Evening star., 1902-01-23
NEW STYLE PAVING
E-tss5s
Commissioners to Make Test Of Btu
minous MRoaaam.
DESCRIBED BY INSPECTOR A. v. dow
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hTsr 4os
At Least Two Blocks to Be Laid
With the Material.
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REPORT REGARDING UTILITY

The District Commissioners have decided
to test an area Of at least two squares Of
a new style OF pavement, known as bisumi-
nous macadam. Mr.. Al. w. Dow, the In
spector Of asphaIts and cements, has re-
Gently returned from Charleston, s. c.,
where he went to examine into the merits
Of the new pavement, and has submitted
a favorable report to the Engineer Com
missioner. MI. c. B. Hunt. the computing
engineer. has reported that the funds avail
able for laying new payements during the
current fiscal year are practically allotted
to the construction Of asphalt and asphalt
block. He recommends that at least two
blocks Of the new pavement be laid. how
ever. In view of the favorable report of the
inspector Of asphalts and cements Mr.
Dow describes the pavement in his report
in the following fashiona. 2 4
This pavement is Laid by first rolling the
subsoil thoroughly with a heavy road
roller. On this foundation is spread a three
inch layer of clean broken stone. about
three inches in their largest dimensions,
and rolling until well settled; over these
are then sprinkled a soft coal tar Bit
umen. On this is laid three-inch
course Of bituminous mixture composed
of one and ene-half-fnch4 stone, about 90
per cent: ee-fourths-inch stone about
1S per cent; ten mesh material. about 10
per cent: 6 per cent of dust and about 6 per
Process of Applying. :.
This bituminous mixture is mixed at q
paving plant which I will describe later
and comes to the street at temperature Of
$50 to 200 degrees Fahrenheit. This mix
ture is then rolled while hot with the heavy
road roller until thoroughly compressed
After this the surface Of the pavement re-
sembles that of an asphalt surface with
shallow intnrGticeS
up and give a perfectly smooth surface to
the pavement this surface Is flushed with a
moderately soft coal tar pitch, softened
with a drying oil, and made still more fluid
diately after flushing, dry sand is rubbed
into the flush coat and worked into the
interstices until the entire surface is per-
fectly smooth. Over this Is then strewn a
thin layer of one-quarter-ineh dry crushed
stone, which Is rolled into the surface with
the steam roller. The object of this flush
coat and small stone Is to fill up the un-
evenness Of the pavement and by having
the pitch softened With drying OIL It
makes 1t all the more easily rolled into the
unevenness of the pavsm syTt- In day or
two this drying oil eyapoRates from the
flush coat, leaving a THAN hard coat on the
surface. "a
when the pavement is fist completed it
has the appearance Of d maeadannized road,
but in time the loose stone and dust on
the surface gets eitherresmpressed into the
ment with a smooth-Wearfhg surface re-
sembljng somewhat the appearance of the
surface Of an asphalt blockI
Method of Preparation.
1.-The mixing Of the biturhanous concrete
for the body Of the pavement Is accom-
plished at very simple paving plant con-
sisting essentially OF one induced draught
drying drum. one melting kettle ana q
double shaft asphalt mixer. The broken
stone, sand and stone dust are mixed in the
proportions that 1t Is desirable to use and
this mixture passed through the. heating
drum, where 1t Is dried and heated to q
temperature approximating .1S0f degrees
Fahrenheit When the heated material
comes from the drum 1t Is passed through a
rotary screen which separates 1t into dust,
ten mesh material INSTRUMENTATION ma
terial and coarse stone. These several
screenings are stored Ia. separate bins and
when the mixture Is to be made with the
tar, definite proportions of each grade Of
stone and dust are measured into a box.
Ihts box OF material issthen emptfed into
the asphalt mixer along with a definite
quantity OF melted tar. I should Judge
about six per cent In the case of the work
at Charleston. After these materials have
been thoroughly mixed they are dumped
into cart and hauled to the street, where
1t is laid as previously described.
ana contract, and can be driven over with
a heavy load Immediately after completion
without showing the slightest marking.
Gives Promise Of Success.
This pavement gives promise Of being
one Of the most successful constructions
that has ever been attempted in road build
Ing The use of the large stone with just
sufficient small material to give minimum
OF yoids gives such rigidity that a very
soft bituminous cement can be employed as
the binding material. For this reason the
life OF such pavement is entirely depend
ent on the wearing on the stone used. as the
b1tuminous cement used, II Of fairly good
quality, Is so soft as to retain its life for
thirty years or more. -. .r-,&
.! am of the belief that such a pavement
could be used by the District with safety
on streets Of light travel in place Of asphalt,
and on country roads where a good quality
OF macadam Is now used. AS to the price
OF this pavement, Mr.. Warren will quote
nothing definite, but states that his price
will be about one-third off from the price
of asphalt.