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Concrete Construction - Methods and Costs
by Halbert P. Gillette
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"A gang of men simply shifted on alternate days from end to end of the conduit, although several sections were in progress at one time; and of course, finally, when a junction was made between any division, say of 1,000 ft. to another 1,000 ft., one small form was left in at this junction inside of the conduit, and had to be taken down and taken out the entire length of the conduit.

"The centers for a 16-ft. length of this conduit cost complete for labor and material, $18.30, but they were used over and over again; and, after this conduit was completed, they were taken away for use at other points, so that the cost is hardly appreciable, and the only charge to centers that we made after the first cost of building the centers, was on account of moving them daily. Part of this conduit was built double (two 6-ft. conduits) and part single, the only difference being that, where the double conduit was built, two forms were placed side by side, and not so much was undertaken in one day.

"These conduits, when completed and dried out, rung exactly like a 60-in. cast-iron pipe, when any one walked through them or stamped on the bottom."

Mr. Woollard gives the following analysis of the cost per cubic yard of the concrete-steel conduit above described:

Per cu. yd. 1.3 bbl. cement $1.43 10 cu. ft. sand 0.35 25 cu. ft. stone 1.10 26 sq. ft. expanded metal, at 3 cts. 0.78 Loading and hauling materials 2,000 ft. to the mixing board (team at $4.50) 0.50 Labor mixing, placing, and ramming 1.38 Labor moving forms 0.60 ——- Total $6.14

Wages were 17 cts. per hr. for laborers and 50 cts. per hr. for foremen. The concrete was 1-2-5, a barrel being assumed to be 3.8 cu. ft. The concrete was mixed by hand on platforms alongside the conduit. The cost of placing and ramming was high, on account of the expanded metal, the small space in which to tamp, and to the screeding cost. When forms were moved they were scraped and brushed with soft soap before being used again.

From Mr. Morris R. Sherrerd, Engineer and Superintendent, Department of Water, Newark, N. J., we have received the following data which differ slightly from those given by Mr. Woollard. The differences may be explained by the fact that the cost records were made at different times. Mr. Sherrerd states (Sept. 26, 1904,) that each batch contains 4 cu. ft. of cement, 8 cu. ft. of sand, and 20 cu. ft. of stone, making 22 cu. ft. of concrete in place. One bag of cement is assumed to hold 1 cu. ft. He adds that a 10-hour day's work for a gang is 63 lin. ft. of single 6-ft. conduit containing 47.4 cu. yds. of concrete and 1,260 sq. ft. of expanded metal. This is equivalent to cu. yd. of concrete per lin. ft. The total cost of material for one complete set of forms 64 ft. long was $160; and there were 7 of these sets required to keep two gangs of men busy, each gang building 63 lin. ft. of conduit a day. Since the total length of the conduit was 3,850 ft., the first cost of the material in the forms was 18 cts. per lin. ft.

Cost of Labor on 6-ft. Conduit:

Per day. Per cu. yd. 1 foreman on concrete $ 3.35 $0.07 1 water boy 0.75 0.01 11 men mixing at $1.75 19.25 0.39 5 men mixing at $1.50 7.50 0.16 4 men loading stone at $1.40 5.60 0.12 4 men wheeling stone at $1.40 5.60 0.12 2 men loading sand at $1.40 2.80 0.06 2 men wheeling sand at $1.40 2.80 0.06 1 man placing concrete at $1.75 1.75 0.04 6 men placing concrete at $1.50 9.00 0.19 2 men supplying water at $1.50 3.00 0.06 1 man placing expanded metal at $2. 2.00 0.04 1 man placing expanded metal at $1.50 1.50 0.03 ——— ——- Total labor on concrete $64.90 $1.35

Cost of Labor Moving Forms:

Per day. Per cu. yd. 4 carpenters placing forms $13.00 $0.27 2 helpers placing forms 4.00 0.08 1 carpenter putting up boards for outside forms 2.75 0.06 1 helper putting up boards for outside forms 2.25 0.05 2 helpers putting up boards for outside forms 3.50 0.07 1 team hauling timber 4.50 0.09 1 helper hauling lumber 1.75 0.04 ——— ——- Total labor moving $31.75 $0.66

It will be noted that it required two men to bend and place the 700 lbs., or 1,260 sq. ft., of expanded metal required for 63 lin. ft. of conduit per day, which is equivalent to c per lb., or 3 cts. per sq. ft., for the labor of shaping, placing and fastening the metal.

CIRCULAR SEWER, SOUTH BEND, INDIANA.—In building 2,464 ft. of 66-in. circular reinforced concrete sewer at South Bend, Ind., in 1906, the method of construction illustrated in Figs. 257, 258 and 259 was employed. The sewer has a 9-in. shell buttressed on the sides and is reinforced every 12 ins. by a 3/161-in. peripheral bar in the sides and roof and 3 ins. in from the soffit. Each bar is composed of three pieces, two side pieces from 15 ins. below to 6 ins. above springing lines and a connecting roof bar attached to the side bars by cotter pins. Two grades of concrete were used, a 1-3-6 bank gravel concrete for the invert and a 1-2-4 bank gravel concrete for the arch. The invert was given a -in. plaster coat of 1-1 mortar as high as the springing lines.



Forms and Concreting.—In constructing the sewer the trench was excavated so as to give a clearance of 1 ft. on each side and was sheeted as shown by Fig. 257. The sewer was built in 12 ft. sections as follows: The bottom of the trench was shaped as nearly as possible to the grade and shape of the base of the sewer. Four braces to each 12 ft. section were then nailed across the trench between the lowest rangers on the trench sheeting. A partial form consisting of a vertical row of lagging was set on each of the outside lines of the sewer barrel as shown by Fig. 257. Each section of this lagging was held by stakes driven into the trench bottom and nailed at their tops to the cross braces as shown by Fig. 258. A template for the invert was then suspended from the cross braces by pieces nailed to the four ribs of the template and to the cross braces as shown by Fig. 257. The concrete was now placed and carried to the top of the template, which was then removed. The side pieces of the reinforcing bars were then set and fastened as shown by Fig. 258. The side forms extending up to the springing lines were then placed. They were held in position by braces nailed to their ribs at the tops and by other braces fitting into notches in the ends of their ribs at the bottom. The concrete was then carried up to the springing lines, the arch centers in two pieces were placed; the arch bar of the reinforcement was placed and the extrados forms erected up to the 45 lines, all as shown by Fig. 259. The placing of the arch concrete completed the sewer barrel. The outside forms and bracing were removed about 24 hours after the completion of the arch and back filling the trench was begun immediately, but the inside forms were left in place for two weeks; they were then removed by the simple process of knocking out the notched braces. By building several lengths of invert first and following in succession by the side wall construction and then by the arch construction, the form erection and the concreting proceeded without interruption by each other. It was also found that, by making bends in the form of polygons with 10 ft. sides instead of in the form of curves, there was a material saving in expensive form work. To overcome the friction of the angles in such bends an additional fall was provided at these places. All concrete was made in a Smith mixer mounted on trucks so that it could be moved along the bank of the trench and discharging into a trough leading to the work.

Labor Force and Cost.—With a gang of 12 men from 24 to 36 ft. of sewer was built per 10-hour day, working only part of the time on actual concreting. The disposition of the force mixing and laying concrete and the wages were as follows:

Item. Per day. Six wheelers, at 18.5 cts. per hour $11.10 One mixer, at 22.5 cts. per hour 2.25 One dumper, at 18.5 cts. per hour 1.85 Four placers, at 22.5 cts. per hour 9.00 ——— Total $24.20

There were 0.594 cu. yd. of concrete per lineal foot of sewer and its cost is given as follows:

Item. Per cu. yd. Cost of gravel $0.774 Cost of sand 0.36 Cost of cement 1.50 Cost of steel reinforcement 0.84 Cost of labor, mixing and placing concrete 1.094 Cost of moving forms, templates, etc. 0.757 Cost of forms, templates, etc. 0.589 Cost of finishing, plastering, etc. 0.639 Cost of tools and general expenses 0.841 ——— Total $7.394

SEWER INVERT, HAVERHILL, MASS.—In constructing sewers with concrete inverts at Haverhill, Mass., in 1905, use was made of the traveling form or mold shown by Fig. 260. The form consists of an inner and an outer shell, the annular space between which forms the mold; in operation the annular space is filled with concrete, then the outer shell is pulled ahead from underneath, leaving the inner shell in place. A second inner shell is then adjusted to the outer shell in its new position, the annular mold is concreted and the outer shell again pulled ahead. Continued repetition of the operations described completes the invert. The merit of the device lies in the fact that the inner shell is not moved until the concrete has attained some degree of rigidity; when, in such devices, the inner mold is slid ahead on the green concrete it is likely so to "drag" forward the material that a rough and pitted surface results.

Mold Construction.—Referring to the drawings of Fig. 260, A is the outer mold of sheet steel bent to the required shape of the outer surface of the conduit to be constructed. A rib, or angle, B, is riveted to the inside of the mold at its front end and a diaphragm C of plank is securely fastened to the rear side of the rib. The opposite or rear end of the mold is open. Angles D forming tracks are riveted inside the mold a short distance below the edges and reaching their full length. The inner mold comprises a steel shell E curved to the form of the inside of the conduit; inside this steel shell is a reinforcing lagging, and at each end there is a wooden diaphragm F. Passing through both end diaphragms and having its ends flush with the end planes of the mold is a timber G. Rearward projecting lips e are secured to the lagging at the rear end of the mold and on each side of the timber G. The diaphragms F have each two arms f which project horizontally beyond the surface of the inner mold and engage the tracks D; locking dogs H are pivoted to the arms f so as to hook under the track angles D and hold the inner form from rising. Setting on the inner mold is an inverted V-shaped deflector I; its edges are flush with the sides of the mold and its purpose is to facilitate the placing of the concrete. There is also a movable diaphragm K, fitting loosely inside the outer mold A and bearing against the end of the inner mold E. The length of the inner mold E is about one-half that of the outer mold A; as a rule several inner molds are provided with one outer mold.



Mode of Operation.—In using the device described the outer mold A is first placed in the trench with its rear end at the end of the trench. An inner mold E is then suspended on the tracks of the outer mold and locked therein by the dogs H, with its rear end flush with the rear end of the outer mold. The partition K is then placed in position against the forward end of the inner mold and a jack J of any suitable form is interposed between diaphragms K and C, the jack being extended sufficiently to press diaphragm K firmly against the front end of the inner mold. The deflector I is next placed in position on the inner mold and the concrete is forced down with an iron rammer between the two molds, so as to fill completely the annular space. The deflector aids in directing the concrete into this space, as will be obvious. After the mold has been filled and the concrete compacted as much as possible, the jack is operated to separate the diaphragms K and C, and as the partition K is pressed against one end of the mass of concrete which has been laid, the opposite end of which abuts against the end of the trench, it follows that any backward movement of the diaphragm K will compress the concrete. This movement will be practically inappreciable in distance, but enough to compact thoroughly the concrete and fill any voids. The action of the jack will also push forward the diaphragm C and the outer mold A, the latter being withdrawn from beneath the inner mold and the newly laid concrete, the tracks D of the outer mold being drawn from beneath the arms f of the inner mold, leaving the latter behind resting on the freshly laid concrete. Further compression of the concrete after it has been left by the outer mold will fill the spaces between the inner mold and the surface of the trench. The outer mold is moved forward in this manner a distance equal to the length of the inner mold, and then the diaphragm K is drawn forward and another inner mold is lowered into the outer mold exactly as was the first one. The jack is then placed, the concrete deposited and the outer mold again advanced exactly as before. As the outer mold advances, the inner molds become disengaged one after another and are set ahead; in practice, enough inner molds are provided to enable the concrete to harden sufficiently to keep its position when it becomes necessary to take up successively the rearmost molds and place them ahead.

Haverhill Sewer Work.—The work at Haverhill, Mass., previously mentioned in which the form just described was used, was a 24-in. circular sewer with 6-in. walls. The outer form was 36 ins. in diameter and 6 ft. 2 ins. long; the inner form was 24 ins. in diameter and 3 ft. long. Angle B was 3 ins. and the track angles D were 1 ins.; diaphragm K was made of two thicknesses of 3-in. plank and diaphragm C of one thickness of 3-in. plank, the other diaphragms were of 2-in. plank. The shells of the molds were of -in. steel plate; the jack was an ordinary screw jack. Eight inner molds were used.

The form used at Haverhill was built by the city carpenter, the metal portions being made in a boiler shop. Its cost was not ascertained, but was, it is thought, about $75. The concrete used was a 1-3-5 stone mixture, with cement costing $2 per barrel, sand $1.50 per load of 36 cu. ft., and stone $2.50 per load of 36 cu. ft. The men were paid 25 cts. per hour. Records kept on 265 ft. of invert, or, theoretically, 19.3 cu. yds. of concrete, gave the following figures:

Per Per lin. ft. cu. yd. Labor, setting and moving forms, 42 hours, at 25 cts. $0.05 $0.67 Labor, mixing, placing and wheeling concrete, 179 hours, at 25 cts. 0.16 2.19 ——- ——- Total labor cost $0.21 $2.86

With the ordinary 1-3-5 mixture the cost of materials would run about as follows:

Per cu. yd. Cement, 0.96 bbl., at $2. $1.92 Sand, 0.47 cu. yd., at $1.13 0.53 Stone, 0.78 cu. yd., at $1.88 1.47 ——- Total cost materials $3.92

Two men were worked in the trench, one alternately ramming the concrete into place and working the jack, and the other shaping the trench ahead and assisting in bringing the rear forms ahead.

The form described was invented by Mr. Robert R. Evans, of Haverhill, Mass., and has been patented by him.

29-FT. SEWER, ST. LOUIS, MO.—The following account of the method and cost of constructing 162 ft. of very large sewer section at St. Louis, Mo., is compiled from information furnished by Mr. Curtis Hill.

The cross-section of the sewer is given by Fig. 261, which also shows the arrangement of the reinforcing bars. Johnson corrugated bars, old style, are used for reinforcement. The sections of the various reinforcing bars are: Longitudinal bars, 0.18 sq. in.; invert bars, 0.7 sq. in., and arch bars, 0.7 sq. in. The spacing of the bars and the arrangement of the splices are indicated on the drawings of Fig. 261. All splices have a lap of 36 ins. Some gravel concrete has been used in the invert, but most of the concrete has been crushed limestone and Mississippi River channel sand. The proportions were 1-3-6 in the invert and 1-2-5 in the arch. The arch was computed by Prof. Greene's method. The ultimate strength of concrete in compression was taken as 2,000 lbs. per sq. in. and the working strength at 500 lbs. per sq. in. The elastic limit of the reinforcing bars was taken at 50,000 lbs.



The trenching was done by wheel scrapers to the amount of waste. Then a cableway was erected spanning the entire length of the section and the remainder of the material taken out. The last 4 or 5 ft. in depth were in limestone and the excavated rock was taken by cableway to dump carts which took it to the crusher and returned with crushed rock to be used for concrete. This rock foundation was taken advantage of to reduce the amount of invert concrete.

In constructing the sewer proper the invert was first concreted to template to the height shown in Fig. 262. The arch forms were then placed as shown in Fig. 262, and the roof arch concreted. Both templates and arch forms were constructed of wood. The arch forms were moved ahead on iron rails and jacked into place. The ribs were 210-in. pieces and were spaced 4 ft. on centers; the lagging was 2-in. tongue and grooved stuff and was smeared with crude oil. The reinforcing bars shown in Fig. 261 were bent to proper radius by means of a wagon tire bender and were held in place by templates. The concrete was all mixed by two Chicago Improved Cube mixers operated by electric power.



The cost records of constructing the section of 29-ft. sewer so far built are not susceptible of complete analysis, but the following figures can be given. The prices of materials were as follows:

Cement, per barrel $1.80 Sand, per cubic yard 0.75 Broken stone, per cubic yard 1.00 Reinforcing bars, per pound 0.02 Vitrified brick, per 1,000 12.00

The wages paid different classes of labor were:

Per hour. Firemen $0.50 Laborers 0.175 Laborers 0.20 Laborers 0.25 Laborers 0.28 Laborers 0.3025 Bricklayers 0.66 2/3 Helpers $0.25 Carpenters 0.55 Engineers 0.50 Timekeepers 0.25 Watchmen 0.175 Hostlers 0.175 Teams 0.60

Taking up the several items of work in order, the excavation amounted to 21,400 cu. yds., of which 1,400 cu. yds. were rock excavation. The cost of excavation was as follows:

Total. Per cu. yd. Earth, excavation $7,640 $0.38 Earth bracing 2,000 0.10 Rock excavation 1,400 1.00 Rock, dynamite, tools, etc. 560 0.40

The cost of crushing the excavated rock and returning it to the mixer was $1 per cu. yd.

The cost of the concrete work was as follows:

Per cu. yd. 1.30 bbl. cement at $1.80 $2.34 .044 cu. yd. sand at 75 cts. 0.33 1 cu. yd. broken stone at $1 1.00 ——- Total concrete materials $3.67

There were 1,600 cu. yds. of concrete placed at a cost of for:

Total. Per cu. yd. Mixing and placing $1,180 $0.7375 Forms 2,000 1.25 Moving forms 400 0.25 ——— ———- Total for forms and labor $3,580 $2.2375

For reinforcing the concrete 86,600 lbs. of steel, or about 55 lbs. per cu. yd. were used. The cost of placing and bending this steel was as follows:

Total. Per lb. Cost of placing $172 0.1986 ct. Cost of bending 52 0.06 ct.

We can now summarize the cost of the concrete work proper of this sewer as follows:

Items. Per cu. yd. Cement, sand and stone $3.67 55 lbs. steel at 2 cts. 1.10 Forms, labor and materials 1.25 Mixing and placing concrete labor 0.74 Placing steel at 0.1986 ct. per lb. 0.11 Bending steel at 0.06 ct. per lb. 0.03 Moving forms 0.25 ——- Total labor and materials $7.15

To get the total cost of the sewer proper we must add the cost of the vitrified brick invert paving. There were 71 cu. yds. of this paving and its cost was as follows:

Per cu. yd. 0.6 bbls. cement at $1.80 $1.08 0.25 cu. yd. sand at 75 cts. 0.19 450 bricks at $12 per M. 5.40 Labor laying, 71 cu. yds. at $180.33 2.54 ——- Total $9.21

None of the preceding figures includes the plant charges. The plant cost $12,000 and the cost of running it during the work described was $2,000. In explanation it should be noted that the plant served for building some 1,340 lin. ft. of 27-ft. sewer as well as for the section described.

SEWER AT MIDDLESBOROUGH, KY.—In constructing an oval sewer 4 ft. high at Middlesborough, Ky., two steel forms in 10-ft. sections were used. As shown in Fig. 263, T-iron ribs were spaced 5 ft. apart, fastened together at the top by longitudinal angle irons, and at the bottom by a sheet of steel 22 ins. wide, forming the bottom of the invert. The lagging for the sides consists of movable 5-ft. lengths of channel iron, secured by sliding bolts. After the bottom of the trench has been roughly shaped with concrete, a 10-ft. section of invert forms is lowered and suspended by the cross-beams, and the space beneath packed with concrete; then a channel iron is slid into place and bolted, and concrete packed behind it, and so on until the invert is made. The next 10-ft. section is then built while the first is hardening. Upon the completion of the second section, the channel iron sides of the first section are removed, and then the rib framework is lifted out. Wood arch centers are then put in place and an inch of 1:2 plaster spread over the lagging before placing the concrete for the arch, which is 6 ins. thick.



The cost per 100 ft. of this sewer was as follows (prices being assumed for cement and labor):

Bottom concrete. Cost per 100 ft. 18.5 bbls. cement, at $1.50 $ 27.75 2.7 cu. yds. sand, at $1.00. 2.70 15 cu. yds. stone, at $1.00 15.00 17 days labor, at $1.50 25.50

Bottom concrete. Cost per 100 ft. 25.25 bbls. cement, at $1.50 37.85 7.5 cu. yds. sand, at $1.00 7.50 22 days labor, at $1.50 33.00

Sewer Arch. 26 bbls. cement, at $1.50 39.00 3.9 cu. yds. sand, at $1.00 3.90 13.6 cu. yds. stone, at $1.00 13.60 21 days labor, at $1.50 31.50 ———- Cost per 100 ft. $237.30



INTERCEPTING SEWERS, CLEVELAND, O.—An intercepting sewer some 3 miles long, of the form and construction shown in Fig. 264, was built at Cleveland, Ohio, in 1904. The construction consists of a plain concrete invert lined with two courses of shale bricks, and having two rows of anchor bars set in the side walls so that the bars of one row are staggered with respect to those of the other row. The anchor bars are 2-in. steel, and are spaced 30 ins. apart in each row. To the anchor bars are bolted arch reinforcing bars arranged as shown, and these arch bars have bolted to them eight lines of 1-in. longitudinal bars. A natural cement concrete is used for the invert and side walls. The arch is Portland cement concrete of normally a 1-3-7, 1-in. screened stone mixture, but where the voids in the broken stone exceeded 40 per cent., it is a 1-3-6 mixture. The invert bricks are laid in Portland cement mortar and the arch has a mortar lining and is waterproofed with 1-in. of mortar on top.

Forms.—Separate forms were used for the invert and for the arch ring. Regarding these, the engineer, Mr. Walter C. Parmley, remarks:

One of the first forms used in the sewer was like a piece of segmental arch centering inverted, and with the lagging nailed fast to the ribs. The trouble with this form is that it is difficult to tamp concrete under the bottom portion of the form, and hence a very rough surface is produced. Much better results were obtained by omitting the lagging boards on the bottom and at the sides till a point was reached where the inclination of the concrete surface was about 45. The concrete for the bottom could then be worked down between the ribs, thorough tamping done, and a good surface obtained. The ribs serve as a guide, so that the workman produces the proper shape. From this point up to the vertical, good results can be secured with the ribs attached to the lagging. Some contractors found it more convenient to use ribs that were connected with each other by a skeleton framework only, and then to slip the lagging in, one piece at a time. For some of the sewers, in which the brick lining was not carried quite up to the spring line, a separate side form of skeleton ribs and loose lagging was set upon brace legs bearing on the bottom of the invert. This form carried the concrete from about 2 ft. below to about 2 ft. above the springing line. The arch ribs then became segmental and rested upon the middle braces. This method has the advantage of using ribs that are lighter and more easily handled than those that are semi-circular. For arch centering, it is necessary and convenient to use independent ribs and loose lagging, for the centers can then be carried forward piece-meal, the falsework upholding the green arch and re-erected at the advance end of the work. In these matters each contractor prefers to use his own ingenuity, and so long as the work is properly built, the engineer can well give him considerable latitude as to use of methods. One thing, however, the engineer must insist upon—that all centering and falsework be as nearly rigid as possible. Even a slight settlement of the centers at the crown under the load of concrete and back-fill will cause the arch to kick out at the quarters, and if the green concrete arch is not cracked at the crown, it will be crushed on the inside, about half way between the crown and springing line. A reinforced arch is no more immune to this danger than is a plain concrete arch. However, with a few days of hardening, although the damage may be serious, the danger of actual collapse is less. A point to be guarded against, especially in reinforced construction, is any foolish act on the part of contractor or workman, due to his overconfidence in the strength of the structure because it contains embedded steel.

The mode of procedure in constructing the arch ring was to erect the centers with lagging complete. The lagging was then covered with building paper waterproofed with paraffine. The arch reinforcing bars were then bolted to the anchor bars and the longitudinals connected up. The lining of Portland cement mortar was first laid on the lagging. Before this mortar had set, concrete was rammed in between it and the sheeting to a height of 18 ins. above the springing line, and then the remainder of the concrete placed without outside forms. The top of the arch ring was finally finished with a 1-in. mortar coat. In regard to the concrete, Mr. Parmley remarks:

"Concrete will flush up to the forms and produce a better surface, and the voids in the stone will be much better filled if it is so wet as to require but little tamping; moreover there is less danger of obtaining a weak, porous wall should a workman neglect thorough tamping, than there is where only a moist mixture is used. It is also to the contractor's interest to use wet concrete for much less labor is required in mixing and placing it. Small broken stone or gravel is preferable in concrete for sewers. The walls being comparatively thin, unless there be a considerable excess of mortar, if coarse stones are used, the concrete will be honeycombed with voids. The stones should be well graded in size from large to fine, but the largest fragments should not exceed 1 ins. in greatest dimension."

Cost.—A number of records of cost of constructing short sections of the sewer described are given by Mr. Parmley, as follows:

Labor placing anchor bars. Per day. 1 man, at $3.50 $3.50 1 man, at $1.75 1.75 4 hours carrying steel at 20 cts. 0.80 ——- $6.05

The anchor bars were placed for 40 lin. ft. of sewer, or about 1,504 lbs. of metal at a cost of 0.4 ct. per lb.

The concreting gang for the sides consisted of:

5 men wheeling and mixing at $1.75 $8.75 1 man tamping 1.75 2/3 time man lowering brick and concrete at $2.25 1.50 1 man carrying concrete 1.75 ——— $13.75

This gang built the side wall for 40 ft. of sewer daily, or 13 cu. yds. Cost of labor per cu. yd. was, therefore, $1.06. The concrete was tamped behind the brick lining as the latter was built up by the mason.

Cost of single ring brick lining at sides:

2 masons at 70 cents per hour $1.20 1 man mixing mortar 2.25 1/3 time man lowering at $2.25 0.75 3 men wheeling sand, filling buckets and dumping 5.25 ——— Total labor for 40 lin. ft. of sewer $19.45 Quantity of brick masonry laid, cu. yd. 6.38 Labor per cu. yd. 3.05

An account was kept of labor performed on 85 lin. ft. of arch work, or 14 1-6 ft. daily. The force was as follows:

1 man putting mortar lining on centering $1.75 2 men mixing mortar, screening and wheeling sand 3.50 1 man tamping concrete 1.75 8 men on mixing board at $1.75 14.00 ——— $21.00 No. cu. yd. placed daily 25.64 Labor per cu. yd. 0.82 Placing centering and arch bars: 2 men at $1.75 $3.50 1 man at $3.50 3.50 ——- $7.00

Costs, for 14 1-6 ft. daily, $0.49 per lin. ft.

As nearly as could be judged, about two-thirds of the labor was used in erecting the centering and one-third in putting the steel in place. The amount of steel placed daily was 785 lbs., at cost, therefore, of 0.3 of a cent per lb., and the cost of erecting and moving centers, $0.33 per lin. ft. of arch.

Another record of 39.27 ft. on a curve, gave for the cost of the brick work at sides the same result as above, but the inspector's record of men working on concrete backing at sides showed a less cost, as follows:

4 men mixing at $1.75 $7.00 2/3 time man lowering at $2.25 1.50 1 man in bottom 1.75 ——- $10.25

They placed 12.7 cu. yd. at a cost of $0.81 per cu. yd. This figure probably more nearly represents the average cost than the $1.06 reported in the first instance.

The cost of placing the anchor bars on straight sewer, representing average progress, at another time, was found to be:

1 man $3.50 1 man 1.75 ——- $5.25

They placed the steel for 44 ft. of sewer or 1,650 lb. at a cost of 0.32 of a cent per lb.

Further notes for 6 days' work, when it seemed to represent as nearly as possible the general average for the whole were:

Labor on arch concrete:

Daily progress was 13 1-6 ft.

The force employed was: 7 men making concrete, at $1.75 $12.25 1 man plastering the center 1.75 1 man mixing mortar 2.00 1 man tamping 1.75 ——- $17.75

On straight arch work they placed 24.1 cu. yd. daily at a cost of $0.74 per cu. yd. In three days' work on a curve, the same gang placed 26.37 cu. yd. daily at a cost of $0.675 per cu. yd.

On centering and steel for arch, three men kept up with the regular progress of the arch-concreting gang. The cost, therefore, is:

1 man $3.50 2 men at $1.75 3.50 ——- $7.00

They averaged 13 ft. daily, or at a total cost of about $0.54 per lin. ft. of sewer.

Two-thirds of this labor was on the centering or $0.36 per lin. ft. of arch; $0.18 per lin. ft. placed the steel ready for embedding, or about 55.5 lb. per ft. of arch, at a cost of 0.32 of a cent per lb.

For the double ring brick lining at the bottom, the regular daily rate of progress was 28 ft. or 11.15 cu. yd. with:

2 bricklayers $11.20 5 men at $1.75 8.75 1 man at $2.25 2.25 ——- $22.20

or at a cost of $1.98 per cu. yd. This is given only because it is of interest in connection with the cost of the concrete.

Other observations on cost of placing steel skeleton and concrete did not vary materially from the figures given. It will be observed that no charge for superintendence or anything for the general expenses is included in the estimates of cost. These charges were, of course, impossible to obtain. On another contract with machine mixing, as high as 36 lin. ft. of 13 ft. 6 in. arch were built in a day, but no data as to cost were taken, though it was evidently less than for the work with hand-mixed concrete.

REINFORCED CONCRETE SEWER AT WILMINGTON, DEL.—Records of a notable job of sewer construction at Wilmington, Del., in 1903, are furnished by Mr. T. Chalkley Hatton. The sewer was built by day labor for the city; its cross-section at various points is shown by Fig. 265. The cross-section of sewers in trenches deep enough to cover the arch are marked "deep cutting"; the sections where the arch projects above the ground surface are marked "light cutting." The section through the marsh was 700 ft. long, the cutting being 8 ft. deep, and at high tide the marsh was flooded 1 to 4 ft. The material was a soft mud that would pull a tight rubber boot from a workman's foot. The cost of this marsh excavation including cofferdams, underdraining, pumping, etc., was $4.60 per cu. yd. For 1,100 ft. the 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 spaces 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.



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 shifting and watering blocks, and 1 foreman. With a little practice each molder could turn out 175 blocks a day; and since each block measured 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.



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.

The contract price was $3 per lin. ft. of this sewer, as against a bid of $3.40 per ft. for a brick sewer.

When the trenching had reached to the level of the top of the invert, two rows of stakes were driven in the bottom, stakes being 6 ft. apart in each row, and rows being a distance apart -in. greater than the outer diameter of the sewer. These stakes were driven to such a grade that the top of a 24-in. cap or "runner" set edgewise on top of them was at the proper grade of the top of the invert. The excavation for the invert was then begun, and finished to the proper curve by the aid of a templet drawn along the 24-in. runners. In gravel it was impossible to hold the true curve of the invert bottom. Concrete was then placed for the invert. To hold up the sides of the invert concrete, a board served as a support for the insides, but regular forms were more satisfactory in every respect except that they were in the way of the workmen. A form was tried, its length being 6 ft. It was built like the center for an arch, except that the sheeting was omitted on the lower part of the invert. It was suspended from the cross-pieces resting on the "runners." After the concrete had been rounded in place, the form was removed and the invert trued up. This form worked well in soil that could be excavated a number of feet ahead, so that the forms could be drawn ahead instead of having to be lifted out; but in soil, where the concreting must immediately follow the excavation for the invert, the form is in the way. The invert was trued up by drawing along the runners a semi-circular templet having a radius of 21 ins. Then a -in. coat of 1-2 mortar was roughly troweled on the green concrete. Another templet having a 21-in. radius was then drawn along the runners to finish the invert.

When the plaster had hardened, two courses of concrete blocks were laid on each shoulder of the invert, using a 1-2- mortar, the part being lime paste. The lime made the mortar more plastic and easier to trowel. Then the form for the arch was placed, and as each 8-ft. section of the arch was built, a grout of 1-1 mortar was poured over the top to fill the joints. Earth was thrown on each shoulder and tamped, and the center moved ahead.

Common laborers were used for all the invert work, except the plastering which was done by masons who were paid 30 cts. per hr. Masons were also used to lay the concrete blocks in the arch. Mr. Gifford states that two masons would lay at the rate of 100 lin. ft. of arch per day, if enough invert were prepared in advance. As there were 11 blocks in the ring of the arch, this rate would be equivalent to 7 cu. yds. of arch laid per mason per day.



COST OF BLOCK MANHOLES.—The following costs of constructing concrete block manholes for electric conduit at Rye, N. Y., were recorded by Mr. Hugh C. Baker, Jr. The arrangement of the blocks, their size and shape and the dimensions of the completed manholes are shown by Fig. 267. The blocks were molded of 1-2-5-in. broken stone concrete in 30 wooden molds made by a local carpenter at a cost of from $3.50 to $12 each. The concrete was placed in the molds very wet, with very little tamping, and was allowed to set for seven days before the blocks were moved to the work. The molds were left in place from 24 to 36 hours. With the facilities at hand six complete sets of top blocks were made each day by four men, when no wall blocks were being made, and half a set (15) wall blocks and two sets of top blocks were made each day by four men. The cost of the block manholes complete was as follows, per manhole:

30 wall blocks, 2 cu. yds. $21.00 6 cover blocks, 1 cu. yds. reinforced 4.27 I-beams for cover, in place 5.40 Supervision, freight, hauling 5.6 tons concrete 9.38 Labor placing cover, 3 hrs. at 15 cts. 0.45 Labor placing walls, 20 hrs. at 15 cts. 3.00 ——— Total, exclusive of iron cover $43.50

CEMENT PIPE, CONSTRUCTED IN PLACE.—In constructing 8-in. cement sewer for the Foster Armstrong Piano Co.'s works at Rochester, N. Y., a gang of seven men averaged 300 ft. of pipe per 10-hour day, using a Ransome pipe mold. The mold is shown by Fig. 268. It is made of sheet steel, with an inner core 10 ft. long, the front end of which is surrounded with a sheet steel shell that serves as an outer form for the pipe. The mortar mixed rather dry was packed into the annular space between core and shell by one man, using a short wooden rammer. A second man kept the mold slowly moving forward by operating the lever, which by means of a ratchet and drum winds up a wire rope stretched ahead to a deadman in the trench bottom. As the mold moves ahead it leaves behind it the cement pipe. A third man carefully filled under the invert and over the haunches of the green pipe with earth to give it support. The following was the itemized cost per day, 300 ft. of pipe laid:

6 men at $1.70 per 10-hour day $10.20 1 foreman 3.00 3 bbls. cement at $1.25 3.75 3.3 cu. yds. sand at 85 cts. 2.80 Water 0.15 ——— Total for 300 lin. ft. $19.90

This is equivalent to 6.63 cts. per lin. ft. of pipe.



In Trans. C. E., Vol. 31, 1894, p. 153, James D. Schuyler gives the cost of cement pipe made by the Ransome system for the Denver Water Works. There is a wrought iron shell of the size of the inner diameter of the pipe forming the inner mold. To this shell is attached a "leader" and "saddle" of larger diameter forming the outer mold. These molds are drawn slowly along the trench by a cable and horse whim, and the concrete is shoveled continuously into the core space between the molds and rammed on a long incline. The top half, or arch, of the pipe is supported by sheet iron plates (2 ft. wide), placed one after another on the forward end of the mold; and, being clamped together at the top and sides, remain in position after the mold is slid out from under them. After the mold has passed along, these iron plates are supported by upright sticks and by horizontal clamping rods. The plates are left in place for 24 to 48 hrs. The concrete, made 1-3, river sand and gravel, was machine mixed. A gang of 30 men mixed, wheeled, shoveled and tamped the concrete, attended to the plates, cleaning and greasing them, etc. This gang would make short runs at the rate of 900 lin. ft. of pipe a day, but counting stoppages, the average rate was 300 ft. a day. The inner diameter of the pipe was 38 ins., and its bottom was molded flat for a width of 18 ins. The concrete shell was 2 to 3 ins. thick. The pipe was washed with pure cement grout, applied with brushes after removing the iron plates. With cement at $3.75 per bbl., gravel at $1.25 per cu. yd., and labor at $1.75 to $2 per day, the cost of this pipe was $1.35 to $1.50 per ft., after the gang was well organized.

PIPE SEWER, ST. JOSEPH, MO.—In constructing extensions to 36-in., 42-in., 48-in. and 72-in. sewers at St. Joseph, Mo., reinforced concrete pipe of the form shown by Fig. 269 was employed. The thickness of shell for the various sizes was 4 ins., 4 ins., 5 ins., and 7 ins. All sizes were made in 3-ft. lengths, one end of which is rebated and beveled to form a spigot and the other end of which is chamfered on the inner edge to receive the bevel of the spigot. This jointing leaves a circumferential groove, into which the hooked ends of the longitudinal reinforcing bars project in such a way that a circular hoop can be threaded through them to connect successive lengths. The reinforcement is of the same form for all sizes of pipe, but seven longitudinals were used in the 72-in. size and five for all smaller sizes; the circumferential bars were in all cases spaced one 9 ins. from each end. The pipe, as described, is the standard pipe made by the Reinforced Concrete Pipe Co., of Jackson, Mich., and is covered by patents. The practice of this company is to manufacture the pipe itself on the ground and furnish it to the contractor. It does not contract to build sewers nor does it dispose of rights to manufacture to contractors.



Pipe Molding.—The pipe is molded endwise. A bottom plate so shaped as to form the hub or receiving end of the pipe is set up. On the upper or inner flange of this cast iron bottom plate is set the core defining the inside diameter of the pipe; this core is in four segments of sheet steel. The longitudinal reinforcing bars are next inserted in slots in the bottom plate and the outside form of sheet steel is then set up on the lower and outer flange of the bottom plate. Spacing clips on the top edge of the outer shell hold the tops of the reinforcing bars in position. The concrete is then shoveled into the annular mold and tamped until it reaches the level for the first circumferential reinforcing bar; this is then placed by removing the spacing clips, threading the hoop over the longitudinal bars and sliding it down to position. Filling and tamping then proceeds until the second hoop is to be placed; this is placed exactly like the first, and filling and tamping then proceeds until the mold is filled. At the St. Joseph work a 1-2-3 mixture, with crushed limestone aggregate ranging from pea size to 1-in. stone was used. The molding was done in tents which were heated by coke fires in salamanders in freezing weather.

Pipe Laying.—In laying, the pipes are handled and lowered into position just as are cast iron water pipe. Successive lengths are placed by inserting the spigot ends into the chamfered hub ends and then threading the tie hoop through the hooked ends of the projecting longitudinal reinforcing bars. A strip of galvanized iron is then passed under the pipe and bent up so as to girdle the circumferential groove except for a space at the top; the groove is then poured with a wet 1-2 cement mixture, which, when hardened, completes the joint.

COST OF MOLDING SMALL CEMENT PIPE.—Mr. Albert E. Wright gives the following account of the method and cost of molding and laying 6 to 12-in. cement pipe for irregular work at Irrigon, Ore.: The pipe was 6 to 12 ins. inside, made of Portland cement and clean, sharp sand of all sizes up to very coarse. The mortar was mixed rather dry, but very thoroughly, using 14.1 cu. ft. of sand to 1 bbl. of cement, or very closely a 1 to 4 mixture. From six to seven buckets of water were used to each barrel of cement, except for the 6-in. pipe, for which the mortar had to be made somewhat stiffer in order to remove the inner form, which was not made collapsible as in the larger sizes.

The forms were sheet iron cylinders with a longitudinal lap joint that could be expanded after molding the pipe, and removed without injuring the soft mortar. The inner form was self-centering, so that there was little variation in the thickness of the pipe.

Four men were required in making cement pipe by hand; one mixed the mortar, and wheeled it to the place of work; another threw it into the form a little at a time with a hand scoop; a third rammed it with a tamping iron, and a fourth kept the new pipe sprinkled, and applied a coat of neat cement slurry to the inside when it was sufficiently hard. In molding, the form of the bell at the bottom was secured by an iron ring that was first dropped into the form, and the reverse or convex form at the top was made with a second ring. While still in its form the pipe was rolled or lifted into its place in the drying yard, and the form was then carefully removed. A very slight blow in removing the form would destroy the pipe, and a considerable number, especially of the larger sizes, collapsed in this way, and had to be remolded. To avoid handling, the pipe was stacked on end a few feet from the place of mixing, the form being moved as the yard filled with pipe. One crew of four men could make about 250 joints or 500 lin. ft. of pipe a day.

As soon as hard enough, the pipe was turned end for end, and was then kept wet for several weeks before being laid. The coating of neat cement on the inside was applied with a short whitewash brush, and was a small item in the cost.

In laying, the trench was carefully finished to grade in order to have the joints close nicely, and the ends were well wet with a brush. The mason then spread mortar, mixed 1 to 2, on the end of the pipe, and laid a bed of mortar at the bottom of the joint. He then jammed the section into place, and swabbed out the inside of the joint with a stiff brush, to insure a smooth passage for the water. A band or ring of mortar was spread round the outside of the joint as an additional reinforcement. One barrel of cement would joint about 300 sections of pipe. The materials cost as follows: Portland cement, per bbl., $4.45; labor, per day, $2; foremen, per day. $2.50 to $3; hauling, per load mile (1 cu. yd.), 20 cts.; sand, free at pit; water, free.

The pipe was all of a 1-4 sand and cement mortar, and the amount of cement in one foot of pipe was arrived at by assuming that where the sand has voids in excess of the cement used, the mortar will occupy 1.1 (see Chapter II) times the space of the dry sand, which yields the following formula:

Where—

c = cost per bbl. of cement, or $4.45. n = cu. ft. in one bbl. (taken at 3.5 here). s = ratio of sand to cement, or 4. d = inside diameter in inches. t = thickness of pipe in inches. l = length of pipe considered, or 1 ft. here.

Then:

c l [pi] (dt + t) Cement-cost per foot = —————————————, n s 1.1 144

which gives here =

4.45 1 3.142(dt + t) ———————————————- = 0.00631(dt + t). 3.5 4 1.1 144

This gave the following cement costs per lineal foot:

Diameter, Thickness, Cost ins. ins. per foot. 6 1 $0.0571 8 1 0.0730 10 1-3/8 0.0998 12 1 0.1278

The sand cost was based on 15 cts. per cubic yard for loading, and a haul of two miles of 1 cu. yd. to the load, making five trips per day, at $4 for man and team. It bears a constant ratio to cement cost, being 11.2 per cent. of the cement cost. The labor cost of making was based on the foreman's estimate that a foreman, tamper, mortar mixer, and water man should finish 250 joints a day of 6 or 8-in. pipe. For the 10 and 12-in. pipe, the labor was assumed to be greater in proportion to the material. The foreman was taken at $3, one man at $2.50 and two at $2. The cement for painting the inside was neglected. Hauling the pipe to place was taken at twice the cost of hauling the sand per mile, and a haul of 4 miles was assumed. The cost of laying was based on a foreman's estimate of 2 cts. per foot for trench, and that one man to lay, one man to plaster the joints, one helper and one man to back-fill would lay 600 ft. per day of 6 or 8-in. pipe. The larger sizes were assumed to cost more in proportion to their material.

These various costs gave the following results for small size pipe:

—Cost per foot for— 6-in. 8-in. 10-in. 12-in. pipe. pipe. pipe. pipe.

Cement $0.057 $0.073 $0.099 $0.128 Sand 0.006 0.008 0.011 0.014 Labor 0.019 0.019 0.026 0.034 Hauling 0.024 0.032 0.044 0.056 Laying 0.024 0.024 0.032 0.042 Trench 0.020 0.020 0.020 0.020 ——— ——— ——— ——— Totals. $0.15 $0.176 $0.232 $0.294

The above costs show that the pipe in place costs about twice as much as pipe in the yard, even with cement at $4.45.



MOLDED PIPE WATER MAIN, SWANSEA, ENGLAND.—As a good example of foreign practice in molded pipe conduit work a water main constructed at Swansea, England, has been selected. This pipe line had to operate under a head of 185 ft.; it was constructed under the patents of the French engineer, Mr. R. Bordenave, who has built many miles of the same type of conduit on the Continent.

Fig. 270 shows the construction of the pipe, the drawing being a part longitudinal section through the shell at the joint. The pipe consists of an inner and an outer reinforcement separated by a sheet steel tube and all embedded in a 1-2 mortar. Both inner and outer reinforcements consists of longitudinal bins of cruciform (+) section wound by a spiral bar of the same section wired to them at every intersection. Only the outer reinforcement and the steel tube are considered in calculating the strength of the pipe, the inner reinforcement being considered as simply supporting the mortar.

Fabrication of Reinforcement.—The steel tube is made of 1 mm. (0.04 in.) thick sheets of steel bent to a cylinder and jointed longitudinally by welded butt joints, welded by a blow pipe using acetylene and oxygen. Tests of this welded joint by R. H. Wyrill, Waterworks Engineer, Swansea, showed it to be quite as strong as the unwelded steel cut from the shell. The circumferential joints of the tube were made by turning up the edges of the sheets and welding them; this gives a flexible watertight joint. The tube was made in lengths of 9 ft. 9 ins. and its ends were turned up all around; just back from the turned-up ends a vertical sheet steel collar was welded to the tube to form a strip end for the external coating. These details are shown in Fig. 270. When the tube for a length of pipe is completed the inside shell reinforcement previously made is slipped into it and the outside shell reinforcement is formed on it as a mandril, as shown by Fig. 271.



Molding.—When the three positions of the steel skeleton were completed, as shown by Fig. 271, they were set on curved wooden curbs made to the exact shape necessary to center them and preserve the correct thickness of cement coating. A collapsible core was lowered into position in the inside, and a two-part sheet steel mold was erected outside; the space between core and mold was then poured with a thin mortar of one part Portland cement to two parts clean river sand. During the process of pouring, the outer steel mold is sharply struck with wooden mallets to facilitate the escape of air bubbles. The mortar was mixed on an elevated traveling platform which is shown in Fig. 272, which also shows a completed pipe, a core being withdrawn, a filled mold and a section of reinforcement set up. The difficult feature of the molding process was found to be the determination of the time for withdrawing the core and removing the exterior mold; the time of setting of the mortar was different in warm and in cool weather and varied with the wetness of the mixture, the brand of cement, etc. By using a single brand of cement that ran very uniform in quality and time of setting it was possible, however, for the workmen, after a little practice, to gage very accurately the correct time for removing the molds. With four sets of molds a gang of eight men would curb 16 pipes per day under favorable conditions, but when the temperature was low it was not possible to make more than six or eight pipes. The pipes were allowed to stand four or five days after the removal of the mold; they could then be removed by a crane and laid in stock until used. It was found advisable to let the pipes age about four weeks before laying; by this time, it is stated, they would stand as much rough usage as cast iron pipe.

Laying.—The pipes were laid much in the same way as cast-iron pipes are laid; they were each 9 ft. 9 ins. long and weighed each about 12 cwt., and were handled by ordinary tackle. In laying, the pipes were adjusted end to end and the joint enclosed by a temporary steel ring inside which the bitumen seal, Fig. 270, was run and allowed to set when the steel ring was removed. The joint was then encircled by a collar of similar construction to the pipe itself and the space between collar and pipe was poured with cement mortar. About ten lengths of pipe were laid per day by one gang of men, one jointer and his assistant making all the cement and bitumen joints as fast as the gang could lay the pipes.



CHAPTER XXII.

METHODS AND COST OF CONSTRUCTING RESERVOIRS AND TANKS.

Floor, wall and roof work of structurally very simple character sum up the task of the constructor in reservoir and tank construction. The only intricacy involved lies in form design and construction for cylindrical tank work. Several examples of such work are given in this chapter, and in each the construction and handling of the forms are described. To repeat details here would serve no purpose, but one general instruction may be enunciated. No care is too great which ensures rigidity and invariable form, both in the construction of the individual form units and in the assembling of these units into the complete form. This is particularly true of cylindrical tank work and especially high cylindrical tank work where the forms are moved upward as the work progresses. To the designer it may be suggested that any beauty he may gain by giving the walls of his standpipe a batter is paid in the extra cost of form work.

Concreting in tank work is expensive. The reasons are two. The work has to be done in a narrow space, commonly pretty well filled with a network of steel rods or bars. Again the work has to be done uniformly well, not only for appearance sake but because of the necessity of watertightness. Making a reservoir watertight is, when all things are said, the one difficult constructional task in tank work and the contractor who accepts the task lightly courts trouble. Exceptionally good concreting is essential in tank work if watertightness is to be secured.

The illustration of these general admonitions will be found in the specific examples of tank and reservoir work which follow.

SMALL COVERED RESERVOIR.—The reservoir was designed to hold 75,000 gallons of water for fire purposes. As it is of a type which is certain to be frequently constructed and as we have personal knowledge of the costs recorded we describe the work in some detail. The specifications stipulated that the reservoir must be absolutely watertight and that the roof should be capable of sustaining a load of 300 tons evenly distributed and a live load of 5,000 lbs. on two wheels. Figure 273 shows a plan, Fig. 274 a longitudinal section, Fig. 275 a transverse section and Fig. 276 the column construction.



Quantities of Work.—The excavation called for the removal of 579 cu. yds. of earth. There were 83 cu. yds. of concrete in the structure, although the plans called for less, the additional amount being used in increasing the two 4-in. walls to 6-in. and increasing the bottom and top, on one end, so as to give perfect drainage. The yardage was divided as follows:

Cu. yds. Footings 3.5 Columns 6.8 Sides 22.6 Girders 11.0 Top 20.0 Floor 19.1 —— Total 83.0



A manhole had to be put in the top and a sump in the bottom. Several pipes also had to be placed in the concrete. None of these details is shown on the plan. The structure had to be waterproofed.

Excavation.—The excavation was made with pick and shovel and the material hauled away in carts, the distance to the dump being 700 ft. The top was shoveled directly into the carts, while the rest was handled two and three times. When the reservoir was finished dirt had to be filled in around the sides and puddled.

Wages.—The following rates of wages were paid on the job:

Foreman $3.00 Carpenter 3.50 Carts and driver 3.50 Laborers 1.50

The carpenters worked 8 hours a day and were paid time and a half for overtime. The rest worked ten hours per day and were paid regular rates for overtime.



Forms.—Carpenters framed and erected the forms, but laborers did all the carrying for them. Laborers also tore down the forms. For the girders and columns 2-in. boards were used, but for the sides 1-in. boards with 34-in. scantlings were used. The props for supporting the girder and top forms were 34. Except for columns and girders and some props, all the forming was used three times. The lumber cost:

400 ft. B. M. at $24 $ 9.60 8,000 ft. B. M. at $18 144.00 ———- Total $153.60



This makes an average price per 1,000 ft. of about $18.30, which price we shall use in giving costs.

The cost of framing and erecting the forms was $167.27 for the sides, columns, girders and top. In the forms for the sides, forming was only used on one side of the concrete for two sides, the earth bank being used for the other side of the forms, but on the other two sides the banks had caved in, and forming was used on both sides of the wall. The cost per cubic yard for forms was:

Lumber $2.54 Framing and erecting 2.77 Tearing down .54 ——- Total $5.85

This cost is for the yardage of 60.4 on which forms were actually used. For the total yardage in the tank the cost was:

Lumber $1.85 Framing and erecting 2.01 Tearing down .40 ——- Total $4.26

The common labor cost of assisting to erect the forms was 15 per cent of the total. Nothing is allowed for foreman, for the contractor acted as his own foreman.

The cost of forms per 1,000 ft. for the amount of lumber purchased was:

Lumber $18.30 Framing and erecting 19.90 Tearing down 4.00 ——— Total $42.20

As the lumber was used three times, the cost per thousand for all work and materials on the forms would be just one-third of this—namely: $14.06.

Since the framing, erecting and tearing down cost $19.90 plus $4, or $23.90 per M. ft. B. M. purchased, and since the lumber was used three times, the labor cost nearly $8 per M. each time that the lumber was used. It will be noted that 8,400 ft. B. M. were required for the 83 cu. yds. of concrete, or a trifle more than 100 ft. B. M. per cubic yard.

It will be of interest to see the labor costs of forms for the various parts of the structure.

For the sides the cost of framing and erecting the forms was $4.19 per cubic yard. Of this cost 4 per cent. was for common labor and the rest for carpenters. The tearing down cost 47 cts. per cubic yard. For the columns the erecting was $2.35, of which 1 per cent. was for common labor. The tearing down cost 47 cts. For the girders and top the erecting cost $1.83, of which 35 per cent. was common labor. The tearing down cost 61 cts. per cubic yard. A summary would show:

Girders Sides Columns and per per top per cu. yd. cu. yd. cu. yd. Framing and erecting $4.19 $2.35 $1.83 Tearing down .47 .47 .61 ——- ——- ——- Total $4.66 $2.82 $2.44

The greater cost of the columns forms over the girders and top was due to the fact that the columns forms were handled almost exclusively by the carpenters, and also in setting them great care and much time had to be used to get them plumb and in line. The cost of the forms for the sides was about twice as great as that for the top and girders. The reasons for this are evident. The walls had forms on both sides, while the top needed forming only underneath it, the area covered on the forms being about 2,200 sq. ft. as compared to 1,000 sq. ft. The side forms had to be set plumb and kept so. The framing was done ahead, but nearly half of the lumber in the sides was erected as the concrete was being put in place. The forms for the top were all put in place before any concreting was done on the top, and the carpenters discharged. A much larger per cent. of common labor could be used in placing forms for top and girders than on the sides. The props were nearly all put in place by laborers. The extra cost of tearing down the forms for the top was due to the fact that the lumber all had to be handled one piece at a time through a small manhole in the top, and carried about 150 ft. to be piled.

To all the costs for forming should be added 6 cts. per cubic yard for nails, wire and lines used on the forms.

Concrete.—The mixtures varied for the different members. The cost of materials was as follows:

Cement, 110 bbls. @ $1.12 $123.20 -in. stone, 80 cu. yds., @ $1.86 148.80 Gravel, 3 cu. yds., @ $1.33 4.00 Sand, 42 cu. yds., @ $1.20 50.40

The sides were first put in place, then the center columns were built, following which the bottom was placed. Then the forms were erected for the top and the girders, and these cast. In building the sides, one side and half of the two ends were built at one time, and then forms erected for the other half of the sides. For the sides the mixing was done in the bottom of the reservoir. For the rest of the structure it was done on the ground, the mixing board being along side of the reservoir. The labor cost of the concrete work for the various members and the average per cubic yard was as follows:

Columns and Sides. Footings. Bottom. Girders. Top. Average. Cubic yards 22.6 10.3 19.1 11 20.0 83. Preparing and cleaning up $0.166 $0.060 $0.095 $0.065 Handling materials 1.022 .306 $0.070 .198 $0.187 .404 Cleaning out forms .040 .070 .053 .032 Mixing and placing 1.542 .728 .353 .792 1.080 .952 Ramming 1.090 .540 .455 .450 .597 .673 Handling steel .890 .020 .395 .083 .324 ——— ——— ——— ——— ——— ——— Total $4.750 $1.654 $0.878 $2.000 $2.000 $2.450

The total cost of labor was $203.35. The mixing was done entirely by hand. Some plastering was done to the walls after the forms were taken off, and the sides and bottom were washed with a brush with cement and water. The plastering cost $6.60, including a barrel of cement and the washing or grouting, two coats, cost $9.10, including a barrel of cement. This added a cost of 19 cts. per cubic yard to the concrete work, making the total cost per cubic yard $2.65.

It was a mistake to have mixed the concrete for the sides in the bottom of the reservoir, as it made two handlings of the materials and compelled all the concrete to be raised by hand to place it in the forms. This accounts for the high cost of these two items.

The handling of the steel was high for the side walls, as it was all separated and put into piles for the different panels and members in getting it out of the pile for the sides. The rammers not only rammed the concrete but they also bent down the prongs of the steel to get them in place in the narrow forms, and afterwards had to pull out these prongs. This had to be done for every piece of steel used, and readily doubled the cost of ramming. The high cost of ramming the top was caused by the fact that the 6 ins. of concrete had to be placed in three layers and each rammed. The steel handling was high on account of the prongs entangling the pieces with others, making them hard to handle. The cost of handling steel per ton was about $4, or 0.2 ct. per pound. The steel was all handled by common laborers.

The stock piles of material had to be made along a street and alley and thus caused the material to be handled in wheelbarrow several hundred feet.

The preparing to mix concrete, the cleaning up afterwards and the cleaning out of forms are items that are seldom kept separate from the others.

The cost of mixing and placing is high, owing to the fact that working space was small and the mixers had to wait until the concrete was taken off the board and placed in the forms before starting another batch. This also meant an increased cost in the ramming, as the rammers were idle some time waiting for a new batch to be mixed.

The total cost of concrete, including labor and materials, per cubic yard on a basis of the 83 cu. yds. was:

Per cu. yd.

Cement, 1-1/3 bbls., @ $1.12 $ 1.49 Stone, 1 cu. yd. 1.86 Sand cu. yd. .60 Steel 4.76 Forms, 100 ft. B. M., @ $18.30 1.85 Labor on forms 2.41 Labor on concrete and steel 2.65 ——— Total $15.62

The cost of a foreman is not included in this, as the contractor looked after the men himself.

Waterproofing.—The waterproofing of the structure proved a serious problem. It was thought at first that the concrete itself would be nearly water tight, but the tank leaked like a sieve. After considering several methods, an agent of a European waterproofing mixture prevailed upon those interested to try his compound. To apply it, the walls had to be dry, so a large coal burning stove was put in the reservoir and a fire kept up day and night. While this drying process was going on several light falls of snow occurred, and this had to be cleared away to make the walls and roof dry. Two coats of the mixture were applied according to the agent's instructions, and the reservoir was tested. The water fell nearly half a foot in an hour's time.

Then a waterproofing contractor agreed to make the reservoir water tight with paper and tar, by applying it on the inside. Three thicknesses of paper were laid on the bottom and run well up on the sides, each layer of paper being well covered with a preparation of tar. Upon testing it, it was found that the leaking had been reduced about 50 per cent. A preparation of asphalt was then placed over this, but upon a third test the tank still leaked. As the sub-contractor had verbally agreed to make it water tight for $125, only this amount was paid him. After this last test he refused to do any more work.

After these attempts the sides of the reservoir were exposed on the outside by excavating around it, and a one-brick-wall built up a few inches from the concrete. This space was filled in with rich cement mortar and the ground once more filled in around the structure. This work and the materials used in it cost $1,240. Upon a fourth test the reservoir was found to be water tight. Thus more than a third of the cost of the entire work was in waterproofing the structure, and this made the contract a money losing one, as this heavy cost was not anticipated.

Several items of miscellaneous work are listed in the total cost of the reservoir, such as filling in and puddling around reservoir and replacing cobble paving. The top of the structure was used as a bin for the storage of coal. For this purpose eight I-beams were embedded in concrete around the top to be used as posts for the sides of the bin. The cost of placing these is given.

Total Cost.—The cost of the structure without any profits was:

579 cu. yds. excavation @ $.896 $ 529.65 Steel 395.00 Crushed stone 148.80 Gravel 4.00 Sand 50.40 Cement 123.20 Lumber 153.60 Labor on forms 200.09 Labor on concrete 203.35 Plastering 6.60 Sides and bottom 9.10 Nails, wire, etc. 4.98 Bailing water 21.19 Building temporary fence 1.65 Extra excavation for forms, footings, etc. 13.90 Setting I-beams in concrete 17.65 Filling in and pudding around reservoir 34.47 Replacing cobble paving 4.30 Hauling tools 3.60 Heating reservoir and handling snow 14.50 Waterproof mixture 29.00 Labor applying it 9.74 Applying paper and tar, labor and materials 125.00 Labor and materials of final waterproofing 1,240.00 Tools 48.75 General expense 210.00 ————- Total $3,602.52

COVERED RESERVOIR, AT FORT MEADE, SOUTH DAKOTA.—The following account of the method and cost of constructing a 500,000-gallon reservoir is compiled from information furnished by Mr. Samuel H. Lea, M. Am. Soc. C. E. As shown by Fig. 277, the reservoir consists of two equal compartments, each 5060 ft. inside dimensions, with rounded corners. Both compartments are covered with a 3-in. slab roof carried on the walls and interior columns.

The concrete was a 1-2-4 Portland cement, sand and broken stone mixture, mixed by hand on a movable platform. A concrete gang consisted of four men who were each paid $2.75 per day. They wheeled the materials from the supply piles to the mixing platform, mixed the concrete and deposited it in place. During the construction of the footings and floor two concrete gangs were employed, but after the walls were started, one gang only was required for concrete work; the other gang was then put to work assisting the carpenters.



The sand and stone were wheeled to the platform in iron wheelbarrows of 2 cu. ft. capacity. The cement was in -bbl. sacks and each sack was taken as 1 cu. ft. Each batch of concrete contained the following quantity of material:

2 sacks of cement 2 cu. ft. 2 wheelbarrows of sand 5 cu. ft. 4 wheelbarrows of stone 10 cu. ft.

The quantities of sand and stone were adjusted so as to form the proper proportion for making a dense concrete. From time to time, as the work progressed, experiments were made to determine the percentage of voids both in the sand and the crushed stone; and, in this way, uniformity in composition was secured. The mixture was made quite wet in order to insure a free flow around the reinforcing bars. On account of the narrow space inside the forms and the number of reinforcing bars therein care was taken to cause the mixture to be well distributed throughout. The wet concrete was well spaded in an effort to secure a smooth surface next to the forms. This was generally accomplished, but some rough places which showed after the removal of the forms required patching up.

In constructing the footings some concrete was first deposited in place and the metal reinforcement was embedded therein. For the floor reinforcement the lower bars were carefully embedded in the concrete after it had been brought to a suitable height; the upper bars were then placed crosswise upon the lower ones and kept in position until the remainder of the concrete had been deposited around and over them. In the wall footings a depression or groove, several inches deep, was left under the wall space for its entire length. This ensured a good bond between the wall proper and the footing.

The concrete floor in each compartment was built in one continuous operation, the object being to secure a practically monolithic construction. The lower reinforcing bars in the floor were embedded at the proper depth in the fresh concrete and the upper bars were then placed crosswise upon the lower ones; the two sets were then wired together at a sufficient number of places to prevent displacement while the remaining concrete was being deposited around and over them.

The reinforcement for the walls and columns was erected in place upon the footings and formed a steel skeleton around which the forms were erected. The upright bars in the walls were held together and at the proper distance apart by means of templates consisting of wooden strips in which holes were bored at suitable intervals to receive the bars. The templates were maintained in a horizontal position and were moved upward as the concrete advanced in height. The horizontal reinforcing bars were wired in place to the upright bars; they were placed in position ahead of the concreting as the wall was built up.

The corrugated bars in beam and girders were placed in position in the forms and held up by blocks which were removed as the forms were filled with concrete. The expanded metal reinforcement for the roof slab was placed so as to be close to the lower face of the slab, but far enough up to be entirely enveloped in the concrete.

The wall forms were made of 2-in. planks, surfaced on the inner side and placed horizontally on edge. They were held in place by 44-in. posts spaced at intervals of about 4 ft., in pairs on opposite sides of the wall. The posts were firmly braced on the outside; they were prevented from spreading by connecting wires passing through the wall space between the edges of adjacent planks. At the rounded corners of the reservoir the pairs of posts were spaced about two feet apart and the curve was made by springing thin boards into place to fit the curve and nailing them to the posts. The posts were high enough to reach to the top of the wall; the siding was built up one plank at a time as the concrete work progressed. Column forms were made of 2-in. planks on end, extending from floor to girder. Three sides were enclosed and one side was left open to receive the concrete; this side was closed up as the concreting advanced in height.

The beam and girder forms were open troughs of the required dimensions, made of 2-in. plank, surfaced on inner faces. The form of centering for the roof slab consisted of a smooth, tight floor of 2-in. planks, extending between the open tops of column, beam and girder forms over the entire area between enclosing walls of the reservoir. The centering and the beam and girder forms were supported by 66-in. posts resting upon the floor below.

The regular carpenter gang consisted of a foreman carpenter at $5 per day, a carpenter at $3.50 per day, and two helpers at $2.75 per day. During the early concrete work of making footings and floor, where forms were not required, the carpenter force was employed in erecting the steel skeleton for the walls. The upright bars were placed in position and secured by temporary wooden stays extending from the upper portion of bars to the surface of ground outside of excavation. These stays were removed after concreting had advanced to a sufficient height to hold the steel securely in place.

The wages paid the concrete gang which mixed and placed all the concrete and the carpenter gang which constructed and erected the forms and placed the reinforcement have been given above. The costs of construction materials on the site were:

Cement, per barrel $2.57 Sand, per cu. yd. 1.80 Stone, per cu. yd. 3.15 Lumber, per M. ft. B. M. 27.50

The quantities in the completed concrete structure were as follows:

Total volume of concrete in reservoir 704.71 cu. yds. Total volume of steel reinforcement in reservoir. 5.57 cu. yds. ——— Total volume of material in completed structure. 710.28 cu. yds.

The steel was, therefore, about 0.8%.

Volume of material in structure exclusive of roof slab 648.35 cu. yds. Volume of material in roof slab 61.93 cu. yds. ——— Total 710.28 cu. yds.

The cost of the structure per cubic yard of concrete, exclusive of the roof slab, was as follows:

Item. Per cu. yd. Crushed stone $ 3.168 Sand .842 Cement 3.859 Reinforcement 4.959 Labor, mixing and placing concrete 1.721 Forms, labor and material 2.960 ———- Total $17.509

In constructing the roof slab the expanded metal reinforcement raised the unit cost. For this portion of the work the costs were:

Item. Per cu. yd. Expanded metal reinforcement $ 5.241 Other items, same as above 12.550 ———- Total $17.791

The floor and the inside surface of reservoir walls were covered with a coating of cement mortar composed of one part Portland cement and one part sand. The wall plastering was from in. to in. thick; it was applied in two coats. The floor finish was laid in alternate strips about 1 in. thick and 3 ft. wide. After the strips first laid had hardened the remaining strips were laid, the edges being grouted to ensure tight joints.

The outside of walls and roof was covered with a coating of tar which was heated in an open kettle to a temperature of about 360 F. and then applied with a brush or mop.

The cost of wall and floor plastering was 44.4 cts. per square yard, itemized as follows:

Cement 26.4 cts. Sand 2.6 cts. Labor 15.4 cts. ——- Total 44.4 cts.

The cost of outside waterproofing was 4 cts. per square yard, distributed as follows:

Material 2.5 cts. Labor 1.5 cts —- Total 4.0 cts.

While some of the cost items are apparently high when compared with the cost of similar work in other places, it should be remembered that the isolated locality and the local conditions were unfavorable for low cost. Owing to the isolated location of the reservoir with respect to large markets and also to local sources of supply the cost of material and labor was quite high. All construction material, except some of the stone for crushing, had to be hauled over a mountain road from 3 to 4 miles to the top of the hill selected for the reservoir site. Labor was scarce and commanded a wage of $2.50 per day for ordinary work; the laborers mixing concrete were paid $2.75 per day. Another source of much relative expense was the high cost of lumber and carpenter work on the forms. On account of the thinness of the walls and roof, the cost of lumber and labor required per cubic yard of concrete was considerable. A part of the lumber was used the second time in forms, but it was found impracticable to delay the work by waiting for the concrete to harden before beginning the new portions of the walls. This lumber was sold after the completion of the work, but the salvage was inconsiderable, amounting to less than 10 per cent. of the original cost.

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