Concrete Construction: Methods and Costs

PIERS, CALF KILLER RIVER BRIDGE.—The following methods and costs of building two new piers and extending three old piers with concrete are given by Mr. J. Guy Huff. The work was done by the railway company's masonry gangs. Figure 94 shows the arrangement of the several piers and the character of the work on each and Fig. 95 gives the detail dimensions of the three main piers.

The sand and aggregate, consisting of blast furnace slag, were unloaded from cars to platforms on a level with the top of rail, placed about 100 ft. south from the south end of the bridge. A cubical 1/6 cu. yd. mixer was used. This was operated by a gasoline engine, and was located on a platform about 50 ft. south of the south end pier. A tank near the mixer to supply water was elevated enough to get the desired head, and was kept filled by a pump run by another gasoline engine located down by the river bank. The cement house was located between the mixer platform and slag pile.

Slag and sand were delivered to the mixer by means of wheelbarrows. The mixer was so placed that it would dump onto a platform, and the concrete could then be shoveled into a specially designed narrow-gage car. This car ran on one rail of the main track and an extra rail outside. A turnout for clearing passing trains was provided at both ends of the bridge. The track over the bridge from the mixer had a descending grade of about 1 per cent., so that with a little start the concrete car would roll alone down to the required points on the bridge. Only in returning the empty cars to the mixer was it necessary to push them by hand, and then only for a distance of never more than 400 ft.

Over the piers on the bridge in the center of the concrete car track openings were sawed to let the concrete pass to the forms below. To get the concrete into the forms, there were used zig-zag chutes with arms about 10 ft. long, which sections were removed as the concrete in the forms was increased. These chutes were a convenience by their ends alternating from one side to the other as the arms were removed in coming up.

The cost of the concrete work was as follows:

The wages given are the average wages. The men worked a 10-hour day. The concrete was a 1-3-6 mixture. The cofferdam work was done in connection with the construction of the fourth pier, this pier being the only one coming in the bed of the river to be built entirely new. The work on this was started in water about 6 ft. deep. The 37 cu. yds. of concrete is included in the total of 460 cu. yds. in the above tabulation. By itself the cost of the cofferdam work, not including cost of cement, sand and slag was as follows:

METHOD AND COST OF CONSTRUCTING 21 BRIDGE PIERS.—The following account of the methods and cost of constructing 21 concrete piers for a railway bridge consisting of 20 50-ft. plate girder spans has been compiled from records kept by Mr. W. W. Colpitts, Assistant Chief Engineer, Kansas City, Mexico & Orient Ry. The shape and dimensions of the piers are shown by Fig. 96 and Fig. 97 shows the construction of the forms. Sheet pile cofferdams to solid rock were used for constructing the foundations.

The 1-3-5 concrete was mixed in a Smith mixer having a batch capacity of 9 cu. ft. The mixer was located on the slope of the embankment approach, with the main track at its rear and facing a temporary material track. This temporary track turned out from the main track about 500 ft. beyond the mixer and extended diagonally down the embankment approach on a 3 per cent. grade and across the river bottom alongside the pier sites. The portion of the track in the river bottom was supported on bents of spliced ties, jetted to the rock, and wired to the cofferdam to avoid the danger of loss in case of high water. The sand and crushed rock were delivered by cars from the main line track, immediately above the mixer, and the cement was stored in a shanty at one side of the mixer. The concrete materials and machinery were, in this manner, very conveniently located for rapid work and well above the high water line. The concrete was transported to the pier sites in improvised dump boxes, set on push cars. These dump boxes were hinged longitudinally and discharged directly into the cofferdams. The grade of the temporary track carried the push cars by gravity to the cofferdams and they were returned by teams, for which purpose a straw and brush road had been built paralleling the track. As the work progressed farther into the stream, more cars were added properly to balance the work. While the concrete in the base was still fresh, a number of steel reinforcing bars, 8 ft. in length, were set in place along each end to insure a good bond between the base and shaft.

In general, the work of putting in the bases was organized so that about the same time was required in filling a cofferdam with concrete, in excavating the sand from the next, and in driving the sheet piling for the third. These three operations were thus carried on simultaneously and, although interruptions in one part of the work or the other occurred frequently, the gangs were interchangeable and no appreciable loss was suffered, except in time, because of such delays.

In piers 19 and 20, where the rock was from 17 to 19 ft. below the surface, some difficulty was encountered due to the presence of fissures in the rock, from which it was necessary to remove the sand to fill with concrete. In such cases, the larger leaks were stopped as much as possible by driving sheet piles against the outside face of the cofferdam and into the fissures, and the smaller leaks by manure in canvas bags rammed into the openings.

Upon the completion of all the bases, the forms for several shafts were set in position and the work of filling with concrete proceeded as in the case of the bases, except that a derrick erected on a flat car and stationed at the pier was utilized to raise the dump boxes in depositing the concrete in the forms. As soon as the concrete in one shaft had set sufficiently to permit of it, the forms were removed and placed on the pier ahead. Four sets of forms were used for the shafts.

The following are the average prices paid for materials and labor:

Materials.—Lumber for forms, etc., $16.50 per M. ft., B. M.; cement, Kansas Portland, $1.50 per bbl.; broken limestone, 45c per cu. yd.; sand, Arkansas River, 15c per ton.

Labor.—General foreman, $110 per month; assistant foreman, $75 per month; timekeeper, $60 per month; riveters, 35c per hour; blacksmith, 30c per hour; blacksmith assistant, 20c per hour; carpenters, 22½c and 25c per hour; enginemen, 25c per hour; firemen, 20c per hour; night watchman, 20c per hour; laborers, 17½c and 20c per hour; team (including driver), 40c per hour. The prices quoted for lumber, cement, limestone and sand are prices f. o. b., Louisiana, Iola, Kan., El Dorado, Kan., and Wichita, Kan.

The total and unit cost of constructing the concrete piers and abutments and of erecting the steel superstructure are given in the following tabulation. Altogether there was about 2,300 cu. yds. of concrete in the substructure, most of which, as stated above, was a 1-3-5 mixture.

The sheet piling took 63,500 ft. B. M. of lumber; the cost per 1,000 ft. B. M. for the sheet piling was then:

This gives us for 2,300 cu. yds. of concrete a cost of $3.47 per cu. yd. for materials, including freight, storage, and unloading charges of all kinds. A line on the proportion of the cost contributed by these latter items may be got by taking the prices of the materials f. o. b. at the places of production and assuming the proportions for a 1-3-5 concrete. According to tables in Chapter II, a 1-3-5 broken stone concrete requires per cubic yard 1.13 bbls. cement, 0.48 cu. yd. sand and 0.80 cu. yd. broken stone. We have then:

This leaves a charge of $1.32 per cubic yard of concrete for freight and handling materials. The cost of mixing concrete and placing it in the forms was $3,490.87, or $1.52 per cu. yd. We have then:

The miscellaneous expenses of the work comprised:

To this has to be added $1,134.28, the cost of excavating the cofferdams. The total and unit costs of the different items of the concrete substructure work can now be summarized as follows:

COST OF PERMANENT WAY STRUCTURES KANSAS CITY OUTER BELT & ELECTRIC RY.—The following cost of concrete work including retaining walls, abutments and box culverts, for the permanent way of the Kansas City Outer Belt & Electric Ry., is given by Mr. W. W. Colpitts. These figures are of particular interest, for the variation in prices of materials during the two-year period while work was in progress and as giving the average cost of the work on the whole line as well as for individual structures. The culverts were all box culverts with wing walls and the abutments were for girder bridges. Walls and abutments were of L section with triangular or trapezoidal counterforts at the back between base slab and coping. The form work was thus rather complex.

All work was reinforced concrete, and was done by contract under the following conditions: The work of preparing foundations, including excavation, pile driving, diversions of streams, etc., was done by the railroad company, which also bore one-half the cost of keeping foundations dry while forms were being built and concrete placed. The railroad company also furnished the reinforcing bars at the site of each opening. The concrete work was let at $9 per cu. yd., which figure covered all the labor and materials necessary to complete the work, other than the exceptions mentioned. The concrete proportions were 1-3-5. The cement used was Iola Portland and Atlas Portland. The sand was obtained from the bed of the Kansas River in Kansas City. The rock used was crushed limestone, passing a 2-in. ring and freed from dust by screening. Corrugated reinforcing bars, having an elastic limit of from 50,000 to 60,000 lbs. per sq. in., manufactured by the Expanded Metal & Corrugated Bar Co. of St. Louis, Mo., were used exclusively. The concrete in the smaller structures was mixed by hand, in the larger by a No. 1 Smith mixer. In the first structures built 2-in. form lumber was used, with 2 by 6-in. studs placed 3 ft. on centers. This was abandoned later for 1-in. lumber with 2 by 6-in. studs, 12 ins. on centers, and was found to be more satisfactory in producing a better face. The structures were built in the period from April, 1905, to May, 1907.

The cost of materials and the wages paid labor were as follows:

With these prices and wages the average cost of concrete work for the whole line was:

The following are the costs of specific structures built at different times:

Example I.—Indian Creek Culvert. 14×15 ft., 250 long, completed November, 1905:

Example II.—Third Street Abutments and Retaining Wall. Completed November, 1906:

Example III.—Abutments, Overhead Crossing with Union Pacific and Rock Island. Completed May, 1907:

COST OF PLATE GIRDER BRIDGE ABUTMENTS.—The following record of the construction of 20 abutments for 10 four-track plate girder bridges over streets in Chicago, Ill., are given by Mr. W. A. Rogers. The work was done between May 1 and Oct. 1, 1898, in which time 8,400 cu. yds. of concrete were placed, all the work being done by company labor. The forms were made of 2-in. plank and 6×6-in. posts bolted together at the top and bottom with ¾-in. rods. The lumber was used over and over again. When the dressed plank became too poor for the face it was used for the back. The concrete was 1 Portland cement, 3 gravel and 4 to 4½ limestone (crusher run up to 3-in. size). A mortar face 1½ ins. thick was built up with the rest of the concrete. The concrete was made quite wet, and each man ramming averaged 18 cu. yds. a day rammed. The concrete was mixed by a machine of the Ransome type, operated by a 12-HP. portable gasoline engine. The load was very light for the engine, and 8 HP. would have been sufficient. The engine made 235 revolutions per minute, and the pulley wheels were proportioned so that the mixer made 12 revs, per minute. One gallon of gasoline was used per hour, and the mixing was carried on day and night so as not to give the concrete time to set. The time required for each batch was 2 to 3 mins., and about ½ cu. yd. of concrete was delivered per batch. The average output was 70 cu. yds. per 10-hr, shift, with a crew of 28 men; but as high as 96 cu. yds. were mixed in 10 hrs. The concrete was far superior to hand mixed concrete. The water for the concrete was measured in an upright tank and discharged by a pipe into the mixer. The sand and stone were delivered to the mixer in wheelbarrows, and the concrete was taken away in wheelbarrows. No derricks were used at all. Each wheelbarrow of concrete was raised by a rope passing over a pulley at the top of a gallows frame, one horse and a driver serving for this raising. A small gasoline hoisting engine would have been more satisfactory than the horse which was worked to its full capacity. After the barrows were raised (12 ft.), they were wheeled to the abutment forms and dumped. The empty wheelbarrows were lowered by hand, by means of a rope passing over a sheave and provided with a counterweight to check the descent of the barrow. The cost of the concrete (built by company labor) was as follows:

The labor cost includes moving plant from one bridge to the next, building runways, gasoline for engine, oil for lights at night and unloading materials, as well as mixing, transporting and placing concrete. Wages were $1.75 per 10-hour day for laborers and $2.50 for carpenters.

COST OF ABUTMENTS AND PIERS, LONESOME VALLEY VIADUCT.—Mr. Gustave R. Tuska gives the following on the concrete substructure of the Lonesome Valley Viaduct, near Knoxville, Tenn. There were two U-shaped abutments and 36 concrete piers made of a light limestone that deteriorates rapidly when used for masonry. Derricks were not needed as would have been the case with masonry piers, and colored labor at $1 for 11 hrs. could be used. The piers were made 4 ft. square on top, from 5 to 16 ft. high, and with a batter of 1 in. to the foot. The abutments average 26 ft. high, 26 ft. long on the face, with wing walls 27 ft. long; the wall at the bridge seat is 5 ft. thick, and the wing walls are 3½ ft. wide on top. Batters are 1 in. to the foot.

The forms were made of 2-in. tongued and grooved plank, braced by posts of 2×10-in. plank placed 3 ft. c. to c. for the abutments, and at each corner for the piers. At the corners one side was dapped into the other, so as to prevent leakage of cement. The posts were braced by batter posts from the earth. For the piers a square frame was dropped over the forms and spiked to the posts. The abutment forms were built up as the concreting progressed. The north abutment forms were made in sections 6 ft. high, held by ¾-in. bolts buried in the concrete. The lower sections were removed and used again on the upper part of the work, thus saving plank. The inside of forms was painted with a thin coat of crude black oil. The same form was used for several piers.

The concrete was 1-2-5, the barrel being the unit of measure, making about ¾ cu. yd. of concrete per batch. The mortar was mixed with hoes, but shovels were used to mix in the stone. By passing the blade of a shovel between the form and the concrete, the stone was forced back and a smooth mortar face was secured. Rammers weighing 30 to 40 lbs. were used for tamping. Two days after the completion of a pier the forms were removed. The concrete was protected from the sun by twigs, and was watered twice a day for a week. It was found by actual measurement that 1 cu. yd. Of concrete (1-2-5), the ingredients being measured in barrels, consisted of 1¼ bbls. of Atlas cement, 10 cu. ft. of sand, and 26½ cu. ft. of stone. The total amount of concrete was 926 cu. yds. of which two-thirds was in the two abutments. The work was done (in 1894) by contract, for $7 per cu. yd., cement costing $2.80 per bbl., sand 30 cts. per cu. yd., and wages $1 a day. A slight profit was made at this price. A gang of 15 men and a foreman would mix and lay about 40 cu. yds. in 11 hrs. when not delayed by lack of materials. The cost of making the concrete, with wages at $1 a day, was:

COST OF HAND MIXING AND WHEELBARROW WORK FOR FOUR BRIDGE PIERS.—The following figures of the cost of hand-mixed concrete for bridge piers and abutments are given by Mr. Fred R. Charles of Richmond, Ind. The figures cover three jobs. All concrete was mixed by hand and with one exception noted below was moved to place in wheelbarrows. The concrete was a 1-2½-5½ mixture. In this connection it is well to note that in one or two of the jobs where the proportion of the aggregate seems too small for the yardage of concrete the difference is accounted for by the fact that large stones were placed in the foundations, these stone being on the ground and costing nothing but the labor to throw them in.

Job I.—The first job consisted of the construction of one abutment and six piers for a bridge over the Miami River at Fernald, O. The stone was procured on the site and crushed by a portable crusher run by a traction engine. The rough stone cost 10 cts. a cubic yard, and this, with the cost of handling, fuel and hire of engine and crusher, made the cost of crushed stone about $1 per cu. yd. Sand was obtained close to the work, but the cement had to be teamed 10 miles. Labor was paid $1.75 per day. The cost of materials and labor per cubic yard of concrete in place was as follows:

Job II.—The second job was the construction of two abutments containing 434 cu. yds. of concrete for a viaduct at Ernst Street, Cincinnati, O. The abutments were constructed at the street and the excavation was clay and shale. Labor received $1.75 per day. The cost of materials and labor per cubic yard of concrete in place was as follows:

Job III.—This job consisted in placing 570 cu. yds. of concrete in the pedestals for a viaduct at Quebec Avenue, Cincinnati, O. The pedestals were 5 ft. square on top and from 8 to 20 ft. high. The location of the work was very inconvenient for the delivery of materials, all materials having to be teamed or wheeled. Labor was paid $1.75 per day. The cost of labor and materials per cubic yard of concrete in place was as follows:

Job IV.—This job consisted in placing 2,111 cu. yds. of concrete in a railway viaduct at Cincinnati, O. For one pier 56 ft. high the concrete was raised to place by a derrick; for the remainder of the work it was wheeled or teamed to place. Labor was paid $1.75 per day. The cost of labor and materials per cubic yard of concrete in place was as follows:

CHAPTER XIII.

METHODS AND COST OF CONSTRUCTING RETAINING WALLS.

Concrete retaining walls may for construction purposes be divided into two classes: Plain concrete walls of gravity section and reinforced concrete walls consisting of a thin slab taking the thrust of the earth as a cantilever anchored to a base slab or as a flat beam between counterforts. The reinforced wall requires much less concrete for a given height than does the plain, gravity wall, but the concrete is more expensive owing to the reinforcement and to the more complex form of construction, and, in some measure, to the greater cost of placing the mixture in narrow forms and around reinforcement. It is common, too, to require a richer concrete for the reinforced than for the plain wall.

COMPARATIVE ECONOMY OF PLAIN AND REINFORCED CONCRETE WALLS.—Prior to the construction of some 2,000 ft. of retaining wall ranging in height from 2 ft. to 38 ft., at Seattle, Wash., calculation was made by the engineers of the Great Northern Ry. to determine the comparative economy of plain concrete and reinforced concrete sections. The sections assumed were those shown by Fig. 98, and comparisons were made at heights of 10, 20, 30 and 40 ft., with the following results: