396 REIBLING AND REYES. 



Part II. 



THE SEASONING OF PORTLAND CEMENT. 



The practice of exposing unsound Portland cements to the atmosphere 

 until they became sound dates back to the beginning of their manufacture. 

 Although certain producers in Europe grind their cement in the presence 

 of live steam and others weather their clinker in the open, unprotected 

 from the sun and rain, the majority of cements still are seasoned under 

 cover by aerating the clinker or the ground material in storage bins. 



Much has been written on the subject of aeration, 20 but the various 

 conclusions which have been drawn to explain results so diversified have 

 tended rather to promote confusion than certainty. 



Seasoning improves the soundness of unsound cements and therefore 

 an almost universal belief seems to. exist that seasoning improves all 

 Portland cements. 



Important concrete specifications frequently demand a well-seasoned cement. 

 For instance, the rigid concrete specifications for the Galveston causeway, 30 

 require that "all cement must have been seasoned, or subjected to aeration for at 

 least thirty days, previous to leaving the mill." 



On the other hand, W. Lawrence Gadd 31 recently conducted experiments from 

 which he concluded that "Portland cement made from rotary cement kiln clinker 

 does not improve on aeration, but on the contrary becomes more expansive." 



This contradiction alone should convince the consumer that if he places an 

 age limit on Portland cement, his reason for so doing should be based upon 

 something more tangible than the simple belief that age improves it. 



Although it now generally is conceded that Portland cement properly made 

 should stand all standard tests without seasoning as soon as it has lost the heat 

 it receives in grinding, some writers, such as R. K. Meade, believe that the engineer 

 need not "concern himself whether the manufacturer prefers to make cement which 

 is sound when fresh, or whether he prefers to age it sound in his stock house. 

 Cement which has seasoned sound is just as good as one which was sound when 

 freshly made." 



The effects of aeration on commercial cements Avere discussed in a 

 previous paper from this laboratory 32 and it was shown that the changes 

 produced by aeration were often sufficient so to alter the tests as to give 

 unsatisfactory instead of satisfactory results. It also developed that ad- 

 ditional seasoning would often cause some normal cements to become 

 quick setting and others to become more susceptible to change in setting 

 time at different temperatures, and that the strength of all perfectly 



-° Candlot, M., Cement et Chaux Hydrauliques, Paris, (1891); Spalding, 

 Frederick C, Hydraulic Cement, New York (1904), 4, 56, 80; Taylor & Thompson, 

 Concrete, Plain and Reinforced, New York (1907), 62; Meade, Richard K., 

 Chem. Eny. (1907), 5, 341. 



30 Concrete (1910), 10, 52. 



11 Cement Age (1906), 6, 47. 



« 2 This Journal, Sec. A (1908), 3, 137. 



