Evening star., 1936-11-15

M Highways are
- n constructed for
the travelling
Af' public, and this
department realizes it is the re-
sponsibility of the engineer to carry
on construction with a minimum Of
delay. Methods for obtaining early
strength of concrete. which have re-
Gently been learned through research,
are followed whereby the normal
street opening time for concrete is
approximately three to four days in
place of the minimum OF two weeks
which was formerly required.
An important advancement in the
construction of both concrete pave
ments and concrete bases for bitum-
inous pavements has been the use Of
the most improved type of expansion
Joint which allows free movement OF
the concrete during the heat Of the
Summer as well as during the cold OF
the Winter months. This provision
for free movement prevents the break
ing UP of the concrete which has oc-
CURED in the older pavements.
Jack" Simple but Valuable.
Almost simple, yet valuable develop
ment in apparatus. especially appli-
cable to municipal conditions has been
that of the "mud-jack." During re-
cent years research and experience
have established definite information
relating to soils and soil characters
tics, and to methods OF placing and
:compacting of soils to obtain dense
and stable subgrades for subsequent
road surfaces. This information Is OF
particular value where it is necessary
to construct streets over bitches re-
1uired in the installation of various
utility conduits. The construction
of q 100000 cubic yard fill for the ap-
reaches to the New Hampshire Avenue
Viaduct represents the application OF
these soil principles on mai scale.
This fill has been in service for more
than two years and has shown no
settlement whatever.
However, due to various factors,
particularly that Of underground con-
struction, settlement of pavements
ind sidewalks does occur. BY drilling
q two-inch hole at various intervals
In such pavement sections and pump
ing a mixture of fine soil together with
a. very small amount of cement under
these sections, by the use Of the mud
Jack" referred to, it is possible to LIT
the payements into their original posi1
tion. BY this method hundreds OF
square yards of pavements have been
salvaged with but little inconvenience
to the public, and with result per-
manent impr provement. The forcing
under low pressures OF q soil mixture
conpacts the subgrade to satisfactory
density before 1t starts raising the
slab into proper position, insuring
permanent improvement OF the SUD-
Grade and proper placement OF the
pavement. The removal and replace
nent of such pavement or sidewalk
areas, unless considerable amount OF
the Door subgrade is removed ana
properly replaced, would not afford the
permanent improvement that the use
of the mud-jack provides. Platforms
and parking areas near public buildings
under which the fill material adjacent
to the building has settled have been
brought into proper elevation and en-
ormous economic savings realized as
well as the inconvenience OF construc-
ton work avoided.
Repair Cost Lessened.
AS bituminous pavements approach
the end of satisfactory service 1t Is
q difficult problem to properly ano
vet economically maintain them. IL
is the practice in many localities 10
tear out the entire depth Of pavement
where such failures, whether OF the
surface or base, occur. 1t Is dlmcuit
then to make use Of these new por-
tions when it is found necessary 10
reconstruct these pavements. FOR
several years the highway department
of the District of Columbia has adopt
ed q method Of maintenance which
has proven very satisfactory with re-
spect to service, and yet economical,
and does not require complete re-
placement of the failed portions SO
that when 1t is necessary to recon-
struct the remainder Of the street
these portions will be removed and a
complete new project constructed.
Sheet asphalt payementS consist OF
a layer of bituminous material about
3 inches in thickness, placed on a
concrete foundation. In most cases
where a repair is required the top
surface Of this layer only is affected
extending to a depth Of only II inch
or less, the underlying 21s inches be-
ing adequately sound. To remove this
sheet asphalt layer to its total depth
In such cases would not be economi-
cally advantageous, as it would result
in the needless waste of a large pei
cent of the original material, which !:
still satisfactory. Therefore, the tor
half inch of such surfaces Is removed
the depth removed being replaced
with new sheet asphalt material. The
surface to be replaced must first bt
softened by means of large heaters
after which removal Is comparatively
easy. The new replacement materia
is spread and compacted in the same
manner as In the original construc.
ton. BY use of this type of main.
tenance, substantial savings ar'
effected annually. An added advan'
tage of this method Of repair is thai
In most instances an uninterruptec
fiow of trafic is provided for through
out the improvement process.