John C. (John Cresson) Trautwine.

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Elongation 108

Bending test 109

Max allowable stresses 110

Adhesion 113

Length and lapping 116

Protection 117

Permits 118

Clearance 119

Fireproof bldgs 120

Girders and columns 122

Cinder concrete 127

Columns 129

Rods tied together 133

Requirements 136

Cross-section area 138

Eccentric loading 142

Attachment to girders 143

Hooped 144

With structural steel 150

Beams and floors 151

Assumptions, theory 151

Stresses 155

Adhesion 156

Span 158

Shrinkage, etc 159

Shear 160

Cement finish 163

Web reinforcement 164

Steel in comp side 165

Slabs acting as flanges 167

Moments 174

Continuity 176

Tests.. ..183



Cll



1 186 CONCRETE.

For lists of Specifications for Concrete, see pp 1184, 1185.

In order to compare intelligently the requirements of diff specfns, the
character of the work involved must of course be taken into account.

DIGEST.

Cement.

1. Brand. Portland or natural, M" Y ; Port just under lower miter sill,
nat elsewhere in foundations, Port in lock walls except for a backing, 2 ft
deep, at base, Port and nat bonded together, 1M: for reinforced work,
Portland, G; Am Port, CS, BB, Hb, FW ; "Universal" Portland
cement, SJE ; cem made by mfr of established reputation (in successful opera-
tion not less than 2 yrs, F), brand in continuous successful use (in America, F)
for the last 5 yrs (3 yrs, CS) G ; in satisfactory use in similar quantities by U.S.
Engr Dept at Large, TB; of tried uniformity, in use not less than 3 yrs in
similar climate, CB, lib: only one brand to be used, G; except for good
reasons, F ; only one brand in any monolith, FP. Portld in reinfd work and
where subject to shocks or vibrations or to stresses other than direct comp;
nat in massive work where weight is more important than strgth, and where
economy is the governing factor; pu/zolan only for foundations underground,
not exposed to air or to running water, JC.

2. Bequireinents. For Strengths, etc., see Digest of Specfn for
cem, by A S T M, p 940, Report of Board of U. S. Engr Officers, Prof'l Papers
No 28, Corps of Engrs, U.S.A., '01, p 937, and Digest of Specfn by Engng
Standards Comm of Great Britain, p 940. For tests, see Digest of
Specfn of A SC E, p 942. Slow setting, FP; must have been tested < 6 mos,
> 12 mos, prior to issue of permit, Li;must meet requirements of Prof'l
Paper No. 28, Corps of Engrs, U.S.A., '01, p 940, BB, AH, TB, CB,
FW, Wv, FP, Kb.

either 380 Ibs or some even
cloth bags, BfO ; bag, 93 Ibs
lined with paper, CB, WH ;
in cloth bags, Ci ; may be delivered in paper bags, Wv.

4. Storage at site of work. In weather-tight bldg, with floor raised
(< 6", T fc T) above ground, G ; and holding < 2 wks' supply under ay con-
ditions of work, Ci ; cem in bags may be used after 3 mos storage, rejected
if it becomes lumpy or otherwise deteriorated within that time, BB; cem,
kept over winter, re-tested before using, W T v.

Sand.

5. General. Silica, hard, clean, sharp, G. Reasonably clean, coarse,
F ; water worn, voids == 35 %, SE. "Sharpness",purposely omitted, T fe T.
River sand, Ci, a.

6. Size. Well graded, with fine, medium and coarse grains, F, Ev,
XO, Co. Coarse, or coarse and fine, mixed, CS, T fc T. Coarse pre-
dominating; coarse preferred at double or treble cost, T fc T. Medium,
Ci, a. Largest to pass screen of %" mesh, G. > 10 % coarser than %",
STO ; < 50 % retained on No. 30 sieve (holes 0.022" D),WH. > 40 % to
pass No. 50 sieve (2500 meshes / D"), Hb. > 3 % very fine, XO, Co,
Ci, a. > 5 % very fine, Bu.

Foreign matter (clay, loam, sticks). None, CS, TfcT; > 2%
XO, > 3 %, Co, Ev ; > 5 %, W r v, OD, TB, CB, Bu. > 10 % clayey,
AH. > 3 % clay, etc, > 2 % mica, FW ; > 4 % free loam, Hb ; sand may
be moist, not wet, TB ; stored on a board platform, CB ; or in bins, Wv.

7. Screenings. Crusher dust, passing %" screen, from broken stone,
may be substituted for part or all of the sand, T & T; "screenings & crusht
stone may be substituted for sand and gravel under special conditions,"
F ; screenings permitted, BB, CB ; if passing Y' screen, TB ; screenings
preferred to sand, AH.

Aggregate ("Ballast").

8. Kind. Sand grit, gravel or broken stone, BB ; gravel or broken stone,
G; or both, BB; gravel, L.V; (see Screenings); sea-washed gravel, I/p;
water-worn pebbles of igneous rock, SJE ; clean stone, gravel, broken hard
bricks, terra cotta, furnace slag or hard clean cinders, Un; broken stone
preferred, gravel permitted for interior of piers, pedestals and abuts, W r H ;
broken stone, AH.



3. Shipment. Packages to "contain either 380 Ibs or some
division of 380 Ibs, " L.V ; in cooperage or in cloth bags, BfO ; bag,
(94 Ibs, Co) net, bbl = 4 bags, NO ; in bbls, lined with paper, CB,



CONCRETE SPECIFICATIONS. 1187

For abbreviations, symbols and references, see p 947 I.

9. Requirements. Clean, hard, durable; free from dust, loam,
clay and perishable matter; washed or screened if reqd, G; approx cubical,
CS, AH ; free from long thin pieces, BR, NO, CS; < 125 Ibs/cu ft, FP;

< 130 Ibs/cu ft, Mb ; voids = 31 %, SE ; drenched before using, tr ; but not
to carry water, Wv ; kept thoroly sprinkled, IM, Hb.

10. Sizes, inches: min, H, <*; 3/g, FW, Me; max %, Un ; 1 }/%, Bu;
2, G; 2M,H; 3, NO, o, Ci, a, FP, SE: gravel, 3, F; stone, run of
crusher, F, Me, AH; 1 to 2^, according to grade of work, AH; for
foundations, 2 ; for superstructure, 1% ; for beams, cols and girders, 1, I*;
gravel, < 90 % over 1 14 > 10 % sand, Hb.

1 cubic foot of stone, gravel or sand grit contained

Agg cu ft Ibs cu ft Ibs cu ft Ibs

Stone; coarse, 0.63 53.8; fine, 0.33 30.4; dust, 0.11 11

Gravel;.. . pebbles, %", 0.80 81.5; sand, 0.29 29.2;

Sand grit; gravel, 1 A" to W, 0.47 47.2; sand, 0.59 59.3;

BB.

11. Storage. Stored on wooden platforms, CR, Wv ; or in bins, Wv.

12. Cinder concrete. Allowed only for floors, roofs and filling, Ms.
Reinfd cinder cone to be used only upon special permit of Inspector of
Bldgs, I,.

13. ' ' May be used for all bldgs in which fireproof construction is mandatory
by this Chapter, or where ordinary constr, mill constr or slow burning constr
may be used," not for cols, piers or walls. Clean, thoroly burnt steam-
boiler cinders; mix, Port cem, not poorer than 1 : 7. Cinders must pass 1"
sq mesh, Cll.

14. "All other special requirements and methods of calculation for
reinfd cone as reqd in this Chapter shall modify and regulate the use of
cinder cone in bldgs," Cll.

15. Large Stones.

Hard, sound, durable, as large as can be conveniently handled; washed
clean; placed wet; one dimension < 12"; no dimension less than 4"; no
stone Jess than 2" from faces exposed in finished work, cone joggled into
place with light rammers, Co.

16. > 100 Ibs. < 3" from forms or from other large stones. (From
Specfn for a Soldiers' Home.)

17. Permitted in walls > than 18" thick, diam > quarter of the thick-
ness of wall, vol of stone > one-fifth vol of wall, Yo.

18. One-man stones and larger, roughly cubical; long flat pieces to be
broken or rejected; stones somewhat uniformly scattered thruout the work;

< 8" apart, < 2 ft from crest or down-stream face; dropped separately
into bed of wet cone, pounded down if- necessary; if necessary, cone spaded
under and around the stones; each stone to be covered with cone before
other stones are deposited. Use as many stones as possible without violating
these conditions, Me.

19. "Plums." Stones, from one-man to several tons (sometimes from
old masonry), aggregating abt 30 % of the finished work < 1 ft from wall
surf. Set in top layer of cone and so as to form bond with next layer by
projecting upward into it, L<p.

20. Proportions, see pp 1086 to 1090.

Measurement of Ingredients.

21. Cem measd " as if compacted so that 380 Ibs of dry Port shall have a
vol of 3.8 cu ft," L.V; cem measd loose, CS, WH; 1 bag cem < 93 Ib = 1
cu ft, NO, Ci. Cem measd as packt by mfr, OI>, L, T fc T. Sand and
agg measd as thrown loosely into measuring box, G. All measd loose, CS,
WH; 100 Ibs cem considered to occupy the vol of 1 cub ft, F.

Consistency.

22. In general, "very wet," NO; water to come to surf with moderate
ramming, CS ; without serious quaking, OI>, TR; sufficiently fluid to
require no ramming, Me; little or no tamping, Hb.



1188 CONCRETE.

Tor lists of Specifications for Concrete, see pp 1184, 1185.

23. (a) For ordinary mass cone, such as foundations, heavy walls,
large arches, piers and abuts; medium mixture, of a tenacious jelly-like
consistency, quaking on ramming. T fc T.

(b) For rubble cone and for reinfd cone, such as thin bldg

walls, cols, doors, conduits, tanks; very wet or mushy, so soft that
it must be handled quickly to prevent its running off the shovel. T fc T.

(c) In dry locations for mass foundations, which must with-
stand severe comp within 1 mo after placing, "dry " cone, consistency of
damp earth, provided it be spread in 6" layers and rammed until water
flushes to surf. Not permissible in reinfd work, T & T.

24. ** Sloppy." Men, spreading cone in ultimate position, wear water-
tight leather knee-boots, and are ankle-deep Jn the cone, Lp.

25. In foundations, "sufficient water to cohere when rammed in
place by 30-lb iron-shod rammers;" in lock walls, enough for complete
hydration of cem; enough for coherence after thoro mixing; more plastic
than damp sand; thoro ramming must bring water to surf; incipient
quaking marks the limit; any excess of water in one charge may be corrected
in the next; consistency varied, from time to time, to suit conditions of
weather and constituents, OI.

26. Cone for substructure much dryer than that for superstructure, SE.
Cone, placed under water to be semi-dry, Ph.

27. Water per batch, approx:

3.5 cu ft per batch of 43.2 cu ft, making 28.5 cu ft rammed; p 180;

2.5 " 28.8 20.0 " " ; p 179, BB.

Mixing 1 .

28. Hand vs machine. By hand for foundations, by cubical mixers
for lock walls, IM ; by cubical mixer, SE ; by machine, F, BR, AH, NO,
Bu, Co, Ci, b; by machine when amount of work exceeds 1000 cu yds,
<JS; by machine in general, TB, Hb, WH ; "preferably by approved
mixers of the continuous type which automatically measure and feed the
correct proportions in small streams into the mixing chamber," F; by
batch machine, Bu, Ci, b ; " mechanical batch mixer . . , except when limit-
ed quantities are reqd or when the condition of the work makes hand mixing
preferable; hand mixing. . .only when approved by the Bureau of Bldg
Inspection," Ph; batch mixer, Hb, CR, Wv, FW; < 100 cu yds per
8 hour day, FW ; batch mixers preferred, continuous mixers only by special
written permission of engineer, WH.

Method. Materials mixt dry before adding water, CS, NY ; turned
< 100 times, Ci, b. "In all mixing the material shall be measd for each
batch;" agg, if hot and dry, to be wetted before going to mixer, Ph. One
batch completely discharged before the next is introduced. Not less than 25
revolutions for each batch, turning cone over not less than once each revo-
lution, Un; order of charging, 1st gravel, 2d cem, 3d stone, 4th water, each
batch turned < 2 mins, > 9 revolutions per min, extra turns to be given
when time permits, IM.

29. Batch mixing. Cem (2 cub ft per batch) mixt into a rough paste
on platform. First pebbles, then sand and cem paste, then broken stone,
dumped, thru hole in platform, into box on car below. Box dumped into
mixer; 5 to 10 revolutions; 7 to 14 batches per hr. With 14 batches, 12
men reqd for ramming, BB; first sand, then cem, then agg, then water,

30. Hand mixing. Cem and sand mixt dry; wet stone added; water
added, C'S. Cem and sand mixt dry, water added, agg spread not more than
6" thick, sprinkled, mortar spread over agg and mixt, Ph. Cem and sand
mixt dry, water added, mortar mixt, agg (wetted) added, all mixt, Hb;
mixture of sand and agg first spread in thin layer on a timber platform,
cem spread on top, mixt dry, turnd over as water is gradually added;
broken stone, if used with gravel, is added wet to the wet mass, WH.

31. On tight platform, large enough for 2 batches of not over 1 cu yd
each. Cem and sand spread in thin layers and mixt dry until of uniform
color.

Then use either one of 3 optional methods, as follows :
(1) Mixture of cem and sand spread upon layer of stone;



CONCRETE SPECIFICATIONS. 1189

For abbreviations, symbols and references, see p 947 I.

(2) Stone shoveled upon mixture of cem and sand. In (1) or (2), turn
3 times, adding water in first turning.

(3) Mixture of cem and sand made into mortar and spread upon stone.

Mass of mortar and stone turned twice, T fe T.

32. In any case, result must be a loose cone of uniform color and appear-
ance, stones thoroly incorporated into mortar. Consistency uniform thru-
out, T fc T.

33. "As the gravel box was being filled, the cement was added to it
gradually, so that, when the gravel box was full, the cement box was
empty. The box was then removed, and the heap leveled off to a uniform
thickness of > 1 ft, and was then mixed by casting backward and forward
twice," water added at time of second casting, Lp.

Forms.

34. Lagging. Of well seasoned boards, 2" thick, drest all over, tongued
and grooved, o, b ; 2" X 6" pine, drest on all sides, Mb ; boards planed on
one side and two edges; one edge slightly beveled and placed against the
square edge of the next plank, Yo ; boards preferably 2" X 6", dressed-and-
matched flooring, WH ; forms for exposed faces, of planed lumber, tongued
and grooved or beveled; wall forms to be braced, and, where possible, to
have their sides wired together, Ci ; butt joints square, and either on posts
or reinfd, Hb ; joints, showing spaces, to be filled with stiff clay immedy
before placing cone, Hb.

Used lagging, if not scarred, may be used again; but, for exposed work,
must be cleaned and oild, Hb.

Posts. Generally 3" X 8" pine, drest on both edges, of full height of
wall, > 4 ft apart, Hb.

Centers and forms to be wet, IM; if reqd, before laying, JfO, Ci,b;
or oiled, 5fO. According to circumstances, forms to be wetted (except in
freezing weather) or greased with crude oil, before placing cone, T fc T;
oild just before use, Hb; painted or oild before re-using, CR; dampend
just before placing cone and kept damp until work has hardened, TK, Wv.

For removal of forms, see p 1191.

35. On up-stream face of dam, molds need be only smooth enough to
give good substantial work, free from voids. On crest and down-stream
face, molds must have planed surfs, so as to leave the finished work smooth,
Me.

36. Tie rods, left in cone, must not come nearer to cone surf than 2",
CR: projecting ends of iron bolts and rods to be cut off smooth and flush
with cone face, UK, AH ; not chiseled, but sawn or otherwise removed
without jarring the work, AH; aids for holding molds not to be inserted
within 4 ft of top of walls, UB ; no bolts, etc, to show in the completed work.
OD.

Placing, Churning and Ramming.

37. Night work prohibited in general, TK. Time of placing ;
cone must be placed within 30 mins after mixing, AH, N O, Ci, b ;
> 30 mins "betw wetting the cem and the undisturbed cone in final place,"
F ; before initial set, TR, Ol>, CR, Wy, F W, Hb, Hn ; after mixing,
mass kept in motion until placed in vehicle for transportation, TR. No
retempering or rehandling permitted, TR, CR, NO, Bu, o ? ',Ci,b,
JC. Cone, in which the materials have separated, must be remixt (by
hand mixing, BR, AH); before laying, TAT.

Manipulation. In very wet cone, air must be churned out, stones
workt back from face, and cone workt under rods, etc., G ; by means of
thin steel or iron blades, about 4" X 6", with handles of adjustable length,
so that workmen need not stand in cone, NO, Ci,b. Cone to be joggled
or worked into place by light ramming, Bu, Co ; ram until mortar comes
to surface, AH, BR ; until all voids are filled and water flushes to the surf,
CS; one tamper to not more than 2 cu yds per hr, BR; rammers with
striking area not less than 36D", weighing not more than 10 Ibs, Co;
face 6" sq, weight, with handle, about 20 Ibs, CR ; 30-lb iron-shod rammers,
face area not more than 30Q", IM ; 40-lb rammers, SE ; cone placed
without ramming, FP.



1190 CONCRETE.

For lists of Specifications for Concrete, see pp 1184, 1185.

38. Dry cone moistend by sprinkling, not pouring, CR.

39. Cone must be continuously worked around reinfmt, with
suitable tools, as put in place. Complete filling of forms, and subsequent
puddling, prohibited. Partly set cone must not be subjected to shocks, Ch.

40. Placing-, in layers. Care taken to remove all scum, arising
from the cem, before laying the next layer, L<p, JC.

41. Cone dumped from receiving box or car, or shoveled directly into
place, use of slides and shutes forhtlden, OI>, Wv, FP, TR, CR; not
dropt further than 6 ft? FP ; 3 ft, Wv.

42. Xo walking on finished wall until set, O, Co.

43. Thickness of layers. Not over 6", Wv, BR, OI> ; about
6", CR ; about 6" after ramming, TR ; 6 to 8", CS ; > 6", F ; > 4", SE ;
with dry mix, on slopes, > 4", F ; > 4" in foundations, about 6" in back
walls, IM; > 9", Hb; > 12", WH ; such that each layer can be incor-
porated with the preceding one, T fc T.

44. No layers permitted, Bu, Co ; layers not run out to thin edge, FP ;
each layer completed (rammed, CR) before the next is laid, FP, CR;
each layer of a day's work laid before the layer next below has set, TR.

45. On rock foundation. Rock cleaned and washed with wire
brooms, roughened if reqd, covered with thick neat cem grout, CR ; bed
of wet mortar, F W; W thick, TR ; cone anchored to rock with steel rods,
if reqd, CR.

Joints.

46. Avoidance of horizontal joints. Walls, etc, built in alter-
nate sections, so short that they can be constructed as monoliths; these
sections keyed together by vertical tongue-and -groove joints, <B for gov't
specfns; joints continuous from foundation to coping, CR ; " joints shall be
formed betw adjoining sections of cone for 4 ft down from the deck, by a
layer of tarred paper," BR ; dovetailing to have a thin coat of mortar, 1 : 5
or weaker, to set before new cone is placed against it, Hb.

47. Joints between old and new work. Exposed surfs shaded
and kept moist until work is resumed, CR ; chipped or broken edges cut
away, CR ; old surf to be left stepped, to form bond, and to be cleaned and
wet before adding new work, FW, O ; cleaned with stiff wire brush and
stream of water, FP, BR, Hb ; if reqd, F,I/v ; roughed up with a pick,
if reqd, BR ; wooden strips, 4 to 6" wide, with beveled sides, to be embedded
< 3", and removed before cone has thoroly hardened, XO ; between old arid
new work, bed of 1 : 3 cem mortar 1" thick, X O, Co ; K" layer of mortar,
FP; old surf covered with neat cem grout of molasses consistency, BR: or
dry cem, OI> ; dry cem, brushed in, Hb ; with layer of mortar, TR,
FW ; old surf mopped with 1 : 2 mortar, CIS ; with heavy neat cem grout
worked into surf with brooms, CR; keyed as directed, FW.

48. In hqr joints in thin walls, or in walls to sustain water pros,
or in other important locations, mortar joint may be reqd. Tanks, etc,
with thin walls to hold water, should be built as monoliths, without inter-
ruption, the work proceeding, if necessary, night and day, T fc T.

49. When work is suspended for more than an hour, the outer
edges of the last layer are to be leveled, and the center portion of the surf
is to be left about 6" lower than the edges, CR. .

50. Bond betw new cone and old wall. Dovetailed pockets, 24" wide at
face, 33" at back, 15" deep, cut vert in old masonry, 4 ft apart, I^p.

51. Last layer deposited to be left as rough as possible, imbedded bould-
ers projecting. Surf to be cleaned, washed, and sprinkled with neat cem,
Me.

Placing under Water.

52. Under water. No cone to be laid under water (without explicit
permission, F; except to stop leaks and springs, TR;) water not allowed
to rise on new work until thoroly set, IM, Wv, TR, OD; not less than
24 hrs after set, I/v, BTO, Co, Ci,b ; if placed under water before set-
ting, mixture to be 1 : 2 : 3, WH ; 80 % of work built in place below (fresh)
water level, SE ; cone, placed in water, must be semi-dry, Ph ; bags to be
lowered to within a few ins of surf on which cone is to be deposited, FW.



CONCRETE SPECIFICATIONS. 1191

For abbreviations, symbols and references, see p 947 1.

53. When forms extend down to below high water, leaks under forms
to be stopped, in order to prevent undermining before set; bags, filled with
sand, placed outside; or jute canvas, underlying the cone 12", nailed along
bottom of form on the inside, FW.

Rain.

54. Rain. During rain storms, no new work to be laid, IM, Bu,
CR, AH, FP ; freshly laid work to be protected by canvas, Bu.

Frost.

55. Freezing 1 . No concrete or mortar to be made when temp is below
35 F. in shade; cone work stopped from Nov 20 until April 1; during freez-
ing weather, no cone to be mixed or deposited without engineer's consent,
IM, Bu; ice and frost to be removed, water and sand heated, gravel
steamed, work covered and kept warm by steam pipes, lv ; cone not to be
placed when frozen; if reinfd, must be kept above 32 F for < 48 hours
after placing, use of frozen sand and agg prohibited, Ch. No laying per-
mitted when temp > 32 F., Un, AH, BR, < 32 F, OB; < 30 F,
CR, < 34 F., TR, FP ; when likely to freeze before set, Wv ; before
final set, OB; before set sufficiently to prevent injury, BR, CR. Cone,
frozen in place, to be removed, Un. No cone to be laid when temp is
below 20 F; water to be heated when temp is below 35 F, Me. Use of icy
materials prohibited; placed cone must be protected against freezing, Ph.

56. Natural eement concrete must never be exposed to frost until
thoroly hard and dry, T fe T.

57. "No cone, except that laid in large masses, or heavy walls having
faces whose appearance is of no consequence, shall be exposed to frost until
hard and dry. Materials employed in mass cone in freezing weather shall
contain no frost. Surfs shall be protected from frost. Portions of surf
cone, which have frozen, shall be removed before laying fresh cone upon
them." T & T.

58. Forms, under cone placed in freezing weather, "to remain until
all evidences of frost are absent from the cone, and the natural hardening
of the cone has proceeded to the point of safety." Ch, Ph.

Moistening-.

59. Moistening 1 . Freshly laid cone to be protected from the sun (by
boards or tarpaulins, FP, lib, IM;) and kept wet, Me, IM ; < two
weeks, or until covered with earth, F; < 10 days, SE, AH; 6 ds,
CR ; 3 ds, FW ; 48 hrs, BR ; until set, Wv ; until hard set, Hb ; unfinished
surfs until work can be resumed, CR; with wet tarpaulins < 3 days, CR.
When a section of wall is completed, coping to be covered with a thick layer
of wet sand, mass of wall kept sprinkled until cone is thoroly set, IM ; cone
to be drenched twice daily, Sundays included, for a week after placing, in
hot weather, Ch, Ph.

60. Moisten by sprinkling with fine spray at short intervals or by covering
with moistened burlap, or etc, O.

Removal of forms.

61. Forms must be left in place < 4 days, IM ; < 7 ds; longer if reqd
by engineer, I^v ; 72 hrs, OB ; 48 hrs, AH, BR ; until cone has stood at
least 36 hrs, WH ; until removal is authorized by engineer, or until cone
has become hard, Ci.b; until cone can carry its load safely, Ms; forms
removed after 48 hrs, SE.

62. Props, under floors and roofs, to remain in place < 2 weeks. Forms,
for cols, < 4 days; for slabs, beams and girders, < 1 wk and at least until
the floor can sustain its own weight. "No load or wt shall be placed on
any portion of the constr where the said centers have been removed."
Ch, Ph.

63. Time for removal of forms and centering, 24 hrs to 60 days, depending
upon temp and other atmospheric conditions and upon the commissioner
of bldgs, Un.



1192 CONCRETE.

For lists of Specifications for Concrete, see pp 1184, 1185.

64. Not until cone is hard. Min time, days:

Apr 1 to Dec 1 Dec 1 to Apr 1

Slabs and lintels, cols and monolithic walls 10 15

Posts and bottom supports for joists, beams

and girders 14 21 I*.

65. Forms, under cone placed in freezing 1 weather, "to remain
until all evidences of frost are absent from the cone and the natural harden-
ing of the cone has proceeded to the point of safety." Ch, Ph.

Surface finish, waterproofing, etc.

66. Finish kept smooth by manipulation during placing, not by subse-


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