PHYSICAL AND CHEMICAL PROPERTIES OF PORTLAND 

 CEMENT. PART III. 



By W. C. Reiblixg and P. D. Reyes. 



{From the Laboratory of General, Inorganic and Physical Chemistry, Bureau of 



Science, Manila, P. I.) 



THE SETTING PROPERTIES OF PORTLAND CEMENT. 

 GEKERAL CONSIDERATIONS. 



A study of the important hardening properties of Portland cement 

 concerns itself with two essentially different processes. The preliminary 

 one by which the soft or plastic paste is converted into a friable mass is 

 termed the "setting" and is so distinguished from the subsequent "hard- 

 ening," which is slow, long continued, and practically permanent. 



Experience has shown that the efficiency of Portland cement is vitally 

 affected by the way in which it sets, and although manufacturers are now 

 producing a product which is rapidly becoming more and more uniform, 

 certain Portland cements are still encountered the setting properties of 

 which are erratic, undesirable and at times even dangerous. The manu- 

 facturer usually succeeds in making a cement which sets nonnally, but 

 he often fails to produce one which will remain so under all ordinary 

 conditions of storage. Therefore, it frequently happens that a cement 

 develops unsatisfactor}^ setting qualities after it has left the mill. Un- 

 fortunately, when this occurs, so little is known of the phenomena which 

 have caused the change that it has often proved impossible to find a 

 remedy against its recurrence. The practical problem in this respect, 

 therefore, concerns itself essentiall}- with the control of the set. 



Scientific knowledge on the subject has remained very limited and 

 indefinite, because of the experimental difficulties in isolating and iden- 

 tifying hydraulic compounds which decompose or become altered on 

 contact with water, and the individual particles of which are largely 

 sub-microscopic. Eesearch work, founded on observ'ations of physical 

 changes have only served to supply the manufacturer with contradictory 

 and inexplicable data. We believe this to be due to a somewhat general 

 misconception of the true nature of Portland cement, the investigators 



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