120 F. M. GUMMOW. 



is claimed an increase of strength, either by adhesion or 

 mechanical means. 



The mechanical means to assist the adhesion of the con- 

 crete to the iron becomes unnecessary in all such concrete- 

 iron constructions, which, besides strength, take due con- 

 sideration of the preservation of the iron, by using such 

 concrete mixtures, which experience has proved to be 

 water-tight. The mixtures usually adopted are one part 

 cement, two parts of sand, with aggregate not exceeding 

 three parts of gravel or small broken stone, which when 

 used in a plastic state, can be relied upon to surround the 

 iron so thoroughly and closely that the preservation of the 

 iron is ensured, besides creating sufficient adhesion for all 

 practical purposes, as has been demonstrated by exhaustive 

 tests and experience. 



Concrete-iron constructions built with poorer mixtures 

 may be cheaper in the first place, but such saving is obtained 

 by sacrificing thereby the perfect preservation of the iron, 

 one of the most important factors of such combination, 

 besides reducing the adhesion between the two materials, 

 so that mechanical means must be resorted to, to make up 

 for the loss. The form of such mechanical means may take 

 numerous shapes, and has on that account been taken 

 advantage of to form distinctive features for various 

 systems advocated by competing firms as offering special 

 advantages. 



The above description outlines the most general applica- 

 tion of concrete-iron, and as all other applications embody 

 more or less the principles enumerated, only two specific 

 types will be further noticed, viz.: — 1. Its use in the manu- 

 facture of piles, sheet piles, etc., which present a novel 

 feature, inasmuch as that they can be driven similarly to 

 those of timber. 2. Its use in the manufacture of pipes 

 for water supply purposes, and as such subject to internal 

 stresses. 



