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AJs are high stability concrete armour units that are used in river, lake, and coastal applications to control erosion, stabilize shorelines, and provide habitat.  In open channel applications they are used for bank and toe protection, flow and grade control, bridge pier scour protection, energy dissipation, and habitat.  These small units may be fabricated in standard block machines.  In coastal applications AJs are typically used for reefs, revetments, breakwaters, and jetties and may also be used to provide habitat. The photographs below show a range of AJ sizes from 600 mm (35 kg) to 2400 mm (3.6 tonne).

Small sized AJsMedium sized AJs


AJs have a high degree of interlock and porosity, leading to high stability coefficients in waves and currents. Units may be placed in random or uniform patterns.


AJs are designed to optimize fabrication efficiency. The geometry allows for the use of very simple forms. Smaller sized units can be manufactured in conventional block machines which significantly reduces fabrication costs. Units may also be flat cast, fabricated in gang molds, and in 3-D clam shell molds.

Uniform palacement

Flat formGang formClam shell form

River and coastal AJs

River and Coastal AJs

AJs are used in both river and coastal applications. Structural loads are significantly higher in coastal applicatons and thicker AJs which are more structurally robust are used. The slender units are temed River units and the thick AJs are termed Coastal units.


AJs are placed in a single layer and have high hydraulic stability. This, combined with simple fabrication and efficient placement methods, make AJs both a stable and cost effective armour unit.