The long-term performance of the materials out of which breakwaters and coastal protection works are constructed depends not only on physico-chemical degradation processes but also on the mechanical abrasion resistance of the rock or concrete used. The abrasion of breakwater armourstone affects the armour layer stability directly by causing weight loss from the rock blocks. Another important though unquantified source of stability reduction in the armour layer is the progressive rounding of armour by abrasion leading to poor interlocking between individual blocks and their neighbours (see the discussion of this phenomenon by Dibb et al. 1983). Gupta (1985) and others have demonstrated that there is a relative decrease in aggregate (macro)porosity for rounded compared with angular fragments. Such a decrease in an armour layer porosity due to the rounding of blocks may have a deleterious effect on energy absorbing properties of the layer. The assessment of abrasion resistance is therefore of great interest to the engineer concerned with in-service deterioration of armour layer performance. New quantitative methods for measuring the effects of abrasion on the entire profile of the breakwater armour layer were reported by Latham & Poole (1986). Several standard engineering tests and analytical procedures have been recommended for the assessment of suitability of a particular rock for breakwater core and armour material (Fookes & Poole 1981; Allsop et al. 1985). The test values recommended for acceptance by Allsop et al. are drawn from a list of tests which does not include an abrasion resistance test, although several abrasion

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