| Item. | Per cu. yd. |
| Portland cement at $2.15 per bbl. | $2.292 |
| Labor mixing and placing | 3.017 |
| Cost of forms | 0.187 |
| Labor screening gravel | 0.471 |
| Carting | 0.592 |
| Miscellaneous | 0.146 |
| ——— | |
| Total | $6.705 |
The cost of the invert was thus $1.002 per lin. ft. of sewer.
Collapsible metal forms for manholes and catch basins are made by several firms which make block and pipe molds. A cylindrical wooden form construction is shown by Fig. 250. The outside form consists of three segments of a cylinder made of 2-in. lagging bolted to hoops. Bent lugs on the ends of the hoops, were provided with open top slots and were bolted together through 1×⅜-in. bars which extended the full length of the form between lugs. The assembled form was collapsed by pulling up on the bars, thus lifting the bolts out of the slots. The inner mold is also made in three sections with strap hinges at two of the joints and at the third joint a wedge-shaped stave. The other details are shown by the drawing. To mold the top of the basin two cone-shaped forms are used, an outer form made in one piece and an inner form made in sections. Some 26 catch basins were built in Keney Park, Hartford, Conn., by Mr. H. G. Clark, at a cost of $7 apiece for concrete in place, and there was closely 1 cu. yd. of concrete in each.
Fig. 250.—Form for Circular Catch Basin or Manhole.
CONCRETING.—Except for pipes of small diameter, the concreting is done in sections, each section being a day's work. Continuity of construction has not proved successful, except for pipes of moderate size, in the few cases where it has been tried. Examples of continuous construction methods are given in succeeding sections. Methods of molding and laying cast concrete pipe are also best shown by the specific examples given further on. In concreting large diameters, the work may be done by molding successive full barrel sections, or by molding first the invert and then the roof arch, each in sections. The engineer's specifications generally stipulate which plan is to be followed. Construction joints between sections are molded by bulkhead forms framed to produce the type of joint designed by the engineer; the most common type is the tongue and groove joint.
Fig. 251.—Cross-Section of Pinto Creek Irrigation Conduit.