4o; 



Journal of Agriculture. 



[8 July, 1907. 



In all ordinary cases, the strength of the concrete is that of the cement 

 mortar or "compo," so that it is best to have the metal with as few \oids 

 as possible, the metal being cheaper than the "compo." This end is 

 achieved by using gravel or metal screenings with the metal, thus to a 

 large e.vtent reducing voids. Brieflv, the office of the metal and gravel 

 is to enable a comparatively small amount of cement mortar to occupy a 

 large volume without any serious diminution of its strength. The process 

 is carried so far as to permit the use of large boulders weighing several 

 hundredweights each, imbedded in the mass of the concrete. The voids 

 can be found by filling a kerosene tin with the metal or gravel, making a 



THE CONCRETE SILO, BALLARAT ORPHAN ASYLUM. 



lailk of 4 gallons; the whole is then weighed, allowance being made for 

 weight of the tin. Water is poured in until flush with the surface and 

 the tin with its contents is again weighed. As water weighs 10 pounds to 

 the gallon, the difference in the two weights will give the void space in 

 gallons and thus the percentage is arrived at. For instance, a kerosene 

 tin full of metal weighed 60 pounds deducting the weight of the tin. 

 When filled with water, it weighed 78 pounds. Consequentl\- the void 

 space was represented by 18 pounds of water while the whole volume, 

 4 gallons, weighed 40 pounds. Thus the percentage of void was found to 

 be 45. A good mixture in this instance would be 6' parts of metal, 

 2 parts of sand, and i part of cement. 



