The floor consisted of six inches of concrete, 3/8 inch cement mortar, one coat liquid asphalt and one coat harder asphalt. The slope lining was of six inches concrete, one coat asphalt, one layer of brick dipped in asphalt and laid flat, and a final finishing coat of asphalt. The concrete was composed of one barrel Portland cement, one-tenth cubic yard sand, five-tenths cubic yard gravel and nine-tenths cubic yard of crushed stone, these quantities of the ingredients making one cubic yard of concrete. Here we have an instance of the use of a mixture of broken stone and gravel, a practice which has already been commended as resulting in a small amount of voids.

The concrete of the floor was laid in blocks twenty feet on a side, molds of two by six inch plank forming the outside edges of a block, and serving as a guide to the straight edge used in finishing, as in concrete walk construction. The finishing coat was of two parts fine sand to one of Portland cement and was applied, before the concrete base had begun to set, by two finishers with smoothing trowels. When the next block was to be laid, the plank were replaced by one-half inch weather boarding. When the concrete had thoroughly set, these boards were removed and the joints so formed were run full of asphalt, when the first layer of this material was spread.

The concrete on the sides was also six inches thick and laid in sheets ten feet wide, extending up and down the slopes, expansion joints being provided on the inclined joints only. The finishing coat of mortar was not used here, but all inequalities in surface were smoothed by using a little mortar from the next batch of concrete.

710. Each concrete gang was composed of twenty men and one water boy. All concrete was mixed by hand on movable platform in half-yard batches. On the entire work 1.84 cubic yards of concrete per day were mixed and placed per man employed, and on the floor alone this quantity was increased to 2.35 cubic yards, an excellent showing for this class of work. The cost of concrete per cubic yard, without profit, was as follows:

1 Trans. A. S. C. E., December, 1896.

On Slopes: Cement, at $2.45 per bbl......... $2.82

Other materials............ 1.94

Labor................. 1.07

Total per cubic yard for 600 yards.......$5.83

On floor: Cement, at $2.45............$2.64

Other materials............. 1.92

Labor..................68

Total Cost per cubic yard for 680 yards.....$5.24

The costs of the slope lining and floor complete, per square foot, are given as follows:

Slope: 6 inches concrete..............$0.1187

.649 inch asphalt...............0100

Brick in asphalt...............0889

.851 inch asphalt...............0131

Chinking crevices..............0030

Ironing...................0036

Total Cost per square foot of slope.......$0.2373

Bottom: 6 inches concrete.............$0.1031

Cement mortar finish........... .0113

.537 inch coat asphalt...........0077

.573 inch coat asphalt...........0082

Total Cost of bottom per square foot......$0.1303

711. Forbes Hill

The Forbes Hill reservoir 1 forms a part of the distribution system of the Metropolitan water Works of Boston and was built under the direction of Mr. Dexter Brack-ett, M. Am. Soc. C. E. The reservoir is two hundred eighty by one hundred feet, -partly in embankment. The soil under the embankment was first stripped to a depth of two and one-half feet at the toe, increasing to five feet stripping at the inner edge of the slope. The material was hard pan, and the embankments were built in four inch layers, rolled with four thousand pound rollers, so made as to leave a slightly corrugated surface. The bank was extended one foot inside of the finished line to assure a compact face, and afterward trimmed to grade.

1 Described by Mr. C. M. Saville, M. Am. Soc. C. E., Division Engineer, before the N. E. water Works Assn. Abstracted in Engineering News, March 13, 1902.

712. The bottom of the reservoir was covered first with a layer of concrete about four and one-half inches thick, composed of one part natural cement, two parts sand, and five parts stone. The sand was of good quality; the stone came from the excavation and was washed before crushing. This layer of natural cement concrete was covered by a layer of Portland cement mortar one-half inch thick, made of two parts sand to one cement, and finished with a richer mortar, one part sand to four of cement.

This half-inch layer was laid in strips four feet wide and finished like a cement sidewalk. Although this mortar coat was kept well moistened, some cracks developed which were filled with grout before applying the second layer of concrete. If no joints were used in the lower layer or base concrete, and joints in the coat of mortar were provided in one direction only, as appears to have been the case, the cracking should have been anticipated. At any rate, the value of the mortar coat between the two concrete layers was greatly impaired by this cracking, and the experience points to the advisability of placing the upper layer of concrete on the mortar before the latter has set, thus avoiding the expense of finishing the mortar layer.

The upper layer of concrete was composed of one part Portland cement, two and one-half parts sand and four parts broken stone, and was laid in blocks ten feet square. These blocks were laid alternately each way.

The slope was first lined with Portland concrete of 1 to 2 1/2 to 6 1/2, then one-half inch layer of mortar as for the bottom. The upper layer of concrete on slope was same as the upper layer of the bottom lining, but the blocks were eight by ten feet and finished with one inch of granolithic, in which stone dust and particles smaller than three-eighths inch were substituted for the one and one-half inch stone of the concrete. , 713.

Cost

The Cost of lower layer of concrete on bottom, natural 1 to 2 to 5, was as follows:

1.25 bbl. natural cement, at $1.08....... $1.350

.34 cu. yd. sand, at $1.02 ...........347

.86 cu. yd. stone, at $1.57 .......... 1.350

Materials in concrete.......... $3.047

forms, lumber, at $20.00 per M ... $0.090

forms, labor................ 0.100

Total forms.............. .190

General expenses..............$0.08

mixing and placing............. 1.17

1.250

Total Cost per cu. yd.......... $4.487

Cost of lower layer on slopes, Portland 1 to 2 1/2 to was as follows:

1.08 bbls. Portland cement, at $1.53......$1.652

.37 cu. yd. sand, at $1.02 ...........377

.96 cu. yd. stone, at $1.57 .......... 1.507

Materials in concrete ......... $3.536

forms, lumber, at $20.00 per M........$0.016

forms, labor................ 0.121

Total forms.............. .137

General expenses..............$0.177

mixing and placing............. 1.213

- 1.390

Total Cost per cubic yard........ $5.063

The Cost of the upper layer on bottom and slopes, including the finish on slopes, Portland 1 to 2 1/2 to 4, was as follows:

1.37 bbls. Portland cement, at $1.53...... $2.09

.47 cu. yd. sand, at $1.02...........48

.745 cu. yd. stone, at $1.57.......... 1.17

Materials in concrete.......... $3.74

forms, lumber, at $20.00 per M........ $0.25

forms, labor................ 0.26

Total forms.............. .51

General expenses.............. $0.15

mixing and placing.............. 1.53 - 1.68.

Total Cost per cu. yd.......... $5.93

The Cost of the half-inch plaster coat between the layers of concrete was twenty cents per square yard.

714. Rock Ford

A reservoir for the city of Rockford, 111.,1 was built almost entirely of concrete after plans prepared by the City Engineer, Mr. Chas. C. Stowell. The soil was a loose gravel, and after excavation was completed, parallel lines of drain tile were laid in trenches nine to ten feet centers and leading to a fifteen inch vertical sewer pipe carried to the surface of the street and capped. This sewer pipe served as a sump for a pump should it be found necessary at any time to repair the bottom. These trenches were filled with broken stone and the whole area of the foundation covered with three inches of clay. The concrete bottom was in two layers, eight inches and seven inches thick, respectively, and composed of two parts sand and five parts stone to one of Portland cement.

The walls were of similar concrete for the bottom twelve feet, natural cement being used in the upper eight feet of the walls. The thickness at the bottom was 4 1/2 feet, walls being straight on outside with one to ten batter on inside. The entire inner surface of floor and walls was plastered with one-half inch of Portland mortar, one to one. The cost of concrete in the work averaged $6.50 for Portland and $4.00 for natural, and the finishing coat Cost seventy-five cents a square yard.

715. The roof was of concrete, expanded metal lath, and steel rods, the finished thickness being but two inches. This was supported by ribs of concrete, each twelve inches thick at the crown and having a seven-inch channel on the under side. The springing line of the ribs was eight feet below the top of the walls, giving a good depth at the skew back. Ribs were spaced about seven feet centers. The span of the roof was about fifty-five feet, and rise about eleven feet. The Cost of roof was less than twenty-five cents a square foot.

716. Concord

The groined arch roof of the Concord, Mass.,1 sewage storage well, designed by Mr. Leonard Metcalf, Assoc. M. Am. Soc. C. E., was fifty-seven feet diameter and contained about one hundred cubic yards of masonry. The Cost of the roof per square foot of surface was as follows:

1 Described in Engineering News, Feb. 22, 1894.

Centering................$0.18

Concrete materials ........... .15

Labor and supervision...........05

Total...............$0.38

717. Albany

The Albany filter plant roof,1 designed by Mr. Allen Hazen, Assoc. M. Am. Soc. C. E., was also of the groined arch type, the arches having the same span and rise as the Wellesley reservoir. The Cost of the roof per square foot of area was as follows:

.029 cu. yd. concrete, at $6.30.......$0.182

Piers...................054

Earth filling and seeding......... .014

Manholes, entrances, etc.......... .027

Total cost per sq. ft......... $0.277

For a list of reservoirs and filter beds, in the roofs of which groined arches have been used, giving in tabular form the general dimensions, the proportions used in the concrete, and in several cases the Cost of the roof per square foot of reservoir, the reader is referred to Engineering News of December 24, 1903.

1 Trans. A. S. C. E., June, 1900.