The Birmingham age-herald. [volume] (Birmingham, Ala.) 1902-1950, 1910-06-22
JOHNSON TELLS Of
MATERIAL FOR ROADS
Engineer Writes Interestingly
on Road Building
QUALITIES USE OF STAG
rhipk. Tran Rock Is Best Material in
World But That Certain Kinds of
Stag Are Also Very Valua-
BILE for Highways

| Guv r Johnson, the well-known con
sulting and contracting engineer, has
written an interesting article on roao
building in which he calls attention TO ths
practicability of various materials for use
on highways. Mr.. Johnson writes:
To the Editor of The Age-Herald:
| notice in Sundays issue some inter
views concerning good roads, and should
like to have the privilege of your columns
to make some remarks thereon
! In the first plate. referring to the mat
| ter of Stag versus ebert and other ma
terial for road making, it Is universally
conceded by engineers that the best road
making material in the world is trap
rock. This rock is, of course, of igneous
derivation, and l have never seen 1t III
Alabama, although it Is probable that II
may be found along the line of the Blue
Ridge mountains.
After trap rock there are great num-
Der of other rocks in common use, one
of the best of whit h is hard lime stone.
Most of our limestone is rather too sort
to make a first-class road, although l
have seen in the distri0 some deposits OF
rather siliceous stone, vhich would make
excellent road building material. The
dolomites are almost universally too soft.
ebert is the result of the decomposition
of limestone. The rock material in chert
is quartz, composed principally of iilica,
and may or may not be kald enough to
resist wear. Silica is also the principal
Ingredient in sandstone, and sandstone
varies tremendously in hardness.
For instance, the Oriskany sandstone,
which shows at Gate City, is so soft that
it can almost be worked with pick and
shovel. On the other hand there Is plenty
of sandstone which can hardly be
drilled. So that when, all is said and
done, it is a matter over which we have
little control and we can only use jldg-
ment in the selection of material.
This brings me to the question of Stag.
Stag is, roughly speaking. a silicate OF
lime and alumina, and there is as much
difference in Stag as in natural rock. "
the silica predominates then we have an
impure glass, which is very hard, has
little coresive power. but good wearing
qualities If, as is the case with many
of the slags in this district, large pro"
portion of the calcium In Stag is re-
placed by magnesium we get Stag With
almost no adhesive or binding property
and which may be hard or soft. depend
ing on the amount of silica, If we nave
a Stag in which there is little magnesium,
and the sum of the bases, /. e., calcium
and magnesium, predominates, and the
magnesia does not run over 3 Ter cent,
we have a Stag which has a strong bind
ing power, great elasticity and gooo
wearing qualities in most cases.
The theory of good road making calls
first, for a road which shall be imperv-
ious to moisture; and, second, shall be
of such material as will give the maxi
mum wear for the minimum ofNupkeep.
The first condition can be fulfilled with
almost any material. provided the road Is
we'll rounded up, with good bitches on
each side, and Is so thoroughly compacted
by rolling that the water will run off
to the sides instead of penetrating
The second has to be governed largely
by local conditions. My'own conclusion,
which rises from several years of prac-
teal work, Is that well-selected Stag with
a top dressing of either limestone screen
ings or rather sandy clay, will give the
best results, when trap rock is not avail
able. In building such road, OF course
1t Is necessary to prepare the underlying
earth properly. My personal practice has
always been to lay out the grade exactly
hull
on the Stag In two layers For first
class road l use nine inches In the CEN
ter, tapering down to four inches on the
Sides This gives a rise of five inches
In the ordinary 16-foot road; or in other
words, FIVE inches in eight feet. 1 put the
Stag on In two layers. rolling thoroughly,
and dampening the Stag with each appli-
cation of the roller. On top OF this
comes the clay or limestone screenings,
which should also be well dampened and
thoroughly rolled.
quite as much attention should be paid
to the side bitches as to the road. They
should be laid out and excavated SO
that no water can stand in them. Where
It is necessary to cross from one side to
the other substantial culverts of cast or
wrought iron or concrete should be used.
and every precaution should be taken to
carry the water away as fast as 1t falls.
and to avoid allowing the water TO run
over the surface Of the road
1t is hardly necessary to say that I ad-
vocate most heartily the use of the heavy
residual oils as a top dressing. This both
keeps the moisture out and prevents the
wear on the surface of the road.
To use a homely adage-"The proof OF
the pudding is the chewing Of the string.
Roads that built in east Tennessee along
the lines indicated above have stood the
wear and tear of Is years, and are still
good roads.
In conclusion want to again point Out
| the necessity for constant attention. A
very small hole soon developes into a bis
one. A road that is not kept crowned ur
develops ruts and chuck holes As soor
as q road Is allowed to get into such g
condition that water will stand on 1t 1t.
deterioration becomes very rapid.
] have recently been over all the roat
mentioned by Mr.. Brett Brown and car
say most emphatically that while tn,
| major part of the road is in poor condi
ton, comparatively little work in the way
Of bitches and browning would put It II
| excellent shape. Yours truly,
GUY r. JOHNSON,
Consulting Engineer.
| Birmingham, June 81, 1870.