EXPANSION AND CONTRACTION OF CONCRETE. 13 



ficially for a period of 10 days. 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- 

 drained 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- 



