323 
PARK AND CEMETERY. 
concrete mixer. Two machines of 
this character were built for the 
South Park Commissioners and are 
now being operated upon the boule- 
vards with great success. The char- 
acter of pavement being laid is a mix- 
ture of asphalt with crushed limestone 
and sand laid over the old macadam 
surface. Where the traffic is heavy 
this layer of asphaltic concrete is 
made about two inches thick after 
compression, but where more moder- 
ate travel may be expected it may be 
made one inch or less in thickness. 
About 3,000 square yards of this 
kind of surfacing about three-quarters 
of an inch thick after compression were 
applied in June, 1908, to the surface 
of old macadam, without the addition 
of any new stone, on Grand Boule- 
vard, where the daily traffic amounts 
to from 3,000 to 5,000 vehicles per 
day, the year around. Up to date 
this piece of pavement has shown 
absolutely no signs of wear. 
Certain slight imperfections, such 
as marks left by the roller in turning, 
lines of joints, etc., were apparent in 
the surface when opened to traffic and 
are still to be seen practically un- 
changed. 
In February of this year (1909) a 
small piece of heavily traveled drive- 
way in Washington Park was sur- 
faced with this bituminous material 
not exceeding one-half inch in thick- 
ness, laid on top of the old macadam, 
which was left loose and unfilled on 
top. By this plan the bituminous ma- 
terial was forced down under the 
roller into the interstices of the coarse 
macadam acting as a filler and binder. 
The travel over this experimental 
section amounts to as much as 6,000 
vehicles on holidays and 3,500 on or- 
dinary week days. Up to date there 
is no appearance of wear. 
It must not be understood that such 
a thin layer of bituminous material 
is advocated for streets with heavy 
teaming and iron tired traffic. But 
it has been demonstrated that a layer 
of asphaltic concrete as much as two 
inches thick will carry any usual traffic 
short of very heavy city teaming 
where nothing perhaps except granite 
blocks will stand. In other words, a 
pavement two inches of asphaltic con- 
crete, on a sound base will stand any 
traffic a sheet asphalt will, and in 
many cases will give better service. 
On Michigan Avenue one block 
was laid two inches thick in May, 
1908, also about 2,000 square yards 
on the Lake Shore Drive in Jackson 
Park where the waves in stormy 
weather dash over the road and 
quickly destroy anything in the way 
of macadam. These pieces are giving 
excellent satisfaction. 
The machine with which this pav- 
ing mixture is prepared is portable 
and is intended to be used on the 
street or roadway being paved. It 
consists of a drier for the stone and 
sand, a melting tank for the bitumen, 
an elevator, storage hopper, automa- 
tic measuring devices for both the 
bitumen and the mineral aggregate, 
and a mixer, all mounted on the same 
truck. 
One fire box dries and heats the 
stone and sand and melts the asphalt, 
bringing it all to the desired working 
temperature of from 250 to 300 de- 
grees. If tar was being used prob- 
ably a lower working temperature 
would be desirable. From the mixer 
the material is dumped into wheel- 
barrows or two-wheeled hand carts 
and spread on the street surface with 
hot rakes. The mixed material 
reaches the street surface without any 
appreciable loss of heat and without 
the separation of the bitumen from 
the stone, which often occurs when 
hauled in wagons any distance. The 
roller is brought on it almost immedi- 
ately after being raked, thereby secur- 
ing the maximum compression. A 
five to eight ton roller may be suc- 
cessfully used on the hot material, but 
if as heavy as a ten-ton roller is used 
it should be allowed to cool some- 
what. The proportions of material 
used in the pavement now being laid 
by the South Park Commissioners are 
60 per cent of crushed limestone, 
crusher run from three-quarters of an 
inch down to one-quarter of an inch, 
20 per cent of coarse torpedo sand 
and 20 per cent of fine sand. This 
gives a fairly well graded mixture 
from three-quarters of an inch down 
to 200 mesh, with about 4 per cent 
each of 100 and 200 mesh material. 
To this mineral aggregate is added 9 
per cent by weight of asphalt. The 
stone and sand are proportioned by 
wheelbarrow loads as fed into the ma- 
chine, but after being dry mixed as 
heated, the aggregate is accurately 
measured in an automatic measuring 
box and dumped into the mixer. Two 
levers control the whole operation of 
putting a charge into the mixer. 
The feeding of the machine is, 
therefore, continuous, but the dis- 
charge from the mixer is by batches. 
However, it amounts to practically a 
continuous discharge, as not more 
than a half minute need be consumed 
in mixing. 
The record of the operation of the 
two machines owned by the South 
Park Commissioners is briefly as fol- 
lows for those who want details: 
i\o. 1 machine was put m opera- 
tion June 2nd, and No. 2 June 14th. 
The month of June was very W'et, ram 
having fallen in measurable quanti- 
ties on 13 days, and a trace of rain on 
five more days, making 18 days in all 
during the month upon which some 
rain fell. July has been a much more 
favorable month for such work. The 
average amount of two-inch pavement 
laid with each machine per working 
day since being started is 760 square 
yards. The average per machine dur- 
ing July was 988 square yards. The 
maximum amount laid any one day 
was 2,570 square yards. Over 2,300 
square yards with both machines was 
laid on 3 days. Both machines being 
used together on the same street it 
was impracticable to secure an accur- 
ate measurement of the work done by 
each separately. On July 23d, the 
work laid out on Michigan avenue was 
completed, the total yardage being 
50,000 square yards. The average cost 
per square yard of the pavement was 
50 cents, exclusive of administration 
and engineering and depreciation of 
plant; five cents per square yard would 
be an ample allowance for the latter 
item and five cents for the former. 
Ordinary repairs and upkeep of the 
plants are included in the daily record 
of costs. The preparation of the sub- 
grade for the reception of the paving 
material cost ten cents per square 
yard, including a small amount of new 
stone added here and there. 
To sum up the whole cost, there- 
fore, of the two inches of bituminous 
paving material was 60 cents. Includ- 
ing preparation of the base the cost 
was 70 cents per square yard. 
TWO NEW WASHINGTON 
PUBLIC MONUMENTS 
With elaborate military and civic 
pageantry, and a presidential address, 
the monuments shown on the cover 
were unveiled in Washington, D. C., 
last month in memory of two Polish 
heroes who fought under Washington 
for the independence of the United 
States — General Thaddeus Kosciuszko 
and Casimir Pulaski. 
The Pulaski statue, for which the 
government appropriated $50,000, was 
modeled by Kasimierz Chodzinski, of 
New York. The sculptor has repre- 
sented his heroic countryman in the 
Polish hussar uniform. 
The Polish Alliance raised about 
$60,000 for the Kosciuszko memorial, 
and in a competition among Polish 
sculptors the commission was award- 
ed to Antoni Popiel of Poland, an 
artist of wide reputation in Poland. 
