is provided by Core-loc North America?   

The following support is included as part of a standard license agreement:            

Preliminary design
Provision of standard technical specification
Quotes for manufacturing of moulds
Assistance with model tests
Assistance with evaluation of manufacturing and placing of Core-locs   

What requirements apply to specifying Core-locs in a tender document?  

CLA needs to approve the preliminary and final design to ensure the appropriate application of the unit. The tender document should also make reference to the standard License Agreement setting out the basis for using the unit.  It will be required that the owner or contractor responsible for the project constructioin enters into the sub-license agreement under which the units will be permitted to be manufactured.  The contract needs to make allowance for this. A copy of the sub-license agreement is available on request.  

Who should I contact?   

Anton Holtzhausen (

Allan Wijnberg (