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.
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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.