EXPANSION AND CONTRACTION OF CONCRETE. 29 
These, comparisons of the actual change with the theoretical 
change, considering temperature alone to be the cause, are inter- 
esting. Observe that in Section I the agreement of the theoretical 
with the actual change in length is quite close, indicating that tem- 
perature was almost the sole cause of the change, and indicating, 
moreover, that the resisting effect of friction at the base must have 
been small. In Section II the agreement is not quite so close, and 
in Section III the agreement is poor. The actual unit change in 
many cases is in excess of the calculated temperature change, thus 
indicating that moisture is causing some expansion and also that 
the restraining effect of friction in preventing expansion and con- 
traction may be quite small. 
The discrepancies between the measured changes and theoretical 
changes are very noticeable in Section III. It will be seen from 
the description of Section III that it lies at the bottom of two 
6 per cent grades and the conditions are very favorable for a wet 
sub-base. Moreover, this section of the road was covered continually 
with mud tracked in from adjacent roads, and this aided in pre- 
serving the road in a moist condition. The actual change in length 
on June 15 and February 22 was greater than the calculated change, 
and these days were preceded by a considerable period of wet 
weather, as shown by the precipitation curve. These conditions 
were promotive of a wet sub-base, and this probably accounts for 
the increase in expansion of the actual over the theoretical. On 
June 15 the actual expansion is 0.000148 minus 0.000132, or 0.000016. 
On February 22 the excess unit expansion equals 0.000127 inch. 
As shown by laboratory measurements, this is approximately the 
amount of expansion produced in concrete by continued moisture, 
and this measurement therefore tends to confirm the presumption 
that the moisture effect is causing the difference between the actual 
expansion and calculated temperature expansion. The apparently 
small effect of friction in preventing expansion is interesting and 
is not unreasonable when it is considered that the pavement is sub- 
jected to continued vibration which would tend to relieve tem- 
porarily any friction between a wet clay sub-base and the concrete. 
Moreover, the slow yielding of the sub-base as the concrete creeps 
helps to relieve the stresses of friction. 
The foregoing expansion and contraction measurements are pre- 
sented in the hope that they will be of assistance to the engineer 
having charge of concrete road construction. Much theory might be 
developed from these measurements, but this development, together 
with the practical application of the results, will be left for the 
present to the constructing engineer. Some broad conclusions may 
be stated as the result of the investigations described, combined 
with the investigations of others. 
