[Ill.u.s.tration: Fig. 110.--End View of Forms for Retaining Wall, New York Central Terminal Work.]
~WALL FOR RAILWAY YARD.~--For building a retaining wall 7 ft. high, forms were made and placed by a carpenter and helper at $8 per M., wages being 35 cts. and 20 cts. an hour, respectively. Concrete materials were dumped from wagons alongside the mixing board. Ramming was unusually thorough. Foreman expense was high, due to small number in gang; 2 cu.
yds. were laid per hour by the gang.
[Ill.u.s.tration: Fig. 111.--Corner Detail of Retaining Wall Forms, New York Central Terminal Work.]
Per day. Per cu. yd.
7 mixers, 15 cts. per hour $10.50 $0.53 2 rammers, 15 cts. per hour 3.00 0.15 1 foreman 30 cts. per hr., 1 waterboy 5 cts. 3.50 0.17 ------- ------ Total labor $17.00 $0.85
The total cost was as follows per cubic yard:
Per cu. yd.
0.8 bbls. Portland cement, at $2 $1.60 Sand 0.30 Gravel 0.70 Labor mixing and placing 0.85 Lumber for forms, at $16 per M. 0.56 Labor on forms, at $8 per M. 0.28 ------ Total, per cubic yard $4.29
The sheathing plank for the forms was 2-in. hemlock.
~CONCRETE FOOTING FOR RUBBLE MASONRY RETAINING WALL.~--In constructing a footing for a retaining wall at Grand Rapids, Mich., a 1-2-5 natural cement concrete was used. It was found that 1 cu. yd. of concrete was equivalent to 29.8 cu. ft. of material composed of 3.6 cu. ft. or 1.1 bbls. of cement, 8.4 cu. ft. or 2.7 bbls. of sand and 17.8 cu. ft. or 5.5 bbl. of broken stone. The labor cost of 15.5 cu. yds. of concrete was as follows:
Item. Total. Per cu. yd.
Foreman, 14 hours at 40 cts. $ 5.60 $0.3613 Foreman, 20 hours at 22.5 cts. 4.50 0.2903 Laborers, 49 hours at 12.5 cts. 6.11 0.3942 Mason, 2 hours at 35 cts. 0.70 0.0451 ------ -------- Total labor $16.91 $1.0909
All material was furnished by the railway company, the contractor furnishing labor only; his contract price for this was $1 per cu. yd.
~TRACK ELEVATION, ALLEGHENY, PA.~--The wall was 6,100 ft. long and 75 per cent. was on curves. The first wall built had a top width of 2 ft. and a bottom width of 0.4 the height with the back on a smooth batter. Later the back was stepped and last the wall was proportioned as follows: Calling the height from top of foundation to under coping, then width of base was 0.45 (h + 3), the top measuring 2 ft. The back was arranged in steps 24 ins., 30 ins. and 36 ins. high, and the thickness of wall at each step was, calling h equal to height of step from base, 0.45 (h + 3).
Several forms of expansion joints were tried. The first was tarred paper extending through the wall every 50 ft.; the second was -in.
boards running through the wall every 50 ft.; the third was -in. board extending 2 ft. into the wall, with a -in. cove at the angles, every 25 ft. The third construction gave perfect satisfaction.
A 1-2-5 natural cement and a 1-3-6 Portland cement concrete mixed fairly wet were used. The concrete was laid in 8-in. courses and faced with a 1-2 mortar. The forms were 2-in. white pine faced and jack planed on the edges; upon removal of the forms board marks and other defects were removed and a wash of neat cement was applied. One contractor used hand mixing. The sand and gravel were measured in wheelbarrows and wheeled onto the platform; the sand and cement were spread in thin layers, one over the other, and thoroughly mixed dry; the gravel was then spread over the mixture, the whole was shoveled into barrows or the pit again shoveled into place and rammed. The other contractor used a cubical mixer. A charging box holding 1 cu. yds. and graduated to show the correct proportions of sand and gravel was filled by shoveling; cement was placed on top and the box hoisted and dumped into the mixer. A barrel holding the correct amount of water was emptied into the mixer which was turned 10 or 15 times and discharged into cars. The costs of mixing by hand and by machine were as follows:
Hand mixing. Total. Per cu. yd.
foreman at $3 $ 1.50 $0.025 3 men wheeling barrows at $1.50 4.50 0.075 10 men wheeling materials at $1.50 15.00 0.250 3 men mixing sand and gravel at $1.50 4.50 0.075 6 men mixing concrete at $1.50 9.00 0.150 1 man sprinkling at $1.50 1.50 0.025 ------ ------ Total $36.00 $0.600
The output of the hand mixing gang was 60 cu. yds. per day.
Machine mixing. Total. Per cu. yd.
1 foreman at $3.50 $ 3.50 $0.035 1 stationary engineer at $3 3.00 0.030 foreman at $1.75 0.87 0.009 15 men loading charging bucket at $1.50 22.50 0.225 2 men dumping charging bucket at $1.75 3.50 0.035 2 tagmen at $2, time 2.00 0.020 1 man at trap at $2, time 1.00 0.010 ------ ------ Total $36.37 $0.364
The output of the cubical mixer was 100 cu. yds. per day.
The costs of placing concrete in the forms above the foundation by hand below 12 ft., and by cars and derricks any height, were as follows:
By hand (barrows) below 12 ft. Total. Per cu. yd.
4 men loading concrete at $1.50 $ 6.00 $0.100 1 foreman time at $3 1.50 0.025 10 men wheeling at $1.50 15.00 0.250 1 man sc.r.a.ping barrows at $1.50 1.50 0.025 2 men placing concrete at $1.50 3.00 0.050 1 man placing mortar face at $1.50 1.50 0.025 2 men mixing and carrying mortar at $1.50 3.00 0.050 ------ ------ Total $31.50 $0.525
By cars and derricks-- 1 horse and driver at $3 $ 3.00 $0.030 2 men dumping concrete time at $1.50 1.50 0.015 1 fireman time at $1.75 0.88 0.009 3 tagmen at $1.50 4.50 0.045 8 men placing and ramming conc. at $1.50 12.00 0.120 2 men mixing mortar at $1.50 3.00 0.030 2 men placing mortar at $1.50 3.00 0.030 2 men carrying mortar at $1.50 3.00 0.030 1 foreman at $3 3.00 0.030 1 stationary engineer at $3 3.00 0.030 2 men attending hook at $1.50 3.00 0.030 ------ ------ Total $39.88 $0.399
The costs of placing concrete in the foundations were as follows:
By hand-- Total. Per cu. yd.
1 foreman time at $3 $ 1.50 $0.025 4 men shoveling concrete at $1.50 6.00 0.100 1 man placing concrete at $1.50 1.50 0.025 1 man ramming concrete at $1.50 1.50 0.025 ------ ------ Total $10.50 $0.175
By machine-- 1 horse and driver at $3 $ 3.00 $0.030 3 men pushing and unloading car at $1.50 4.50 0.045 5 men placing and ramming at $1.50 7.50 0.075 1 foreman at $3 3.00 0.030 2 men dumping mixer at $1.50 3.00 0.030 ------ ------ Total $21.00 $0.210
~COST OF RETAINING WALL.~--The following figures of the cost of a concrete retaining wall are given by C. C. Williams:
Cost of Material.
Unit Kind and amount of material-- Price. Cost.
Stone, 441 tons $ .70 $308.70 Sand, 182.5 yds. .55 100.37 Cement, 536 bbls. .85 453.60 ------- Total $862.67
Lumber value $205.33 Wheelbarrows, value, 6 at $3.50 15.75 ------- Total $221.08
Excavation-- Labor, 4,002 hours at 15 cts. $600.30 Carts, 800 hours at 12 cts. 100.00 Foreman, 460 hours at 35 cts. 171.00 Waterboy, 240 hours at 10 cts. 24.00 ------- Total $895.30
Concrete-- Labor, 2,398 hours at 15 cts. $359.70 Foreman, 224 hours at 35 cts. 77.40 ------- Total $437.10
Handling material-- Unloading cars, 380 hours at 15 cts. $ 57.00 Foreman, 40 hours at 35 cts. 14.00 -------
Total $ 71.00
Forms-- Carpenters, 997 hours at 22 cts. $224.33
Work to support bridge-- Carpenters, 542 hours at 22 cts. $121.95 Labor, 458 hours at 15 cts. 68.70 -------
Total $190.65
Superintendence and office-- Superintendent, 30 hours at 50 cts. $15.00 Office 20.00 -------- Total $35.00 -------- Grand total $2,937.13
Proportional costs-- Cost Per Per Cent.
Yard of of Total Item. Cost. Concrete. Cost.
Concrete materials $ 862.67 $2.02 46.7 Laying concrete 437.10 1.03 23.4 Lumber 205.33 .48 11.3 Building forms 224.33 .53 12.3 Handling material 71.00 .17 03.8 Wheelbarrows 15.75 .04 01.0 Supt., etc. 35.00 .07 01.5 --------- ----- ------ Total $1,851.18 $4.34 100.00 Work on bridge 190.65 Excavation 895.30 --------- $2,937.13
CHAPTER XIV.
METHODS AND COST OF CONSTRUCTING CONCRETE FOUNDATIONS FOR PAVEMENTS.
Contractor"s skill or want of skill in systematizing and managing labor counts as high in street work as in any cla.s.s of concrete construction.
As previously demonstrated, the cost of mixing is a very small portion of the labor cost of concrete in place; the costs of getting the materials to the mixer and the mixed concrete to the work are the big items, and in street work the opportunity for increasing the cost of these items through mismanagement is magnified by the large area of operations involved per cubic yard of concrete placed. One cubic yard of concrete makes 6 sq. yds. of 6-in. pavement foundations and 100 cu. yds.
of concrete make a 6-in. foundation for 300 ft. of 30-ft. street, while 4 to 5 cu. yds. will build 100 ft. of ordinary curb and gutter. Thus the haulage per cubic yard is considerable at best, and lack of plan in distributing stock piles and handling the concrete can easily result in such increased haulage expenses as to change a possible profit into a certain loss. A little thought and skill in planning street work pays a good profit.
~MIXTURES EMPLOYED.~--A comparatively lean concrete will serve for pavement foundations; mixtures of 1-4-8 Portland cement or 1-2-5 natural cement are amply good and it is folly, ordinarily, to employ richer mixtures. Until recently, natural cement has been used almost exclusively; a 1-2-5 natural cement mixture requires about 1.15 bbls. of cement per cubic yard of concrete. A 1-4-8 Portland cement mixture requires about 0.7 bbl. of cement per cubic yard. In the opinion of the authors a considerably leaner mixture of Portland concrete is sufficiently good when it is well mixed in machine mixers--for a 6-in., foundation 0.5 bbl. per cu. yd. The mixtures actually employed are proportioned about as stated and their cost, or that of any other common mixture, may easily be computed from Tables XII and XIII, giving for different mixtures the quant.i.ties of cement, sand and stone per cubic yard of concrete; the product of these quant.i.ties and the local prices of materials in the stock piles gives the cost. When the concrete is mixed by hand the ordinary labor cost of foundations is 0.4 to 0.5 of a 10-hour day"s wages per cubic yard of concrete; occasionally it may be as low as 0.3 of a day"s wages where two mixing gangs are worked side by side under different foremen and with an exacting contractor. Data for machine mixing are too few to permit a similar general statement for machine work, but in one case coming under the authors" observation, the cost figured out to a little less than 0.2 of a day"s wages per cubic yard.
~DISTRIBUTION OF STOCK PILES.~--a.s.suming a 30-ft. street and a 1-3-5 concrete laid 6 ins. thick, the quant.i.ties of concrete materials required per lineal foot of street are: Cement 0.60 bbl., sand 0.27 cu.
yd., stone 0.44 cu. yd. The stock piles should be so distributed that each supplies enough materials for a section of foundation reaching half way to the next adjacent stock pile on each side, and they should not contain more or less material, otherwise a surplus remains to be cleaned up or a deficiency to be supplied by borrowing from another pile. A little care will ensure the proper distribution and it is well paid for in money saved by not rehandling surplus or borrowed materials. For a given mixture and a given width and thickness of foundation, the sizes of the stock piles are determined by their distance apart and this will depend upon whether hand or machine mixing is employed and upon the means adopted for hauling the raw materials and the mixed concrete. It is worth while always in stock piles of any size, to lay a flooring of plank particularly under the stone pile; if dumped directly on the ground it costs half as much again to handle stone. Current practice warrants everything from a continuous bank, to piles from 1,000 to 1,500 ft. apart, in the s.p.a.cing of stock piles.