STATE GEOLOGIST. 115 
It is quite questionable whether a perfect union between the two masses of 
concrete can be secured. The gain in cost is so small when the question 
of the greater allowable proportion of aggregate with the Portland cement 
over that with natural cement is considered, that it does not pay to risk 
the character of the work to make the gain. 
The cost of cement walks, well constructed, in 1896 to 1898, varied 
from II to 14 cents per square foot. In 1902 and 1903, prices of material 
and labor being higher, the same class of work cost from 14 to 17 cents 
per square foot. 
As to the life of a first class concrete walk, there appears to be no 
limit. The writer knows of one walk that has been down some twenty- 
One years or more that is as good today as the day it was laid. 
Fig. 61.—Concrete Sidewalk Built in 1880 at Conneaut, Ohio. 
One of the walks along the Capitol Block in Indianapolis has been 
down over thirty years. It was constructed of excellent material, but 
with no special attention to the preparation of the sub-bed, consequently 
water has percolated into the soil beneath and heaved the blocks badly 
and they have become broken. The blocks are cut about 18 or 20 inches 
square with lines running diagonally across the walk. Where they have 
had reasonable support, however, they are still in good condition. If 
