150 



REIBLING AND SALINGER. 



Many engineers maintain with good judgment that a cement should 

 not develop dangerous properties on exposure to tlie air and if it does 

 so it merits rejection, especially if the unexposed samples show irregular- 

 ity, since it is only practicable to test one barrel out of every ten or 

 twenty in stock. It is also true that barrels often become Ijroken in 

 shipment, and should the cement which is so received develop dangerous 

 properties, the strength of a whole structure might be weakened by its 

 use. 



Portions of the original samples of the cement the tests of which are 

 recorded by diagrams numbers 1 and ,8 were preserved and the tests 

 after aeration in paper bags are shown in Table XII. All of these tests 

 were manipulated in the same laboratory, and they show that this 

 cement is more or less readily subject to the influence of aeration. 



Table XII. — Test of cement shoion in diagrams numhers 1 and 2, after aeration in 



paper iags. 



Sample No. 



Initial set, in minutes, after 



storage in paper bags tor 



ttie times given. 



Range of 



Specific gravity after- 



tempera- 

 ture dur- 

 ing set- 

 ting. 



Storage in bags. 



1 



Heating 



to red 



heat, 23 



weelis' 



exposure. 



1 day.« 



31 days." 



23 weeks.* 



31 days. 



23 weeiis. 



XI 



220 

 130 

 120 



140 

 110 

 85 



45 

 65 

 30 



°C. 

 27-30 



27-30 



27-30 





3.02 

 3.03 

 3.02 



3.14 

 3.14 



X2 - 



3.06 

 3.02 



X4 . 





1121 per cent water. 



'22 per cent water. 



THE DISPOSAL OF CAKED CEMENT. 



It is usually specified that cement shall be screened through a 20-mesh 

 sieve and thoroughly mixed before testing. The object of the sieving 

 is to break wp lumps and remove wood splinters, stones and other foreign 

 substances. Such a procedure is of course proper. However, under 

 certain conditions, the disposal of caked cement when it is present in 

 considerable quantity should be more fully described. 



Cement literature has repeatedly pointed out that the tensile strength 

 of a caked cement is considerably below that of the original material 

 before it formed lumps. This is due to the absorption of moisture and 

 the subsequent partial setting. The difference that may result from 

 such a change is illustrated in Table XIII, which gives the tensile strength 

 developed by two samples of the same cement, one free from lumps and 

 the other caked. 



