CONCRETE LINING FOR IRRIGATION CANALS. 55 
The general average coefficient of expansion measured was 
0.00000627 for slab 1 and 0.00000632 for slab 2. 
Slab 3 was kept at a temperature of about 80° F., though at times 
it fell to 70° and even 65° during Saturdays and Sundays. Daily 
observations were made early in the work, but later on observations 
were made only once a week. It is interesting to note (fig. 2) the 
immediate and rapid expansion following pouring, lasting about one 
week. This caused a change of length of about 0.00012 foot per foot. 
This action was doubtless due to the physical rearrangement of the 
particles of concrete in the process of crystallization. So far as its 
effect upon concrete lining for canals is concerned, if joints were not 
provided, it would cause severe compression of the slab as a whole for 
about a week or 10 days, which might cause a slight buckling and 
crushing. Where joints are used and filled with asphaltum or similar 
material the tendency would be to force some of it out of place, and 
for this reason the filling material should not be placed until about 
two weeks after the lining has been laid. It will be noted, however, 
that the expansion is only 0.012 foot in 100 feet, which accounts for 
its effect being of no marked importance in practice. 
It will also be noted (fig. 2) that following the expansion period in 
slab 3 there is a period of contraction lasting about 75 days and 
during which there is a total contraction at the rate of about 0.042 
foot in 100 feet, thus leaving the slab 0.03 foot shorter for a 100- foot 
length than when laid. If this factor were considered for a concrete 
lining, assuming that its contact with the material through which the 
canal were constructed would not retard the expansion, having a 
coefficient of expansion of 0.0000045, it would allow a total rise of 
temperature of about 67° F. before two adjoining slabs would be in 
contact after the contraction due to setting had been completed. It 
is evident, therefore, that if a slab were laid in the winter at a tem- 
perature of 40° F., the joints opened by contraction would not be 
closed until the slab had reached a temperature of 106° F. in the 
summer. Concrete lining is usually placed in canals during the 
winter or at least when the weather temperatures are cold enough for 
the above conditions to obtain. If the water carried in the canal is 
at a temperature of between 40° and 60° F., it is evident that the 
effect of contraction in concrete lining laid at corresponding tempera- 
tures will be most noticeable at a time when water-tightness is most 
desired. For this reason it is essential that some provision be made 
to secure water-tight joints. It may also be quite necessary to use 
some elastic material like tar paper to allow for expansion in excess 
of that which can be taken up by the space formed due to contraction 
in setting, for in some sections of the West temperatures are likely 
to be met which will cause this extra expansion, and unless a com- 
pressible material is provided buckling or crushing is very likely to 
occur. 
