6,000 bbls. cement at $2.05 $12,300 2,500 cu. yds. sand at $0.80 2,000 5,000 cu. yds. stone at $0.85 4,250 260 M. ft. B. M. lumber at $17 4,420 ———- Total $22,970
Cofferdams, excavation and pumping $ 3,000 Forms, falseworks and centers 2,000 Mixing and placing concrete 4,000 Placing reinforcement 400 Removing falseworks, forms, etc. 1,200 One coat pitch and paper 150 Building plant, etc. 2,250 ———- Total $13,000
Mr. Harrison states that including plant cost, delays, floods and incidentals the cost per cubic yard of concrete was $8 and that excluding these items the cost was $6 per cu. yd.
COST OF CONSTRUCTING CONCRETE HIGHWAY BRIDGE, GREENE COUNTY, IOWA.—The following is the itemized cost of constructing a reinforced concrete slab highway bridge, one of several built by the Highway Commissioners of Greene County, Iowa, in 1906. The figures are given by Messrs. Henry Haag and D. E. Donovan, the last being the foreman of the concrete gang doing the work. All bridges consist of 10 to 12-in. slabs reinforced with old steel rails and of abutments and wing walls reinforced with old rods, bars or angles selected from junk. This junk metal cost 0.6 cts. per pound and the rails cut to length cost 1.15 cts. per pound f. o. b. cars. The work was done by a special gang, the men receiving $1.50 per day and board. As a rule the footings were made 2 ft. wide and as high as need be to get above the water and dirt. Before the footing concrete set steel rods, bars or angles were placed; they were long enough to reach the height of the wall and 3 to 6 ins. into the slab. The forms for the abutment and wing walls and for the floor slab were then erected complete before any more concrete was placed. No carpenter was employed, every man on the job having been taught to take his certain place in the work, then, the forms being erected, every man had his particular place in the work of mixing and placing the concrete. The foreman saw that the reinforcement was properly placed and watched over the accuracy of the work generally. The concrete was allowed to set on the centers for from 30 to 40 days; the other form work was taken down after three days and travel over the bridge permitted after three or four days. The concrete was mixed wet. The bridge whose cost is given was 22 ft. wide and 16 ft. span with 2-ft. wing walls.
The foundations are 4 ft. deep and 2 ft. wide. The walls on top of the foundations are 7 ft. high, 18 ins. wide at the base, and battered up to 14 ins. at the top for wings and 12 ins. at top for walls. The floor is 22 ft. by 18 ft. and 1 ft. thick. The wheel guard is 12 ins. thick by 14 ins. wide and 32 ft. long. The itemized cost of this bridge, containing 73 cu. yds. of concrete, is as follows:
Materials. Total. Per cu. yd. 70 cu. yds. gravel at 70 cts $ 49.00 $0.6726 10 cu. yds. broken stone at 70 cts 7.00 0.0959 75 bbls. cement at $2.20 165.00 2.2603 7,000 lbs. steel rails at 1.15 cts 80.50 1.1027 1,000 lbs. junk rails at 0.6 cts 6.00 0.0819 200 ft. B. M. lumber wasted at $29 5.80 0.0794 15 lbs. nails at 3 cts 0.45 0.0061
Labor and Supplies: 2 days excavation at $14 28.00 0.3835 day foundation at $14 10.00 0.1369 1 days building forms at $14 21.00 0.2876 2 days filling forms at $14 28.00 0.3835 Hauling lumber and tools 8.00 0.1096 Hauling cement and tools 18.00 0.2465 Taking off forms 2.30 0.0315 1,000 lbs. coal at $4 per ton 2.00 0.0274 ——— ———- Total cost $431.05 $5.9054
In round figures the cost per cubic yard of concrete in the finished bridge was $5.90. Summarizing we have the following cost per cubic yard of concrete in place:
Item. Per cu. yd. Cement $2.26 Steel 1.22 Lumber 0.22 Gravel and stone 0.76 Labor 1.41 Coal 0.03 ——- Total $5.90
The average cost of concrete in place for all the work done in Greene County by day labor was $6.25 per cu. yd. In the job itemized above the bank caved in, causing an extra expense for removing the earth. The gravel used in this bridge was very good clean river gravel.
METHOD AND COST OF CONSTRUCTING TWO HIGHWAY GIRDER BRIDGES.—The following account of the methods and costs of constructing two slab and beam highway bridge decks on old masonry abutments is taken from records kept by Mr. Daniel J. Hauer. The first bridge was a single span 15 ft. long that replaced wooden stringers and floor that had become unsafe; the second was two short spans of a steel bridge that was too light for the traffic of the road, and it was torn down and moved elsewhere, by the county authorities. The work was done by contract, and in each case consisted of building the reinforced floor and girders on the old masonry walls that were in good condition. While the work was going on traffic was turned off the bridges, fords being used instead. Figure 154 shows a sketch of the cross-section of the floor and girders. In Example I the girders had a depth below the floor of 12 ins. and were of the same width. In Example II the girders were 14 ins. wide and had a depth below the floor of 18 ins. The floors on both bridges were 6 ins. thick. Kahn bars were used for reinforcement.
Example I.—This bridge was but little more than 5 ft. above the stream, which was shallow and not over 7 ft. wide, unless swollen by floods. The bottom for several hundred feet on either side of the bridge was covered with coarse sand and gravel, that had pebbles in it from the size of a goose egg down. This was taken from the stream by men with picks and shovels and hauled to the site of the work with wheelbarrows, and then screened so as to separate the gravel from the sand. As it was found that the sand was so coarse that it would take more cement than the specifications called for in a 1-2-5 mixture, some much finer sand was bought and mixed with it. For the privilege of taking the sand from the stream $1 was paid the property owner. This was done to get a receipt and release from him, rather than as an attempt to pay royalty on the gravel and sand. This dollar is included in the cost of the labor in getting these materials.
The cost of materials per cubic yard for the bridge was as given below, the mixture being as stated above. The cement cost $1.40 per barrel, delivered at the bridge.
Per Cu. Yd. Steel $2.50 Gravel and sand .75 Sand (bought) .30 Cement 1.57 ——- Per cubic yard $5.12
It is of interest to note the cost of the gravel and sand, as this includes the cost of digging it, wheeling it in a wheelbarrow an average distance of 100 ft., and then screening it and putting it in two stock piles. The proportion of bought sand used with the creek sand was one-half.
The old wooden floor and stringers had to be torn down. This was done at a cost of $1.30 per M. ft. B. M., and furnished 60 per cent. of the lumber needed for forms. The floor boards were 3-in. yellow pine planks, and the stringers 612-in. timbers, rather heavy, but money was saved by using them. The 612-in. timbers were used for props for the centering. Additional lumber was bought, delivered at the site of the bridge, for $20.84 per M. ft. B. M.
In framing and erecting the forms the carpenter had laborers helping him, he doing only carpenter's work, the laborers carrying and lifting all pieces wherever possible. The carpenter's work was about 40 per cent. of the total labor cost, which was as follows per cubic yard of concrete:
Tearing down old bridge $0.08 Lumber .85 Nails .15 Labor, carpenter .77 Labor, laborers .96 ——- $2.81
The forms were torn down by laborers, with the assistance of a man and his helper, who were given the boards for this labor and to haul them away. This reduced this item somewhat, as it only amounted to 20 cts. per cu. yd.
The cost of the forms per thousand feet board measure was:
New lumber $20.82 Nails 1.44 Labor, carpenter 7.60 Labor, laborers 9.50 Tearing down 2.00 ——— $41.36
All the men, including the carpenter, worked 10 hours per day, and were paid at the following rates:
Carpenter $2.50 Sub-foreman 2.00 Laborers 1.50
A regular foreman was not employed, but an intelligent and handy workman was given 50 cts. additional to lead the men and look after them when the contractor was not present.
A gang of six men did the work of mixing and placing, and as the stock piles were close by the mixing board no extra men were needed to handle materials. Water was secured from the stream in buckets for mixing. The mixture was made very wet. The cost per cubic yard for the entire structure was as follows:
Preparing for mixing $0.04 Cleaning out forms .06 Handling steel .03 Mixing and placing 1.15 Ramming .23 ——- $1.51
The cost of the contractor's expense of bidding, car fare, etc., is listed under general expense, and gives a total cost per cubic yard of:
Materials $ 5.12 Erecting forms 2.81 Tearing down forms .20 Labor 1.51 General expense 2.00 ——— $11.64
Example II.—For this bridge both the stone and sand had to be bought. The bridge floor was nearly 14 ft. above the bottom of the stream, which was shallow. The wages paid were as follows for a 10-hour day:
Foreman $3.00 Laborers 1.50
Carpenters were paid $3 for an 8-hour day and time and a half for all overtime, which they frequently made.
For the girders a 1-2-4 mixture was used. The cement, delivered at the bridge, cost $1.21 per barrel, there being 8 cts. a barrel storage and 8 cts. a barrel for hauling included in this. The sand was paid for at an agreed price per cartload delivered, which averaged $1.34 per cu. yd. The stone was crushed so as to pass a 1-in. ring in all directions. It was delivered at the bridge for $2.75 per cu. yd. This makes the cost per cubic yard for materials as follows:
Steel $1.41 Cement 2.18 Sand .67 Stone 2.75 ——- $7.01
For the floor a 1-3-5 mixture was used, making a cost for material of:
Steel $1.02 Cement 1.69 Sand .67 Stone 2.75 ——- $6.13
Two-inch rough pine boards were used to make the troughs for the girders, while 1-in. rough boards were used for the floors. These were all supported by 34-in. pine scantlings. This lumber cost delivered $17.50 per M. ft. B. M. Carpenters did all the framing, and erected it with the help of laborers. All the carrying of the lumber was done by laborers. This reduced the cost of the work, as the laborers' wages amounted to one-third of the whole cost. As soon as the forms were all in place, which was before the mixing of concrete commenced, the carpenters were discharged. The cost per cubic yard for forms was:
Lumber $2.82 Nails .05 Labor, carpenters 1.24 Laborers .62 ——- $4.73
The tearing down of the forms was done entirely by laborers at a cost of 61 cts. per cu. yd.
On concrete work it is also advisable to keep the cost of forms per thousand feet board measure, so as to have such data for estimating on new work. The cost per M. ft. on this job was:
Lumber $17.50 Nails .30 Labor, carpenters 7.65 Laborers 3.85 Tearing down 3.80 ——— $33.10
The concrete was mixed by hand, water being carried in buckets from the creek. Ten to twelve men were worked in the gang under a foreman, and the concrete was wheeled from the mixing board to the forms in wheelbarrows. The mixture was made wet enough to run. The cost per cubic yard for the girders in detail was as follows:
Foreman $0.41 Preparing for mixing 0.14 Cleaning out forms 0.07 Handling materials 0.30 Handling and placing steel 0.40 Mixing and placing 0.87 Ramming 0.45 ——- $2.64
The cost of labor for the floor was:
Foreman $0.28 Preparing for mixing 0.08 Cleaning out forms 0.05 Handling materials 0.14 Handling and placing steel 0.08 Mixing and placing 0.87 Ramming 0.36 ——- $1.86
This gives a total cost per cubic yard for the concrete in the girders in the completed bridge as follows:
Materials $ 7.01 Erecting forms 4.73 Tearing down forms 0.61 Labor 2.57 General expense 1.60 ——— $16.52
The cost per cubic yard for the floor was:
Materials $ 6.13 Erecting forms 4.73 Tearing down forms 0.61 Labor 1.86 General expense 1.60 ——— $14.93
Included with this is an item for general expense, being expenses of the contractor in bidding on the work, car fare, and other items of expense in looking after the contract.
It will be noticed that a record is here given of three different mixtures and that the labor cost of mixing and placing increases with the richness of the mixture. This is because it takes a greater number of batches to the cubic yard. Record has also been given of cost of preparing the mixing board and other work necessary to start and clean up each day; also when stock piles could not be arranged close to the mixing board, of the cost of handling the materials. These items, it will be noticed, are large enough to be considered in estimating on new work. The cost of sweeping and cleaning out the forms has also been listed, as this work is extremely important.
The cost of the reinforcing steel is given in with the materials, but the labor of handling it and placing it in the forms is listed under labor. This naturally varies with the amount of steel needed, and with the Kahn bar it will vary from 10 cts. to 75 cts. per cubic yard, as the prongs of the bar must be bent into proper position and at times straightened, when bent in shipment. This cost seems large, but it is done with the ordinary labor, while with round rods a large amount of blacksmith work has to be done and a smith and his helper frequently must place them. The patent bars are all lettered and numbered as structural steel is, and can be placed under the direction of the foreman.
One striking lesson can be learned from the forming. It will be noticed that the cost for common labor for handling and helping to erect the forms was much larger in Example I than in Example II, although the bridge was higher in the latter instance. This was caused by the heavy timber that was used, and equaled an extra cost nearly 50 per cent. of the price of new lumber. It certainly speaks volumes against the use of unnecessarily heavy timber for concrete forms.
In bridge work the height of the floor above the stream to some extent governs the cost of the forms. This is made so by the extra lumber needed as props or falsework to support the forming, and also by the fact that men at some height above the ground do not work as quickly or as readily as they do nearer the ground. For high and long spans a derrick is sometimes needed for the work of placing the centering.
On these jobs the concrete was made so wet that with the proper tamping and cutting of the concrete in the forms the surfaces were so smooth that no plastering was needed.
MOLDING SLABS FOR GIRDER BRIDGES.—The bridges carry railway tracks across intersecting streets; the slabs rest on two abutments and three rows of columns so that there are two 24-ft. spans over the street roadway and one 10-ft. span over each sidewalk. The larger slabs were 24 ft. 3 ins. long, 33 ins. thick and 7 ft. wide; each contained 16 cu. yds. of concrete and weighed 36 tons. The smaller slabs were 10 ft. 9 ins. long, 17 ins. thick and 7 ft. wide; each contained 3.65 cu. yds. of concrete and weighed 7.8 tons. The weights were found by actual weighing. They make the weight of the reinforced slab between 160 and 162 lbs. per cu. ft. The concrete was generally 1 part cement and 4 parts pit gravel. The reinforcement consisted of corrugated bars. The method of molding was as follows:
A cinder fill yard was leveled off and tamped, then the forms were set up on both sides of two lines of railway track arranged as shown by Fig. 155. The exact construction of the forms for one of the larger slabs is shown by Fig. 156. The side and end pieces were so arranged as to be easily taken down and erected for repeated use. About 100 floors were used and they had to be leveled up each time used as the lifting of the hardened slab disarranged them. The side and end pieces were removed in about a week or ten days, but the slabs stood on the floor 90 days, being wetted each day for two weeks after molding.
The plant for mixing and handling the concrete was mounted on cars. A flat car had a rotary drum mixer mounted on a platform at its forward end. Beneath the mixer was a hopper provided with a deflector which directed the concrete to right or left as desired. Under the hopper were the ends of two inclined chutes extending out sidewise beyond the car—one to the right and one to the left—and over the slab molds on each side. Above the mixer was another platform containing a charging hopper, and from the rear of this platform an incline ran down to the rear end of the car and then down to the track rails. A car loaded with cement and gravel in the proper proportions was hauled up the incline by cable operated by the mixer engine, until it came over the topmost hopper into which it was dumped. This hopper directed the charge into the mixer below; the mixer discharged its batch into the hopper beneath from which it flowed right or left as desired into one of the chutes and thence into the mold. The chutes reached nearly the full length of the molds and discharged as desired over the ends into the far end of the mold or through a trap over the end of the mold nearest the car.
To the rear of the mixer car came a cement car provided with a platform overhanging its forward end. Two hoppers were set in this platform each holding a charge for one batch. Coupled behind the cement cars came three or four gravel cars. These were gondola cars and plank runways were laid along their top outer edges making a continuous runway for wheelbarrows on each side from rear of train to front of cement car. The sand and gravel were wheeled to the two measuring hoppers and the cement was handed up from the car below and added, the charge was then discharged into the dump car below and the car was hauled up the incline to the mixer as already described. Two measuring hoppers were used so that one was being filled while the other was emptied, thus making the work continuous.
The molding gang consisted of 33 laborers, two foremen and one engineman. This gang averaged 7 of the large slabs per 10-hour day and at times made as many as 9 slabs. When molding small slabs an average of 12 were made per day. This record includes all delays, moving train, switching gravel cars on and off, building runways, etc. The distribution of the men was about as follows:
Handling Materials: No. Men.
Shoveling gravel into wheelbarrows 9 Wheeling gravel to measuring hoppers 9 Emptying cement into measuring hoppers 2 Handling cement to men emptying 1 In charge of loading dump car 1 On top of cement car 1 Sub-foreman in charge 1
Mixing and Placing:
Engineer 1 In charge of mixer 1 Hoeing and spreading in mold 2 Spading in mold 2 Finishing sides of block 2 General laborers 3 Foreman in charge 1 — Total men 36
This gang mixed and placed concrete for 7 blocks or 117 cu. yds. of concrete per day. Assuming an average wage of $2 per day the cost of labor mixing and placing was 61.4 cts. per cu. yd. or $10.28 per slab. It is stated that the slabs cost $11.80 per cu. yd. on storage pile. This includes labor and materials (concrete and steel); molds; loading into cars with locomotive crane, hauling cars to storage yard and unloading with crane into storage piles, and inspection, incidentals, etc. To load the slabs into cars from storage piles, transport them to the work and place them in position is stated to have cost $2 per cu. yd. The slabs were placed by means of a locomotive crane being swung from the flat cars directly into place.
METHOD AND COST OF CONSTRUCTING CONNECTICUT AVE. BRIDGE, WASHINGTON, D. C.—The Connecticut Ave. Bridge at Washington, D. C., consists of nine 150-ft. spans and two 82-ft. spans, one at each end, all full centered arches of mass concrete trimmed with tool-dressed concrete blocks. Figure 157 is a part sectional plan and elevation of the bridge, showing both the main and spandrel arch construction. This bridge is one of the largest concrete arch bridges in the world, being 1,341 ft. long and 52 ft. wide, and containing 80,000 cu. yds. of concrete. Its total cost was $850,000 or $638.85 per lin. ft., or $10.63 per cu. yd. of masonry. It was built by contract, with Mr. W. J. Douglas as engineer in charge of construction. The account of the methods and cost of construction given here has been prepared from information obtained from Mr. Douglas and by personal visits to the work during construction.
General Arrangement of the Plant.—The quarry from which the crushed stone for concrete was obtained was located in the side of the gorge at a point about 400 ft. from the bridge. Incidentally, it may be added, the fact that the contractor had an option on this quarry gave him an advantage of some $30,000 over the other bidders. The stone from the quarry was hoisted about 50 ft. by derricks and deposited in cars which traveled on an incline to a Gates gyratory crusher, into which they dumped automatically. The stone from the crusher dropped into a 600-cu. yd. bin under the bottom of which was a tunnel large enough for a dump car and provided with top gates by which the stone above could be dropped into the cars. The cars were hauled by cable to the mixer storage bin and there discharged. Sand was brought in by wagons and dumped onto a platform about 50 ft. higher than the bottom of the main stone bin. A tunnel exactly similar to that under the stone bin was carried under the sand storage platform. The sand car was hauled from this tunnel by cable to the mixer storage bin using the same cable as was used for the stone cars, the cable being shifted by hand as was desired. Cement was delivered to the mixer platform from the crest of the bluff by means of a bag chute.
The mixer used was one of the Hains gravity type. It had four drops and was provided with four mixing hoppers at the top. The concrete was made quite wet. The proportions of sand and water were varied to suit the stone according to its wetness and the percentage of dust carried by it. The head mixer regulated the proportions and his work was checked by the government inspector. From the bottom hopper the mixed concrete dropped into a skip mounted on a car.
To distribute the skip cars along the work a trestle was built close alongside the bridge and at about springing line level. This trestle had a down grade of about 2 per cent. from the mixer. Derricks mounted along the centering and on the block molding platform lifted the skips from the cars and deposited them where the concrete was wanted. The skip cars were large enough for three skips but only two were carried so that the derricks could save time by depositing an empty skip in the vacant space and take a loaded skip away with one full swing of the boom. Altogether nine derricks were used in the bridge, four having 70-ft. booms and five having 90-ft. booms. These derricks were jacked up as the work progressed.
Forms and Centers.—The forms for wall and pier work consisted of 1-in. lagging held in place by studs about 2 ft. on centers and they in turn supported by wales which were connected through the walls by bolts, the outer portions of which were removed when the forms were taken down.
The centers for the five 150-ft. arches were all erected at one time; those for the 82-ft. arches were erected separately. The seven centers required 1,500,000 ft. B. M. of lumber or 1,404 ft. B. M. per lineal foot of bridge between abutments, or 1,640 ft. B. M. per lineal foot of arch span. The centers for the main arch spans are shown in detail by Fig. 158; this drawing shows the sizes of all members and the maximum stresses to which they were subjected from the loading indicated, that is the arch ring concrete. The centers as a rule rested on pile foundations. Four piles to each post were used for the intermediate posts and two piles for the posts in the two rows next the piers. Concrete foundations, however, were put in Rock Creek and on the line of Woodley Lane Bridge where it was impracticable to drive piles. As considerable difficulty was experienced in driving the piles, the ground consisting mostly of rotten rock, it is thought that it would have cost less if the contractor had used concrete footings throughout.
Some of the costs of form work and centering are given. The cost of lumber delivered at the bridge site was about as follows:
M. ft. B. M. Rough Virginia pine $25 Dressed Virginia pine lagging 23 Rough Georgia, sizes up to 1212 ins. 33 Rough Georgia, sizes over 1212 ins. 35 Rough oak lumber 35
The following wages were paid: Foreman carpenter, $3.50; carpenters, $2 to $3; laborers, $1.70, with a few at $1.50. An 8-hour day was worked.
The cost, of formwork is given in summary as follows:
Lagging per M. ft. (used twice): Lumber at $23 $11.50 Erection 15.00 ——— Total cost erected $26.50
Studding and rough boards used in place of lagging per M. ft. (used twice):
Lumber at $25 $12.50 Erection 10.00 ——— Total cost erected $22.50
Wales per M. ft. (used six times):
Lumber at $36 $ 6.00 Erection 10.00 ——— Total cost erected $16.00
The total cost of the main arch span centers to the District of Columbia was $54,000 or $59 per lineal foot of arch span, or $37.33 per M. ft. B. M. The cost of center erection and demolition was as follows:
Erection below springing line per M. ft. $15 Erection above springing line per M. ft. 25 Demolition 5
The salvage on the centers amounted to $11 per M. ft. B. M.
The spandrel arch centers were each used twice and cost per M. ft. B. M. for
Lumber at $25 per M. ft. $12.50 Erecting at $25 per M. ft. 25.00 Moving at $5 per M. ft. 5.00 Total per M ft. 42.50
Molding Concrete Blocks.—The bridge is trimmed throughout with molded concrete blocks, comprising belt courses, quoin stones, chain stones, ring stones, brackets and dentils. The blocks were made of a 1-2-4 concrete faced with a 1-3 mixture of Dragon Portland cement and bluestone screenings from 3/8-in. size to dust. They were cast in wooden molds with collapsible sides held together by iron rods. Each mold was provided with six bottoms so that the molded block could be left standing on the bottom to harden while the side pieces were being used for molding another block. The molding was done on a perfectly level and tight floor on mud sills, the perfect level of the molding platform having been found to be an important factor in securing a uniform casting. The blocks were molded with the principal showing face down and the secondary showing faces vertical. The facing mortar was placed first and then the concrete backing. Care was taken to tamp the concrete so as to force the concrete stone into but not through the facing. Mr. Douglas remarks that the back of the block should always be at the top in molding since the laitance or slime always flushes to the surface making a weak skin which will develop hair cracks. In this work the backs of the blocks were mortised by embedding wooden cubes in the wet concrete and removing them when the concrete had set. These mortises bonded the blocks with the mass concrete backing. The blocks were left to harden for at least 30 days and preferably for 60 days and were then bush hammered on the showing faces, some of the work being done by hand and some with pneumatic tools.
Some precautions necessary in the molding and handling of large concrete blocks were discovered in this work and merit mention. In designing blocks for molding it is necessary to avoid thin flanges or the flanges will crack and break off; blocks molded with a 2 in. flange projecting 1 ins. gave such trouble from cracking on this work that a flange 5 ins. thick was substituted. Provide for the method of handling the block so that dog or lewis holes will not come in the showing faces. Dog holes can be made with a pick when the concrete is three or four weeks old. When it is not practicable to use dogs, two-pin lewises can be used. The lewis holes should be cast in the block and should be of larger size than for granite; they should not be located too near the mortar faces. In turning blocks it is necessary to provide some sort of cushion for them to turn on or broken arrises will result. When the work will permit, it is desirable to round the arrises to about a 3/8-in. radius.
The following general figures of the cost of block work are available. Foreman cutters were paid $5 per day; foreman concrete workers $3 per day; stonecutters $4 per day; concrete laborers $1.70 per day, and common laborers $1.50 to $1.70 per day. Plain and ornamental blocks cost about the same, the large size of the ornamental blocks bringing down the cost. The following is given as the average cost of block work per cubic yard:
Cement $ 1.95 Sand 0.35 Stone 1.14 Forms, lumber and making 0.80 Mixing and placing concrete 1.50 Dressing 4.73 Handling and setting 2.00 Superintendence, plant, incidentals at 25 per cent. 3.12 Condemnation at 5 per cent. 0.78 ——— Total cost blocks in place $16.37
It will be seen that the largest single item in the above summary of costs is the item of dressing. This was done, as stated above, partly by hand and partly by pneumatic tools. Hand tooling cost about twice as much as machine tooling, but its appearance was generally better. The average cost of tooling the several forms of blocks is shown by Table XIX. For 42,190 sq. ft. the average cost was 26 cts. per sq. ft. or $2.34 per sq. yd., or $4.73 per cu. yd. of block work. This tooling was done by stone cutters, and was unusually high in cost.
Mass Concrete Work.—All parts of the bridge except the molded block trim were built of concrete deposited in place. Briefly, the molded blocks were set first and then backed up with the mass concrete deposited in forms and on centers. The only features of this work that call for particular description are those in connection with the main arch ring and the spandrel arch construction.
The main arch rings were concreted in transverse sections; Fig. 158 shows the size and order of construction of these sections. Back forms were necessary up to an angle of 45 from the spring line after which the concrete was made somewhat drier and back forms were not used. After Sections 1, 2, 3 and 4 had been concreted they were allowed to set and then the struts and back forms were taken out and the intervening sections were concreted. The large Sections 6 and 7 were concreted in five sections each, in order to permit the taking out of the timber struts supporting the sections above. The concrete in all sections was placed in horizontal layers as a rule and it is the judgment of the engineers in charge of this work that this is the preferable method.
TABLE XIX.—SHOWING COST OF TOOLING CONCRETE ORNAMENTAL BLOCKS FOR CONNECTICUT AVENUE BRIDGE.
=============================================================================== Per Superficial Foot of Per Cubic Foot. Showing Face. - - DESCRIPTION. Num- Number ber Super- Cost super. 1: 2: 4 Concrete Backing Total cubic Total Cost ficial Total per ft. to 1: 3 (Mortar Face). Number feet cubic per feet super- super- one Stones in feet cubic in ficial ficial cubic Cut. each. cut. foot. each. feet. foot. foot. - - - Brackets under Lamps and Rail Posts (Cap and Base) 344 16.0 5,500 $0.27 10.5 3,630 $0.41 0.66 Moulding under coping 770 5.9 4,560 0.30 3.8 2,930 0.47 0.64 Dentils between Moulding 520 5.5 2,860 0.20 8.0 4,160 0.14 1.45 Coping 494 61.2 30,220 0.12 35.4 17,490 0.21 0.58 Pedestal (3 courses) 162 27.2 4,400 0.15 14.1 2,290 0.29 0.52 Rail Posts (Top and Base) 296 7.1 2,100 0.50 17.3 5,100 0.21 2.43 Lamp Posts and Parapets over Piers (Top and Base) 248 22.9 5,690 0.17 26.5 6,580 0.15 1.16 - - - Average of above Totals 2,834 19.5 55,330 $0.17 14.8 43,190 $0.26 0.77 - - -
TABLE XX.—SHOWING COST OF MASS CONCRETE WORK PER CUBIC YARD.
[Transcriber's note: Table split]
=========================================================================== Cost Delivered on Mixer. Description. - Average Yardage Propor- for Days Total tions. Run. Cement. Sand. Stone. Materials. - - - -+ Class A, in Piers 1:2:4 150 1.65 0.39 1.08 3.12 Class A, in Arches 1:2:4 200 1.65 0.39 1.08 3.11 Class B, in Piers Solid Work 1:3:6 160 1.40 0.42 1.23 3.05 Class B, in Piers Hollow Work 1:3:6 110 1.40 0.42 1.23 3.05 Class B, in Spandrel Walls 1:3:6 110 1.40 0.42 1.23 3.05 Class B, in Spandrel Arches 1:3:6 200 1.40 0.42 1.23 3.05 Class B, in Abutments 1:3:6 150 1.40 0.42 1.23 3.05 Class C, Filling over Bridge 1:3:10 145 0.90 0.31 1.30 2.51 -+ - - -
=============================================== Cost of Mixing and Placing. Description. Total Mixing and Mixing. Placing Placing - Class A, in Piers 0.09 0.21 0.30 Class A, in Arches 0.05 0.28 0.33 Class B, in Piers Solid Work 0.09 0.18 0.27 Class B, in Piers Hollow Work 0.11 0.36 0.47 Class B, in Spandrel Walls 0.11 0.40 0.51 Class B, in Spandrel Arches 0.07 0.26 0.33 Class B, in Abutments 0.11 0.24 0.35 Class C, Filling over Bridge 0.11 0.28 0.39 -
========================================================================= Cost of Form Work. Description. - - - Taking Total Total Cost Erecting. Down Lumber. Form Work per Yard.[G] - - - - Class A, in Piers 0.17 0.05 0.16 0.38 $3.80 Class A, in Arches 0.08 0.03 0.10 0.21 3.66 Class B, in Piers Solid Work 0.17 0.05 0.16 0.38 3.70 Class B, in Piers Hollow Work 0.77 0.25 0.64 1.66 5.18 Class B, in Spandrel Walls 0.85 0.28 0.73 1.86 5.42 Class B, in Spandrel Arches 0.94 0.30 0.86 2.10 5.48 Class B, in Abutments 0.10 0.03 0.12 0.25 3.65 Class C, Filling over Bridge 0.00 0.00 0.00 .... 2.90 - - - -
[Footnote G: Add 25% to the cost here tabulated for superintendence, plant and incidentals.]
Considerable difficulty was experienced in building the large arches with a concrete block facing on account of the fact that the edges of the blocks are liable to chip off when any concentrated pressure is brought on them. In order to permit the ring of blocks to deform as the centering settled under its load, sheet lead was placed in the joints between blocks at the points corresponding with the construction joints between sections of the mass concrete backing. The deflection of the centers at the crown was a maximum of 3 ins. and a minimum of 2 ins.
TABLE XXI—Detail Cost of Engineering and Inspection for Different Classes of Work.
Engineering. Inspection. Kind of Work. Total. Unit. Total. Unit. Class A, concrete, 23,500 cu. yds $3,055.00 $0.13 $1,762.50 $0.075 Class B, concrete, 36,580 cu. yds 3,658.00 0.10 1,646.10 0.045 Class C, concrete, 2,150 cu. yds 107.50 0.05 53.75 0.025 Class D, concrete, 6,250 cu. yds 1,875.00 0.30 4,687.50 0.75 1,000 M. ft. B. M. centering 1,000.00 1.00 440.00 0.44 Cement, 73,000 barrels 365.00 0.005 730.00 0.01 Earth filling, 50,000 cu. yds 1,000.00 0.02 500.00 0.01
The centering of the main arches was not struck until the spandrel arches and all the work above the main arches to the bottom of the coping had been completed. The first and third spandrel arch on each side of the piers was made with an expansion joint in the crown. To permit further of the adjustment of the portion of the masonry above the backs of the main arches, the crown of the middle arch of each set of spandrel arches was left unconcreted until the center of the main arches had been struck. It may be noted here that the expansion joints in the first and third arches were carried up through the dentils and coping, and observations show that these joints are about 1/8 in. larger in winter than in summer.
The cost of the mass concrete work is shown in Table XX. These figures are based on the wages already quoted and the following: Foreman riggers, $4.50; riggers, $1.50 to $1.75 and $2; skilled laborers, $2; engineers, $3.50. The detail cost of engineering and inspection is shown in Table XXI.
ARCH BRIDGES, ELKHART, IND.—At the new Elkhart, Ind., yards of the Lake Shore & Michigan Southern Ry. the tracks are carried over a city street by concrete arches 40, 60 and 160 ft. long. These arches all have a span of 30 ft., a height of 13 ft. and a ring thickness at crown of 28 ins. The reinforcement consists of arch and transverse bars; the arch bars are spaced 6 ins. on centers 2 ins. from both extrados and intrados, and the transverse bars are spaced 24 ins. on centers inside both lines of arch bars. The proportions of the concrete were generally 1 cement, 3 gravel and 6 stone. The gravel was a material dug from the foundations and was about 50 per cent. sand and 50 per cent. gravel, ranging up to the size of pigeons' eggs. The concrete was machine mixed and was mixed very wet.
The work was done by the railway company's forces, and Mr. Samuel Rockwell, Assistant Chief Engineer, gives the following figures of cost:
Total. Per cu. yd. Temporary buildings, trestles, etc. $ 752.33 $0.15 Machinery, pipe fittings, etc. 416.34 0.08 Sheet piling and boxing 1,006.12 0.21 Excavation and pumping 1,619.74 0.33 Arch centers and boxing 3,528.92 0.73 ————- ——- Total $7,323.45 $1.50
Concrete masonry: Cement 8,860.55 1.84 Stone 1,788.50 0.36 Sand 240.00 0.05 Drain tile 103.03 0.02 Labor 8,091.41 1.68 ————— ——- Total concrete $19,083.49 $3.95 Steel reinforcing rods $ 3,028.39 $0.63 Engineering, watching, etc. 508.40 0.11 ————— ——- Grand total (4,833 cu. yds. concrete) $29,943.73 $6.19
ARCH BRIDGE, PLAINWELL, MICH.—The following figures of cost of a reinforced concrete arch bridge are given by Mr. P. A. Courtright. The bridge crosses the Kalamazoo River at Plainwell, Mich., and is 446 ft. long over all with seven arches of 54 ft. span and 8 ft. rise. The arch rings were reinforced with 4-in., 6-lb. channels bent to a radius of 70 ft. and spaced 1.9 ft. c. to c. The contract price of the bridge was $19,900.
The concrete was made of Portland cement and a natural mixture of sand and gravel in the proportions of 1-8 for the foundations, 1-6 for arches and spandrel walls and 1-4 for the parapet wall. The proportions were determined by measure; the wagon boxes being built to hold a cubic yard of sand and gravel. A sack of cement was taken as 1 cu. ft. For foundations the pit mixture was used without screening; stones over 4 ins. in diameter being thrown out at the pit or on the mixing board. For the arches and spandrel walls the gravel was passed over a 2-in. mesh screen on the wagon box. The aggregate for the parapet walls was screened to 1 in. largest diameter. The concrete was mixed in a McKelvey continuous mixer which turned the material eight times. The mode of procedure was as follows: The gravel was loaded upon wagons in the pit and hauled to a platform at the intake of the mixer. Half of the cement required in the concrete was then spread over the top of the load in the wagon box and the whole was dumped through the bottom of the wagon box onto the platform and spread with shovels. The remainder of the cement was spread over the mixture and the whole was shoveled by one man to a second man who shoveled it into the mixer. Water was added after the mixture had passed about one-third of the way through the mixer. The mixer delivered the concrete directly into wheelbarrows, by which it was delivered to the work. The concrete was spread in layers from 2 to 4 ins. in thickness and thoroughly rammed with iron tampers; two men were employed tamping for each man shoveling. The arches were concreted in three longitudinal sections, each section constituting a day's work. The work was done in 1903 and the concrete cost for mixing and placing:
Labor: Per day. Per cu. yd. 13 men at $1.80 $23.40 $0.78 Engine and mixer 5.00 0.17 1 team 3.00 0.10 1 foreman 3.00 0.10 ——— ——- Totals for labor $34.40 $1.15
Materials: 0.65 bbl. cement at $2 $1.30 0.9 cu. yd. gravel at $0.50 0.45 ——- Total for materials $1.75 Grand total $2.90
METHODS AND COST OF CONSTRUCTING A FIVE-SPAN ARCH BRIDGE.—This bridge consisted of five elliptical arch spans of 40, 45, 60, 87 and 44 ft., carried on concrete piers. The arch rings were 12 ins. thick at the crowns and 18 ins. thick 5 ft. from the centers of piers and carried 4-in. spandrel walls; there were 1,000 cu. yds. of concrete in the arches and 600 cu. yds. in the piers. Each arch ring was reinforced by a grillage of longitudinal and transverse rods.
Forms and Centers.—Figure 159 is an end view of the center arch. It consists of a series of bents, 6 ft. c. to c., the posts of each bent being 5 ft. c. to c. These posts are made of 26-in. Washington fir. Upon the heads of the posts rest 26-in. stringers, extending from bent to bent. Resting on these stringers are wooden blocks, or wedges, which support a series of cross-stringers, also of 26-in. stuff, spaced 2 ft. c. to c. On top of these cross-stringers rest the sheeting planks, which are 16-in. stuff, dressed on the upper side, and bent to the curve of the arch. This sheeting plank was not tongue and grooved, and a man standing under it, after it is nailed in place, could see daylight through the cracks. It looked as if it would leak like a sieve, and let much of the wet concrete mortar flow through the cracks, but, as a matter of fact, scarcely any escapes. Figure 160 shows a front view of a bent, and indicates the manner of sway bracing it with 14-in. stuff. Figure 161 shows the outer forms for the parapet wall, or concrete hand railing, and it will be noted that the cross-stringers are allowed to project about 3 ft. so as to furnish a place to fasten the braces which hold the upright studs. The inner forms for the parapet wall are shown in dotted lines. They are not put in place until all the concrete arch is built. Then they are erected and held to the outer forms by wire, and are sway braced to wooden cleats nailed to the top surface of the concrete arch.
For the five spans the total amount of lumber in the centers was in round figures 28 M. ft., distributed about as follows:
Item. Ft. B. M. 16-in. sheeting 5,600 26-in. longitudinal stringers 2,600 26-in. cross stringers 2,600 26-in. posts 4,000 38-in. sills 1,500 14-in. braces 3,000 Outer forms for spandrel walls 4,000 Inner forms for spandrel walls 4,000 ——— Total 27,300
The aggregate span length of the arches was 276 ft., so that a little less than 100 ft. B. M. of lumber was used for centering per lineal foot of span. The superintendent at $5 per day and five carpenters at $3.50 per day erected the five centers in 18 days at a cost of $400, or a trifle more than $14 per M. ft. B. M.; the cost of taking down the centers was $2 per M. ft. B. M., and the lumber for the centers cost $24 per M. ft. B. M. making a grand total of $40 per M. ft. B. M. for materials and labor. As there were 1,000 cu. yds. of concrete in the arches and spandrels, the cost of centers and forms was $1.12 per cu. yd. This form lumber was, however, after taking down, used again in erecting a reinforced concrete building. Assuming that the lumber was used only twice, the cost of centers and forms for these five arches was less than 80 cts. per cu. yd. of concrete.
Shaping and Placing Reinforcement.—The 60 and 87-ft. spans were reinforced with 32 1-in. round longitudinal rods held in place by -in. square transverse rods wired at the intersections; the reinforcement of the smaller spans was exactly the same except that 1-in. diameter rods were used. To bend the longitudinal rods to curve, planks were laid on the ground roughly to the curve of the arch; the exact curve was marked on these planks and large spikes were driven part way into the planks along this mark. The end of a rod was then fastened by spiking it against the first projecting spike head and three men taking hold of the opposite end and walking it around until the rod rested against all the spikes on the curve. It took three men two 8-hour days to bend 46,000 lbs. of rods. Their wages were $2.50 each per day, making the cost of bending 0.03 ct. per pound, or 60 cts. per ton. It took a man 5 mins. to wire a cross rod to a longitudinal rod. With wages at $2.50 per day the cost of shaping and placing the reinforcement per ton was as follows:
Item. Per ton. Bending rods $0.60 Shearing rods to lengths 0.40 Carrying rods onto bridge 0.40 Placing and wiring rods 2.35 ——- Total $3.75
Including superintendence the labor cost was practically $4 per ton, or 0.2 cts. per lb. Altogether 66,000 lbs. of steel was used for reinforcing 1,000 cu. yds. of concrete, or 66 lbs. per cu. yd. The cost of steel delivered was 2 cts. per lb., and the cost of shaping and placing it 0.2 ct. per lb., a total of 2.2 cts. per lb. or 2.2 66 = $1.45 per cu. yd. of concrete.
Mixing and Placing Concrete.—A Ransome mixer holding a half-yard batch was used. The mixer was driven by an electric motor. The concrete for the piers was a mixture of 1 part Portland cement to 7 parts gravel; for the arches, the concrete was mixed 1 to 5. The gravel was piled near the mixer, a snatch team being used to assist the wagons in delivering the gravel into a pile as high as possible. Run planks supported on "horses" were laid horizontally from the mixer to the gravel, so that big wheelbarrow loads could be handled. The barrows were loaded with long-handled shovels, and the men worked with great vigor, as is shown by the fact that four men, shoveling and wheeling, delivered enough gravel to the mixer in 8 hrs. to make 100 cu. yds. of concrete. We have, therefore, estimated on a basis of six men instead of four. The mixer crew was organized as follows:
Per day. 6 men shoveling and wheeling $12 2 men handling cement 4 1 man handling water 2 1 man dumping concrete 2 2 men handling dump cars 4 2 men handling hoisting rope 4 4 men spreading and ramming concrete 8 1 engineman 4 1 foreman 5 Fuel, estimated 3 —- Total $48
The output of this crew was 100 cu. yds. per day. The concrete was hauled from the mixer in two small dump cars, each having a capacity of 10 cu. ft. The average load in each car was cu. yd. Ordinary mine cars were used, of the kind which can be dumped forward, or on either side. The cars were hauled over tracks having a gage of 18 ins. The rails weighed 16 lbs. per yard, and were held by spikes 2 ins. Larger spikes would have split the cross-ties, which were 34 ins. Only one spike was driven to hold each rail to each tie, the spikes being on alternate sides of the rail in successive ties. No fish plates or splice bars were used to join the rails, which considerably simplifies the track laying.
Two lines of track were laid over the bridge. The tracks were supported by light bents, the cross-tie forming the cap of each bent, as shown in Fig. 162. The bents were spaced 3 ft. apart. There were two posts to each bent, toe-nailed at the top of the tie, and at the bottom to the arch sheeting plank. Two men framed these crude bents and laid the two rails at the rate of 150 lin. ft. of track per day, at a cost of 4 cts. per lin. ft. of track. As stated, there were two tracks, one on each side of the bridge, but they converged as they neared the concrete mixer, so that a car coming from either track could run under the discharge chute of the mixer; Fig. 163 shows the arrangement of the tracks at the mixer. The part of each rail from A to B (6 ft. long) was free to move by bending at A, the rail being spiked rigidly to the tie at A, leaving its end at B free to move. To move the end B, so as to switch the cars, a home-made switch was improvised, as shown in Figs. 163 and 164.
It will be remembered that this bridge was a series of five arches. There was a steep grade from the two ends of the bridge to the crown of the center arch. Hence the two railway tracks ascended on a steep grade from the mixer for about 175 ft., then they descended rapidly to the other end of the bridge. Hence to haul the concrete cars up the grade by using a wire cable, it was necessary to anchor a snatch block at the center of the bridge. This was done by erecting a short post, the top of which was about a foot above the top of the rails. The post stood near the track, and was guyed by means of wires, and braced by short inclined struts. To the top of the post was lashed the snatch block through which passed the wire rope. Fig. 165 shows this post, P. About 10 ft. from the post P, on the side toward the mixer, another post, Q, was erected, and a snatch block fastened to it. When the hoisting engine, which was set near the concrete mixer, began hauling the car along the track, a laborer would follow the car. Just before the car reached the post Q, he would unhook the hoisting rope from the front end of the car, then push the car past the post Q, and hook the hoisting rope to the rear of the car. The car would then proceed to descend in the direction T, being always under the control of the wire rope, except during the brief period when the car was passing the post Q. Each of the two cars was provided with its own hoisting rope, and one engineer, operating a double drum hoist, handled the cars. The hoist was belted to an 8 HP. gasoline engine, no electric motor being available for the purpose.
Where hauling is done in this manner with wire ropes, it is necessary to support the ropes by rollers wherever they would rub against obstructions. A cheap roller can be made by taking a piece of 2-in. gas pipe about a foot long, and driving a wooden plug in each end of the gas pipe. Then bore a hole through the center of the wooden plugs and drive a 1-in. round rod through the holes, as shown in Fig. 166. The ends of this rod are shoved into holes bored into plank posts, which thus support the roller. Where the rope must be carried around a more or less sharp corner, it is necessary to provide two rollers, one horizontal and the other vertical, as shown in Fig. 167.
When conveying concrete to a point on the bridge about 300 ft. from the mixer, a dump car would make the round trip in 3 mins., about min. of its time being occupied in loading and another min. in dumping. One man always walked along with each car, and another man helped pull the wire rope back.
Including the cost of laying the track and installing the plant, the cost of mixing and placing the 1,600 cu. yds. of concrete was only 55 cts. per cu. yd., in spite of the high wages paid. However, the men were working for a contractor under a very good superintendent.
Summing up the cost of the concrete in the arches of this bridge, we have:
Per cu. yd. 1.35 bbl. cement at $3 $4.05 1 cu. yd. gravel at $1 1.00 66 lbs. of steel in place at 2.2 cts. 1.45 Centers in place (lumber used once) 1.12 Labor, mix and place concrete 0.55 ——- Total $8.17
The cost of the nails, wire, excavation and plant rental is not available, but could not be sufficient to add more than 10 cts. per cu. yd. under the conditions that existed in this case.
CONCRETE RIBBED ARCH BRIDGE AT GRAND RAPIDS, MICH.—The bridge consisted of seven parabolic arch ribs of 75 ft. clear span and 14 ft. rise. The five ribs under the 21-ft roadway were each 24 ins. thick, 50 ins. deep at skewbacks and 25 ins. deep at crown; the two ribs under the sidewalks were 12 ins. thick and of the same depth as the main ribs. Each rib carried columns which supported the deck slab. Columns and ribs were braced together across-bridge by struts and webs. All structural parts of the bridge were of concrete reinforced by corrugated bars. The abutments were hollow boxes with reinforced concrete shells tied in by buttresses and filled with earth. There were in the bridge including abutments 884 cu. yds. of concrete and 62,000 lbs. of reinforcing metal, or about 70 lbs. of reinforcing metal per cu. yd. of concrete. Of the 884 cu. yds. of concrete 594 cu. yds. were contained in the abutments and wing walls and 290 cu. yds. in the remainder of the structure. (Fig. 168.)
Centers.—The center for the arch consisted of 4-pile bents spaced about 12 ft. apart in the line of the bridge. The piles were 1212 in.24 ft. yellow pine and they were braced together in both directions by 210-in. planks. Each bent carried a 312-in. plank cap. Maple folding wedges were set in these caps over each pile and on them rested 1212-in. transverse timbers, one directly over each bent. These 1212-in. transverse timbers carried the back pieces cut to the curve of the arch. The back pieces were 212-in. plank, two under each sidewalk rib and four under each main rib of the arch. The back pieces under each rib were X-braced together. The lagging was made continuous under the ribs but only occasional strips were carried across the spaces between ribs. This reduced the amount of lagging required but made working on the centers more difficult and resulted in loss of tools from dropping through the openings. Work on the centers and forms was tiresome owing both to the difficulty of moving around on the lagging and to the cramped positions in which the men labored. Carpenters were hard to keep for these reasons.
Concrete.—A 1-7 bank gravel concrete was used for the abutments and a 1-5 bank gravel concrete for the other parts of the bridge. The concrete was mixed in a cubical mixer operated by electric motor and located at one end of the bridge. The mixed concrete was taken to the forms in wheelbarrows. The mixture was of mushy consistency. No mortar facing was used, but the exposed surfaces were given a grout wash. In freezing weather the gravel and water were heated to a temperature of about 100 F.; when work was stopped at night it was covered with tarred felt, and was usually found steaming the next morning.
Cost of Work.—The cost data given here are based on figures furnished to us by Geo. J. Davis, Jr., who designed the bridge and kept the cost records. Mr. Davis states that the unit costs are high, because of the adverse conditions under which the work was performed. The work was done by day labor by the city, the men were all new to this class of work, the weather was cold and there was high water to interfere, and work was begun before plans for the bridge had been completed, so that the superintendent could not intelligently plan the work ahead. Cost keeping was begun only after the work was well under way. Many of the items of cost are incomplete in detail.
The following were the wages paid and the prices of the materials used:
Materials and Supplies: No. 1 hemlock matched per M. ft. $20 No. 1 hemlock plank per M. ft. 17 No. 2 Norway pine flooring per M. ft. 19 No. 2 yellow pine flooring per M. ft. 20 1212-in.16-ft. yellow pine per M. ft. 29 1212-in.24-ft. yellow pine, piling per M. ft. 27 Maple wedges per pair 50 cts. -in. corrugated bars per lb. 2.615 cts. -in. corrugated bars per lb. 2.515 cts. 7/8-in. corrugated bars per lb. 2.515 cts. Coal per ton $4 Electric power per kilowatt 6 cts. Medusa cement per bbl. $1.75 Aetna cement per bbl. 1.05 Bank gravel per cu. yd. 0.85 Sand per cu. yd. 0.66 Carpenters per day $3 to 3.50 Common labor per day 1.75
The summarized cost of the whole work, with such detailed costs as the figures given permit of computation, was as follows:
General Service: Total. Per cu. yd. Engineering $451 $0.512 Miscellaneous 75 0.084
Pumping: Total 110 days. Coal at $4 per ton $210 Machinery, tools and cartage 283 Labor 497 —— Total $990
This gives a cost of $9 per day for pumping.
Excavation: Total cost. P. C. Total. Timber cartage, etc. $ 375 17.6 Tools 69 3.3 Labor at $1.75 1,687 79.1 ——— ——- Total $2,131 100.0
Filling 5,711 cu. yds.: Total. Per cu. yd. Earth $1,142 $0.20 Labor including riprapping 396 0.07 ——— ——- Total $1,538 $0.27
Removing Old Wing Walls: Total. Labor and dynamite $ 346 Tools and sharpening 64 ——- Total $ 410
Hand Rail, 150 ft.: Total. Per lin. ft. Material $ 278 $1.85 Labor 29 0.19 ——- ——- Total $ 307 $2.04
Wood Block Pavement, 296 sq. yds.: Total. Per sq. yd. Wood block, etc. $ 695 $2.35 Labor 57 0.19 ——- ——- Total $ 752 $2.54
Steel, 62,000 lbs.: Total. Per lb. Corrugated bars, freight, etc. $1,498 2.41 cts. Plain steel, wire, etc. 75 0.12 cts. Blacksmithing, tools and placing 438 0.71 cts. ——— —— Total $2,011 3.24 cts.
Concrete. Centering: Total. Per cu. yd. Lumber and piles $ 332 $1.14 Labor 272 0.95 ——- ——- Total $ 604 $2.09
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
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
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 space 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.
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 scraper 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 pass under it. A team operating a drag scraper 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 spaced 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 butt 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 quantity 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.
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.
Cost.—The cost of the 1,217 cu. yds. of concrete in the culvert was as follows:
Item. Per cu. yd. 1.08 bbls. cement at $1.72 $1.85 0.47 cu. yd. sand at 30 cts. 0.14 0.25 cu. yd. broken stone at 51 cts. 0.13 0.8 cu. yd. slag at 26 cts. 0.21 Lumber in forms, etc. 0.30 Miscellaneous materials 0.05 Labor, unloading materials 0.11 Labor, mixing and placing concrete 0.42 Labor, building forms 0.55 Labor, not classified 0.18 Labor, excavating 40 cts. per cu. yd. 0.28 Labor, back filling and tearing down forms 0.10 ——- Total $4.32
CULVERTS FOR NEW CONSTRUCTION, WABASH RY.—The following data relate to culvert work carried out in constructing the Pittsburg extension of the Wabash Ry. in 1903. All the work was done by contract.
Plant I: This plant was located on a hillside with the crushing bins above the loading floor or platform which extended over the top of the mixer, so that the crushed stone could be drawn directly from the chutes of the bins and wheeled to the mixer. The sand was hauled up an incline in one-horse carts and dumped on this floor, and was also wheeled in barrows to the mixer. The proportions used were 4 bags of cement, 4 barrows of sand and stone dust and 7 barrows of crushed stone. A 7/8-cu. yd. mixer was used and it averaged 40 cu. yds. per 10-hour day at the following cost for labor:
Item. Per day. Per cu. yd. 1 foreman $ 3.00 $0.08 3 men charging with barrows 4.50 0.11 1 man attending engine and mixer 2.50 0.06 2 men loading concrete barrows 3.00 0.08 4 men wheeling concrete barrows (100 ft.) 6.00 0.15 4 men ramming concrete 6.00 0.15 4 men wheeling and bedding rubble stones 6.00 0.15 ——— ——- Totals $31.00 $0.78
Assuming 1/3 ton of coal per day at $3 per ton, we have 2 cts. more per cubic yard for fuel.
Plant II.—At this plant a Smith mixer was used with a loading floor 4 ft. above the ground, this low platform being made possible by having a hole or sump in which the skip receiving the concrete was set. A derrick handled the skips between the sump and the work. The batch was made up of 2 bags of cement, 2 barrows of sand and 4 barrows of stone. The output was 50 cu. yds. per day of 10 hours at the following cost:
Item. Per day. Per cu. yd. 1 man feeding mixer $1.50 $0.03 1 mixer runner 2.50 0.05 1 derrick engineman 2.50 0.05 2 tagmen swinging and dumping 3.00 0.06 6 men wheeling materials 9.00 0.18 2 men tamping concrete 3.00 0.06 1 foreman 3.00 0.06 ——— ——- Totals $24.50 $0.49
The cost of fuel would add about 3 cts. per cubic yard to this amount.
SMALL ARCH CULVERT COSTS, PENNSYLVANIA R. R.—Mr. Alex. R. Holliday gives the following figures of cost of small concrete culvert work carried out under his direction. The culvert section used is shown in Fig. 171. This section gives a slightly larger waterway than a 36-in. cast iron pipe. Eight culverts, having an aggregate length of 306 ft. were built, using a mixture of Portland cement and limestone and screenings. Each culvert had a small spandrel wall at each end.
The work was done by a gang of six men, receiving the following wages:
Foreman, cents per hour 27.5 Assistant " " " 17.5 Laborers " " " 15.0 Teams " " " 35.0
The materials were hauled about 1 mile from railway to site of work. Cement, including freight and haulage, cost $1.97 per barrel. Limestone and screenings cost 50 cts. per cu. yd. f. o. b. at quarry. No freight charges are included in cost of any of the materials except cement. The cost of the 306 ft. of culvert was as follows:
Item. Total. Per lin. ft. Per cu. yd. Labor $443.14 $1.45 $3.35 Stone and screenings 78.50 0.25 0.60 Cement 307.53 1.01 2.34 Forms 12.00 0.04 0.09 ———- ——- ——-
Total $841.17 $2.75 $6.38
26-FT SPAN ARCH CULVERT.—The culvert was 62 ft. long and 26-ft. span and was built of 1-8 and 1-10 concrete mixed by hand. The wages paid were: General foreman, 40 cts. per hour; foreman, 25 cts. per hour; carpenters, 22 to 25 cts. per hour, and laborers, 15 cts. per hour. The cost of the concrete in place, exclusive of excavation but including wing walls and parapet, was as follows:
Per cu. yd. 0.96 bbl. cement, at $1.60 $1.535 1.03 tons coarse gravel, at $0.19 0.195 0.40 tons fine gravel, at $0.21 0.085 0.32 tons sand, at $0.36 0.115 Tools, etc. 0.078 Lumber for forms and centers 0.430 Carpenter work on forms (23 cts. hr.) 0.280 Carpenter work platforms and buildings 0.050 Preparing site and cleaning up 0.210 Changing trestle 0.085 Handling materials 0.037 Mixing and laying, av. 15 cts. per hr. 1.440 ——— Total per cu. yd $4.540
There were 1,493 cu. yds. of concrete in the work. The excavation cost $463 and the total cost was $7,243.
COST OF RAILWAY CULVERT.—The culvert was for a single track railway and contained 113 cu. yds. of concrete and required 36 cu. yds. of excavation. The figures are given by C. C. Williams as follows:
Cost of Material.
Kind and Amount of Material. Unit Price. Cost. Stone, 113.2 tons $.70 $ 79.24 Sand, 46.8 yds. .55 25.74 Cement, 137 bbls. .85 116.45 ———- Total $221.43
Lumber 52.50 Rail and bolts 36.60 ———- Total $ 89.10
Labor, 189 hours at .15 $ 28.35 Foreman, 60 hours at .30 18.00 ———- Total $ 46.35 Concrete.
Labor, 683 hours at .15 $102.45 Foreman, 130 hours at .30 39.00 ———- Total $141.45
Forms. Carpenters, 313 hours at .225 $ 70.42 Labor, 30 hours at .15 4.50 ———- Total $ 74.92
Moving material, 245 hours at .15 $ 36.75 Unloading material, 95 hours at .15 14.25 Foreman, 20 hours at .30 6.00 ———- Total $ 57.00
Superintendence and Office.
Superintendent, 6 hours at .50 $ 3.00 Office 10.00 ———- Total $ 13.00 ———- Grand total $643.25
Per cent. Cost of Total Per Yard Cost of Item. Cost. Concrete. Concrete. ——— Concrete material $221.43 $1.96 7.1 Laying concrete 141.45 1.25 23.6 Lumber 52.50 .46 08.7 Rail and bolts 36.60 .32 06.1 Building forms 74.92 .67 13.3 Handling material 56.90 .50 09.0 Superintendent and office 13.00 .12 02.2 ——- ——— Total $5.28 100.00 Excavation 46.35 1.28 ———- Total $643.15
113 yds. concrete at $5.95 $672.35 36 yds. excavation at .30 10.80 ———- Total $683.15 Total cost 643.15 ———- Profit, 5.9% of contract price $ 40.00
12-FT. CULVERT, KALAMAZOO, MICH.—A portion 1,080 ft. long of a new channel built in 1902-3 for a small stream flowing through the city of Kalamazoo, Mich., was constructed as an arch culvert of the form shown by Fig. 172. The concrete section is reinforced on the lines indicated by a double layer of woven steel wire fabric. The concrete was approximately a 1 cement, 6 sand and gravel mixture.
The centers were built in sections 12 ft. long of the form and construction shown by Fig. 173, and a sufficient number was provided to lay twelve sections of invert and six sections of arch. The arch centers were arranged to be uncoupled at the crown; this with the hinges at the quarter points permitted the two halves to be separated and each half to be folded so that it could be carried from the rear of the work through the forms still in place and erected again for new work. When in place the center ribs rested on the side forms which set on the invert concrete and are braced apart by the hinged cross-strut. This cross-strut was the key that bound the whole structure together; the method of removing this key is indicated by Fig. 174. From his experience with these centers the engineer of the work, Mr. Geo. S. Pierson, remarks:
"In work of this kind it is very important to have the centering absolutely rigid so it will not spring when concrete is being tamped against it and thus weaken the cohesion of the concrete. It is also important to have the arrangement such that all the centering can be removed without straining or jarring the fresh concrete. The centers were generally removed in about three or four days after the concrete arch was in place."
The invert concrete was brought to form by means of templates, Fig. 173, and straight edges. The side forms were then placed and braced apart by the struts and concreting continued to the skewback plane indicated in Fig. 173. The arch form was then placed; it rested at the edges on the side forms and was further supported by center posts bearing on boards laid on the bottom of the invert. A template, Fig. 175, was used to get the proper thickness and form of arch ring. Outside forms were used to confine the concrete at the haunches but nearer the crown they were not required.
Much of the work was done when the thermometer, during working hours, ranged from 12 to 25 above zero. When the temperature was below freezing, hot water was used in mixing the concrete and on a few of the coldest days salt was dissolved in the water. In addition each section of the work was covered with oiled canvas as soon as completed, and the conduit was kept closed so far as was practicable to retain the heat. Concreting was never stopped on account of cold weather.
Account was kept of the cost of all work, and the figures obtained are given in the following tables:
Labor Force, Materials Used and Progress of Work.
Average progress per day in feet 18.0 Greatest number of feet laid in one day 28 Average number of laborers per day mixing and wheeling 10.04 Average number of laborers per day placing concrete 5 Average number of laborers per day setting up forms 4.57 Cubic yards of concrete mixed and wheeled per day per man 1.96 Cubic yards of concrete placed per day per man 3.54 Cubic yards of concrete per lin. ft. 0.95 Barrels of cement per lin. ft. 1.18 Barrels of cement per cu. yd. 1.24 Proportion of cement to sand and gravel 1-6