The evening times. [volume] (Washington, D.C.) 1895-1902, 1900-01-17

In addition to the report made to the
Commissioners some time ago by the
Chemist Of the Engineer Department re-
garding the disintregation OF asphalt
payements, he has prepared report on
the cause Of the disintregations Of such
surfaces in spots. Il was rather surpris-
ing 10 some OF the District officials TO
learn that many such defective places in
the pavement was caused by Illuminating
gas and other substances or ySDOrs which
were thought to be entirely f,reign TO
such matters. Chemist Dow states
"As there are several causes, all
foreign TO each other. for the disintegra-
tion of pavements in spots, it viii be i'm
possible to discuss them as a whole, so 1
Will treat each case separately.
when a pavement is laid with a sur
face mixture deficient in asphalt cement
and the asphalt cement is 20 hard as to
be very brittle in cold weather the pave
ment Will be ground away BY ;-aiiic. and
as there are always spots wsaAer than
others the disintegratiOn will naturally
take place more rapidly In these places.
Such pavement will disintegrate more
rapidly in cold weather, and is also like
" to crack badly at the same time.
Causes of DIsIntegrnfiOn-
There are. cases Of disintegration in
spots occasionally met with Il at are caus-
ed by a rolling or softenlng OF the asphalt
| surface by oils coming from the binder.
! This occurs most frequently in pavements
! laid with coal-tar binders, as there APP
pears to be a constituent OF some coal tRrs
/ which is readily absorbed by the surface
\ mixture. sOftening IL greatly and appar-
emily making il more susceptible TO the
/ action Of water Pavements affected this
way first give signs OF their disintegratiOn
! by slight depression over the affected
spots. In time numbers OF small cracks
appear. running parallel with the street
/ These gradually increase in prominence.
. accompanied with transverse cracks, until
. the pavement has the appearance Of alli-
. gator skin.
"Ou examining a section OF the surface
mixture cut from the affected spot il will
be found TO be quite soft near the binder
Il the disintegration has not proceeded for
a !ougth Of time; IL older the soft zone
. VIII be nearer the surface. while the bot
. tom of the mixture will show the disinte-
. grating effect of the water that has likely
/ entered the pavement through the crack.
The affected piece OF mixture will smell
. Stron sly Of coal tar, and viii, in all cases.
in carbon disulphide. The portion of the
. pavement thus acted on will be crowded
or worn out by traffic until nothing is left
OF it. II the surface mixture is soft the
pavement will roll a. this place. the sO7
affected material crowding before the traf-
Gc.
As the use Of coal tar in binder was
discontinued in this city some time age
these cases WI occur less frequently each
wear. Binder made with asphalt cement
IN some few cases affects the surface mix
ture in this way II is UseIy caused BY
the presence Of some free oil, which may
not have been properly Incorporated with
the asphalt in making the binder cement
Absorption of Gas.
/ "DisutegratiOn Of pavemeuts from The
absorption Of Illuminating gas. escaping
from leaky gas pipes or mains under the
pavement: There are several streets in the
city being ruined By this means. and IL ap-
pears 70 be a common thing ia all cities
having gas. The pavements are affected in
very much the same way as when disin-
tegrSted by coal tar binder, except the fine
cracks, running parallel with the street,
make their appearance some time before
the pavement begins 10 crowd. Pieces OF
the surface mixture taken Up smell very
strongly Of Illuminating gas. and i'm some
cases tho gas can be ignited by applying a
match 90 the under surface when it has
just been taken up In nearly every case
enough gas viii be given on by heating a
small piece OF The affected pavement in a
tube To- have il fash by igniting
As iJ has been doubted by some that
this disintegration is really due 10 illu-
miDatiug gas. 1 have made a most thor
ouSh Investigation Of the subject and be-
leve have positively proven that gas is the
| cause. Samples Of pavements were OBJ
I tanned from several affected spots. end in
all cases have been able 10 obtain from
! them gas that exploded by passing an
/ electric spark after mixing with air The
method employed to obtain the gas from
| samples Of the surface mixture was by
I heating them under boiling water and col
4 lecins the gas given OF in an inverted
! unEal
/ Those not acquainted with the proper
| ties OF asphalts might suggest that heat
/ ing any asphalt TO this temperature might
| make it, give OF a gas This is impossible
| rs an asphalt cement such as is used in
| paving viii lose only 3 or per cent. at the
/ most. on being kept at a temperature Of
/ 400 degrees Farenheit for thirty hours
! and only an infir.tesimal part Of this loss
| is gas at ordinary temperatures. To
/ make a more practical demonstration OF
! this. two samples Of a pavement were
/ taken, one from an affected spot and the
l hhAt4 AAbLti a ENjN IlhAliou OF the pavement
! about ten feet away. These samples were
/ treated under boiling water until they
/ ceased to evolve gas. The affected GAMBLE
| gave several times more gas than did the
| other. On testing the gas from the good
sample was found TO consist of oxygen and
] nitrogen, which was evidently Just the air
/ from the voids OF the pavement
! Having now found that a gas is present
! in the pavement so affected, let us proceed
/ to examine as 10 its source. il cannot be
| a natural gas or marsh gas, for there is
! no analysis OF such gases on record that
I contains appreciable amounts OF heavy
| hydrocarbons, while the gas from the pave
ment is rich in these compounds The
! same would also apply to sewer air or gas.
The only remaining source is illuminating
gas.
The source OF the Gas.
ION comparing the composition Of the
gas given of from the disintegratlng pave
ment with the Illuminating gas. Il was seen
that they are not at all similar to compo-
sition. At first glance it would not seem
/ possible that the former gas could originate
from the latter hut when tho Of