Armor Unit Comparisons

Economic Advantage

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

The following table indicates the costs of various armor units relative to Core-locs including an allowance for the royalties:

Table 1: Costs of different armor unit types relative to Core-locs.

Core-loc Accropode Dolos Tetrapod Cube
100% 123% 135% 235% 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 the licensee CLNA 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” armor 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. To illustrate the significance of this concept the following Table 2 shows the equivalent sizes and total number of units that would have been required for the Port St Francis (South Africa) breakwater:

Table 2: Comparison of armor units for equal total volumes of concrete. Case Port St Francis.

Unit Mass (t) Number of Units Total Concrete
Mass (t)
Design Wave
height (m)
3-D Image
Core-loc 15.0 800 12 000 7.1
Accropode 11.8 1 017 12 000 6.0
Dolos 6.3 1 905 12 000 5.1
Tetrapod 3.2 3 750 12 000 4.1
Cube 2.2 5 454 12 000 2.6


Table 2 shows that Core-locs are relatively larger and more stable than other units for the same volume of concrete. 

Alternatively if all units were designed to survive a similar wave height, the relative unit size (Accropode, Dolos, Tetrapods, Cube) would be greater than the Core-loc size as illustrated in the economic comparison in Tables 1 and 3. 

It must be borne in mind that many other factors will apply in the final design of a specific breakwater such as plant capability, access, materials availability, typical sea conditions that affect visibility and ease of construction, breakwater crest and slope design. 

Table 3: Comparison of armor units for equivalent design wave height. Case Port St Francis.


Mass (t)

Total Concrete Mass (t)

Total Concrete Mass (%)

Design Wave height (m)

3-D Image



12 000





14 400





17 800





29 400





33 000



Table 3 shows the cost saving that can be expected when using Core-locs. The choice of stability coefficients, armor slope angles and risk of failure criteria can influence these figures, but the cost savings shown here reflect values typically used for design purposes.