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SAND-LIME BRICK. 325 
forms of brick which, when properly laid, result in broken and 
bonded horizontal as well as vertical joints,’ or by interlocking 
or reinforcible building blocks, similar to concrete blocks now 
in use, both of which can be easily manufactured. 
RAW MATERIALS. 
Sand brick or reconstructed stone can be manufactured on a 
commercial basis with either calcium carbonate or calcium hydro- 
silicate as the binding material. The former has for its advantage 
a minimum fuel consumption, while the latter withstands best 
the effects of fire and, in all probability, atmospheric and chemical 
influences. The calcium carbonate process is not dependent upon 
the chemical composition of a sand or stone, but silica in a 
suitable chemical or physical condition is essential to the steam- 
ing process. With the exception of these differences, further 
consideration can be limited to the calcium hydrosilicate, the 
so-called sand-lime brick process. 
Siliceous material.—Generally speaking, common siliceous sand 
is the most desirable and the cheapest source of silica for the 
sand-lime brick industry. A fairly good sand-lime brick can 
be obtained with almost any sand, but economy in manufacture 
limits the physical and chemical properties rather sharply. A 
comparatively pure and fine sand is essential to a cheap and 
durable product, and silica which is capable of combining with 
the lime must be present in quantity. Sand grains too large 
to pass a sieve having 8 meshes to the centimeter (20 meshes 
to the inch) are undesirable, and particles sufficiently fine and 
numerous to enable sufficient silica to combine with the calcium 
oxide are necessary.’ In order to produce a dense brick, there 
should be a good gradation of sizes and a low percentage of 
voids. Very few natural sands have this desirable granulari- 
metric composition, and the influence of fineness upon the quality 
of the brick is so great that usually it is advisable to resort to 
screening and grinding or what is known as the division method. 
Sereens are employed to remove the large particles, and granu- 
larimetric gradation is accomplished by grinding part of the 
sand and then remixing this pulverized product with the whole. 
The lime is ground with the sand in order to secure as thorough 
a mixture as possible. 
*Strale, A. N. H., Pat. No. 1,021,851, April 2, 1912. 
®Gasenapp, M., Tonind.-Ztg. (1901), 762. 
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