PORTLAND CEMENT CONCRETE ROADS. 21 
vertical as little as 5°, this movement was likely to occur ancl 
it was found difficult in construction work to avoid even greater 
variations. 
These findings led to the experiment of building pavements with- 
out expansion joints, and it was found in pavements so built that the 
transverse cracks did not occur more frequently than in those built 
with expansion joints and that the shrinkage due to the setting and 
initial drying out of the concrete provided sufficient room for such 
expansion as occurred later from changes in temperature and mois- 
ture content, except in pavements laid in cold weather. In pave- 
ments laid in cold weather it appeared that the shrinkage due to set- 
ting and initial drying out did not provide sufficient space for subse- 
quent expansion caused by changes in temperature and moisture, and 
local failures of the pavement were not infrequent. 6 Experience, 
therefore, indicates that transverse joints are unnecessary in pave- 
ments laid when the air temperature is generally above 50° F., but 
are necessary in pavements laid in cold weather. The majority of 
plain concrete pavements are now constructed without joints. Trans- 
verse cracks will occur in pavements so constructed at more or less 
regular intervals, averaging 30 to 50 feet apart. These cracks in 
general are less objectionable than joints. They do not adversely 
affect the riding qualities of the pavement, slipping of the slabs rarely 
occurs, the cost of maintaining them is no greater, and, if properly 
maintained, they do not materially injure the pavement. 
It is customary to construct transverse joints in reinforced pave- 
ments. They are generally spaced from 40 to 80 feet apart. The 
method most often used in constructing transverse joints is to sep- 
arate the sections of the pavement by means of specially prepared 
bituminous felt boards. These are usually held in place by means 
of properly shaped steel templates until the concrete is deposited 
against them, after which the templates are removed and the con- 
crete flows around the boards. The thickness of this joint has varied 
in common practice from one thicknessi of two-ply tar paper up to 
about one-half inch. A thickness of one-quarter inch seems to give 
very satisfactory results when the joints are spaced not more than 
40 feet apart. Joints of this kind are sometimes provided with metal 
armor, which is intended to keep the adjacent edges of the concrete 
from spalling off. It is claimed that armored joints require less 
maintenance than other types, but they are more expensive to con- 
struct. As the amount of abrasive traffic on country pavements is 
steadily decreasing, there does not appear to be any necessity for this 
type of joint except under unusual conditions. 
6 A full discussion of the expansion and contraction of concrete roads may be found in 
U. S. Department of Agriculture Bulletin 532. 
