Core-loc™ is a concrete armour unit for breakwaters and shore protection works.

The Core-loc™ concrete armour unit which is patented by the United States Army Corps of Engineers represents the latest technology in armour units. The unit has been used in coastal breakwater structures since 1996 when PRDW (then AR Wijnberg Inc.) pioneered the first application at Port St Francis in South Africa.

There are currently more than 65 structures worldwide where Core-loc™ have been used. The development of the Core-loc™ represents the culmination of many years of research at the US Army Waterways Experiment Station’s Coastal and Hydraulics Laboratory (CHL). The armour unit has been developed to produce an efficient use of concrete with sufficient strength and robustness to achieve a cost effective, highly stable structure.

The Core-loc™ is available world wide through a network of five exclusive international licensees covering specific geographical areas of the world. The licensees work together with CHL on research and development, project technical advice and quality control to support users in the appropriate and correct use of the unit.

A royalty for the use of the unit is charged to cover the development, research, and project specific technical assistance on design and construction. This advice is available to the project owners, project designers and construction contractors.

PRDW is the licensee for United States of America, Mexico, Canada and Parts of Africa and surrounding Islands.

Economic Advantage

Published research has shown that the Core-loc™ offers improved stability over other armour units, permitting a single layer of armour with higher stability and lower cost in many applications.

The costs of various armour units relative to Core-locs, including an allowance for the royalties, is indicated below:

> Core-loc™ = 100%
> Accropode = 123%
> Dolos = 135%
> Tetrepod = 235%
> Cube = 247%

In addition to the savings produced by using the Core-loc™, the project benefits from the technical back-up and quality control input of PRDW and the licensor CHL.

Design Philosophy

The design philosophy of the Core-loc™ is based on the use of a single layer of units. Slender interlocking units with high voids ratio such as dolosse can be lighter than the equivalent stable concrete cubes. Such slender units need to be placed in a double layer to allow for movement and breakage. Cubes on the other hand are robust but need to be more massive because of their lower stability characteristics. The Core-loc™ is intended to benefit from both good interlocking characteristics and the intrinsic strength of a more bulky unit.

A “single layer” armour system is sometimes incorrectly interpreted as less reliable than “double layer” systems. To compare the reliability with which units can be applied, the same volume of concrete should be considered. If a “double layer” approach is to use the same volume of concrete as that of a single layer, it implies that its unit size needs to be decreased to achieve the required coverage, increasing the number of units to be placed. A reduced unit size implies a reduced design wave height that the structure could withstand.

Project Enquiry

If you would like to investigate the use of Core-loc™ for a specific project please contact us with the following information:

> Project location
> Preliminary layout (if available)
> Range of water depths along structure location
> Design wave information

Please e-mail project information to either Gordon Prestedge at or Anton Holtzhausen at
Alternatively you can phone them on: +27 21 418 3830.

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