Concrete Construction Part 18

"The forms were of the same character as those used on the first locks, except that for lining the inner face, 310-in. hard pine planks were subst.i.tuted for the 48-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 810-in. posts. A strip 1 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 k.n.o.bs 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, 212-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 1 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

[Footnote 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, Ca.n.a.l LOCK FOUNDATION.~--Mr. Geo. P.

Hawley gives the following record of mixing and placing 4,000 cu. yds.

of 1-4 gravel concrete for the foundation of a lock constructed for the Illinois and Mississippi Ca.n.a.l in 1897. The concrete was mixed on 1416-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 const.i.tuted 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 7 cts 0.65 ----- Total labor per cu. yd., cents. 60.62

~BREAKWATER AT MARQUETTE, MICH.~--The breakwater extends out from the sh.o.r.e 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 sh.o.r.e the base width was reduced to 20 ft., and in the sh.o.r.e 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.

[Ill.u.s.tration: 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.

[Ill.u.s.tration: 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 sh.o.r.e 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 $0.21-7/8 $ 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 $0.21-7/8 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 28-in.

dressed plank floor on 1212-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

[Ill.u.s.tration: 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 a.s.sembled 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 sh.o.r.e, 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:

Per Materials-- Total. cu. yd.