Spaded or mortar finishes are used for class (b). The following rules should be observed:

Rule 1. Spading is best done with a special flat-bladed spade, having the blade perforated with holes or slots, which will screen back the stones and allow the mortar to pass.

Rule 2. In a mortar finish, the facing mortar and concrete backing are placed at the same time and are tamped together. The tamping should not be so hard as to force pieces of stone through the facing, but hard enough to bond thoroughly the facing mortar and backing.

Rule 3. The preferable method of construction is to use a facing form between the lagging and the backing. Fill between the facing form and the lagging with mortar, then fill behind the facing form with the backing, and finally withdraw the facing form and tamp backing and facing together.

Moulded Blocks, Piles, Ornamental Castings, Etc.-Three general processes are employed for moulding cast concrete work:

(a) A dry mixture is heavily tamped into a mould and the block is immediately released and set aside for curing.

(b) A liquid mixture is poured into moulds where the blocks remain until hard.

(c) A medium wet mixture is compressed into moulds by hydraulic presses or other means of securing great pressure.

The following rules should be observed for Dry Mixture Blocks.— Rule 1. For dry mixtures the mixing and tamping must be thorough and the water uniformly distributed. Tamping should begin with the first shovelful and should be continued until the mould is filled.

Rule 2. Dry mixtures should have a consistency such that the block will part from the mould without sticking, sloughing, sagging, or loss of form. Dryness in excess of these requirements should not be allowed.

Rule 3. Moulds must be rigid and adequately clamped. The construction should be such that the green blocks are not injured when removed.

Rule 4. After removal, the dry mixture blocks must be stacked in a horizontal position on immovable supports and freely sprinkled with water. A dry mixture block does not have enough mixing

water to enable the cement to set and harden perfectly, and this deficiency must be supplied by sprinkling. The sprinkling should begin within an hour after moulding and should continue for at least ten days. While the block is soft, the sprinkling should consist of a gentle spray, that will not wash the concrete.

Rule 5. Blocks should be cured for at least 30 days before they are removed from the storage yards for use in construction.

The following rules apply to wet mixtures: Rule 1. The mixture must be thoroughly stirred and churned to eliminate air voids, prevent arching and fill corners and edges of moulds.

Rule 2. The mould must not be removed until the concrete has thoroughly set and is hard enough to do without its support.

Rule 3. The block must be true to shape and exact in dimensions, with faces true to plane, and edges true to line. Mouldings and other ornamentations must be perfect. A moulded block should be equal in perfection to cut stone in all particulars of shape and dimensions.

Rules for Concrete Piles.-Concrete piles are driven (a) by punching a hole in the ground by means of a metal mould and filling with concrete; (b) by casting the piles in moulds and driving by aid of a water jet.

The following rules should be observed for concrete piles in place:

Rule 1. In driving the shell for new piles, care must be taken that adjacent piles in which the concrete is still green are not jarred and injured.

Rule 2. In concreting piles in place, the concrete must be lowered in small buckets or in such a way that the cement is not separated from the stone.

Rule 3. The reinforcement must be set parallel to and concentric with the axis of the pile. The best practice is to assemble the reinforcement into a unit frame, and to place it as a unit.

The following should be observed for cast piles:

1. Cast piles should be straight, the metal points, when used, firmly attached and the pile should be without cracks or chipping. None of the reinforcing metal should be exposed. If cored for sinking by water jet, the cores must be open and unobstructed. If fluted on the sides to provide passages for the rise of

water used in jetting, the flutes or corrugations must not be obstructed.

2. Moulds should be straight and kept true to line and level.

3. The reinforcement must be kept parallel to and concentric with the axis of the mould.

4. The concrete should be poured at several points along the mould to prevent flowing and segregation.

5. The driving should be done in such a way that the pile is not fractured in the body. The head should be protected by a cushion cap to take the direct blow of the hammer. If the driving is done by a water jet, the pile should settle to a firm bearing.

6. Cast piles should not be dragged along the ground or otherwise roughly handled.

Ornamental Castings.-In ornamental castings, great care must be taken in the moulding, handling, and setting in place to preserve the true lines, flutings, and other ornamentations. When white cements, stainless mortars, or other special materials are required, the inspector should take particular pains to insure the use of the proper ingredients. The general rules for cast blocks and piles apply with additional force to all ornamental work.

CHAPTER XXXIII

COST OF CONCRETE WORK

General Cost of Main Classes of Work.-Elements of Cost.-Cost of Materials.Cost of Mixing.-Cost of Placing.-General Expenses.—Summary of Costs.—Cost of Mortar.-Actual Examples of Cost.-Building Blocks.—Paving.-Removing Efflorescence.-Stucco.-Forms.-Cost of Buildings in Terms of Cubical Contents.-Cost of Residences.-Cost of Sewers.-Concrete Pipes.-Bridge Piers and Bridges.-Piles.-Trestles, Sidewalks, Curbs, and Gutters.-Fence Posts.-Poles. -Roofs.-Tunnel Lining.-Waterproofing.-Cost of Concrete Dams.

THE Cost of concrete construction is made up of the combined cost of materials and labor. The cost of materials for any given class of work is readily determined from the dimensions of the structure and the market prices of cement, sand, broken stone, timber, steel, etc.; the labor cost, however, is dependent not only upon the prevailing rate of wages, but also upon the efficiency of the men employed, the amount of form work, and the character of the construction.

The cheapest construction is obtained when the concrete is deposited in large masses and when the transportation, mixing, and depositing in place is performed by machinery. When laid in thin sections, as in tunnel linings, small arches, thin walls, etc., the use of forms and of hand labor per cubic yard of concrete is very largely increased, which greatly augments the unit cost of the construction.

General Cost of Main Classes of Work.-Where Portland cement can be obtained at $1.50 per barrel, sand at 80 cents per cubic yard, and broken stone at $1.50 per cubic yard delivered on the work; and where the cost of form timber does not exceed $25.00 per M; while the rate of wages for carpenters is $3.50, laborers, $1.75, and teams $3.75 per ten-hour day, the cost of concreting, including interest and depreciation on plant, but with no allowance for profits, will run about as follows:

Heavy mass constructions, as large dams, reservoir

walls, pavements, heavy foundations, abutments, rubble 【 $3.50 to $5.00 per cu. yd. concrete, etc.

Foundation footings and difficult mass construction.
Thin rough walls, sewers, and culverts....

Thin tooled or reinforced walls and heavy buildings and bridges, difficult pneumatic and submarine constructions which are subject to delays, reinforced-concrete retaining walls, etc.

Light reinforced-concrete buildings having thin walls,

6.00 to 8.00 per cu. yd. 8.00 to 10.00 per cu. yd.

10.00 to 15.00 per cu. yd.

slabs, and columns, light reinforced-concrete bridges, 15.00 to 20.00 per cu. yd. arches, etc.

Elements of Cost.-The various elements which enter into the cost of plain and reinforced concrete may be summarized as follows: 1. Cost of cement, aggregate, and reinforcement at the work. 2. Cost of loading the materials into barrows, buckets, or cars, and of their transportation to the mixer and dumping.

3. Cost of mixing: (a) Hand-mixing; (b) Machine-mixing. 4. Cost of loading the concrete into barrows, buckets, or cars, and of its transportation to the work.

5. Cost of bending, placing, and wiring the reinforcement into position.

6. Cost of dumping, spreading, slicing, spading, and ramming. 7. Cost of forms: (a) Timber, nails, wire, and other materials; (b) Carpenter's labor.

8. Cost of plant, storage house, runways, etc.

9. Cost of engineering, inspection, time-keeping, and general

expenses.

10. Interest on the investment, repairs, depreciation of plant, etc. II. Profits.

Cost of Cement.-The cost of cement depends upon the class, brand, quantity, kind of package, freight-rates by rail or water, and cartage.

At New York, the prices in large lots delivered alongside of the docks are at the time of publication as follows for large lots:

At the mill Portland cement can be obtained in bulk at $1.00 per barrel.

On many of the irrigation projects in the West, where the haul