Total. Per cu. yd.
Forms $ 3,312 $ 3.75 Concrete 5,532 6.25 ------- ------ Grand total $18,113 $20.50
In more detail the cost of the various items of concrete work was as follows for the whole structure, including abutments, wing walls and arch containing 884 cu. yds.:
Form Construction: Total. Per cu. yd.
Lumber and cartage $1,547 $1.75 Nails and bolts 129 0.15 Tools 110 0.12 Labor, erecting and removing 1,526 1.72 ------ ----- Total $3,312 $3.74
Concrete Construction.
Materials: Aetna cement at $1.05 $1,218 $1.37 Medusa cement at $1.75 499 0.56 Sand at 66 cts. per cu. yd. 37 0.04 Gravel at 85 cts. per cu. yd. 915 1.04 ------ ----- Total materials $2,669 $3.01
Mixing: Machinery and supplies $ 549 $0.62 Power at 6 cts. per kw. 52 0.06 Tools 22 0.02 Labor 737 0.83 ----- ----- Total mixing $1,360 $1.53
Placing concrete $ 609 $0.69 Tamping concrete $ 481 $0.54
Heating Concrete: Apparatus and cartage $ 47 $0.05 Fuel 96 0.11 Labor 270 0.31 ----- ----- Total heating $ 413 $0.47 Grand total $8,844 $9.98
Considering the abutment and wing wall work, comprising 594 cu. yds., separately, the cost was as follows:
Forms: Per cu. yd.
Materials $1.20 Labor 1.09 -----
Total $2.29 Concrete: Materials $2.92 Labor 2.38 -----
Total $5.30 Heating water and gravel $0.70 Grand total $8.29
Considering the arch span, comprising 290 cu. yds., separately, the cost was as follows:
Forms: Per cu. yd.
Materials $3.70 Labor 3.03 -----
Total $6.73 Concrete: Materials $3.22 Labor 3.57
Total $6.79 Grand total $13.52
CHAPTER XVIII.
METHODS AND COST OF CULVERT CONSTRUCTION.
Culvert work is generally located on the line of a railway or a highway, so that the facilities for getting plant and materials onto the work are the best, and as culverts are in most cases through embankment, under trestle or in trench below the ground level the advantage of gravity is had in handling materials to mixer and to forms. Ordinarily individual culverts are not long enough for any material economy to be obtained by using sectional forms unless these forms are capable of being used on other jobs which may occasionally be the case where standard culvert sections have been adopted by a railway or by a state highway commission. Various styles of sectional forms for curvelinear sections are given in Chapter XXI, and centers suitable for large arch culverts are discussed in Chapter XVII. Figure 169 shows an economic form for box sections; it can be made in panels or with continuous lagging as the prospects of reuse in other work may determine. For curvelinear sections of small size some of the patented metal forms have been successfully used.
~BOX CULVERT CONSTRUCTION, C., B. & Q. R. R.~--Mr. L. J. Hotchkiss gives the following data. Box sections of the type shown by Fig. 169 are used mostly; they range in size from single 44-ft. to double 2020-ft. and triple 1620-ft. boxes. These boxes are more simple in design and construction than arches, and for locations requiring piles they are less expensive. The form work is plain and the s.p.a.ce occupied is small as compared with arches, so that excavation, sheeting and pumping are less and the culvert can be put through an embankment or under a trestle with less disturbance of the original structure. Finally, less expensive foundations are required.
For small jobs where it does not pay to install a power mixer a hand power mixer mounted on a frame carried by two large wheels has been found at least as efficient as hand mixing; more convenient and easier on the men. The machine is turned by a crank driving a sprocket chain; it is charged at the stock piles and then hauled to the forms to be discharged. Local conditions determine the capacity of power mixer to be used. Difficulties in supplying material or in taking away the concrete may readily reduce the output of a large machine to that of one much smaller, and the small machine is cheaper in first cost and in installation and operation. Where the yardage is sufficient to justify the installation of equipment for handling the materials and output of a large mixer it is found preferable to a small one, as the increase in plant charges is not proportionately so great as the increase in the amount of concrete handled. Again it may occur on a small job that the concrete must be taken a long distance from the mixer, that a large batch can be moved as quickly and as easily as a small one and the time consumed in doing it is sufficient for the charging and turning of a large mixer before the concrete car or bucket returns to it. Here a large mixer, while it may stand idle part of the time, is still economic.
[Ill.u.s.tration: Fig. 169.--Box Culvert and Form, C., B. & Q. R. R.]
The plant lay-outs vary with the local conditions, as the following will show. In one case of a culvert located under a high, short trestle the following arrangement of plant was employed: A platform located on each side of the approach embankment about 8 ft. below the ties was built of old bridge timbers. A track was laid on each platform and ran out over a mixer located on the end slope of the embankment. Two mixers, one for each platform, were used. From each mixer a track led out over the culvert form and a track along the top of this form ran the full length of the culvert. Gravel and sand were dumped from cars onto the side platforms and thence shoveled into small bottom dump cars, which were pushed out over the mixer and dumped directly into it. Cars on the short tracks from mixers to culvert form took the mixed concrete and dumped it into the distributing cars traveling along the form. The cars were all hand pushed.
An entirely different lay-out was required in case of a long box culvert located in a flat valley some 600 ft. from the track. A platform was built at the foot of the embankment with its outer edge elevated high enough to clear two tracks carrying 5 cu. yd. dump cars. The sand and gravel was dumped from cars onto the side of the embankment, running down onto the platform so that sc.r.a.per teams moved it to holes in the platform where it fell into the dump cars. These cars were hauled by cable from the mixer engine and dumped at the foot of an inclined platform leading to a hopper elevated sufficiently to let a 1 cu. yd.
dump car pa.s.s under it. A team operating a drag sc.r.a.per by cable moved the material up the inclined platform into the hopper, whence it fell directly into the car to which cement was added at the same time. The charging car was then pulled by the mixer engine up another incline, at the top of which it dumped into the mixer. The concrete car was hauled up another incline to a track carried on the forms and reaching the full length of the culvert work.
The placing of the reinforcement is given close supervision. When a wet concrete is used it is found necessary to securely fasten the bars in place to prevent them being swept out of place by the rush of the concrete. A method of supporting the invert bars is shown by Fig. 169; 22-in. stakes are large enough and they need never be s.p.a.ced closer than 6 ft. The longitudinal bars are held on the stakes by wire nails bent over and the transverse bars are wired to them at intersections by stove pipe wire. The vertical wall bars are placed by thrusting the ends into the soft footing concrete and nailing them to a horizontal timber at the top; the horizontal wall bars are wired at intersections to the verticals. In the roof slab the stakes are replaced by metal chairs, or by small notched blocks of concrete.
The form construction is shown by Fig. 169. It is not generally made in panels, since, as the work runs, the locations of boxes of the same size are usually so far apart that transportation charges are greater than the saving due to use a second time. No general rule is followed in removing forms, but they can usually be taken down when the concrete is a week old.
The boxes are built in sections separated by vertical joints, one section being a day"s work. The vertical joints are plain b.u.t.t joints; tongue and groove joints give trouble by the tenons cracking off in the planes of the joints. A wet mixture is used and smooth faces obtained by spading.
~ARCH CULVERT COSTS, N. C. & ST. L. RY.~--The cost of arch culvert construction for the Nashville, Chattanooga & St. Louis Ry. is recorded in a number of cases as follows:
~18-ft. Arch Culvert.~--Mr. H. M. Jones is authority for the following data: An 18-ft. full-centered arch culvert was built by contract, near Paris, Tenn. The culvert was built under a trestle 65 ft. high, before filling in the trestle. The railway company built a pile foundation to support a concrete foundation 2 ft. thick, and a concrete paving 20 ins.
thick. The contractors then built the culvert which has a barrel 140 ft.
long. No expansion joints were provided, which was a mistake for cracks have developed about 50 ft. apart. The contractors were given a large quant.i.ty of quarry spalls which they crushed in part by hand, much of it being too large for the concrete. The stone was shipped in drop-bottom cars and dumped into bins built on the ground under the trestle. The sand was shipped in ordinary coal cars, and dumped or shoveled into bins. The mixing boards were placed on the surface of the ground, and wheelbarrow runways were built up as the work progressed. The cost of the 1,900 cu. yds. of concrete in the culverts was as follows per cu.
yd.:
1.01 bbls. Portland cement $2.26 0.56 cu. yds. of sand, at 60 cts. .32 Loading and breaking stone .25 Lumber, centers, cement house and hardware .64 Hauling materials .04 Mixing and placing concrete 1.17 Carpenter work .19 Foreman (100 days at $2.50) .13 Superintendent (100 days at $5.50) .29 ------ Total per cu. yd. $5.29
It will be seen that only 19 cu. yds. of concrete were placed per day with a gang that appears to have numbered about 21 laborers, who were negroes receiving about $1.10 per day. This was the first work of its kind that the contractors had done. It will be noticed that the cost of 42 cts. per cu. yd. for superintendence and foremanship was unnecessarily high.
~Six Arch Culverts 5 ft. to 16 ft. Span.~--All these arches were built under existing trestles, and in all cases, except No. 2, bins were built on the ground under the trestle and the materials were dumped from cars into the bins, loaded and delivered from the bins in wheelbarrows to the mixing boards, and from the mixing boards carried in wheelbarrows to place. Negro laborers were used in all cases, except No. 5, and were paid 90 cts. a day and their board, which cost an additional 20 cts.; they worked under white foremen who received $2.50 to $3 a day and board. In culvert No. 5, white laborers, at $1.25 without board, were used. There were two carpenters at $2 a day and one foreman at $2.50 on this gang, making the average wage $1.47 each for all engaged. The men were all green hands, in consequence of which the labor on the forms in particular was excessively high. The high rate of daily wages on culverts Nos. 1 and 3 was due to the use of some carpenters along with the laborers in mixing concrete. The high cost of mixing concrete on culvert No. 2 was due to the rehandling of the materials which were not dumped into bins but onto the concrete floor of the culvert and then wheeled out and stacked to one side. The cost of excavating and back-filling at the site of each culvert is not included in the table, but it ranged from 70 cts. to $2 per cu. yd. of concrete.
Cost of Six Concrete Culverts on the N., C. & St. L. Ry. & St. L. Ry.
No. of culvert 1 2 3 4 5 6 Span of culvert 5 ft. 7.66 ft. 10 ft. 12 ft. 12 ft. 16 ft.
Cu. yds. of concrete. 210 199 354 292 406 986 Ratio of cement to stone 1:5.5 1:6.5 1:5.8 1:5.8 1:6.1 1:6.5 Increase of concrete over stone 16.0% 9.9% 6.3% 12.3% 8.3% 5.3% Bbls. cement per cu.
yd. 1.02 0.90 1.06 1.01 1.00 1.09 Cu. yds. sand per cu.
yd. 0.43 0.49 0.44 0.46 0.46 0.47 Cu. yds. stone per cu. yd. 0.86 0.90 0.95 0.89 0.94 0.94 Total days labor (inc. foremen and supt.) 702 607 784 726 768 1,994 Av. wages per day (inc. foremen and supt.) $1.61 $1.33 $1.59 $1.19 $1.47 $1.46 Cost per cu. yd.-- Cement 2.18 1.94 2.27 1.82 2.11 2.01 Sand 0.17 0.20 0.18 0.18 0.19 0.14 Stone 0.52 0.52 0.47 0.54 0.47 0.58 Lumber 0.88 0.43 0.48 0.43 0.31 0.57 Unload, materials 0.23 0.17 0.18 0.18 0.16 Building forms 1.07 0.33 0.62 0.47 0.72 0.41 Mixing & placing 1.59 1.74 1.69 1.35 1.23 1.26 ------ ------ ------ ------ ----- -----
Total per cu. yd. $6.64 $5.33 $5.89 $4.97 $5.19 $4.97
~14-ft. 9-in. Arch Culvert.~--Mr. W. H. Whorley gives the following methods and cost of constructing a 12-ft. full centered arch culvert 204 ft. long. The culvert was built in three sections, separated by vertical transverse joints to provide for expansion; the end sections were each 61 ft. long and the center section was 70 ft. long. Fig. 170 is a cross-section at the center; for the end sections the height is 14 ft. 9 ins., the crown thickness is 1 ft. 9 ins., and the side walls at their bases are 5 ft. thick. The concrete was a 1-3-6 mixture, using slag aggregate for part of the work and stone aggregate for a part. The culvert was built underneath a trestle which was afterwards filled in.
_Mixing and Handling Concrete._--The height of the track above the valley permitted the mixing plant to be so laid out that all material was moved by gravity from the cars in which it was shipped until finally placed in the culvert. Sand and aggregate were received in drop bottom cars and were unloaded into bins in the trestle. These bins had hopper bottoms with chutes leading to a wheeling platform, which was placed between two trestle bents and extended over a mixer placed outside the trestle. The cement house was erected alongside the trestle at the wheeling platform level and a chute from an unloading platform at track level to the opposite end of the house enabled the bags to be handled directly from the car to the chute and thence run by gravity to the cement house. Sand and aggregate were chuted from the bins into wheelbarrows, wheeled about 23 ft., and dumped into a hopper over the mixer. Water was pumped by a gasoline engine from a well just below the trestle to a tank on the trestle, whence it was fed to the mixer by a flexible connection, a valve so regulating the flow that the necessary amount was delivered in the time required to mix a batch.
[Ill.u.s.tration: Fig. 170.--Section of Arch Culvert, N., C. & St. L. R.
R.]
The mixer was a No. 5 Chicago Improved Cube Mixer, operated by a gasoline engine; a larger size would have been preferable since a batch required only two-thirds of a bag of cement which had to be measured which required the services of an additional man. The mixer was in operation 194 hours and mixed 7,702 batches (1,217 cu. yds.), or a batch every 87 seconds, or 6.3 cu. yds. per hour. During the last ten days it mixed a batch every 78 seconds while running. The best short record made was 291 batches in five hours, or one batch every 63 seconds, this being at the rate of 58 batches equal to 9.2 cu. yds. of concrete in place per hour, or nearly 1/6 cu. yd. per batch. It took about minute to mix the concrete and about the same length of time to charge and discharge the mixer.
To convey the concrete from the mixer to the culvert walls a 1 cu. yd.
drop bottom car was used. This car ran on 30-in. gage tracks carried on a trestle straddling the culvert walls and having its floor high enough to clear the arch. A track ran lengthwise of the trestle over each culvert wall, and a cross track intersecting both with turntables ran to the mixer. Three men handled the car, a round trip to the extreme end of the trestle being made in about 3 minutes. In the meantime the mixer was discharging into a small hopper which unloaded into the car on its return. One only of the three sections, of the culvert was built at a time, both walls being brought up together. After a point had been reached about 2 ft. above the springing on both walls, one track was removed and the other was shifted to the center of the trestle.
_Forms._--There was used in the forms 15,000 ft. B. M. of 2-in. dressed lagging for face work, 21,000 ft. B. M. rough lumber for back work, and old car sills for studding. No charge was made for studding except the cost of loading, the cost of the remaining lumber was $16 per M. for dressed and $12.50 per M. for rough. A credit of one-third the cost was allowed for the old material recovered. The total cost of the labor of erecting the material in forms, bins and platforms was $666. The work was done by a bridge crew of white men, the average rate of wages per man, including the bridge foreman"s time, being $2.20 per day. In addition a mason at $3.50 per day and a carpenter at $2.25 per day worked with the bridge crew in erecting forms.