122 HARBOUR CONSTRUCTION. 



" I am convinced, from recent experience, that the proportion of 

 1 of cement to 9 of gravel and sand, adopted at Fraserburgh, is too 

 weak for such exposed works. The proportion adopted for Sandhaven 

 and Portsoy, of 1 part of cement to 6 parts of gravel and sand, has 

 been proved to form concrete of more snitable strength. All the 

 plans hitherto tried along the north-east coast of Scotland, for con- 

 crete-work below low water, have been more or less inadequate to 

 withstand the strains to which 'they are subjected during heavy 

 gales." l 



For the Kustenjie breakwater the blocks were composed of 



1 part of Portland cement. 

 2 parts clean, sharp sand. 

 5| broken stone. 



When, as was sometimes the case, it was necessary to use 

 sand of inferior quality, the proportion of cement was slightly 

 increased. 



These blocks were sometimes placed in the work when only 

 twelve to fourteen days old. This is, however, in my opinion, not 

 a prudent course to adopt at all events if weight, in the shape 

 of additional blocks or otherwise, is to be shortly placed upon 

 them. 



Blocks, when stacked in a block-yard too " green," notwith- 

 standing that the greatest care may be taken, are often found 

 broken when they are again lifted. The same may happen to 

 them when placed in the work, without the fact being known, 

 and trouble or failure may result therefrom. 



In all the foregoing examples proportions were by measure, 

 not by weight. 



Concrete made with Roman Cement may often be employed 

 with advantage in exposed situations, where the wash of the sea 

 would render the use of Portland cement difficult. Owing to its 

 greasy nature and quick-setting properties, work in which it lias 

 been used will resist the action of the water, even if it should 

 come over it within, say, ten to fifteen minutes of its being 

 deposited. It should be mixed only as required, and be put into 

 the work without delay. 



Medina Cement has much the same properties as Koman 

 cement, but its nature is even more greasy. When fresh, it sets 

 a few minutes after mixing ; and it will withstand the wash of 



1 Min. Proo. Imt. C.E., vol. Ixxxvii. p. 131. 



