Concrete Construction Part 56

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 s.p.a.ce 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 s.p.a.ce 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 antic.i.p.ated.

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 a.s.sisting the carpenters.

[Ill.u.s.tration: Fig. 277.--Reservoir at Ft. Meade, S. D.]

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 quant.i.ty of material:

2 sacks of cement 2 cu. ft.

2 wheelbarrows of sand 5 cu. ft.

4 wheelbarrows of stone 10 cu. ft.

The quant.i.ties 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 s.p.a.ce 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 s.p.a.ce 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 s.p.a.ced 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 pa.s.sing through the wall s.p.a.ce between the edges of adjacent planks. At the rounded corners of the reservoir the pairs of posts were s.p.a.ced 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 quant.i.ties 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.