PORTLAND CEMENT TESTING. 



173 



properties, chemical examination will nsnally show that it has not the 

 proper "hydraulic index." 



Underburned cements usually have a very low specific gravity, because 

 they absorb water and carbon dioxide more rapidly than well-burned 

 cements and because all the carbonic acid may not be driven oS. during 

 the burning of the raw material. The compounds formed by underburn- 

 ing are not as stable as those of a well-burned cement and hence are 

 more readily influenced by atmospheric conditions. 



TJnderburning is readily detected by the soundness test provided the 

 cement is "fresh;'' but seasoning often eliminates the unsoundness and 

 therefore renders this test of no value for its detection. We must then 

 depend upon the specific gravity, loss on ignition, color, and other tests 

 to disclose the fact. A high loss on ignition is not characteristic of the 

 best brand of Portland cement, even after prolonged storage. 



R. & W. Fresenius -° consider "that the limiting value of the loss on ignition 

 of good Portland cement shotild not exceed 3.4 per cent." 



The following table illustrates this contention : 



Conditions. 



Cement A. 



Cement B. 



Cement C. 



Specific 

 gravity. 



Loss on 

 ignition. 



Specific 

 gravity. 



Loss on 

 ignition. 



Specific 

 gravity. 



1 

 Loss on 

 ignition. 





2.92 



3.105 



3.115 



3.59 

 0.66 

 0.27 



3.04 

 3.15 

 3.18 



1.47 

 0.59 

 0.19 



2192 



5.39 



Slightly Iritted _ 



3.00 

 3.19 



2.36 

 0.24 



Very strongly fritted _ 





3.05 



0.65 



3.05 



0.28 









Sabin -"' remarks "that the determination of water and CO, may give some idea 

 of the deterioration of a cement on storage. M. Candlot considers that in the ease 

 of Portland cement a loss on ignition (water and CO.) exceeding 3 per cent indi- 

 cates that the cement has undergone sufficient alteration appreciably to diminish 

 its strength. Spalding =* affirms that "if the quantity of CO, be large, it indicates 

 either that the burning has been incomplete or that the lime has become car- 

 bonated by subsequent exposure. The energy of the lime is thus diminished, the 

 portion of lime in combination with CO, being inert." 



While we have not enough data to cover every instance and to formulate 

 this as a general rule, it has been our experience that the absorption of 

 carbonic acid and water decreases the tensile strengtii of every sound 



"^SoG. Chem. Industry (1894), 13, 252. Ztschr. Anal. Chem. (1893), 32, 433, 



445. 



' Sabin, Louis Carlton : Ibid., 34. 

 'Ibid., 4. 



