PORTL/VND CEMENT TESTING. 



149 



effect of exposure is considerable, troublesome variability of the brand 

 may be readily attributed to this cause and the manufacturer will then 

 know how to improve his product accordingly. 



Changes caused by the atmosphere penetrate very slowly into the mass 

 of the cement in l^arrels, because the wooden staves and heads keep the 

 air from the produc't to a considerable extent and tlie nuxss of material 

 is large, therefore, alterations whicli may develop very rapidly in a small 

 sample exposed in the hiboratory would not take place in the barrel 

 until a iiuieli longer period of time liad elapsed. Spalding '^- states that 

 "the effect upon cement of retaining it a long time before using depends 

 upon the nature of the cement and the method of keeping it. When 

 the cement is inclosed so as to prevent the access of air, as in barrels, it 

 may usually be preserved for a considerable time without experiencing 

 anj^ alteration, provided it is ke|)t dry." 



The fact that cements stored in good barrels undergo very little 

 change by a month's seasoning is illustrated by the original and the 

 re-test of the following cement,' the results of which are recorded in 

 Table XL The samples for the re-test were taken a month after the 

 original ones. All the sampiles were protected from aeration before 

 testing, and the re-test gave only slightly, lower results, although sub- 

 sequent experiments showed that the cement rapidly deteriorated in 

 time of setting and tensile streng-th when subjected to air exposure. 



Table XI.° — Original and re-test {one month later) of cement stored in barrels. 



ORIGINAL TEST. 



Sample No. 



Fine- 

 ness. 



Sp. gr. 



Initial 

 set. 



Final 

 set. 



Tensile strength, neat. 



Tensile strength, 

 1: 3 mortar. 



Iday. 



7 days. 



28 days. 



7 days. 



28 days. 



1 - __- 



95. S 

 96.5 

 96.2 

 96.0 

 97.0 



3.07 

 3.07 

 3.08 

 3.08 

 3. OS 



h. m. 

 2 10 



2 15 



2 10 



2 10 



2 00 



h. m, 

 5 00 



5 10 



5 00 



5 00 



5 00 



392 

 351 

 354 

 351 

 312 



516 

 563 

 532 

 558 

 542 



640 

 605 

 687 

 610 

 653 



240 

 200 

 221 

 232 

 222 



285 

 278 

 300 

 296 

 300 



2 



S 



4 



5 



.Average - 



96.3 



3.08 



2 9 



5 2 



352 



542 



639 



223 



292 



RE-TEST ONE MONTH LATER. 



1 



94.5 

 94.0 

 95.0 

 94.7 



3.08 

 3.08 

 3.08 

 3.08 



2 25 

 2 20 

 2 20 

 2 10 



4 20 

 4 15 

 4 40 

 4 35 



322 

 349 

 312 

 325 



570 

 566 

 531 

 5.59 



594 

 621 

 583 

 612 



210 

 195 

 200 

 199 



283 

 278 

 300 

 281 



2 



3 



1 



4 



Average _ 



94.5 



3.08 



2 19 



4 28 



327 



556 



G02 



201 



285 



"^The soundness of all samples was satisfactory. 



71978- 



^-Ibid., 67. 



