SOME TESTS OF PAVING BRICK. 
BY THOS. U. TAYLOR, M. C. E.* 
Constituents: Paving bricks are made from some form of clay 
which is generally found impure. Kaolin or pure clay has about the 
following constituents : 
46 per cent 
40 per cent 
14 per cent 
Silicon 
Alumina 
Water . 
Total 
100 per cent 
Pure clay is a very rare product and as for forming the constituent 
for paving brick it can be eliminated as a factor inasmuch as practi- 
cally all paving brick clay is of impure varieties. These impurities 
consist of Soda, Ferric Oxide, Magnesia, Potash, Lime, etc. It is 
well known that pure Alumina is capable of resisting high temper- 
atures and that it is easily moulded but that it shrinks and cracks 
on drying. The presence of Silica prevents the shrinking and crack- 
ing but renders it less responsive to moulding processes. The pres- 
ence of lime and magnesia, while infusible in themselves or with 
alumina, readily fuse in an excess of silica and form vitrified brick. 
The commercial paving brick is manufactured from some form of 
clay which is often impregnated with other impurities. Great cau- 
tion has to be observed not only in mining the clay but also in the 
complete process throughout from the mining to the completing of 
the brick. The clay is generally reduced to a powder and then 
thoroughly mixed so as to form a uniform product. They are burnt 
in an up-draft or down-draft kiln and statistics show that the down- 
draft run will turn out from 80 to 90 per cent of the charge as good 
pavers. 
It is not the object of this paper to deal with the full details of 
the manufacture of paving brick but to give some results of tests 
made at the University of Texas of the different paving bricks used 
west of the Mississippi, and before giving the result of these tests 
I call attention to the following Specifications for Paving Brick as 
given by the National Brickmakers Association as published in 1901. 
“1. Dimensions of the Machine: The standard machine shall be 
28 inches in diameter and 20 inches in length, measured inside the 
*Professor of Civil Engineering, The University of Texas. 
