The evening times., 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 disintregaton of asphalt
: pavements, he has prepared report on
the cause of the disintregations of such
surfaces in spots. 1t was rather surpris-
ing TO some of the District officials 10
learn that many such defective places in
the pavement was caused by illuminating
gas and other substances or vapors which
were thought to be entirely foreign TO
such matters. Chemist Dow states:
"As there are several causes, all
foreign 20 each other. for the disintegra-
tion of pavements in spots, it will be i'm
possible to discuss them as whole, so I
viii treat each case separately.
when a pavement is laid with sur
face mixture deficient in asphalt cement
and the asphalt cement is so hard as to
! be very brittle in cold weather the pave
ment viii be ground away by traffic, and
as there are always spots weaker than
| Others the disintegration will naturally
take place more rapidly in these places.
Such pavement will dsintegrate more
rapidly in cold weather, and is also like
ly to crack badly at the same time.
Causes af DisiBtegrafion.
There are cases of disintegration in
spots occasionally met with that are caus-
ed by rolling or softening of the asphalt
surface by oils coming from the binder.
| This occurs most frequently in pavements
| laid with coal-tar binders, there ap-
| pears to be a constituent of some coal tars
| which is readily absorbed by the surface
! mixture. sOftening it greatly and appar-
emily making il more susceptible to the
/ action OF water. PaYements 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.
"On examining a section Of the surface
mixture cut from the affected spot il will
he found to be quite soft near the binder
If the disintegration has not proceeded for
a length of time: If 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
4 The affected piece of mixture will smell
4 sly of coal tar, and viii, in all cases,
give a greenish fiuorescence to a solution
in carbon disulphide. The portion of the
. pavement thus acted on will be crowded
. OF worn out by traffic until nothing is left
. Of it. IL the surface mixture is soft the
pavement viii roll at this place. the son
/ affected material crowding before the traf
lie
As the use of coal tar in binder was
discori inued 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 ulely caused by
the presence OF some free oil which may
not have been properly Incorporated with
the asphal. in making the binder cement
Absorption of Gas.
/ 'Disintesration of pavements from the
! absorption Of Illuminating gas. escaping
( from lealy gas pipes or mains under the
pavement There are several streets in the
city being ruined by this means. and il ap-
pears 10 be a common thing in all cities
having gas. The pavements are affected in
very much the same way as when disin-
tegrated by coal tar binder except the fine
cracks, running parallel with the street,
make jheiT appearance some time before
the pavement begins to crowd. Pieces of
the SuTff &c mixture taken up smell yeiy
strongly Of Illuminating gas, and in some
cases h. gas can be ignited by applying a
match 10 the under surface when it has
gust been taken up. In nearly every case
enough gas viii be given OF by heating 1
small piece OF The affected pavement in a 4
tube 10 have il fash by igniting.
As it has been doubted by some that 1
this disintegration is really due 10 illu-
miDating gas. | have made a most thor /
ough investigation OF the subject and be-
ieTe have positively proven that gas is the
cause. Samples of pavements were OBJ
talned from several affected spots, end in
all cases ! have been able TO obtain from
them a 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
heating them under boiling water and col
lecting the gas given of in an inverted
funnel
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.
as an asphalt cement such as is used in
paving Will 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 infritesimal part of this loss
is gas at ordinary temperatures. To
make a more practical demonstration of I
this. two samples of a pavement were
taken, enc from an affected spot and the
other from a good portion of the pavement d
3bout ten feet away. These samples We're
treated under boiling water until they ;
ceased to evolve gas. The affected sample (
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 u
rom the Voids of the pavement I
Having now found that gas is present
IN the pavement so affected, let us proceed
10 examine as to its source. II cannot be
4 natural gas or marsh gas, for there is
40 analysis Of such gases on record that
contains appreciable amounts of heavy
while the gas from the pave
nent is rich in these compounds. The
anne would also apply to sewer air or gas
he only remaining source is Illuminating
as.
The Source of the Gas.
''On comparing the composition of the
as given off from the disintegrating pave
lent with the Illuminating gas, 1t was seen
hat they are not at all similar to compo-
iuon. At first glance it would not seem
ossibie that the former gas could originate
rom the latter, but when the properties of
sphalt are considered it is easily ex-
lained
Heavy hydrocarbons, TO which class as
halts belong, are known to absorb ether
aseons hydrocarbons; the heavier the gas
Ne more afnnity between il and the heavy
ydrccarhons. Knowing this, the ingredi-
nts CT the Illuminating gas that asphalt
ouid nave the greatest affinity for would
e the heavy hydrocarbon gases, slight
fifnity for the marsh gas or mefhane.
nd no ahlnity Tor any of the other in