SAND-LIME BRICK. 829 
PROCESS OF MANUFACTURE. 
While there are several processes and machines, there are 
but two distinct systems for controlling the raw mix; namely, 
the “silo system” and the “pre-hydrating system.” 
Silo system.—The lime is pulverized, mixed with sand, moist- 
ened, and placed in a bin where it is allowed to remain a 
sufficient time for the lime thoroughly to hydrate or slake. 
According to E. Leduc and Ch. de la Roche,” “‘stale or partly 
carbonated limes account for a great number of failures in the 
manufacture of sand-lime brick,” where the silo system is used. 
Their results (Table V) show considerably less strength when 
the lime had been exposed to air for four days, and they also 
obtained less strength when the quicklime had been less finely 
subdivided or less thoroughly mixed. 
TABLE V.—Effects of air slaking and screening the lime and negligent 
mixing (bricks steamed for six hours at 120 pounds pressure). 
Average resistance to pressure in pounds 
per square inch. 
Mix No. 1. |Mix No. 2. |Mix No. 3.|Mix No. 4. 
aan Initial 
Lime in | {Sand in | compres- s 
the mix- | the mix-| sion of Hes cle Now ee 
ture. ture. | the mix- ope e,| Same as | cept that | Same as 
ture. » |W? a x ’| No. 1 ex- | the lime | No. 1 ex- 
Yee at ~ | cept that |was partly| cept that 
eereenad the mixing] carbon- | the lime 
lime, and | 5 less | ated by a | was not 
a ail sane thorough.| 4-day ex- | sieved. 
gs an posure to 
eb the air. 
Per cent. | Per cent.| Pounds. | 
8 92 8, 750 1, 680 1,340 1, 088 1,340 
10 90° 3, 750 2, 025 1, 470 1,515 1, 530 
12 88 8, 750 2, 005 1, 480 1,575 1, 845 
8 92 7, 500 2,145 1,750 1, 546 1,742 
10 90 7, 500 2, 456 1, 865 1,772 1,818 
12 88 7, 500 2, 615 2, 130 1, 988 2, 080 
The pre-hydrating system.—This process consists in the hydra- 
tion of the lime in the hardening cylinders before it is mixed 
with the sand. This method of slaking utilizes the heat of 
hydration and insures the use of lime which will not undergo 
further slaking during the steaming process; but according to 
P. L. Simson, pre-hydrating systems are gradually being elimi- 
“Cem. & Eng. News (1911), 23, 281. 
© Ibid. (1912), 24, 164. 
114047——3 
