Concrete Construction - Methods and Costs
by Halbert P. Gillette
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The concrete was hand mixed in 6-cu. ft. batches at the foot of the column, by three men with a fourth turning over and filling the buckets. The buckets, 12 ins. in diameter and 16 ins. high, were hoisted by a pulley line arranged as shown and pulled by a mule driven by a man, at $1 per day for the mule and $1.50 for the man, the cost of hoisting being 25 to 40 cts. per cu. yd., depending on the rapidity of the man inside the form. This man tamped the concrete which was emptied from the buckets by a man on the scaffolding. Each batch raised the level in the form 15 ins., and between batches a set of ties for the column rods was placed by the man during the tamping. It took from 1 to 2 days to concrete a column of 12 cu. yds. The concrete was a 1-3.8-5.7 limestone screenings mixture, mixed wet enough to be easily pushed into the forms and worked around the reinforcement. The form construction is shown by Fig. 224. The form for one column required 650 ft. B. M. of lumber, and on an average, each form was used twice. As a matter of fact, the side strips and outside braces were used three times, while much of the 7/8-in. sheathing was destroyed by being used once. The lumber for shoring cost $23 per M. ft. B. M., and the light lumber for forms cost $18 per M. ft. B. M. All lumber was yellow pine. All labor was negro, at 15 cts. per hour; foremen who worked. 22 cts. per hour. The cost of the several parts of the work compiled from records furnished by Mr. Keith O. Guthrie, engineer in charge, was as follows:

Cost per Cost per Concrete. column cu. yd.

Lumber for forms $ 4.81 $0.40 Setting up and removing forms 11.32 0.95 Cement, 10.17 bbls. at $2.40 24.40 2.03 Sand, 5.87 yds. at $0.90 5.28 0.44 Stone, 8.75 yds. at $1.35 10.94 0.91 Mixing and wheeling 15.73 1.31 Hoisting by mule with driver 4.80 0.40 Handling bucket on scaffold 2.93 0.25 Tamping inside column 2.93 0.25 Painting with grout 3.89 0.32 Clearing away rubbish 1.97 0.16 Rigging, etc. 2.64 0.21 Tools 0.59 0.05 Moving scaffold 2.94 0.25 Moving mix board and rigging hoist 1.62 0.14 ——— ——- Total cost of concrete $96.79 $8.07

Cost per Cost cts. per Reinforcement. column. lb. of bars. Iron bars, 1,034 lbs. $20.68 $2.00 Drilling iron bars 1.44 0.14 Setting iron bars in place 1.23 0.12 Bolts for splicing and spacing 3.98 0.40 Wire cross ties at 2, cts. lb. 1.39 0.14 Labor forming 130 cross ties 1.13 0.11 ——— ——- Total cost of iron and steel $29.85 $2.91

Summary of Cost.

Per column. Per cu. yd. Concrete in place $96.79 $8.07 Steel in place 29.85 2.49 Cutting out and removing brick 8.36 0.70 Shoring floors and roof, labor 5.87 0.49 Ditto for lumber used 3 times 3.44 0.29 ———- ——— Total $144.31 $12.04

FLOOR AND COLUMN CONSTRUCTION FOR SIX-STORY BUILDING.—The building was 91112 ft.; 56 columns spaced 16 ft. apart carried the girder system shown by Fig. 225, which in turn supported a 3-in. floor slab. The walls and partitions were not concrete. The following records were kept by the authors:

Forms.—The column forms were built as shown by Fig. 226. The boards were 1-in. stuff, surfaced on four sides; the yokes were spaced 2 ft. apart. The 16-in. pieces were nailed to the 24's with 8-d. nails with heads left projecting for easy pulling. The girder forms, Fig. 227, rested on the column forms and on intermediate posts half-way between columns. These intermediate posts were 34's with 4412-in. head blocks nailed to their tops and wedges under their bottoms. The girder molds were 1-in. stuff, and to the side pieces were nailed 14-in. cleats; the bottom and side pieces were connected by 3/84-in. lag screws spaced 28 ins. apart. The floor slab stringers were carried on the 14-in. cleats; they were spaced 28 ins. apart and were not nailed; neither were the 16-in. lagging boards nailed to the stringers. The point to be noted is the design and construction of the forms so that they could be put together and taken apart easily. The lumber required for forms for one floor 91112 ft., or, say, 10,200 sq. ft., was as follows:

Lumber for columns, ft. B. M. 9,000 Lumber for 1010-in. beams, ft. B. M. 7,600 Lumber for 510-in. beams, ft. B. M. 2,700 Intermediate 34-in. posts, ft. B. M. 1,000 Lagging, 16-in. boards, ft. B. M. 9,000 Stringers, 34 ins., ft. B. M. 4,500 ——— Total ft. B. M. 33,800

In round numbers, we can say that 34,000 ft. B. M. of lumber were used for 10,000 sq. ft. of floor area, or 3.4 ft. B. M. per 1 sq. ft. Enough forms were provided to erect two complete floors; the forms for the lower floor being removed and erected again for the second floor above, thus using all the lumber three times. With carpenters at $3.50 for 8 hours, the forms were framed ready for erection for $4 per M. ft. B. M. The lumber framed ready to erect cost them:

Lumber, cost per M. ft. B. M. $26.00 Labor, framing per M. ft. B. M. 4.00 ——— Total per M. ft. B. M. $30.00

Since the lumber was used three times, $30 3 = $10 is the charge against each 1,000 ft. B. M. needed to encase the concrete on a floor. There were nearly 34,000 ft. B. M. per floor, hence the cost of lumber ready for erection was $340 per floor. There were as shown below, 200 cu. yds. of concrete per floor, so that the cost was $340 200 = $1.70 per cu. yd. of concrete for forms ready for erection. It took a gang of 5 men 7 days to tear down and carry up the forms for one floor; hence 5 $2 7 = $70 per floor, or practically $2 per M. ft. B. M., or $0.35 per cu. yd. of concrete for taking down and carrying forms two stories. It took a gang of 10 carpenters 7 days to erect these forms, which at $3.50 per day was $245 per floor, or $7 per M. ft. B. M., or $1.20 per cu. yd. of concrete.

Concrete.—The amount of concrete per floor was as follows:

Floor slab 3 ins. thick, 10,200 sq. ft. 110 cu. yds. Beams, 1010 ins. 40 cu. yds. Beams, 510 ins. 20 cu. yds. Columns, 1515 ins. (average) 30 cu. yds. ——- Total concrete per floor 200 cu. yds.

A concrete mixer, a hoist and a gang of 14 men mixed and placed the concrete for a floor in 7 days. At $2 per day for labor this gives 14 7 $2 = $196, or say $1 per cu. yd. for mixing and placing the concrete.

Reinforcement.—In each of the 1010-in. beams there were 4, 1-in. round rods, 2 straight and 2 bent, and stirrups of 1/81-in. straps spaced 5 ins. apart at columns and 15 ins. at the center. In each 510-in. beam there was half as much steel as in a 1010-in. beam. The floor slab reinforcement consisted of -in. rods spaced 5 ins. apart and 2 cross-rods in 7-ft. panel. The column reinforcement consisted of 4 rods averaging 1 in. in diameter. In round numbers the amount of steel required for each floor was, therefore, as follows:

Lbs. steel rods in 1010-in. beams 16,200 Lbs. steel rods in 510-in. beams 4,000 Lbs. stirrups in beams 3,000 Lbs. steel rods in floor slabs 3,800 Lbs. steel rods in columns 1,400 ——— Total pounds steel per floor 28,400

This is equivalent to 142 lbs. of steel per cubic yard of concrete, or about 1 per cent of the total volume of reinforced concrete was steel. The steel in the beams was about 3 per cent. It required a gang of 5 laborers 7 days at $2.25 per day, to bend and place the steel for each floor or $86 for labor on 28,400 lbs. of steel. This is equivalent to 0.3 ct. per lb., or 45 cts. per cu. yd. of concrete.

Summary of Costs.—Summarizing the figures given we have the following cost per cubic yard of concrete in floors and columns:

Per cu. yd. 142 lbs. steel at 2 cts. $ 3.55 1 bbl. cement 2.50 1 cu. yd. gravel 1.10 cu. yd. sand 0.55 170 ft. B. M. lumber ready to erect at $10 (1/3 of $30) 1.70 170 ft. B. M. torn down at $2 0.35 170 ft. B. M. erected by carpenters at $7 1.20 Mixing and placing concrete 1.00 Shaping and placing steel 0.45 Superintendence 0.25 ——— Total $12.65

WALL AND ROOF CONSTRUCTION FOR ONE-STORY CAR BARN.—The barn was 50 ft. wide and 190 ft. long, divided into three rooms by two transverse partitions and covered with a 4-in. roof having a pitch of in. per foot. The main walls were 12 ins. thick and the partition walls 10 ins. thick. The main room 110 ft. long had four car tracks its whole length with pits under each and a 6-in. reinforced concrete floor slab between. The floor girders, one under each rail, were 12 ins. square, each reinforced by three 1-in. rods, and were carried on 1212-in. pillars. The total yardage of concrete was 874 cu. yds. divided as follows:

Walls and foundations, cu. yds. 614 Pillars and girders in track pits, cu. yds. 44 Reinforced floors, cu. yds. 55 Roof 160 —- Total, cu. yds. 873

A 1-2-5 concrete was used for floors, roofs and girders and a 1-3-6 concrete for foundations and walls. There were 26 tons of reinforcing steel, or 61 lbs. per cu. yd., or 0.45 per cent. of the volume of the concrete was steel. The wages paid were: Foreman, $2.50; blacksmith, $2; engineer, $1.75; laborers, $1.50; two-horse team and driver, $3.67; one-horse team and driver, $2.92; carpenter, $2.25; carpenters worked 9 hours; all others 10 hours.

Forms.—Carpenters framed and erected forms and common laborers under foreman carpenter took them down. Lagging was all 2-in. stuff and uprights 34-in. stuff. Props for roof forms were 18-ft. round timber procured on the job. They were 6 ins. in diameter at the top and cost 50 cts. each, 91 being used. These props are not included in the lumber listed below, but their cost is included in the costs given. No record was kept of the number of times the lumber was used, but as 54,643 ft. B. M. were bought and about twice this much would be needed to enclose the concrete if used only once, we will assume that all lumber was used twice. Including the props there were about 60,000 ft. B. M., or 70 ft. B. M. per cu. yd. of concrete. The cost of the lumber was $1,520.86, and the cost of labor on the forms was $1,660.60, so that the cost of forms was:

Item. Per cu. yd. Per M. ft. Per sq. ft. Lumber $1.74 $13.50 $0.038 Labor 1.90 14.07 0.041 ——- ——— ——— Total $3.64 $27.57 $0.079

If the lumber had been used only once the cost per cubic yard would have been $5.38, and per M. ft. B. M., $41.07.

Concrete.—A railway track was run the full length of the building upon what was eventually the fourth track of the car barn and a Ransome mixer was set up as close to the track as possible allowing a platform to be built between it and the track. Cars were brought up to this platform and the materials handled by wheelbarrows direct from cars to mixer. Both platform and mixer were moved twice as the work progressed. The concrete was taken by wheelbarrows on runways to the side walls. For the roof it was hoisted by a horse by means of a mast having an arm with a three-quarters swing; the barrows were hoisted direct using a hook for the wheel and two rings for the handles.

The cost of the concrete for materials was:

1.1 bbl. cement at $1.21, per cu. yd. $1.33 ton sand at 75 cts., per cu. yd. 0.55 Aggregate, per cu. yd. 0.88 61 lbs. steel at 1.9 cts., per cu. yd. 1.15 Lumber, 70 ft. B. M. at $27, per cu. yd. 1.74 ——- Total per cu. yd. $5.65

The cost of labor per cubic yard was:

Forms, per cu. yd. $1.900 Mixing, per cu. yd. 0.210 Placing, per cu. yd. 0.310 Finishing, per cu. yd. 0.143 Handling cement, per cu. yd. 0.017 Handling sand, per cu. yd. 0.104 Handling steel, per cu. yd. 0.270 Handling aggregate, per cu. yd. 0.222 Coal, at $4.25 per ton, per cu. yd. 0.010 Foreman, per cu. yd. 0.133 Teams and laying pipe line, per cu. yd. 0.087 ——— Total, per cu. yd. $3.406

Summarizing, we have the following cost per cubic yard:

Concrete materials, per cu. yd. $2.76 Labor mixing and placing concrete 1.01 Forms, materials and labor 3.64 Reinforcement, materials and labor 1.42 Fuel, foreman and pipe line labor 0.23 ——- Total, per cu. yd. $9.06

The cost for handling steel, making stirrups, welding, etc., was $8.90 per ton, or 0.45 ct. per lb.

CONSTRUCTING WALL COLUMNS FOR A ONE-STORY MACHINE SHOP.—The building was 53600 ft.; each side wall consisted of 40 columns of channel section carried on footings of channel section somewhat heavier than that of the column. The columns were spaced 15 ft. on centers and each was 7 ft. wide so that there were 7 ft. spaces between columns, which were filled with 3-in. curtain walls extending 7 ft. above the floor. Figures 228 and 229 show the column and footing construction. Each column contained 125 cu. ft., or 4.63 cu. yds. of 1-3-5 1-in. crushed slag concrete above the footing and the costs given here relate only to the columns above footings. In the 80 columns there were 370 cu. yds. of concrete.

Forms.—A column form is shown by Fig. 230; it contains approximately 1,000 ft. B. M. of lumber. Ten of these forms were used, so that 10,000 ft. B. M. of form lumber were required for 370 cu. yds. of concrete, or 27 ft. B. M. per cu. yd. of concrete. Each column had a superficial area excluding ends of about 420 sq. ft., so that 420 80 = 33,600 sq. ft. was the superficial area of all the columns and 10,000 ft. B. M. 33,600 sq. ft. = 0.3 ft. B. M., or, say, 1/3 ft. B. M., of form lumber was used per square foot of concrete enclosed. The cost of the forms per 1,000 ft. B. M., and, therefore, per form, was:

Lumber, 1,000 ft. B. M., at $31.75 $31.75 Labor constructing form 16.39 ——— Total per 1,000 ft. B. M. $48.14

This gives us a cost per cubic yard of concrete for materials and labor constructing forms of $480 370 = $1.30, and per square foot of outside wall area of $480 (146 80) = 4.1 cts.

The erection and taking down of the forms, owing to the weight of some of the pieces, was done by means of special derricks. The footings were brought to within in. of grade and a tenon form of the exact shape of the channel section of the column was placed on top and filled with grout to a depth of 1 in. These tenons served as guides in setting the column forms, and proved to be much quicker and more accurate than points.

The forms were assembled on the ground and erected by a 35-ft. A-frame derrick mounted on wheels. The construction is shown by Fig. 231. This derrick had a capacity of about 4 tons and carried a Ransome friction crab hoist driven by a 5 h.p. Meitz & Weiss kerosene oil engine. It was the practice to set a number of forms before filling any. This enabled the carpenter gang to be plumbing up the first form while the erecting gang were setting others. The forms had to be very securely guyed and braced to withstand the impact of the falling concrete. Very little trouble was had in keeping them well lined up.

Two gangs were employed in assembling forms and a portion of the men in each gang also shaped and placed the reinforcement and placed and tamped the concrete in the forms so that no exact division of labor is possible. The organization of these gangs and the wages paid were as follows:

Derrick Gang:

1 foreman, at 36 cts. per hour $ 3.94 1 crabman, at 30 cts. per hour 2.70 2 topmen, at 27 cts. per hour 4.86 2 bottom men, at 23 cts. per hour 4.14 ——— Total per 9-hour day $15.64

Assembling Gang:

1 boss carpenter, at 47 cts. per hour $ 4.23 2 carpenters, at 36 cts. per hour 6.48 2 carpenters, at 30 cts. per hour 5.40 2 carpenters' helpers, at 25 cts. per hour 4.50 4 men forming and placing reinforcing steel and rethreading bolts, at 23 cts. per hour 8.28 ——— Total per 9-hour day $28.89 ——— Grand total $44.53

These gangs assembled and erected the molds and concreted 80 columns in 22 working days, including 2 days lost on account of cold weather, so that 4 columns were completed per day of 9 hours. We can subdivide the cost as follows:

Item. Per cu. yd.

Erecting forms and concreting $0.81 Assembling forms and reinforcement 1.56 ——- Total $2.37

Charging the 4 men placing reinforcement and rethreading bolts to forming and placing reinforcement alone we can figure the cost of fabrication and erection of reinforcement very closely. There were 160 lbs. of reinforcing steel in each column, hence $8.28 (160 4) = 1.3 cts., was the cost per pound of forming and placing it. This includes handling.

The stripping of the forms was carried on by another gang using a derrick similar to the first one described, except it could be of lighter construction as it had to handle only the separate parts of each form and not the forms assembled. The derrick shown in Fig. 232 was a 33-ft. A-frame, with wheels at the bottom of each leg. It had a friction crab hoist driven by an electric motor, both of which were fastened to the derrick frame between the shear legs.

The operation of stripping required only four men and the crabman. The outside flat panel was removed first, and left leaning up against the concrete while the inside trough shaped panel was pried loose and lowered onto the ground with its inside face uppermost. The side panels being comparatively light, were stripped without the use of the derrick, and these panels were assembled on the ground with the inside piece. The derrick then picked up the outside panel again, and placed it in its proper place. After the bolts were put in place, the assembled form was moved on rollers to another point in the line of columns where it was again erected. The arrangement of derricks for erecting and stripping forms is shown in Fig. 233.

The gang stripping forms was made up as follows:

1 foreman, at 30 cts. per hour $ 2.70 1 crabman, at 27 cts. per hour 2.43 1 topman, at 27 cts. per hour 2.43 2 bottom men, at 23 cts. per hour 4.14 ——— Total per 9-hour day $11.70

This gang of five men stripped 4 columns containing 18.52 cu. yds. of concrete each day, so that the cost of stripping was $11.70 18.52 = 62.7 cts. per cu. yd.

Concrete.—The concrete was mixed in a No. 2 Ransome mixer and delivered to the work in Ransome concrete carts. These carts were pushed along a runway which terminated in a slight incline under the derrick so that their contents could be emptied into the derrick buckets.

The concrete was hoisted in an 8-ft. bottom dump bucket, using the derrick described above. It was necessary to stir up the concrete thoroughly with long-handled slicers as it was being deposited in order to prevent segregation. This expedient combined with a wet mixture and tight molds was found to overcome this difficulty very effectually.

The gang mixing and wheeling concrete was made up as follows:

1 mixer foreman and engineer at 27 cts. per hour $ 2.43 4 laborers charging mixer at 18 cts per hour 6.48 4 laborers wheeling concrete at 18 cts. per hour 6.48 ——— Total per 9-hour day $15.39

This gang mixed and wheeled concrete for four columns, or 18.52 cu. yds., hence the cost per cubic yard was 82.6 cts.

With cement at $1.60 per bbl., sand at $1 per cu. yd. and slag at $1.10 per cu. yd. the cost of materials per cubic yard of concrete was $3.

Summarizing the above figures we have the following cost per cubic yard of concrete in place:

Item. Per cu. yd. Concrete materials $3.00 Reinforcing steel 0.73 Forms, lumber and framing 1.30 Forms, erecting and concreting 0.81 Forms, assembling and reinforcement 1.56 Forms, stripping 0.63 Mixing and wheeling concrete 0.83 ——- Total $8.86

CONSTRUCTING ONE-STORY WALLS WITH MOVABLE FORMS AND GALLOWS FRAMES.—In constructing the walls for an 8530-ft. factory building at Old Bridge, N. J., Mr. A. E. Budell made use of movable forms and gallows frames to construct the curtain walls and columns in one piece. Each side wall was built its full height in successive 50-ft. lengths by depositing the concrete between two forms which were moved upward as the concreting progressed. Fig. 234 indicates the mode of procedure. The form was raised and lowered by means of two gallows frames fitted with blocks and tackle. A steel cable, with a trolley affixed, extending from one frame to the other, provided a convenient mode of hoisting material to the form, and the gallows frames took the place of ladders for climbing onto the structure. No scaffolding whatever was used and only one man was required overhead to dump the buckets and tamp the concrete into place.

The two walls were carried up simultaneously, one form being shifted into place and filled while the other was left in place until the concrete was sufficiently hard. It was found that 18 hours was amply sufficient to allow the concrete to set hard, after which the form was removed and lifted to a higher level. Thus the men were continuously engaged in lifting and filling first one form and then the other. The average length of time required to remove, raise and fill one form was 5 to 6 hours. Thus, two forms could be raised and filled almost every day. The construction of the forms and of the gallows frames is shown by Figs. 234 and 235. The cost of one set of forms and gallows frames was as follows:

320 ft. B. M. of 210 in.10 ft. plank at $34 $ 10.88 150 ft. B. M. of 34 in.16 ft. spruce at $33 5.25 135 ft. B. M. 18 in. yellow pine at $30 4.08 335 ft. B. M. 16 in. spruce at $33 11.05 4 posts 68 in.26 ft. = 416 ft. B. M. at $30 12.48 4 sills 68 ins.16 ft., 2 caps 66 ins.9 ft., 4 braces 66 ins.16 ft. = 490 ft. B. M. at $30. 14.70 3 pieces 310 ins.20 ft. = 150 ft. B. M. at $30 4.50 ———- Total lumber (1,996.5 ft. B. M.) $ 62.94


Bolts for trussing, 675 lbs. at 2 cts. $ 13.50 Iron guy rope and clips 7.00 Blocks 8.00 One coil of -in. rope 28.00 ———- Total accessories $ 56.50

Labor making one outfit: 2 men, 8 days, at $2.75 per 9 hrs. $ 44.00 ———- Grand total $163.44

This sum covered the cost of forms for one side of the building 85 ft. long and containing 150 cu. yds. of concrete, hence the cost of forms was in round figures $1.10 per cu. yd. of concrete. Each cubic yard of concrete required 1,997 150 = 13-1/3 ft. B. M. of form lumber.

The concrete was a 1-2-4 mixture. A careful record for 15 days, showed an average of 2.8 cu. yds. of concrete placed in 6 hours by a gang of 6.3 men. From this we can figure the cost of concrete in place to be about as follows:

2.8 cu. yds. concrete at $3 for materials $ 8.40 6.3 men 6 hours at 15 cts. 5.67 1 foreman 6 hours at $4 per day 2.00 ——— Total per cu. yd. $16.07

Thus the cost of concrete in place was $16.07 2.8 = $5.73 per cu. yd. Adding the cost of forms we get $5.73 + $1.10 = $6.83 per cu. yd. as the cost for labor and materials in constructing forms and mixing and placing concrete.

Offsets and molding decorations were easily made, although they were 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.

FLOOR AND ROOF CONSTRUCTION FOR FOUR-STORY GARAGE.—The building was 53200 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

The lumber had a considerable salvage value which is not allowed for in the above figures.

Concrete.—The concrete was a Portland cement, -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 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.



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.

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.

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.

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, hr., at $0.15 0.15 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 -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 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 2 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 2 cts. 56.50 Erecting steel, at 0.08 ct. per lb. 1.80 Erecting forms 4.77 ——- Total $75.37

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 1-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.

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


Molding $75.00 $15.00 Erecting 7.87 1.57 ——— ——— Totals $82.87 $16.57

In this same building the roof was composed of 126 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 116 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 0.687 116 lbs. steel, at 2 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 8816 ins., and after molding the faces were bush hammered and the edges tooled. The pilasters, consisting of four blocks laid around an 88-in. hollow space, were solidified by pouring the 88-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.

The materials used for the block were Sandusky Portland cement and -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 8816 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, 8932 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 = 25 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 35 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 91032-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. 8932 33-1/3 120 10932 33-1/3 150 12932 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 8932-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.



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.

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.

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 7/81-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 1 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 13/8-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.

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.

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.

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 1-2-4 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 2-in.5 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 7-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, -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.

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 13 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.

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 -in. pipe and on the other side with 1-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.

All the conduits were built in sections from 12 ft. to 13 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 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 13 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 8-ft. reinforced concrete conduit for the Jersey City water supply, use was made of forms without bottoms. Each form was made of segmental sections 12 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 1-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.

"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 24 material, surfaced on both sides, with the edges beveled to the radius of the circle. These pieces of 24 were nailed with two 10d. nails to each segment. The segments were held together by four -in. bolts, which passed through the center, and 1-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 32 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 23, 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 212 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 2-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.

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