John C. (John Cresson) Trautwine.

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by the agitation so caused. The discharge is effected, in the Smith (double
cone) machine, by tilting the machine (like a Bessemer steel converter)
about its trunions, placed at cen of grav of drum; and, in the Ransome
(cylindrical drum) machine, by inserting a tilting trough, which, in the dis-
charging position, catches the material as it falls from the blades.

43. To provide against break-downs, extra parts should always
be furnished with each mixer.

44. Mounting-. Mixers are. either stationary, or mounted on skids
or wheeled trucks, with or without steam engine, engine and boiler, gasoline
engine or electric motor.

45. The mixer, with its framing, is sometimes lifted bodily from its old
location, and deposited in a new one, by a derrick or cableway.

46. Wheeled cone mixers, with revolving drums, into which the
ingredients are loaded, and in which they are mixt by means of the forwd
movemt of the vehicle, have been used. The motive force may be given
by hand, by horse-power or by gasoline engine; and the relation, betw
forward speed and speed of rotation, may be regulated by gearing.

47. Small hand-power batch mixers are furnished; capacity claimed
> 450 cu ft per day.

48. In the choice of a mixer, reliability, as established by success-
ful use, is of prime importance, especially where continuity of work is essential.

49. Shortage of output may be due to shortage of power behind
the mixer, as well as to the mixer itself.

50. The mixer should be cleaned after each day's work.

>! The best cone may be rendered almost worthless by carelessness or
improper method in the placing.

52. When cone is dnmpt from a considerable height, there
would seem to be danger that the even distribution of materials may be

disturbed. Hence, if lowered in buckets, these should be brought close to
already done, before dumping. However, in the construction of

the work


>nc piers for a bridge at Bethlehem, Pa., by Cramp & Co. (E R, '09 /Mar /6,
280) cone was delivered, thru an inclined wooden shute, lined with sheet



iron, at a point vert'y 74 'ft below the mixer; and the method was found

to be economical, and the] cone uniformly good, and there was no difficulty

from separation of ingredients.

53. In work that will show, the layers are usually restricted to about
6 ins in depth, owing to the difficulty of spading the face work when the
layers are thicker; but in foundations, and in heavy work above ground,
if to be faced with masonry, or if appearance is not important, layers of
wet cone as deep as 2 feet may be used.

54. If the cone, after placing, is found to be too wet, it is better to
correct the trouble by placing drier cone upon it. When surplus water
is bailed out, some cem is carried with it and thus wasted.

55. Excessive face spading brings up water from below, and this
washes cem from the face.

56. Worlts of considerable length, such as dams and walls,
are commonly built in sections alternately, thus: sees 1, 3, 5, etc, are first
built separately, and, when they have hardened, sec 2 is built betw sees 1
and 3, section 4 betw sees 3 and 5, etc. The sides of sees 1, 3, 5, etc, thus
serve as part of the forms for sees 2, 4, etc. This method facilitates bonding
betw the sees, by means of vertical dove-tail grooves, formed, by the molds,
in the sides of the sees first built. The cone of the remaining sees, placed
later, enters and fills these grooves.

57. In freezing 1 weather, cone can be laid in large masses in water
or below the ground surf. In excavations, if the ground water is permitted
to rise over the work during the night, it will usually prevent frost from reach-
ing the cone.

58. At Chaudiere water power dam, cone was laid in temps as low as
20 F. A mixing house was erected, and the temp, within, was kept,
by stoves, above freezing. Materials were lowered into the house by
derricks thru hatchways in the roof. Water was kept in casks, and kept
lukewarm by steam jets. Sand was heated outside the house. Stone, in
piles 3 to 4 ft deep, was heated (but not dried) by steam jets from a perfo-
rated pipe, passing under the piles. After placing, the cone was loosely
covered with canvas, under which the nozzle of a steam hose was introduced.


59. In wall foundations, the trench itself may constitute the form; and,
in dams and arches of cone blocks, the first blocks, placed alternately,
often serve as parts of the forms for the ^remaining blocks; but ordinarily
a considerable amount of timber framing is required. See 1f 56.

GO. The economy of the work depends so largely upon the design
of the forms, that it is often advisable to modify the design of the work
itself, or to use more cone than would otherwise be nec'y, in order to secure
economy. The design should be such that commercial sizes of lumber
may be used, and with a min of wasteful cutting; and such that the forms
may be readily erected and removed with a minimum of damage to them-
selves and no damage to the work, and used repeatedly. Where practi-
cable, the forms are made in sections, small enough to be conveniently
moved and handled separately. Cutting is economically done by power
saw benches.

61. Even in building work, where much of the "centering" must be
built in place, and where it can be removed only by taking it to pieces,
the lumber may be used two or three times before it is discarded. Where
the forms can be assembled in panels, and these panels removed as units,
they may be used many times.

62. The requirements of different works, executed under diff conditions,
vary so widely, that no useful details, as to the construction of the forms,
etc, except for buildings (see UH 63 etc), can be given within the limits
at our disposal. The designer should witness the removal of his forms
before estimating their success.



Forms for Buildings.

63. In reinfd building construction, the forms are chiefly :

(a) Column forms,

(b) Beam, slab, floor and roof forms,

(c) Wall forms.

64. A typical column form. Figs 1 and 2. The boards, G, 1%
ins thick, are held in place by cleats, H, IH X 5 ins, and by "column
clips," C, made of pieces 4X4 ins, and boards, B, 1 Yi X 5 ins. These
"column clips" must be spaced to take the pres due to the cone. At the
bottom of a column 18 ft high, they should be > 10 ins, cen to cen. At
the bottom, 4 boards, A, are used, to hold the form in shape, and the boards,
G, are cut, on one side of the box, at F, 2 or 3 ft from the bottom, to form
a door (cleats, on door, not shown), thru which all rubbish may be brushed.
The door is then held shut by the lower two "column clips," and the form
is filled. Triangular fillets, T, are used to bevel the corners of the col.

Fig 1.

Figs 1 and 2.

Column Form.

65. Column forms should be so designed that they may be removed
without disturbing the forms for the beams and girders. The col forma
may then be bared for inspection, before being loaded.

Fig 3. Beam Form,



66. Typical beam or girder forms. Fig 3. The forms, or beam-
boxes, often miscalled "centers," are supported, betw columns, by tempo-
rary struts or shores, /, 4 X 4 ins, about 6 ft apart, resting on wedges, J,
and the plank K. Corbels, H, 4 X 4 ins, are placed directly under the
bottoms, G (1 M ins thick) and sides, C (1 M ins thick), of the beam boxes.
The sides, C, are held together by cleats, E, 1 M X 5 ins, 2 ft apart, to which
are nailed the strips, D (1 H X 6 ins), upon which rest the ledgers, B, 2 X 6
ins, about 27 ins apart. These support the panel boarding, A, \% ing
thick; and this, in turn, supports the slabs. Small triangular fillets, T,
in the corners of the beam boxes, make the box tight and give beveled cor-
ners to the beam. Beam forms should be given a slight camber.

67. Typical forms for floors betw steel beams, Figs 4 to 6, vary
with span and load. The forms are hung from the bottom flange of the
I-beams, by "hanger bolts," A, Figs 4 and 6, % inch diam, with washers
and handle nuts. These bolts secure the pieces, E, of 2 X 4 or 3 X 4, upon

Fig 4.

Fig 5.

Figs 4, 5 and 6.

Fig 6.

Floor Forms.

which the boards, H H H are supported by 2 X 6 or 2 X 8 ledgers, D
(about 27 ins c to c, for % inch boards). Wooden blocks or sticks, B,
Figs 4 and 5, are sometimes used under the ledgers to reduce their depth.
Short cone blocks, C, Fig 4, are used, to keep the forms away from the
lower flange of the steel beam. These remain permanently in the work.
In order to promote adhesion betw the lower flanges of the I-beams and
the thin mass of cone below them, the flanges are often wrapped with metal
lath, before the blocks, etc, are placed.

68. Wall forms are usually made up in panels, so that they can be
used several times. The panels are bleated together, and are usually about
3 X 12 ft. The panels are kept at the proper dist apart by separators,
of wood or cone, and are held in place by bolts or wire ties. When wood
separators are used, they must be removed just ahead of the concreting.
Cone block or tube separators are sometimes used. These remain in the
wall. When bolts are used that are to be later withdrawn and used again,
they should be loosened by means of a wrench, about 24 hours after con-
creting; otherwise it will be difficult to remove them.

69. In the Wiederholdt system of reinfd cone wall construction,
the cone is deposited within small hollow tile blocks, which form the finished
exterior surface, and no wooden or other temporary forms are used. The
blocks are shaped to meet the requirements of the work. Tiling and con-
creting are carried up simultaneously.

FORMS. 1097

70. To reduce the cost of forms in reinfd building construction, columns,
beams, slabs, etc, may be cast on the ground, and afterward erected
and placed as desired; at the sacrifice, however, of the rigidity due to the
monolithic character of ordinary reinfd work.

71. Metal forms. When the structure is of small and uniform
cross section, permitting the repeated use of the same forms, as in sewers,
conduits, tunnels, etc, the lagging, for the wooden forms, may be 9f sheet
metal. In tunnels and similar works, of considerable extent, and in small
ornamental work, forms composed entirely of metal may be used.

72. Both careless and over-careful alignment are to be avoided.
Mr. W. J. Douglas (E N '06/Dec/20, p 646) suggests the allowance of " ^
inch departure from established lines on ' finished ' work, 2 ins on ' unfinished '

73. Avoid fine detail, and detail with sharp angles. Corners should
be rounded or beveled, to facilitate the flow of cone and the removal of forms,
and to render the corners less liable to subsequent injury.

74. Wooden forms, within which the cone is to be placed, should be
fairly watertight, smooth, and of sufficient strgth and stiffness to hold to
line under the pres of the green cone.

75. The forms are usually of dimensioned timber, faced with planed
boards or planks. The opening of joints betw the planks may be partially
prevented by the use of matched boards or of tongued-and-grooved plank.

76. Mortar, exuding thru open joints, leaves voids or stone pockets on
the surface. Hence, in forms for facework, joints should be made
tight, if necessary, by the use of mortar, putty, plaster of Paris, sheathing
paper or thin metal.



their edges slightly beveled, and the sharp angle of the edges of adjacent
boards placed in contact. Swelling will then crush the edges rather
than bulge the board.

I. ii in her for Forms.

78. White pine is best for fine face-work, and quite essential for ornamental
construction when cast in wooden forms.

79. Spruce, fir, Norway pine and the softer kinds of Southern pine are
more liable to warp than white pine, but are generally stiffer and therefore
better for struts and braces.

SO. Partially dry lumber is usually best. Kiln dried lumber is unsuit-
able, as it swells when the wet cone touches it. In very green lumber,
especially Southern pine, the joints are apt to open. Green lumber is heavy,
and does not hold nails well.

81. For wall-panel forms, tongued-and-grooved or bevel-edge stuff is
preferable to square-edge. Tongued-and-grooved gives smoother surface
and less opening of joints, than square or bevel edge, but is more expensive,
owing to waste in dressing, and there is more wear at joints if the forms are
used often.

82. Even for rough forms, planing on one side may save money by re-
ducing the cost of cleaning after using. Studs should always be planed on
one side, to bring them to size.

83. Thickness. For ordinary walls, \Y 2 ins; for heavy construction,
using derricks, 2 ins. For floor panels, 1 inch b ards are most used; but,
in tall buildings, they become much worn, and give b^d finish to under sides of
floors. For sides of girders, 1 inch or 1 }/i inch answers, but 2 inch is better
for bottoms. Col forms usually of 2 inch plank.

84. Studding is usually from 3 X 4 to 4 X 6 inch; 4X4 inch is the most
useful size. Spacing, usually 2 ft for 1 inch boards, 4 ft for 1 V* inch, 5 ft
for 2 inch.

85. Since beams and columns sustain greater stresses than floor slabs,
their forms should be left in place longer, and should therefore be indepen-
dent of the slab forms.

86. Sides of beam forms should be clamped or wedged together, to pre-



vent their springing away from the bottom boards, under the pressure of
the cone.

87. Hardwood wedges, at tops and bottoms of struts facilitate the
setting and removing of the struts, and testing for deflection.

88. Light joists (say 2 X 8 or 2 X 10), with frequent shores, are prefer-
able to heavier sizes, difficult to handle.

Strength of Forms.

89. The strength, required for the forms, may be estimated, where
wet cone is used, by assuming the pres of the cone as equal to that of a liquid
weighing about 150 Ibs per cu ft.* If dry and hard-rammed cone be used,
the wedging of the stone, due to the tamping, will considerably increase the

90. Permissible loads, in Ibs, on wooden struts for floor construc-

length, ft

Cross section of strut, inches

3 X 4 = 12

4 X 4 = 16

6 X 6 = 36

8 X 8 = 64


sq in


sq in



1 1 9ftO

sq in



sq in

1 1 0O






































91. In timber beams, calculated for strgth, the extreme fiber stress

is to be taken at 750 Ibs per sq inch.

92. Construction live load, liable to come upon cone while setting,
75 Ibs per sq ft on slabs; 50 Ibs per sq ft in figuring beam and girder forms.
This includes weight of men, barrows filled with cone, and structural ma-
terial piled on floor, but not piles of cem sand or stone, which should not
be permitted unless specially provided for.

93. Floor for

than upon strength.


us should


3 W L*

384 El

be based upon allowable deflection, rather
6 fc3


d = deflection, ins;

W = total load on plank or timber;

L = distance, ins, between supports;

E = elastic modulus of lumber used = 1,300,000 Ibs per sq inch;

7 = moment of inertia of cross section of plank or joist;

b = breadth of plank or joist;

h = depth of plank or joist.

In the usual formula for deflection (see p 480) 1 /384 is the coeff for beams
with fixed ends, while 5/384 is that for merely supported ends.
Weight of cone, including reinforcemt, 154 Ibs per cub ft.
(Sanford E. Thompson, Assn Am Portland Cem Mfrs, Bulletin 13, 1907.)

Details of Forms.

94. Too much nailing increases the difficulty of taking the forms apart
without injury. Wire nails can be pulled with less damage to the wood than
can cut nails.

* Mr. W. J. Douglas (E N, '06/Dec/20, p 646) assumes that the cone is a
liquid of % its own weight, or 75 Ibs per cub ft.

FORMS. 1099

95. Iron or steel wall ties, extending thru the wall and fastening
the forms in place, are usually removed and used again, if > M inch indiam.
If > M inch diam, they are usually allowed to remain; but, if their ends
reach to the outer surface of the wall, they produce unsightly rust stains.
To prevent this, the cone, surrounding their ends, is chipped out, and the
rods are cut off, back from the surface. The holes, thus formed, are after-
ward plugged with mortar.

96. Separators (patented by Wm. T. McCarthy, 1 Madison Ave..
New York city), molded of cem mortar, in the form of hollow cylinders, and
in lengths of 4 and 6 ins, encircling the bolts, are sometimes used After
the bolt is withdrawn, the hole in the cyl is filled with mortar.

97. Forms are liable to disturbance by blows from the cone bucket, or
by the running of machinery in contact with the forms.

98. Any cone, adhering to a form, must be removed before the form is
again used.

Adhesion to Forms.

99. Adhesion to forms. If the wood is new, and if the forms are
thoroly wet before cone is placed, the cone, if hard, is not apt to adhere
to the forms when these are removed. If the forms are to be removed
before the cone is hard, they should, before concreting, be greased with
material thin enough to flow and fill the grain of the wood. Crude oil,
linseed oil, soft soap and other lubricating substances are used.

100. New work is apt to adhere to old sticks, where cone has previously
adhered, even tho this has been cleaned off.

101. Oil, applied to forms (to prevent their absorption of water or to
facilitate their removal, K 99), is apt to find its way to joints betw old and
new work, and prevent the formation of a satisfactory bond. Soap and soft
soap are of course harmless in this respect.

Removal of Forms.

102. Premature removal of forms and props has caused many
failures of cone buildings; but undue delay, in their removal, means delay
in the work and increase in the number of forms reqd.

103. The French law requires that test blocks and sample beams be
made for every section cast. These enable the engineer to judge intelli-
gently as to the condition of the actual work.

104. Props should be removed from one beam or girder only at a time,
and should be at once replaced after the forms for that beam have been
removed. This permits the discovery and repair of defects.

105. The forms may be removed earlier in warm and dry
than in cold and damp weather, earlier from under light than from under
heavy loads, earlier with quick-setting than with slow-setting cem, and
earlier with dry than with wet mixtures. See Specifications, p 1191.

106. To release the beam boxes, the posts may be supported on
wedges and capped. The posts and caps should not be removed, from more
than one beam at a time. After the beam boxes have been removed, the
posts and caps should be replaced before removing the forms from any
other beams. Or, the posts may be supported solidly, and capped with
a corbel forming the bottom and supporting the side-boards of the beam
boxes. The side-boards may then be removed, leaving the posts and
corbels undisturbed.

107. Prying against the cone, in removing the forms, may
injure it.

Joints in Concrete.

108. Difficulty. In large work, the joints, betw work done on diff days
or even before and after an hour's interval, are apt to give trouble, espe-
cially where watertightness is reqd.

109. Causes. The difficulty appears to be due partly to a surface skin
or glaze, on the surf of the hardened cone, and partly to the presence of oily
or dusty materials, laitance or sawdust, betw the two surfs. Oil, used
upon the forms, or saturating the clothing of the workmen, is apt to find its
way to the joints. Sawdust is particularly difficult to remove. The bond
is especially weak if the older surf is frozen.



110. Remedies. Many remedies have been proposed, advertised and
used, fcut none has been fully tested by time. See Specifications, p 1190.
Cleanliness of surface and the use of wet mixtures are probably the best
preventives. Water, used in scrubbing joints, should be rinsed off with
clean water. A jet of live high-pres steam is very effective, removing even
sawdust. Hydrochloric acid is used to advantage. Patented methods of
securing bond, at joints, include the use of metallic binders, with their ends
left projecting from the older surf, to bond with the newer. Another method
employs a layer of prepared honey-comb slag, sprinkled over the still soft
older surf; loose slag being removed after the hardening of the older surf and
before the placing of the newer material.

111. Where cone is used in reinforcing and protecting old stone
masonry, a stone should be removed here and there from the old masonry,
and the joints cleaned out and washed. Key-bolts, with large washers on
their heads, may also be driven into the face and left projecting into the con-
crete. The cone should also be carried far enough down the back of the
wall to prevent water from working down into the horizontal joints on the
tops of the wing walls and main walls.


112. Ramming of cone is necessary only with relatively dry mixtures.
When properly done, it consolidates the mass about 5 or 6 %, rendering it
less porous, and very materially stronger. For rammers, see spec'ns, p 1189.
The men, using them, if standing on the cone, should wear gum boots.

113. IJnder water, ramming can be done only partially, and when
the cone is enclosed in bags. A rake may be used gently for leveling loosely
deposited cone under water.

114. Ramming should be discontinued before setting commences. Ex-
cessive ramming disturbs the homogeneity of the cone.

Placing under Water.

115. Concrete ma.v readily be deposited under water in

the usual way of lowering it, soon after it is mixed, in a dredge bucket, or in a
V-shaped box of wood or plate iron, with a lid that may be closed while the
box descends. The lid, however, is often omitted. This box is so arranged
that, on reaching bottom, a pin may be drawn out by a cord reaching to
the surf, thus permitting one of the sloping sides to swing open below, and
allow the cone to fall out. The box is then raised to be refilled. In large
works the box may contain a cu yd or more, and should be suspended from
a traveling crane, by which it can readily be brought over any required spot
in the work. The cone may if necessary be gently leveled by a rake soon
after it leaves the box. Its consistency and strgth will of course be impaired
by falling thru the water from the box; and moreover it cannot be rammed
under water without still greater injury. Cone has been safely deposited
in the above-mentioned manner in depths of 50 ft.

116. The Tremie, sometimes used for depositing cone under water, is
a box of wood or of plate iron, round or square, open at top and bottom,
and of a length suited to the depth of water. It may be about 18 ins diam.
Its top, which is always kept above water, is hopper-shaped, for receiving the
cone more readily. It is moved laterally and vertically by a traveling
crane or other device suited to the case. In commencing operations, its
lower end resting on the river bottom, it is first entirely filled with cone,
which (to prevent its being washed to pieces by falling through the water
in the tremie) is lowered in a cylindrical tub, with a bottom somewhat like
the box described in U 115, which can be opened when it arrives at its proper
place. When filled, the tremie is kept so by fresh cone, thrown into the
hopper to supply the place of that which gradually falls out below, as the
tremie is lifted a little t9 allow it to do so. The weight of the filled tremie
compacts the cone as it is deposited. A tremie had better widen out down-
ward to allow the cone to fall out more readily.

117. The area upon which the cone is deposited must previously be sur-
rounded by some kind of inclosure, to prevent the cone from spreading
beyond itsproper limits; and to serve as a mold to give it its intended shape.
This inclosure must be so strong that its sides may not be bulged outward by
the weight of the cone. It is usually a close crib of timber or plate iron
without a bottom; and will remain after the work is done. If of timber it
may require an outer row of cells, to be filled with stone or gravel for sink-


ing it into place. Care must be taken to prevent the escape of the cone

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Online LibraryJohn C. (John Cresson) TrautwineConcrete → online text (page 8 of 23)