Concrete Construction Part 53

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 9 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 s.p.a.ces on the inner surface. Concrete for the invert was 1-2-6, the stone being 1-in. and smaller, and the sand being crusher dust. The arch was 1-2-5.

The reinforcing metal used in the 9-ft. sewer was No. 6 expanded metal, 6-in. mesh, in sheets 85 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.

[Ill.u.s.tration: 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 5 ft. wide and 100 ft. to the roll. The wire is No. 8, with a 64-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 9 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 18 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 4 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 26-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 1-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 2 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 -in. stones or smaller were used in the arch, the inside was honeycombed; but, where 1 to 1-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 1 to -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.

9-ft. sewer through marsh $32.00 9-ft. sewer in cut averaging 24 ft. 24.00 6-ft. sewer in cut averaging 12 ft. 10.00 5-ft. sewer in cut averaging 11 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 5 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, 1230 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 1230-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 s.h.i.+fting and watering blocks, and 1 foreman. With a little practice each molder could turn out 175 blocks a day; and since each block measured cu. ft., the output of the 14 men was 19 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.

[Ill.u.s.tration: Fig. 266.--Sewer with Monolithic Invert and Block Arch.]

Each batch of concrete, containing 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.