Concrete Construction Part 17

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 ca.n.a.lization, 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 44 ft.

cube mixer, driven by a 1016-in. engine. The top floor of the mixer house stored the cement, 2,000 bbls. The concrete was a 1-3-5 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.

[Ill.u.s.tration: 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 212-in.

planks 4 ins. from the laggings, being kept to distance by 24-in.

s.p.a.cers, placing and ramming the concrete behind them, then withdrawing them, filling the 6-in. s.p.a.ce 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 68-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 68-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 310-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 Ca.n.a.l.~--The locks and practically all other masonry for the Illinois & Mississippi Ca.n.a.l 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 28-in. planks, dressed on both sides, 28-in. studs s.p.a.ced 2 ft. on centers and 46-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 46-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

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

[Footnote 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.

[Ill.u.s.tration: Fig. 72.--Concrete Mixing Plant for Lock Walls, Illinois & Mississippi Ca.n.a.l.]

_Piers for Taintor Gates._--The masonry at this point consisted of three piers 630 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 ( 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 -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 ill.u.s.trated was slightly changed as the result of experience in constructing the guard lock. The charging hopper was lowered 6 ins. and the s.p.a.ce 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.

[Ill.u.s.tration: Fig. 73.--Stone Crushing Plant for Lock Walls, Illinois & Mississippi Ca.n.a.l.]

[Ill.u.s.tration: Fig. 74.--Forms for Guard Lock, Illinois & Mississippi Ca.n.a.l.]

_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 a.s.sumption 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 (th 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

[Ill.u.s.tration: Fig. 75.--Forms for Regular Lock Walls, Illinois & Mississippi Ca.n.a.l.]

_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 (th 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 (th 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 1-2.

"In 1898 this cost received another severe cut, and Major Marshall's instructions stated that the facing should not exceed 1 ins. in thickness nor be less than -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 1-2-2.

This lower step is one-third of the height, or about 7 ft.

[Ill.u.s.tration: Fig. 76.--Sketch Showing Method of Attaching Lagging to Studs, Illinois & Mississippi Ca.n.a.l.]