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 3Vas 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 

 fining, 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 fining 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 ver} r likely to 

 occur. 



