An attempt was made to build the invert concrete without forms (seeing that a rough finish was desired, as previously explained, to form a key for possible sub-track concrete), but it proved a failure.
The typical working force (excluding transport) was as follows:
| 1 | Foreman | @ | $3.25 | per | shift. |
| 2 | Spaders | " | 2.00 | " | " |
| 9 | Laborers | " | 1.75 | " | " |
The average time taken to lay a 30-ft. length of invert was 7 hours; the two spaders remained one hour extra, smoothing off the surface.
For setting the form, the force was:
| 1 | Foreman | @ | $4.50 | per | shift. |
| 5 | Carpenters | " | 3.25 | " | " |
| 6 | Carpenters' helpers | " | 2.25 | " | " |
The average time taken to erect a form was 2 hours, 1 carpenter and 1 helper remaining until the concrete was finished.
Duct Bench Concrete.—The duct bench (as described previously) is the portion of the concrete on which the ducts are laid. The exact height of the steps was found by trial, so as to bring the top of the ducts into the proper position with regard to the top and the face of the bench.
Both kinds of duct bench forms were of the same general type. A drawing of one of them is shown on [Plate XLII]. The form consisted of a skeleton framework running on wheels on a track at the level of the temporary transportation tracks. The vertical faces of the steps were formed by boards supported from the uprights by adjustable arms. The horizontal surfaces were formed by leveling off the concrete with a shovel at the top of the vertical boards. Where the sheets of expanded metal used for bonding came at a step, the lower edge of the boards forming the back of the step was placed 1 in. above the one forming the front of it; but, when the expanded metal came in the middle of a step, a slot 1 in. wide was left at that point to accommodate it.