Chapter XI, “Municipal Public Works,” by the author.

Footnote 73:

Concrete combined curb and gutter is suitable for use on the great majority of residence streets, and others where the travel is not excessive, or where it will not be subjected to specially severe use, as on business streets where heavy vehicles are likely to be often backed against the curb. If properly constructed it will have sufficient hardness and strength to withstand all ordinary usage; it makes a better appearance, particularly on residence streets, than any other kind of curbing, is durable, and is usually less expensive than any other suitable, equally durable and equally well-finished curbing of natural stone, since the gutter displaces an equal area of pavement.

Footnote 74:

The sketch here presented conforms pretty closely to usual practice except in the width of the gutter. It is not uncommon to make the gutter from two to three feet wide. This is not necessary or desirable. A width of 15 to 18 inches forms a sufficient gutter to carry away all drainage except during very heavy rainfalls. Where the gutter projects out into the street sufficiently far to be exposed to large numbers of heavily loaded wheels the outer corner is likely to become broken off or unduly abraded.

Footnote 75:

Curbing of all kinds is more likely to be injured by freezing and the heaving of frost under and around it than from any other cause. Good drainage is the best protection against such injury. It is important that these drains shall be connected with sewers, drains or other outlets, so that water will not stand in them.

Footnote 76:

The most notable departure of these specifications from usual practice is the use of a solid body of rich, homogeneous concrete for the whole section of the structure, thus avoiding the use of two courses and qualities of concrete—the core concrete and the facing. The most common cause of failure of concrete curbs and gutters is the separation, more or less, of the facing from the core concrete. Without doubt this can be prevented by the use of proper materials, careful work, and the strict observance of the rule that the facing course must be applied before the core concrete has begun to set. But it is difficult to always secure these favorable conditions. Computation will show that the difference in cost of materials, between the usual two-course construction and a single body of rich concrete throughout, is not very great, while the saving in cost of labor is so considerable as to make the actual difference in cost of the two types very small. There can be no doubt that the simpler construction and the consequent greater certainty of securing a durable and satisfactory job is greatly in favor of the construction here recommended.

Footnote 77:

The appearance of “hair cracks” on the surface of rich concrete, finished by troweling, and the blotched appearance of the surface of concrete curbing, are usually caused by improper finishing. The glazed surface produced by troweling, particularly where pure, dry cement or neat mortar is applied is almost sure to develop hair cracks, and the varying texture of the surface is likely to absorb water unevenly and thus produce, in time, the unevenly colored or blotched surface so often seen.

Footnote 78:

The utility and durability of hydraulic concrete sidewalks depends largely on the quality of materials and workmanship employed in the work. Too frequently, specifications for this work are not sufficiently full, or not prepared with the requisite care, or the work is not properly supervised or inspected while in progress. The aggregate importance and cost of this sidewalk work in our cities warrants more care and attention than it generally receives.

Footnote 79:

Determined by the thickness of the drainage course adopted.

Footnote 80:

It is customary in many cities to require that the drainage course under the concrete shall have a depth of twelve or more inches. This deep-drainage is designed to prevent the heaving of the sidewalk by freezing. Experience seems to prove that this is not necessary, particularly if tile drains are provided to carry off the water from the drainage course, as specified. Comparatively dry material, even earth, does not heave with freezing; on the other hand, if the material and the trench in which it is placed is wholly or partly filled with water, heaving is liable to occur in severe freezing weather, whatever the depth of the drainage course. Experience has proven, however, that four inches of drainage material is sufficient if the water is drained out of it, while if allowed to stand saturated with water, deeper drainage will give little if any better results. Where the soil is sandy or the natural drainage is otherwise good, no drainage course is necessary.

Footnote 81:

Except in the matter of low first cost cinders are not desirable for the drainage course. In time, this material is likely to slack, or decompose, and shrink in volume more or less and to allow the sidewalk to settle. The hollow sound one often notices when walking over a sidewalk and the cracks that frequently appear, are usually caused by the irregular settlement of the drainage course. The object of wetting down the cinders several days before they are used is to cause as much as possible of this slacking to take place before the cinders are used in the drainage course.

Footnote 82:

There is a good deal of diversity of practice in the thickness of the concrete to be used. For all ordinary sidewalks three inches of bottom course and one inch of surface-course are ample, and in many cases the thickness of the surface course has been reduced to one-half inch with satisfactory results. Three-fourths inch of surface-course, if fairly uniform in thickness and of good quality, will generally be ample for ordinary sidewalks.

Footnote 83:

It is customary to make the surface-course concrete much richer than this, but it is not necessary if the materials are good and the work well done.

Footnote 84:

This requirement is very important and should be strictly enforced, otherwise there is danger that by the action of water, frost, and time, the two courses may separate and the surface-course break up—a condition not infrequently observed.

Footnote 85:

The troweling not only helps to secure a true surface, but tends to produce a dense surface on the concrete; but it is not desirable that this surface shall be smooth and glassy, hence the slight roughening of the surface with a wire brush.

Footnote 86:

Care must be taken to make and leave these expansion joints open to their full width entirely through the concrete. The practice of forming these expansion joints by partitions of iron plate, against which the blocks of sidewalk are built is not advised, for the reason that they are likely to prevent the thorough compression of the concrete surface against or near the plates.

TRANSCRIBER’S NOTES

1. Silently corrected obvious typographical errors and variations in spelling. 2. Retained archaic, non-standard, and uncertain spellings as printed. 3. Re-indexed footnotes using numbers and collected together at the end of the last chapter. 4. Enclosed italics font in _underscores_. 5. Enclosed bold font in =equals=. 6. Denoted subscripts by an underscore before a series of subscripted characters enclosed in curly braces, e.g. H_{2}O.