Description. Cost Delivered on Mixer.
Proportions.Average Yardage for Days Run. Cement. Sand. Stone. Total Materials.
Class A, in Piers 1:2:4½ 150 1.65 0.39 1.08 3.12
Class A, in Arches 1:2:4½ 200 1.65 0.39 1.08 3.11
Class B, in Piers —Solid Work 1:3:6 160 1.40 0.42 1.23 3.05
Class B, in Piers —Hollow Work 1:3:6 110 1.40 0.42 1.23 3.05
Class B, in Spandrel Walls 1:3:6 110 1.40 0.42 1.23 3.05
Class B, in Spandrel Arches 1:3:6 200 1.40 0.42 1.23 3.05
Class B, in Abutments 1:3:6 150 1.40 0.42 1.23 3.05
Class C, Filling over Bridge 1:3:10 145 0.90 0.31 1.30 2.51
Description. Cost of Mixing and Placing.
Mixing. PlacingTotal Mixing and Placing
Class A, in Piers 0.09 0.21 0.30
Class A, in Arches 0.05 0.28 0.33
Class B, in Piers —Solid Work 0.09 0.18 0.27
Class B, in Piers —Hollow Work 0.11 0.36 0.47
Class B, in Spandrel Walls 0.11 0.40 0.51
Class B, in Spandrel Arches 0.07 0.26 0.33
Class B, in Abutments 0.11 0.24 0.35
Class C, Filling over Bridge 0.11 0.28 0.39
Description. Cost of Form Work.
Erecting. Taking Down Lumber. Total Form Work Total Cost per Cubic Yard.[G]
Class A, in Piers 0.17 0.05 0.16 0.38 $3.80
Class A, in Arches 0.08 0.03 0.10 0.21 3.66
Class B, in Piers —Solid Work 0.17 0.05 0.16 0.38 3.70
Class B, in Piers —Hollow Work 0.77 0.25 0.64 1.66 5.18
Class B, in Spandrel Walls 0.85 0.28 0.73 1.86 5.42
Class B, in Spandrel Arches 0.94 0.30 0.86 2.10 5.48
Class B, in Abutments 0.10 0.03 0.12 0.25 3.65
Class C, Filling over Bridge 0.00 0.00 0.00 .... 2.90

[G] Add 25% to the cost here tabulated for superintendence, plant and incidentals.

Considerable difficulty was experienced in building the large arches with a concrete block facing on account of the fact that the edges of the blocks are liable to chip off when any concentrated pressure is brought on them. In order to permit the ring of blocks to deform as the centering settled under its load, sheet lead was placed in the joints between blocks at the points corresponding with the construction joints between sections of the mass concrete backing. The deflection of the centers at the crown was a maximum of 3¼ ins. and a minimum of 2½ ins.

Table XXI—Detail Cost of Engineering and Inspection for Different Classes of Work.

Engineering.Inspection.
Kind of Work.Total.Unit.Total.Unit.
Class A, concrete, 23,500 cu. yds$3,055.00$0.13$1,762.50$0.075
Class B, concrete, 36,580 cu. yds3,658.000.101,646.100.045
Class C, concrete, 2,150 cu. yds107.500.0553.750.025
Class D, concrete, 6,250 cu. yds1,875.000.304,687.500.75
1,000 M. ft. B. M. centering1,000.001.00440.000.44
Cement, 73,000 barrels365.000.005730.000.01
Earth filling, 50,000 cu. yds1,000.000.02500.000.01

The centering of the main arches was not struck until the spandrel arches and all the work above the main arches to the bottom of the coping had been completed. The first and third spandrel arch on each side of the piers was made with an expansion joint in the crown. To permit further of the adjustment of the portion of the masonry above the backs of the main arches, the crown of the middle arch of each set of spandrel arches was left unconcreted until the center of the main arches had been struck. It may be noted here that the expansion joints in the first and third arches were carried up through the dentils and coping, and observations show that these joints are about ⅛ in. larger in winter than in summer.

The cost of the mass concrete work is shown in Table XX. These figures are based on the wages already quoted and the following: Foreman riggers, $4.50; riggers, $1.50 to $1.75 and $2; skilled laborers, $2; engineers, $3.50. The detail cost of engineering and inspection is shown in Table XXI.

ARCH BRIDGES, ELKHART, IND.—At the new Elkhart, Ind., yards of the Lake Shore & Michigan Southern Ry. the tracks are carried over a city street by concrete arches 40, 60 and 160 ft. long. These arches all have a span of 30 ft., a height of 13 ft. and a ring thickness at crown of 28 ins. The reinforcement consists of arch and transverse bars; the arch bars are spaced 6 ins. on centers 2½ ins. from both extrados and intrados, and the transverse bars are spaced 24 ins. on centers inside both lines of arch bars. The proportions of the concrete were generally 1 cement, 3 gravel and 6 stone. The gravel was a material dug from the foundations and was about 50 per cent. sand and 50 per cent. gravel, ranging up to the size of pigeons' eggs. The concrete was machine mixed and was mixed very wet.