20 
BULLETIN 906, U. S. DEPARTMENT OE ACtRICTLTVEE. 
joint after the thimble has been forced halfway down into the lower 
half of the pipe, as shown in figure 4. The remainder of the joint is 
then finished. The concrete is expected to slide over this metal strip. 
Joints made in this manner in the laboratory leaked badly when 
under pressure where a prepared asphalt compound was used to coat 
the metal strip. If oil be used, it is probable that the bond would be 
too strong to allow slipping. 
A simple expansion joint (fig. 5) has been tried out that seems 
to work well under all conditions. A strip or thimble of copper 
or lead is welded to make a continuous ring, which is about 4 
inches wide and the same diameter as the center of the shell of the 
pipe. This strip is then crimped and cemented into a short section 
of pipe. When the pipe expands or contracts the crimp in the 
metal gives. Such joints have been found to be water-tight under 
125 feet head. 
METAL RING OILEDJ 
T 
GA L VA NfZED IRON RING 
W 
v'. 
X^ SPHA LT OR TAR PA PER 
Fig. 4. — Expansion joints for v^ry low pressure. 
Expansion joints are made and sold by steel pipe manufacturers 
that are adapted to the use of steel pipe. Such joint? are expensive 
and are not advisable except under unusual conditions. Bolted 
joints fitted with rubber gaskets that are commonly used with 
riveted steel pipe can be used, and will be found to be much cheaper 
than the commercial expansion joints. Cast-iron collars that fit 
over the joint and are packed with oakum and asphalt, represent 
another type. One engineer has suggested using a short length of 
light weight corrugated iron pipe to be cemented at intervals in the 
concrete pipe line. Any expansion joint made with steel or iron is 
subject to corrosion, however. 
Alkali will sometimes disintegrate concrete drain tile and may 
attack a porous, dry mixed pipe when used for irrigation. Drain 
tile is subjected to the most unfavorable conditions. The tile is 
laid where the alkali salts are continually being drained into it. 
The joints are not cemented and the tile is often only partly full of 
water. Drain tile is often made inferior to irrigation pipe, the 
small sizes being made of sand and cement onlv. with a deficiency of 
