clean-cut joint between them so as to make each section an independent unit. Any concrete in excess of that needed to complete a section at the stopping of work shall not be used. Workmen shall not be permitted to walk on the freshly laid concrete. In no case shall concrete be deposited upon a frozen sub-grade or sub-base.

44. Reinforcing.-Slabs having an area of more than one hundred (100) sq. ft., or having dimensions greater than ten (10) ft., shall be reinforced with wire fabric or with plain or deformed bars. The reinforcement shall be placed two (2) inches below the finished surface of the walk. The reinforcement shall not cross joints and shall be lapped sufficiently to develop the full strength of the metal.

45. Finishing.-After the concrete has been brought by means of a strike-board to a surface one-quarter (4) inch above the established grade, it shall be rolled transversely with a metal roller having a smooth even surface approximately 3 ft. in length, and from 6 to 8 inches in diameter, and weighing not more than 50 lbs. The rolling must be done from the side, or in such a manner that the surplus water is displaced from the surface of the concrete. The rolling must be continued at intervals of 15 to 40 minutes until all excess water is removed.

Unless protected by metal the surface edges of all slabs shall be rounded to a radius of one-half (2) inch.

(Cross out the following sections except for the surface desired.)

(a) Smooth Surface. Following the rolling above described the surface of the concrete shall be troweled with a steel trowel to a smooth, even surface free from depressions or irregularities of any kind. Excessive working of the surface with the trowel shall be avoided.

(b) Medium Rough Surface.-Following the rolling above described the surface shall be floated with a wooden float only, producing an even, gritty finish. On wide sidewalks, after rolling, the finishing may be done with two applications of a canvas belt, not less than 6 inches wide, and about 2 feet longer than the width of the sidewalk. For the first application, the belt shall be drawn across the surface with vigorous strokes at least 12 inches long, and moved ahead very slightly at each stroke. The second application shall be given immediately after the water glaze or sheen disappears, and the stroke of the belt shall be not more than 4 inches, while the longitudinal motion shall be greater than during the first application.

(c) Rough Surface. Following the rolling above described, the surface shall be floated with a wooden float leveling all sags and producing an even surface. After being floated in this manner the roughening shall be done by slapping the surface of the concrete with the face of the float, raising the float vertically from the concrete after each stroke.

STANDARD SPECIFICATIONS FOR CURBS

THE TEST FOR QUALIFICATIONS OF CURB STONE

If a test is desired it shall be provided for in the local specifications. 1. Abrasion. The loss by abrasion shall be determined by the "Rattler Test" specified in pages 524-531 of the A. S. M. I. 1914 Proceedings, for Brick.

The rattler, abrasive charge, the test and record shall be as described therein. Four blocks of the material to be tested shall be axed or hammered to about 5x6x10 inches and dried (these 4 blocks will weigh from 110 to 120 pounds, approximating the weight of 10 brick).

For the present a loss of 12 per cent by abrasion will be permissible. If made through the "Deval Abrasion Test" as described in Bulletin 347, U. S. Dept. of Agriculture, March, 1926, a co-efficient of wear of seven (7) is permissible.

2. Absorption.-The dry blocks shall be weighed, then immersed in water for 48 hours, drained off for 5 minutes and then weighed. The increase in weight is the absorption and should not exceed 22 per cent.

SETTING CURB

3. Grading. Curb shall not be set until the rough grade has been prepared and rolled, if the latter is specified.

4. Temperature.-Curb shall not be laid in concrete when there is indication of freezing. If overtaken by temperature falling to 35 degrees F., the concrete in place shall be covered with dirt from the street or otherwise protected as the engineer directs.

For Setting Curb in Concrete

5. Curb Trench.-The curb trench should be 18 inches wide, 6 inches in front of the curb and 12 inches back from face of curb. It should be at least 22 inches deep. If the back of the trench suggests caving in, it should be held with planks so as to insure the full width of concrete throughout its depth, with square shoulder at the top.

6. Concrete.-Shall be made with Portland cement, aggregates and water, conforming to those specified for paving base, except that the coarse aggregate should pass a 1-inch mesh. These are mixed in the proportion of one (1) part of cement to three (3) of fine and seven (7) of the coarse aggregate.

Should a gravel carrying adequate sand be used, the engineer shall specify the more exact proportions according to run of material and the details for mixing.

The concrete shall be spread in the bed not more than ten (10) feet in advance of placing the curb.

As soon as the curb is bedded to its true line and grade, the trench should be filled with the concrete in front of the curb to the bottom of

the paving base and back to the curb to within 6 inches of the top of the curb. A light tamping or spading is advisable, but the curb must not be disturbed. The remainder of the trench back of the curb shall be filled with dirt from the street or with a specified material.

7. Drain Tile.-If drain tile is required, the bottom of the trench should be 36 inches below the top of the curb, and at least six (6) inches wide.

The tile should be a commercial size, not less than 3 or 4 inches inside diameter. It shall be laid to line and grade and connected by vitrified tile, closed joint, to sewers or catch-basins. If outlet is available it is best to make these connections about 300 feet apart. The tile shall be covered with screened gravel or broken stone, none of which shall pass a 1/2-inch screen (the coarse aggregate for concrete may be used). This covering shall be carried up to the bottom of the curb trench, thus it will be 14 inches deep.

8. If Not Set in Concrete.-If the curb is not set in concrete, the trench and drain tile should be as above.

9. Drain Tile Not Used.-If, however, drain tile is not required, the curb trench may be of such depth and may be drained off as local conditions suggest.

[Note. In the trench described above about 1.3 to 1.5 cubic feet of concrete will be required for one (1) linear foot of curb.]

DRESSING OR CUTTING

10. The face shall be dressed to vary not more than 3% inch from a plane surface, for a depth of 12 inches from the top. The remainder of the face shall be free from projections of more than 1⁄2 inch.

The back shall likewise be dressed parallel to the face for a depth of 1 inch from the top. The remainder of the back shall be free from projections of more than 1 inch.

The top shall likewise be dressed having a bevel or rise of 1/4 inch from face to back of curb.

The ends shall likewise be dressed at right angles to the face and top to vary not more than 1 inch from a plane surface for a depth of 12 inches from the top.

11. Circular Curb for round corners and closures should meet the above except as to length.

12. Bull Nose or round edge curb are regarded as special features and entail extra cutting to meet local practice.

13. Headers or Protection curb shall be dressed to a plane surface on top, ends cut at right angles to the face and top to a 3-inch joint for a depth of 8 inches.

[Note.-Except for special purposes the standard methods of dressing or cutting as employed for the several kinds of stone are regarded as acceptable. Unnecessary cost is incurred by specifying a particular method.]

GRANITE CURB

The curb shall be straight split, medium grained, of uniform texture and color, free from seams, excess of mica and disintegration.

14. If Set in Concrete the following dimensions are recommended: The granite splits more readily into shapes where the depth is three times the width:

Length not less than four (4) feet.

Top width 5 inches or as required, having in mind the quarrying proportion of one-third the depth.

Bottom width should be not less than three (3) inches rough squared. Depth-For not less than three-fourths of the length, the depth should be 16 inches for a curb 5 inches wide.

15. If Not Set in Concrete a special depth up to 20 or 26 inches may be required.

HARD SANDSTONE

16. The curb shall be of best quality hard sandstone, uniform color, free from seams and laminations.

17. If Set in Concrete the following dimensions are recommended: Length not less than 36 inches nor more than 42 inches.

Top width 4, 5 or 6 inches, as required.

Bottom width should be not less than one-half the width specified for the top.

Depth-For not less than three-fourths of the length, the depth should be 16 or 18 inches for the five or six-inch width respectively. 18. If Not Set in Concrete a special depth up to 20 or 25 inches may be required.

BLUESTONE AND LIMESTONE

19. Same as for Hard Sandstone, except that the length may be from 36 to 48 inches.

SOFT SANDSTONE AND LIMESTONE

20. Soft Sandstone and Limestone.-As the softer stone are often machine-cut or sawed, the dimensions need not be limited by strata or natural cleavage, but for handling and laying they should, if set in concrete, have a length not less than 4 (four) feet nor more than 6 (six) feet. Top width 5 or 6 inches. Bottom width not less than top. Top width 5 or 6 inches.

Bottom width same as top.

Depth-For a length not less than three-fourths of the top length, the depth should be 16 or 18 inches for a 5 or 6-inch width respectively. If Not Set in Concrete a depth up to 24 inches may be required. 21. Header or Protection Curb should have a depth of 12 to 14 inches, a width not less than 4 inches and length not less than 24 inches.

It shall be set in a concrete bed 6 inches deep and 18 inches wide and backed with concrete to within 8 inches of its top on the paving side and flush with the top on the unpaved or exposed side.

SPECIFICATIONS FOR CONCRETE CURB

22. Dimensions.-Standard cross-section for straight curb shall be not less than 6 inches at top and 8 inches at bottom and 18 inches in depth. The top corner on face of curb shall be rounded to a radius of one inch.

23. Proportions.-The curb shall be made of Portland cement concrete in either of the following proportions. 1 part (by volume) of Portland cement to 3 parts (by volume) of mixed aggregate, or 1 part Portland cement to 2 parts fine aggregate to 4 parts course aggregate

Materials

24. The cement shall meet the requirements of the current standard specifications for Portland cement of the American Society for Testing Materials.

25. Mixed Aggregate shall consist of natural sand, gravel or screenings from hard, tough, crushed rock or gravel, consisting of quartz grains or other hard material, clean and free from any surface film or coating and graded from fine to coarse, the latter particles predominating. Mixed aggregate, when dry, shall pass a screen having 34-inch circular openings; not more than 20 per cent shall pass a sieve having fifty (50) meshes per linear inch, and not more than 5 per cent shall pass a sieve having one hundred (100) meshes per linear inch. It shall not contain injurious vegetable or other organic matter as determined by the colorimetric test nor more than five (5) per cent, by volume, of clay or loam.

That portion of the mixed aggregate which passes the ten (10)-meshper-linear-inch screen shall be of such quality that the mortar composed of one (1) part Portland cement and three (3) parts aggregate to be tested, by weight, when made into briquets or cylinders, shall show tensile and compressive strength, at seven (7) and twenty-eight (28) days, at least equal to the strength of briquets or cylinders composed of one (1) part of the same cement and three (3) parts standard Ottawa sand by weight. The percentage of water used in making the test specimens of cement and aggregate to be tested shall be such as to produce mortar of the same consistency as that of the Ottawa sand test specimens of standard consistency. In other respects all briquets or cylinders shall be made in accordance with the methods of testing cement recommended by the American Society for Testing Materials (See Cement Specifications, A. S. T. M.).

26. Fine Aggregate shall consist of natural sand or screenings from hard, tough crushed rock or gravel consisting of quartz grains or other