vin, A, 2 



Reibling: Portland Cement 



113 



better burned, finer ground, and contains less free lime than 

 sample No. 2. Its great superiority to No. 2 is shown by Table II. 



Table II. — Tests which show the difference in efficiency betweeen cements, 

 both of which passed all the requirements of standard specifications. 





Sample 

 No. 



Strength in pounds per square inch. » 



Relative efficiency, 



based on the 

 strength of No. 2. 



7 days. 



28 days. 



3 months. 



2| years. 



3 months. 



2 years. 



Tensile strength of neat 



1 

 2 



1 



2 



1 



2 



1 

 2 



739 

 653 



4,080 

 7,050 



310 

 313 



2,580 

 2,080 



745 

 707 



6,030 

 8,250 



422 

 379 



3,470 

 2,565 



756 



718 



8,800 

 7,550 



429 

 364 



3,700 

 2,660 



b716 

 c651 



11,450 

 9,890 



418 

 278 



4,860 

 3,537 



105.3 

 100.0 



116.6 

 100.0 



117.9 

 100.0 



139.1 

 100.0 



110.0 

 100.0 



115.8 

 100.0 



150.0 

 100.0 



137.4 

 100.0 



Do 



Compressive strength of 



Do 



Tensile strength of 1 : 3, 



Ottawa-sand mortar.. 



Do 



Compressive strength 

 of 1:3, Ottawa-sand 

 mortar 



Do 





* Each value represents the average of ten determinations. 



b Total change in the length of a bar of neat cement No. 1 == 0.047 per cent expansion. 



'Total change in the length of a bar of neat cement No. 2 = 0.098 per cent expansion. 



The above does not represent an unusual or an abnormal 

 experience. Some Portland cements which pass standard speci- 

 fications are far inferior to sample No. 2 and some are superior 

 to sample No. 1. In this case the superiority of sample No. 1 

 manifests itself in the specified tests, but very often the direct 

 opposite is true, as the decrease in strength or the change in 

 volume with age may be very great. In fact, some cements have 

 given very satisfactory early results, and then, after several 

 months, have disintegrated entirely. 



Contracts awarded to the lowest bidder have not always 

 secured the poorest cements. The location and operating con- 

 ditions of some plants are so favorable that in certain markets 

 they can undersell all other competitors without supplying in- 

 ferior cement. For example, it is known that one manufacturer 

 pays only 80 centavos per ton for limestone and 3.10 pesos for 

 coal, while the same quantity of material costs another plant, 

 which competes for the same markets, 1.70 pesos for limestone 

 and 6.50 pesos for coal. Accordingly, in some localities, such 

 as the Philippines, certain manufacturers can underbid other 

 competitors and still supply a high-grade cement at a fair margin 



116737 3 



