The Leavenworth echo. [volume] (Leavenworth, Wash.) 1904-current, 1912-06-28

fully met the requirements for hard sur
face improvements and the cost of its
construction has been reduced to a low
figure. The pavement is simple, as
may be seen in the accompanying
drawing. 1t consists of properly con-
structed concrete base and thin wear
ing surface of Ditumen and sand which
has been extensively developed and
used in all cases in the streets of Ann
Arbor, Michigan, and to slightly less
extensive amount in other cities and
towns.
About four years ago, in order to
prolong the life of the asphalt block
pavements, which at that time showed
considerable wear, E. w. Groves, city
engineer at Ann Arbor, as an expert
ment, tried covering the surface of the
pavement with thin coating of coal
tar and sand. After being subjected
to various conditions of traffic for two
years this thin wearing surface proved
to be so satisfactory that Mr.. Groves
determined to try it for new construct
ion work on concrete base. During
the summer OF 1909 one block on a
residence street was paved with con-
crete having coal tar and sand wear
ing surface. In 1910 approximately
$4,000 square yards of this pavement
were laid, the same type of construc-
ton having been adopted on nine main
streets and alleys. Last year there was
laid in the neighborhood of 10000
square yards, petitions having been re-
ceived for a greater yardage than it
was possible for the city to construct.
Ann Arbor has we'll drained, some
what sandy sub-soil, and the concrete
pavement is laid directly upon the sub
grade without using a sub-base, which
would be necessary where a heavy,
wet, poorly drained sub-soil is encoun-
tered. The concrete pavement proper
consists of Gin. gravel concrete base,
machine mix, in medium consistency
and deposited on the sub-soil in the
usual manner. Where crushed rock
was available. this was preferred. When
conditions necessitated the carrying on
Of traffic where the improvement was
being constructed, the concrete was
laid in strips one-half the width Of the
street and every 25 feet an expansion
joint "a inch wide was inserted diago-
nal to the axis. An expansion joint
was also placed at the curb line.
The surface of the concrete was Civ
en- a wood-foat finish and slightly
roughened by brushing with an ordi-
nary hand street broom. After finish
ing a section, as described, the form
at the center or crown of the street was
removed, and the pavement for the
other half of the street laid, the new
concrete being deposited against that
which had been previously placed, so
that while there was a joint at the
crown of the street it was hardly per-
ceptible. This joint would be de-
cidedly Objectionable were it not pro-
tected by the wearing surface of btu
umen and sand that was later applied.
This type of construction can be cas-
lily eliminated by laying the pavement
in sections extending across the full
width OF the street. This method is
common practice and has been sue
cessfully done where concrete pave
ments have been laid on other streets
outside the city Of Ann Arbor. Where
the street had car tracks, one side of
the street was taken as the unit.
The materials required for the con-
struction of this pavement are to be
found, or are easily obtained in all To-
calities, and the equipment necessary,
besides the usual tools owned by ev-
cry contractor, consists simply of a
concrete mixer, a tank wagon for
sprinkling bitumen, an ordinary street
sweeper and wagon provided with
sand spreader.
First-class construction for this type
Of pavement should consist Of 6-inch
concrete base mixed one part cement
to ~ parts clean, coarse sand and
five parts of crushed stone, or screened
gravel laid upon properly compacted
sub-grade where porous, well-drained
sub-soil is encountered, or upon a
prepared sub-base upon a i
heavy, wet, poorly drained clay soil.
In some cases it will also be necessary
to lay tile drains provided with suitable
outlets.
The ordinary concrete pavement
without a wearing surface OF bitumen
and sand has been extensively used on
city streets and public highways
throughout the country, and where
constructed with suitable ma
terials has given splendid satisfaction.
Such a pavement is, however, not as
noiseless or resilient as asphalt, maca-
dam or wood block. In addition to
the noise there is occasionally some
objection to the appearance of and the