PROPERTIES OF PORTLAND CEMENT. 



397 



sound cements was lowered by additional seasoning. These changes were 

 attributed to the slaking of lime and subsequent reaction with carbon 

 dioxide, the lime thereby being rendered an inert substance. It was 

 pointed out that only those cements which contained an excess of lime, 

 or which were improperly burned, were improved by seasoning. Because 

 of these and other considerations the belief was expressed that underburn- 

 ing is fatal to the efficiency of Portland cement to be used in the Tropics, 

 and exception was taken to the published statements of several author- 

 ities on this subject concerning the significance and value of the specific 

 gravity and soundness tests. 



As our studies of aerating cements progressed we soon convinced 

 ourselves that different methods of seasoning and storing the same 

 cement produced different effects upon its physical and chemical prop- 

 erties, and that different cements were influenced in unlike manners by 

 the same conditions of seasoning. Consequently, we found it necessary 

 thoroughly to consider all of these questions in our work. 



THE SEASONING OP GROUND CE1IENT. 



The penetration of air into a mass of undisturbed commercial cement 

 is shown in Tables IX and X. 



The same experiment was repeated on a larger scale with brand 

 cement. 



About 2 kilograms of Portland cement (brand U, Table A) were placed in an 

 open, cylindrical glass jar. The cement was not packed nor tamped, but was 

 rendered only slightly compact by tapping the sides of the cylinder. In this 

 manner it was exposed in the laboratory for one month during the dry season, from 

 August 24 to September 24, 1908, at the end of which time samples were taken 

 from different depths and the percentage of loss by ignition, moisture, and 

 carbon dioxide in each determined. (Table IX.) 



Table IX. — Penetration of air into undisturbed cement. 



Sample number. 



Average dis- 

 tance from 

 surface 



Loss 

 by igni- 

 tion." 



Carbon 

 diox- 

 ide. 



Mois- 

 ture. 1 " 



1 ._ 



mm. 



0- 3 



3- 6 



64- 13 



13i- 25 



254- 51 



51-127 



1274-203 



Per ct. 

 8.96 

 7.57 

 4.89 

 4.44 

 4.44 

 4.34 

 4.34 



Per ct. 

 4.86 

 3.68 

 0.92 

 0.72 

 0.67 

 0.65 

 0.65 



Per ct. 

 0.97 

 0.77 

 0.66 

 0.55 

 0.51 

 0.43 

 0.44 



2 



3 _- 



4 _ -. _ 



5 _ 



6 







1 Since only part of the combined water is driven off at a low red heat, the percentage 

 of the latter can not be determined from this table. However, Table XII gives us this 

 information. 



b The term "moisture" refers to water which is expelled below 110°. 



