206 
PARK AND 
CEMETERY. 
MODERN BITUMINOUS ROAD CONSTRUCTION 
Address by S. D. Foster at American Road Congress. 
The subject of bituminous construction, 
the one upon which I have been invited to 
speak, is such a broad one, and one upon 
which so much has been said and written, 
that I will not attempt to discuss its mer- 
its, compare it with other types of pave- 
ments, or take up the correct method of 
maintenance after construction, but will 
deal entirely with the two types of con- 
struction most commonly used by engineers 
today, viz., the bituminous road constructed 
by the penetration method, and the bitum- 
inous road constructed by the mixing 
method. 
Speaking generally of the two methods 
of construction, and taking into account the 
hundreds of miles of bituminous roads al- 
ready constructed, I feel safe in saying that 
there is probably no other type of con- 
struction about which there is less abso- 
lute information concerning the physical 
and chemical characteristics of the bitum- 
inous materials and the road metals which 
will bring about the best results. There is 
no type of road construction which requires 
more care or more consistent expert super- 
vision and inspection than that involved in 
the use of bituminous material, and until 
such time as we are able to thoroughly edu- 
cate and instruct efficient and capable en- 
gineers and inspectors in this type of con- 
struction, the same will remain in an ex- 
perimental stage. In general, also, I would 
state that the preparation of the subgrade, 
the drainage, and the foundation are ex- 
tremely important factors in the success of 
bituminous pavements, and, unless properly 
constructed, will bring about their destruc- 
tion. I might state at this time that, to my 
mind, the experimental stage in foundation 
work has been passed, and that for the or- 
dinary country traffic to which the average 
highways must be subjected an 8-inch tel- 
ford foundation or a 5-inch cement con- 
crete foundation, when properly construct- 
ed, is sufficient for the carrying of any 
class of pavement which we may desire to 
place thereon. 
Presuming that the foundation has been 
properly completed, I do not believe that 
I can better describe the method of build- 
ing thereon a bituminous penetration pave- 
ment than by quoting from the Pennsyl- 
vania State Highway Department’s specifi- 
cations, to-wit : 
“Upon a suitable foundation there shall 
be spread a layer of broken stone of such 
quality as may be suitable. The stone shall 
be broken in fairly uniform and regular 
cubes, free from dirt or dust, and compara- 
tively free from flakes or splinters. The 
stone shall be of such size that they will 
pass a l T /-inch circular opening and over 
a -kjbffich circular opening. This layer of 
stone shall be of such thickness that, when 
it has been rolled with at least a 10-ton 
power macadam roller, it shall have a thick- 
ness of 3 inches. 
“The surface must be firm and, when 
completed, correspond to the grade in 
proper crown and cross section. Upon each 
square yard of this surface shall be evenly 
spread, by means of an approved pressure 
distributor or fan-spout sprinkling pot, from 
l A to 1^4 gallons of bituminous material, 
of a penetration from 90 to 120. 
“The bituminous material shall be heat- 
ed to a temperature of approximately 350 
degrees Fahrenheit. Immediately thereafter, 
sufficient dry, dustless screenings, passing a 
J/ 2 -inch screen, shall be spread in sufficient 
quantities to evenly cover the entire sur- 
face of the road and take up excess bitum- 
inous material. The road shall then be 
rolled until firm and a smooth surface re- 
sults and conforms to the longitudinal and 
transverse section. 
“While the surface is clean and warm, 
a seal coat of bituminous material of 
proper consistency to be flexible when cold, 
shall be spread one-half gallon to the 
square yard. It shall be applied while at a 
temperature of 350 degrees Fahrenheit, 
and while the bituminous material is in a 
liquid state there must be spread a top 
dressing of clean, dry, torpedo sand, or 
dustless stone chips, in sufficient quantities 
to cover the entire surface of the road 
and take up any excess of bituminous ma- 
terial. 
“Immediately thereafter the road shall 
again be thoroughly rolled; if so directed, 
the stone, stone chips and sand must be 
heated. In rolling, the roller should start 
from the side line and work toward the 
center, and, in all cases, continued until 
thorough compression is secured.” 
By following these instructions, a first- 
class penetration pavement can be con- 
structed, but, in the experience of the de- 
partment, the engineer has frequently 
found the several conditions which I am 
about to enumerate, any one of which, es- 
caping his attention, will be bound to pro- 
duce a weak spot in the pavement. The 
first of these conditions is the presence of 
water in the foundation, due either to wet 
weather springs, or to rainfall after the 
foundation has been placed. This condition 
results in water working up through the 
telford stone and thence through the stone 
comprising the aggregate of the pave- 
ment. It attacks the bituminous material, 
which, losing its binding powers, readily 
disintegrates the pavement. Another con- 
dition, often occurring, is due to the con- 
tractor not napping his telford properly 
and attempting to bring the same to the 
proper crown and cross section by the use 
of stone spalls. These cannot be thor- 
oughly rolled into the foundation, and 
when the stone which is to be treated with 
bituminous material is hauled on the road, 
the spalls continually work up through the 
smaller stone and produce weak places in 
the finished pavement. 
The use of soft stone, especially in dis- 
tricts where local stone is used for road 
Do you en- 
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have written a series of twenty diplo- 
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Would you like to look them over? 
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Munsey Bld’g Baltimore, Md. 
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FORT ATKINSON .... WISCONSIN 
