The concrete, which was mixed very dry, in a 1⁄2-cu. yd. batch, "Smith" mixer, was thoroughly tamped with a 22-lb. tamper, and worked until it was of a stiff jelly-like consistency, the wire rings being added as the concrete was placed. The best results were obtained with the minimum quantity of water. The upper joint was moulded with a heavy cast-iron ring. The jacket and core forms were loosened immediately, and placed over other rings, a sufficient number of bottom rings being used for a day's work. For the pipes required for curves, special forms were used to give the necessary bevel to the joint. After 24 hours the finished pipes were lifted from the bottom ring with a special lifter, and ranged in position for coating internally with a Portland cement grout to which a little freshly slaked lime was added. The pipes were all numbered, and were kept moist for 10 days by constant sprinkling. They were not hauled to the work until 28 days after they were moulded, although this rule was sometimes broken, to the detriment of the pipes. More than 32,000 pipes were
manufactured, but some were used for purposes other than the Estanzuela Aqueduct.
Cost of Pipes.—The contractor brought with him experienced concrete pipe makers from California, and these were afterward assisted by Mexican labor. In a day two tampers could manufacture from 45 to 50 pipes of the larger (63.5-cm,), and from 55 to 60 of the smaller (55.9-cm.) size.
The cost varied from 2.75 to 3.25 pesos per pipe for the smaller, and from 3.50 to 4.00 pesos for the larger size.
The approximate cost of manufacturing is as follows: Taking, as a fair example, one week's work during March, 1908, the wages paid to the 74 men comprising the total pay-roll (though part of this labor was intermittent) amounted to 981 pesos. This includes a general foreman at 10 pesos per day, four American tampers at 7.50 pesos, and Mexican labor varying from 4 to 1 peso, and all labor necessary to handle and finish the pipes, including coating the interiors. During this week there were made 1,126 of the 63.5-cm. and 1,095 of the 55.9-cm. size. The pay-roll includes 520 pesos for the larger pipes (46 cents each) and 461 pesos for the smaller pipe (42 cents each). Table 5 shows the quantities and cost of the materials used in the manufacture of these pipes.
TABLE 5.—Cost of Concrete Pipe.
| For 1,126 pipes 63.5 cm. in diameter. | For 1,095 pipes 55.9 cm. in diameter. | |||||||||
| Materials. | ||||||||||
| Quantities. | Cost. | Quantities. | Cost. | |||||||
| Portland cement, at 8.00 pesos per bbl., delivered at pipe-making yard. | 401 | bbl. | 3,208.00 | pesos. | 303 | bbl. | 2,424.00 | pesos. | ||
| Sand, at 2.65 pesos per cu. m. | 85 | cu. m. | 225.25 | " | 68 | cu. m. | 180.20 | " | ||
| Crushed rock, 19-mm. (3⁄4-in.), at 2.65 pesos per cu. m. | 62 | cu. m. | 164.30 | " | 50 | cu. m. | 132.15 | " | ||
| No. 6 galvanized-wire hoops. 4 rings to each pipe. | 4,504 | 203.00 | " | 4,380 | 183.00 | " | ||||
| Totals. | ... | 3,800.55 | pesos. | ... | 2,919.45 | pesos. | ||||
| Cost per pipe. | ... | 3.37 | pesos. | ... | 2.66 | pesos. | ||||
From Table 5 it is seen that the cost of the 63.5-cm. pipes was 3.37 pesos for material plus 0.46 peso for labor = 3.83 pesos per pipe, or 6.26 pesos per lin. m. (1.91 pesos per lin. ft.).
The cost of the 55.9-cm. pipes amounted to 2.66 pesos for material plus 0.42 peso for labor = 3.08 pesos per pipe, or 5.05 pesos per lin. m. (1.54 pesos per lin. ft.).
The cost of cement included hauling from the bodega to the yard, a distance of about 5 km. At a later date, after the Company had commenced using the "Hidalgo" cement, some additional 55.9-cm. pipes were manufactured, so as to have them on hand as a reserve in case of emergency. In this work only Mexican labor was used, as the previous gang had been dispersed, but the tampers had previous experience. Taking the cost of 418 pipes made during one period of 9 days, the detailed cost was as given in Table 6.