EXPANSION AND CONTRACTION OF CONCRETE. 13 
ficially for a period of 10 clays. It is then subjected to all of the 
changes of temperature and moisture of the atmosphere. In addi- 
tion to atmospheric influences, however, the condition of the sub-base 
has an effect on the condition of the concrete. If the sub-base be not 
well drained, there will be very little tendency for the concrete to dry, 
irrespective of weather conditions. On the other hand, with a well- 
drainecl sub-base the moisture may disappear rapidly after a heavy 
rain, and the concrete then will dry out quickly. In either case the 
concrete will absorb much moisture from the underlying soil by 
capillarity, so that the extreme drying experienced by laboratory 
specimens rarely will take place in the concrete road. The shrinkage 
changes of laboratory specimens therefore should be expected rarely 
in actual construction, as the conditions are not generally favorable. 
It is possible, however, that expansion due to the absorption of mois- 
ture will be accentuated in the concrete road. 
A special instrument was designed by one of the authors in order 
to study the effect of temperature, moisture, and any other physical 
influences on the expansion and contraction of concrete roads. As 
the movements in the concrete undoubtedly were small, it was neces- 
sary that the measuring apparatus possess great accuracy. It also 
was necessary, in view of the great temperature ranges to which the 
instrument would be subjected throughout the day's work and at 
various seasons of the year, to have some means of correction for 
these changes in temperature. It was considered advisable, in view 
of the extremely small changes in length expected in the concrete, 
to make the measurements over quite a large gauge length, and for 
this reason 10 feet was selected as the length of the instrument. The 
device (fig. 12) in its final shape as used on the road, is made up of 
two gauge tubes, one of steel and one of brass, supported so that they 
can not bend, and provided with rounded tips against which meas- 
urements are made with micrometer screws. By means of these 
micrometer measurements, corrected to constant temperature, the 
changes in length between plugs set in the concrete road are obtained. 
The tubes A and B are the gauge tubes, and they are supported 
at frequent intervals by brass disks, D, fastened within a brass casing, 
E, 2 inches in diameter. This casing extends the full length of the 
instrument and is surrounded and supported at intervals by another 
casing, F, 3 inches in diameter. At the ends of this outer casing are 
two collars, N, which rest in the supporting blocks, G. These blocks 
are provided with pins, H, whose conical ends fit into holes drilled 
in bronze plugs set in the road during its construction. One end sup- 
porting block, G, is provided with flat-ended contact pins, J, and the 
block at the other end of the instrument carries micrometer screws. I. 
Adjusting screws, M, shown in the end view are provided merely to 
support the instrument on the road, when not in use. The fiber col- 
