"You may consider the following figures a fair average of the plant referred to, working to its capacity. To these amounts, however, must be added the interest on the investment, the cost of wrecking the plant and the depreciation of the same, superintendence, and the pay roll that must be maintained in wet weather. I am assuming the street as already brought to grade and rolled.
"With labor at $1.75 per day of 10 hours, teams at $4, engineer and foremen at $3, and engine at $5 per day, concrete mixed and put in place by the above method costs:
| Per cu. yd. | |
| To mix | $0.12 to $0.15 |
| To deliver to street | 0.10 to 0.14 |
| To spread and tamp in place | 0.08 to 0.11 |
| ——————— | |
| Total | $0.30 to $0.40 |
"The mixers are No. 2½ Smith, sold by the Contractors' Supply Co., Chicago, Ill., and a ½ yd. cube, sold by Municipal Engineering & Contracting Co., Chicago.
"The above figures are on the basis of a batch every 2 minutes, which is easily maintained by using the loading car, as by this means there will be no delay in the operation of the plant owing to the irregularity of the arrival of the teams.
"My experience leads me to believe that a better efficiency can be obtained by using mixers of 1 cu. yd. capacity, and that the batch mixer is the only type of machine where any certainty of the proportion of the mixture is realized."
Fig. 115.—Chicago Improved Cube Traction Mixer for Pavement Foundation.
FOUNDATION CONSTRUCTION USING A TRACTION MIXER.—In laying a 6-in. foundation for an asphalt pavement in Buffalo, N. Y., an average of 100 sq. yds., or 16.6 cu. yds., of concrete in place was made per hour using the traction mixer shown by Fig. 115. This mixer was made by the Municipal Engineering & Contracting Co., of Chicago, Ill., and consisted of one of that company's improved cube mixers operated by a gasoline engine and equipped with the regulation mechanical charging device and also with a swinging conveyor to deliver the mixed concrete to the work. The feature of the apparatus in its application to paving work is the conveyor. This was 25 ft. long and pivoted at the mixer end so as to swing through an arc of 170°. The mixer discharged into a skip or bucket traveling on the conveyor frame and discharging over the end spreading its load anywhere within a radius of 25 ft. In operation the mixer traveled along the center of the street, backing away from the finished foundation and toward the stock pile, which was continuous and was deposited along the center of the street. The bulk of the sand and stone was thus shoveled direct into the charging bucket and the remainder was wheeled to the bucket in barrows. As the charging bucket is only 14 ins. high the barrows could be dumped directly into it from the ground. The gang worked was 17 including a foreman and one boy, and with this gang 100 sq. yds. of 6-in. foundation was laid per hour. Assuming an average wage of 20 cts. an hour the cost of mixing and placing the foundation concrete was 3.4 cts. per sq. yd. or 20.4 cts. per cu. yd. for labor alone.
FOUNDATION CONSTRUCTION USING CONTINUOUS MIXER.—The foundation was 6 ins. thick for an asphalt pavement and was laid in Chicago, Ill. The concrete used was exceptionally rich for pavement foundation work, it being a 1-3-6 Lehigh Portland cement, broken stone mixture. The mixing was done by machine, a mixer made by the Buffalo Concrete Mixer Co., Buffalo, N. Y., being used. This mixer was equipped with an elevating charging hopper and was operated as a continuous mixer. The mixer was mounted on wheels and was pulled along the center of the street ahead of the work with its discharge end toward the work. Moves of about 25 to 30 ft. were made, the mixer being pulled ahead for this distance each time that the concrete came up to its discharge end. The stock piles were continuous, sand on one side and stone on the other side of the street. Cement was stored in a pile at each end of the block. All materials were wheeled from stock piles to mixer in wheelbarrows. The men wheeling sand and stone loaded their own barrows, wheeled them to the mixer and discharged them directly into the elevating hopper. No runways were used, the barrows being wheeled directly on the ground. The cement was brought in barrows, two or three bags being a load, and dumped alongside a cement box which was located close to and at one side of the elevating hopper. A man untied the bags and emptied them into the cement box and another man scooped the cement out of the box in bucketfuls and emptied it over the sand and stone in the elevating hopper. The mixer discharged onto a sheet iron shoveling board, and the concrete was carried in shovels from shoveling board to place, the length of carry being a maximum of 25 to 30 ft. Two men were required to pull down the cone of concrete at the discharge end of the mixer and to keep the stone from separating and rolling down the sides. The gang was organized as follows: