152 REIBLING AND REYES. 
TABLE XLI.—The strength of rotary- and set-kiln products of brand O 
cement. 
Fineness. E Tensile strength. 
b 
5 Neat. 1:3 Ottawa sand mortar. 
: Material. : : by flog = |e: 
No. ateri 4 e 2 . Z Z E z 
id lene eine atoll ee i 24 
(=) (=) SS —E 
Be fey |) de eB es] tor es oe eRe ese eee 
1 | Rotary cement ---_| 77.6 | 93.2 | 3.114 | 642 | 725 | 678 | X | 752 | 296 | 388 | 330| 291 
2 | Set-kiln cement -__-| 79.2 | 95.4 | 3.093 | 503 | 614 | 637 | % | 752 | 216 | 272 | 300] 289 
83 | Rotary cement ----| 79.7 | 98.2 | 3.10 | 688 | 645 | 680 | X | 708 | 240 | 298 | 313 | 302 
4] Sound, clinker 
from set kiln ___-| 80.6 |100.0 | 3.05 | 605 | 701 | 718 | 740 | 748 | 248 | 288 | 345 | 864 | 340 
5 | Disintegrated 
clinker from set 
2.794 | 290 | 391 | 495 | 582 | 600 | 88 |'144 | 224 | 245 | 275 
Cements numbered 8, 4, and 5 contained 1.6, 1.5, and 1.5 per 
cent, respectively, of gypsum. 
Cements 1 and 2 were typical examples of the better class, 
commercial, rotary- and set-kiln cements then produced by this 
factory. Cement 4 was obtained by separating the well-burned 
clinker from the other inferior, disintegrated products (5). 
‘Compared with a hard-burned rotary cement (3) of practically 
the same ultimate chemical composition and fineness, cement 
4 shows the same characteristic features even to drop in strength 
of the one-year sand mortar values. The results obtained with 
cement 5 clearly demonstrate that the presence of underburned 
cement is the cause of the characteristic low early strength of 
the average set-kiln products. 
The strength of our high-limed rotary products is not mate- 
rially affected by quenching the clinker in water except in so 
far as this quenching affects the free lime, and rapid cooling is 
not essential to the preservation of the high-limed silicates and 
low-limed aluminates in Portland cement. There is little oppor- 
tunity for molecular changes to occur after the clinker has begun 
to cool because the burning is accomplished very quickly and 
only reaches the incipient state, the percentage of calcium oxide 
is high, and the clinker cools fairly rapidly through the eutectic 
temperatures. 
The strength of a cement increases with the burning tem- 
perature and, to a certain point, with the quantity of combined 
lime, and few Portland cements pass our standard specifica- 
tions unless the clinker contains at least 60 per cent of cal- 
cium oxide and is sufficiently sintered to form the high-limed 
silicates and low-limed aluminates. 
