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.
Fig. 273.—Sectional Plan of 75,000-Gallon Reservoir.
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 |
Fig. 274.—Longitudinal Section of 75,000-Gallon Reservoir.
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.
Fig. 275.—Transverse Section of 75,000-Gallon Reservoir.
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 3×4-in. scantlings were used. The props for supporting the girder and top forms were 3×4. Except for columns and girders and some props, all the forming was used three times. The lumber cost:
Fig. 276.—Column Construction for 75,000-Gallon Reservoir.
| 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:
| Sides per cu. yd. | Columns per cu. yd. | Girders and top per 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 |
| ¾-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:
| Sides. | Columns and 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, 1⅓ bbls., @ $1.12 | $ 1.49 |
| Stone, 1 cu. yd. | 1.86 |
| Sand ½ 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 50×60 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.
Fig. 277.—Reservoir at Ft. Meade, S. D.
The sand and stone were wheeled to the platform in iron wheelbarrows of 2½ cu. ft. capacity. The cement was in ¼-bbl. sacks and each sack was taken as 1 cu. ft. Each batch of concrete contained the following quantity of material:
| 2½ sacks of cement | 2½ 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 4×4-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 6×6-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 ½ in. to ¾ 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 360º 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.
Fig. 278.—Reservoir Forms. Bloomington, Ill.
CIRCULAR RESERVOIR, BLOOMINGTON, ILL.—An open circular reinforced concrete reservoir was constructed in 1905-6 for the water-works of Bloomington, Ill. This reservoir is 300 ft. in diameter, 15 ft. deep at the circular wall and 25 ft. deep at the center of the spherical bottom. The wall construction is shown clearly by Fig. 278, and the floor is a 6-in. spherical slab reinforced by a mat of ¼-in. round rods placed 6 ins. on centers in both directions. The wall reinforcement is corrugated bars. Neither the wall nor the bottom has expansion joints.
Concrete.—The specifications required not less than 1 part Portland cement to 2 parts sand and 5 parts clean gravel, and stipulated that there should always be more than enough cement to fill the voids in the sand more than enough mortar to fill the voids in the gravel. The proportions were varied, depending on the character of the available material and on the location the concrete was to occupy. The stipulations regarding the minimum quantities of cement and mortar were, however, always at least fulfilled. A 1-3-4 mixture of cement, broken stone and gravel was largely used in the footing and wall. The gravel was fine and contained 40 to 50% of sand; the broken stone was the crusher-run, with the dust screened out, and the maximum-sized pieces not larger than those which would pass a 2-in. screen. The mortar facing on the front face of the wall was made of 1 part cement to 4 parts fine gravel, containing sand. Some gravel from the excavation was used in the concrete for the floor. This gravel was so fine that about one-quarter of it was replaced with broken stone and the mixture made 1-6. Both faces of the wall were painted with a 1-1 mixture of cement and sand; the inner face was also painted with a 1-1 mixture of waterproof Star Stettin Portland cement and sand. The sidewalk finish on the surface of the floor consisted of 1-1½ mortar.
Mixing and Handling.—The concrete mixing plant was set up outside of the site of the reservoir along a side track from the railroad. The concrete materials were delivered on the side track, except some gravel from the excavation that was used. A Foote portable continuous mixer was used in making the concrete for the wall footings and the wall. It was mounted so it could discharge into dump cars on a service track laid on the ground. A double hopper was built up over the mixer, one compartment for sand and one for broken stone. The end of a service track leading from the side track was laid on an inclined trestle up to a floor level with the top of this double hopper, the materials being hauled in dump cars from the side track to the hopper. The service track from the mixer extended entirely around the wall, and 10 ft. from it, on the embankment made there with earth from the trench for the wall-footing. The concrete was dumped from the cars on the service track to portable shoveling platforms near the point where work on the wall was in progress. It was shoveled by hand from these platforms to place in the forms as the presence of the reinforcement bars in the narrow forms precluded dumping in large quantities. The footing was built without forms up to the right-angle joint between it and the base of the wall at the front, and to the top of the 45° slope on its rear face. A layer of concrete 2.5 in. thick was first placed in the completed trench. The reinforcement bars near the bottom were then laid on this green concrete, the vertical bars near the front face of the wall usually being erected at the same time. The concrete in the toe of the footing and in the footing proper up to the top layer of reinforcement was then laid. After the top layer of reinforcing bars had been laid, the footing was completed, except for a top layer about 2 ins. thick at the base of the front face of the wall and 15 ins. thick at the toe of the footing. This left a strip of surface about 6 ft. wide, sloping at about 1 in 6 from the wall toward the center of the reservoir, and furnished the widest and best possible bond for the joint which had to be made when floor was laid.
Location and Construction of Forms and Wall.—The design of the wall of the reservoir, although simple in itself, required unusually accurate work in the location and construction of the forms for it. The location was made with very little difficulty, however, by an arrangement devised by the contractor which enabled the foreman, without the aid of an engineer, to set the necessary grade and reference stakes. A post, 10 ins. in diameter, was set very accurately and firmly in the ground at the center of the reservoir. This post was sawed off squarely on top so that the line of collimation of an engineer's transit set on it without a tripod would be exactly at the grade of the top of the completed wall of the reservoir. A 200-ft. steel tape was used to measure the radial distance from a nail in the center post to the posts of the back, or outside forms for the wall. In the form for the back face of the wall 2×6-in. posts, spaced one one-hundredth of the circumference apart, were set considerably in advance of any concrete work, and were made the basis of all measurement in building the forms. The forms as originally planned are shown in Fig. 278.
The wall, when started, was built continuously in both directions from the starting point. The back forms consisted of planks for lagging nailed to vertical posts, which were accurately set and firmly braced. The front forms were made in lengths equal to one one-hundredth of the circumference of the reservoir, and when set up were fastened to the back forms. Twenty-one of these front form sections were built and all set up at once. Concrete was filled in between the front and back forms, starting at the central form, and was rammed in inclined layers, sloping, at about 1 on 6, both ways towards the end forms. This method was adopted in order that the concrete might be laid continuously and without joints. The lagging of 1-in. boards on the vertical portion of the sections was nailed to the vertical posts, and was carried up just ahead of the concrete filling.
When the concrete had reached the top of the central one of the 21 sections of the forms, and the concrete in that section had set sufficiently, the section was broken up and removed, leaving two sets of 10 sections of the forms. Subsequently the other forms could be removed in turn as desired without being broken up. As the filling-in proceeded between the two sets of 10 forms each, the form in each set nearest the starting point was removed, carried forward, and put in place at the other end of its set of forms. Twelve men were required to take down and transport one of the front form sections.
In setting up a front form, its inner toe was firmly supported by a stake driven into the ground and by the horizontal board, nailed transversely under the bottom 4×4-in. horizontal stringers, which rested on the ground. The upper part of the form was then securely fastened to the 2×6-in. posts of the back forms by temporary wooden connecting strips, which were removed as the concrete filling was carried up. The sections of the front forms were also securely tied to each other.
A facing of gravel concrete, rich in cement and with no pebbles larger than ½-in. was placed on the front face of the wall, extending from the back edges of the vertical reinforcing bars to the surface. A sheet-iron plate, about 8 ins. wide by 5 ft. long, was placed vertically just back of those bars. The concrete was shoveled in loose to the top of these iron plates, and then the mortar was poured in between the latter and the front face forms from buckets. The iron plates were next drawn by handles attached to them, and the mortar and concrete tamped together before either had set. In making joints, the old concrete surfaces were always brushed and wet down, and, if necessary slushed with a grout of neat cement before new concrete was laid on them.
Construction of Floor.—The excavation over the site of the reservoir floor was brought accurately to grade 6 ins. below the surface of the finished concrete by hand after the scoop-bucket excavator had passed over. In making the excavation the levels were given on radial lines drawn from the ends of the 10-ft. sections of the wall to the center. A rod, on which the elevations of the sub-grade at every 10 ft. from the wall to the center of the reservoir were clearly marked, was used in connection with a transit on the center post in locating the elevations of different points in the reservoir floor. By using this method the elevations required were easily found by the foreman in charge without the assistance of an engineer. When the work approached the center, the post was removed and the transit was placed on a portable pedestal which was set on points of known elevation on the finished concrete.
The slanting surface left on the top of the footing inside the wall formed, together with the projecting reinforcement rods, an excellent bond between the concrete of the wall and that of the floor, when the latter was laid. A circular strip of the floor, 16 ft. wide, was put down next to the wall first, and the remainder of the floor was laid according to the progress of the excavation. The lower 3½ ins, of the concrete was usually first spread out over an area 12 or 16 ft. square, then the reinforcement was placed, and after that the top 2 ins. of concrete and a ½-in. sidewalk finish surface were laid.
Fig. 279.—Standpipe at Haverhill, Mass.
The ¼-in. rods in the bottom are 6-ins. on centers in both directions. They were in 12 and 16-ft. lengths and were partly woven together in mats before being placed. The rods in one direction were all laid out and woven with four or five of those in the other direction, the joints being tied with small wire. The remaining cross rods were laid after the mat had been placed. The mats were overlapped 1 ft. This method of placing proved economical and efficient, giving at the same time something permanent on which to lay the remaining concrete.
STANDPIPE AT ATTLEBOROUGH, MASS.—The stand pipe was 50 ft. in diameter and 106 ft. high inside, with walls 18 ins. thick at the bottom and 8 ins. thick at the top. Figure 279 shows the general arrangement of the reinforcement. Round bars of 0.4 carbon steel were used; the bars came in 56½-ft. lengths, so that three lengths with laps of 30 ins., made a complete ring around the tank. The concrete was a 1-2-4 mixture of ¼ to 1½-in. broken stone with screenings used as portion of sand.
The floor was built first, and on it was erected a tower to a height of 60 ft. and a derrick with a 40-ft. boom was set on its top. The derrick was operated by an engine on the ground which also had a revolving gear attached. When the work had reached the top of this tower, the tower was raised to 110 ft. in height and the derrick shifted to the new elevation. The forms were convex and concave sections 7½ ft. high and about 11 ft. long. The concave or outside forms were made in 16 panels, with horizontal ribs and vertical lagging; two complete rings of panels were used. The panels were joined into a ring by clamps across the joints, this clamping action and the friction of the concrete holding them in place. The inside forms consisted of vertical ribs carrying horizontal lagging put in place a piece at a time as the filling proceeded. They were supported by staging from the derrick tower. The remaining plant comprised a Sturtevant roll jaw crusher feeding to screens which discharged fines below ¼-in. into one bin, medium stone into another bin and coarse stone into a third bin. These bins fed to the measuring hopper of a Smith mixer, which discharged into the derrick bucket.
The mode of procedure was as follows: The reinforcing rings were erected to a height of 7½ ft. The bars were bent by being pulled through a tire binder and around a curved templet by a steam engine. The bending gave some trouble, due, it was thought, to the stiffness of the high carbon steel. Vertical channels 4 ins. deep were set with webs in radial planes or across wall at four points in the circumference. The flanges of these channels were punched exactly to the vertical spacing of the reinforcing rings. Through the punched holes were passed short bars on the opposite ends of which the reinforcing rings were supported and wired. The three sections of rod of which each ring was composed, were lapped 30 ins. and connected by Crosby clips. Considerable difficulty was had in holding the reinforcing rings in line by the method employed; it is stated by the engineer that a greater number than four channels would have been much better.
The reinforcement being in place, an inside and an outside ring of forms was erected. Concreting was then carried on simultaneously from four points on the circumference and a ring 7½ ft. high was concreted in one operation. Several facts were brought out in the concreting; careful and conscientious spading was necessary to get a smooth dense surface; a too wet mixture allowed the stone to settle and segregate; care was necessary in this thin wall containing two rings of bars to keep the stone from wedging among and around the bars and thus causing voids. The engineer states that for this reason the substitution of mortar for concrete in tank walls is worth considering. He estimates that in this work, costing $35,000, that the use of a 1-2 mortar in place of the 1-2-4 concrete would have increased the cost by $2,300, a 1-2½ mortar by $1,500, and a 1-3 mortar by $750. It was also found that there was danger from a movement of the reinforcement in the concrete and of the forms in placing the concrete.
When a ring of wall 7½ ft. high had been concreted, the reinforcement was placed as before described for another ring. The two rings of forms below those just filled were removed from the wall, hoisted up and set in place on top. These two operations of placing reinforcement and setting forms for another ring of wall took three days, so that the top surface of the wall to which new concrete was to be added, had become hard. This hard surface was very thoroughly washed and then coated with neat cement immediately before depositing the fresh concrete. Water was admitted to the tank as the work progressed, being kept about 20 ft. below the work in progress. Numerous small leaks developed, but only two were large enough for the water to squirt beyond the face of the wall. These leaks appeared to grow smaller as time went on. To do away with them entirely, the inside wall was plastered. The first coat of plaster was not successful in stopping the leaks, so the standpipe was emptied and replastered, five coats being used in the lower 20 ft. This did not serve so resort was had to a Sylvester wash. A boiling hot solution of 12 ozs. to the gallon of water of pure olive oil castile soap was applied to the dry wall. In 24 hours this was followed with a 2 ozs. to the gallon solution of alum applied at normal temperature. Four coats of each solution were applied, which reduced the leakage to a small amount. To do away with all leakage another four-coat application of Sylvester wash was used.
Details of the cost of the work are not available. There were 770 cu. yds. of concrete in the walls and 185 tons of steel bars. Altogether 3,000 Crosby clips, costing $1,100 were used. The cost of the concrete in place was about as follows:
| Cement, per cu. yd. of concrete | $ 4.80 |
| Sand and stone, per cu. yd. of concrete | 3.90 |
| Mixing, per cu. yd. of concrete | 0.40 |
| Placing, per cu. yd. of concrete | 2.20 |
| Forms, per cu. yd. of concrete | 2.65 |
| ——— | |
| Total per cu. yd. of concrete | $13.95 |
GAS HOLDER TANK, DES MOINES, IOWA.—The tank was 84 ft. in diameter and 21 ft. 5 ins. deep. It had a horizontal floor 16 ins. thick 5 ft. below ground level and a wall 21 ft. high, 18 ins. thick at base and 12 ins. thick at top under coping and with alternate pilasters and piers around the outside. The concrete for the floor was a 1-2½-5 2-in. stone mixture and the concrete for the walls was a 1-2-4 1-in. stone mixture. The floor was constructed first, with a circular channel for the wall footing, and then the wall was constructed.
Piles were driven in the bottom and their heads cut to level and filled around with tamped cinders. Two circumferential rows of posts were driven around the edge so that a pair of posts, one inner and one outer, came on each radius through a wall pilaster or pier. These posts served primarily to carry the frames for the wall forms and secondarily for holding the forms for the circular wall footing channel as shown by the sketch Fig. 280. The floor concrete was put in in diamond-shaped panels between forms, whose top edges were set to floor level. Each form was designed to make a groove in the edge of the slab so that adjacent slabs would bond with it. The concrete was wheeled to place in barrows, thoroughly tamped, roughly floated to surface and finally given a trowel finish.
Fig. 280.—Forms for Constructing Channel for Wall in Reservoir Floor.
To construct the walls, the posts before mentioned, were cut off to exact level 6 ins. above the finished floor. A bent for the wall forms was then erected on each radial pair as shown by Fig. 281. The bents were erected by hand and carefully plumbed and lined up, both radially and circumferentially. The pier and pilaster forms were then erected across wall opposite each bent as shown by Fig. 281. The forms for the wall between pilasters and piers consisted of panels 4 ft. high.
Fig. 281.—Frame for Forms for Circular Reservoir Wall.
Fig. 282.—Form Panels for Circular Reservoir Wall.
A panel for the inner face of the wall is shown by Fig. 282, the panel for the outer face was similar in construction but was, of course, concave instead of convex. Enough panels of each kind were made to reach entirely around the tank. The inside panels were bolted at the ends to the uprights of the bents; the outside panels were similarly lag screwed to the uprights of the pier and pilaster forms; Fig. 281 shows the holes for bolts and lag screws. The spaces between ends of inside panels in front of the bents was closed by a ½×6-in. steel plate the full height of the wall; this plate was bolted to the bents and had anchor bolts every 3 ft., reaching into the wall. This anchoring of the plate to the wall permitted the diagonal bracing of the bents to be removed to allow runways to be laid on the cross-pieces, since the plate held firmly the bent post to which it was bolted as indicated by Fig. 283. A complete circle of inside and outside forms was erected and filled, then the forms were raised 3 ft. by block and tackle from cross timbers across wall between bent and pilaster form, and this depth concreted and the forms raised again. The forms were oiled on the faces coming against the concrete. It took about half a day to raise and set a complete circle of forms. The concrete was mixed outside the tank and was wheeled up inclines and dumped onto runways laid on the cross pieces of the bents and then loaded and wheeled to place. The runway was raised to successive horizontals as the work progressed.
Fig. 283.—Sketch Showing Filler for Joint Between Form Panels.
Only a few general cost figures are available. The labor for mixing and placing concrete was as follows:
| For floor, per cu. yd. | 3.4 hrs. |
| For walls, per cu. yd. | 5.2 hrs. |
| For cornice, per cu. yd. | 5.4 hrs. |
The cost of unloading the reinforcing steel from cars and placing it in the structure was $7 per ton, or 0.35 ct. per lb. The cost of form lumber, framing, erecting and taking down forms was 9 cts. per square foot of wall covered.
GAS HOLDER TANK, NEW YORK CITY.—The tank for the Central Union Gas Co.'s gas holder at 136th St. and Locust Ave. has an interior diameter of 189 ft. and a depth of 41 ft. 6 ins. The exterior wall is 42 ft. 6 ins. deep, 5 ft. 6 ins. thick at the base and 4 ft. 6 ins. thick at the top; concentric with it and 11 ft. 6 in. away is the interior wall 166 ft. in external diameter and 16 ft. 6 ins. high with a uniform thickness of 2 ft. 6 ins. The bottom of the tank enclosed by the interior wall is a truncated cone whose base is at the level of the wall top. Fig. 284 shows the arrangement.
It was specified that the diameter of this tank should not vary more than 2 ins. and that the exterior wall should not vary more than 1 in. from the vertical. The main form was a circular drum whose exterior face formed the inner face of the main wall. Its framework consisted of 40 vertical trusses or radial frames 6 ft. deep and 42 ft. high set equidistant around the tank, these trusses being braced together on both edges by circumferential timbers. Radial horizontal pieces nailed across the radial frames and projecting beyond their faces carried vertical iron guide strips against which the movable panels of lagging were seated. These panels were cylindrical segments 5 ft. high and long enough to span between two radial frames or 14 ft. 11⅝ ins. The panels were adjusted radially by wedges to give ⅛ in. clearance in respect to inner face of wall; enough of them were made to form a complete circle and they were set with 1-in. clearance between vertical edges of adjacent panels to allow for swelling when wetted.
Fig. 284.—Section of Gas Holder Tank, New York City.
The concrete bottom of the annular space between walls was first constructed. On this floor were set 6×6-in.×8-ft. sills for the radial frames; these were located accurately by transit. The radial frames were then set on the sills by a derrick, adjusted to exact radial position by a measuring wire swiveled to the center point of the tank and plumbed by transit. A complete circle of lagging panels was then adjusted to the frames at the bottom of the trench. For concreting, the wall was divided circumferentially into three sections. These sections were separately concreted to the top of the lagging panels, that is to a height of 5 ft. After the concrete had set 48 hours the panels were hoisted 4 ft., so that their lower edges still overlapped the concrete 12 ins., and another ring of wall was concreted. This procedure was repeated until the wall was completed. The back of the wall was formed against the side of the trench where possible and in other places against rough board lagging held in position in any convenient way.
For handling the concrete, four equidistant panels of the form framework were converted into double compartment elevator shafts providing for two balanced cars controlled by a sheave provided with a friction brake. Three mixers supplied concrete to these elevators. Considering a single elevator, two barrows of concrete were wheeled from the mixer onto the car at the top of the elevator frame, the friction brake was released and the loaded car descended to the work hoisting at the same time its twin car loaded with two empty barrows. The elevators distributed to wheeling platforms cantilevered out from the outer face of the framework and located successively 5 ft., 15 ft., 20 ft., etc., above the bottom of the trench. On these platforms the concrete was distributed as required, the maximum wheeling distance being never over one-eighth the circumference of the tank. The concrete was mixed very wet and deposited in 6-in. layers.
The inner and outer surfaces of the wall were both painted with two coats of stiff cement grout neat, and in addition the inner surface was rubbed smooth by carborundum brick. Regarding this finishing work Mr. Howard Bruce, Engineer of Construction, writes:
"The scouring was done on each section of the wall immediately after the forms supporting these sections had been removed. The object was to rub this interior surface with carborundum before the surface of the concrete had taken its final set. By rubbing the concrete at this stage and at the same time applying with a brush a coating of neat cement grout, we believe the face of the concrete was made more or less impermeable, as examination shows the pores of the concrete are very largely filled up. We have no accurate figures as to the cost per square yard of this treatment, but one can readily see that this cost would be insignificant as compared with the possible improvement of the work. The carborundum brick was selected on account of its hardness. I believe practically any stone would answer the same purpose. In addition to filling the pores of the concrete, this treatment gives the surface a good smooth finish."
LINING A RESERVOIR, QUINCY, MASS.—The following methods and costs are given by Mr. C. M. Saville, M. Am. Soc. C. E., for lining the Forbes Hill Reservoir at Quincy, Mass. This reservoir is 100×280 ft. on the floor, with side slopes of 1 on 1.75, and was built by contract in 1900-1901.
Fig. 285.—Section of Reservoir Lining, Quincy, Mass.
Figure 285 is a section of the concrete lining; the bottom layer for the floor was a 1-2-5 natural cement concrete, and for the sides a 1-2½-6½ Portland cement concrete; the top layer on both floor and sides was a 1-2½-4 Portland cement concrete; 2½-in. stone was the maximum size allowed in any concrete and 1½-in. the maximum allowed in the top layer. Smaller stone was used for special surface work, as noted further on. The stone was cobbles turned up in the excavation work and had to be gathered from scattered piles and washed before crushing. A 9×15 Farrel crusher, operated by a 12 HP. engine did the crushing; it was rated at 125 tons a day, but averaged only about 40 tons. The fine dust was screened out and the remainder discharged into a 30-cu. yd., three-compartment bin, one compartment for stone less than 1½ ins., another for 1½ to 2½-in. stone and a third for returns. The stone had 46 per cent. voids and weighed 95 lbs. per cu. ft. The sand was of excellent quality. Atlas and Beach's Portland and Hoffman natural cement were used.
All concrete was mixed and placed by hand, the concrete gang consisting generally of 1 sub-foreman, 2 men measuring materials, 2 men mixing mortar, 3 men turning concrete three times, 3 men wheeling concrete, 1 man placing concrete and 2 men ramming concrete. Two gangs were ordinarily employed, each mixing and placing about 20 cu. yds. per day, or 1.43 cu. yds. per man per day. The materials (sand and stone) were measured in bottomless boxes, the following sizes being used:
| —Sand Box— | —Stone Box— | |||
| Prop. of Mix. | Size. | Vol. cu. ft. | Size. | Vol. cu. ft. |
| 1-2½-4[H] | 2'9"×2'×1'8" | 9.25 | 5'×4'5½" | 14.8 |
| 1-3-6[H] | 2'9"×2'×2' | 11.1 | 5'×6'8" | 22.2 |
| 1-2-5 | 2'9"×2'×1'4" | 7.4 | 5'×6'6⅝" | 18.5 |
| 1-2½-6½ | 2'9"×2'×1'8" | 9.25 | 5'×7'2½" | 24.05 |
[H] These mixtures were used for gate house and standpipe foundation work.
The bottom layer was placed in a continuous sheet; the top layer was laid in 10-ft. squares on the floor and in 8×10-ft. squares on the sides; these squares alternated in both directions, one-half being first laid and allowed to set. In laying the sides the surface was left 1 in. low and then before the concrete had set was brought to plane by a 1-in. layer of 1-2½-4 mixture using stone and stone dust less than ⅜ in. The concrete for the floor was mixed rather wet and rammed until it quaked; on the sides a drier mixture was necessary to prevent flow. The cost of the lining concrete was as follows:
| Bottom Layer on Floor: 1-2-5 Mixture: | |
| 1.25 bbls. natural cement at $1.08 | $1.350 |
| 0.34 cu. yd. sand at $1.02 | 0.347 |
| 0.86 cu. yd. stone at $1.57 | 1.350 |
| 4½ ft. B. M. lumber at $20 per M. | 0.090 |
| Labor, on forms | 0.100 |
| Labor mixing and placing | 1.170 |
| Labor general expenses | 0.080 |
| ——— | |
| Total | $4.487 |
| Bottom Layer on Sides: 1-2½-6½ Mixture: | |
| 1.08 bbl. Portland cement at $1.53 | $1.652 |
| 0.37 cu. yd. sand at $1.02 | 0.377 |
| 0.96 cu. yd. stone at $1.57 | 1.507 |
| Lumber for forms (about 1 ft. B. M.) at $20 | 0.016 |
| Labor, on forms. | 0.121 |
| Labor, mixing and placing | 1.213 |
| Labor, general expenses | 0.177 |
| ——— | |
| Total | $5.063 |
| Top Layer on Floor and Sides: 1-2½-4 Mixture: | |
| 1.37 bbls. Portland cement at $1.53 | $2.09 |
| 0.47 cu. yd. sand at $1.02 | 0.48 |
| 0.75 cu. yd. stone at $1.57 | 1.17 |
| 12½ ft. B. M. form lumber at $20 per M. | 0.25 |
| Labor, on forms | 0.26 |
| Labor, mixing and placing | 1.530 |
| Labor, general expenses | 0.150 |
| ——— | |
| Total | $5.93 |
The side finish with 1-2½-4 concrete of ⅜-in. stone cost $0.154 per sq. yd. 1 in. thick. This work was done by a gang of 3 plasterers and 3 helpers.
The layer of plaster between the concrete layers was put down on 4-ft. strips and finished similarly to the surface of a granolithic walk. This layer consisted of 1-2 mortar finished with a 4-1 mortar. To keep the plaster from cracking it was covered with strips of coarse burlap soaked in water; this precaution was not entirely successful, some cracks appeared and had to be grouted. Three gangs, each consisting of 1 plasterer and 1 helper, did the plastering, each gang laying about 700 sq. yds. per day. The cost of the plaster layer was as follows:
| Item. | Per 100 sq. ft. | Per sq. yd. | Per cu. yd. |
| Cement at $1.53 | $1.15 | $0.103 | $7.42 |
| Sand at $1.02 | 0.13 | 0.012 | 0.86 |
| Burlap | 0.02 | 0.002 | 0.14 |
| Labor | 0.92 | 0.083 | 6.00 |
| —— | ——— | ——— | |
| Totals | $2.22 | $0.200 | $14.42 |
It will be noted that it took over 5 bbls. of cement per cubic yard, and that the labor cost was $6 per cubic yard.
RELINING A RESERVOIR, CHELSEA, MASS.—The following account of relining the Powder Horn Hill Reservoir at Chelsea, Mass., is taken from a paper by Mr. C. M. Saville. This reservoir which holds about 1,000,000 gallons is oval in shape, 98×175 ft. at the top, 68×148 ft. at the bottom and 15 ft. deep, with side slopes about 1 on 1. The work was done by day labor. For sake of completeness the costs of excavation and back-filling are given here as well as the concrete costs.
The top of the bank was too narrow to allow the use of carts and an 18-in. gage railroad was decided upon as most convenient for handling materials. A 65-ft. boom derrick with a 70-ft. mast was used for removing the excavated material and for depositing concrete. The derrick was operated by a 15-h.p. double drum hoisting engine, was held in place by six wire guy ropes, and had a reach such that only one moving was necessary after it was placed. The engine and derrick were set up on the floor of the reservoir, and the work of excavation was begun at about the middle of the south side. In order to facilitate the work, a platform supported on A frames was set up. These frames were spaced about 15 ft. apart and rested on the bottom and slope of the reservoir, being held in place by bolts driven into the floor.
The paving blocks on the top of the slope were removed and piled up to be taken away. The old lining and the material excavated from the bank were shoveled into the scale pan of the derrick, hoisted to the cars on the top of the bank, and then run by gravity to a dump a short distance down the hillside. Here the cars were run out on a rough trestle, the load dumped, and the empties hauled back to the work by a rope carried through pulleys to the winch head on the hoisting drum of the engine.
For the storage of some of the materials, two small portable storehouses were set up—one 8×10×7 ft., the other 11×16 x 7 ft. The bulky portions, such as cement, sand, and stone, were delivered as necessary, a few days' supply only being kept on hand. A branch from the railroad was so arranged that it passed the storehouses and stone piles, while the sand was piled close to the concrete mixing board. The intention on the work was to do nothing by hand that could possibly be done by steam, except that all of the concrete was mixed by hand. As great a proportion of water was used as could be done without causing the material to slide when rammed in place.
The lower layer of concrete was of the proportion by volume of 1 cement, 2½ sand, and 6½ crushed stone (sizes from ¾ to 1½ ins.). This was rather a lean mixture, and as it could not be rammed enough to flush all over, the surface was finished where necessary by a thick mortar made in the proportion of 1 cement to 6 sand, and applied with heavy brushes. Before placing any of the concrete, the bank back of the old concrete left in place was thoroughly rammed with iron railroad tampers, and the edge of the old concrete was scrubbed with water and a stiff brush and then coated with 1 to 4 grout, which was allowed to fill in the angle between the concrete and the slope. Just before placing the concrete the earth bank was well wet in order that moisture might not be drawn from the concrete while it was soft.
In order to make the new lining as waterproof as possible, a layer of asphalt was placed on top of the lower layer of concrete and brought up on the exposed edge of the old layer at the bottom of the new work. This, it was expected would make an elastic and watertight joint between the new and the old work.
Venezuela asphalt, "Crystal Brand," was used, being poured upon the top of the concrete layer and allowed to run down the slope, care being taken that the concrete was entirely and perfectly covered. After the first layer of asphalt was cool, a second layer was similarly applied, and the resulting sheet was about ¼ in. thick. Any inclination to crawl down the slope when exposed to the sun was readily stopped by throwing on a pailful of cold water. A most particular part of this work was to get the asphalt as hot and liquid as possible and yet not burn it. All of the concrete was protected from the sun and kept damp by being covered with strips of burlap, which were moistened by sprinkling.
The upper layer of concrete was composed of a much richer mixture of concrete than that used in the bottom layer, the proportions by volume being 1 cement, 1¼ sand, 1¼ stone dust, and 4 broken stone of the sizes mentioned above. On account of the steep slope it was possible to do only a little ramming, and the material was laid as wet as possible. To make this layer more impervious and also to obtain a smooth surface, the concrete was left about an inch below and a finish coat applied by expert granolithic finishers. This coating was applied as soon as it was possible to do so after the main layer was in place, but on account of the steepness and the liability of the wet concrete to flow, care had to be taken not to begin work too soon.
The top finishing coat was made in the proportion of 1 part cement, 1⅔ part sand, and 3⅓ parts stone dust. In order to help in bonding, the last ramming on the concrete was done with rammers studded with pieces of iron about 1 in. long and ½ in. deep.
The finishing was done in three operations: The material was spread on the concrete and thoroughly worked into it by the finishers, using rough wooden floats; after this it was gone over and partially smoothed down with a thin steel float; and finally it was worked to give the finished appearance and an impervious surface.
The under layer of concrete was placed in a continuous sheet. The upper layer was put down in alternate strips, 10 ft, long (the whole length of the layer) and 5 ft. wide. These blocks were built up in forms, which were not removed until the concrete had set. Finally, the back or edge of the block toward the bank was well wet and thoroughly plastered, to prevent, as far as possible, the infiltration of any water. The plaster was mixed in the proportion of 1 part cement to 4 parts sand. When the forms were wholly removed, the space between the concrete and the bank was refilled, to within about 6 ins. of the top, with a clayey material previously excavated, and the space was filled and graded to the top of the bank with loam. During the work two holidays intervened; the men were also transported to and from the work. Charges were made for these items, amounting to $209.77, and this sum, together with the cost of installing the plant ($716.03) are proportionally charged against the work as follows:
| Per cent. | Total. | Per cu. yd. | |
| Excavation | 70.3 | $651 | $2.17 |
| Lower concrete | 12 | 111 | 1.16 |
| Upper concrete | 15.4 | 143 | 1.11 |
| Back fill | 2.3 | 21 | .28 |
The detailed cost of repairing the reservoir lining is given in the following tabulations:
The cost of the concrete work in the lower and upper layers can be still further detailed as shown below:
| Lower Layer Concrete. | ||||
| 95.5 cu. yds., 1-2½-6½ concrete. | ||||
| Materials: | Rate. | Per cu. yd. | ||
| Atlas cement | 1.11 | bbl. | $1.35 | $1.50 |
| Sand | .39 | cu. yd. | 1.10 | 0.43 |
| Broken stone (.97 cu. yd.) | 1.23 | tons | 1.35 | 1.66 |
| Miscellaneous, plant, coal, etc. | 1.28 | |||
| Labor: | ||||
| Mixing and placing | $2.09 | |||
| Carpenter work on forms at $24.00 per M. | .34 | |||
| —— | ||||
| Total per cu. yd. in place | $7.30 | |||
| Upper Layer Concrete. | ||||
| 129.2 cu. yds., 1-1¼-1¼-4 concrete. | ||||
| Materials: | Rate. | Per cu. yd. | ||
| Atlas cement | 1.37 | bbl. | $1.35 | $1.85 |
| Sand | .24 | cu. yd. | 1.10 | 0.26 |
| Stone dust (.25 cu. yd.) | .32 | ton | 1.50 | 0.48 |
| Broken stone (.75 cu. yd.) | .96 | ton | 1.35 | 1.30 |
| Lumber | 0.31 | M. ft. | 21.00 | 0.65 |
| Miscellaneous, plant, etc. | 1.32 | |||
| Labor: | ||||
| Mixing and placing | 1.85 | |||
| Carpenter work on forms at $21.00 per M. | 0.66 | |||
| —— | ||||
| Total per cu. yd. in place | $8.37 |
The following approximate labor costs are also given: Transporting, erecting and removing derrick, $260.85. Equivalent time: Foreman, 6 days; engineer, 4 days; laborer, 85 days.
Transporting, laying and removing track, $125.03. Equivalent time: Foreman, 4 days; laborer, 40 days.
Caring for dump and disposing of surplus by rough grading, $70.28. Equivalent time: Foreman, 1 day; laborer, 33 days.
The total cost of the work was $3,503.66, divided up as follows:
| Excavation | $480.79 | |
| Lower layer concrete | 614.15 | |
| Upper layer concrete | 937.94 | |
| Back plaster | 84.73 | |
| Surfacing | 186.04 | |
| Asphalting | 170.94 | |
| Back filling | 103.27 | |
| Installing plant | 716.03 | |
| Transportation and holidays | 209.77 | |
| ———— | ||
| Grand total | $3,503.66 |
LINING JEROME PARK RESERVOIR.—The bottom of the reservoir that was lined covered 250 acres, and the concrete lining was 6 ins. thick. The lining was laid in alternate strips 16 ft. wide between forms set to grade. The concrete was mixed in 18 Ransome mixers provided with charging hoppers and mounted on trucks without boilers. Steam was supplied to the mixer engines from the boilers of the contractor's locomotives. One locomotive supplied steam for three or four mixers. Tracks were laid in parallel lines across the reservoir bottom from 150 to 200 ft. apart. Sand and stone were hauled in on these tracks. The sand was dumped in stock piles at intervals; the stone was shoveled from the cars directly into the charging hopper and the sand was delivered by wheelbarrows to the same hopper. Four men shoveled the stone for each mixer. To deliver the concrete from the mixer to the work required six men with wheelbarrows. Two men leveled off the concrete discharged by the barrows and two other men floated the surface by means of a straight-edge spanning the 16-ft. strips and riding on the forms. By using a wet but not sloppy concrete and moving the straight-edge back and forth a good surface was secured. The gang mixing and placing consisted of 20 men for each mixer and 18 gangs laid approximately 1½ acres per 10-hour day. The gang organization and wages were as follows:
| Item. | Per 10 hours. |
| 4 men shoveling stone at $1.50 | $ 6.00 |
| 2 men wheeling sand at $1.50 | 3.00 |
| 2 men delivering cement at $1.50 | 3.00 |
| 1 man dumping mixer at $1.50 | 1.50 |
| 1 man tending engine and water at $1.50 | 1.50 |
| 6 men wheeling concrete at $1.50 | 9.00 |
| 2 men spreading concrete at $1.50 | 3.00 |
| 2 men leveling concrete at $1.50 | 3.00 |
| 1 foreman | 3.00 |
| ——— | |
| Total per day | $33.00 |
These costs do not include the fraction of a day's labor for fireman or the cost of fuel.
RESERVOIR FLOOR, CANTON, ILL.—The following costs are given by Mr. G. W. Chandler for lining the bottom of a 160×80-ft. reservoir with corners of 20-ft. radius and vertical brick sidewalls. A 1-3½-7½ crushed stone concrete was used; it was mixed by hand in batches of 2.7 cu. ft. cement, 9 cu. ft. sand and 20¼ cu. ft. stone. The sand and stone were measured separately, the sand and cement mixed dry, then shoveled into a pile with the rock, well wetted, shoveled over again and then shoveled into wheelbarrows. The stone had 40 per cent. voids and the sand 30 per cent. voids. The lining was 10 ins. thick including a ¾-in. coat of 1-2¼ mortar spread and worked smooth with a trowel. The cost per cubic yard of the lining in place was as follows:
| 0.856 bbl. cement at $2.50 | $2.14 |
| 10.1 bu. sand (100 lbs. per bu.) at 5¾ cts | 0.58 |
| 0.857 cu-yd-stone at $2.17 | 1.86 |
| Labor, mixing and placing at 19 cts. per hr. | 0.80 |
| —— | |
| Total | $5.38 |
RESERVOIR FLOOR, PITTSBURG, PA.—The following methods and costs of laying a reservoir floor are given by Mr. Emile Low, M. Am. Soc. C. E., for the Hiland Reservoir constructed at Pittsburg, Pa., in 1884, by contract. There were 7,681 cu. yds. of concrete in the floor which was 5 ins. thick and laid on a clay puddle foundation.
Natural cement costing $1.35 per barrel was used. The broken stone varied in weight from 147 to 152 lbs. per cu. ft.; it was quarried and hauled 20 miles by rail and then unloaded into small cars and hauled ½ mile to the reservoir. The cost of the stone per cubic yard delivered was:
| Quarrying, per cu. yd. | $0.45 |
| Breaking, per cu. yd. | 0.35 |
| Transporting, per cu. yd. | 0.50 |
| Total | $1.30 |
The sand was obtained on the site at the cost of excavation, or 1¼ cts. per bushel.
The method of proportioning and mixing the concrete was as follows: Platforms 10×16 ft. of 2-in. plank were laid on the puddle foundation and by these were set 5×4×1½-ft. boxes on legs. Into these boxes 1 bbl. of cement and 2 bbls. of sand were emptied and thoroughly mixed dry, then mixed with water to a thin grout. Five barrels of stone were placed on the platform and thoroughly wetted; the grout was then emptied over the stone and the two turned over three times with shovels. The concrete was rammed until the mortar flushed to the surface. The following costs cover various periods as follows:
| Two Days Work (101 cu. yds.): | Total. | Per cu. yd. |
| 27 laborers, 2 days, at $1.25 | $72.90 | $0.7217 |
| 1 foreman, 2 days, at $2.50 | 5.00 | 0.0495 |
| ——— | ——— | |
| Total | $77.90 | $0.7712 |
| One Month's Work (1,302 cu. yds.): | ||
| 642 days, laborers, at $1.35 | $ 866.70 | $0.6649 |
| 17 days, water boy, at $0.60 | 10.20 | 0.0078 |
| 22 days, foreman, at $2.50 | 55.00 | 0.0421 |
| ——— | ——— | |
| Total | $931.90 | $0.7148 |
| Two Days Work (101 cu. yds.): | Total. | Per cu. yd. |
| 27 laborers, 2 days, at $1.25 | $72.90 | $0.7217 |
| 1 foreman, 2 days, at $2.50 | 5.00 | 0.0495 |
| ——— | ——— | |
| Total | $77.90 | $0.7712 |
| One Month's Work (1,302 cu. yds.): | ||
| 642 days, laborers, at $1.35 | $ 866.70 | $0.6649 |
| 17 days, water boy, at $0.60 | 10.20 | 0.0078 |
| 22 days, foreman, at $2.50 | 55.00 | 0.0421 |
| ——— | ——— | |
| Total | $931.90 | $0.7148 |
| Total Work (7,861 cu. yds.): | ||
| Quarrying stone | $0.45 | |
| Transporting stone | 0.50 | |
| Breaking stone | 0.35 | |
| 1⅓ bbl. natural cement | 1.80 | |
| 8 bu. sand | 0.10 | |
| Water | 0.05 | |
| Labor mixing and laying at $1.25 | 0.75 | |
| Incidentals | 0.05 | |
| —— | ||
| Total | $4.05 |
The contract price was $6 per cu. yd.
Fig. 286.—Form for Constructing Silo.
CONSTRUCTING A SILO.—The form construction shown in Fig. 286 was employed in building a silo 28 ft. high, 22 ft. 3 ins. interior diameter, and having 6-in. walls. The bottom of the silo was made 9 ins. thick and set 2 ft. below the surface. The reinforcement consisted of ten 2½×3/16-in. rings spaced equally in the lower half and of woven wire fencing in the upper half. The iron rings were hoops removed from an old wooden silo. The concrete was a 1-6 mixture of Portland cement and sandy gravel. Figure 286 is a section through the forms. There were twenty T-shaped posts, which extended perpendicularly from the ground to a height of 28 ft., being secured at top and bottom by a system of guy ropes and posts. The rings, of which there are four, two inside and two outside, were built of weather boards with their edges reversed. Four thicknesses of board were used in each ring. The curbing consisted of 2×8-in. sticks 4 ft. long. Wedges driven between the vertical posts and the rings held the latter in place. When the forms were to be removed the wedges were knocked out and the rings sprung enough to permit the removal of the curbing. The rings were then pushed up and fastened in place for another section. The average rate of progress was one 4-ft. section per day. The forms were filled in the afternoon and moved up the following forenoon. Five-foot sections could have been built just as readily.
The work was all done by farm laborers hired by the month and 100 man-days of such labor were required, excluding seven days work of a mason brushing and troweling the surface. The cost of the work, not including the old hoop iron or the old lumber used in forms, was as follows:
| Item. | Total. | Per cu. yd. |
| Cement | $100.00 | $2.62 |
| Gravel and sand | 35.00 | 0.92 |
| 1 20-rod roll of fencing | 5.20 | 0.01 |
| New lumber | 18.00 | 0.47 |
| 100 days labor at $1.75 | 175.00 | 4.60 |
| 7 days mason troweling at $3.50 | 24.50 | 0.64 |
| ——— | —— | |
| Total, 38.2 cu. yds. | $357.70 | $9.26 |
The external area of the silo is 1,950 sq. ft., which makes the cost of brushing and troweling 1¼ cts. per sq. ft. There were about 2,300 ft. B. M. of lumber used in the forms, or about 61 ft. B. M. per cu. yd. of concrete.
GROINED ARCH RESERVOIR ROOF.—The following data are given by Mr. Allen Hazen and Mr. William B. Fuller, in Trans. Am. Soc. C. E. 1904. The concrete was mixed in 5-ft. cubical mixers in batches of 1.6 cu. yds. at the rate of 200 cu. yds. per mixer day. One barrel of cement, 380 lbs. net, assumed to be 3.8 cu. ft., was mixed with three volumes of sand weighing 90 lbs. per cu. ft., and five volumes of gravel weighing 100 lbs. per cu. ft. and having 40 per cent voids. On the average 1.26 bbls. of cement were required per cu. yd. The conveying plant consisted of two trestles (each 900 ft. long) 730 ft. apart, supporting four cableways. The cables were attached to carriages, which ran on I-beams on the top of the trestles. Rope drives were used to shift the cableways along the trestle. Three-ton loads were handled in each skip. The installation of this plant was slow, and its carrying capacity was less than expected. It was found best to deliver the skips of concrete to the cableway on small railway track, although the original plan had been to move the cableways horizontally along the trestle at the same time that the skip was traveling.
The cost of mixing and placing the concrete was as follows:
| Per cu. yd. | |
| Measuring, mixing and loading | $0.20 |
| Transporting by rail and cables | 0.12 |
| Laying and tamping floors and walls including setting forms | 0.22 |
| —— | |
| Total | $0.54 |
The cost of laying and tamping the concrete on the vaulting was 14 cts. per cu. yd. The vaulting is a groined arch 6 ins. thick at the crown and 2½ ft. thick at the piers.
The lumber of the centering for the vaulting was spruce for the ribs and posts, and 1-in. hemlock for the lagging. The centering was all cut by machinery, the ribs put together to a template, and the lagging sawed to proper bevels and lengths. The centers were made so that they could be taken down in sections and used again. The cost of centering was as follows:
These centers covered two filters, each having an area of 121⅓×258 ft. There were six more filters of the same size, for which the same centers were used. The cost of taking down, moving and putting up these centers (313 M.) three times was as follows:
| Foreman, 2,359 hrs. at 35 cts. | $825.65 |
| Carpenters, 12,766 hrs. at 22½ cts. | 2,872.35 |
| Laborers, 24,062 hrs. at 15 cts. | 3,609.30 |
| Team, 430 hrs. at 40 cts. | 172.00 |
| 3,000 ft. B. M. lumber, at $20 | 60.00 |
| 3,000 lbs. nails, at 3 cts. | 90.00 |
| ———— | |
| Total cost of moving centers to cover 196,660 sq. ft. | $7,629.30 |
Fig. 287.—Forms for Constructing Grain Elevator Bins.
The cost of moving the centers each time was $8.10 per M., showing that they were practically rebuilt; for the first building of the centers, as above shown, cost only $6.37 per M. In other words, the centers were not designed so as to be moved in sections as they should have been. Although the centers were used four times in all, the lumber was in fit condition for further use. The cost of the labor and lumber for the building and moving of these centers for the 8 filter beds, having a total area of 259,220 sq. ft., was $15,438, or 6 cts. per sq. ft.
GRAIN ELEVATOR BINS.—In constructing cylindrical bins 30 ft. in diameter and 90 ft. high for a grain elevator the forms shown by Fig. 287 were used. For the inside wall a complete ring of lagging 4 ft. high nailed to circular horizontal ribs of 2×8-in. planks was used. For the outside wall two, three or four segments fitting the clear spaces between adjoining tanks were used, these panel segments being also 4 ft. high. The inside and outside rings were held together by yokes constructed as shown, and bolted to the inner and outer ribs. A staging built up inside the tank carried jack screws, on which were seated the inner legs of the yokes.