MATERIALS. 121 



The proportions of Portland-cement concrete used in making 

 the blocks for the south breakwater at Aberdeen were 



1 part Portland cement. 



4 parts sand. 



5 gravel. 



Large pieces of rubble stone were also incorporated. 



For the Colombo breakwater the proportions used were 



1 part Portland cement. 



2 parts sand. 



6 broken stone. 



The moulds were removed from these blocks after a lapse of 

 three days. Blocks were lifted and stacked when three and a 

 half weeks old, and they were set in the work when six weeks 

 old. 



At Newhaven (Sussex), the proportions used in the concrete 

 for bag- work and mass -work, of which the breakwater is entirely 

 composed, were the same, viz. 



1 part Portland cement. 



2 parts sand. 



5 shingle. 



At Fraserburgh, the proportions first adopted for bag-work 

 were 



1 part Portland cement. 



7 parts sand and gravel. 



But as the current increased with the extension of the break- 

 water, it was found necessary to reduce the proportion of sand 

 and gravel to 4J. 



The proportions used for mass-work during fine summer 

 weather were 



1 part Portland cement. 

 9 parts sand and gravel. 



During more stormy weather, the proportions used were 



1 part Portland cement. 

 7 parts sand and gravel. 



At each of the harbours of Portsoy and Sandhaven, the pro- 

 portions used in the piers were 



1 part Portland cement. 

 6 parts sand and gravel. 



In the paper on these harbours, which the late Mr. Willet 

 read before the Institution of Civil Engineers, he stated 



