John C. (John Cresson) Trautwine.

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cantilevers (including dams and retaining walls), in columns, and in
arches where the rise is either very great or very small, relatively to the
span. Reinforcement permits the use of much lighter sections than would
have been safe when use was made only of the compressive strength of the
material.

For reinforced concrete, seep 1110.

4. Disadvantages. Cone is rather weaker than good rubble masonry,
and has only about half the strength of first class ashlar masonry of granite
with thin joints in cem. Like both the stone and the mortar in masonry,
it is subject to deterioration, especially in sea water; but this difficulty is
being eliminated by the care which is being given to the manufacture of
cem and which is fostered by its extensive use and by the conduct of its
manufacture upon a large scale. As in all human work, and notably in the
laying of masonry, care is necessary in order to secure faithful performance,
upon which the success of the structure so intimately depends. The quality
of the finished work may, however, be tested by borings.

5. Cone is used for bringing np uneven foundations to a level
before starting the masonry. By this means the number of hor joints in
the masonry is equalized, and unequal settlement is thereby prevented.

6. On railroad work, the use of cone may obviate the nse of der-
ricks, which are a source of interference with, and danger to, trains.

7. Cone is used to advantage in reinforcing and protecting old stone
masonry ; but, unless special precautions are taken, the two construc-
tions are liable, in time, to separate, owing to unequal settlement, especially
if the ramming has not been thoro.

Natural Cement.

8. Natural cement is now seldom used in cone, except in mass work
where it is not subjected to the wearing action of water or frost, and where
early strength is not reqd. It is suitable for footings and for low retaining
walls not subject to serious vibration.

9. In dams, breakwaters, etc, the core is frequently of natural cement
cone; with a substantial outer shell of Portland cem cone.

Proportions.

10. The proportions of cement, sand and aggregate should
theoretically be determined, either all by wt, or all by measure in loose
condition; but, in practice, the cem is measured by the number of pack-
ages used (the contents of the packages being known; see "packages,"
under "Cement") and the sand and agg are measured loose.

* Without chemical affinity for other materials.



PROPORTIONS. 1087

"Natural Mix."

11. It is customary to designate the quantities of cem, sand
and agg, in a cone, by proportions. Thus: 1:2:4 means 1 part cement
to 2 parts sand and 4 parts aggregate. Such designation is necessary
in instructions to workmen; and, where the ranges of size of the particles
are known, it indicates the character of the cone. The proportions are
of course governed by the character of the work; but it is inadvisable
to affect distinctions between nearly similar classes of work.

12. Usual proportions for Portland cement concrete :

Exceptionally massive work (leveling for foundations, dams, breakwaters),

1 : 1.5 : 8 to 1 : 5 : 10; with nat cem, 1:2:5.
Foundations, ordinarily, 1:3:6; sometimes as poor as 1 : 4 : 8.
Piers, pedestals, abutments, 1 : 2.5 : 5.5 to 1 : 3.5 : 7.
Piers and vaulting in filters, 1 : 2.5 : 5.5.

Reinforced walls and beams, 1 : 3 : 6; light sections, 1 : 2.5 : 5.
Foundation walls, 1 : 2.5 : 5.5; retaining walls, 1 : 2.5 : 5.5 to 1:3: 6.
Spandrel walls, 1:3:6.

Conduits, drains, sewers, 1 : 2.5 : 5.5 to 1:3: 6.
Reservoir, filter and tank walls, 1 : 1.5 : 3.5 to 1 : 2.5 : 5.5.
Subaqueous work, 1:2:3.

Floor systems (girders, beams, slabs) 1:2:4 to 1 : 2.5 : 5.5.
Stairways and roofs, 1 : 2 : 4.
Arches, 1 : 2.5 : 5; light sections, 1:2:4.
Copings and bridge seats, 1:1:2 to 1;2:4.

But the essential requisite is that all the voids, between the particles
of sand and agg, be filled with cem mortar. Hence, unless the grading
of sizes, of sand and of agg, is known or assumed, the bare statement of
proportions, of cem, sand and agg, in a mixture, gives but little useful
information as to the value of the cone.

13. In reinforced work, in general, richer mixtures should be used
than those that would be permissible in large mass work. In order to
obtain proper and reliable adhesion, which is of the first importance, the
bars must be completely surrounded by cem.

Materials Required.

14. Materials required for a en yd of rammed Portland
cement concrete, c = cement, bbls; s = sand, cu yds; a = aggre-
gate, cu yds. Dust screened out. Stones not larger than 1 inch.

Mixture c s a



4 1.46 0.44 0.89

5.5 1.19 0.46 0.91

5 1.11 0.51 0.85

6 1.01 0.46 0.92

7 0.91 0.42 0.97

7 0.83 0.51 0.89

8 ...0.77 0.47 0.93



With 2.5 inch stone, the quantities of all the materials, per cu yd cone,
were increased from 2 to 5 %. With gravel, > % inch, they were decreased
about 9 %. (Chas. A. Matcham, Natl Builders' Supply Assn, 1905.)

15. Let

B = No. of barrels of cement reqd per cu yd cone

= No. of times 0.141 cu yd cement reqd per cu yd cone;

P = parts of sand (or agg) to 1 part cem.

Then

l/B = No. of cu yds cone from 1 bbl cem;

0.141 P = No. of cu yds sand (or agg) to 1 bbl cem;

0.141 PB = No. of cu yds sand (or agg) to 1 cu yd cone



1088



CONCRETE.



Voids. See Weight, p 1103.

16. Reduction of voids. If stone having 50 % voids, and sand
having 50 % voids, be used, with cem, in the proportions:

Cement, 1 part = 0.25 cu yd

Sand, 2 parts = 0.50 cu yd

Stone, 4 parts = 1.00 cu yd

the resulting cone will measure something more than 1 cu.yd, and yet it
will contain unfilled voids.

17. These proportions, however, are not economical By selecting a
sand having a range of size, or by mixing two or more sands having
grains of diff sizes, the voids in the sand can be reduced to say 33 %. Simi-
larly, the voids in the stone can be reduced to say 35 %. We should then
have, say:

Cement, 1 part = 0.12 cu yd
Sand, 3 parts = 0.36 cu yd
Stone, 8 parts = 1.00 cu yd,

with results as good as with the 1:2:4 mixture above, although using
only half as much cement.

18. Mr. Geo. W. Rafter (Trans A S C E, Dec, 1899, Vol 42, p 106) recom-
mends that the proportions be stated by means of the ratio of the vol of
the mortar to the vol of agg. Thus: a cone containing 75 vols of agg and 25
vols of mortar, would be a 33 % % cone.

19. Under usual conditions, the voids in the agg should be filled
with as rich a mortar as the strength of the work demands. A better cone
may result from the use of a lean mortar which fills the voids, than with a
richer mortar but partially filling the voids.

20. The mortar cannot be perfectly distributed thru the agg, and some
of the voids are too small to admit the sand grains. Moreover, the mixture
is liable to disturbance in depositing. Hence, there will be voids in the
cone- unless there is an excess of mortar over the measured voids of the agg.

21. In practice, the excess of volume of mortar required, over
the measured voids in the agg, in order to secure the filling of the voids,
is usually from 15 to 25 % of the vol of the voids. But by 15 exp'ts with
limestone, Prof. Baker found that the voids were not entirely filled unless
the vol of the mortar exceeded the vol of the voids by 40 %. (Table 13 c,
p 112 b, Baker's Masonry Construction, 1907.)

22. Mr. John Watt Sandeman (Procs, Instn C E, Vol 121, p 219, 1895)
believes that, to insure water tightness, the vol of mortar should
be 50 % of the vol of agg having 35 % voids; or, excess mortar = 43 %
vol of voids.



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1 1} 2

Diameter, d, in inches.

Fig 1. Parabola of Maximum Density, See 1j 23, p 1089.



PROPORTIONS.



1089



Density. See Weight, p 1103.

23. Mr. Wm. B. Fuller (T & T, p 197) finds that the greatest density

is obtained, and consequently the smallest amount of cem reqd ; when the
agg and the sand are so graded that the percentages, by wt, passing the
various sieves, are as represented by the ordinates of the parabola in Fig.
1, where the abscissas represent the diams, d, of the openings in the sieves;
while the ordinates below the parabola represent the percentages retained,
and those above the parabola the percentages passed, by these openings
respectively.

24. In this parabola, d = P 2 M ; where d = a given diam; P =
proportion of particles smaller than d; M = max diam of stone ( = 2 ins
in the Fig).

25. Exp's (Trans A S C E, Vol 59, pp 67, &c, 1907) show that a saving
of 12 % in quantity of cem may be effected, and a more impervious pro-
duct obtained, by thus grading the sizes of the sand and agg; but the reduc-
tion may sometimes be offset by the additional cost of so grading, especially
on small work.

26. In the lining of the tunnel for the Sudbury aqueduct, Boston Water
Works, the proportions were

1 cask of Portland cem as it came from the dealer = 3.425 cu ft
2% casks of loose sand ......................... = 7.35 cu ft

5 Yi casks of loose crushed stone ................. = 18.56 cu ft



Total ......................................... 29.335 cu ft.

By slightly shaking the sand and stone, the proportions became practically
1:2:5.

These 29.335 cu ft produced from 20 to 21 cu ft cone, rammed in place;
or say 38 cu ft materials = 1 cu yd cone

27. Mr. Wm. B. Fuller (Natl Assn of Cem Users, Procs, '07, p 95) tested
cone beams, 30 days old, of 1:2:6, 1:3:5, 1:4:4, 1:5:3,
1:6:2 1:8:0, (all 1 : 8). The strgths compared as in Fig 2.



!

P TOO












319


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00

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209


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151


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102


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1 2 3 d
Aggregate* Parti.


5 6
i.



Fijjf 2. Proportions ; strength.

28. From this it appears that, so long as the voids in the agg are filled
with mortar, the comp strength of cone seems rather to increase than
diminish as the proportion of stone increases, and to depend largely upon
the richness of the mortar.

29. Proportioning- by trial mixtures : (Wm. B. Fuller, Trans
A S C E, Vol 59, pp 77, &c).

Having determined the particular sand and stone to be used OM any
work, provide a strong and rigid cylinder, such as a short piece of 10 inch
wrought iron water pipe capped at one end.

SO. On a piece of sheet steel or other non-absorbent material, weigh out
and mix together all the ingredients, to the consistency required for the
work. Place the mixture in the cylinder, tamping carefully and continu-

05



1090 CONCRETE.

ously, and note the height to which the cyl is filled. Before the mixture
has time to set, empty and clean the cyl

31. Make up another batch, using the same wts of cem and of water as
before, and the same total weight of sand and stone, but with a slightly
diff ratio of weights of the sand and stone.

32. Note the height, in the cyl, reached by this second and by subsequent
mixtures. The best mixture is that which gives the least height in the cyl,
provided that it works well while mixing, and that its appearance in the cyl
shows that all the stones are covered with mortar.

33. This method enables the engineer to select the best from the materials
available in any given case.

Consistency. See also Mortar, p 947/.

34. Skill and care, in placing, and uniformity of consistency are more
mportant than the consistency itself,

35. The extremes of practice are: (1) Cone with mortar about as
moist as damp earth; only enough water used to show on the top surf
after prolonged and hard tamping, (2) enough water used to cause the cone
to quake when first placed, and to allow only of spading into place. The
proper consistency depends largely upon the character and purpose of the
work.

36. I>ry cone is generally preferable in large open work where it can
be thoroly rammed, and where early strength is reqd, as in arch skew-backs.
When thoroly tamped, it develops much higher compressive strength at its
early ages, and may have somewhat greater permanent strength, than
wetter mixtures; but imperfect tamping of such mixtures may result in
very weak cone, while thorough tamping may render the work more expen-
sive than the increased strength will justify.

37. Medium. Present practice favors the use, in general, of mixtures
wet enough to require only spading; but, even in such work, ramming may
be reqd from time to time for occasional dry batches.

38. Wet cone is more easily mixt with thoroness, more readily and
more cheaply laid, and more easily forced into the narrow spaces betw
reinforcing bars. It comes into more perfect contact with the molds,
thus giving smoother and more nearly watertight surf. It is therefore
generally preferable (as in buildings) in forms of complicated shape, or in
thin sections, or where smooth surfaces are reqd.

39. Wetness retards setting, gives better bond between successive
courses, gives a compact mass with less tamping, and provides the surplus
water reqd by absorption in wooden forms. Wet cone is less liable than
dry to injury by bad workmanship; but an excess of water reduces the
strgth, and increases efflorescence.

40. In " cyclopean" cone, more "plums" can be used with wet cone,
which allows them to settle down into it, and which bonds better with them.

41. Mixtures, wet enough to be poured into the forms for columns
of floors, are frequently used.

42. The quantity of water required, for a given consistency, is materially
reduced by wet weather.

43. Water works upward thru placed cone. Hence a less pro-
portion of mixing water may suffice toward the end of a day's work.

ii A \ ui.i \<; A M> mxrao.

Handling Ingredients.

1. In designing a plant for handling and mixing cone, the quanti-
ties to be handled, the areas over which they must be distributed, the
facilities for procuring and receiving the raw materials, and the working
space available, must be considered; and each case will present other factors,
peculiar to itself.

2. The arrangements of such a plant are as various in character
as are the different kinds of work. In general, these arrangements must be
specially designed for each important work; and success and economy
depend largely upon the excellence of the design of the handling plant.



HANDLING AND MIXING. 1091

3. Materials may reach the site by cars, boat or team. Be on guard
against mud and dirt in bottom of vehicle. Sand and agg may be dredged
from stream at the site.

4. After reaching the work, the materials are carried to the bins, by
carts, barrows, small cars, dredge buckets, or belt or chain conveyors.
From the bins they are usually carried by gravity, thru hoppers, to the
mixer.

5. Storing. Gem is commonly stored in sheds or other warehouses, and
is handled, separately from sand and agg, in bags or bbls, often by means
of chain conveyors.

6. For bringing the materials from the bins to the mixers, and
the cone from the mixers to the work, carts, barrows or small cars are used.

7. Where the work covers a limited hor area, as in the case of a building,
or of a pier or abut, the mixer need not be frequently moved, and
the arrangements for handling are relatively simple.

8. Where the work covers a large hor area, as in a slow filtration plant,
or where it crosses a valley, as in a dam; cable conveyors, with towers, are used :
or one or more mixing plants are installed in central positions.

9. Where the work extends along a line of considerable length, as in walls,
sewers or aqueducts, a railway track, often of broad gage and with three or
more lines of rails, is laid alongside, and the materials handled from derrick
cars, often of designs specially prepared for the work in hand.

10. The work is facilitated by having the cars, barrows, buckets, etc,
of known capacity, so that they may serve as measures in proportioning
the sand and agg. Thus, the cars may hold enough sand or agg for one
batch, and may dump into larger boxes, each holding enough sand and agg
for one batch. The cem is usually measured separately, by counting the
bags or bbls emptied.

11. Where cars are used, they may be moved by locomotive or by cable,
reaching the bins by means of an inclined plane.

12. In the case of a belt conveyor, sand and stone, each enough for
a batch or other known quantity of cone, and afterward the cem for the same
quantity, are dropped upon the belt from their respective bins.

13. Commonly the measuring platform (or the measuring hopper
for batch machines) is placed directly over the mixer.

14. For max output, there should be two sets of measuring hoppers,
one to be dumping into the mixer while the other is filling.

For washing sand, see SAND, 1 34, p 947&



15. Aii'ii' may be washed in a revolving cylindrical screen, by a jet
of water under high pressure.

16. Work is often done at night by means of electric or other artificial
illumination.

17. Portable (flat-car) cone mixing plant. Two 6X8 tim-
bers, 58 ft long, 4 ft apart, laid upon floor or a 34 ft standard-gage flat
car, their ends projecting 1 2 ft beyond each end of car, and guyed to an ele-
vated framework on center of car. Each projecting end carried a 2 cu yd
hopper. Sand and gravel were shoveled into this hopper and discharged
from it upon a belt conveyor, running hor'y under the hopper and then
upward to a hopper (3 cu yds) 15 ft above the car floor, over the center
of the car. This elevated hopper discharged the sand and gravel into a
% cu yd Smith mixer, placed at the center of the car. Cem supplied to
the mixer by hand; water from a pipe, laid along the work and provided
with hose connections. A bbl, filled with water, was carried on the elevated
framework, to ensure a supply for immediate use. The conveyor belt,
2 ft wide, consisted of two link-belt chains, with a heavy double-thickness
canvas belt between them. Belt supported by wrought-iron pipe cross-
pieces 18 ins apart. The belt forms pockets between the cross-pieces.
Conveyors, driven by a 9 X 16 inch single-cylinder steam engine, mounted
on one end of the car. Average capacity, 275 cu yds per day. One lower
hopper was found sufficient to supply the mixer. (The Chalmette Docks
of the New Orleans Terminal Co, E. R, '06/Jul/28, p 90.)

18. In constructing works which are circular in plan, the mixt cone.
for floors, columns, girders and roof, may be carried to the forms by mean-
of a truss bridge, spanning the work from a central tower to a track on the



1092 CONCRETE.

circumferential wall. The bridge then forms a revolving crane, carry-
ing mixers at its outer end.

Mixing.

19. General. Each sand grain should be coated with cem, and the
mortar should coat every fragment of stone in the agg and should be evenly
distributed thru the whole vol. The stone, if dry, should be wetted before
adding it to the mortar.

SO. Thoroness of mixing is of the greatest importance; especially
when the cone is poor in cem or of dry consistency.

21. The great strgth of the cone in the Munderkingen bridge is attributed
to its thoro mixing. The materials were mixt 2 mins dry and 3 mins wet,

22. Variation in color of mixture indicates change in the proportions
of the ingredients.

23. See that any cem, thrown out as defective, is replaced by good cem.

24. Lifting concrete. Where the mixing platform cannot be built
near the level of the top of the structure, the cone may be raised by a power
lift to the proper level, and then wheeled on level runways. For low lifts
and small quantities, horsepower lifts are used; for higher lifts -and larger
quantities, a small steam or gasoline engine.

25. In some cases, the mixer and its enclosing frame are lifted bodily
by the derrick which supplies materials, and deposits them over or near the
work.

26. Hand mixing is inadvisable and uneconomical, except on small
jobs.

27. In hand mixing, it is usual to mix the sand and cem dry, usually
by turning with shovels two or three times, until the mixture is of uniform
color, and each sand grain is coated with cem.

28. Water is then added, and the mortar is mixed before the agg is added;
or the agg may be spread over the dry mixed sand and cem, or these thrown
upon the agg, and the whole then wet and mixed by two or more turnings
with shovels, until the water is thoroly incorporated.

29. Mixing the cem and sand first, as above, reduces the total labor by
omitting unnecessary manipulation of the agg.

30. Weather. Hand mixing should be well protected against wind
and rain. Wind blows away the finest (and therefore best) of the cem,
and rain prevents proper (dry) mixing of cem and sand.

31. For the sub-station of the Brooklyn Rapid Transit Co., two bottom-
less rectangular frames were provided, one of which had a capacity of Y^
cu yd, and was first filled with sand. Seven bags of cement were then
emptied on top of it, and the mass was turned several times by five shovelers
until the color was uniform. It was then leveled, the other frame (1 cu
yd capacity) was placed on top and filled with broken stone, and water
was put on with a hose. The mass was then turned four times, shoveled
into wheelbarrows and deposited in the forms.

32. With equal care, machine mixing gives better and more
reliable results than hand mixing, and is more economical on large work.

33. The output must be carefully watched, as the accidental
and unsuspected choking of a hopper may change its character.

Mixers.

34. Mixers are of two principal types; "continuous," and "batch."

35. In continuous mixers, the raw materials are fed continuously
into the machine at one end, and the mixed cone is delivered continuously
from the other end.

36. The gravity (continuous) mixer is a stationary shute or trough,
set nearly vert, and equipped with fixed projecting pins or baffles, against
which the material impinges as it descends, and upon which the mixing
depends. Water is admitted by a spray pipe, at the top of the shute.
Power is required only to elevate the materials to the top of the mixer,
usually a lift of about 8 feet.

37. Other continuous mixers are in the form of open troughs,
nearly hor, and having a longitudinal revolving shaft, with screw-like bladea



MIXERS. 1093

attached, which convey the material, fed in at the upper end, thru the
length of the trough, to the lower or discharging end. Water is provided
by means of perforated pipes along the sides of the trough.

38. Measuring 1 . Continuous mixers require some means of propor-
tioning the ingredients of the cone. Various automatic measurers have been
used to a limited extent. Sometimes the sand, cem and agg are spread,
in layers, on the platform of the mixer, and shoveled into the mixer. Some-
times, dependence is placed upon assigning, for instance, one shoveler
for the cem, three for the sand and six for the stone; but this method is
much too crude for most cases.

39. Batch mixers deliver the cone in batches, the size of which is
determined by the capacity of the mixer. They have a wider range than
gravity mixers, and give better control of the proportioning of the ingre-
dients.

40. The oldest and simplest batch mixer consists of a revolving cubical
iron box, plain inside, mounted on bearings at its diagonally opposite cor-
ners, and provided, on one side, with a sliding gate, f9r admitting the raw
materials and discharging the cone. Power is applied thru gearing on
the shaft. The ingredients may be mixed dry for a number of turns, and
the water then added thru the hollow trunions; or the water may be added
before any mixing is done. The older cubical mixers had to be stopped,
both at the time of charging and when delivering the cone.

41. At Superior Entry, Wis., the U. S. Govt used a cubical cone mixer,
charging and discharging without stopping and without variation of speed. It
was operated by a 7 X 10 inch vertical single steam engine, and turned
out a batch of very perfectly mixt cone in 80 sees. The cone was plainly
visible during the entire process. (Clarence Coleman, Rept of Chf of Engrs,
U. S. A., 1904, Part IV, p 3784.)

42. In later batch mixers the cubical box is replaced by a drum
(either cylindrical or made up of two cones), rotated by means of a chain
on a ring encircling the drum, and provided with vanes or blades fixed upon the
inside. These blades first carry up and then drop the material, mixing it


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