Concrete Construction: Methods and Costs

by Halbert Powers Gillette; Charles Shattuck Hill

METHODS AND COST OF HEAVY CONCRETE WORK IN FORTIFICATIONS, LOCKS, DAMS, BREAKWATERS AND PIERS.

The construction problem in building concrete structures of massive form and volume is chiefly a problem of plant arrangement and organization of plant operations. In most such work form construction is simple and of such character that it offers no delay to placing the concrete as rapidly as it can be produced. The same is true of the character of the structure, it is seldom necessary for one part of the work to wait on the setting and hardening of another part. As a rule, there is no reinforcement to fabricate and place and where there is it is of such simple character as not to influence the main task of mixing, handling, and placing concrete. Stated broadly, the contractor in such work generally has a certain large amount of concrete to manufacture, transport and deposit in a certain space with nothing to limit the rapidity of these operations, except the limitations of plant capacity and management. Installation and operation of mixing and conveying plant, then are matters to be considered carefully in heavy concrete work.

In the following sections we have given one or more examples of nearly every kind of heavy concrete work excepting bridge foundations and retaining walls, which are considered in Chapters XII and XIII, and except rubble concrete work, which is considered in Chapter VI. In each case so far as the available records made it possible, we have given an account of the plant used and of its operation.

FORTIFICATION WORK.—Concrete for fortification work consists very largely of heavy platforms and walls for gun foundations and enclosures and of heavily roofed galleries and chambers for machinery and ammunition. The work is very massive and in the majority of cases of simple form. A large number of data are to be found in the reports of the Chief of Engineers, U. S. A., on all classes of fortification work, but the manner in which they are recorded makes close analysis of relative efficiencies of methods or of relative costs almost impossible. The following data are given, therefore, as examples that may be considered fairly representative of the costs obtained in fortification work done under the direction of army engineers; these data are not susceptible of close analysis because wages, working force, outputs, etc., are nearly always lacking.

Gun Emplacements, Staten Island, N. Y.—The work comprised 5,609 cu. yds. of concrete in two 12-in. gun emplacements, and 3,778 cu. yds. of concrete in two 6-in. gun emplacements. Concrete was mixed in a revolving cube mixer with the exception of 809 cu. yds. in the 6-in. emplacements which were mixed by hand at a cost of 56 cts. more per cubic yard than machine mixing cost. The body of the concrete was a 1-3-5 Portland cement, beach sand and broken trap rock mixture. The floors and upper surface of the concrete had a pavement consisting of 6 ins. of 1-3-5 concrete surfaced with 2 ins. of 1-3 mortar. Wages are not given, but for the time and place should have been about $1.50 per 8-hour day for common labor. The cost of materials was:

Alpha Portland cement, per bbl.	$1.98
Broken trap rock, per cu. yd.	0.81
12-in. emplacement, hauling sand per cu. yd.	0.175
6-in. emplacement, hauling sand per cu. yd.	0.20

The cost of the concrete in place was as follows:

Body Concrete——	12-in., per cu. yd.	6-in., per cu. yd.
Cement, at $1.98 per bbl.	$2.546	$2.546
Broken stone, at 81 cts. per cu. yd.	1.041	1.041
Sand, at 17½ and 20 cts. per cu. yd.	0.225	0.257
Receiving and storing materials at 11.6 cts. per cu. yd. and 8.4 cts. per bbl.	0.149	0.180
Mixing, placing and ramming	0.879	1.110
Forms, lumber and labor	0.477	0.950
Superintendence and miscellaneous	0.190	0.150
	———	———
Total	$5.507	$6.234
Concrete Pavement—
Materials	$2.97	$3.06
Labor	4.63	4.72
	———	———
Total	$7.60	$7.78

Fig. 68.—Sketch Plans of Concrete Making Plant for Mortar Battery Platform.

Mortar Battery Platform, Tampa Bay, Fla.—The platform contained 8,994 cu. yds. of concrete composed of a mixture of Portland cement, sand, shells and broken stone. The broken stone and cement were brought in by vessel and the sand and shells were obtained from the beach near by. The plant for the work was arranged as shown by the sketch, Fig. 68. Sand, stone and shells were stored in separate compartments in the storage bins. Box cars, divided into compartments of such size that when each was filled with its proper material, the car would contain the proper proportions for one batch of concrete, were pushed by hand under the several compartments of the bin in succession until charged; then they were hooked to a cable and hauled to the platform over the mixer and dumped. The charge was then turned over with shovels and shoveled into the hopper of a continuous mixer, located beneath. Two cars were used for charging the mixer, running on separate tracks as shown. The mixer discharged into buckets set on flat cars, which were hauled by mules under the cableway, which then lifted and dumped the bucket and returned it empty to the car. By using three bucket cars, one was always ready to receive the mixer discharge as soon as the preceding one had been filled, so that the mixer operated continuously. The cableway had a working span of 270 ft., the cable being carried by traveling towers 69 ft. high; the cableway was very easily operated back and forth along the work. The cableway complete, with 497 ft. of six-rail track for each tower, cost $4,700. The cost of materials and labor for the 8,994 cu. yds. of concrete was as follows:

	Per cu. yd.
1 bbl. cement at $2.46	$2.46
0.89 cu. yd. stone, at $2.95	2.622
0.315 cu. yd. shells, at $0.45	0.142
0.51 cu. yd. sand, at $0.12	0.062
Mixing and placing	0.693
	———
Total	$5.979

The above batch tamped in place to 30 cu. ft., or 1-1/9 cu. yds., which gives the cost as follows:

	Per cu. yd.
Cost of concrete tamped in place	$5.381
Cost of form work	0.370
	———
Total cost	$5.751

In the preceding prices of cement and stone, 59 cts. and 29 cts. per cubic yard, respectively, are included for storage. The costs of sand and shells are costs of screening and storing. Rough lumber for forms cost $10.25, and dressed lumber $12.75 per M. ft. B. M.

Emplacement for Battery, Tampa Bay, Fla.—The emplacement contained 6,654 cu. yds. of Portland cement, sand, shells and broken stone concrete. The plant arrangement is shown by Fig. 69. The sand and shells were got near the site, using an inclined cableway running from a 40-ft. mast near the mixer to a deadman at the shell bank. All the sand for the fill around the emplacement was obtained in the same way. The other materials were brought by vessel to a wharf, loaded by derrick onto cars operated by an endless cable, and taken to the work. The storage bins and mixing plant were operated much like those for the mortar battery work, previously described. A cube mixer was used, and the concrete was handled from it to the work by a crane derrick covering a circle of 100 ft. in diameter. The cost of materials and concrete was as follows:

Cement, plus 7 cts. for storage per bbl.	$ 2.532
Stone, plus 38 cts. for storage per cu. yd.	3.047
Shells, excavating and storage.	0.481
Sand, excavating and storage.	0.250
Lumber, rough per M. ft. B. M.	10.25
Lumber, dressed per M. ft. B. M.	12.75

Fig. 69.—Sketch Plans of Concrete Making Plant for Battery Emplacement.

A batch made up as follows, tamped in place to a volume of 30 cu. ft. or 1-1/9 cu. yds.:

1 bbl. cement, at $2.532.	$ 2.532
0.315 cu. yd. shells, at $0.481.	0.151
0.51 cu. yd. sand, at $0.25.	0.130
0.89 cu. yd. stone, at $3.047.	2.710
Mixing and placing.	0.761
	————
Total for 30 cu. ft.	$ 6.284

This gives a cost per cubic yard of concrete in place as follows:

Concrete in place, per cu. yd.	$ 5.655
Forms, per cu. yd. of concrete.	0.220
	————
Total cost of concrete per cu. yd.	$ 5.875

United States Fortification Work.—The following methods and cost of mixing and placing concrete by hand and by cubical mixers is given by Mr. L. R. Grabill for U. S. Government fortification work done in 1899.

Hand Mixing and Placing.—The work was done by contract, using a 1 cement, 2 sand, 2 pebbles and 3 stone mixture turned four times. A board large enough for three batches at a time was used; one batch was being placed, one being mixed and one being removed at the same time so that the mixers moved without interval from one to the other. Two gangs were worked, each mixing 64 batches of 0.75 cu. yd., or 48 cu. yds. of concrete per day at the following cost:

Hand Mixing 9,000 Cu. Yds.—	Per day.	Per cu. yd.
6 men wheeling materials	$ 7.50	$0.16
8 men mixing	10.00	0.21
8 men wheeling away	10.00	0.21
6 men placing and ramming	7.50	0.16
1 pump man	1.25	0.02
1 waterboy	1.00	0.02
1 foreman	2.00	0.04
	———	———
Totals	$39.25	$0.82

The entire cost of plant for this work was about $500.

Machine Mixing and Placing.—The concrete was mixed in a 4-ft. cubical mixer operated by a 12 hp. engine which also hauled the material cars up the incline to the mixer. These cars passed by double track under the material bins where the compartments of the car body were filled through trap doors; they then passed the cement house where the cement was placed on the load, then up the incline to the mixer and dumped, and then empty down an opposite incline. Seven turns of the mixer mixed the charge which was discharged into iron tubs on cars hauled by horses to two derricks whose booms covered the work. One gang by day labor mixed and placed 168 batches of 0.7 cu. yd., or 117.6 cu. yds. per day at the following cost:

Machine Mixing 4,000 Cu. Yds.—	Per day.	Per cu. yd.
32 men at $1.25	$40.00	$0.34
1 pumpman	1.25	0.01
1 teamster and horse	2.00	0.02
2 waterboys at $1	2.00	0.02
1 engineman	1.70	0.02
1 derrickman	1.50	0.01
1 fireman	1.50	0.01
1 foreman	2.88	0.03
Fuel (cement barrels largely)	1.25	0.01
	———	———
Totals	$54.08	$0.47

The cost of the plant was about $5,000.

Fig. 70.—Concrete Making Plant for Constructing Lock Walls, Cascades Canal.

LOCK WALLS, CASCADES CANAL.—Four-fifths or 70,000 cu. yds. of lock masonry was concrete, the bulk of which was mixed and deposited by the plant shown by Fig. 70. The concrete was Portland cement, sand, gravel and broken stone. Cement was brought in in barrels by railway, stored and tested; from the store house the barrels were loaded onto cars and taken 250 ft. to a platform onto which the barrels were emptied and from which the cement was shoveled into the cement hopper and chuted to cars which took it to the charging hopper of the mixer. The stone was crushed from spalls and waste ends from the stone cutting yards, where stone for wall lining and coping and other special parts was prepared. These spalls and ends were brought in cars and dumped into the hopper of a No. 5 Gates crusher, with a capacity of 30 tons per hour. From the crusher the stone passed to a 2½-in. screen, the pieces passing going to a bin below and the rejections going to a smaller Blake crusher and thence to the bin. The dust and small particles were not screened out. The sand and gravel were obtained by screening and washing pit gravel. The gravel was excavated and brought in cars to the washer. This consisted of a steel cylinder 2 ft. 6½ ins. in diameter and about 18 ft. long, having an inclination of 1 in. per foot. An axial gudgeon supported the cylinder at the lower end and it rested on rollers at the other end and at an intermediate point. The gravel was fed by hopper and chute into the upper end and into this same end a 3-in. perforated pipe projected and extended to about mid-length of the cylinder. The cylinder shell was solid and provided with internal fins for about half its length from the feed end. For the remainder of its length nearly to the end, the shell was perforated with 2½-in. holes. For a length of 4 ft. beyond mid-point it was encircled by a concentric screen of ⅛-in. holes, and this screen for 3 ft. of its length was encircled by another screen of 30 meshes to the inch. The pit mixture fed into the cylinder was gradually passed along by the combined inclination and rotation, being washed and screened in the process. The sand fell into one bin and the gravel into another, and the waste water was carried away by a flume. The large stones passed out through openings at the lower end of the shell and were chuted into cars. The cars came to the mixer as clearly shown by Fig. 70.

The stone and gravel cars were side dump and the cement car was bottom dump. The mixers were of the cube type 4 ft. on each edge and operated by a 7×12-in. double cylinder engine at nine revolutions per minute. The usual charge was 32 cu. ft. of the several ingredients, and it was found that 15 revolutions requiring about 1½ minutes were sufficient for mixing. The average work of one mixer was 17 batches or about 13 cu. yds. per hour, but this could be speeded up to 20 batches per hour when the materials were freely supplied and the output freely removed. Two cars took the concrete from the mixer to the hopper, from which it was fed to the work by chute. The hopper was mounted on a truck and the chute was a wrought iron cylinder trussed on four sides and having a 45° elbow at the lower end to prevent scattering. The chute fed into a car running along the wall and distributing the material. It was found impracticable to move the chute readily enough to permit of feeding the concrete directly into place. As the concreting progressed upward the trestle was extended and the chute shortened. It was found that wear would soon disable a steel chute so that the main trussed cylinder had a smaller, cheaply made cylinder placed inside as a lining to take the wear and be replaced when necessary.

The plant described worked very successfully. Records based on 9,614.4 cu. yds. of concrete laid, gave the following:

	Cu. yds.
Concrete mixed by hand	1,777.0
Concrete mixed by machine	7,837.4
Total concrete laid	9,614.4
Concrete placed by derricks	2,372.0
Concrete placed by chute	7,242.4
Concrete 1-2-4 mixture	156.0
Concrete 1-3-6 mixture	1,564.0
Concrete 1-4-8 mixture	6,892.0

The average mixture was 1 cement, 3.7 sand, 4.8 gravel and 2.6 broken stone. The average product was 1.241 cu. yds. concrete per barrel of cement and 1.116 cu. yds. of concrete per cubic yard of stone and gravel. The average materials for 1 cu. yd. of concrete were: Cement 0.805 bbl., sand 0.456 cu. yd., gravel 0.579 cu. yd., and stone 0.317 cu. yd.

The cost of these 9,614.4 cu. yds. of concrete in place was:

Hand Mixed and Placed by Derrick—	Per cu. yd.
Labor mixing 1,777 cu. yds	$1,072
Repairs, fuel, etc	0.016
	———
Total cost mixing	$1,088
Labor placing 2,372 cu. yds.	0.6025
Fuel, tramways, etc.	0.1958
	———
Total cost placing	$0.7983

Machine Mixed and Placed by Chute—
Labor mixing 7,837 cu. yds.	$0.388
Repairs, fuel, etc	0.046
	———
Total cost mixing	$0.434
Labor placing 7,242 cu. yds	0.414
Fuel, tramways, etc.	0.045
	———
Total cost placing	$0.459
Materials and Supplies 9,614 cu. yds.—
Timbering	$0.145
Cement	3.289
Sand and gravel	1.073
Broken stone	0.536
Cement testing, repairs, etc.	0.223
	———
Total	$5,266
Plant and Superintendence, 9,614 Cu. Yds.—
Engineering, superintendence, repairs, etc.	$1,508
20% cost of plant	0.165
	———
Total	$1,673

The comparative cost of hand and machine mixing and handling was thus:

Item—	Hand.	Machine.
Mixing per cu. yd.	$1.088	$0.434
Placing per cu. yd.	0.798	0.459
Materials, etc., per cu. yd.	5.466	5.466
Plant, etc., per cu. yd.	1.673	1.right
	———	———
Totals	$9.025	$8.032

The average total costs of all the concrete placed were:

Mixing per cu. yd.	$0.555
Placing per cu. yd.	0.543
Materials per cu. yd.	5.266
Plant, etc., per cu. yd.	1.673
	———
Total	$8.037

LOCKS, COOSA RIVER, ALABAMA.—The following methods and costs are given by Mr. Charles Firth for constructing lock No. 31 for the Coosa River canalization, Alabama. This lock is 420 ft. long over all, 322 ft. between quoins, 52 ft. clear width, 14.7 ft. lift and 8 ft. depth of water on sills; it contained 20,000 cu. yds. of concrete requiring 21,500 bbls. cement, half Alsen and half Atlas.

Figure 71 shows the concrete mixing plant, consisting of two 4×4 ft. cube mixer, driven by a 10×16-in. engine. The top floor of the mixer house stored the cement, 2,000 bbls. The concrete was a 1-3-5½ stone mixture. Each mixer charge consisted of 3 cu. ft. cement, 9 cu. ft. sand and 16.5 cu. ft. stone; the charge was turned over four times before and six times after watering at a speed not exceeding eight revolutions per minute. The average output of the plant was 200 cu. yds. per 8-hour day, or 100 cu. yds. per mixer, but it was limited by the means for placing.

Fig. 71.—Concrete Mixing Plant for Lock Construction, Coosa River, Alabama.

The concrete was mixed dry, deposited in 6 to 8-in. layers, and rammed with 30-lb. iron rammers with 6-in. square faces. For all exposed surfaces a 6-in. facing of 1-3 mortar was placed by setting 2×12-in. planks 4 ins. from the laggings, being kept to distance by 2×4-in. spacers, placing and ramming the concrete behind them, then withdrawing them, filling the 6-in. space with mortar and tamping it to bond with the concrete. The walls were carried up in lifts, each lift being completed entirely around the lock before beginning the next; the first lift was 10.7 ft. high and the others 6 ft., except the last, which was 4.5 ft., exclusive of the 18-in. coping. The coping was constructed of separately molded blocks 3 ft. long, made of 1-2-3 concrete faced with 1-1 mortar and having edges rounded to 3 ins. radius.

In constructing the forms a row of 6×8-in. posts 24 ft. long and 5 to 7 ft. apart was set up along the inside of each wall and a similar row of posts 12 ft. long was set up along the outside. From the tops of the short posts 6×8-in. caps reached across the wall and were bolted to the long posts; these caps carried the stringers for the concrete car tracks. The lagging consisted of 3×10-in. planks dressed on all sides. The backs of the walls were stepped and as each step was completed the rear 12-ft. posts were lifted to a footing on its top and carried in the necessary distance. The front posts remained undisturbed until the wall was completed. The lagging was moved up as the filling progressed. As no tie bolts were permitted, these forms required elaborate bracing.

From the mixing plant, which was located on the bank above reach of floods, the concrete cars were dropped by elevator to the level of the track over the walls and then run along the wall and dumped onto platforms inside the forms and just below the track. This arrangement was adopted, because it was found that even a small drop separated the stone from the mortar. The concrete was shoveled from the platforms to place and rammed. The cars were bottom dumping with a single door hinged at the side; this door when swinging back struck the track stringers and jarred the form so that constant attention was necessary to keep it in line. It would have been much better to have had double doors swinging endwise of the car. Another point noted was that unless the track was high enough to give good head room at the close of a lift the placing and ramming were not well done.

The cost of 8,710 cu. yds. of concrete placed during 1895 by day labor employing negroes at $1 per 8-hour day was as follows per cubic yard:

1 bbl. cement	$2.48
0.88 cu. yd. stone at $0.76	0.67
0.36 cu. yd. sand at $0.34	0.12
Mixing, placing and ramming	0.88
Staging and forms	0.42
	——
Total	$4.57

LOCK WALLS, ILLINOIS & MISSISSIPPI CANAL.—The locks and practically all other masonry for the Illinois & Mississippi Canal are of concrete. The following account of the methods and cost of doing this concrete work is taken from information published by Mr. J. W. Woermann in 1894 and special information furnished by letter. The decision to use concrete was induced by the fact that no suitable stone for masonry was readily available (the local stone was a flinty limestone, usually without bed, or, at best, in thin irregular strata, and cracked in all directions with the cracks filled with fire clay) while good sand and gravel and good stone for crushing were plentifully at hand. The concrete work done in 1893-4 comprised dam abutments, piers for Taintor gates and locks.

Dam Abutments.—Four dam abutments were constructed, three of which were L-shaped, with sides next to the river 40 ft. long and sides extending into the banks 20 ft. long; the top thickness was 3 ft., the faces were vertical and the backs stepped with treads of 14 to 16 ins., and the width of base was 0.4 of the height. Each of these abutments was built in four 30-cu. yd. sections, each section being a day's work. The forms consisted of 2×8-in. planks, dressed on both sides, 2×8-in. studs spaced 2 ft. on centers and 4×6-in. braces. For the first two of the four abutments, the forms were erected in sections, the alternate sections being first erected and filled. When these sections had hardened the forms were shifted to the vacant sections and lined up to and braced against the completed sections. This method did not give well aligned walls, so in subsequent work the forms were erected all at once.

The concrete was mixed by hand. The sand and cement were mixed dry, being turned four times and spread in a layer Pebbles and broken stone previously wetted were spread over the sand and cement and the whole turned four times, the last turn being into wheelbarrows; about five common buckets of water were added during the mixing. The mixture sought was one that would ram without quaking. Two forms of rammers were used; for work next to forms a 4×6-in. rammer and for inside work 6-in diameter circular rammer weighing 20 lbs. The gang mixing and placing concrete consisted usually of:

Item.	Per Day.	Per Cu. Yd.
2 handling cement and sand	$ 3.00	$0.10
3 filling barrows with aggregate	4.50	0.15
8 mixing concrete	12.00	0.40
2 shoveling concrete into barrows	3.00	0.10
5 wheeling concrete to forms	7.50	0.25
1 spreading concrete	1.50	0.05
5 tamping concrete	7.50	0.25
	———	——
Total, 26 men	$39.00	$1.30

These cubic yard costs are based on 30 cu. yds. of wall completed per 8-hour day. The cost in detail of two abutments containing 254 cu. yds. was per cubic yard as follows:

Item.	Per Cu. Yd.
1.65 bbls. Portland (Germania) cement	$ 5.60
0.5 cu. yd. crushed stone	2.07
0.24 cu. yd. gravel	0.59
0.53 cu. yd. sand	0.24
Lumber, forms, warehouses, platforms[D]	0.55
Carpenter work[E] ($9 per M.)	1.10
Mixing and placing	1.47
20 per cent. first cost of plant	0.31
Engineering and miscellanies	0.31
	———
Total	$12.24

[D] Charging ¼ of first cost of $18 per M. ft.

[E] Carpenters $3.50, laborers $1.50 per day; there was one laborer to two carpenters.

The large amount of cement 1.65 bbls. per cubic yard was due to facing the abutments with 8 ins. of 1-2 mortar. The concrete in the body of the wall was 1 cement, 2 sand, 2 gravel and 2 broken stone mixture. A dry mixture was used and this fact is reflected in the cost of ramming, 25 cts. per cu. yd. The cost of mixing was also high.

Fig. 72.—Concrete Mixing Plant for Lock Walls, Illinois & Mississippi Canal.

Piers for Taintor Gates.—The masonry at this point consisted of three piers 6×30 ft., and two abutments 30 ft. long, 6 ft. thick at base and 4 ft. thick at top, with wing walls; it amounted to 460 cu. yds. The feet of the inclined braces were set into gains in the horizontal braces and held by an 8-in. lag screw; after the posts were plumbed a block was lag-screwed at the upper end of each brace. These forms proved entirely satisfactory. The cost of the work per cubic yard was as follows:

Item.	Per Cu. Yd.
1.45 bbls. Portland cement	$4.330
0.55 cu. yd. crushed stone	0.604
0.252 cu. yd. pebbles	0.328
0.465 cu. yd. sand	0.419
40,000 ft. B. M. lumber (¼ cost of $16 per M.)	0.348
Carpenter work on forms	0.780
Mixing and placing concrete	1.909
20 per cent. cost of plant	0.090
Miscellaneous	0.182
	———
Total	$8.99

Mixing Plant.—The concrete for all the lock work of 1893-4 was mixed by the plant shown by Figs. 72 and 73. The mixer plant proper consisted of a king truss carried by two A-frames of unequal height; under the higher end of the truss was a frame carrying a 4-ft. cubical mixer and under the lower end a pit for a charging box holding 40 cu. ft. This charging box was hoisted by ½-in. steel cable running through a pair of double blocks as shown; the slope of the lower chord of the truss was such that the cable hoisted the box and carried it forward without the use of any latching devices. On two sides of the pit were tracks from the sand and stone piles and on the other two sides were the cement platform and water tank. The charging box dumped into the hopper above the mixer and the mixer discharged into cars underneath. A 15-HP. engine operated the hoist by one pulley and the mixer by the other pulley. Nine revolutions of the mixer made a perfect mixture. The plant as illustrated was slightly changed as the result of experience in constructing the guard lock. The charging hopper was lowered 6 ins. and the space between the mixer and lower platform reduced by 9 ins.; diagonal braces were also inserted under the timbers carrying the mixer axles. This plant cost for framing and erection $300 and for machinery delivered $706. The crushing plant shown by Fig. 73 consisted of a No. 2 Gates crusher delivering to a bucket elevator.

Fig. 73.—Stone Crushing Plant for Lock Walls, Illinois & Mississippi Canal.

Fig. 74.—Forms for Guard Lock, Illinois & Mississippi Canal.

Guard Lock.—The forms employed in constructing the guard lock are shown by Fig. 74, and in this drawing the trestle and platform for the concrete cars are to be noted. The walls were concreted in sections. A batch of concrete consisted of 1 bbl. cement, 10 cu. ft. sand and 20 cu. ft. crushed stone. The average run per 8-hour day was 40 batches of facing and 60 batches concrete, representing 100 bbls. cement. The gang worked was as follows:

Duty.	No. Men.	P. C. Cost.
Handling cement	3	5.26
Filling and pushing sand car	5	8.77
Filling and pushing stone car	9	15.79
Measuring water	1	1.75
Dumping bucket on top platform	3	5.26
Opening and closing door of mixer	1	1.75
Operating friction clutch	1	1.76
Attending concrete cars under mixer	1	1.76
Dumping cars at forms	2	3.51
Spreading concrete in forms	3	5.26
Tamping concrete in forms	10	17.54
Mixing mortar for facing	6	10.53
Finishing top of wall	2	3.51
Hauling concrete cars with 1 horse	1	3.51
Engineman operating hoist	1	3.51
Engineman operating engine	1	3.51
Foreman in charge of forms	1	3.51
General foreman	1	3.51
	—	———
Total	52	100.00

The percentages of cost in this statement have been calculated by the authors upon the assumption that each laborer received one-half as much wages as each engineman, foreman and horse and driver per 8 hours, which would make the total daily wages equivalent to the wages of 57 men. Wages of common labor were $1.50 per day. Considering the size of the gang the output of 40 batches of mortar and 60 batches of concrete per day was very small. The total yardage of concrete in the guard lock was 3,762 cu. yds., 2,212 cu. yds. in the walls and 1,550 cu. yds. in foundations, culverts, etc. Its cost per cubic yard was made up as follows:

Item.	Total.	Per Cu. Yd.
5,246 bbls. Portland cement	$15,604}	$4.170
152 bbls. natural cement	84}
2,910 cu. yds. stone	2,901	0.771
126 cu. yds. pebbles	113}	0.401
1,970 cu. yds. sand	1,398}
145,000 ft. B. M. lumber (¼th cost)	659	0.175
Iron for forms, trestles, etc.	90	0.024
Coal, oil, miscellaneous	327	0.087
Carpenter work	2,726	0.724
Mixing and placing concrete	6,693	1.780
Pumping, engineering, misc.	742	0.197
20 per cent of plant	550	0.146
	———	———
Total	$31,887	$8.475

Fig. 75.—Forms for Regular Lock Walls, Illinois & Mississippi Canal.

Lock No. 37.—The character of the forms used in constructing the lock walls is shown by Fig. 75. The walls were built in sections and work was continuous with three 8-hour shifts composed about as specified for the guard lock work except that one or two men were added in several places making the total number 58 men. The average output per shift was 65 batches of concrete and 31 batches of facing mortar. The cost of the work, comprising 3,767 cu. yds., was as follows:

Item.	Total.	Per Cu. Yd.
4,564 bbls. Portland cement	$14,181	$3.764
2,460 cu. yds. crushed stone	4,521	1.200
250 cu. yds. pebbles	325	0.086
1,750 cu. yds. gravel	2,335	0.619
450 cu. yds. sand	450	0.119
180,000 ft. B. M. lumber (¼th cost)	990	0.236
Fuel, light, repairs, etc.	1,171	0.311
Carpenter work	2,526	0.671
Pumping	270	0.071
Mixing and placing concrete	6,170	1.632
20% cost of plant	730	0.193
	———	———
Total	$33,669	$8.902

Lock No. 36.—The forms used were of the construction shown by Fig. 75. Three shifts were worked, each composed as specified for the guard lock, except that the number of tampers and spreaders was doubled, bringing the gang up to 65 men. The average output per gang per shift was 76 batches of concrete and 35 batches of facing mortar. The cost of 2,141 cu. yds. of concrete in this lock was as follows:

Item.	Total.	Per Cu. Yd.
3,010 bbls. Portland cement	$9,057	$4.23
1,377 cu. yds. broken stone	1,922	0.90
393 cu. yds. pebbles	354	0.17
459 cu. yds. gravel	310	0.15
500 cu. yds. sand	889	0.42
150,000 ft. B. M. lumber (¼th cost)	600	0.28
Fuel, light, repairs, etc.	253	0.68
Carpenter work	1,472	0.11
Mixing and placing concrete	3,897	1.82
20% cost of plant	650	0.30
	———	——
Total	$19,404	$9.06

The preceding data, made public by Mr. Woermann in 1894, are supplemented by the following information prepared for the authors:

"If any criticism was to be made of the concrete masonry erected in 1893 and 1894, it would probably be to the effect that it was too expensive. The cost of the masonry erected during those two seasons was $8 to $9 per cu. yd. Our records showed that about 45 per cent. of this cost was for Portland cement alone, and moreover, that 40 per cent. of the total cement used at a lock was placed in the 8-in. facing and 5-in. coping. So in the seven locks erected in 1895 on the eastern section, the facing was reduced to 3 ins. and the proportions changed from 1-2 to 1-2½.

"In 1898 this cost received another severe cut, and Major Marshall's instructions stated that the facing should not exceed 1½ ins. in thickness nor be less than ¾-in., while the layer of fine material on top of the coping was to be only sufficient to cover the stone and gravel. The amount of sand was again increased so that the proportions were 1-3.

"The cost of the Portland cement concrete was likewise cheapened by increasing the amount of aggregates. On the earlier work the proportions were 1-2-2-3, while on the work in 1898 the proportions were 1-4-4. The cost of the walls was further cheapened by using Utica cement in the lower steps of the wall, with 2 ft. of Portland cement concrete on the face. The proportions used in the Utica cement concrete were 1-2½-2½. This lower step is one-third of the height, or about 7 ft.

Fig. 76.—Sketch Showing Method of Attaching Lagging to Studs, Illinois & Mississippi Canal.

"The forms were of the same character as those used on the first locks, except that for lining the inner face, 3×10-in. hard pine planks were substituted for the 4×8-in. white pine. The hard pine was damaged less by the continuous handling, and the cost was practically the same. There was also an important change made in the manner of fastening the plank to the 8×10-in. posts. A strip 1¾ ins. square was thoroughly nailed to each post, once for all, with 20d. spikes, and the planking was then nailed from the outside, as shown in Fig. 76. This kept the face of the plank in a perfectly smooth condition, and prevented the formation of the little knobs on the face of the concrete which represented all the old nail holes. This style of forming was also easier to take apart after the setting of the concrete. Rough pine planks, 2×12-in., were used for the back of the form, the same as before.

"In order to keep ahead of the concrete force it was necessary to use two gangs of carpenters, erecting the forms for the next two locks. Each gang consisted of about 20 carpenters (at $2.25) and 10 helpers (at $1.50); but men were transferred from one to the other, according to the stage of completion of the two locks. In addition to these two gangs, two carpenters were on duty with each concrete shift to put in the steps in the back of the forms. Sufficient lumber was required for the forms for three complete locks, and 14 locks (Nos. 8 to 21) were built.

"The same type of mixer has been used as on the earlier work at Milan, namely, a 4-ft. cubical steel box mounted on corners diagonally opposite. On account of the greater number of locks to be built on the eastern section, however, two mixers were found necessary, so that while the concrete force was at work at one lock, the carpenters and helpers were erecting the mixer at the next lock. The facing was mixed by hand. After turning over the dry cement and sand at least twice with shovels, the mixture was then cast through a No. 5 sieve, after which the water was incorporated slowly by the use of a sprinkling can so as to avoid washing. The secret of good concrete, after the selection of good materials, is thorough mixing and hard tamping. Each batch of concrete, consisting of about 1.2 cu. yds. in place, was turned in the mixer for not less than 2 mins. at the rate of 9 revolutions per minute. The amount of tamping is indicated by the fact that about 16 men out of 72 on each shift did nothing but tamp. The rammers used were 6 ins. square and weighed 33 lbs. The bottom of the rammer consisted of three ridges, each 1-in. in height, so as to make more bond between the successive layers.

"On the eastern section the top of the lock walls was higher above the ground, as a rule, than at the Milan locks, and the cars were run up an incline with a small hoisting engine. A 15-HP. portable engine and boiler operated the bucket hoist from one pulley, the mixer from the other pulley, and also furnished steam for the hoist which pulled the cars up the incline. The incline made an angle of about 30° with the ground. The practice of carrying on two sections at once was continued the same as on the western section. Each main wall was systematically divided into 11 sections, making each section about 20 ft. long. The corners of the coping were dressed to a quadrant of about 3 ins. radius with a round trowel like those used on cement walks. In fact, the whole method of finishing the coping was the same as is used on concrete walks. The mortar was put on rather wet and then allowed to stand for about 20 mins. before finishing. This allowed the water to come to the surface and prevented the formation of the fine water cracks which are sometimes seen on concrete work. After its final set the coping was covered with several inches of fine gravel which was kept wet for at least a week.

"The last concrete laid during the season was in November, on Lock No. 21, and Aqueducts Nos. 2 and 3. Portions of these structures were built when the temperature was below freezing. The water was warmed to about 60° or 70° F., by discharging exhaust steam into the tank. Salt was used only in the facing, simply sufficient to make the water taste saline. The maximum amount used on the coldest night when the temperature was about 20° F. was 1½ per cent.

The concrete force on each shift was as follows:

	Men.
Filling and pushing stone car	10
Filling and pushing gravel car	8
Measuring cement	3
Measuring water and cleaning bucket	2
Dumping bucket on top platform	2
Operating mixer	2
Loading concrete cars	1
Pushing and dumping cars on forms	3
Switchmen on forms	2
Spreading concrete in forms	12
Tamping concrete in forms	16
Mixing facing	3
Water boys	2
	—
Total laborers	66
Operating hoists	2
Finishing coping	2
Fireman	1
Sub-overseers	2
Overseer	1
	—
Total force	74

The cost of material and labor at Lock No. 15 (10-ft. lift), which contains 2,559 cu. yds. of concrete, was as follows:

Materials.	Per cu. yd.
0.56 bbl. Portland cement (0.96 per cu. yd.)	$1.42
0.64 bbl. Utica cement (1.58 per cu. yd.)	.30
0.58 cu. yd. stone	1.15
0.60 cu. yd. gravel	.52
14 ft. B. M. lumber[F] at $15 per M.	.21
0.6 lb. spikes	.01
Coal (10 tons in all, at $1.70)	.01
0.35 gal. kerosene	.03
	——
Total materials	$3.65
Labor.
Erecting forms ($7 per M.)	.45
Removing forms ($2 per M.)	.13
Erecting and removing mixer ($161)	.06
Loading and unloading materials at yards and lock sites	.23
Track laying ($86)	.03
Train service (narrow gage road)	.09
Delivering materials to mixer	.28
Mixing concrete	.11
Depositing concrete	.21
Tamping concrete	.21
Mixing, depositing and tamping, 69 cu. yds. face mortar ($160)	.23
General construction ($553)	.22
	——
Total labor	$2.25

[F] The lumber was used nearly five times, which accounts for its low cost per cu. yd.

There were 1,430 cu. yds. of Portland cement concrete. 69 cu. yds. of Portland cement mortar facing, and 1,059 cu. yds. of Utica cement concrete. The Portland concrete cost $6.43 per cu. yd.; the Utica concrete, $4.77 per cu. yd. The following is the cost of labor on Lock No. 20 (11-ft. lift.; 2,750 cu. yds.):

	Per cu. yd.
Erecting forms ($7 per M.)	$.434
Removing forms ($1.70 per M.)	.113
Erecting and removing mixer ($151)	.058
Loading and unloading at yards, lock sites, etc.	.614
Tracks	.024
Train service (narrow gage)	.016
Pumping	.114
Delivering material to mixer	.288
Mixing concrete	.134
Depositing concrete	.205
Tamping concrete	.192
Mixing, depositing and tamping, 85 cu. yds. face mortar	.071
General construction	.246
	———
Total	$2.509

COST OF HAND MIXING AND PLACING, CANAL LOCK FOUNDATION.—Mr. Geo. P. Hawley gives the following record of mixing and placing 4,000 cu. yds. of 1-4½ gravel concrete for the foundation of a lock constructed for the Illinois and Mississippi Canal in 1897. The concrete was mixed on 14×16-ft. board platforms, from which it was shoveled directly into place. The materials were brought to the board in wheelbarrows. Two boards were used, the usual gang for each being 4 men wheeling gravel, 4 men mixing, 1 man sprinkling, 2 men depositing and leveling and 2 men tamping. The two gangs were worked against each other. Ten hours constituted a day's work, and the average time and cost per cubic yard for mixing and placing were:

	Cts.
Foreman, 0.21 hr., at 30 cts	6.30
Laborers, 3.339 hrs., at 15 cts	50.09
Pump runner, 0.129 hr., at 20 cts	3.58
Water boy, 0.087 hr., at 7½ cts	0.65
	——
Total labor per cu. yd., cents.	60.62

BREAKWATER AT MARQUETTE, MICH.—The breakwater extends out from the shore and consists of a prism of concrete resting on timber cribs filled with stone. Originally the cribs carried a timber superstructure; this was removed to give place to the concrete work. A typical cross-section of the concrete prism is shown by Fig. 77; the prism is 23 ft. wide on the base. Farther in shore the base width was reduced to 20 ft., and in the shore section the prism was changed to a triangular trapezoid by continuing the first slope to the bottom cutting off the berm and second slope. The wooden structure was removed to a level 1 ft. below mean low water and on it a concrete footing approximately 2 ft. thick was constructed for the prism proper. This footing reached the full width of the crib and was constructed in various ways during the 5 years through which the work continued. At first the footing concrete was deposited loose under water by means of bottom dumping buckets; later the stone filling of the cribs was simply leveled up by depositing concrete in bags, and last toe and heel blocks were molded and set flush with the sides of the crib and filled between. Methods of construction and records of cost are reported for portions only of the work and these are given here.

Fig. 77.—Cross Section of Marquette Breakwater.

Footing Placed under Water with Buckets.—Besides the material track which was constructed along the old wooden structure the plant consisted of a mixing scow and a derrick scow, which were moored alongside the work. The sand, stone and cement were brought out in cars between working hours and stored on the mixing scow, enough for one day's work at a time. The derrick handled a 40-cu. ft. bottom dump bucket, which sat in a well on the mixing scow with its top flush with the deck. The concrete was mixed by hand on the deck and shoveled into the bucket; the bucket was then handled by the derrick to the crib and lowered and dumped under water. The gang consisted of 24 men, 1 foreman, 1 master laborer, 14 men shoveling and mixing, 3 men wheeling materials, 1 derrick man and 3 men placing and depositing concrete. No record of output of this gang is available. The cost of the concrete in place with wages $1.25 to $1.40 per day for common labor is given as follows:

Materials.	Per cu. yd.
1.21 bbls. (459 lbs.) cement at $2.20	$2.657
1 cu. yd. stone at $1.58	1.580
0.5 cu. yd. sand at $0.50	0.250
2.02 lbs. burlap at $0.037	0.075
Twine and needles	0.005
	———
Total materials	$4.567
Labor.
Loading scow with materials	$0.4114
Mixing concrete	0.8459
Depositing concrete	0.5242
	———
Total labor	$1.7815
Grand total	$6.348

These figures are based on some 757 cu. yds. of concrete footing. In explanation of the items of burlap, etc., it should be said that the cribs were carpeted with burlap to prevent waste of concrete into the stone fill.

Fig. 78.—Cross Section of Marquette Breakwater Showing Manner of Constructing Footing with Bags of Concrete.

Leveling Off Cribs with Concrete in Bags.—The sketch, Fig. 78, shows the method of leveling off the cribs with concrete in bags. The concrete was mixed by hand on shore and filled into 8-oz. burlap bags, 6 ft. long and 80 ins. around, holding 2,000 lbs. The bags were filled while lying in position in a skip holding one bag. A skip was lifted by gallows frame and tackle onto a car and run out to the work where the derrick scow handled the skip to the crib, lowered it into the water and dumped the bag. The cost of making and placing some 375 cu. yds. of concrete in bags is given as follows:

Materials.	Total.	Per cu. yd.
453 bbls. cement at $2.627	$1,190.03	$3.173
375 cu. yds. stone at $1.619	607.13	1.619
180 cu. yds. sand at $0.392	70.56	0.188
3,220 yds. burlap at $0.03304	106.39	0.283
Twine and needles	6.36	0.017
	————	———
Total materials	$1,980.47	$5.280
Labor Mixing.
108 hrs. master laborer at $0.21⅞	$23.42	$0.062
1,750 hrs. labor at $0.175	306.25	0.816
Superintendence	12.55	0.033
	————	———
Total labor mixing	$ 342.22	$0.911
Labor transporting.
306 hrs. labor at $0.175	$53.55	$0.142
Superintendence	5.25	0.014
	————	———
Total labor transporting.	$58.80	$0.156
Labor Depositing.
108 hrs. engineman at $0.25	$27.00	$0.072
108 hrs. master laborer at $0.21⅞	23.42	0.062
510 hrs. labor at $0.175	89.25	0.238
Superintendence	13.25	0.035
	————	———
Total labor depositing	$ 152.92	$0.407
Grand total labor	$ 553.94	$1.477
Grand total materials and labor	$2,534.41	$6.757

Molding Footing Blocks.—The blocks used at the toe of the prism were of the form and dimensions shown by Fig. 79. They were molded in a temporary shed heated to 50° to 65° F., and provided with a 2×8-in. dressed plank floor on 12×12-in. sills. The floor formed the bottoms of the block molds. Four molds were used, each consisting of four sides. Three laborers molded one block, 2.22 cu. yds. per day, wheeling, mixing, erecting and removing forms, placing concrete and doing all other work. The cost of making 40 blocks was recorded as follows:

Materials.	Total.	Per cu. yd.
126 bbls. cement at $2.75	$346.50	$3.893
88.9 cu. yds. screenings at $1.10	97.79	1.098
40.1 cu. yds. sand at $0.45	18.04	0.203
5 gals. oil at $0.65	3.25	0.036
	———	———
Total materials	$465.58	$5.230
Labor.
1,000 hrs. labor at $0.125	$125.00	$1.404
Watchman	29.15	0.327
Labor cutting wood for fuel	23.80	0.267
Superintendence	42.66	0.480
	———	———
Total labor	$220.61	$2.478
Total labor and materials	$686.19	$7.708

Fig. 79.—Details of Toe Blocks for Footing, Marquette Breakwater.

Molding Concrete Prism in Place.—The concrete prism was molded in alternate sections 10 ft. long; the form for the isolated sections consisted of eight pieces so constructed that when assembled in place and secured with bolts and turnbuckles the form was self-contained as to strength and required no outside support or bracing. The form once in place, all that remained to be done was to fill it, the block with the gallery through it being molded in one operation. The forms for the connecting blocks consisted of two slope panels, a panel for the harbor face and the gallery form, the blocks previously molded making the other sides of the form. The concrete was mixed by hand on shore, conveyed to the work in 1 cu. yd. cars and shoveled into the forms, where it was rammed with 35-lb. rammers. The following record covers 1,231 cu. yds. of concrete prism. In this concrete some 214 cu. yds. of rubble stone were embedded. The costs given are as follows:

Materials—	Total.	Per cu. yd.
1,780 bbls. natural cement at $1.068	$1,901.04	$1.545
963½ cu. yds. stone at $1.619	1,559.91	1.267
53½ cu. yds. screenings at $0.392	20.97	0.017
485.6 cu. yds. sand at $0.392	190.36	0.154
Miscellaneous materials	78.15	0.063
	————	———
Totals	$3,750.43	$3.046
Labor Mixing—
254 hrs. master laborer at $0.21⅞	$55.56	$0.045
4,470 hrs. labor at $0.175	782.42	0.635
Superintendence	18.20	0.015
	————	———
Total labor mixing	$ 856.18	$0.695
Labor Transporting and Placing—
35 days overseer at $2.33⅓	$81.67	$0.066
1,949 hrs. labor at $0.175	342.07	0.277
Superintendence	34.98	0.028
	——— —	———
Total labor transporting and placing	$ 458.72	$0.371
Grand total, labor	$1,314.90	1.066
Total labor and materials	$5,065.33	4.112

No charge is made under materials for rubble stone as the only cost for this was cost of handling and this is included in transporting and placing.

BREAKWATER, BUFFALO, N. Y.—The following methods and costs of mixing and placing some 2,561 cu. yds. of concrete are given by Mr. Emile Low, for 10 parapet wall sections and 17 parapet deck sections for a breakwater at Buffalo, N. Y.

The concrete used was a 1 cement, 1 gravel, 1 sand grit and 4 unscreened broken stone. One bag of cement was assumed to measure 0.9 cu. ft. The voids in the sand grit and gravel were 27 per cent. and in the unscreened stone 39 per cent. The hardened concrete weighed 152 lbs. per cu. ft.

Fig. 80.—Sketch Plan of Concrete Mixing Plant for Buffalo Breakwater.

Figure 80 shows the arrangement of the mixing plant. The mixer was a 5-ft. cube mixer holding 125 cu. ft., mounted on a trestle and operated by a 9×12-in. horizontal engine taking steam from a 4×10-ft. locomotive boiler, also supplying steam to two derrick engines. The material scow contained two pockets for sand, one for gravel and one housed over for cement. Two inside cement men passed out the bags in lots of six to one outside cement man who cut and emptied them into the charging bucket. Three sand shovelers each loaded a 3.6 cu. ft. barrow and wheeled them tandem to the bucket, and two gravel men each loaded a 2.7 cu. ft. barrow and wheeled them tandem to the bucket. The broken stone was loaded by eight shovelers into another bucket, also containing 21.6 cu. ft. The two buckets were alternately hoisted and emptied into the mixer hopper, there being a dump man on the mixer who dumped the buckets and attended to the water supply. A charger put the mixer in operation and when the charge was mixed the car men dumped it into a skip resting on a small car which was then run out on the track under the mixer to the derrick which handled the skip to the work. Derrick A handled the materials from the scows and derrick B handled the mixed concrete. The force on the derricks consisted of two enginemen, four tagmen and the fireman.

The ten parapet wall sections containing 841 cu. yds. were built in 46 hours, making 17 batches of 1.07 cu. yds., or 18.2 cu. yds. placed per hour. The 17 parapet deck sections containing 1,720 cu. yds. were built in 88 hours, making 18.8 batches of 1.08 cu. yds., or 19.5 cu. yds. placed per hour. For the parapet deck work the force was increased by 2 men handling materials and 1 man on the mixer. The labor cost of mixing and placing the concrete was as follows:

Loading Gang—	Per day.	Per cu. yd.
1 assistant foreman	2.00	$0.011
3 cement handlers	5.25	0.029
3 sand shovelers	5.25	0.029
2 gravel shovelers	3.50	0.020
8 stone shovelers	14.00	0.076
1 hooker on	1.75	0.010
	———	———
Totals	$31.75	$0.175
Mixer Gang—
1 dumpman	$ 1.75	$0.010
1 charging man	1.75	0.010
2 car men	3.50	0.020
2 enginemen at $3.25	6.50	0.035
4 tagmen at $2	8.00	0.044
1 fireman	2.00	0.011
	———	———
Totals	$23.50	$0.130
Wall Gang—
1 Signalman	$ 1.75	$0.010
1 dumper	1.75	0.010
6 shovelers at $2	12.00	0.065
4 rammers	7.00	0.038
1 foreman	4.00	0.022
	———	——
Totals	$26.50	$0.145
Grand totals	$81.75	$0.450

Fig. 81.—Concrete Blocks for Pier at Port Colborne Harbor.

Fig. 82.—Forms for Molding Blocks, Port Colborne Harbor Pier.

Fig. 83.—Device for Handling Blocks, Port Colborne Harbor Pier.

PIER CONSTRUCTION, PORT COLBORNE, ONT.—In constructing the new harbor at Port Colborne, Ont., on Lake Erie, the piers consisted of parallel rows of timber cribs set the width of the pier apart and filled in and between with stone blasted and dredged from the lake bottom in deepening the harbor. The tops of the cribs terminated below water level and were surmounted by concrete walls set on the outer edges. These walls were filled between with stone and the top of the filling was floored part way or entirely across, as the case might be, with a thick concrete slab. The footings of the walls to just above the water level were made of concrete blocks 4½×4×7 ft., constructed as shown by Fig. 81. The wall above the footing course and the floor slab were of concrete molded in place. The concrete work consisted of molding and setting concrete blocks and of molding concrete wall and slab in place.

The blocks were molded on shore, shipped to the work on scows and set in place by a derrick. Figure 82 shows the construction of the forms for molding the blocks; the bottom tie rods passed through the partitions forming the ends of the molds. The sides were removed in 48 hours and used over again. Figure 83 shows the hooks used for handling the molded blocks. Considerable trouble was had in setting these blocks level and close jointed, owing to the difficulty of leveling up the stone filling under water.

Fig. 84.—Scow Plant for Mixing and Placing Concrete, Port Colborne Harbor Pier.

The mass concrete was mixed and placed by the scow plant, shown by Fig. 84. The scow was loaded with sufficient sand and cement for a day's work and towed to and moored alongside the pier. Forms were set for the wall on top of the block footing. These forms were placed in lengths of 60 to 75 ft. of wall and resembled the block forms with partitions omitted. The bottoms of the rear uprights were held by being wedged into the grooves in the blocks, and the bottoms of the front uprights were held by bolts resting on top of the blocks. The tops of the uprights were held together across the wall by tie bolts. The forms being placed, the mode of procedure was as follows:

The crusher fed directly into a measuring box. After some 6 ins. of stone had run into the box the door of the crusher spout was closed. A wheelbarrow load of sand was spread over the stone in the box and over this were emptied and spread two or three bags of cement. Another layer of stone and then of sand and of cement were put in and these operations repeated until the box was full. The box was then hoisted and dumped into the hopper of a gravity mixer of the trough type which ran along a track on the scow and fed directly into the forms. The gang worked consisted of 1 foreman, 1 derrickman and 18 common laborers. This gang placed from 65 to 75 cu. yds. of concrete per day at a labor cost of 50 cts. per cu. yd.

Fig. 85.—Cross-Section of Concrete Pier, Superior, Wis.

CONCRETE BLOCK PIER, SUPERIOR ENTRY, WIS.—The methods and cost of constructing a concrete pier 3,023 ft. long and of the cross-section shown by Fig. 85 at Superior entry, Wisconsin, are given in the following paragraphs.

Molds and Molding.—About 80 per cent. of the concrete was deposited in molds under water, according to a plan devised by Major D. D. Galliard, corps of engineers. In brief the concrete was built in place in two tiers of blocks, the lower tier resting directly on piles and being entirely under water and the upper tier being almost entirely above water. As shown by Fig. 85, a pile trestle was built on each side of the proposed pier and a traveler for raising and lowering the molds spanned the space between trestles.

The molds were bottomless boxes built in four pieces, two sides and two ends, held together by tie rods. Fig. 86 shows an end and a side of one of the shallow water molds and Fig. 87 shows in detail the method of fastening the end to the side. It will be seen that the 1¼-in. turnbuckle rods pass through the ends of beams that bear against the outside of the mold. These tie rods have eyes at each end in which rods with wedge-shaped ends are inserted. The molds were erected on the trestle by a locomotive crane and were then lifted by the mold traveler, carried and lowered into place. The largest one of these molds with its iron ballast, weighed 40 tons. To remove a mold, after the block had hardened, the nuts on the wedge-ended rods were turned, thus pulling the wedge end from the eye of the tie rod and releasing the sides of the mold from the ends. The locomotive crane then raised the ends and sides, one at a time, and assembled them ready to be lowered again for the next block. The time required to remove one of these 40-ton molds, reassemble and set it again rarely exceeded 60 minutes and was sometimes reduced to 45 minutes.

Fig. 86.—Mold for Concrete Block for Pier at Superior, Wis.

The concrete was deposited in alternate blocks and the molds described were for the first blocks; for the intermediate blocks molds of two side pieces alone were used, the blocks already in place serving in lieu of end pieces. The two side pieces were bolted together with three tie rods at each end; the tie rods were encased in a box of 1-in. boards 4×4 ins. inside which served as a strut to prevent the sides from closing together and as a means of permitting the tie rods to be removed after the concrete had set. The mold was knocked down just as was the full mold described above and the boxes encasing the tie rods were left in the concrete.

Fig. 87.—Device for Locking End and Side of Mold for Concrete Blocks for Pier at Superior, Wis.

An important feature was the device for handling the molds; this, as before stated, was a traveler, which straddled the pier site, it having a gage of 31 ft. It carried a four-drum engine, the drums of which were actuated, either separately or together, by a worm gear so as to operate positively in lowering as well as in raising. The load was hung from four hooks, depending by double blocks and ⅝-in. wire rope from four trolleys suspended from the trusses of the traveler; this arrangement allowed a lateral adjustment of the mold. The hoisting speed was 6 ft. per minute and the traveling speed 100 ft. per minute. The locomotive crane also deserves mention because it was mounted on a gantry high enough to permit material cars to pass under it on the same trestle, thus making it practicable to work two cranes.

Fig. 88.—Bucket for Depositing Concrete Under Water for Pier at Superior, Wis.

The concrete was received from the mixer into drop bottom buckets of the form shown by Fig. 88. The buckets were taken to the work four at once on cars, and there lifted by the locomotive crane and lowered into the mold where they were dumped by tripping a latch connected by rope to the crane. To prevent the concrete from washing, the open tops of the buckets were covered with 3×4 ft. pieces of 12-oz. canvas in which were quilted 110 pieces of 1/16×1×3-in sheets of lead. Two covers were used on each bucket and were attached one to each side of the bucket top so as to fold over the top with a lap. This arrangement was entirely successful for its purpose.

Concrete Mixing.—The proportions of the subaqueous concrete were 1-2½-5 by volume, or 1-2.73-5.78 by weight, cement being assumed to weigh 100 lbs. per cu. ft.; the proportions of the superaqueous concrete were 1-3.12-6.25 by volume, or 1-3.41-7.22 by weight. The dry sand weighed 109.2 lbs. per cu. ft., the voids being 35.1 per cent.; the pebbles weighed 115.5 lbs. per cu. ft., the voids being 31 per cent.

The pebbles for the concrete were delivered by contract and were unloaded from scows by clam-shell bucket into a hopper. This hopper fed onto an endless belt conveyor which delivered the pebbles to a rotary screen. Inside this screen water was discharged under a pressure of 60 lbs. per sq. in. from a 4-in. pipe to wash the pebbles. From the screen the pebbles passed through a chute into 4-cu. yd cars which were hauled up an incline to a height of 65 ft. by means of a hoisting engine. The cars were dumped automatically, forming a stock pile. Under the stock pile was a double gallery or tunnel provided with eight chutes through the roof and from these chutes the cars were loaded and hauled by a hoisting engine up an inclined trestle to the bins above the concrete mixer. The sand was handled from the stock pile in the same manner. The cement was loaded in bags on a car in the warehouse, hauled to the mixer and elevated by a sprocket chain elevator.

Chutes from the bins delivered the materials into the concrete mixer, which was of the Chicago Improved Cube type, revolving on trunnions about an axial line through diagonal corners of the cube. The mixer possessed the advantage of charging and discharging without stopping. It was driven by a 7×10-in. vertical engine with boiler. The mixer demonstrated its ability to turn out a batch of perfectly mixed concrete every 1⅓ minutes. It discharged into a hopper provided with a cut-off chute which discharged into the concrete buckets on the cars.

Labor Force and Costs.—In the operation of the plant 55 men were employed, 43 being engaged on actual concrete work and 12 building molds and appliances for future work. The work was done by day labor for the government and the cost of operation was as follows for one typical week, when in six days of eight hours each, the output was 1,383 cu. yds., or an average of 230 cu. yds. per day. The output on one day was considerably below the average on account of an accident to the plant, but this may be considered as typical.

Pebbles from Stock Pile to Mixer—	Per cu. yd.
4 laborers at $2	$0.0348
1 engineman at $3	0.0131
Coal, oil and waste at $1.03	0.0043
Sand from Stock Pile to Mixer—
5 laborers at $2	$0.0434
1 engineman at $2.50	0.0109
Coal, oil and waste at $0.82	0.0035
Cement from Warehouse to Mixer—
5 laborers at $2	$0.0434
Mixing Concrete—
1 engineman at $2.50	$0.0109
1 mechanic at $2.50	0.0108
Coal, oil and waste at $1.29	0.0056
Transporting Concrete—
4 laborers at $2	$0.0348
1 engineman at $3	0.0130
Coal, oil and waste at $0.66	0.0028
Depositing Concrete in Molds—
4 laborers at $2	$0.0348
1 engineman at $3	0.0130
1 rigger at $3	0.0130
Coal, oil and waste at $1.18	0.0051
Assembling, Transporting, Setting and Removing Molds—
4 laborers at $2	$0.0347
1 engineman at $3.25	0.0141
1 carpenter at $3	0.0130
1 mechanic at $2.50	0.0109
Coal, oil and waste at $1.39	0.0060
Care of Tracks—
1 laborer at $2	$0.0086
1 mechanic at $2.50	0.0109
Supplying Coal—
3 laborers at $2	$0.0260
Blacksmith Work—
1 laborer at $2	$0.0086
1 blacksmith at $3.25	0.0141
1 waterboy at $0.75	0.0032
	———
Total per cubic yard	$0.4473
Add 75% of cost of administration	0.1388
	———
Total labor per cu. yd.	$0.5861

The total cost of each cubic yard of concrete in place was estimated to be as follows:

	Per cu. yd.
Ten-elevenths cu. yd. pebbles at $1.085	$0.9864
Ten-twenty seconds cu. yd. sand at $0.00	0.0000
1 26 bbls. cement at $1.77	2.2302
Labor as above given	0.5861
Cost of plant distributed over total yardage	0.8400
	———
Total	$4.6427

It will be noted that the sand cost nothing as it was dredged from the trench in which the pier was built, and paid for as dredging. The cost of the plant is distributed over this south pier and over the proposed north pier work on the basis of only 20 per cent. salvage value after the completion of both piers. It is said, however, that 80 per cent. is too high an allowance for the probable depreciation.

DAM, RICHMOND, INDIANA.—The dam shown in cross-section in Fig. 89 was built at Richmond, Ind. It was 120 ft. long and was built between the abutments of a dismantled bridge. The concrete was made in the proportion of 1 bbl. Portland cement to 1 cu. yd. of gravel; old iron was used for reinforcement. The foundations were put down by means of a cofferdam which was kept dry by pumping. On completion it was found that there was a tendency to scour in front of the apron and accordingly piling was driven and the intervening space rip-rapped with large stone. Labor was paid as follows per day: Foreman, $3; carpenter, $2.50; cement finisher, $2; laborers, $1.50. The concrete was mixed by hand and wheeled to place in wheelbarrows. The cost of the work was as follows:

Materials—	Per cu. yd.
204 bbls. cement at $1.60	$1.485
Sand and gravel	0.800
Lumber	0.610
Tools, hardware, etc.	0.445
	———
Total materials	$3.34
Labor—
Clearing and excavating	$0.96
Setting forms and mixing concrete	1.01
Pumping	0.27
	———
Total labor	$2.24
Total materials and labor	$5.58

Fig. 89.—Concrete Dam at Richmond, Ind.

DAM AT ROCK ISLAND ARSENAL, ILLINOIS.—The dam was in the shape of an L with one side 192 ft. and the other side 208 ft. long; it consists of a wall 30½ ft. high, 3½ ft. wide at the top and 6½ ft. wide at the bottom with a counterfort every 16 ft., 26 in all. Each counterfort extended back 16 ft. and was 4 ft. thick for a height of 6 ft. and then 3 ft. thick. There were 3,500 cu. yds. of concrete in the work, which was done by day labor under the direction of the U. S. Engineer in charge.

The forms consisted of front and back uprights of 8×10-in. stuff 24 ft. high, connected through the wall by ¾-in. rods which were left in the concrete. The lagging was 2×12-in. plank dressed down 1¾ ins. placed inside the uprights. These forms were built full height in 16-ft. sections with a counterfort coming at the center of each section. Each section contained 95 cu. yds. of concrete and was filled in a day's work. The concrete was a 1-4-7 mixture wet enough to quake when rammed. Run of crusher limestone was used of which 50 per cent. passed a 1-in. sieve, 17 per cent. a No. 3 sieve and 9 per cent. a No. 8 sieve. The concrete was mixed in Cockburn Barrow & Machine Co.'s screw-feed mixer which discharged into 2-in. plank skips 2 ft. wide 5⅓ ft. long and 14 ins. deep, holding ¼ cu. yd. These skips were taken on cars to a derrick crane overhanging the forms and by it hoisted and dumped into the forms. The derrick was moved along a track at the foot of the wall as the work progressed. The concrete was spread and rammed in 6-in. layers. The men were paid $1.50 per 8-hour's work and the work cost including footing, as follows:

Item—	Total.	Per cu. yd.
Cement	$1,500.00	$0.429
Sand	400.00	0.114
Storing and hauling cement	460.00	0.131
Taking sand from barge to mixer	96.00	0.027
Crushing stone	1,450.00	0.414
Mixing concrete	4,825.00	1.378
Placing concrete	1,670.00	0.477
Lumber for forms, etc.	600.00	0.171
Erecting and taking down forms	2,450.00	0.700
	—————	———
Totals	$13,451.00	$3.841

DAM AT McCALL FERRY, PA.—The dam was 2,700 ft. long and 48 ft. high of the cross-section shown by Fig. 90 and with its subsidiary works required some 350,000 cu. yds. of concrete. The plant for mixing and placing the concrete was notable chiefly for its size and cost. Parallel to the dam, which extended straight across the river, and just below its toe a service bridge consisting of a series of 40-ft. concrete arch spans was built across the river. This service bridge was 50 ft. wide and carried four standard gage railway tracks besides a traveling crane track of 44 ft. gage. This very heavy construction of a temporary structure was necessitated by the frequency of floods against which only a solid bridge could stand; it was considered cheaper in the long run to provide a bridge which would certainly last through the work than to chance a structure of less cost which would certainly go out with the floods. The concrete service bridge was designed to be destroyed by blasting when the dam had been completed. The method of construction was to build the dam in alternate 40 ft. sections, mixing the concrete on shore, taking it out along the service bridge in buckets on cars and handling the buckets from cars to forms by traveling cranes.

Fig. 90.—Steel Forms for McCall Ferry Dam.

The concrete mixing plant is shown by Fig. 91. Cars loaded with cement, sand and stone were brought in over the tracks carried on the wall tops of the bins and were unloaded respectively into bins A, B and C, of which there were eight sets. Each set supplied material by means of measuring cars to a 1 cu. yd. Smith mixer. Two sets of cars were used for each mixer so that one could be loading while the other was charging. The mixers discharged into 1 cu. yd. buckets set two on a car and eight cars were hauled to the work in train by an 18-ton "dinky." At the work the buckets were picked up by the traveling cranes and the concrete dumped into the forms. Figure 90 shows the construction of the steel forms. Six sets of forms were used. Each set consisted of five frames spaced 10 ft. apart and braced together in the planes parallel to the dam, and each set molded 40 ft. of dam. The lagging consisted of wooden boxes 8½ ft. wide and 10 ft. long. For the vertical face of the dam these boxes were attached by bolts to the vertical post, for the curved face they were bolted to a channel bent to the curve and held by struts from the inclined post of the steel frame.

Fig. 91.—Concrete Mixing Plant for McCall Ferry Dam.

In construction the footing and the body of the dam to an elevation of 5 ft. above the beginning of the curve were built continuously across the river; above this elevation the dam was built in alternate 40-ft. sections. The strut back to the service bridge shown in the lower right hand corner of Fig. 90, shows the manner of bracing the first 30-ft. section of the inclined post to hold the lagging for the continuous portion. The lagging was added a piece at a time as concreting progressed. The ends of each set of frames for a 40-ft. section were for the isolated sections closed by timber bulkheads carrying box forms to mold grooves into which the concrete of the intermediate sections would bond.

Fig. 92.—Traveler for Concreting Dam, Chaudiere Falls, Quebec.

The concrete used was a 1-3-5 mixture, the stone ranging in size from 2 to 5 ins. Rubble stone from one man size to ½ ton were bedded in the concrete. The capacity of the concrete plant was 2,000 cu. yds. per day or about 250 cu. yds. per mixer per 10-hour day.

DAM, CHAUDIERE FALLS, QUEBEC.—The dam was 800 ft. long and from 16 to 20 ft. high, constructed of 1-2-4 concrete with rubble stone embedded. The rubble stones were separated at least 9 ins. horizontally and 12 ins. vertically and were kept 20 ins. from faces. At one point the rubble amounted to 40 per cent. of the volume, but the average for the dam was 25 to 30 per cent. The stone was broken at the work, some by hand, but most by machine, all to pass a 2-in. ring. Hand-broken stone ran very uniform in size and high in voids, often up to 50 per cent. Stone broken by crusher with jaws 2 ins. apart would run 20 to 30 per cent. over 2 ins. in size and give about 45 per cent. voids; with crusher jaws 1½ ins. apart from 98 to 100 per cent. was under 2 ins. in size and contained about 42 per cent. of voids. It was found that if the crushers were kept full all the time the product was much smaller, particularly with Gates gyratory crusher, though a little more than rated power was required when the crusher was thus kept full. This practice secured increased economy in both quantity and quality of product. The concrete was made and placed by means of a movable traveler shown by Fig. 92. Concrete materials were supplied to the charging platform of the traveler by means of a traveling derrick moving on a parallel track. In placing the concrete on the rock bottom it was found necessary in order to secure good bond to scrub the rock with water and brooms and cover it with a bed of 2 ins. of 1-2 mortar. The method of concreting in freezing weather is described in Chapter VII.

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