quite numerous on the building in question, at least more so than would
ordinarily be the case in mill building construction. The offset of 1
ft. at every column was made very readily by sliding wooden shoulder
pieces into place on the inner face of the form, which pieces in turn
received 2-in. faced planking, the latter being slid into place from
above. Thus the entire system was collapsible and small alterations were
easily made whenever the form was shifted. Flat surfaces or offsets
could be obtained at will by either removing or setting in the shoulder
pieces. Molding effects were made on the front face of the wall by
tacking molding strips to the form wherever necessary. The entire work
was done with common labor and the finished building presented a smooth,
homogeneous surface which required very little dressing.
[Illustration: Fig. 237.--Details of Cantilever Girders for Mezzanine
Floor for Four-Story Garage.]
~FLOOR AND ROOF CONSTRUCTION FOR FOUR-STORY GARAGE.~--The building was
53×200 ft., and 4 stories high, with provision for 2 additional stories
in the design of footings and columns. Two rows of wall columns
connected by transverse girders carrying the floor and roof slabs made a
comparatively simple construction, except for a mezzanine floor carried
on cantilever beams and except for the use of cantilever footings;
these two special details are shown by Figs. 236 and 237. The amount of
concrete in the building was 1,910 cu. yds., distributed as follows:
Cu. yds.
Footings, reinforced 190
Columns, reinforced 450
Floors and roof, reinforced 1,100
Floor on ground, not reinforced 170
-----
Total 1,910
The amount of reinforcing metal used was 237 tons, distributed as
follows:
Item. Tons. Lbs. per cu. yd.
Footings 42 442
Columns 20 90
Floors and roof 175 318
--- ---
Total and average 237 272
This is equivalent to 2 per cent. of steel in 1,910 - 170 = 1,740 cu.
yds.
_Forms._--The total area of concrete covered by forms (1,740 cu. yds.)
was 94,000 sq. ft., distributed as follows:
Footings, sq. ft. 4,000
Columns, sq. ft. 20,000
Floors and girders, sq. ft. 70,000
------
Total, sq. ft. 94,000
For the work 50,000 ft. B. M. of old lumber was used and 170,000 ft. B.
M. of new lumber was bought, the cost being as follows:
50 M. ft. B. M. at $13 per M. $ 650
170 M. ft. B. M. at $26 per M. 4,420
------
220 M. ft. B. M. at $23 $5,070
This is equivalent to 126 ft. B. M. per cu. yd. of concrete. New forms
were made for each floor except the sides of the girder molds which were
re-used so far as they would fit, but the roof forms were made from
lumber used for the floors. In all no more than 20 per cent of the form
lumber was used a second time. In round figures new lumber was required
for 80,000 sq. ft. of concrete; this gives a cost for lumber of 6.4 cts.
per sq. ft. The construction of the column and floor forms is shown by
Fig. 238. A force of 15 carpenters at $4.40 per day under a foreman at
$35 per week erected and tore down forms; the carrying was done by
laborers at $1.70 per day working under a foreman at $35 per week;
carpenters worked an 8-hour and laborers a 10-hour day. Forms for one
floor were framed and erected in 8 to 10 days. The cost of forms for
1,740 cu. yds. and 80,000 sq. ft. of concrete and per M. ft. B. M. was
as follows:
Item. Per cu. yd. Per sq. ft. Per M. ft.
Lumber $2.90 $0.064 $23.00
Framing, erecting and removing. 2.00 } 15.67
} 0.057
Handling lumber 1.10 } 8.70
----- ------ ------
Totals $6.00 $0.121 $47.37
[Illustration: Fig. 238.--Column and Floor Forms for Four-Story Garage.]
The lumber had a considerable salvage value which is not allowed for in
the above figures.
_Concrete._--The concrete was a Portland cement, ¾-in. trap rock
mixture, mixed wet in two Chicago Improved Cube Mixers equipped with
charging buckets. The mixers were located on the ground floor, one at
the rear and one at the front of the building, both discharging directly
to a hoist. With a gang of 30 men at $1.70 per 10-hour day under a
foreman at $35 per week a floor was concreted in 2 days, the columns
being concreted the first day and the floor being concreted the second
day. The labor cost for mixing and placing concrete and for fabricating
and setting reinforcement was as follows:
Item. Per cu. yd.
Mixing and placing concrete $1.95
Erecting and setting steel 2.05
-----
Total $4.00
The cost of concreting includes the cost of granolithic surface for the
floor slabs. The girder reinforcement was made up into unit frames and
the frames were set as a unit, horses set over the molds being used to
suspend and lower them into place. The cost of $2.05 per cu. yd. is
equivalent to ¾ ct. per lb. Summarizing, we have the following cost for
materials and labor on forms and for labor mixing and placing concrete
and reinforcement:
Per cu. yd.
Lumber for forms $ 2.90
Labor on forms 3.10
Labor on concrete 1.95
Labor on steel 2.05
-----
Total $10.00
This $10 total does not include the cost of the concrete nor of the
steel.
CHAPTER XX.
METHOD AND COST OF BUILDING CONSTRUCTION OF SEPARATELY MOLDED MEMBERS.
This chapter deals exclusively with the methods and cost of molding and
erecting separately molded wall blocks, girders, columns and slabs. The
structural advantages and disadvantages of this type of construction as
compared with monolithic construction will not be considered. The data
given in succeeding paragraphs show how separate piece work has been
done and what it has actually cost to do it in a number of instances.
~COLUMN, GIRDER AND SLAB CONSTRUCTION.~--European engineers have developed
several styles of open web or hollow girder and column shapes, but in
America solid columns and girders have been used except in the
comparatively few cases where one of the European constructions has been
introduced by its American agents.
~Warehouses, Brooklyn, N. Y.~--In constructing a series of warehouses in
Brooklyn, N. Y., the columns and girders were molded in forms on the
ground. For molding the columns, forms consisting of two side pieces and
one bottom piece, were used, saving 25 per cent. in the amount of lumber
required for a column form, and doing away with yokes and bolts, since
only simple braces were required to hold the side forms in place. It was
found that the side forms could readily be removed in 24 to 48 hours,
thus considerably reducing the time that a considerable portion of the
form lumber was tied up. It was figured by Mr. E. P. Goodrich, the
engineer in charge of this work, that this possible re-use of form
lumber reduced the amount required another 50 per cent. as compared with
molding in place. Girders were molded like columns in three-sided forms;
the saving in form work was somewhat less than in the case of columns,
but it was material. In general, Mr. Goodrich states, the cost of
hoisting and placing molded concrete members is higher per yard than
when the concrete is placed wet. That is in mass before it is hardened.
[Illustration: Fig. 239.--Sketch Showing Forms and Reinforcement for
Visintini Girder.]
~Factory, Reading, Pa.~--In constructing a factory at Reading, Pa., an
open or lattice web type of girder invented by Mr. Franz Visintini and
extensively used in Austria was adopted; columns were molded in place in
the usual manner with bracket tops to form girder seats. The girders
were reinforced with three trusses made up of top and bottom chord rods
connected by diagonal web rods; one truss was located at the center of
the beam and one at each side. The method of molding was as follows: The
trusses were made by cutting the chord rods to length and threading the
web diagonals and verticals onto them. To permit threading the web
pieces were bent, when rods were used, with an eye at each end; when
straps were used the ends were punched with holes. The work was very
simple and was done mostly by boys in the machine shop of the company
for which the building was being erected. The girders were molded two at
a time in forms constructed as shown by the sketch. Fig. 239. A form
consisted of a center board, two side boards, two end pieces and the
proper number of cast iron cores, all clamped together by three yokes.
Triangular cast iron plates, A, were screwed to the bottom boards for
spacers. The side, center and end boards were then set up and the end
clamps were placed. The cast iron hollow cores, B, were then set over
the spacers, and the form was ready for pouring. A layer of concrete was
placed in the bottom of the mold and the first side truss was placed;
the concrete was then brought half way up and the middle truss was
placed; concreting was then continued up to the plane of the second side
truss which was placed and covered. Cores and forms were all cleaned and
greased each time they were used. The cores were removed first by means
of a lever device and generally within three or four hours after the
concrete was placed. The remainder of the form was taken down in two to
four days and the beam removed.
~Kilnhouse, New Village, N. J.~--In constructing a kiln house for a cement
works one story columns with bracket tops and 50-ft. span roof girders
were molded on the ground and erected as single pieces. The columns by
rough calculation averaged about 2 cu. yds. of concrete and 675 lbs. of
reinforcement each or about 337 lbs. of steel per cubic yard. The
girders averaged by similar calculation 5 cu. yds. of concrete and 2,260
lbs. of steel, or 452 lbs. per cubic yard of concrete. The average
weight of columns was thus not far from 41.3 tons and of girders fully
11 tons.
[Illustration: Fig. 240.--Arrangement for Molding Ten Single-Bracket
Columns.]
Several combinations of arrangements were used for molding the columns
and girders. For wall columns having one bracket the arrangement shown
by Fig. 240 was adopted. The concrete slab molding platform was covered
with paper, and on this the two outside and the middle columns were cast
in forms. When those columns had set the forms were removed, the
intervening spaces were papered and the two remaining columns were cast.
Ten columns, five sets of two columns in line, were cast on each base.
The remaining columns were cast in combination with girders as shown by
Fig. 241. The two outside lines of columns (1) were molded in forms,
allowed to stand until set and then stripped. Using a column surmounted
by a shallow side form for one side and a full depth side form for the
other side molds were fashioned for the two outside girders, Nos. 2 and
3. One full depth side form and the side of girder No. 2 formed the mold
for girder No. 4. Girder No. 5 was then molded between girders No. 3 and
No. 4.
[Illustration: Fig. 241.--Arrangement for Molding Four Four-Bracket
Columns and Four Roof Girders]
[Illustration: Fig. 242.--Forms for 50-ft. Roof Girders.]
The construction of the girder forms is shown by Fig. 242. This drawing
shows one of the four main sections making up a complete form. A full
size form of this construction contained about 1,100 ft. B. M. of
lumber, and three were built, so that 3,300 ft. B. M. of form lumber
were used for molding 20 girders, or 33 ft. B. M. per cubic yard of
concrete. A full size column form contained about 225 ft. B. M. of
lumber, and eight were constructed, so that 1,800 ft. B. M. of form
lumber were used for molding 56 columns, or about 16 ft. B. M. per cubic
yard of concrete.
The following was the cost of erecting a full column form including
lining, plumbing, bracing and yoking, but excluding lumber and original
construction:
1 carpenter, 3 hrs., at $0.25 $0.750
1 helper, 3 hrs., at $0.175 0.525
1 helper, 1 hr., at $0.175 0.175
1-5 boss carpenter, 3 hrs., at $0.30 0.180
------
Total $1.630
This gives a cost of $7.25 per M. ft. B. M. for erecting column forms.
The cost of erecting a full size girder form including lining, plumbing,
bracing and setting six bolts was as follows:
2 carpenters, 5 hrs., at $0.25 $2.50
2 helpers, 5 hrs., at $0.175 1.75
2 laborers, ½ hr., at $0.15 0.15
¼ boss carpenter, at $0.30 0.375
------
Total $4.775
This gives a cost of $4.35 per M. ft. B. M. for erecting girder forms.
The reinforcement was erected inside the forms for both columns and
girders. The cost of erection for one column was:
2 laborers, 4 hrs., at $0.15 $1.20
1/3 foreman, 4 hrs., at $0.225 0.30
-----
Total $1.50
This gives a cost of about 0.22 cts. per pound for erecting column
reinforcement, including the bending of the horizontal ties or hoops.
The girder reinforcement was erected by piece work at a cost of $1.80
per girder--or about 0.08 ct. per pound.
The concrete used was a 1-6 mixture of Portland cement and crusher run
stone all passing a ½-in. sieve and 10 per cent. passing a 200 mesh
sieve. No trouble was had in handling this fine aggregate. It was mixed
in a Ransome mixer, elevated so as to deliver the batches into cars on a
standard gage track. This track ran between the base slabs on which the
molding was done. Each car held about 3 cu. yds. and discharged through
a side gate and spout directly into the forms, the mixture being made so
wet that it would flow readily. The company used its own cement and
stone for concrete and charged up the cement at $1 per barrel and the
stone at 60 cts. per cubic yard. At these prices, and assuming that a
cubic yard of concrete of the mixture above described would contain
about 1.25 bbl. of cement and 1.5 cu. yd. of stone, we have the
following cost of materials per cubic yard of concrete:
1.25 bbls. of cement, at $1 $1.25
1.5 cu. yds. stone, at $0.60 0.90
-----
Total $2.15
The actual cost of mixing the concrete and delivering it to the cars was
as follows:
Item. Per cu. yd.
1 foreman, at 20 cts per hour $0.0300
3 men shoveling stone, at 15 cts. per hour 0.0675
3 men filling hopper, at 15 cts. per hour 0.0675
1 man bringing cement, at 18 cts. per hour 0.0225
1 man dumping cement, at 15 cts. per hour 0.0225
9 h.p., at ½ ct. per h.p. hour 0.0450
Superintendence, repairs, etc. 0.0270
-------
Total $0.2820
The cost of hauling the concrete from mixer to forms ran about 2.7 cts.
per cubic yard, so that we have a cost for concrete in place of:
Concrete materials, per cu. yd. $2.150
Mixing concrete, per cu. yd. 0.281
Hauling concrete, per cu. yd. 0.027
------
Total cost, per cu. yd. $2.458
The cost, then, per column or girder molded, assuming that it was
necessary to erect a full form, was about as follows:
Columns:
2 cu. yds. concrete, at $2.46 $ 4.92
675 lbs. steel, at 2½ cts. 16.77
Erecting steel, at 0.22 ct. per lb. 1.50
Erecting forms 1.63
------
Total $24.82
Girders:
5 cu. yds. concrete, at $2.46 $12.30
2,260 lbs. steel, at 2½ cts. 56.50
Erecting steel, at 0.08 ct. per lb. 1.80
Erecting forms 4.77
-----
Total $75.37
[Illustration: Fig. 243.--View Showing Method of Hoisting Molded
Columns.]
These figures give a unit cost of $12.41 per cu. yd. for molded columns,
and of $15.07 per cu. yd. for molded girders, The columns were erected
by a Browning locomotive crane, which lifted and carried them to the
work and up-ended them into place. To facilitate lifting the columns
from the molding bed a 1½-in. pipe 8 ins. long was cast into both ends;
pins inserted into these sockets provided hitches for the tackle. The
column was lifted off the molding bed and blocked up, then iron clamps
were attached, one at each end, as shown by Fig. 243. A gang of 1
foreman and 14 men erected from 5 to 7, or an average of 6 columns per
10-hour day. The average wages of the erecting gang were 21 cts. per
hour. The cost then of column erection was (14 × $2.10) ÷ 6 = $5.25 per
column, or $2.63 per cu. yd. of concrete.
[Illustration: Fig. 244.--Sketch Showing Sling for Erecting 50-ft. Roof
Girders.]
The roof girders had 1-in. eye-bolts 24 ins. long cast into them
vertically about 4 ft. from the ends. They were lifted off the molding
bed by tackle by the locomotive crane to these eye-bolts and blocked up
to permit the adjustment of the sling. This sling is shown by the
sketch, Fig. 244, and as will be observed acts as a truss. At first it
was used without the vertical, but the cantilever action of the
unsupported ends caused cracks. The girders were loaded onto cars by the
locomotive crane and taken to the work, where they were hoisted and
placed by a gin pole. The girder erecting gang consisted of 1 foreman
and 14 men, working a 10-hour day at 21 cts. per hour. This gang erected
four girders per day, at a cost of (15 × $2.10) ÷ 4 = $7.87 per girder,
or $1.57 per cu. yd. of concrete.
The cost of girders and columns in place was thus about as follows:
Columns: Per unit. Per cu. yd.
Molding $25.00 $12.50
Erecting 5.25 2.63
------ ------
Totals $30.25 $15.13
Girders:
Molding $75.00 $15.00
Erecting 7.87 1.57
------ ------
Totals $82.87 $16.57
[Illustration: Fig. 245.--View Showing Method of Handling Roof Slabs.]
In this same building the roof was composed of 12×6¼ ft.×4-in. slabs
molded in tiers; a slab was molded and when hard was carpeted with paper
and the form moved up and a second slab molded on top of the first. This
operation was repeated until a tier of slabs had been molded. By molding
each slab with a 3-in. overlap, as shown by Fig. 245, they could be
easily separated by lifting on hooks inserted under the overhanging
ends. Each slab contained 0.925 cu. yd. of concrete and about 116¾ lbs.
of reinforcement. The cost of molding one roof slab, including
materials, forms and labor, was as follows:
Materials: Per slab. Per cu. yd.
1 bbl. cement, at $1 $1.000 $1.081
1.06 tons stone, at $0.60 0.636 0.687
116¾ lbs. steel, at 2¼ cts. 2.647 2.862
------ ------
Total $4.283 $4.630
Forms:
Lumber and making $0.104 $0.112
92 sq. ft. paper, at 33-1/3
cts. per 500 sq. ft. 0.055 0.059
Labor erecting and removing 0.5625 0.608
------- ------
Total $0.7215 $0.779
Mixing, Hauling and Placing:
Mixing $0.222 $0.240
Hauling 0.025 0.027
Placing concrete and steel 0.170 0.183
------ ------
Total $0.417 $0.450
General Expenses:
Housing and heating $0.700 $0.757
Superintendence, power, etc. (10%) 0.612 0.661
------ ------
Total $1.312 $1.418
Grand totals $6.7335 $7.277
The roof slabs were raised from the casting beds by means of the
locomotive crane and hooks, as shown by Fig. 245, and loaded onto cars;
eight slabs made a carload. The cars were run to the work, where the gin
poles hoisted the slabs one at a time to cars running on a track built
on timbers laid on top of the roof girders. A small derrick on rafters
picked the slabs from the hand car and set them in place. A gang of 15
men erected from 18 to 20 slabs per 10-hour day. With average wages at
21 cts. per hour the cost of erection was (15 × $2.10) ÷ 19 = $1.66 per
slab, or $1.79 per cu. yd. The total cost of slabs in place was thus:
Item. Per slab. Per cu. yd.
Molding $6.73 $7.27
Erecting 1.66 1.79
----- -----
Total $8.39 $9.06
In studying these cost figures their limitations must be kept in mind.
Because of the character of the available data quantities had in several
cases to be estimated from the working drawings. The cost of lumber for
and of framing column and girder forms is not included, but this is
partly balanced at least by the assumption that each form was erected
complete for each column and girder, which was not the case, as has been
stated. Cost of plant is not included nor is cost of shoring the columns
until girders and struts were placed, nor are several minor
miscellaneous items.
~HOLLOW BLOCK WALL CONSTRUCTION.~--Three general processes of molding
hollow wall blocks of concrete are employed: (1) A dry mixture is
heavily tamped into a mold and the block is immediately released and set
aside for curing; (2) a liquid is poured into molds, where the block
remains until hard: (3) a medium wet mixture is compressed into a mold
by hydraulic presses or other means of securing great pressure. The
molds used may be simple wooden boxes with removable sides or mechanical
molds of comparative complexity. Generally mechanical molds, or concrete
block machines as they are commonly called, will be used. There are a
score or more kinds of block machines all differing in construction and
mode of operation. None of them will be described here, but those
interested may consult "Concrete Block Manufacture" by H. H. Rice or
"Manufacture of Concrete Blocks and Their Use in Building Construction"
by H. H. Rice, Wm. M. Torrance and others.
~Factory Buildings, Grand Rapids, Mich.~--The buildings ranged from one to
four stories high and altogether occupied some 74,000 sq. ft. of ground.
The owners installed a block making plant fully equipped with curing
racks, two Ideal machines, two National concrete mixers, 5 h.p. gasoline
engine, platens, tools and a Chase industrial railway.
The walls were constructed of 24-in. square pilasters of blocks arranged
as shown by Fig. 246, connected by curtain wall belt courses of single
blocks. The blocks were 8×8×16 ins., and after molding the faces were
bush hammered and the edges tooled. The pilasters, consisting of four
blocks laid around an 8×8-in. hollow space, were solidified by pouring
the 8×8-in. space and all but the three outside block cavities with wet
concrete. The interior of the building was of regulation mill
construction, and as the pilasters reached the heights for beam supports
cast iron plates with downward flanges were set in the concrete. These
plates had a cast pin projecting upward to fasten the beam end.
[Illustration: Fig. 246.--Concrete Block Pilaster for a Factory
Building.]
The materials used for the block were Sandusky Portland cement and ¾-in.
bank gravel well balanced from fine to coarse. The blocks were molded
with 1-3 mortar faces, the mortar being waterproofed by a mixture of
Medusa waterproofing compound. All concrete was machine mixed. The men
operating the block machines were paid 1 ct. for each block molded, so
that their pay depended upon the energy with which they worked. The men
handling materials and engaged in handling and curing the blocks were
paid $1.75 per day. The gravel was shoveled from the railway cars onto
the screens and from the screen piles to the mixers. The gang was
organized as follows:
Item. Per day.
8 men handling materials, at $1.75 $14.00
5 men operating molds, at 1 ct. per block 15.00
1 man mixing facing mortar, at $1.75 1.75
2 men loading blocks onto trucks, at $1.75 3.50
2 men unloading blocks from trucks, at $1.75 3.50
3 men sprinkling blocks, at $1.75 5.25
------
Total, 21 men molding and curing blocks $43.00
The average daily run was 1,500 blocks, or 300 blocks per machine.
This output was easily maintained after the gang got broken in;
sometimes it ran higher and sometimes lower, but the average was as
given. The men operating the block machines thus earned $3 each per day.
The labor cost of molding and curing per block was thus 2.87 cts. As the
blocks had about 25 per cent. hollow space, each block 8×8×16 ins.
contained 0.45 cu. ft. of concrete; a cubic yard of concrete, therefore,
made 60 blocks, so that the labor cost of making the blocks was 60 ×
2.87 cts. = $1.72 per cubic yard. This cost does not include foreman's
time, materials, interest, depreciation or general expenses. It was
estimated by the owners that the blocks cost them 9 cts. apiece cured,
or about $5.40 per cubic yard of concrete. This 9 cts. evidently
includes materials and labor alone.
Upon removal from the molds the blocks were loaded onto cars, taken to a
large shed and there unloaded onto shelving arranged to hold five rows
of blocks one above the other, two blocks opposite each other on each
shelf. The blocks were left in the shed 24 to 48 hours to get the
preliminary set, then they were loaded on small cars and taken to the
yard, where they were removed from the cars and stacked. They were
sprinkled every day for six days, being kept covered meanwhile with
oiled cotton cloth. The labor costs given above include molding,
sprinkling and handling the blocks up to this point.
To lay the blocks they were again loaded on cars and run to an elevator
in a wooden tower outside the building. The elevator lifted the car to
the floor on which the blocks were to be used, where it was run off onto
a track reaching the full length of the building. The blocks were
unloaded directly behind the masons. Where the walls were high enough
for scaffolding the blocks were unloaded directly onto the first
scaffold and, when necessary, handed up to the scaffolds above. The
masons employed were regular stone masons receiving the regular scale of
wages of $3.50 per day. The number of blocks laid by each mason was 125
per day in building pilasters and 200 per day in building plain wall.
Sometimes 250 blocks per day per man were laid in plain wall work. The
cost per block of laying above was thus 2.8 cts. pilasters and 1.75 cts.
in plain wall. This cost does not include transporting the blocks from
yard or of handling them to the scaffold behind the masons, nor does it
include the cost of materials and labor for mixing and delivering
mortar.
One of the features of this work was the method of transporting the
blocks by cars. A complete system of tracks was provided covering the
block plant and yard, the building sites and the several floors of the
buildings themselves. All blocks and other materials were transported by
cars running on these tracks, both cars and tracks being of the type
made by the Chase Foundry & Manufacturing Co. of Columbus, Ohio.
~Residence, Quogue, N. Y.~--The following record of methods and cost of
constructing a concrete block residence is furnished by Mr. Noyes F.
Palmer: A mixture of sand and pebbles was had on the site; screening was
necessary merely to sort out the odd size stones. A mixture of 1 cement
and 5 sand was really a 1-2-3 mixture, the 2 being the finest grades of
sand and the 3 being various gravel sizes--none too large, none too
small--so that the proportion was 2/5 fine sand and 3/5 gravel.
The concrete was hand mixed, and as the gravel had always just been
excavated it contained moisture and did not have to be wetted. The sand
and gravel were mixed and turned three or four times and spread out
thin, and the cement was carefully spread over them in a uniform layer.
The mass was then turned three or four times until the eye could detect
no difference in color; that is, each grain large enough for the eye to
discern seemed to be coated with cement. After this dry mixing, water
was added in a fine spray--not a deluge from a pail--but only enough to
moisten the mixture. The mass was then turned three or four times. The
mixture was then shoveled into the mold, no special face mixture being
used, so as to about half fill it, and was then tamped by two men, one
standing on each side of the machine. Altogether three layers of
material were so placed and tamped and then a shovelful of sand and
cement mixture was spread over the top to permit an even "strike-off."
As each block was molded it was carried on the working plate and set
down on skids properly spaced to fit the marks on the plate. This is an
important detail and Mr. Palmer comments on it as follows: "The writer
saw inexperienced men careless about it and who would break the backs of
many blocks by not having the skids properly placed. After the blocks
have been at rest for half an hour commence to spray them with a
revolving garden sprinkler or by carefully wetting with a sprinkling pot
on the center of the block only. The blocks should not be allowed to dry
out for at least ten days after removal from the working plate. The
removal from the working plate can be done the morning after molding and
should never be done before even if the block was made in the morning.
In removing the green block from the skids let there be cones of sand
between the rows of blocks and up-end each working plate so as to let
the end of the block come upon the sand cushion. Don't twist and turn
the block, and to remove the working plate pass a stick through the core
holes in both block and plate so that the plate will not fall when
loosened. A slight rap on the center of the plate will loosen it. As
soon as the blocks are up-ended commence the spraying and soak the sand
underneath the block. It may seem unnecessary to dwell on these points
so long, but barrels of cement and barrels of money have been wasted by
neglecting to supply the hardening block with water. Curing is just as
important as molding in making concrete blocks."
The block construction had been detailed by the architect from cellar to
roof, so that it was known beforehand how many blocks of given size were
to be made. The unit of length was 32 ins.; this afforded fractional
parts of 8 ins., 16 ins. and 24 ins., therefore all openings were in
multiples of 8 ins. Odd sizes were made, by inserting "blanks" in the
mold box, to inches or fractions of an inch if desired. This unit
length was less mortar joints, while the unit of height was 9 ins., or
the same as four ordinary bricks with joints. The floor levels were
calculated in multiples of 9 ins., so that the wall could be finished
all around where the beams were to be seated. This beam course was made
of solid blocks; that is, no cores were used in molding them. With the
machine used no change was required to mold these solid blocks except to
remove the cores. The core holes in the working plate were simply
covered with pieces of tin. The shape of the block was the same and the
same materials were used.
The best record in making blocks for this work was 30 blocks, 8×9×32
ins., in one hour, working six men, three mixing and three on the
machine, and using one barrel of cement for 16 blocks. This was a record
run, however, a fair average being 20 blocks per hour, or 200 per ten
hours, which was the day worked. We have then the cost of making blocks
as follows:
1 foreman, at $2.50 $ 2.50
5 helpers, at $2 10.00
13 barrels cement, at $2 26.00
10 cu. yds. sand and gravel, at $1 10.00
Interest and depreciation on machine 2.00
------
Total for 200 blocks $50.50
This gives a cost per block of $50.50 ÷ 200 = 25¼ cts. The displacement
in the wall of each block is 1.75 cu. ft., or the same as 30 bricks.
The cost of laying blocks is the most uncertain item in the whole
industry. Mr. Palmer states that he has known of instances where it cost
only 5 cts. per block and of other instances where, because of the
difficulty of getting help and its inexperience, it cost 15 cts. per
block. In this particular building one mason and three helpers laid 100
blocks per day. The building had no long walls, but it did have many
turns. The cost of laying, then, was as follows:
1 mason, at $4 $ 4.00
3 helpers, at $2 6.00
-----
Total for 100 blocks $10.00
This gives a cost for laying of 10 cts. per block. We have, then:
Making 2,000 blocks $505
Laying 2,000 blocks 200
----
Total $705
This gives a cost of 35¼ cts. per block for making and laying.
The use of a derrick for laying the blocks proved a considerable item of
economy in this work. This derrick cost $50 and two men could mount and
move it on the floor beams. It had a boom reaching out over the wall and
was operated by a windlass. A plug and feather to fit the center 6-in.
hole in the block was used for hoisting the blocks. By this means blocks
only seven days old were laid without trouble. It may be noted that the
walls were kept drenched with water to make sure that the blocks did not
dry out until they were at least 28 days old. In laying the blocks a
thin lath was used to keep the mortar back about one inch from the face.
This precaution will prevent much labor in cleaning the walls from
mortar slobber.
~Two-Story Building, Albuquerque, N. M.~--The following record of cost of
making 9×10×32-in. hollow blocks in a Palmer machine and of laying 2,000
of them in two-story building walls is given by Mr. J. M. Ackerman. Sand
cost 60 cts. per cu. yd., and cement cost $3 per barrel. Lime cost 30
cts. per bushel. One barrel of cement made 20 blocks, using a 1-4 sand
mixture. In making 2,000 blocks about 100 blocks, or 5 per cent., were
lost by blocks breaking in hauling from yard to building or by cutting
blocks to fit the work. The blocks were molded by piece work for 5 cts
per block, all materials, tools and plant being supplied to the molders.
Three men with one machine made from 100 to 150 blocks per day. The cost
was as follows:
Item. Per block.
Cement, at $3 per bbl. $0.15
Molding, at 5 cts. per block 0.05
Sand, at 60 cts. per cu. yd. 0.03
Carting, yard to building 0.02
Lime and sand for mortar 0.03
Laying in wall 0.10
Loss in making and cutting 0.01
-----
Total $0.39
As each block gave 9 × 32 = 288 sq. ins., or 2 sq. ft., of wall surface,
the cost of the wall per square foot was 19.5 cts. Assuming 40 per cent.
hollow space, each block contained 1 cu. ft. of concrete, which cost 23
cts., or $6.21 per cu. yd., for materials and molding. Blocks in the
wall cost $10.55 Per cu. yd. of concrete.
~General Cost Data.~--The following data are given by Prof. Spencer B.
Newberry. The average weights of three sizes of hollow blocks are as
follows:
Size, ins. P. C. Hollow Space. Weight, lbs.
8×9×32 33-1/3 120
10×9×32 33-1/3 150
12×9×32 33-1/3 180
Costs of materials are assumed as follows:
Item. Per 100 lbs.
Cement, at $1.50 per bbl. $0.40
Hydrated lime, at $5 per ton $0.25
Sand, gravel or screenings, at 25 cts. per ton $0.012
Mixed in batches of 750 lbs., sufficient for six 8-in. or four 12-in.
blocks, the cost of materials per batch and per block will be for a 1-4
mixture as follows:
Item. Per Batch. 8-in. Block. 12-in. Block.
150 lbs. cement $0.60 $0.10 $0.15
600 lbs. sand 0.072 0.012 0.018
------ ------ ------
Total $0.672 $0.112 $0.168
In general a factory producing 600 8-in. blocks per day will require 25
men to operate it. At an average wage of $1.80 per day the following is
considered as a fair estimate of cost:
Item. Per Day. Per Block.
Materials for 600 blocks $ 60 $0.10
25 men, at $1.80 45 0.075
Repairs 10 0.017
Office and miscellaneous 20 0.034
---- ------
Total $135 $0.226
This gives for 8×9×32-in. blocks a cost of about $6.78 per cu. yd. of
concrete for materials and molding or of 11.3 cts. per sq. ft. of face.
Mr. L. L. Bingham gives the following as the average cost per square
foot of face for 10-in. wall from data collected from a large number of
block manufacturers operating in Iowa in 1905:
Cement at $1.60 per bbl. 4.5 cts.
Sand 2.0 cts.
Labor at $1.83 per day 3.8 cts.
---------
Total cost per square foot 10.3 cts.
Assuming one-third hollow space, the cost for materials and molding was
$5.05 per cu. yd. of concrete not including interest, depreciation,
repairs, superintendence or general expenses.
CHAPTER XXI.
METHODS AND COST OF AQUEDUCT AND SEWER CONSTRUCTION.
Aqueducts and sewers in concrete are of three kinds: (1) Continuous
monolithic conduits, (2) conduits laid up with molded concrete blocks,
and (3) conduits made up of sections of molded pipe. Block conduits and
conduits of molded pipe are rare in America compared with monolithic
construction; examples of each are, however, given in succeeding
sections, where forms, methods of molding, etc., are described. The
following discussion refers to monolithic construction alone.
~FORMS AND CENTERS.~--Forms and centers for conduit work have to meet
several requirements. They have to be rigid enough not only to withstand
the actual loads coming on them, but to keep from being warped by the
alternate wetting and drying to which they are subjected. They have also
to be constructed to give a smooth surface to the conduit. To be
economical, they have to be capable of being taken down, moved ahead and
re-erected quickly and easily. The carpenter costs run high in
constructing conduit forms, so that each form has to be made the most of
by repeated use.
Three different constructions of traveling forms are described in the
succeeding sections. For small work, such forms appear to offer certain
advantages, but for conduits of considerable size their convenience and
economy are uncertain. The experience with the large traveling form
employed on the Salt River irrigation works in Arizona was, when all is
said, rather discouraging. The authors believe that for work of any size
where the concrete must be supported for 24 hours or more, forms of
sectional construction will prove cheaper and more expeditious than any
traveling form so far devised.
No class of concrete work, perhaps, offer so good an opportunity for the
use of metal forms as does conduit work. The smooth surface left by
metal forms is particularly advantageous, and there is a material
reduction in weight and a large increase in durability due, both to the
lack of wear and to freedom from warping. Steel forms of the Blaw type
shown by Fig. 247, have been used for conduits up to 25 ft. in diameter.
The form illustrated, Fig. 247, was for a 12-ft. 3-in. sewer; in this
case a roof form alone was used, but full circular and egg-shape forms
are made. The Blaw collapsible Steel Centering Co., of Pittsburg, Pa.,
make and lease steel forms of this type.
[Illustration: Fig. 247.--Blaw Collapsible Steel Centering for Conduit
Construction.]
Sectional wooden forms for conduits of large diameters are shown by the
drawings in several of the succeeding sections. Figures 248 and 249 show
such forms for small diameters. The form shown by Fig. 248 is novel in
the respect that after being assembled a square timber was passed
through it lengthwise, occupying the holes B and having its ends
projecting and rounded to form gudgeons. The form was mounted with
these gudgeons resting on horses, so that it could be rotated and thus
wound with a narrow strip of thin steel plate. Thus sheathed, the form
was lowered into the trench and the concrete was placed around it. When
the arch had been turned, the wedges A were driven in until the ribs
C dropped into the slots a and clear of the steel shell; the arch form
was then pulled out and finally the invert form, leaving the steel shell
in place to hold the concrete until hard. The strip of steel was then
removed by pulling on one end until it unwound like cord from the inside
of a ball of twine. Steel strips 6 ins. wide and 1/24 in. thick were
used successfully in constructing a 5-ft. egg-shaped sewer in
Washington, D. C. The forms were made in sections 16 ft. long, and were
taken out as soon as the concrete had been placed.
[Illustration: Fig. 248.--Sectional Steel Wrapped Wooden Form for
Conduit Construction.]
[Illustration: Fig. 249.--Invert Form for Conduit Construction.]
The form shown by Fig. 249, is an invert form, used in constructing the
sewer shown by Fig. 249, built at Medford, Mass., in 1902, by day labor.
The concrete was 1-3-6 gravel. The forms for the invert were made
collapsible and in 10-ft. lengths. The two halves were held together by
iron clamps and hook rods. The morning following the placing of the
concrete the hook rods were removed and turnbuckle hooks were put in
their places, so that by tightening the turnbuckle the forms were
carefully separated from the concrete. The concrete was then allowed to
stand 24 hours, when the arch centers were set in place. These centers
were made of 7/8×1½-in. lagging on 2-in. plank ribs 2 ft. apart, and
stringers on each side. Wooden wedges on the forward end of each section
supported the rear end of the adjoining section. The forward end of each
section was supported by a screw jack placed under a rib 2 ft. from the
front end. To remove the centers, the rear end of a small truck was
pushed under the section about 18 ins.; an adjustable roller was
fastened by a thumb screw to the forward rib of the center; the screw
jack was lowered allowing the roller to drop on a run board on top of
the truck; the truck was then pulled back by a tail rope until the
adjustable roller ran off the end of the truck; whereupon the truck was
pulled forward drawing the center off the supporting wedges of the rear
section. Each lineal foot of sewer required 1¼ cu. yds. of excavation
which cost 74.2 cts. per foot, and 1 cu. ft. of brick arch which cost
$12.07 per cu. yd., or 44.2 cts. per lineal foot of sewer. The invert
required 4 cu. ft. of concrete per foot, which cost as follows:
Item. Per cu. yd.
Portland cement at $2.15 per bbl. $2.292
Labor mixing and placing 3.017
Cost of forms 0.187
Labor screening gravel 0.471
Carting 0.592
Miscellaneous 0.146
------
Total $6.705
The cost of the invert was thus $1.002 per lin. ft. of sewer.
Collapsible metal forms for manholes and catch basins are made by
several firms which make block and pipe molds. A cylindrical wooden form
construction is shown by Fig. 250. The outside form consists of three
segments of a cylinder made of 2-in. lagging bolted to hoops. Bent lugs
on the ends of the hoops, were provided with open top slots and were
bolted together through 1×3/8-in. bars which extended the full length of
the form between lugs. The assembled form was collapsed by pulling up on
the bars, thus lifting the bolts out of the slots. The inner mold is
also made in three sections with strap hinges at two of the joints and
at the third joint a wedge-shaped stave. The other details are shown by
the drawing. To mold the top of the basin two cone-shaped forms are
used, an outer form made in one piece and an inner form made in
sections. Some 26 catch basins were built in Keney Park, Hartford,
Conn., by Mr. H. G. Clark, at a cost of $7 apiece for concrete in place,
and there was closely 1 cu. yd. of concrete in each.
[Illustration: Fig. 250.--Form for Circular Catch Basin or Manhole.]
~CONCRETING.~--Except for pipes of small diameter, the concreting is done
in sections, each section being a day's work. Continuity of construction
has not proved successful, except for pipes of moderate size, in the few
cases where it has been tried. Examples of continuous construction
methods are given in succeeding sections. Methods of molding and laying
cast concrete pipe are also best shown by the specific examples given
further on. In concreting large diameters, the work may be done by
molding successive full barrel sections, or by molding first the invert
and then the roof arch, each in sections. The engineer's specifications
generally stipulate which plan is to be followed. Construction joints
between sections are molded by bulkhead forms framed to produce the type
of joint designed by the engineer; the most common type is the tongue
and groove joint.
[Illustration: Fig. 251.--Cross-Section of Pinto Creek Irrigation
Conduit.]
For small diameters built with traveling forms, a comparatively dry
concrete is essential, but when the centers are left in place until the
concrete has set, a wet mixture is preferable, as it is more easily
placed and worked around the reinforcement in the thin shells. Mixers
are commonly specified even for small work, because of their generally
more uniform and homogeneous product. Portable mixers hauled along the
bank and discharging into the forms through chutes, furnish a cheap and
rapid arrangement where the section being built has a considerable
yardage. The examples given in succeeding sections present various
methods of mixing and placing concrete in conduit work.
[Illustration: Fig. 252.--Traveling Form for Pinto Creek Conduit.]
~REINFORCED CONDUIT, SALT RIVER IRRIGATION WORKS, ARIZONA.~--The pipe had
the cross-section shown by Fig. 251, and formed a syphon carrying water
under the bed of a creek. The concrete was a 1-2½-4 fine gravel mixture,
mixed by hand on boards 150 ft. apart along the line. The shell was
reinforced as shown.
The forms consisted of an outside form constructed as shown by Fig. 251,
by inserting 2½-in.×5½ ft. lagging strips in the metal ribs. The inside
form was designed to permit continuous work by moving the form ahead as
the concreting progressed. It consisted as shown by Fig. 252, of an
invert form on which an arch form was carried on rollers. The invert
form was pulled along by cable from a horsepower whim set ahead, being
steered, aligned and kept to grade by being slid on a light wooden
track. It had the form of a long half cylinder, with its forward end
beveled off to form a scoop-like snout. The arch center consisted of
semi-circular rings 2 ft. long, set one at a time as the work required.
Each ring, when set, was flange-bolted to the one behind, and each was
hinged at three points on the circumference to make it collapsible. In
operation, the invert form was intended to be pulled ahead and the arch
rings to be placed one after another in practically a continuous
process. So that the arch rings might continue supported after the
invert form was drawn out from under them, invert plates similar to the
arch plates were inserted one after another in place of the shell of the
invert form. The plan provided very nicely for continuous work, but
continuous work was found impracticable for all but about 2,500 ft. of
the 6,000 ft. of conduit built. The reason for this seems to have been
at least in a great measure, the slow setting cement made at the cement
works established by the Government, at Roosevelt. In building the first
300 ft. of conduit, a commercial cement was used and a progress of 120
lin. ft. of pipe per 24 hours was easily made. This work was done in
June. Later, but still in warm weather, using the Government cement and
70 ft. of arch plates, not more than 70 ft. of pipe could be completed
in 24 hours; if the plates were taken down sooner, patches of concrete
fell out or peeled off with them. As the weather grew colder, this
difficulty increased, until finally, the idea of continuous work was
abandoned and for some 3,500 ft. of conduit only one 8-hour shift per
day was worked. In December and January the plates had to remain in
place three days, so that the progress was only 24 ft. per day; in warm
weather this rate was increased to 40 ft. per day.
Costs were kept on two sections of one of the lines and the figures
shown in the accompanying table were obtained.
A gang consisted of a foreman at $175 per month, a sub-foreman at $3.50
per day, and the following laborers at $2.50 per day: one bending the
reinforcement rings; two placing the reinforcement; four taking down,
moving and erecting the stationary plates; four placing the concrete and
outside lagging; two wheeling concrete; six mixing concrete; one
wheeling sand and gravel; one watering the finished pipe; four laying
track for the steering apparatus, moving the superstructure and hangers,
mixing boards, runways, etc.; one pointing and finishing inside the
pipe; and one on the whim and doing miscellaneous work. The labor was
principally Mexican, and only fairly efficient.
It is important to note that the costs given in the table are labor
costs only of mixing and placing concrete and moving forms; they do not
include engineering, first cost of forms, concrete materials,
reinforcement or grading.
May, '06. July, '06.
Wages 714 1,009 Cost Per
Per Lin. Ft. Lin. Ft. Per Cu.
Day. Cost. Cost. Lin. Ft. Yd.
{ Laying track for
{ steering alligator $ 5.00 $ 71.48 $ 43.98 $0.0670 $0.16
4 men { Moving and erecting
{ superstructure 5.00 299.94 358.44 0.3821 0.93
4 men Moving plates 10.00 202.50 253.44 0.2646 0.65
Repairs to alligator 58.50 2.50 0.0354 0.08
1 man Bending rings 2.50 32.87 59.87 0.0538 0.13
2 men Placing reinforcement 5.00 126.94 138.13 0.1538 0.38
12 men Mixing and placing
concrete 30.00 709.68 949.74 0.9631 2.34
1 man Watering finished pipe. 2.50 45.00 78.27 0.0716 0.17
1 man Painting and
brush-coating inside 2.50 96.50 117.37 0.1241 0.31
Blacksmith's work 30.00 25.00 0.0319 0.08
1 man Whim 2.50 23.87 28.75 0.0306 0.07
1 man Screening and hauling
sand and gravel 2.50 183.13 300.00 0.2804 0.68
--------- --------- ------- -----
Total $1,880.41 $2,335.49 $2.4584 $5.98
~CONDUITS, TORRESDALE FILTERS, PHILADELPHIA, PA.~--At the Torresdale plant
of Philadelphia filtration system the clear water conduits are
reinforced concrete. The following description is composed from
information furnished the authors in 1904 by the Bureau of Filtration,
Mr. John W. Hill, then chief engineer. The lengths of the several
conduits are as follows: 576 ft. of 7½-ft., 782 ft. of 8-ft., 1,050 ft.
of 9-ft., and 1,430 ft. of 10-ft. horseshoe conduit. All sizes of
conduit have the same cross-sectional form--the cross-section of the
9-ft. conduit is shown by Fig. 253, and all are reinforced by expanded
metal arranged as indicated. The concrete is a 1-3-5, ¾-in. stone
mixture. The conduits were first designed with circular sections, but
before construction had been begun on these plans, experience had been
obtained in building a circular sewer that made a change to the
horseshoe section appear desirable. In the circular sewer work, great
difficulty had been found in properly placing and ramming the concrete
in the lower quarters of the circular section.
[Illustration: Fig. 253.--Section of 9-ft. Conduit, Philadelphia Filter
Plant.]
_Forms._--The forms used for the several sizes of conduit were all of
the same general type, but improvements in detail were made as
successive sizes were built. The last form to be designed was that for
the 9-ft. section and this was the best one; it is shown by Fig. 254.
The forms were built in sections from 12 ft. to 13½ ft. long. They were
covered with No. 27 galvanized sheet iron, and this covering was found
of advantage both in giving a smooth finish and in prolonging the life
of the centers. The important feature is the construction in sections
which could be set up and broken down by simply inserting and removing
the connecting bolts. Three sets of forms were made for each size of
conduit.
[Illustration: Fig. 254.--Form for 9-ft. Conduit Philadelphia Filter
Plant.]
_Procedure of Work._--The first operation in building a section of
conduit was to set to exact line and grade and the length of the form in
advance of the finished work the bulkhead shown by Fig. 255. In this
space the invert concrete was deposited and formed to a plane 1 in.
below the finished invert bottom. The two bottom sections of the form
were then assembled and located by bolting one end to the last preceding
form and inserting the other end into the bulkhead. About two tons of
pig iron were then placed on the invert form to keep it from floating
while the liquid granolithic mixture was being poured into the 1-in.
space between the form and the invert concrete. In building up the sides
a facing form was used for placing the granolithic finish. This
consisted of "boards" of sheet steel ribbed transversely on one side
with ¾-in. pipe and on the other side with 1½-in. pipe. Two boards were
used on each haunch, slightly lapping in the center, as follows: The
board was placed with the small ribs against the form and the larger
ribs kept the expanded metal just 3 ins. from the face of the form. A
6-in. depth of concrete was placed between the metal board and the
outside form or planks, then 6 ins. of granolithic was poured into the
1-in. space between the center and the board and finally the board was
raised 6 ins. and the concrete and granolithic mixture tamped together.
With the board in its new position, another layer of concrete and
granolithic was placed. Toward the crown the granolithic mixture was
made stiff and simply plastered onto the mold. The expanded metal was
cut into sheets corresponding to the length of the sides of the form and
lapped 6 ins. in all directions; the bulkhead having a slot as shown to
permit the metal to project 6 ins. from the face of the concrete in
order to tie two sections together and also having a rib which formed a
mortise in the face of the shell of concrete to key it to the succeeding
section.
[Illustration: Fig. 255.--Bulkhead Form for Conduits, Philadelphia
Filter Plant.]
All the conduits were built in sections from 12 ft. to 13½ ft. long, and
there was very little, if any, difference in the labor required to build
a section, in from eight to ten hours, of any of the three sizes. One
foreman and 18 men on the top of the trench mixed and handled the
concrete and granolithic mortar while one foreman, one carpenter and
seven men in the trench set the forms and placed and rammed the concrete
for one section in generally eight hours. About one-third of the
concrete for the whole work was mixed in a portable cubical mixer of ½
cu. yd. capacity, and the remainder was mixed by hand. Owing to the
relatively small amount of concrete used per day, about 20 cu. yds., it
was found that there was practically no difference in the cost of
machine mixing and of hand mixing. The 9-ft. conduit as an average of
the three sizes, contained 20 cu. yds. of concrete, 1,200 sq. ft. of
expanded and required 125 bags of cement for a section 13½ ft. long. The
cost of the work excluding excavation and profit, but including forms,
metal, concrete materials and labor, was about $10.50 per cu. yd.
~CONDUIT, JERSEY CITY WATER SUPPLY.~--In constructing the 8½-ft.
reinforced concrete conduit for the Jersey City water supply, use was
made of forms without bottoms. Each form was made of segmental sections
12½ ft. long of wood covered with sheet steel. They were set end to end
in the trench, resting on 6-in. concrete cubes which were finally
permanently embedded in the invert concrete. In each form there was a
scuttle about 2 ft. square at the crown, and the bottom was open between
the curves of the invert haunches. The form being set and greased and
the reinforcement placed, the concrete was deposited on the outside and
forced by means of tamping bars down the curve of the invert haunches
until it filled the whole space between the form and the earth and
appeared at the edges of the bottom opening in the form. Concrete was
then thrown through the scuttle and the invert screeded into shape. The
concreting of the sides and crown of the arch was then completed, using
outside forms except for about 5 ft. of the crown, the scuttle, of
course, being closed by a fitted cover. The centers were left in place
about 48 hours. The concrete was a 1 cement 7 sand and run of the
crusher 2-in. broken stone mixture, and was made so wet that it would
flow down an incline of 1 on 8. The mixing was done in portable Ransome
mixers, set on the trench bank alongside the work and discharging by
chute into dished shoveling boxes provided with legs to set on the
erected forms. Coal scoops were used in shoveling from the box into the
forms and were found superior to shovels in keeping the relative
proportions of water and solids constant.
~TWIN TUBE WATER CONDUIT AT NEWARK, N. J.~--In constructing the Cedar
Grove Reservoir, at Newark, N. J., two conduits side by side were built
across the bottom from gate house to tunnel outlet. A section of one of
the conduits showing the form construction and the arrangement of the
reinforcement is given by Fig. 256. The concrete was a 1-2-5 1½-in.
stone mixture and the reinforcement was No. 10 3-in. mesh expanded
metal. The method and cost of construction are given as follows, by Mr.
G. C. Woollard, the engineer for the contractors.
[Illustration: Fig. 256.--Conduit for Cedar Grove Reservoir, Newark. N.
J.]
"The particular thing that was insisted upon by both Mr. M. R. Sherrerd,
the chief engineer of the Newark Water Department and Mr. Carlton E.
Davis, the resident engineer at Cedar Grove Reservoir, in connection
with these conduits, was that they be built without sections in their
circumference, that the whole of the circumference of any one section of
the length should be constructed at one time. They were perfectly
willing to allow us to build the conduit in any length section we
desired, so long as we left an expansion joint occasionally which did
not leak.
"The good construction of these conduits was demonstrated later, when
the section stood 40 lbs. pressure to the square inch, and, in addition,
I may say that these conduits have not leaked at all since their
construction. This shows the wisdom of building the conduit all round in
one piece, that is, in placing the concrete over the centers all at one
time, instead of building a portion of it, and then completing that
portion later, after the lower portion had had an opportunity to set.
"The centers which I designed on this work were very simple and
inexpensive, as will be gathered from the cost of the work, when I state
that this conduit, which measured only 0.8 cu. yd. of concrete to the
lineal foot of single conduit, cost only $6.14 per cu. yd., built with
Atlas cement, including all labor and forms and material, and expanded
metal. The forms were built in 16 ft. lengths, each 16 ft. length having
five of the segmental ribbed centers such as are shown in Fig. 256,
viz., one center at each end and three intermediate centers in the
length of 16 ft. These segments were made by a mill in Newark and cost
90 cts. apiece, not including the bolts. We placed the lagging on these
forms at the reservoir, and it was made of ordinary 2×4 material,
surfaced on both sides, with the edges beveled to the radius of the
circle. These pieces of 2×4 were nailed with two 10d. nails to each
segment. The segments were held together by four ½-in. bolts, which
passed through the center, and 1½-in. wooden tie block. There was no
bottom segment to the circle. This was left open, and the whole form
held apart by a piece, B, of 3×2 spruce, with a bolt at each end
bolted to the lower segment on each side.
"The outside forms consisted of four steel angles to each 16 ft. of the
conduit, one on each end, and two, back to back, in the middle of each
16 ft. length. These angles were 2×3, with the 2-in. side on the
conduit, and the 3-in. side of the angle had small lugs bolted on it at
intervals, to receive the 2×12 plank, which was slipped down on the
outside of the conduit, as it was raised in height. The angles were held
from kicking out at the bottom by stakes driven into the ground, and
held together at the top by a 2½-in. tie-rod.
"The conduit was 8 ins. thick, save at the bottom, where it was 12 ins.
The reason for the 12 ins. at the bottom was that the forms had to have
a firm foundation to rest on, in order to put all the weight required by
the conduit on them in one day or at one time, without settling. We
therefore excavated the conduit to grade the entire length, and
deposited a 4-in. layer of concrete to level and grade over the entire
length of the conduit line. This gave us a good, firm foundation, true
and accurate to work from, and this is the secret of the good work which
was done on these conduits. If you examine them, you will say that they
are one of the neatest jobs of concrete in this line that has been
built, especially with regard to the inside, which is true, level and
absolutely smooth. [The authors can confirm this statement.] When the
conduit is filled with water, it falls off with absolutely no point
where water stands in the conduit, owing to its being out or the proper
amount of concrete not being deposited.
"The centers were placed in their entirety on a new length of conduit to
be built, resting upon four piles of brick, two at each end as shown.
The first concrete was placed in the forms at the point marked X and
the next concrete was dropped in through a trap door cut in the roof of
the conduit form at the point marked Y. This material was dropped in
to form the invert, and this portion was shaped by hand with trowels and
screeded to the exact radius of the conduit. The concrete was then
placed continuously up the sides, and boards were dropped in the angles
which I have mentioned, and which served as outside form holders till
the limit was reached at the top, where it was impossible to get the
concrete in under the planking and thoroughly tamped. At this point the
top was formed by hand and with screeds.
"Each 16-ft. length of this conduit was made with opposite ends male and
female respectively, that is, we had a small form which allowed the
concrete to step down at one end to 3 ins. in thickness for 8 ins. back
from the end of the section, and on the other end of the section it
allowed it to step down to 3 ins. in thickness in exactly the opposite
way, making a scarf joint. This was not done at every 16 ft. length,
unless only 16 ft. were placed in one day. We usually placed 48 ft. a
day at one end of the conduit with one gang of men. This was allowed to
set 24 hours, and, whatever length of conduit was undertaken in a day,
was absolutely completed, rain or shine, and the gang next day resumed
operations at the other end of the conduit on another 48 ft. length.
This was completed, no matter what the weather conditions were, and,
towards the close of this day the forms placed on the preceding day were
being drawn and moved ahead.
"The method used in moving these forms ahead for another day's work is
probably one of the secrets of the low cost of this work, and it is one
which we have never seen employed before. The bolt at A, Fig. 256, was
taken out, and the tie brace B thrown up. We had hooks at the points
C. A turnbuckle was thrown in, catching these hooks, and given several
sharp turns, causing the entire form to spring downward and inwards,
which gave it just enough clearance to be carried forward, without doing
any more striking of forms than pulling the bolt at A. This method of
pulling the forms worked absolutely satisfactorily, and never gave any
trouble, and we were able to move the forms very late in the day and get
them all set for next day's work, giving all the concrete practically 24
hours' set, as we always started concreting in the morning at the
furthest end of the form set up and at the greatest distance from the
old concrete possible in the 48 ft. length, as the furthest form had, of
course, to be moved first, it being impossible to pass one form through
the other.
"Six 16-ft. sections of these forms were built, and three were used each
day on each end, as shown by the diagram MN, Fig. 256, which gives the
day for the month for the completion of each of seven 48-ft. sections.
"A gang of men simply shifted on alternate days from end to end of the
conduit, although several sections were in progress at one time; and of
course, finally, when a junction was made between any division, say of
1,000 ft. to another 1,000 ft., one small form was left in at this
junction inside of the conduit, and had to be taken down and taken out
the entire length of the conduit.
"The centers for a 16-ft. length of this conduit cost complete for labor
and material, $18.30, but they were used over and over again; and, after
this conduit was completed, they were taken away for use at other
points, so that the cost is hardly appreciable, and the only charge to
centers that we made after the first cost of building the centers, was
on account of moving them daily. Part of this conduit was built double
(two 6-ft. conduits) and part single, the only difference being that,
where the double conduit was built, two forms were placed side by side,
and not so much was undertaken in one day.
"These conduits, when completed and dried out, rung exactly like a
60-in. cast-iron pipe, when any one walked through them or stamped on
the bottom."
Mr. Woollard gives the following analysis of the cost per cubic yard of
the concrete-steel conduit above described:
Per cu. yd.
1.3 bbl. cement $1.43
10 cu. ft. sand 0.35
25 cu. ft. stone 1.10
26 sq. ft. expanded metal, at 3 cts. 0.78
Loading and hauling materials 2,000 ft.
to the mixing board (team at $4.50) 0.50
Labor mixing, placing, and ramming 1.38
Labor moving forms 0.60
-----
Total $6.14
Wages were 17½ cts. per hr. for laborers and 50 cts. per hr. for
foremen. The concrete was 1-2-5, a barrel being assumed to be 3.8 cu.
ft. The concrete was mixed by hand on platforms alongside the conduit.
The cost of placing and ramming was high, on account of the expanded
metal, the small space in which to tamp, and to the screeding cost. When
forms were moved they were scraped and brushed with soft soap before
being used again.
From Mr. Morris R. Sherrerd, Engineer and Superintendent, Department of
Water, Newark, N. J., we have received the following data which differ
slightly from those given by Mr. Woollard. The differences may be
explained by the fact that the cost records were made at different
times. Mr. Sherrerd states (Sept. 26, 1904,) that each batch contains 4
cu. ft. of cement, 8 cu. ft. of sand, and 20 cu. ft. of stone, making 22
cu. ft. of concrete in place. One bag of cement is assumed to hold 1
cu. ft. He adds that a 10-hour day's work for a gang is 63 lin. ft. of
single 6-ft. conduit containing 47.4 cu. yds. of concrete and 1,260 sq.
ft. of expanded metal. This is equivalent to ¾ cu. yd. of concrete per
lin. ft. The total cost of material for one complete set of forms 64 ft.
long was $160; and there were 7 of these sets required to keep two gangs
of men busy, each gang building 63 lin. ft. of conduit a day. Since the
total length of the conduit was 3,850 ft., the first cost of the
material in the forms was 18 cts. per lin. ft.
Cost of Labor on 6-ft. Conduit:
Per day. Per cu. yd.
1 foreman on concrete $ 3.35 $0.07
1 water boy 0.75 0.01
11 men mixing at $1.75 19.25 0.39
5 men mixing at $1.50 7.50 0.16
4 men loading stone at $1.40 5.60 0.12
4 men wheeling stone at $1.40 5.60 0.12
2 men loading sand at $1.40 2.80 0.06
2 men wheeling sand at $1.40 2.80 0.06
1 man placing concrete at $1.75 1.75 0.04
6 men placing concrete at $1.50 9.00 0.19
2 men supplying water at $1.50 3.00 0.06
1 man placing expanded metal at $2. 2.00 0.04
1 man placing expanded metal at $1.50 1.50 0.03
------ -----
Total labor on concrete $64.90 $1.35
Cost of Labor Moving Forms:
Per day. Per cu. yd.
4 carpenters placing forms $13.00 $0.27
2 helpers placing forms 4.00 0.08
1 carpenter putting up boards
for outside forms 2.75 0.06
1 helper putting up boards
for outside forms 2.25 0.05
2 helpers putting up boards
for outside forms 3.50 0.07
1 team hauling timber 4.50 0.09
1 helper hauling lumber 1.75 0.04
------ -----
Total labor moving $31.75 $0.66
It will be noted that it required two men to bend and place the 700
lbs., or 1,260 sq. ft., of expanded metal required for 63 lin. ft. of
conduit per day, which is equivalent to ½c per lb., or 3 cts. per sq.
ft., for the labor of shaping, placing and fastening the metal.
~CIRCULAR SEWER, SOUTH BEND, INDIANA.~--In building 2,464 ft. of 66-in.
circular reinforced concrete sewer at South Bend, Ind., in 1906, the
method of construction illustrated in Figs. 257, 258 and 259 was
employed. The sewer has a 9-in. shell buttressed on the sides and is
reinforced every 12 ins. by a 3/16×1-in. peripheral bar in the sides and
roof and 3 ins. in from the soffit. Each bar is composed of three
pieces, two side pieces from 15 ins. below to 6 ins. above springing
lines and a connecting roof bar attached to the side bars by cotter
pins. Two grades of concrete were used, a 1-3-6 bank gravel concrete for
the invert and a 1-2-4 bank gravel concrete for the arch. The invert was
given a ½-in. plaster coat of 1-1 mortar as high as the springing lines.
[Illustration: Fig. 257.--Form for South Bend Sewer (First Stage).]
[Illustration: Fig. 258.--Form for South Bend Sewer (Second Stage).]
[Illustration: Fig. 259.--Form for South Bend Sewer (Third Stage).]
Forms and Concreting.--In constructing the sewer the trench was
excavated so as to give a clearance of 1 ft. on each side and was
sheeted as shown by Fig. 257. The sewer was built in 12 ft. sections as
follows: The bottom of the trench was shaped as nearly as possible to
the grade and shape of the base of the sewer. Four braces to each 12 ft.
section were then nailed across the trench between the lowest rangers on
the trench sheeting. A partial form consisting of a vertical row of
lagging was set on each of the outside lines of the sewer barrel as
shown by Fig. 257. Each section of this lagging was held by stakes
driven into the trench bottom and nailed at their tops to the cross
braces as shown by Fig. 258. A template for the invert was then
suspended from the cross braces by pieces nailed to the four ribs of the
template and to the cross braces as shown by Fig. 257. The concrete was
now placed and carried to the top of the template, which was then
removed. The side pieces of the reinforcing bars were then set and
fastened as shown by Fig. 258. The side forms extending up to the
springing lines were then placed. They were held in position by braces
nailed to their ribs at the tops and by other braces fitting into
notches in the ends of their ribs at the bottom. The concrete was then
carried up to the springing lines, the arch centers in two pieces were
placed; the arch bar of the reinforcement was placed and the extrados
forms erected up to the 45° lines, all as shown by Fig. 259. The placing
of the arch concrete completed the sewer barrel. The outside forms and
bracing were removed about 24 hours after the completion of the arch and
back filling the trench was begun immediately, but the inside forms were
left in place for two weeks; they were then removed by the simple
process of knocking out the notched braces. By building several lengths
of invert first and following in succession by the side wall
construction and then by the arch construction, the form erection and
the concreting proceeded without interruption by each other. It was also
found that, by making bends in the form of polygons with 10 ft. sides
instead of in the form of curves, there was a material saving in
expensive form work. To overcome the friction of the angles in such
bends an additional fall was provided at these places. All concrete was
made in a Smith mixer mounted on trucks so that it could be moved along
the bank of the trench and discharging into a trough leading to the
work.
_Labor Force and Cost._--With a gang of 12 men from 24 to 36 ft. of
sewer was built per 10-hour day, working only part of the time on actual
concreting. The disposition of the force mixing and laying concrete and
the wages were as follows:
Item. Per day.
Six wheelers, at 18.5 cts. per hour $11.10
One mixer, at 22.5 cts. per hour 2.25
One dumper, at 18.5 cts. per hour 1.85
Four placers, at 22.5 cts. per hour 9.00
------
Total $24.20
There were 0.594 cu. yd. of concrete per lineal foot of sewer and its
cost is given as follows:
Item. Per cu. yd.
Cost of gravel $0.774
Cost of sand 0.36
Cost of cement 1.50
Cost of steel reinforcement 0.84
Cost of labor, mixing and placing concrete 1.094
Cost of moving forms, templates, etc. 0.757
Cost of forms, templates, etc. 0.589
Cost of finishing, plastering, etc. 0.639
Cost of tools and general expenses 0.841
------
Total $7.394
~SEWER INVERT, HAVERHILL, MASS.~--In constructing sewers with concrete
inverts at Haverhill, Mass., in 1905, use was made of the traveling form
or mold shown by Fig. 260. The form consists of an inner and an outer
shell, the annular space between which forms the mold; in operation the
annular space is filled with concrete, then the outer shell is pulled
ahead from underneath, leaving the inner shell in place. A second inner
shell is then adjusted to the outer shell in its new position, the
annular mold is concreted and the outer shell again pulled ahead.
Continued repetition of the operations described completes the invert.
The merit of the device lies in the fact that the inner shell is not
moved until the concrete has attained some degree of rigidity; when, in
such devices, the inner mold is slid ahead on the green concrete it is
likely so to "drag" forward the material that a rough and pitted surface
results.
_Mold Construction._--Referring to the drawings of Fig. 260, A is the
outer mold of sheet steel bent to the required shape of the outer
surface of the conduit to be constructed. A rib, or angle, B, is
riveted to the inside of the mold at its front end and a diaphragm C
of plank is securely fastened to the rear side of the rib. The opposite
or rear end of the mold is open. Angles D forming tracks are riveted
inside the mold a short distance below the edges and reaching their full
length. The inner mold comprises a steel shell E curved to the form of
the inside of the conduit; inside this steel shell is a reinforcing
lagging, and at each end there is a wooden diaphragm F. Passing
through both end diaphragms and having its ends flush with the end
planes of the mold is a timber G. Rearward projecting lips e are
secured to the lagging at the rear end of the mold and on each side of
the timber G. The diaphragms F have each two arms f which project
horizontally beyond the surface of the inner mold and engage the tracks
D; locking dogs H are pivoted to the arms f so as to hook under
the track angles D and hold the inner form from rising. Setting on the
inner mold is an inverted V-shaped deflector I; its edges are flush
with the sides of the mold and its purpose is to facilitate the placing
of the concrete. There is also a movable diaphragm K, fitting loosely
inside the outer mold A and bearing against the end of the inner mold
E. The length of the inner mold E is about one-half that of the
outer mold A; as a rule several inner molds are provided with one
outer mold.
[Illustration: Fig. 260.--Traveling Invert Form for Sewer Construction.]
_Mode of Operation._--In using the device described the outer mold A
is first placed in the trench with its rear end at the end of the
trench. An inner mold E is then suspended on the tracks of the outer
mold and locked therein by the dogs H, with its rear end flush with
the rear end of the outer mold. The partition K is then placed in
position against the forward end of the inner mold and a jack J of any
suitable form is interposed between diaphragms K and C, the jack
being extended sufficiently to press diaphragm K firmly against the
front end of the inner mold. The deflector I is next placed in
position on the inner mold and the concrete is forced down with an iron
rammer between the two molds, so as to fill completely the annular
space. The deflector aids in directing the concrete into this space, as
will be obvious. After the mold has been filled and the concrete
compacted as much as possible, the jack is operated to separate the
diaphragms K and C, and as the partition K is pressed against one
end of the mass of concrete which has been laid, the opposite end of
which abuts against the end of the trench, it follows that any backward
movement of the diaphragm K will compress the concrete. This movement
will be practically inappreciable in distance, but enough to compact
thoroughly the concrete and fill any voids. The action of the jack will
also push forward the diaphragm C and the outer mold A, the latter
being withdrawn from beneath the inner mold and the newly laid concrete,
the tracks D of the outer mold being drawn from beneath the arms f
of the inner mold, leaving the latter behind resting on the freshly laid
concrete. Further compression of the concrete after it has been left by
the outer mold will fill the spaces between the inner mold and the
surface of the trench. The outer mold is moved forward in this manner a
distance equal to the length of the inner mold, and then the diaphragm
K is drawn forward and another inner mold is lowered into the outer
mold exactly as was the first one. The jack is then placed, the concrete
deposited and the outer mold again advanced exactly as before. As the
outer mold advances, the inner molds become disengaged one after another
and are set ahead; in practice, enough inner molds are provided to
enable the concrete to harden sufficiently to keep its position when it
becomes necessary to take up successively the rearmost molds and place
them ahead.
_Haverhill Sewer Work._--The work at Haverhill, Mass., previously
mentioned in which the form just described was used, was a 24-in.
circular sewer with 6-in. walls. The outer form was 36 ins. in diameter
and 6 ft. 2 ins. long; the inner form was 24 ins. in diameter and 3 ft.
long. Angle B was 3 ins. and the track angles D were 1½ ins.; diaphragm
K was made of two thicknesses of 3-in. plank and diaphragm C of one
thickness of 3-in. plank, the other diaphragms were of 2-in. plank. The
shells of the molds were of ¼-in. steel plate; the jack was an ordinary
screw jack. Eight inner molds were used.
The form used at Haverhill was built by the city carpenter, the metal
portions being made in a boiler shop. Its cost was not ascertained, but
was, it is thought, about $75. The concrete used was a 1-3-5 stone
mixture, with cement costing $2 per barrel, sand $1.50 per load of 36
cu. ft., and stone $2.50 per load of 36 cu. ft. The men were paid 25
cts. per hour. Records kept on 265 ft. of invert, or, theoretically,
19.3 cu. yds. of concrete, gave the following figures:
Per Per
lin. ft. cu. yd.
Labor, setting and moving
forms, 42 hours, at 25 cts. $0.05 $0.67
Labor, mixing, placing and wheeling
concrete, 179 hours, at 25 cts. 0.16 2.19
----- -----
Total labor cost $0.21 $2.86
With the ordinary 1-3-5 mixture the cost of materials would run about as
follows:
Per cu. yd.
Cement, 0.96 bbl., at $2. $1.92
Sand, 0.47 cu. yd., at $1.13 0.53
Stone, 0.78 cu. yd., at $1.88 1.47
-----
Total cost materials $3.92
Two men were worked in the trench, one alternately ramming the concrete
into place and working the jack, and the other shaping the trench ahead
and assisting in bringing the rear forms ahead.
The form described was invented by Mr. Robert R. Evans, of Haverhill,
Mass., and has been patented by him.
~29-FT. SEWER, ST. LOUIS, MO.~--The following account of the method and
cost of constructing 162 ft. of very large sewer section at St. Louis,
Mo., is compiled from information furnished by Mr. Curtis Hill.
The cross-section of the sewer is given by Fig. 261, which also shows
the arrangement of the reinforcing bars. Johnson corrugated bars, old
style, are used for reinforcement. The sections of the various
reinforcing bars are: Longitudinal bars, 0.18 sq. in.; invert bars, 0.7
sq. in., and arch bars, 0.7 sq. in. The spacing of the bars and the
arrangement of the splices are indicated on the drawings of Fig. 261.
All splices have a lap of 36 ins. Some gravel concrete has been used in
the invert, but most of the concrete has been crushed limestone and
Mississippi River channel sand. The proportions were 1-3-6 in the invert
and 1-2-5 in the arch. The arch was computed by Prof. Greene's method.
The ultimate strength of concrete in compression was taken as 2,000 lbs.
per sq. in. and the working strength at 500 lbs. per sq. in. The elastic
limit of the reinforcing bars was taken at 50,000 lbs.
[Illustration: Fig. 261.--Harlem Creek Sewer, St. Louis, Mo.]
The trenching was done by wheel scrapers to the amount of waste. Then a
cableway was erected spanning the entire length of the section and the
remainder of the material taken out. The last 4 or 5 ft. in depth were
in limestone and the excavated rock was taken by cableway to dump carts
which took it to the crusher and returned with crushed rock to be used
for concrete. This rock foundation was taken advantage of to reduce the
amount of invert concrete.
In constructing the sewer proper the invert was first concreted to
template to the height shown in Fig. 262. The arch forms were then
placed as shown in Fig. 262, and the roof arch concreted. Both templates
and arch forms were constructed of wood. The arch forms were moved ahead
on iron rails and jacked into place. The ribs were 2×10-in. pieces and
were spaced 4 ft. on centers; the lagging was 2-in. tongue and grooved
stuff and was smeared with crude oil. The reinforcing bars shown in Fig.
261 were bent to proper radius by means of a wagon tire bender and were
held in place by templates. The concrete was all mixed by two Chicago
Improved Cube mixers operated by electric power.
[Illustration: Fig. 262.--Center for Harlem Creek Sewer.]
The cost records of constructing the section of 29-ft. sewer so far
built are not susceptible of complete analysis, but the following
figures can be given. The prices of materials were as follows:
Cement, per barrel $1.80
Sand, per cubic yard 0.75
Broken stone, per cubic yard 1.00
Reinforcing bars, per pound 0.02
Vitrified brick, per 1,000 12.00
The wages paid different classes of labor were:
Per hour.
Firemen $0.50
Laborers 0.175
Laborers 0.20
Laborers 0.25
Laborers 0.28
Laborers 0.3025
Bricklayers 0.66 2/3
Helpers $0.25
Carpenters 0.55
Engineers 0.50
Timekeepers 0.25
Watchmen 0.175
Hostlers 0.175
Teams 0.60
Taking up the several items of work in order, the excavation amounted to
21,400 cu. yds., of which 1,400 cu. yds. were rock excavation. The cost
of excavation was as follows:
Total. Per cu. yd.
Earth, excavation $7,640 $0.38
Earth bracing 2,000 0.10
Rock excavation 1,400 1.00
Rock, dynamite, tools, etc. 560 0.40
The cost of crushing the excavated rock and returning it to the mixer
was $1 per cu. yd.
The cost of the concrete work was as follows:
Per cu. yd.
1.30 bbl. cement at $1.80 $2.34
.044 cu. yd. sand at 75 cts. 0.33
1 cu. yd. broken stone at $1 1.00
-----
Total concrete materials $3.67
There were 1,600 cu. yds. of concrete placed at a cost of for:
Total. Per cu. yd.
Mixing and placing $1,180 $0.7375
Forms 2,000 1.25
Moving forms 400 0.25
------ -------
Total for forms and labor $3,580 $2.2375
For reinforcing the concrete 86,600 lbs. of steel, or about 55 lbs. per
cu. yd. were used. The cost of placing and bending this steel was as
follows:
Total. Per lb.
Cost of placing $172 0.1986 ct.
Cost of bending 52 0.06 ct.
We can now summarize the cost of the concrete work proper of this sewer
as follows:
Items. Per cu. yd.
Cement, sand and stone $3.67
55 lbs. steel at 2 cts. 1.10
Forms, labor and materials 1.25
Mixing and placing concrete labor 0.74
Placing steel at 0.1986 ct. per lb. 0.11
Bending steel at 0.06 ct. per lb. 0.03
Moving forms 0.25
-----
Total labor and materials $7.15
To get the total cost of the sewer proper we must add the cost of the
vitrified brick invert paving. There were 71 cu. yds. of this paving and
its cost was as follows:
Per cu. yd.
0.6 bbls. cement at $1.80 $1.08
0.25 cu. yd. sand at 75 cts. 0.19
450 bricks at $12 per M. 5.40
Labor laying, 71 cu. yds. at $180.33 2.54
-----
Total $9.21
None of the preceding figures includes the plant charges. The plant cost
$12,000 and the cost of running it during the work described was $2,000.
In explanation it should be noted that the plant served for building
some 1,340 lin. ft. of 27-ft. sewer as well as for the section
described.
~SEWER AT MIDDLESBOROUGH, KY.~--In constructing an oval sewer 4 ft. high
at Middlesborough, Ky., two steel forms in 10-ft. sections were used. As
shown in Fig. 263, T-iron ribs were spaced 5 ft. apart, fastened
together at the top by longitudinal angle irons, and at the bottom by a
sheet of steel 22 ins. wide, forming the bottom of the invert. The
lagging for the sides consists of movable 5-ft. lengths of channel iron,
secured by sliding bolts. After the bottom of the trench has been
roughly shaped with concrete, a 10-ft. section of invert forms is
lowered and suspended by the cross-beams, and the space beneath packed
with concrete; then a channel iron is slid into place and bolted, and
concrete packed behind it, and so on until the invert is made. The next
10-ft. section is then built while the first is hardening. Upon the
completion of the second section, the channel iron sides of the first
section are removed, and then the rib framework is lifted out. Wood arch
centers are then put in place and an inch of 1:2 plaster spread over the
lagging before placing the concrete for the arch, which is 6 ins. thick.
[Illustration: Fig. 263.--Invert Form for Sewer Construction.]
The cost per 100 ft. of this sewer was as follows (prices being assumed
for cement and labor):
Bottom concrete. Cost per 100 ft.
18.5 bbls. cement, at $1.50 $ 27.75
2.7 cu. yds. sand, at $1.00. 2.70
15 cu. yds. stone, at $1.00 15.00
17 days labor, at $1.50 25.50
Bottom concrete. Cost per 100 ft.
25.25 bbls. cement, at $1.50 37.85
7.5 cu. yds. sand, at $1.00 7.50
22 days labor, at $1.50 33.00
Sewer Arch.
26 bbls. cement, at $1.50 39.00
3.9 cu. yds. sand, at $1.00 3.90
13.6 cu. yds. stone, at $1.00 13.60
21 days labor, at $1.50 31.50
-------
Cost per 100 ft. $237.30
[Illustration: Fig. 264.--Sewer at Cleveland, Ohio.]
~INTERCEPTING SEWERS, CLEVELAND, O.~--An intercepting sewer some 3½ miles
long, of the form and construction shown in Fig. 264, was built at
Cleveland, Ohio, in 1904. The construction consists of a plain concrete
invert lined with two courses of shale bricks, and having two rows of
anchor bars set in the side walls so that the bars of one row are
staggered with respect to those of the other row. The anchor bars are
2×½-in. steel, and are spaced 30 ins. apart in each row. To the anchor
bars are bolted arch reinforcing bars arranged as shown, and these arch
bars have bolted to them eight lines of 1½×¼-in. longitudinal bars. A
natural cement concrete is used for the invert and side walls. The arch
is Portland cement concrete of normally a 1-3-7½, 1½-in. screened stone
mixture, but where the voids in the broken stone exceeded 40 per cent.,
it is a 1-3-6 mixture. The invert bricks are laid in Portland cement
mortar and the arch has a mortar lining and is waterproofed with 1-in.
of mortar on top.
_Forms._--Separate forms were used for the invert and for the arch ring.
Regarding these, the engineer, Mr. Walter C. Parmley, remarks:
One of the first forms used in the sewer was like a piece of segmental
arch centering inverted, and with the lagging nailed fast to the ribs.
The trouble with this form is that it is difficult to tamp concrete
under the bottom portion of the form, and hence a very rough surface is
produced. Much better results were obtained by omitting the lagging
boards on the bottom and at the sides till a point was reached where the
inclination of the concrete surface was about 45°. The concrete for the
bottom could then be worked down between the ribs, thorough tamping
done, and a good surface obtained. The ribs serve as a guide, so that
the workman produces the proper shape. From this point up to the
vertical, good results can be secured with the ribs attached to the
lagging. Some contractors found it more convenient to use ribs that were
connected with each other by a skeleton framework only, and then to slip
the lagging in, one piece at a time. For some of the sewers, in which
the brick lining was not carried quite up to the spring line, a separate
side form of skeleton ribs and loose lagging was set upon brace legs
bearing on the bottom of the invert. This form carried the concrete from
about 2 ft. below to about 2 ft. above the springing line. The arch ribs
then became segmental and rested upon the middle braces. This method has
the advantage of using ribs that are lighter and more easily handled
than those that are semi-circular. For arch centering, it is necessary
and convenient to use independent ribs and loose lagging, for the
centers can then be carried forward piece-meal, the falsework upholding
the green arch and re-erected at the advance end of the work. In these
matters each contractor prefers to use his own ingenuity, and so long as
the work is properly built, the engineer can well give him considerable
latitude as to use of methods. One thing, however, the engineer must
insist upon--that all centering and falsework be as nearly rigid as
possible. Even a slight settlement of the centers at the crown under the
load of concrete and back-fill will cause the arch to kick out at the
quarters, and if the green concrete arch is not cracked at the crown, it
will be crushed on the inside, about half way between the crown and
springing line. A reinforced arch is no more immune to this danger than
is a plain concrete arch. However, with a few days of hardening,
although the damage may be serious, the danger of actual collapse is
less. A point to be guarded against, especially in reinforced
construction, is any foolish act on the part of contractor or workman,
due to his overconfidence in the strength of the structure because it
contains embedded steel.
The mode of procedure in constructing the arch ring was to erect the
centers with lagging complete. The lagging was then covered with
building paper waterproofed with paraffine. The arch reinforcing bars
were then bolted to the anchor bars and the longitudinals connected up.
The lining of Portland cement mortar was first laid on the lagging.
Before this mortar had set, concrete was rammed in between it and the
sheeting to a height of 18 ins. above the springing line, and then the
remainder of the concrete placed without outside forms. The top of the
arch ring was finally finished with a 1-in. mortar coat. In regard to
the concrete, Mr. Parmley remarks:
"Concrete will flush up to the forms and produce a better surface, and
the voids in the stone will be much better filled if it is so wet as to
require but little tamping; moreover there is less danger of obtaining a
weak, porous wall should a workman neglect thorough tamping, than there
is where only a moist mixture is used. It is also to the contractor's
interest to use wet concrete for much less labor is required in mixing
and placing it. Small broken stone or gravel is preferable in concrete
for sewers. The walls being comparatively thin, unless there be a
considerable excess of mortar, if coarse stones are used, the concrete
will be honeycombed with voids. The stones should be well graded in size
from large to fine, but the largest fragments should not exceed 1½ ins.
in greatest dimension."
_Cost._--A number of records of cost of constructing short sections of
the sewer described are given by Mr. Parmley, as follows:
Labor placing anchor bars. Per day.
1 man, at $3.50 $3.50
1 man, at $1.75 1.75
4 hours carrying steel at 20 cts. 0.80
-----
$6.05
The anchor bars were placed for 40 lin. ft. of sewer, or about 1,504
lbs. of metal at a cost of 0.4 ct. per lb.
The concreting gang for the sides consisted of:
5 men wheeling and mixing at $1.75 $8.75
1 man tamping 1.75
2/3 time man lowering brick and concrete at $2.25 1.50
1 man carrying concrete 1.75
------
$13.75
This gang built the side wall for 40 ft. of sewer daily, or 13 cu. yds.
Cost of labor per cu. yd. was, therefore, $1.06. The concrete was tamped
behind the brick lining as the latter was built up by the mason.
Cost of single ring brick lining at sides:
2 masons at 70 cents per hour $1.20
1 man mixing mortar 2.25
1/3 time man lowering at $2.25 0.75
3 men wheeling sand, filling buckets and dumping 5.25
------
Total labor for 40 lin. ft. of sewer $19.45
Quantity of brick masonry laid, cu. yd. 6.38
Labor per cu. yd. 3.05
An account was kept of labor performed on 85 lin. ft. of arch work, or
14 1-6 ft. daily. The force was as follows:
1 man putting mortar lining on centering $1.75
2 men mixing mortar, screening and wheeling sand 3.50
1 man tamping concrete 1.75
8 men on mixing board at $1.75 14.00
------
$21.00
No. cu. yd. placed daily 25.64
Labor per cu. yd. 0.82
Placing centering and arch bars:
2 men at $1.75 $3.50
1 man at $3.50 3.50
-----
$7.00
Costs, for 14 1-6 ft. daily, $0.49 per lin. ft.
As nearly as could be judged, about two-thirds of the labor was used in
erecting the centering and one-third in putting the steel in place. The
amount of steel placed daily was 785 lbs., at cost, therefore, of 0.3 of
a cent per lb., and the cost of erecting and moving centers, $0.33 per
lin. ft. of arch.
Another record of 39.27 ft. on a curve, gave for the cost of the brick
work at sides the same result as above, but the inspector's record of
men working on concrete backing at sides showed a less cost, as follows:
4 men mixing at $1.75 $7.00
2/3 time man lowering at $2.25 1.50
1 man in bottom 1.75
-----
$10.25
They placed 12.7 cu. yd. at a cost of $0.81 per cu. yd. This figure
probably more nearly represents the average cost than the $1.06 reported
in the first instance.
The cost of placing the anchor bars on straight sewer, representing
average progress, at another time, was found to be:
1 man $3.50
1 man 1.75
-----
$5.25
They placed the steel for 44 ft. of sewer or 1,650 lb. at a cost of 0.32
of a cent per lb.
Further notes for 6 days' work, when it seemed to represent as nearly as
possible the general average for the whole were:
Labor on arch concrete:
Daily progress was 13 1-6 ft.
The force employed was:
7 men making concrete, at $1.75 $12.25
1 man plastering the center 1.75
1 man mixing mortar 2.00
1 man tamping 1.75
-----
$17.75
On straight arch work they placed 24.1 cu. yd. daily at a cost of $0.74
per cu. yd. In three days' work on a curve, the same gang placed 26.37
cu. yd. daily at a cost of $0.675 per cu. yd.
On centering and steel for arch, three men kept up with the regular
progress of the arch-concreting gang. The cost, therefore, is:
1 man $3.50
2 men at $1.75 3.50
-----
$7.00
They averaged 13 ft. daily, or at a total cost of about $0.54 per lin.
ft. of sewer.
Two-thirds of this labor was on the centering or $0.36 per lin. ft. of
arch; $0.18 per lin. ft. placed the steel ready for embedding, or about
55.5 lb. per ft. of arch, at a cost of 0.32 of a cent per lb.
For the double ring brick lining at the bottom, the regular daily rate
of progress was 28 ft. or 11.15 cu. yd. with:
2 bricklayers $11.20
5 men at $1.75 8.75
1 man at $2.25 2.25
-----
$22.20
or at a cost of $1.98 per cu. yd. This is given only because it is of
interest in connection with the cost of the concrete.
Other observations on cost of placing steel skeleton and concrete did
not vary materially from the figures given. It will be observed that no
charge for superintendence or anything for the general expenses is
included in the estimates of cost. These charges were, of course,
impossible to obtain. On another contract with machine mixing, as high
as 36 lin. ft. of 13 ft. 6 in. arch were built in a day, but no data as
to cost were taken, though it was evidently less than for the work with
hand-mixed concrete.
~REINFORCED CONCRETE SEWER AT WILMINGTON, DEL.~--Records of a notable job
of sewer construction at Wilmington, Del., in 1903, are furnished by Mr.
T. Chalkley Hatton. The sewer was built by day labor for the city; its
cross-section at various points is shown by Fig. 265. The cross-section
of sewers in trenches deep enough to cover the arch are marked "deep
cutting"; the sections where the arch projects above the ground surface
are marked "light cutting." The section through the marsh was 700 ft.
long, the cutting being 8 ft. deep, and at high tide the marsh was
flooded 1 to 4 ft. The material was a soft mud that would pull a tight
rubber boot from a workman's foot. The cost of this marsh excavation
including cofferdams, underdraining, pumping, etc., was $4.60 per cu.
yd. For 1,100 ft. the 9¼ ft. sewer was through a cut 22 to 34 ft. deep,
the material being clay underlaid by granite. A Carson-Lidgerwood
cableway was used. Although the crown of the arch was but 8 ins. thick,
it withstood the shock of dumping 1 cu. yd. buckets of earth and rock
from heights of 3 to 10 ft.; and the weight of 25 ft. of loose filling
caused no cracks in the concrete.
Concrete was placed in 4-in. layers (the depth of the lagging) and well
rammed, since it was found that "wet" concrete left small honeycombed
spaces on the inner surface. Concrete for the invert was 1-2-6, the
stone being 1½-in. and smaller, and the sand being crusher dust. The
arch was 1-2-5.
The reinforcing metal used in the 9½-ft. sewer was No. 6 expanded metal,
6-in. mesh, in sheets 8×5½ ft., supplied by Merritt & Co., of
Philadelphia. A single layer was placed around the sewer, 2 ins. from
the inner surface, its position being carefully maintained by the men
ramming, and with but little difficulty as the sheets were first bent to
the radius of the circle. Each sheet was lapped one mesh (6 ins.) over
its neighbor at both ends and sides, and no sheets were wired except the
top ones, which were liable to displacement by men walking over them.
[Illustration: Fig. 265.--Cross-Sections of Sewer at Wilmington, Del.]
The metal used on the rest of the work was a wire-woven fabric furnished
by the Wight-Easton-Townsend Co., of New York. This fabric comes in
rolls 5½ ft. wide and 100 ft. to the roll. The wire is No. 8, with a
6×4-in. mesh. This fabric was placed by first cutting the sheets to the
required length to surround the sewer entirely, embedding it in the
concrete as fast as concrete was placed, in the same manner as was done
with the expanded metal except over the center where, on account of its
pliability, the fabric was held the proper distance from the lagging by
a number of 2-in. blocks which were removed as the concrete was placed.
The wire cloth, being all in one sheet, can be placed a little more
expeditiously than expanded metal, but, on the other hand, the expanded
metal holds its position better in the concrete, since it is more rigid.
We quote now from Mr. Hatton's letter: "The major portion of concrete
was mixed by machine at a cost of 66 cts. per yard, including wheeling
to place, coal and running of mixing machine, wages being $1.50 per day
of 8 hrs, Stone was delivered alongside of machine and all material had
to be wheeled in barrows upon the platform, and after mixing to the
sewer. Placing and ramming concrete around the forms cost 39 cts. per
cu. yd., additional. Setting forms in invert cost 2 cts. per cu. yd.,
setting centers 7 cts. per cu. yd. Cost of setting forms and centers
includes placing steel metal. Each lineal foot of 9¼ ft. sewer contained
1 cu. yd. of concrete, although the section only calls for 0.94 cu. yd.
The excess was usually wasted by falling over sides of forms or being
made too thick at crown.
"This yard of 1-2-5 concrete cost in place as follows (record taken as
an average of several-days' run):
Cement, 1.31 bbls. at $1.30 $1.703
Stone, 0.84 cu. yds. at $1.21 1.016
Stone dust, 0.42 cu. yd. at $1.21 0.508
Labor at 18¾ cts. per hour 0.987
Labor setting forms and setting metal 0.045
Cost of forms (distributed over 1,800 ft. of sewer) 0.082
40 sq. ft. expanded metal at 4¼ cts. 1.700
Labor plastering invert 0.070
------
Cost per ft., or per cu. yd. $6.111
"The forms for the invert were made of 2-in. rough hemlock boards cut
out 4 ins. less diameter than the diameter of the sewer, except for 18
ins. at the bottom of the form which coincided with the inside form of
sewer. The bottom of the sewers was laid to the bottom of this form
before it was set. Then the lagging, consisting of 2×6-in.×16-ft.
hemlock planed, was placed against each side of the form, one at a time,
and the concrete brought to the line of this top in 6-in. layers until
the whole invert was finished. These forms were set in 16-ft. sections,
five to each section.
"The centers consisted of seven ribs of 2-in. hemlock upon which was
nailed 1½-in. lagging, 2 ins. wide, tongued and grooved, and were 16 ft.
long, non-collapsible, but had one wing on each side, 9 ins. wide, which
could be wedged out to fit any inaccuracies in the invert. We used four
of these centers setting two at each operation and worked from two ends.
We left the centers in for 18 hours before drawing.
"The cost of the concrete on the smaller sewers was the same as are the
larger sewers, but the steel metal cost less, as it was wire woven metal
that cost 2½ cts. per sq. ft. It was much easier handled and cut to no
waste as it came in long rolls and was very pliable.
"After training our men, which occupied about one week or 10 days, we
had no difficulty in getting the concrete well placed around the metal,
preserving the proper location of the latter, which, however, bore
constant watching, as a careless workman would often take the temporary
supporting blocks and allow the metal to rest against the wooden center,
in which case the metal would show through the surface inside of the
sewer. The metal was kept 2 ins. away from the inside forms and the
arch. To keep it at this location we had several 2-in. wooden blocks cut
which were slipped under the wire or expanded metal and as soon as some
concrete was pushed under the wire at this point the block was removed.
"After the forms were removed the invert needed plastering, but the arch
was practically like a smoothly plastered wall except where it joined
the invert, where it frequently showed the result of too much hurry in
depositing the first loads of concrete on the arch. We remedied this by
requiring less concrete to be deposited at the start, thus giving the
rammers time to place the material properly.
"An interesting result was obtained in the smoothness of the inside
surface by using a mixture of different sized stones. When ¾-in. stones
or smaller were used in the arch, the inside was honeycombed; but, where
1 to 1½-in. stones (nothing smaller) were used, the inside was perfectly
smooth, and the same was true of the invert, showing that the use of
larger stones is an advantage and secures more monolithic work. When the
run of the crusher from 1½ to ¾-in. stones was used the work was not at
all satisfactory.
"The difference in cost of mixing by hand and machine is practically
nothing on this kind of work. As the moving of the machine to keep pace
with the progress of the work equals the extra cost of mixing by hand
when the mixing can be done close to the point where the cement is being
placed."
The total cost of the sewers, including excavation, etc., was:
Cost per lin. ft.
9¼-ft. sewer through marsh $32.00
9¼-ft. sewer in cut averaging 24½ ft. 24.00
6½-ft. sewer in cut averaging 12 ft. 10.00
5-ft. sewer in cut averaging 11½ ft. 6.70
~SEWER WITH MONOLITHIC INVERT AND BLOCK ARCH.~--The following records of
construction for a sewer built at Coldwater, Mich., in 1901, are given
by Mr. H. V. Gifford. The sewer had a monolithic invert and a block
arch.
The sewer was circular, having an inner diameter of 42 ins., the
thickness of the invert and the arch alike was 8 ins. Figure 266 is a
cross-section. The concrete was 1 of Portland cement to 6 of gravel.
There were 11 concrete blocks in the ring of the arch, each block being
24 ins. long, 8 ins. thick, 8 ins. wide on the outside of the arch and
5¾ ins. wide on the inside of the arch. A block weighed 90 lbs. which
was too heavy for rapid laying; blocks 18 ins. long would have been
better. Some 8,500 blocks were made. Molds were of 2-in. lumber, lined
with tin, for after a little use it was found the concrete would stick
to the wood when the mold was removed. The four sides of the mold formed
the extrados, the intrados, and the two ends of the block; the other two
sides being left open. When put together the mold was laid upon a 1-in.
board, 12×30 ins., reinforced by cleats across the bottom. The sides of
the molds were held together with screws or wedge clamps. When the
blocks had set, the sides of the molds were removed, and the blocks were
left on the 12×30-in. boards for 3 days, then piled up, being watered
several times each day for a week.
A gang of 14 men made the blocks; 2 screening gravel through 1-in. mesh
screen; 4 mixing concrete; 4 molders; 3 shifting and watering blocks,
and 1 foreman. With a little practice each molder could turn out 175
blocks a day; and since each block measured ¾ cu. ft., the output of the
14 men was 19½ cu. yds. a day. Mr. Gifford informs us that the wages
were $1.50 a day for all the men, except the foreman. The daily wages of
the 14 men were $22, so that the labor of making the blocks was $1.10
per cu. yd.
[Illustration: Fig. 266.--Sewer with Monolithic Invert and Block Arch.]
Each batch of concrete, containing ½ bbl. of Portland cement costing
$1.35 per bbl., made 18 blocks. (1 bbl. per cu. yd.) Since the gravel
cost nothing, except the labor of screening it, the total cost of each
block was 11 to 12 cts., which includes 0.85 cent for use of molds and
mold boards, which were an entire loss. At 12 cts. per block the cost
was $4.32 per cu. yd.
The contract price was $3 per lin. ft. of this sewer, as against a bid
of $3.40 per ft. for a brick sewer.
When the trenching had reached to the level of the top of the invert,
two rows of stakes were driven in the bottom, stakes being 6 ft. apart
in each row, and rows being a distance apart ¼-in. greater than the
outer diameter of the sewer. These stakes were driven to such a grade
that the top of a 2×4-in. cap or "runner" set edgewise on top of them
was at the proper grade of the top of the invert. The excavation for the
invert was then begun, and finished to the proper curve by the aid of a
templet drawn along the 2×4-in. runners. In gravel it was impossible to
hold the true curve of the invert bottom. Concrete was then placed for
the invert. To hold up the sides of the invert concrete, a board served
as a support for the insides, but regular forms were more satisfactory
in every respect except that they were in the way of the workmen. A form
was tried, its length being 6 ft. It was built like the center for an
arch, except that the sheeting was omitted on the lower part of the
invert. It was suspended from the cross-pieces resting on the "runners."
After the concrete had been rounded in place, the form was removed and
the invert trued up. This form worked well in soil that could be
excavated a number of feet ahead, so that the forms could be drawn ahead
instead of having to be lifted out; but in soil, where the concreting
must immediately follow the excavation for the invert, the form is in
the way. The invert was trued up by drawing along the runners a
semi-circular templet having a radius of 21½ ins. Then a ½-in. coat of
1-2 mortar was roughly troweled on the green concrete. Another templet
having a 21-in. radius was then drawn along the runners to finish the
invert.
When the plaster had hardened, two courses of concrete blocks were laid
on each shoulder of the invert, using a 1-2-¼ mortar, the ¼ part
being lime paste. The lime made the mortar more plastic and easier to
trowel. Then the form for the arch was placed, and as each 8-ft. section
of the arch was built, a grout of 1-1 mortar was poured over the top
to fill the joints. Earth was thrown on each shoulder and tamped, and
the center moved ahead.
Common laborers were used for all the invert work, except the plastering
which was done by masons who were paid 30 cts. per hr. Masons were also
used to lay the concrete blocks in the arch. Mr. Gifford states that two
masons would lay at the rate of 100 lin. ft. of arch per day, if enough
invert were prepared in advance. As there were 11 blocks in the ring of
the arch, this rate would be equivalent to 7½ cu. yds. of arch laid per
mason per day.
[Illustration: Fig. 267.--Concrete Block Manhole.]
~COST OF BLOCK MANHOLES.~--The following costs of constructing concrete
block manholes for electric conduit at Rye, N. Y., were recorded by Mr.
Hugh C. Baker, Jr. The arrangement of the blocks, their size and shape
and the dimensions of the completed manholes are shown by Fig. 267. The
blocks were molded of 1-2-5¾-in. broken stone concrete in 30 wooden
molds made by a local carpenter at a cost of from $3.50 to $12 each. The
concrete was placed in the molds very wet, with very little tamping, and
was allowed to set for seven days before the blocks were moved to the
work. The molds were left in place from 24 to 36 hours. With the
facilities at hand six complete sets of top blocks were made each day by
four men, when no wall blocks were being made, and half a set (15) wall
blocks and two sets of top blocks were made each day by four men. The
cost of the block manholes complete was as follows, per manhole:
30 wall blocks, 2½ cu. yds. $21.00
6 cover blocks, 1½ cu. yds. reinforced 4.27
I-beams for cover, in place 5.40
Supervision, freight, hauling 5.6 tons concrete 9.38
Labor placing cover, 3 hrs. at 15 cts. 0.45
Labor placing walls, 20 hrs. at 15 cts. 3.00
------
Total, exclusive of iron cover $43.50
~CEMENT PIPE, CONSTRUCTED IN PLACE.~--In constructing 8-in. cement sewer
for the Foster Armstrong Piano Co.'s works at Rochester, N. Y., a gang
of seven men averaged 300 ft. of pipe per 10-hour day, using a Ransome
pipe mold. The mold is shown by Fig. 268. It is made of sheet steel,
with an inner core 10 ft. long, the front end of which is surrounded
with a sheet steel shell that serves as an outer form for the pipe. The
mortar mixed rather dry was packed into the annular space between core
and shell by one man, using a short wooden rammer. A second man kept the
mold slowly moving forward by operating the lever, which by means of a
ratchet and drum winds up a wire rope stretched ahead to a deadman in
the trench bottom. As the mold moves ahead it leaves behind it the
cement pipe. A third man carefully filled under the invert and over the
haunches of the green pipe with earth to give it support. The following
was the itemized cost per day, 300 ft. of pipe laid:
6 men at $1.70 per 10-hour day $10.20
1 foreman 3.00
3 bbls. cement at $1.25 3.75
3.3 cu. yds. sand at 85 cts. 2.80
Water 0.15
------
Total for 300 lin. ft. $19.90
This is equivalent to 6.63 cts. per lin. ft. of pipe.
[Illustration: Fig. 268.--Ransome Continuous Mold for Concrete Pipe
Construction.]
In Trans. C. E., Vol. 31, 1894, p. 153, James D. Schuyler gives the cost
of cement pipe made by the Ransome system for the Denver Water Works.
There is a wrought iron shell of the size of the inner diameter of the
pipe forming the inner mold. To this shell is attached a "leader" and
"saddle" of larger diameter forming the outer mold. These molds are
drawn slowly along the trench by a cable and horse whim, and the
concrete is shoveled continuously into the core space between the molds
and rammed on a long incline. The top half, or arch, of the pipe is
supported by sheet iron plates (2 ft. wide), placed one after another on
the forward end of the mold; and, being clamped together at the top and
sides, remain in position after the mold is slid out from under them.
After the mold has passed along, these iron plates are supported by
upright sticks and by horizontal clamping rods. The plates are left in
place for 24 to 48 hrs. The concrete, made 1-3½, river sand and gravel,
was machine mixed. A gang of 30 men mixed, wheeled, shoveled and tamped
the concrete, attended to the plates, cleaning and greasing them, etc.
This gang would make short runs at the rate of 900 lin. ft. of pipe a
day, but counting stoppages, the average rate was 300 ft. a day. The
inner diameter of the pipe was 38 ins., and its bottom was molded flat
for a width of 18 ins. The concrete shell was 2½ to 3 ins. thick. The
pipe was washed with pure cement grout, applied with brushes after
removing the iron plates. With cement at $3.75 per bbl., gravel at $1.25
per cu. yd., and labor at $1.75 to $2 per day, the cost of this pipe was
$1.35 to $1.50 per ft., after the gang was well organized.
~PIPE SEWER, ST. JOSEPH, MO.~--In constructing extensions to 36-in.,
42-in., 48-in. and 72-in. sewers at St. Joseph, Mo., reinforced concrete
pipe of the form shown by Fig. 269 was employed. The thickness of shell
for the various sizes was 4 ins., 4½ ins., 5 ins., and 7 ins. All sizes
were made in 3-ft. lengths, one end of which is rebated and beveled to
form a spigot and the other end of which is chamfered on the inner edge
to receive the bevel of the spigot. This jointing leaves a
circumferential groove, into which the hooked ends of the longitudinal
reinforcing bars project in such a way that a circular hoop can be
threaded through them to connect successive lengths. The reinforcement
is of the same form for all sizes of pipe, but seven longitudinals were
used in the 72-in. size and five for all smaller sizes; the
circumferential bars were in all cases spaced one 9 ins. from each end.
The pipe, as described, is the standard pipe made by the Reinforced
Concrete Pipe Co., of Jackson, Mich., and is covered by patents. The
practice of this company is to manufacture the pipe itself on the ground
and furnish it to the contractor. It does not contract to build sewers
nor does it dispose of rights to manufacture to contractors.
[Illustration: Fig. 269.--Jackson Concrete Sewer Pipe.]
_Pipe Molding._--The pipe is molded endwise. A bottom plate so shaped as
to form the hub or receiving end of the pipe is set up. On the upper or
inner flange of this cast iron bottom plate is set the core defining the
inside diameter of the pipe; this core is in four segments of sheet
steel. The longitudinal reinforcing bars are next inserted in slots in
the bottom plate and the outside form of sheet steel is then set up on
the lower and outer flange of the bottom plate. Spacing clips on the top
edge of the outer shell hold the tops of the reinforcing bars in
position. The concrete is then shoveled into the annular mold and tamped
until it reaches the level for the first circumferential reinforcing
bar; this is then placed by removing the spacing clips, threading the
hoop over the longitudinal bars and sliding it down to position. Filling
and tamping then proceeds until the second hoop is to be placed; this is
placed exactly like the first, and filling and tamping then proceeds
until the mold is filled. At the St. Joseph work a 1-2-3 mixture, with
crushed limestone aggregate ranging from pea size to 1-in. stone was
used. The molding was done in tents which were heated by coke fires in
salamanders in freezing weather.
_Pipe Laying._--In laying, the pipes are handled and lowered into
position just as are cast iron water pipe. Successive lengths are placed
by inserting the spigot ends into the chamfered hub ends and then
threading the tie hoop through the hooked ends of the projecting
longitudinal reinforcing bars. A strip of galvanized iron is then passed
under the pipe and bent up so as to girdle the circumferential groove
except for a space at the top; the groove is then poured with a wet 1-2
cement mixture, which, when hardened, completes the joint.
~COST OF MOLDING SMALL CEMENT PIPE.~--Mr. Albert E. Wright gives the
following account of the method and cost of molding and laying 6 to
12-in. cement pipe for irregular work at Irrigon, Ore.: The pipe was 6
to 12 ins. inside, made of Portland cement and clean, sharp sand of all
sizes up to very coarse. The mortar was mixed rather dry, but very
thoroughly, using 14.1 cu. ft. of sand to 1 bbl. of cement, or very
closely a 1 to 4 mixture. From six to seven buckets of water were used
to each barrel of cement, except for the 6-in. pipe, for which the
mortar had to be made somewhat stiffer in order to remove the inner
form, which was not made collapsible as in the larger sizes.
The forms were sheet iron cylinders with a longitudinal lap joint that
could be expanded after molding the pipe, and removed without injuring
the soft mortar. The inner form was self-centering, so that there was
little variation in the thickness of the pipe.
Four men were required in making cement pipe by hand; one mixed the
mortar, and wheeled it to the place of work; another threw it into the
form a little at a time with a hand scoop; a third rammed it with a
tamping iron, and a fourth kept the new pipe sprinkled, and applied a
coat of neat cement slurry to the inside when it was sufficiently hard.
In molding, the form of the bell at the bottom was secured by an iron
ring that was first dropped into the form, and the reverse or convex
form at the top was made with a second ring. While still in its form
the pipe was rolled or lifted into its place in the drying yard, and the
form was then carefully removed. A very slight blow in removing the form
would destroy the pipe, and a considerable number, especially of the
larger sizes, collapsed in this way, and had to be remolded. To avoid
handling, the pipe was stacked on end a few feet from the place of
mixing, the form being moved as the yard filled with pipe. One crew of
four men could make about 250 joints or 500 lin. ft. of pipe a day.
As soon as hard enough, the pipe was turned end for end, and was then
kept wet for several weeks before being laid. The coating of neat cement
on the inside was applied with a short whitewash brush, and was a small
item in the cost.
In laying, the trench was carefully finished to grade in order to have
the joints close nicely, and the ends were well wet with a brush. The
mason then spread mortar, mixed 1 to 2, on the end of the pipe, and laid
a bed of mortar at the bottom of the joint. He then jammed the section
into place, and swabbed out the inside of the joint with a stiff brush,
to insure a smooth passage for the water. A band or ring of mortar was
spread round the outside of the joint as an additional reinforcement.
One barrel of cement would joint about 300 sections of pipe. The
materials cost as follows: Portland cement, per bbl., $4.45; labor, per
day, $2; foremen, per day. $2.50 to $3; hauling, per load mile (1 cu.
yd.), 20 cts.; sand, free at pit; water, free.
The pipe was all of a 1-4 sand and cement mortar, and the amount of
cement in one foot of pipe was arrived at by assuming that where the
sand has voids in excess of the cement used, the mortar will occupy 1.1
(see Chapter II) times the space of the dry sand, which yields the
following formula:
Where--
c = cost per bbl. of cement, or $4.45.
n = cu. ft. in one bbl. (taken at 3.5 here).
s = ratio of sand to cement, or 4.
d = inside diameter in inches.
t = thickness of pipe in inches.
l = length of pipe considered, or 1 ft. here.
Then:
c × l × [pi] × (dt + t²)
Cement-cost per foot = --------------------------,
n × s × 1.1 × 144
which gives here =
4.45 × 1 × 3.142(dt + t²)
------------------------------- = 0.00631(dt + t²).
3.5 × 4 × 1.1 × 144
This gave the following cement costs per lineal foot: