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through open spaces under the sides of the crib or inclosure. To this end
the crib may be scribed to suit the inequalities of the bottom when the latter
cannot readily be leveled off. Or inside sheet piles will be better in some
cases; or an outer or inner broad flap of tarpaulin may be fastened all around
the lower edge of the crib, and be weighted with stone or gravel to keep it in
place on the bottom. Broken stone or gravel or even earth (the last two
where there is no current), heaped up outside of a weak crib, will prevent the
bulging outward of its sides by the pressure of the cone. After the cone
has been carried up to within some ft of low water, and leveled off, the
masonry may be started upon it by means of a caisson, or by men in diving
suits. Or, if the cone reaches very nearly to low water, a first deep course
of stone may be laid, and the work thus brought at once above low water
without any such aids.

118. The concrete should extend out from 2 to 5 ft (according
to the case) beyond the base of the masonry. All soft mud should be re-
moved before depositing cone.

119. Bag's partly filled with concrete, and merely thrown into
the water, are used in certain cases. If the texture of the bags is slightly
open, a portion of the cem paste oozes out, and binds the whole into a tolerably
compact mass. Such bags, by the aid of divers, are employed for stop-
ping leaks, underpinning, and various other purposes, that may suggest
themselves. Such bags may be rammed to some extent.

120. Tarpaulin may be spread over deep seams in rock
to prevent the loss of cone; and, in some cases, to prevent it from being
washed away by springs.

121. Concrete, placed in water, should be in large batches, in order
that the ratio of exposed surface to vol may be small. In running water,
lead off the flow in pipes or shutes or by means of bulkheads (for which bag
cone is suitable). If water is pumped out of the pit while concreting, it is
apt to take cem with it. Observe the water flowing from the pump for in-
dications of loss of cem.

122. Cone dock foundation on rock 14 to 19 ft below low water and
covered with mud. Laid with assistance of diver. Mud washed off by
jet. Rock not leveled. Wooden forms built on rock. Spaces, under forms,
filled with bags of cone. Forms held down by means of boxes loaded with
broken stone, anchored, by wire cables, near bottom, to neighboring piles,
and braced, at top, by cross pieces nailed to existing dock. Cone lowered,
by derrick, in ^ yd bottom-dump bucket, and dumped when close to work.
The only cem lost is the little which washes from top of bucket load as
bucket is submerged. The work has smooth faces along the forms, and ap-
pears to be perfectly homogeneous. (E R, '05/Oct/21, p 468.)

123. Placing cone in 90 ft water, in shaft, to stop inrush of water at
bottom of shaft. Cone fed, by hopper, into 8 inch screw-jointed wrought
iron pipe, lower end stopt with wood plug and resting on bottom of shaft.
When the pipe was raised slightly, the plug refused to move and release
cone. Pipe withdrawn, taken apart, and each section emptied. Plug,
not tight, had allowed lowest section to fill with water, which disintegrated
the cone, leaving, at top of lowest section, a plug of neat cem, which pre-
vented the cone, above, from pushing out the wood plug as intended. Expt
repeated, with tight plug. Inside the 8 inch pipe was placed a 1 J^ inch



never set; but the remainder appeared to be solid and homogeneous.
(Assn C E, Cornell Univ, Trans, 1898, p 74.)

124. In a case where hollow iron piles, in clean sandy bottom, were filled
with cone, some of the mortar leaked out, and formed, with the surrounding
sand, masses of cone, which adhered most tenaciously to the piles; suggesting
the use of hollow piles, purposely perforated, in their lower
portions, with small holes, thru which grout, poured into them, at top, can
escape into the sand. (Chas List, Jour Assn Engg Socs, March, 1903, Vol 30,
No 3, p 124.)

125. Superior Entry, Wis. Mixer discharges into a sub-hopper, with
a cut-off shute, which discharges into depositing buckets on cars under the
platform. Upon reaching the work, the buckets are lowered into the sub-



1102 CONCRETE.

merged molds by travelling derricks. Each bucket is provided with two
canvas covers, in two pieces, quilted with sheet lead, and fastened to op-
posite sides of the bucket. When in position, these pieces overlap at the
middle of the buckets, completely covering the otherwise exposed cone.
When the bucket has been set upon the bottom, it is tripped by a specially
designed latch, from which a rope leads to the derrick man on the traveller.
The canvas curtains prevent washing of the cone. A loaded bucket weighs
13,652 Ibs. Impact of loaded bucket, upon cone already laid, seems to
compact the cone sufficiently. Discoloration of water by cem, during de-
scent of loaded bucket, very rarely noticed. (Report of Chief Engr U. S. A.,
1904, Part IV, p 3785.)

SURFACE FINISH.

126. Upon the removal of the usual wooden forms, the cone surface shows
the marks of the grain, knots and joints of the lagging. This appearance
may or may not be objectionable.

127. Plastering with cem mortar gives a good finish in the interior of
buildings, where rain and frost canot affect the plaster; but it usually
scales off when applied to exterior surfaces.

128. Outer surfaces may be washed with thin cement grout,
after pointing, where necessary, with cem mortar. This should be done
while the cone is green, and, if possible, immediately after the removal of
the forms. A thin grout, composed of 1 part Plaster of Paris and 3 parts
cem, applied with whitewash brushes, gives satisfactory results.

129. Cone surfaces may be tooled with the toothed axe, giving a variety
of effects. If picked when the cone is somewhat green, a rough surface is
left, which shows the stone and corresp9nds to rough pointed stone work.
Unless the tool is sharp, the surface is injured. When the cone is older and
harder, picking gives the effect of fine pointing. Compressed air tools and
the sand blast have been used effectively, the former on parts of the Harvard
Stadium.

130. Facings, of specially prepared mortar, are often placed
at the same time with the body of the cone, by means of a sheet metal form
or dam, set on edge. This dam separates the facing from the backing; and
after both facing and backing have been brought level with its top, it is
lifted out of its place and used again upon the layer of work next above.
After the form is lifted, the semi-fluid facing and backing flow together,
uniting in the narrow space vacated by the form.



131. Facing should not be richer than 1 : 3, unless f9r ornamental work;
for plain surfaces, 1 : 4. Too rich a facing, and excessive rubbing, cause a
tendency to form hair cracks in the surface, and are expensive. On Chicago,
Mil. & S. P. R. R., in Chicago, "the cem used in putting a 1 J^ inch facing of
mortar of 1 Portland : 2 sand, on fairly heavy abutments, amounted to
about 9 % of the cem used in the entire neat work."

132. "In the case of a narrow wall, the speed of the work is frequently
impeded by the inability to carry up the facing fast enough, and in any case
two or more extra men are needed, to mix and carry mortar and to attend
to placing the facing inside the form." (W. A. Rogers, R R Gaz, 'OO/Jul/6,
p 461.)

133. With spaded or mortar finish, to protect the work from

frost a layer of tar paper may be placed outside the studs, leaving an
air space, of the thickness of the studs, betw the paper and the lagging. In
this space, the temp will be from 8 to 10 above that of the outside air.
Such a protection is of course most needed on the sides exposed to the wind.
(W. J. Douglas, E N, '06/Dec/20, p 650.)



134. Change of hands, during the progress of finishing work, may result
in loss of uniformity of appearance.

135. Scrubbing before cone is set. Mr. H. H. Quimby (Natl
Cem Users Assn, Procs, 1907) scrubs the fresh cone surf, before hard set,
with a brush and water, thereby removing the film, and, with it, all impres^



PROPERTIES. 1103

sion of the forms, and exposing the clean stone and sand of the cone. A few
rubs of an ordinary house scrubbing brush, with a free flow of water to cut
and to rinse clean, suffice; but a little additional rubbing improves the effect.
The necessity for early removal of the forms, when this method is used,
necessitates special care in their construction, increasing their cost. When
applied to surfaces forming square corners, the projecting sand particles
produce a ragged effect.

136. An effect similar to that obtained by Mr. Quimby's method, may be
produced, after hard set, by washing with an acid solution, which
is afterward removed by the use of an alkaline wash, followed by water.
This method attacks limestone in the agg.

137. Color effects are best produced by using agg of the desired color.



138. The difficulty of making oil paint adhere to fresh cone
surfs is due to moisture and free lime. A wash of dilute acid neutralizes the
lime, but is unsatisfactory, muriatic (hydrochloric) acid forming highly
hygroscopic salts, such as calcium chloride, and sulfuric acid having only a
superficial effect. Dissolve 10 Ibs ammonia carbonate (salts of hartshorne)
in 45 gals water, and apply once with a brush, or give several coats of a
weaker solution, or apply as spray. The ammonia is liberated, and the
carbonic acid forms, with the free lime, an insoluble carbonate, which
soon becomes dry and hard. After exhaustive trials, this was found the
only method which satisfies every requirement. The amm carb keeps, for
any length of time, in fairly tight vesesls. (Fred J. Bosse, "Cement
Age," '09 /Jan, p 48.)

PROPERTIES OF < O\< HI. M .
Weight. See Voids, p 1088, and Density, p 1089.

1. Weights of concrete, in pounds per cubic foot.
Broken stone or gravel concrete, 130 to 160; ordinarily 140 to 150.*

One foot B M = vol of a solid 1 ft square and 1 inch thick, = 144 cu ins =
1 cu ft/12.

144 Ibs per cu f t = 1 Ib per 12 cu ins = 1 Ib per prism 1 inch square and
12 inches long.

Hence, at 144 Ibs per cu ft, the wt of any prism in pounds = area of
cross section in square inches, multiplied by length in feet, = vol in cubic
inches/12.

Wt,lbs/cuft 100 110 120 125 130 140 150 160

Kilograms / cu meter.... 1600 1760 1920 2000 2080 2240 2400 2560

Cinder concrete, 110 to 120;

Sandstone " 143

Limestone 148

Gravel " 150

Trap " 155

With natural cem, 4 to 5 Ibs lighter per cu ft

2. The unit weight varies not only with character of constituents, but
also with proportions, consistency, degree of compacting, etc.

Permeability.

3. Even where the primary object of the cone is not the prevention of
percolation by water, impermeability is of great importance in promoting
the durability of the cone, and especially in protecting metal reinfmt from
corrosion and from loss of adhesion with the cone.

4. Water may pass thru cone, etc, so slowly that evaporation, from the
outside, proceeds more rapidly than the water can reach it, so that the out-
side of the wall may appear dry, altho percolation is actually taking
place.

*144 Ibs per cu ft = 12 Ibs per ft B M. (Board measure).

120 " = 10 " " " "

108 " ." " " = 9 " '



1104 CONCRETE.

5. When made into hardened mortar, well trowelled down on all surfaces
which come into contact with water, neat cement is as nearly im-
permeable as the best of natural rocks used for building purposes- (Wm.
B. Fuller, Trans, A S C E, Vol 51, pp 133-4, Dec 1903.)



6. Mortar or cone, so proportioned as to obtain the max practica-
ble density, and mixt rather wet, is impervious under ordinary conditions.

7. Small blocks of cone, carefully made from materials so graded as to
insure great density, or with an excess of cem, have been repeatedly found
to be as nearly impervious as the best natural stones. See Expts, p 1138.

8. In large masses, in actual construction, it is difficult to produce
an absolutely tight structure without the addition of a lining of material
more nearly impervious than the cone. Variations in the mixture, careless-
ness in manipulation or placing, or in bonding betw successive days' works
(an hour's interruption, in the middle of a hot day, has been known to cause
leakage), or insufficiency of water, will render cone permeable, in spite of

Koper theoretical proportioning and the addition of lime. The mix should
at least wet enough to settle into place with but little ramming=

9. Cone, impervious in itself, may develop cracks thru which water
may permeate. Reinfmt, properly placed, opposes such cracking.

10. Water may permeate thru the mortar, thru the particles of agg, or
betw mortar and agg. Probably most of the percolation takes place thru
the mortar. See Mortar. We here deal with those aspects of permeability
which can better be discussed in connection with the cone as a composite
material.

11. When the leakage consists of mere percolation thru the minute
pores of cone, etc (i e, when there are no actual fissures), leakage gen-
erally diminishes with use, the water (even when apparently clear) blocking
its own passage by depositing, in the pores of the material, either its own
natural sediment, or (in the form of "laitance") lime and other compounds
dissolved out of the cone itself.

12. This action depends upon many factors, notably the pressure, the
sizes and shapes of the pores, the hardness and solubility of the material,
and the character of the sediment carried by the water. Thus, under high
pres, if the material is easily scoured, or if the pores are large and relatively
straight, leakage may be expected to increase, rather than diminish, with
time.

13. Where the nature of the case permits, as in floors, retaining walls, etc.,
it is better to lead the water off by proper drainage, than to attempt to
block its passage by rendering the structure watertight.

14. Where watertightness is required, as in dams, the con-
stituents must be carefully proportioned for max density, there must be an
excess of rich mortar over vol of voids, dry mixtures should be avoided, the
mixing must be thoro, and the construction should be, as nearly as possible,
monolithic.

15. The application of waterproofing'materials may be either (a)
internal, mixt with the ingredients of the cone; (b) superficial, filling the
pores near the surf; (c) external, preventing contact betw water and cone.

16. Internal. For water tight work, the vol of mortar should be 40 to
45 % of the vol of agg, or 40 to 42 % if the agg is graded. (Geo. W. Rafter,
Trans, A S C E, Vol 42, p 149, Dec 1899.)

17. With agg having 35 % voids, the vol of mortar should be < 50 %
of vol of agg; vol of dry sand and cem < % vol of agg; vol of sand >
2 X vol cem. For cem leaving > 10 % on No. 120 sieve, ordinary sands,
and agg with 35 % voids, the following proportions are given:

cem sand agg (sand + agg) -f- cem

1 1.0 3.00 4.00

1 1.5 3.75 5.25

1 2.0 4.50 6.50

See Plain Concrete, ^ 22, p 1088.

18. Every particle of sand must be coated with cem, and every particle
of stone with mortar, so that the stones or the sand grains do not touch.

19. To insure this result, mix by means of one of the newer types of ma-



PERMEABILITY. 1105

chine, introducing first the measured quantity of water and then the cem,
making a liquid grout which will run easily into the most minute voids of
the sand, which, being next introduced, becomes coated in the shortest space
of time. The resulting mortar is still quite liquid, and flows into all the voids
of the stone. (Wm. B. Fuller, Trans A S C E, Vol 51, p 135, Dec 1903.)

For the use of lime, see Expt. 82 a, p 1177.

2O. In making thin slabs with a cone of 2 parts cem to 5 of fine bitumi-
nous ash, reinfd with poultry mesh, Mr. W. K. Hatt (Trans, A S C E, Vol 51,
p 129, Dec 1903) employed a 5 % solution of ground alum, in place of one half



us ausuipnuii uy auuut uu 7/5. JLIIC aua,p auiuwun zuuiie IUUUUIBUOU ztusuip-

tion, but did not strengthen the cone. Sand mortar was not greatly strength-
ened by the soap and alum treatmt, but its absorption was dimin-
ished about 50 %.

21. If joints are inevitable, they may be first wet, and then covered with
neat cem paste or 1 : 1 cem mortar, upon which the new work is to be placed
before the binding course hardens.

22. The permeability of cone linings of aqueducts &c may be diminished
by drilling holes thru them and forcing ill grout behind them by
means of grout pumps. The grout sometimes appears at many points,
indicating that it is passing not only thru the cracks but also thru the
body of the cone. This method was successfully used in the Torresdale
filtered water conduit, Philadelphia.

23. Superficial. For plastering the inside of a covered clear water
well, Mr. Edwd Cunningham used 1.25 Ibs of soft soap for each 5 buckets of
water, and 3 Ibs of alum per bag of cem. The mortar was easy to handle with
the trowel, but had a nauseating odor. 2 coats, not more than 0.5 inch in
all. 18-inch dividing wall showed no leak when one side held 16 ft of water.
The soap was made of clarified fats, and cost 7.5 cts per Ib; much too high.
With 1 part cem to 2 parts sand, 6 to 9 gals of water and 12 Ibs of alum were
required for each bbl of cem. (Trans, A S C E, Vol 51, pp 127-8, Dec 1903.)

24. As an external treatment, Mr. Richd H. Gaines, New York Board
of Water Supply (Trans, A S C E, Vol 59, p 160, Dec 1907) found the
Sylvester soap and alum process (p 928), "fairly effective, but
very expensive for large work. "

25. Asphalt can be successfully applied only to dry surfaces. It
becomes brittle and loses its efficiency upon oxidation; but it will often
prevent leakage until the structure has become tight thru infiltration.
See II 11, p 1104.

26. The cone surface must be clean, and must first be treated with a
thin wash of liquid asphalt, thinned with benzine. This enters the pores
of the cone, and acts as a binder. Without this, the asphalt coating will not
adhere- to the cone.

27. Asphalt coatings should be made continuous, and should be pro-
tected against decay, from creeping and from abrasion, by being placed
between alternate layers of cone, or by being covered with brickwork or
masonry.

28. Tunnels, subways and basements, below water level, have been
thoroughly waterproofed by continuous layers of heavy roofing papers,
well mopped with tar or asphalt, and placed between outer and inner cone
walls.

29. The two basins of Queen Lane reservoir, Philadelphia, originally
lined with cem cone on sandy clay puddle, and holding 383 million gals of
water 30 ft deep, were re-lined with Bermudez asphalt in 1896-7. The floor
received 2 inches of asphalt cone, with a thin top layer of hot liquid asphalt;
the slopes, two layers of hot liquid asphalt, with burlap between them; the
burlap being anchored at top by being lapped around horizontal iron or
wooden bars, let into the asphalt paving. While this work was in progress,
the south basin of the Roxborough reservoir (147 million gals, 25 ft deep)
was similarly lined. In the north basin, Alcatraz (California) asphalt was
used, and the slopes, as well as the sides, were treated with asphalt cone.
All four of these basins have since been in continuous use, without sensible
leakage.

C6



1106 CONCRETE.

Elastic Modulus, E. See Iflf 12 and 13, p 1111.

30. When cone is subjected to compressive test, its stress-strain diagram
is in general curved throughout its length; its elastic modulus,

,., stress, per unit of area ,. . . , .

Jit =* -r - : 77 FI rr , diminishing as the stress increases.

shortening, per unit ot length

Strength.

31. Cone being weak in tension, and brittle, its tensile strength is

usually and properly neglected; dependence is placed chiefly upon its
comp strgth, and its tensile and shearing strgths are usually exprest as
fractions of the comp strgth.

32. The compressive strength is preferably determined experi-
mentally by means of cubic specimens. The unit comp strgth decreases
when the ratio, length/side, increases, and, in similar specimens, when
their dimensions increase.

33. Cone prisms, tested in endwise compression, usually fail
by shearing on planes oblique to the axes of the prisms. Upon these oblique
planes, the unit shear is about half the ult comp stress.

34. The strgth varies widely with the character of the cone.

35. For 13 inch cubes of Portland cem mixtures having from 6 to 18
volumes of (sand + agg) to 1 vol cem, Mr. Edwin Thacher deduces,
from /the data of Expt 18 a, the straight-line formula,

S = MNX
where

S = ult comp strgth, Ibs per sq inch;
X = No of parts of sand to 1 part cem;
M and N = values as below:

Age = 7 days 1 month 3 months 6 months

M = 1800 3100 3820 4900

N = 200 350 460 600

Mr. Thacher holds that, for practical mixtures, "the strgth of cone de-
pends principally on the strgth of the mortar, and not, to any great extent,
upon the amount of stone. " In these tests, the vol of stone was always
twice the vol of sand.

36. But few tests have been made to determine the tensile strength
of cone. It is usually taken as approximately from one-tenth to one-eighth
the comp strength, and the shearing strength as from 1.2 to 1.5 times
the tensile.

37. Prof. L. J. Johnson (Jour, Assn Eng Socs, Vol 38, No 6, p 310, June,
1907) tested 25 reinfd beams, 3 ins X 9 ins X 8 ft, loaded 6 ins from each
support; 19 of the beams were of 1:2:2% scaly trap; 6 of 1 : 2.5 : 5.
All the beams failed by slip of reinfmt; the 1:2:2% beams,
137 to 143 days old, successfully resisted shears of 233 to 573 Ibs per sq in;
av 470; and the 1 : 2.5 : 5 beams, 488 to 750; av 628.

38. In beams, owing to the rising of the neutral axis, under loading,
the ult unit fiber stress, or rupture modulus, is about 1.6 X the unit
tensile strgth.

Setting.

39. Setting is of course a function of the cement paste. See Mortar.
We here treat of setting, as affecting the cone as a composite body.

40. Temperature. In hot weather, cone sets very much faster than in
cool weather, and the load may therefore be applied sooner in hot weather;
but the time required varies with the class of structure and of cone.

41. Gradual loading. Where the loading is static or gradually increased,
the time may be shorter than where the load is applied suddenly or is sub-
ject to impact.

42. "As a general rule, bridge abutments and piers of Portland
cem cone should be allowed to set at least a month before using, if built
during ordinary warm weather. If built during cold weather, their use
should, if possible, be deferred until warm weather sets in." (W. A. Rogers,
RR Gaz, 'OO/Jul/27, p 514.)







BEHAVIOR. 1107



43. Steel girder spans have been placed upon Portland cem cone abut-
ments without injury 2 weeks after the completion of the abuts in hot
weather; but work of the same character, finished early in Dec, was found
not very solid inside, early in the following March.

Effects of Heat and Cold.

44. Freezing nearly always damages nat cem mortar or cone to such
an extent that it must be replaced by new material.

45. With Portland cem cone, freezing suspends the setting

and hardening of the mortar, for the length of time during which the material
has been frozen. The apparent loss of strgth,. in frozen specimens, may often
be due merely to such delay in setting.

46. While freezing seldom results in material reduction of the ult strgth
of Port cem cone, yet it may produce serious results by giving the
cone an apparent hardness; thus causing the premature removal of forms,
or the imposition of undue loads, which may produce failure when the cone
thaws out, if it had not already set sufficiently before being frozen.

47. If, soon after the mortar, thru the entire thickness of a wall, is
frozen, the sun shines on one face of it, so as to soften the mortar of that face,
while the mortar behind it remains hard, it is plain that the wall will be
liable to settle at the heated face, and at least bend outward if it does not
fall.

48. If the freezing does not take place until after the cem has taken its
initial set, there is little danger. Thin work should not be done at <
28 F on a rising, or at < 32 on a falling temp.

49. A thin scale is likely to crack from the surface of cone walks or
walls which have been frozen before the cem has hardened. Granolithic or
troweled finish sometimes spalls up in small patches, when frozen.

Protection.

50. Protection against freezing is expensive and uncertain.
Hence the placing of cone in freezing weather should be avoided when possible.


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