IX, A, 2 Reibling and Reyes: Portland Cement Materials 145 



chemical analysis will reveal nothing out of the ordinary. * * * [The 

 sieve test] will show that that portion of the mix which was capable of 

 combination was over clayed and the coarse particles of limestone in the 

 mix were burned to "quick lime," consequently the resulting cement dis- 

 played the double characteristics of being over clayed and over limed. 



No such difficulties would be experienced with a proper mix- 

 ture of the coralliferous limestones and clay material 47, which 

 latter has a silica-alumina ratio 



• per cent Si02 

 per cent AUOs + per cent Fe203 



which averages a trifle less than 5 and is sufficiently low in 

 lime and alkalies to possess desirable refractory properties. 



ROTARY VERSUS STATIONARY KILNS 



Provided that financial considerations permit, we strongly 

 favor the installation of rotary, rather than stationary, kilns. 

 Underburning is fatal to the efficiency of Portland cement, and 

 while with these raw materials there would be no necessity 

 of producing soft-burned clinker if the rotary process was used 

 the best stationary kilns would yield a considerable amount of 

 underburned cement. In fact, the product of a set kiln, unless 

 well sorted at considerable expense, would not be true Portland 

 cement but a mixture of seasoned, underburned, and well-burned 

 cements containing sintered, nonsintered, and hydrated free lime 

 and fused and sintered compounds of many kinds. 



However, we made a f ew^ tests of underburned clinkers obtained 

 from some of the mixtures already described, and the results 

 obtained are recorded in Table XIII. 



Table XIII. — Characteristics of decidedly underburned cements seasoned 



until sound. 



Test. 



Results. 



No. 2. 



No. 2b. 



No. 3a. 



Aver- 

 age. 



Specific gravity 



Time of setting in hours: 



Initial set - 



Final set 



Tensile strength in pounds per square inch 



7-day, 1 : 3, Ottawa-sand mortar 



28-day, 1 : 3, Ottawa-sand mortar 



3-month, 1 : 3, Ottawa-sand mortar 



2.94 



1.25 

 6.75 



212 

 220 

 325 



2.95 



1.85 

 8.45 



189 

 170 

 315 



2.95 



0.85 

 6.90 



177 

 180 

 322 



2.95 



1.30 

 7.40 



193 

 190 

 321 



