Evening journal. [volume] (Wilmington, Del.) 1888-1932, 1917-05-24

! several hkEftkdlto. SEVERAL OF THESE
experiments are now four years Old.
The later experiments dealt with
concrete pavement and included the
effect hydrated lime has on concrete;
the most economical length OF slab
the various kinds OF reinforcement;
the different kinds OF surface finish;
the different methods OF curing the
results OF using different sands the
advantage OF thoroughly mixing the
ingredients; the use OF various joints,
etc
ION the completed part OF the road
there is a section OF Hassam. a sec
ton OF Warrenite. one Of Amiesite
and a larger section of reinforced
concrete. The Hassam and Warrenite
we're laid in 1912. when the DUPONT
road WIS FIRST started With slight
repairs. both these payements are in
good condition. Part OF the Amiesite
foundation was laid on a concrete
foundation and part on a crushed
stone foundation. This pavement is
about one year old and its appearance
Is excellent.
Reinforced Concrete Used.
"The greater part OF the completed
work on the dupont road is rein
forced concrete This concrete pave
ment Is IA II. wide. ins. deep in the
center and ms. deep on the sides.
and Is laid on a nat subgrade. /. is
reinforced in nearly all instances The
proportions OF the ingredients were
one OF cement. two of sand aud four
OF stone, with different quantities OF
hydrated lime up to 10 per cent. by
volume. After considerable expert
menting Il was found that thorough
mixing greatly increased the strength
OF the concrete. and while expert
ments showed an increase in strength
by mixing up to 4 minutes It was con.
sidered most economical to mix the
concrete for / 10 minutes. The re-
suits of the early tests might lead
one to believe that there was no
economy in longer mixing. but the
long time tests showed a distinct ad-
vantage in the thorough mixing.
Demand Smooth Surface.
y when deciding upon the length oil
= slab that was to be used recourse was
!, had to the concrete roads already
. built II was found the length OF slabs
. varied from 25 up 10 go and 20 A. IN
D. many instances there were nearly as
n many cracks in the shorter slabs as
there were in the longer ones. The
question was naturally asked II &C
l, or 20 It, slab could be constructed
4 and IL could be shown that its length
IL was not an injury to the slab VIII,
N could not this length be increased &
100 or 200 IT,? 10 was therefore de
., cided TO experiment on large scale
~ with this point in concrete road con
struction and TO find where the crack
il, would come Joints were placed onll
"a when the concrete mixers stopped
N for more than fifteen minutes. Thu
"a result was some very long slabs. tn
u. longest being 500 II. So far the slab
n have remained perfect with the "a
m ception OF few transverse cracks
9o While these cracks are not a seriou
"a injury TO the road they are insight,
M. The cracks generally appear in IN
lv longest slabs and their reEularit
Cd seems TO indicate a definite principl
M OF construction. BY these varior
or lengths Of slabs It was learned whit
a the longest slab, without cracks, cou
or. be, as constructed under condition
Ter as they are on the DUPONT roa
in Shorter slabs we're used for the pu
of pose Of getting away from the
,ad cracks. and while this was accol
nv. plished it created a condition mol
vs. serious than the cracks. that is,
ed increased the number OF joints.
ld Great attention was paid 10 secu
in ing a smooth. even surface. A powe
er templet was used on one section an
a very satisfactory surface was oil
he tanned except at the joints On othe
rs sections a steel templet made Of
ey by by 1-2-in. angle iron was use
nd and after the concrete was han
ay iioated a smooth but irregular an
ty somewhat unsatisfactory surface re
OF suited. This was remedied by a sec
W ond templet that was kept about
he It. in the rear OF the first templet. TIL
m second templet consisted of a foa
about IA ms. vide and Of the sam
shape as the crown OF the pavement
m This rested on the forms and wa
n. drawn with a longitudinal motion Tn
at result was a smooth surface Care wa
Id exercised 70 float the concrete as littll
I'd as possible in order to keep the stonl
z. aggregate near the surface.
he After the concrete was finished
a. was protected by canvas covers unit
d. the concrete was hard enough to hol,
he a covering OF earth which was KEEP
re soaked with water for IA days Thi
* cover was not removed until after 81
20 days. A short time was then allowed
re for the concrete TO harden in the al
before allowing any traffic on a.
II Especial care was taken to insure
Ut satisfactory ingredients. The Bureau
lie OF Inspection. Wilmington. Delaware
at tested all the materials and car
C. ried on considerable experimenting
throughout the entire work
Is Details Of the Material.
he "The stone used was a trap rocl
- graded between IA in. and 1 10 ins
is The French co.efiicient OF wear aver
a aged II. The sand was a dredgel
W river sand and especially we'll gradel
y up to IA In. The larger particles o
I'd sand were about the same size as tn
Is smallest pieces OF stone, thus making
IS a graded mixture from the 1 1-2 in
N stone, to the finest particles OF sand.
10 Five different brands OF Lehigl
Valley cement were used The cemen
was tested at the mill and arrived a
Mt destination ready for use.
IS. The experiments with hydratel
~ lime we're especially interesting. Il
n. the laboratory the lime seemed TO in
IN crease the strength Of concrete mad
Il. from some sands, but was detrimer