AD-752 325

DURABILITY AND BEHAVIOR OF PRETENSIONED-PRESTRESSED CONCRETE BEAMS IIEdwin C. RoshoreArmy Engineer Waterways Experiment Station

Vicksburg, Mississippi

December 1963

'N~I"

DISTRIBUTED BY.

iAt

HimNational Technical Inform~in Service

tU. S. DEPARTMENT OF COMMERCE55285 Port Royal Road, Sp~ringfield Va. 272151 •

'

I,

I DURABILITY AND BEHAVIOR OF?RETENSIONED - PRESTRESSED

CONCRETE BEAMS

.t MISCELLANE:OUS PAPER NO. 6.611

IDecem.•r 1963

•- ~NAHFON.AL. TECHNICALi : INFORM•ATION SERV.!CE

S~~U. S. Army E.ngineer \Pat~eiways Expersment Station

n, 7

I~'' '-L• • • ''' • ' '''"..N•• - -- • -- ' "

PREFACE -

Th-'. paper, by Mr. Edwin C. Roshore of the Concrete Division, ;:

U. S. Army Engineer Waterways Experiment Station (WES), -#as prepared •}

for consideration for publication in the Proceedings, American Concrete

IFI

Institute. The manuscript was approved for publication by the Office,

Chief of Engineers, by first indorsement dated 29 April 1963 to a -

letter dated 28 March 1963. It was also reviewed and approved for

publication by Task Committee No. 6 of the Reinforced Concrete Research

Council; and contains revisions based on the results of these reviews.

The manuscript is based on WES Technical Reporj No. 6-570, Report

No. 1.

Col. Edmund H. Lan&, CZ, and Col. Alex G. Sutton, Jr., CE, were

Directors of the WES during the conduct of the work discussed and the Ipreparatiorn of the manuscript; Mr. J. B. Tiffany was Technical Director.

34045 D

-Iq

Contents -E14e

Synopsis . . . . . . . . . . . . . . ..

Purpose and Scope of Investigation ................... .. . 2

Materials . . . . . . . . .

Mixtures aund Specimens .. . . . . . . . . . . . . 3Mixtures . .. .. .. #.. .. .. .. 4.. .. .. .. ..... 3Specimens . . . . . . . . . . . . . . . V. . . . . . . . . 4Prestressing..... . . . . . . . . . . . . 6Placement of concrete ..................... 6Transfer of load . . . . . . . .... .. . .. . . . . . . . . 6

LaboratoryTests and Results .............. ..... ...... 9 .

Camber and sink-in .... .............................. 9Flexural loading . . . . . . . . . . . ...... . . . . . . 10Length and midspan-deflection change with time .... .......... 14.Compressive strength and static modulus of elasticity . . . . . 16Dynamic properties . ............ ........ 21Creep . . . . . . . ......... . . ......... 21Laboratory freezing-and-thawing ................ 22 .2Pulse velocity . ............. . . . . . ....... 22

Field Exposure Tests ..... ......................... 25-

Specimens exposed to sulfate attack ....... .............. ... 25Specimens exposedr to freez-ng-and-thawing...... . . . ... 25

Acknowledo-ments.. . . . . . . . . . . . . . . . . . . . . .. . 29

References ................ .. . . . . . 30

Tables 1-1.3

APPE•NIX A: DESIGN COkOjTATIONS .................. Al

[ iii

TN

- DURABILITY( AN~D BEHAVIOR OF PRETENSIONED-

PRESTRESSED3 CONCRETE BEaMS*

by

Edwin C, Roshore**

.jp~is

To develop data on the factors dffec-ting the durability of prestressed

(pretensioned) concrete beams, 28 large beams containing pretensioning Istrands and 41~2 small companion specimens without pretensioning strands

were fabricated. The concrete in 22 of the beams was air-entraine&]; thatI

in the other .6 was not. 'Aryendix A presents computations used in designing

the mees of the beams were subjected to laboratory tests, which indicated

t1'~at..4he air-entrained be-ams showed less average camber, about the same

average sink-in of' pretensioning strands, less midspan deflection, and an

ability to withstand greater flexural loads than the nonair-entrained

beams. Creep tests are still in progress. Af num~ber of' the auxiliary

specimens were also tested in the laboratory to determnine the strength,

elastic, and plastic properties of the concrete.

The rest of the beams arnd auxi'Liaryj specimens were exposed to natural

wdeathering at stations on the Maine and Florida coasts. In Maine they are

*Based on U. S. Arxry Engineer Water-days Experiment Station, CE,Diarability and Behavior of' Prestressed C!orcrete Bevmnr.; PretensionedConcrate Investigation, Progress to Jully 1960, Technical Report No.6-570, Report 1 (Vicksburg., Miss., June 1961).

SMaterials Engineer (Concrete Research), concrete DivIs ion, U. S. ArmyEngineer Waterways Experiment Station., CE, Vicksburg., Miss.

being subjected to cyclic freezing in air and thawing in seawater,.and

in Florida to sulfate attack in warm seawater. At the Maine station the

nonair-entrained beams failed during the first winter of exposure, whereas

the air-entrained beams remain in good condition after four winters. -No

significant results of the Florida exposure have been observed to date.

Purpose and Scope of Investigation

Factors affecting the durability of conventionally reinforced con-

crete beams representing a variety of concrete conditions, steel types, and

degrees of stress were previously studied. "• The study described herein,

beg-an in 1957, was conducted to obtain infom-ation on the factors affecting

the durability of pretensioned-prestressed concrete beams; these factors in-

clude -:-eep in the steel, creep in the concrete, resulting ralaxatior of the A

prestressing force, and corrosion resistance of th? prestressing elements.

A group of pretensioned-pre.;tressed concrete beams were made. Most

of these were made with air-entrained concrete, but a few were made using

concrete without air-entraining admixture. Because nonair-entrained con-

crete could be expected to deteriorate more rapidly than air-entrained con.-

crete, the nonair-entrained beams were included' in the program to determine

whether arij information could be obtained in a relatively short time on the

effects of severe weathering on pretensioned-prestressed concrete beams

regardless of the type of concrete used. A few beams were made in which

the prestressing strands were not pretensioned. Most of the beams were A

subjected to sustained flexural (rthird-point) load; others were not loaded.

ecRaised nUmerals refer to similarly numbered items in the list of refer-ences at end of text.

IA .s-

3 1

Laboratory tests were conducted on the beams to determine sink-in of steel

strands, camber,. midspan deflection during flexural loading, length and

midspan-deflection change with time, and ultimate strength in flexure. IField exposure tests are being made to determine resistance to natural

. weathering as judged both visually and by measurement of length change and

pulse velocity.Auxilla-y specimens (cylinders and small beans) were molded from the

same concrete batches used for the test beams, and were tested in the labo.,

* ratory to determine compressive strength, flexural strength, creep, modulus

of elasticity in compression, dynamic modulus of elasticity, Poisson's

ratio, and resistance to laboratory freezing-and-thawing. Auxiliary speci-

mens are also being subjected to natural weathering.

In addition to the tests of the beams and auxiliary specimens, tests

were conducted to determine the tensile strength and modulus of elasticity

of the steel pretensioning strands.

Materials

£$

Crushed limestone fine and coarse aggregates, graded to 3/l-in.

maximum size, were used. Physical properties and gradings of the aggre-

gates are shown in table 1. Type III portland cement was used. The air-

entraining admixture was neutralized vinsol resin. The properties of the

high-strength steel strands used for pretensioning are given in table 2.

Mixtures and Siectmens

Mixtures

Data on the two concrete mixtures, each of w-hich was proportioned to

______________________IT I ~ --- - - -

° Ihave a nominal i-3/-in, slump and a nominal 28-day compressive strength of

"6000 psi, are given in table 3.

Specimens

STwenty-eight batches of concrete were mixed in a 10-S rocking-tilting

mixer, and the following specimens were molded from these batches:

SceS.No. per 1Specimen Size, in. Type Batch Total

4-1/2 by 9 by 81 Beams 1 28

6 by 12 Cylinders 5 1403-1/2 by 4-1/2 by 16 Small beams 11* 264

6 by 16 Cylinders 4** 8

S44,0* All batches except batches A, B, C, and D.

• * Batches ? and 16 only.

The 28 beams were molded in wooden forms on an outdoor reinforced-

concrete casting bed. Nine nominal 1/4-in. (I by 7) steel strands were

positioned in each beam as shown in fig. 1. In 214 of the beams, the

strands were tensioned to approximately 70% of their ultimate strength

(approxiamtely 3 tons per strand); the strands in the remaining four beams

were not tensioned appreciably. Twenty-four of the beams (not A, B, C, and

D) also contained eight stainless steel gage pointst located at inidspan for

the measurement of the length change of- the cor.crete. The position of the

gage points is also shown in fig. 1.

The cylinders (both types) and small beams were fabricated indoors in

metal molds. Each 6- by 16-in. cylinder contained one strain meter vn-

bedded axially.

t These gage points were of the type developed by Messrs. H..K. Stephensonand T. R. Jones, Jr., Texas A. &-M. College, C:llege Station, Tex.

- -4 1/-i

BEA

S2. - _-._..__

4 I

- . --_ _ " '1. T -. - -'

STEEL ST£ANO / 2 )fie

I •

SDETAILED END SECTION

Fig. 1. Two vieurs of beam, .showing position of steel• strands and ga•ge poli-.ts

I•"•:,"L-•,,[" ,.,_•. : .$

6

P -restressing

The 5-.by 54-ft casting bed used for tensioning the strands and cast-

ing the beams is shcwn in fig. 2. The bed had two loading posts with steel

header plates at each end which served as buttresses for the pretensioning

(see fig. 3), and :as long enough so that as many as six of the beams could

be fabricated simultaneously. The reaction capacity of the bed was

'i00 tons.

The steel strands were stretched between the buttresses of the cast-

ing bed and tensioned with a 50-ton hydraulic Jack prior to placing of the

concrete (see fig. 4). The strands were fastened to both ends of the cast-

ing bed with quick-release end anchorages. The tensioning load was meas-

"ured by the jack gage (see fig. 4) and by calibrated load cell3 which con-

sisted of aluminum cylinders on which were mounted two resistance-wire

strain gages (see figs. 3 and 5). One load cell was positioned on each,.

strand between the casting bed buttress and the end anchorage. Av.•rage

:tensioning loads for all of the beams tested are given in table 4.

Placement of concrete

After the strands were tensioned as desired, the concrete was placed

and consolidated using electric vibrators. The top surface of each beam

wt.s coated with a white pigmented membrane curing compound; the other sur-

faces of the beams were prctected during curing by the wooden forms, which

were not stripped until the day the -preteinsioning load -was released.

Transfer of load

The beams remained on the casting bed for 10 dkys (only 3 days for

beams A, B, C, and D*-) with the tention g 1g on the steel. strand.s for

Beams A, B, C, and D were cast primarily to develop the techniques and

proce-dures to be used.

1. U

IrI

4 ILOA ~ ~ *IN POT*J

STRANDS

IJA - C F L .%

-~ N --j ri

Fi-3 lseu fnrt n fcatn e

77we

I 1I I*1.R - , -

i k ~3XMl I, , A.

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Fig. 4. Hydraulic Jack and ram in position on2 South end of casting bed

1/4'DIAMETER HOLE ISTRAIN GAGE t OAD CELLSEL

/STEENL

SR-4 STRAIN GAGES

Fig. 5. Strain gages mouzittI..; on load cell

*9~~ % :

F:1

this period. Then the load on the steel strands was released, causing the

lower half of the concrete beam to be in compression (approximately 2800

psi on the outer fiber), and the upper.half to be in tension (approximately

.200 psi on the outer fiber).* After this transfer of load, the strands

were cut and the beams were removed from the Casting bed and water-cured tot

an age of 28 days. The exposed ends of '-he pretensioning strands were coy-

ered with pads of epoxy resin compound to protect the strands from corro-

sion. The disposition made of the 28 beams after curing is listed in

table 5.

Laboratory Tests and Repults

Twenty-two batches of air-entrained concrete were made in this in-

IRvestigation; two had a water:cement ratio of 5.64 gal per bag, and the re-

mainder a water:cement ratio of 5.85 gal per bag. Six batches of nonair-

entrained concrete were made, all of which had a water:cement ratio-of

6.22 gal per bag. The behavior of the air-entrained and nonair-entrained

concretes is compared in the following discussicn of the results of the

various tests.

Camber and sink-in.

Determinations of camber were made on 20 beams after transfer of

load. These measurements were made at the midspan of each beam using dial

gages that measured the camber to the nearest ten-thousandth of an inch..

Measurements (to the neare-st five-thousandth of an inch) weie also made of 3

the sink-in of three £teel strands in each b.!am after transfer of load,

* Appendix A gives the computation.: used in design of the beams. These

cowputations were mede rc(cordinq to thp mcfthods cit.IUned a& relerence 2.

V-P Al

10

using a fiduc•ial mark on the strand and a measuring magnifier. These meas-

urements -were corrected to allow for the elastic shortening of that portion

of the strand between the beam end and the fiducial mark. Results of both

types of measurements are given in table 4 and summarized in the following

tabulation.

Pretensioning Air-Entrained Beams Nonair-Entrained BeamsForce (w:c = 5.85 gal per bag) (wIc 6.22 gal per bag)

(Load per No. Camber SirLk-in No. Camber Sink.;inStrand), lb Tested in. in. Tested in. in6

5744 2 ,Max 0.012.6 0.026 2 0.0250 0.032Min 0.0034 0.022 0.0200 0.021Avg 0.0080 0.024 0.0225 0.026

5662 4- Max 0.0322 0.026 2 0.0304 0.019Min 0.0031 0.017 0.0138 0.019Avg 0.0176 0.022 0.0221 0.019

As can be seen above, the average camber of the nonair-entrained 4

beams was greater than that of the air- entrained beams for the same pre-

-tensioning force. The average sink-in of the pretensioning strands in the

nonair-entrained beams was not significantly different from that in the

air-entrained beams for the same pretensioning force. t -

Flexural loading

Eighteen of the beams were yoked (in pairs) and loaded flexurally III(third-point loading method), using spring and yoke loading framnes. The

loading of the beams was accomplished by use of two hydraulic rams, posi-

tioned near the ends of the beam, to jack the beams against other channel

sections attached to the loading frames by extension rods (see fig. 6).

Two intensities of loading were used: in one, the compression due to pre-

stressin- was Just balanced (100%), and in the other, the compression due

- ~~to prestr,,ss~ng vas; exce'.dc^d so that &pr a.l 0-psi tension exist~ed

------ P -#5FR- --

,- kzY

AL-I

r-7h 4 7

Fig. 6. Loaded and uniloaded control beams during sitorage in the laboratoryshowing flexural loading yokes, dial. gages, and str-ain gage wiring

n M Tm ,, .. ~ - •,

122

in the outer fibers of the beams (108%). The midspen deflection of each.

beam was measured to the nearest ten-tl.ousandth of an inch by means of dial

gages, two gages per beam. Resistance.-wire strain gages were attached to

several of the beams, and strain was measured to the nearest millionth of

an Jnch per inch. Readings were also taken on embedded gage points (see "

fig. 7) with an external strain gage before and after flexural loafing.

"Table 6 summarizes the data obtaIned in these flexural loading tests.

As illastrated by the following typical data, greater average midspan de-

flections were experienced by the nonair-entrained beams than by: the air-

entrained beams with the same pretensionirg force and flexural load.

Pretensioning Flexural Water: w•Force Loading Cement Midspan

(Load per %of No. Ratic Deflection •.Strand), lb Prestress Type Beam Tested gal per bag in.

5662 100 Air-entrained 5.85 Max 0.0555 "dMn 0.0361Avg O. 0477

Nonair-entrained 2 6.22 max O. 0640yi 0.0578Avg O. 0•0 o .

In addition to the tests jl--,t discussed, eight beames of various ages 3

were loaded flexurally (third-point method) to destruction. For these "r

tests, the test beam wac paired with a steel beam and loaded by means of IL,I.L'i'I -fiaure 4f+Iie cornrefin +3neooaler A~e f4wIew~o¶rSIO~JŽ.toe ~~A1 ?two hydraulic ramsA Midspan deflection of the concrete beams was measured ..

by me:;s of dial gages; gage-point readings were also taken to determine Ifiber strain

Results of the flexuraL load tests to destruction are also given in

table 6. The following tabulation shows that for the same pretensioning

forc s and approximately the same age of concrete, the average flexural load

S4.

13

Ig

t-IGO

w~~.-

1 i AS

Fig Cos-u o voda eammod hoin sradsanWhittmoregageIxi-.: t

*1Z

14

required to destroy nonair-entrained beaas was greater than that iequired

to destroy air-entrained beams. 5

Pretensionirig -Age ofForce Water: Cement Concrete at

INo. (Load per Ratio Destruc- Ultimate Lodd'rested Strand)- lb gal per bag tion. flays (Each End), b lb

Air-Entrained Beams

2 5928 5.64 115 and 120 Max 14,935mn 14, 355

Avg 14,645

INonair-Entrained Beams k-

*2 5928 6.22 106 and 113 Max 16, 240-Min 13, 775- ••Avg 15,0Ol0-

The flexural strength of 120 of the small beams was also determined. •••

One small beam from each of 24 concrete batches was tested at each of five

ages: 3, 7, 28, 91, and "'" days ("N" being a selected age which may dif- A

"fer for each batch). Results are given in table 7. The average flexural

strength of the 5.85-gal-per-bag water:cement ratio air-entrained concrete

was higher than that of tr.e nonair-entrained concrete at four of the six

* ages tested, i.e. at 7, 28, 45, and 91 days age (table 7). The nonair-

entrained concrete showed higher flexural strengths at 3 and 35 days age.

Length and midspan-deflection charge with time

Z

Length-change tests, based on readings taken on the embedded gage

points, were conducted on eight of the beams stored in the laboratory.

Four were tested in a loaded conditicn and four in an unloaded condition.

Two of the unloaded beams were pretensioned; two were not. These length-

change test results are shown in fig. 8. Length-change readings were also

~~'-~ A7

0 0

.W _0 0

0 0 0 0 0:a

I0 0 1D ) 00 00 0-

2,z zz 4 z z . 0

0 tO 0 ~ -41.- 41-.4 o

X- a 2z zI 02 z ___l 1,z l 0. J

0a l toW M ,o Z u

.___ 0 U x___I

0 z_ _ a C.CL u

to 0

0 10 0 0 0 000 0 0as a1 a a-AI a

to

0n 04

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0 0

0z 0~ 0 01

+_ ___ -+ __

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a-)~~ M

o o u c w 0 0: 0 0o 0 0 - Q 0 0 < 0 w 0 w

N 2 zo ;; 0 a 0 Z. n

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16

taken using SR-4 strain gages mounted on the outer fiber of four loaded

beams; these results are given in table 8. The length changes of the four

•unloaded beams were also expressed as volume changes, as shown in fig. 9.

The volume change was greater for the pretensioned than for the nonpreten-. r.,

sioned, unloaded beams. Canages in midspan beam deflection with time were

Vi. measured by means of dial gages, and are given in table 9. __

Compressive strength andstatic mcdulus of elasticity

The compressive strength and.static modulus of elasticity of 136 of

the 6- by 12-in. concrete cylinders were determined. One cylinder from

each of the 28 concrete batches was tested at each of five ages: 3, 7,

28, 91, and "Yf' days. Test results are given in table 10. .

The compressive strength test results from table 10 are simnarized in

the following tabulation.

NO. Water: Cement Co-pressive Strength, psiSnecimens Ratio 3 7 28 35 45 91 365Tested gal per bag Days Das Days Days Days Days Days

Air-Entrained Concrete

2 5.64 Max 3570 5110 7140 7300Min 3520 4460 6890 7000

2 Avg 3545 4785 7015 7150 .

20 5.85 Max 4390 4980 6570 5070 6390 7250 7650Min 2990 3930 4820 5040 5480 5710 5910

Avg 3540 4405 5695 5670* 5830* 6545 6925

Nonair-Entrained Concrete A

6 6.22 Max 3860 5410 7290 6640 6360 7220Min 3070 4140 5430 6540 6040 6360Avg 3525 4540 6385 6590** 6200** 6820

• Average of five specimens: only five specimens were tested at the:,eages.

Average of'two specimens; only two specimens were tested at these ages.

i . ..,

+0.0501

B- EAM I - NOT PRETENSIONEDx---- BEAM 2 - NOT PRETENSIONEO

('.000 B EAM 5- PRETENSIONED

-OBEAM 6 - PRETENSSONED 4NOTE: VOLUME CHANG- ~3 T1INES LENGTI' CHANGE.

x 0.5

U

0

-0.2001

-0.150 4C *506072

o icc 200AGE. OA"S

0 68 - 24 268 368 468 563 668DAYS OF TEST

Fi~g. 9.Results of labc.3ratory volu.me-change tests

A1

The indicated average compressive strergth of the air-entrained concrete

with a water:cement ratio of 5.64 gai ,-=r bag was greater than that of the

concretes made with the other two water cement ratios at all ages tested;

however, only two specimens of this conýrete were tested at each age. The

F• average compressive strength of the nonsir-entrained concrete with a water: ,

cement ratio of 6.22 gal per bag was greater than that of the air-entrained

concrete with a water:cement ratio of 5.85 ga!. per bag at 7, 28, 35, 45,

and 91 days age; the average compressive strengths of these two concretes

were essentially the same at 3 days age.

The apparent decrease in strength of the nonair-entrained concrete

between 35 and 45 days age is not regarded as significant. It may hpave re-

sulted from improper consolidation of one or both of the two test specimens ':

which were tested at 45 days age; but since only two specimens were tested,

no definite conclusions are be-lieved warranted. 413

As shown in the following tabulation, the air-entrained concrete with 4

a water:cement raio of 5-64 gal per bag had the highest percentage in-

crease in compressive strength between 3 and 91 days, and the nonair-

entrained concrete had a higher percentage increase than the air-entrained .

concrete with a water:cement ratio of 5.85 gal per- bag.

Percent Increase in ConcreteNo. Water: Cement Compressive Strength with Age

Specimens Ratio 3-7 7-28 28-91 3-91 91-365 4"Tested gal per bag D D D • Days

Air-Entrained Concrete

2 5.64 38 47 2 10220 5.85 24 29 15 85 6

Nonair-Entra. ned Concrete

6 6.22 29, 4l 7 93

:t• •-The increase in compressive strength of the three concretes between 3 and 7

* days age ranged from 24 to 38%, between 7 and 28 days age from 29 to 47%,

ard between 28 and 91 days age from 2 to 15%. The smaller increase between28 and 91 days is presumably characteristic of high-early-strength concrete. t

The strength-gain characteristics of the nonair-entrained concrete

and the 5. 85-gal-per-bag air-entrained concrete are shown in fig. 10. The

rate of strength gain by each concrete apparently decreases greatly when

the average compressive strength reaches a level of approxLmately 6500 psi.

Since concrete compressive strengths in excess of 6000-7000 2si would be

advantageous for some applications involving prezensioning, it woul. be de-

sirable to learn what factors brought about the indicated compressive

strength plateau. Among those that iay have been retponsible are (a) ap-

proximate completion of effective hydration of the cement by self-

desiccation and other processes; (b) effective decline in efficiency of

curing; (c) attainment of a strength level that made the effective strength

of the aggregate a critical Ifactor; and (d) elastic prperties of the test-

ing machine.

The average static modulus of elasticity of the air-entrained con-

crete with a water:cement ratio )f 5.64 gal per bag was generally lower

than that of the other two concretes and ranged from 360 X 106 psi at

63 days age to 4.92 x 10 psi at 91 days age (see table 10). The average n.-

static modulus of elasticity of the air-entrained concrete with a water:

6cement ratio of 5.85 gal per bag ranged from 3.82 x 10 psi at 3 days age

to 5.35 X 10 psi at 91 days age, and was higher than that of the other two

concretes at 3 and 91 days age. The average static modulus of elasticity

6of the nonair-entrained concrete was 3.78 X 10 psi at 3 days age and ,

S:N

.- 3-

02

36.

0

4- *1 20913

CI-F _DYI

Fi.z.Srnt Ci fcnrt

qp __

21

5.12 x 106 psi at 91 days age, and was higher than that of the other two

concretes at 28 days age, and higher than that of the air-entrained con-

crete with a water:cement ratio of 5.85 gal per bag at 35 and 45 days age.

Dynjamic Zroperties dnmco

Young's dynamic modulus of elasticity., the dynamic modulus of rigid-

ity, and Poisson's ratio of 120 of the small concrete beams were deter-

mined. One small beam from each of 24 concrete batches waf, tested at each

of five ages: 3, 7, 28, 91, and "N' days. Results are given in table 11,

* which shr--: the iollowing. The average dynamic modulus of elasticity and

the average modulus of rigidity of the nonair-entrained concrct.e were

greater than those of the p.85-gal-per-bag air-entrained concrete at all

ages tested. The average Poisson's ratio of the nonair-entrained concrete

was greater than that of the air-entrained concrete at fr.ur of the six ages •

tested, i.e. at 28, 35, 45, and 91 days age. At 3 days age, the average

Poisson's ratio of the two concretes was equal; at 7 days age, the air-

entrained concrete had a greater average Poisson's ratic.

Cree-o

Four of the 6- by 16-in. concrete cylinders containing embedded

strain meters, two air-entrained and two nonair-entrained, are being sub-

jected to laboratory creep tests. These specimens were loaded in compres- f

sion to 1000 psi at an age of 10 days; this load is being -maintained by

steel springs. The other four 6- by 16 -in. concrete cylinders containing

embedded strain meters, two air- and two nonair-entrained, are being tested

for autogenous length change,concurrently with the creep-test specimens, to I FS

serve as controls. One each of the air- and nonair-entrained creep cylin-

ders is being tested in a sheathed cordition (outside surface of the

22~

cylinder covered with a neoprene jadket), and the oth.--r two without

.sheaths; the same is true of the autogenous-length-ch znge, cylinders. CreepI

equations for data obtained after approximnately one yci~r of test-ing, and

from which autogenous length change has been subtractc 1, are shown in the

following tabulation. Creep curves are plotted in fJ- ,- 11 and 12.

1000--psiLoad at_10_DaysAge _________

Batch Air Content Seie

No._o__________ Sheathed Creep Equation

2 4~.0 No c =0.-158 ,0.0791 ln (t + 1)Yes e = 0.195 i-3.0381 ln (t + 1)

162.2 NOc =0o.128 +0.0801in (t + 1)Yes G =0.0718 +0.0331 In (t ÷.l) 4

Note: c = a~lastic plus creep strain, millionths off an inch per pound persquare inch

t = time after loading, daysln = nat.ural logarithm

The sheathed air-entraine specimens have exhibited miore creep to

date than the sheathed nonair-entrained specimens. The creep of the un-

sheathed specimens is essentially the same.

Laboratory freezing-and-th-awing

Sevntytwoof the small concrete beams, three from each of 24 -

batches, were subjected to rapid laboratory freezing-and-.1hawing tests in

water, beginning at 14 days age. Results are given in table 12. The aver-

age durability factor (DFE) of the air-entrained concrete beamis was 87,

VrAs shown on page 25,! 4air-entrained concrete bewahdssgtl

hrAs shatn of th ge 2oair- al-entrained concrete wasmi had. sligA

higher initial pulse velocit. ,.z. than the air-entrained beams.-* I

-- 1

,•0.3S -- , T•TFT ~ I4

z 0.60 - - 158+0.791 in(t+

_ _ - .-

IbILL. 0.4S -

A 1 fl+1.b.0.40 -

S- MASU-RED~

MiX-ýiEASURED LGIOnPUTED STTISTICALLY 0- -- 0 4.01. AIR CONTENT. UNSHEATH.E. LOADED AT 10 DAYS AGE

&--CEAS4JRED 1 I:• • I"-'-~~~~COMAPUTED $STATISTICALLY X -'- • .• AIR CONTC.I. G.H"-ATNEO. L.OADED AT 10 DAYS AGE. •,•

0 NOTE: THE T VALUES IN TMlE -QUATIONS REPkES&.HT CLAP4EO TO< IN

SO.OS

0 20 40 60 eO 100 320 140 160 180 2100 220 2,40 260 280 300 320 340 360 •.,

DAYS AFTER LOADING ."

Fig. ll.0 Creep of air-entrained concrete, batch 2

I-i-*~~~i I -- It-3-I

•'.4- .

.. P! J

51

- it

O.S.-

21J.

0.4r

II

0.6

x 042 0.0710 + 0.0831 In t + I,

ci ______ 1i LEGEND

0.15 - - - - - 2.2% AIR CONTENT. UHSHFATýED. LOADED AT 10 DAYS AGE-

COMPUTED STATISTICALLY 2.2% AIR CONTENT. SHEATHED. LOADED AT 10 DAYS AGE

e ASURED NOTE: THE t VALUES IN ThE EQUATIONS REPR$SCNT ELAPSEO TIME INPjjjTE STTISTCL J DAYS AFTER LOADIN.

0 20 40 60 80 100 120 140 160 M80 200 220 290 260 200 300 320 340 3680

DAYS AF`TER LOADING

Fig. 12. Creep of nonsir-entrained concrete, batch 16

Ijd~E~J! .- _-}

- ~ ... <... _ 1 *~ - .- &~.-.- -___

I25

No. Water: CementBeams Ratio PulseTested Ty-pe. Beam gal per bag Velocity, fps

12 Air-entrained 5.85 "Max 15,555Min 14,965Avg 15,225

4 Nonair-entrained' 6.22 Max 15,590Min 15,375Avg 15,,445

Field.Exnosure Tests

Resistance of the concrete beams and auxiliary specimens to natural 4

weathering is being determined by means of exposure of the specs!. ens at

Corps of Engineers exposure stations located at Treat Island, -Maizqe, and .

St. Augustine, Florida. At Treat Island the principal factor affecting

durability is freezing-and-thawing; at St. Augustine it is sulfate attack.

"Speci.mens exposed to sulfate attack

"Three biams .were installed at .half-tide elevation at St. Augustine5

in October 1959. Two of the beams were installed in a loaded condition I"(loaded to cracking, i.e. to "89 of.prestrtss); the other beam was in-

stalled unloaded. The beams are inspeczed biennially, at which time length

changes are determined using an external strain gage,. and pulse velocity

tests are conducted.

Specimens exposed to

freezinR-and-thawing

Seventy-two of the small concrete beams (three beams from each of 24

batches) were installed at Treat Island in October 1958. T•ese beams are

annually inspected and tested for fundamental flexural frequency.. Test. re--

sults obtained to date are given in table 12. No significant'differences

34045

! .126

have been noted in the physical appearance of the small field exposure

beams male from the two concretes. The average durability factor of the

air-entrained concrete after four winters of exposure was L.01, whereas that

of the nonair-entrained concrete was 97. Therefore, it can be seen that

the air-entrained concrete is exhibiting slightly more resistance tod•!

freezing-and-tha-•ing than the nonair-entrained concrete. When more data

are available, these field results will be compared with results of the

laboratory freezing-a---thawing tests.

Sixteen lsarge beams were installed at half-tide elevation at Treat

Island in October 1958. Four were not loaded; the other 12 were loaded,

six to 100% of prestress and six to 108% of prestress. The channels,

springs, and rollers used on the loaded beams were painted to protect the

metal from corrosion, and stainless steel rods and nuts were used. The

embedded gage points were protected by stainless steel cones. The beams

are inspected annually, at whi ch time length changes are determined with ain

r external strain gage, and pulse velocity tests are made using a soniscope.

These pulse velocity readings are taken (one per beam) through the 8 1-in.

dimer-sion ,:f the beam, and the square of the pulse velocity obtained at any

time is expressed as a percentage of the initial pulse velocity sqaared.

Results of the inspections, and of the length-change and velocity tests

are given in table 13.

The 12 beams of air-entrained .concrete have survived four winters of

exposure at Treat Island; the 1962 condition of these beam-s ranged from

"good" to very good" (table 13). The four rnonair-entrained beams f."..led

structurally during the first winter of e..xposure; this failure occurred

considerably earlier than had been expected.

27

The weekly condition of the nonair-entrained pretensioned beams dur-

ing the winter of 1958-1959 until structural failure is given below:

Yoked Pair Loaded Yoked Pair Loadedto 108% of Prestress te 100% of Prestress

* Date Beam 15 Beam 16 Beam 23 Beam 24

12 Dec 1958 sound. Sound Sound Sound

19 Dec 1958 Slightscaling Sound Sound Sound i . l

.26 Dec 1958 Slight •. 2!scaling Sound Sound Sound

2 Jan 1959 Failed Sound Sound Failed -- •i

9 Jan 1959 Moderatespa~lling Sound

16 Jan 1959 * Heavy Moderate ;spalling spalling

23 Jan 1959 -* Failed Moderate

30 Jan 1959 * Heavy .....

s~palling

6 Feb 1959 * HeavyS~~~spaliing**.[:

13 Feb 1959 Failed

e ••tAll s7;-e! wires exposed one-half of their length. each•*All steel wires exposed one-fourth of their Iengtth.

The foregoing results indicate that even though one bea-m of each pair Z_-

deteriorated and failed first, thereby releasing the third-point flexural

load, the other beam continued to deteriorate unti! it failed also. Beams

15 and 24 failed simultaneously (week ending 2 Jan 1959). Beam 23, which

had less initial p::etensioning load than beam 16 (5662 lb per strand versus

Paragraph 301(b) of zheAAmerican Concrete Institute (ACI) Building

Code states "Concrete witbout: air entrainment which will be excposed to

A

285

the action of freezing weather shall have a water content not exceeding _

6 gal per sack of cement." It will be noted that the nonair-entrained con-

crete used in this investigation had a water content of less than 6 gal

per bag of cement.

2 f"Lin wrote "Air entrainment of 3 to 5% improves workability and re- kit

duces bleeding. When well-recognized air-entraining agents are employed,

Shere is no evidence of increased s-rinkage or creep. Hence proper appli- jcation of air entrainment is considered beneficial for prestressed con-

~6crete." The Bureau of Public R staed that "any portland cement and

aggregate may be used ,hich is suitable for ordinary concrete" i:n *re-

stressed concrete bridges. Tne ACII reconendations list air-entraining

portland cement among the types of acceptable por:zlnd ceiments, but fail

to comment on when or whether air entrainment should be employed; no men-

tion of air entrainment is contained in the paragraph on admixtures. This

failure by the writers of authoritative guides to prestressed concrete con-

struction practice to mention whether or not entrained air is needed in

prestressed concrete exposed to weathering has apparently led some to con-

eude that entrained air is not needed in prestressed concrete. This

opinion was expressed during the discussion of an unpublished paper pre-

sented at the 1960 ACI convention in New York.

Most authorities, howeve'-, believe that air entrainment -s necessary

in prestressed concrete exposed to freezing-and-thaiing. Based on labora-17

tory tests, Klieger' concluded: "All. concretes require intentionally en-

trained air to provide a high degree of resistance to freezing and thawing %;.-•. S

and de-icer scaling." In a discussion of a paper by Gutzwiller and

8 9M 8sleh, Kunze sl.ated: "For most concretes used in prestressing, air_l,<U

o.Ao

content of 5 + 1% is reqiared to assure a high degree of resistance to

-freezing and thawing, along "ith low water.-cement ratio and adequate

curIng."1

The results of the fieid exposure tests reported herein appear to

provide conclusive evidence that properly entrained air is necessary to

provide resistance in saturated prestressed members to severe freezing-heol requleevmeon

and-thawing. These results confirm the wisdom of the...... .er.hSthe^,ACI Building Codel . that "Concrete whih i be to J•.

the ̂ o•^^','" .freezing .. ,shall contain entrained air," ( ,SOH 0 ZI

S•Acknowledgments -

The test program reported herein was carried out by personnel of the

Concrete Division of the U. S. Army Engineer Waterways Experiment Station

under the direction and supervision of Messrs. T. B. Kennedy, Bryant -

Mather, E. E. McCoy, Jr., and W. 0. Tynes. The author of this paper was

project leader.

Steel pretensioning strands for this program were furnished free of

charge by the mar.uiacturer. The casting bed used for pretensioning was

designed by Mr. W. J. Flathau of the WES Hydraulics Division, and con-

stracted by the WRES Construction Services Division.

Directors of the Waterways Experiment Station during this investiga-

j tion were Col. A. P. Rollins, Jr., CE, Col. Edmund H. Lang, CE, and I •

Col. Alex G. Sutton, Jr., CE. Technical Director was Mr. J. B. Tiffany. I

3

ii 30Referen'ces

- 1. American Concrete Institute, "Tentative reccmmendations for pre-stressed concrete." American Concrete Institute Proceedings, vol 54(1957), P 545.

2. Lin,; T. Y., Design of Prestressed Concre.ta Structures, 1st ed. JohnWiley and Sons, Inc., New York, N. Y.,. 1955.

3. U. S. Army F.Kgineer Wateirways Experiment Station, CE, Handbook forCon-.crttc and Ceirent. with quarterly supplements. Vicksburg, Miss.,August 1949.

4. Kennedy, Thomas B., "Tensile crack exposure tests of stressedrein-Iforced concrete beams." American Concrete institute Proceedings,vol 52 (1956), pp 1049-1063.V

* 5. U. q. hrmy Engineer War.erways Experiment Station' CE, Investigation ofthe Per1•rmance o2 Concrete and Concreting Materials Exposed to Natu-ral. .eath-trini.. Technical Report No. 6-553, Vicksburg, Miss.,

SJune 1960.

6. U. S. Bareau of ?abiic Roads, Cvzeria foz Prestressed Concrete* Bridges. Department of Commerce, Washington, D. C., 1954. (Reprinted

as Appendix D of Reference 2.)

7. Klie.cr, Paul. "Some aspects of darat'Iity arid volume change ofcone:cete for prestressang." J6urr..tl of the Research and DevelopmentLaboratorjes, Portland Cement Association, vol 2, No. 3 (September •

T 960), pp, 2-12.

8. Gutzwi3.ler, M. J.; >and Musleh, F.' E., "Freezing and thlawing effect.s.or preszressed concrete." Proceedings, American Society of Civil."Engineers (Journal of the Structural Division), vol 86, ST-IO (October"1960), pp 109-124. 4

44

9. Kunze, W1. E., discussion of paper, "Freezing and thawing effects onpxeZezreased concrete," by Gatzwiiler and 1,husleh. Proceedinas, Ameri-can SocieT. o_ Civ~l E,,.ineers (Journal of the Stractural Division),,vcv 67, ST-3 (March 1961), P 57.

10. Ar..ericpan Concrete Instit-ute, "ACI standard building code requL-ementsfor reinforced concrete (ACI 318-56)." American Concrete Institute IPr.oceedin..ts. vol 52 (1956), pp 913-986.'

11. ________, eo z .... ... building code requirements for rein-Sforced concreze (ACI 318-63)." American Concrete Institute Proceed-

i -:s vol 6P (l963), PP ise4&

l) 11963 ACT Boo 6k 5+anetar4S.jQIA

.*---M A,-

N]

Table 1 I

Physical Properties and Grading of Crushed r.imestone Aggregates

Test Fine Aggregate Coarse Aggregai•e

,I Physical Properties

Bulk specific gravity,saturated surfacedry 2.66 2.70

-Absorption, % 1.2 0.7

Soundness, M-S04, % loss 10.0 2.4

Los Angeles abrasion, % loss -- 23.6

i Mortar strength, %

-day 158--

Percent Passing Standard Sieves

S -Seve:

1-n 100 -

i I 3/4-.in. 99

1/2-in. 55

No.4 100o 4 4"No. 3 92

No. 6 62

No. 30 36

No.-50 19

No. 100 9

Fineness modulvts 2.82

t

i:I

I1

S• Table 2

Preoerties of Steel Pretensioning Strands

i Property Description or Value

"- Type of strand* Strcss-relieved 7-wire strand

I ""ominal strand diaxeteer* 1/4 in.

"Strand constructiop* 1 by 7

'Approximate weight per 1000 t*121 lb

Cross-section area* 0.0352 sq in.

Minimum ultimate tensile strength* 238,000 psi

Approximate yield strength*(as det. mined by 0.7% elongation) 6(% of .ultimate strength

Ultimate tensile load and strength:-Manufacturer'x 10,300 ib (292,615 psi)

Elnti 9,600 lb (272,725 psi)SElongation (in 24-in. lengths)** 7.92% (at ultimate load)Strain at stress of 166,600 psift 0.00626 in. per in.Modulus of elasticity: p

Manufacturertt. 26.6 x 10 PsiWESt 23.7 X i06Psi

Relaxationtt 6.7% loss in 1000 hr (at stress"of166,600. psi)

:i A

* Taken from table in reference 2.S** From marn-i'acturer's report.t As determ~ined by Wlaterways E-xperii.ent Station on three strands, each4about 5 ft long.

tT Interpolated from curave for 1/4-in, strand furnished by manufacturer.

CP. 0

wo WCW8 c ccoc cocc0cotoc_ .-o

Cl) -4 Id

-PL 2 o0 ~co0,o CD coC c o oco t

ILI0C

t o

0 -C 4- )

0I 4) 4- - 3 4 - - 34 + - . 341Q ý4 ý

Q cu4( --t .4cu. _:rU( _z1- 1q '-4. - -

14i -- 1-1 133 al1 as M-43 asia 8* UN8~~7t. .-. 1-H.1~4~1') .i4,-i. ~ ~ 3- 04). -'

r_ 1;. 4o 441 A 1 ;1 4A AA A 6 A60 lAI 0VdC) 4)If 4>0.0(

0~ 4J .~ ZC l uC1c i a :

4ý4

(u 14 E

0 t9

Sz 0 . .. , . . Z,. LNb A NC 7% u mWC N I -1 0C5 04_4 1 _:r-: Z- T :r 1 $ _T .0_r: 7 - _r_: )W

G).:.S11 W4 43 0 3

toc

0 :r.

.00

c d -t :! 4- W%0 H' 14 u n m Z-.O0.-C 0 .4 00LA C~-c 0 ' 0 J-t ro 0

4 .4b 3u ?C ?m ML \C --0 ia -\4

To Table 4

Test Data, Zoncrete Bear.s*

Percent Camber

of (Avg of 2 Sink-inAverage (of 9 Ultimate Readings) of Strands

Type Water: Cement Casting Strands) Tensile at - (AvgBeam Con- Ratio Date Tension load Strength Center of of 3 Read-

No. crete psa!/bag 1958 on Strand. lb of Strand Beam, in. ings), in.

A Air 5.6! 26 May 5928 70.8 ..B Air 5.64 26 May 5928 70.8 ..C Nonair 6.22 26 May 5928 70.8 ....D Nonair 6.22 26 may 5928 70.8 .....

1 Air 5.85 30 June 1o6 1.3 .....2 Air 5.85 30 June 106 1.3 .....3 Air 5.85 30 June 106 1.3 .....4 Air 5.85 30 June 106 1.3 .....5 Air 5.85 14 Ju:.y 5791 69.1 0.0055 0.012"6 Aix- 5.85 14 July 5791 69.1 J.0193 0.014

7 Air 5.85 14 July 579). 69.1 0.01,18 0.01148 Air 5.85 14 July 5791 69.1 0.0474 0.0219 Air 5.85 14 July 579L. 69:1 0.0221 0.021

10 Air 5:85 14 July 5791 69.1! 0.0192 O.02411 Air 5.85 28 July 5786 69.1 0.0316 0.01112 Air 5. 85 28 July 5786 69.1 o. Oll4 0.022

13 Air 5.85 28 July "786 69.1 0.0238 0.0141 Air 5.85 28 July )786 69.1 0.0028 0.01615 Wonair 6.22 11 Aug 5(44 68.6 0.0250 0.021

"16 Norair 6.22 11 Aug 5744 68.6 0.0200 0.03217 Air 5.85 11 Aug 5744 68.6 0.0034 0.026

18 Air 5.85 11 Aug 5744 68.6 0.0126 0.022

19 Air 5.85 26 Aug 5662 67.6 0.0125 0.02220 Air 5.85 26 Aug 5662 67.6 0.0322 0.017

21 Air 5.85 26 Aug 5662 67.6 0.0227 0.024222 Air 5.85 26 Aug 566Ž. 67.6 0.0031 0.02623 Nonair 6.22 26 Auug 566? 67.6 0.0038 0.01924 Nonair 6.22 26 Aug 566-.i 67.6 0.0304 0.019

" ~ii

* These determinations were made outdoors on the casting bed. A

I3

U 31

21

Ta~ble 5

Tyznc- of Tost:v Conducted on, and Dswo ition o4 Bca.s

"Pretensioned Laborator- TestsWater: to 70% of Midsan LengthCement Ultimate Deflection and Fleyural

Beam Ratio Strand Flexural Volume loading Field Exposure TestsNo.* galhaw Streng-th Load!ng Chare to Destruction .ocation Condition

Air-Entrained

A 5.64 Yes No No YesB 5.64 Yes No No Yes1 5.85 No No Yes Yes2 5.85 No No Yes No3 5.85 No No NO No Maine Unloaded4 5.85 No No No No Maine Unloaded

5 5.85 Yes No Yes Yes

- 5.85 Yes No Yes No Flori.da Unloaded"7 5.85 Yes No to No MaIne Unloaded

8 5.85 Yes No No No Maine Unloaded9 5.85 Yes Yes Yes Yes

10 5.85 Yes Yes Yes No Florida Leaded, 169%of prestress

11 5.85 Yes Yes No No Maine Loaded, 108%of prestress

12 5.85 Yes Yes No No Maine Loaded, 108%of prestress

13 5.85 Yes Yes No No ,-aine Loaded, 108%of prestress

14 5.85 Yes Yes No No Maine loaded, 108%of prestress

17 5.85 Yes Yes Yes Yes"".1 18 5.85 Yes Yes Yes No Florida Loaded, 189%

"of prestress -q19 5.85 Yes Yes No No Maine loaded, 100%

of prestress20 5.85 Yes Yes No No Maine Loaded, 100%

of prestress21 5.85 •es Yes No No Maine Loaded, J• %

of prestress

22 5.85 Yes Yes No No Maine Loaded, 100%of prestress

llonair---Itrained

C 6.22 Yes Yes lIt Yes

D 6.22 Yes Yes NO Yes

15 6.22 Yes Yes No No Maine Loaded, 108P-.

of prestress16 6.22 Yes Yes No No Maine Loaded, 108%

of prestress23 6.22 Yes Yes No No Maine loaded, 100%

of prestress24 6.22 Yes -fes NO NO Maine loaded, 100%1

of prestressj

"* Thc beam nu.zbvrs of these beams are also their batch numbers.7* -.!s bean vas retaired in the laboratory for continuation of length-change tests;Zee f'-g. 8

di .1 : ,- , &~ -- .: : :: : : '.9 SSS: : : Ii::,1.4

ci Qi - In I P.D CO 0

O.V douS a j .4- S cc3u I' * i a 8 a ii S

+) 4 .4 a4CC 00

d1 to 001 0 0 1 a a a m 01 a1 a.a

I 6c jP'0 0 0 0"0'0

.43 C5

I - . . ~ .~ - . -c

0~~~~ %D.c ciCi L\ oz

1 22 C

Ci~& L 1 l\

03 *1 0 -+ +

oz :. l.2 + + + + + .*+ ++Li e SC =L +S' -. +m 01- -

1- 1, t 4a -0- S. 0'-ici. 1 0anl S aCOC C C-8ic 8- 880 &S

In In 1 -1 a an an Ina11Z QC3 sl-4 mS ol ft p c iCscý cý-ý C o

~~~~~~L r\ U% V\ 0 0~ 0 ,. 5 5 ' s 0 s~J - . 0 0cian -Z zr C-Z an amc mna (55(5 In e1n M na -

aa t. A

*~ 0'5oi 13i

cr co OQ C3 93 M 0 cc c4 a0 0 :

0C C% arsa- Usaf V\5J L.% Lr% L-* V4S~ (v --%

05.-a 5,5 'as. Gt Ca1. US-, AS. 01. Lk. Ci. Ci. i

lad t, -:s

!I . l c q IzS.oJ. Z. S'J ;4.S S.00 l<.0- oF 35 0.01n~ F'i. a- 40

--tt

.. ..

I :•Table 7

Flexaral Streng'h Determinations4

Water:CementFlexural Strength,* psi, a..Water: Cement 3 7 28 35 45 91

Batch Type Ratio Days Days Days Days Days Days 1-YrNo. -Concrete gal/bag Age Age A ge Age Age Are

I Air 5.85 925 106511 lO goo 900 10602 Air 5.85 925 1025 1185 .. .. 1050 9403' Air 5.85 865 1095 1145 .. .. 1050 10754 Air 5.85 955 920 1155 . . 1035 905

* 5 Air 5.85 995 1040 12900 - - 1100 7706 Air 5.85 960 -- 1185 . . 980 955S5 ~~Air 8.1o 99 5 10240 !9 . . I0

Air 5.85 810 1065 1240 -- -- 1135 10108 Air 5.85 1015 1085 1075 1005 895

9 Air 5.85 1000 965 !155 -- 1095 76510 Air 5.85 940 9000 1220 -- 110 !155 --1l0 Air 5.85 920 995 1225 -- 160 1155 --

".12 Air 5-85 880 995 1000 -- l120 860 --

,, . 13 Air 5.85 890 1055 1120 -- 1200 910 --

14_ Air 5.85 845 895 1110 -- 1055 885 --

15 Nonai r 6.22 970 1025 1005 830 860 --

16 Nonair 6.22 840 1120 1085 -- 920 830 --

17 Air 5-85 "780 1020 1055 . . 980 1175' 18 Air 5.85 780 945 955 1140 830 --

19 Air 5.85 920 1ll0 960 890 -- 995 --20 Air 5.85 -920 1065 970 870 -- 850 --

S21 Air .5-85 875 990 960 800 -- 1025 --

22 Air 5.85 770 890 1015 880 -- 960 --

23 Nonair 6.22 935 920 1055 1150 96024 Nonair 6.22 900 940 1045 860 -- 1000 --

-i

AA

II* Flexural strength determined on one 3-1/2- by 4-1/2- by 16 -.in. beam from

each batch, usirg Method CRD-C 17-58 (using simple beam with center-pointloading, reference 3).

IIhI4

1600d C. .

.4 -m

0 0 i"n 0al Zl

0~ 0

It.Mc0 0 01

0.00

U,4 t, t, 0

Fl u

-..

'4 C4 .* - ,

lift

I ~iablv 10ccwer-Ive Stre;,cth und ntatle M;.;./luz of Fit1cety ot Concrete tllnrsat Varlc•zc Ares

?fo. Con~Stttic C~ Steic~ c:~ Stai or C~oncrtet Cylnorsm Static 2c Pv~o ___Coantret.sive Strbnuth.. j.:3. and .tntfc .,odhlus or •Ist|d~t,"*x10"', i.S.|•

i~c i ~ AcD~~A,,- 35 Dkst,. 45 D~-f ;-e 01. Days A;-e_____ ____ __ _ _ _ _V _ _ Static_-_ Static Static Static 3Air-F..tranlrd Circrete, v:c 5.64

"; A 3570 -- 5 .120 -- 7 14o 4•.7.1. .... 73 D0 ' 5.90B 3523 3.60 A46o 4.29 6&90 4.65 -- -4 .. .. 7000 4.95

rmr. Ln rtrj-nd Concr~ete. v:c 6.22

A c 360 -- 541o -- '4.81 .. .. . 6930 4. 5.o3D 3710 3.75 .Uo 7.62 707), k-92

:6 3660 3.81' ,140 4.2.8:, 5L30 :,.S . . 65, 5O 6-370 .5.274

S 2314 370 3.55 4210 4.16 629o 5.20 '66'4o 5.-36 -- 7-2W 5.5724• 3340 3.52 436 o 4.09 6 T7O0 5.31 6 ,540 5.11! -- C960 5 -29 ?4

'Air-2.Rn-uled r:C,ncrcte. O:c ~8

1 3790 3.84 4950 4.03 6570 ".59 . .. .. .. 7183 5.052 3090 3.57 40-0 ý4- . 5230 4.3 -- -- -- - 6ý,20 5.40S , 3 3270 3.59 40., 4.±6 3•o .23 .. . . .. 571o :.ý.9 0

'4 3250 3:82 4.140 4.02 5.:-30 5,~00 - - - 6233 5.155 429 4.24 40 4,141 5:S3 -1 . --4 -- 7190 5.-96 393 ".'-5 1. 1l LAIl 57120 4.6.n An

7 3753, 3.94 4...3 584o .5ý '45 -(... .. . £y",0 5-25

439',0 00~. 413 4.1( 4 - 50--- 63890 *,O..•. 4', O 4:.31 6;433 4.41 . .. . .. -- -o 7050 69

39'0 4.0 : ..30 o30 6,..0 4.55 .. 7250 5.8,!10 3800 :.17 U11. 4.26 5,') 4-25 - - 69 .5 E~ .1

11 3500 3.78 -30 4.02. 5540 4.65 5570 4.31 6640 5 23]2 3430 3.66 "i•.3 3.94 57WO .4 -- 6210 4.15 6960 5.26-13 3700 3.31 3930 3-79 5890 4'30 .. .. 55o0 4.49" 5750 -. 914 3610 .1-3 4•i,3 4.29 5710 4.45 -- 54Po 4.44 6340 5.5-5

•17 3300 3.47 4070 3.96 -•'• L.19 Z- .. .. .. ;60 5.-Z

i8 3320 3.83 41Z0 4.03 k420 4-i 500 4 .39 .. .. 6210 5.-319 3470' 3.55 t233 4.0o 53cO) 4.95 5640 5.00 . . 6-50 5.320 299L3 3.75 4O 4.Cl `60 1.89 6C020 4.71 .. .. 6250 O.Ob21 3310 3.63 4110 4.05 5930 5.G6 6070 5.G• .. .. 6610 5.9- i22 3-,o0 3.92 42o 4-.o9 5C6O 5.00 5570 5.o8 6,. .c .SZ.

100 Dx ': At-n * 13. rayVs Ae 1"5 Dtvs -Are- 120 tkzwy _ze 1 Yea- AgeCc-n St'zic 3 Cc=z St&-tic• F C -P St-n-!c 2 Cc--, Static Z Cc•r S a'Lc E

4 A~r-E~'tr~tneS Conrete,*:c.6

B -- 6700 5.71 : -

S "• o.a-2.-ra - Concrete v:c 6.22

-- 6933 5.25 - - - - -

Lr- :ýz:imcd Concrete, i:c .-68.. .. . .. .. .. .. . z60 5.71

i . . . ..2. . . 69-6C 5-57

3 .6.350 529

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* Co•:ress.ve zt...--th deter,.nea, o one 6- by"'2-In. cyrlnzer at each age (-Lest. .et:od c.- !4-57).

*0 14o'tlus dete-.crnld on one 6- by 12-in. cy-linder at each ate. m1bis nodalux is tie chord l100W psi (T~cst Meth.od Cr32-C 19-55).

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* APPFNDIX A: DESIGN COMPUTATIONS

Notations Used in Corm•utaticna

SA Cross-sectional area of beam, jrn.2

2A: Cross-sectional area of concrete, in.

S As Cross-sectional area of steel, in.

* b Width of beam, in.

d Depth of beam, in.

S"D Diaitý.eter of strand, in.

e Eccentricity, in.

SModulus of eias-.icity for --he concrete, psiEs Modulus of elast'icity for the stceel, psi

ots

I' Compressive stress in concrete, psi!c-S C I

ft Comprssiv srnt in con~crete, psi, at 28 ts g

f Effective prestress -n steel, psi

f. Initial prestress in steel, psi

F Force, lb

I Momeent of inertia of section, in.*4 ?

It Moment of inertia tr ansformed, in.:•

L Effective leligth of beam., in. •

LT ngth of transfer, in.

m Coefficient of friction

M Bending moment. ]b-in.

M Poisson's ratio for cor.•crete

ms Poisson's ratio for steel 1i

n Modular iatio, sta.to concrete (i.e. I)A s/ c

All

APPENDDC A: DESIGN COMPUTATIONS

Notations Used ir. Computatiens

A Cross-sectional area of bea=, ir.-

2Ac Cross-sectional area of concrete, in.I2A s Cross-secti4onal area of steel, inl.

b Width of beam, in.

d Depth of beam, in.

D Diameter of stramnd, in.I

e Eccentricity, in.

E Ec Modulus of elaszicity for the, concrete, psi

MEs odulus of elasticity for the steel, psi

i f Compressive stress in concreze, psi

f' Compressive strength in concrete, pzi, at 28 dkys agec -

fe Effective prestres, - :n steel, ps-I

1f. Initial prestress in steel, psi

F Force, lb

I Moment of inertia of section., LI. L

Moment of inertLia sra-nsformtd, in.

L Rffective length of beam, in.

L_ erngth of transfer, in.

m Coefficient of friction

M Bending moment, ri-in.

M Poisson's ratio for concre-e IMS Poisson's ratio for steel

n Modular ratio, steel to concrete (i.e. %/B c

,:1

-7 *,'

A2

P Load, lb

Q.Statical moment, in.

* St Principa~l tensile str-ess, psi

v, Bond stress, psi

v Shearring stress, psiK V Total shear-, lb

v Total shear carried by concrete, lb

y :Perp.endicular distance from center of gravity (centro-id) of concretesection to outer fiber, in.

At' Loss of prestress in steel, psisV

Z-71 -'y

A3

Design Assumptions

Steel: Cross-sectio~al area per strand =0.0352 in.2

Minimum ultimate tensile strength = 238,000 psiMaximum tensioning stress = 70% ultimate strengthYield strength at 0.7% elongation = 67% ultimate strength

Concrete: Comressive strength at 28 days age = 6000 psiPoisson's ratio = 0.24 6Modulus of elasticity (Ec) = 5 X 10 psi

Loss of vrestress: 15% due to creep and relaxation

ComputatiOnS

Stress distribution fc - + Fey + --

Sp P

2 5;L/71ltt

73-.F = 238,000 x 0.7 x 0.3168 = 52,779 - 15%* loss (7917)

= 44,862 lb

A =4.5 x 9 40.5 sq in.

e =1.75 in. .. ".-i-y = d/2 = 4.5 in.1.7 in"s"

I b13/12.2 273.4 i.

14=- 3

L- 75 in. i

P= 6319 lb at lO8% o+ prestress (exceeds compression in bottom fibers)

P = 5833 lb at 100% of preotress (equals compression in bottoim fibers) 7

* Esti-,ated 15% loss of •restress due to creep and relaxation.

At transfer

P =520. -1303 psi, Fey 52,779 x 1.75 x 4.5

AI46 273.4 1520 Psi

-1520 psi Zi

Mt~rceeD~re~at±n psi 2823 psi

TOP -1303 + 1520 +217 psiBottom = -1303 - 1520 = -2823 Psi ...... .2823 ps--After creeD and relaxation ;•

SF -44,862 F 144,862 x 1.75 x 4.5! "A= 40.5 -- 1108 psi, 27e ±19" sA 1 -z3.4

&18, psi

Top =-0o8 + 1292 +184 psiBottc-m = -1108 - 1292 .= -2400 ipsi -2400 psi

Stress due to F + P Uafter creen and relaxation

At 108% (2400 x 1.08 2592, use 2600), M x3. - 2600 psi

At 10%, 145,825 x 4.52400psI 2773.4

(At 108%, P 6319, M = 6319 x 25 = 157,975 ib--n.)

(At 104, P 5833, M = 5833 x 25 = 145,825 lb-in.)At 108% At 100%Top = +184 -2600 -2416 psi T:p=+184 -2 4 00=2220psi

Bottom =-2400 + 2600 = +200 psi Bottom= -2400 + 2400 = 0

-2416 psi -2216

+200ps0

.-. +- -. - + + + + .+ ++ . + +. + • + . .. . . .

A5

Q 6319 x 14. .6 234 psi max.+ v =•-- =273.4. x 4.5V = total shear = 6319 ib 234 psimC

Q = statical moment, at.•=-• 45.6 in. P

Principal tension(occurs 6 in. from top)

St =4v2 + (fc/2) 2 " (f/2)' = compressive stress at level

4.5 in. from top, St = .234 +554 554. 47 psi

5 in. from top, St V2302 + 492 - 492 51 psi

6 in. from top, St =20e.+ 3692 - 369 54 Psi

S7 in. from top, St 611.2+2462 -246 50 psi

Bond stress (appliesonly to uncracked beams)

VcYflD 6319 x 1.75 x.6 x 0.25 15 psimax

u 4i7t 4 x 273.4

V = total shear carried by concrete, lbC

n =modular ratio, steel to concrete = 6

y = distanc-! from centroid to steel 1.75 in.

D = diameter of strand = 0.25 in.

it= moment inertia transformed

Length of transfer of vrestress*

*t M•) -M] m~ - itI e

0.25 ( 6 166,600 158,781

Lt = 2 x 0.3 0.3 - 5, 000,0001 2(166,600) - 158,781 = 9.4 in.

See T. Y. Lin, DesiEn of Prestressed Concrete Structures, ist ed.John Wiley and Sons, Inc. (New York, N. Y., 1955).

rori ISi 'A6

where

D = diameter of strand 0.25 in.

*m = coefficient of friction = 0.3 (assumed)

M = Poisson's ratio, concrete = 0.24S~ci = Poisson's ratio, steel = 0.30

E = modulus cf elasticity, concrete = 5 x 10 psic

fi = initial prestress in steel

fe = effective prestress in steel

1 f =f. -Af

e 1 s

nF 6 x 166,6o0 x 0.3168s A 40.5 = 7819 psi

c _ _0.n = modular ratio, steel to concrete =6.0

F =f.A

As =area of steel = 0.3168 sq in.

A = area of concrete = 40.5 sq in.

End condition due to loading

Assume 10-in. length of transfer from 0 to full prestress with

i linear distribution along length of transfer.

I'[L 0 vv..mi tension because of P Pi Full co-reso end prestess

0 compression beginning of transfer

.Gra~ically (at 108- load)Distance, in. Compression Residual

From From Due to Pre- Tension Due to Stress atEnd Reaction stress (-), psi Moment (+), psi Bottom Fiber, psi

'28 25 -2400 +2600 +200

26 23 -2400 +2392 -8

- ' (Continued)

A7

SDistance, in. Comprcssion. ResidualFrom From Due to Pre- Tension Due to Stress atEnd React%-ion s~tress (., si moment (÷,pi Bot~tom Fiber,, psi

10 7 -2400 +728 -16728 5 -1920 +520 -14oo6 3 -14-'40 +312 -11234 1 -96o +104, -856 6K 2 0 -480 0 -480

End - 0 0 0End condition appears safe.

Comwressive stress concreteAt transfer = 0.47 f'

C.•

Design = 0.37 V' (100% loading)

Design = 0.40 f' (108-% loading)C

Tensile stress steel

At transfer = 0.70 ulti•-ate strength

Design = 0.60 ultir.a.te strengthTensile stress concrete

At transfer = 217 psi = 0.036 fcDesign = 0 psi (I-0% loading)

Design = 200 psi (108% loading)Shear 234 psi = 0.039 f'

Bond = 15 Psi

Transfer length = 9 in.

ii!I

iii "i!Ii ii