Structures and Materials Test

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STRUCTURES AND MATERIALS

TEST LABORATORY

CIVIL ENGINEERING

COLLEGE OF ENGINEERING

UNIVERSITY OF WISCONSIN

JANUARY 2008

SELF CONSOLIDATING

CONCRETE:

CREEP AND SHRINKAGE

CHARACTERISTICS

BY

PROF. M.G. OLIVA

PROF. S. CRAMER


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Self Consolidating Concrete:Creep and Shrinkage

Characteristics

Report To

Spancrete and County Materials

Prof. Michael G. Oliva

Prof. Steven Cramer

Department of Civil and Environmental Engineering

University of Wisconsin

Madison, Wisconsin

January 2008


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Abstract

Shrinkage and creep characteristics of concrete are significant factors in the design of

prestressed concrete structures. Shrinkage and creep both directly affect the degree to

which the concrete changes in length over time. These changes in length are accompaniedby a change in length of the prestressing tendons which then leads to a loss of prestress,

and may also cause vertical deflections in girders.

The objective of the test program described here was to measure the shrinkage and creep

characteristics of SCC mixes used by Spancrete and County Materials to evaluate

whether they are acceptable for use in precast, prestressed concrete highway bridgegirders. A normal concrete mix from Spancrete was used as a basic reference. A simple

SCC mix and a second SCC mix that included granulated slag were sampled from

Spancrete. A simple SCC mix was sampled from County Materials.

Based on the results and observations, it should be concluded that the SCC mixes from

Spancrete do in fact exhibit high dimension change due to creep and shrinkage. The creepand shrinkage in the County SCC mix was about the same as the Spancrete normal mix.Creep and shrinkage strains, approximately twice that of a normal mix, do constitute a

significant increase in the effects of creep and shrinkage which, in turn, would likely

result in less than expected long term prestress in a girder after losses (if the higher losswas not accounted for in design) and undesirable girder behavior.

Acknowledgements

The work described here was conducted at the University with joint funding provided by

Spancrete and County Materials. A group of UW graduate students contributed to theproject including Paul Georgieff, Dominique Piette, Jeff Barker, Han Ug Bae, and Tung

Doan.


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Table of Contents

Abstract .............................................................. iAcknowledgements ............................................ ii

Problem Definition ............................................. 1

Objectives .......................................................... 1

Scope .................................................................. 1

Tests and Testing Procedures .............................. 21. Shrinkage tests .......................................... 2

2. Creep tests ................................................. 4

3. Other tests ................................................. 7

Test Specimen Matrix ........................................ 9

Test Results ........................................................ 11Slump, Slump Flow, and J-ring Tests ............ 11

Strength and Modulus Tests ........................... 13

Shrinkage Test Results ................................... 16Creep test Results ........................................... 20

Executive Summary ............................................ 30

Flowability ..................................................... 30Elastic Modulus ............................................. 30

Concrete Strength ........................................... 31

Creep and Shrinkage Combined .................... 31Shrinkage ....................................................... 32

Creep .............................................................. 32

Comparison with AASHTO .......................... 33

Conclusions ......................................................... 34


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Problem Definition:

Shrinkage and creep characteristics of concrete are significant factors in the design of

prestressed concrete structures. Shrinkage and creep both directly affect the degree to

which the concrete changes in length over time. These changes in length are accompanied

by a change in length of the prestressing tendons which then leads to a loss of prestress,and may also cause vertical deflections in girders. Therefore, it is important that all

concrete mixes exude acceptable long-term shrinkage and creep characteristics for use inprestressed structures. As a result, the proposed self-consolidating concrete (SCC) mixes

produced by Spancrete and County Materials were subject to testing for the purpose of

establishing their shrinkage and creep characteristics.

Objective:

The objective of the test program described here was to measure the shrinkage and creep

characteristics of SCC mixes used by Spancrete and County Materials to evaluatewhether they are acceptable for use in precast, prestressed concrete highway bridgegirders.

Estimating accurate prestress loss in girders due to shrinkage and creep is critical toensure that sufficient prestress still exists in the girder to resist highway truck loading

over its service life. Unexpected high shrinkage or creep could result in lower than

expected prestress, increased deflections and undesirable girder behavior.

Scope:

The primary goal of this study was to check that the Spancrete and County Materials

SCC mixes do not exhibit high dimension change due to shrinkage and creep. This wasaccomplished by experimentally measuring dimension change over a long period of time.

A measure of what constitutes high dimension change was attained by simultaneously

measuring the dimension change in a standard concrete mix that is currently being usedfor production of highway girders and comparing with the new SCC mixes.

Three basic concrete mixes were examined (with the designations in parenthesis): Standard aggregate mix currently being used in highway girders (N) 3/8 SCC concrete mix developed by Spancrete (S)

SCC mix developed by County Materials (C)A fourth alternate mix was also examined for possible future use:

3/8 Spancrete SCC concrete mix that includes ground granulated blast furnaceslag(GGBFS) (SS)

Each of the mixes were subjected to: 1.) shrinkage tests, 2.) creep tests, 3.) strength tests,

4.) modulus of elasticity measurements, 5.) slump or cone flow measurement, and 6.) J-

ring flow measurement.


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Samples from three different batches were obtained for each of the three differentconcrete mixes to ensure a random sampling of the concrete.

The concrete test specimens were produced under University supervision from concrete

that was batched and mixed at the Spancrete and County Materials plants and supplied tothe University.

Specific details of the tests performed are described in the following sections for eachtype of test.

Tests and Testing Procedures:

Test procedures generally following ASTM standard procedures with some exceptions asnoted in the descriptions below. Deviations from standard procedures are contemplated in

the ASTM standards. The deviations were not judged as critical for the purpose of thistest program since the primary purpose was to compare the behavior of the SCC concretewith the normal aggregate mix. Both sets of specimens were subjected to the same

deviations and comparison of results was valid.

While concrete sample production took place at the Spancrete and County Materials

plants, most of the tests were conducted at the University of Wisconsin - Madison. Only

the slump or cone flow and the J-ring tests were conducted at the Spancrete and County

Materials plants immediately after the concrete was batched and mixed.

1. Shrinkage tests:

Shrinkage tests were conducted following the ASTM C-157 Standard Test

Method for Length Change of Hardened Hydraulic-Cement Mortar and Concrete.

ASTM C-157 specifies that the specimens are to be maintained in an environment

at 73 +/- 3 degrees Fahrenheit and a relative humidity of 50 +/- 4% and that the

air movement past the specimens shall be such that the evaporation is 77 +/-30

mL/(24h) from an atmometer.

The storage conditions at the University met the temperature requirement, but did

not attempt to match the relative humidity or air movement requirements. This

variation was made to reduce the cost of setting up special storage conditions forthis test. Since both the normal and the SCC mixes were subjected to the same

conditions, the measured differences in shrinkage still provided a valid basis forjudgment of the SCC mix.

Shrinkage test specimens were 4-inch square prisms 11.25 inches in length and

were cast at the Spancrete and County Materials plants. The test specimens were


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initially subjected to the same curing conditions during the first 24 hours

(temperature and moisture) as used in the highway bridge girder curing.

The test prisms were placed in water for 30 minutes before initial measurement.

This initial immersion was a variance from the C-157 procedure with lime water

submersion and was deemed appropriate for the purpose of measuring prestressloss in the highway bridge girders.

The initial length readings were taken subsequent to the immersion. ASTM C-157specifies that after the initial readings, the specimens are to be stored in lime

water to 28 days and then in air storage as noted above. However, since the creep

test was started at 2 days of age, it was deemed appropriate to deviate fromASTM in this respect. After the prisms were removed from their molds and held

in water for 30 minutes, they were then kept at room conditions matching those of

the creep specimens - allowing the measurements of the creep specimens to be

corrected for the measured shrinkage under the same temperature and humidity

conditions.

Succeeding length readings were taken at 4, 8, 14, and 28 days after casting,followed by bi-monthly, then monthly readings using an HM-250D Length

Comparator with digital indicator.

Three specimens cast from different batches of each of the four different concrete

mixes were measured. (Spancrete had an additional fourth batch described later.)

Figures 1 3 show shrinkage specimen preparation and testing.

Figure 1: 4 X 4 X 11 concrete prisms were cast at the Spancrete and

County Materials plants which were then transported to the University. At the

University, the prisms were stripped from the molds followed by initial

shrinkage readings and storage.


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2. Creep tests:

The creep testing generally followed ASTM C-512 Standard Test Method for

Creep in Compression.

ASTM C-512 specifies that the creep test specimens be stored at 73.4 +/- 2

degrees Fahrenheit and a relative humidity of 50 +/- 4%. The storage conditions

for this test varied from those specified in C-512, but aimed to meet therequirements described previously for the shrinkage test specimens. As stated

previously, these variations were made to reduce the cost of setting up special

storage conditions for this test. Since both the normal and the SCC mixes weresubjected to the same conditions, the measured differences in creep provide a

valid basis for judgment of the SCC mix.

ASTM C-512 specifies that the length between header plates used to apply a

constant compression force to the test specimens cannot be greater than 70 inches

(5.83 feet). A length of 84 inches (7 feet) was used in these tests to accommodate6 test specimens in series.

The ASTM-specified ages at initial loading (2 days, 7 days, 28 days, 90 days and

1 year) were not used for these tests. The date of initial loading for the primary setof test specimens was selected as 2 days of age to simulate the age at which

bridge girders are subjected to prestress. A second set of specimens was loaded at

Figure 3: Shrinkage prism

readings were performed in

accordance with ASTM C-157.

Figure 2: The HM-250D

Length Comparator with

digital indicator was used to

measure shrinkage at the

University.


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a 28 day reference age for initial loading. Due to initial problems in the creep

testing, one set of Spancrete specimens was inadvertently started at 12 days andanother at 32 rather than 2 and 28 days. An replacement set of specimens was

subsequently obtained (labeled G) from Spancrete and testing was started at 2

days. Thus, for some Spancrete mixes there was one set of specimens started at 2

days and another set at 12 days.

ASTM specifies that the specimens should be loaded at an intensity of not more

than 40% of the compression strength at time of loading. Since these tests weresimulating prestressed girders, the ASTM load intensity was modified.

The stress in the concrete of prestressed girders, adjacent to the steel strands,varies along the length of a girder and varies with age and applied live loading. At

time of prestress transfer, the concrete compression stress near the end of a girder

may reach 3800 psi and may be 3500 psi near the center of the girder. Under

permanent dead load from the bridge structure, the concrete compression stress at

midspan may drop to near zero, while remaining high at the girder end.

For the purpose of this study, (1) the specimens that were loaded at 2 days of agewere to be subjected to 3800 psi for the first 28 days. After 28 days, the

compression load was to be reduced to 2000 psi to simulate the effect of placing

the weight of a concrete deck on bridge girders and reducing the initialcompression at the bottom of the girder. (2) The specimens loaded at 28 days age

were to receive only the 2000 psi of compressive stress.

Creep measurement were conducted for a period of 1 year after the loading was

applied to the specimens.

Six specimens cast from different batches of each of the four different concrete

mixes were measured. Half the specimens were to be loaded at 2 days, while the

other half of the specimens were loaded at 28 or 32 days. One unplanned set wasloaded at 12 days. Figures 4-11 show the creep test setup.

Figure 4:Metal tabs were placed

10 apart on both sides of all creep

test 6 X 12 cylinders with epoxy for

future readings.

Figure 5:A temporary wooden frame

aided in building each creep rig. 6 X

6 cylinders were cut and placed at

each end followed by bearing plates

and tension tendons.


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Figure 7:A spherical head nut

placed at the end of the jack was

used to apply pure axial load while

the dual plates were used to

maintain load after jacking.

Figure 6: Chucks were placed

around each tension strand to

sustain the desired compressive

load on the creep rigs.

Figure 8:An Enerpac cylinder jack

was used to pull the strands into the

desired tensile stress, placing the

creep cylinders under compression.

Figure 9:An Enerpac Hush-Pup

electric pump was connected to the

jack enabling the jack to apply the

load to the creep rigs.


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3. Other tests:

The remaining tests (strength, modulus, slump [ASTM C1611/C1611M-05] andJ-ring [ASTM WK7552]) were conducted at various time intervals. Figures 12

through 19 show the tests being conducted at the plant and lab.

Figure 10:After assembly and loading,

the creep rigs were hung vertically on a

steel suspension system for storage.

Figure 12:All cylinders and

prisms were cast at Spancrete

and County Materials plants

in accordance with ASTM.

Figure 13:J-ring flow tests were performed

on every batch used for shrinkage prisms and

creep cylinders.

Figure 11:A Soiltest multi-length

strain gauge set was used to take

creep readings from the metal tabs.


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Modulus and Strength Tests

Figure 14:In addition to J-

ring tests, slump flow tests

were also performed on every

batch at the Spancrete andCounty Materials plants.

Figure 15: Slump flow was

measured in accordance with

ASTM C1611 standards.

Figure 17:An HM-131

Compressometer/Extensometerwas attached to the loaded

cylinders to obtain vertical and

radial displacements

Figure 16:Both modulus and strength

tests were performed in the STML Labat the University with a SATEC

machine following ASTM standards.


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Test Specimen Matrix:

Three batches (1, 2, and 3) per mix were used to ensure random sampling of concretewith the designations as follows used for specimens. A later fourth additional set of

samples was taken from the Spancrete plant and labeled with the G designation.

Shrinkage tests:1 prism was taken for each batch,

County Materials SCC Mix: C-1, C-2, C-3 Spancrete Standard Mix: N-1, N-2, N-3, N-G Spancrete SCC Mix: S-1, S-2, S-3, S-G Spancrete SCC w/ slag Mix: SS-1, SS-2, SS-3, SS-G

(Shrinkage readings corresponded with the creep readings)

Creep tests:multiple cylinders were taken for each batch,

County Materials SCC Mix:o Batch 1: C-1A, C-1Bo Batch 2: C-2A, C-2Bo Batch 3: C-3A, C-3B

(A cylinders were tested starting at 2 days age, the B at 28 days)

Figure 18:After modulus

testing, each cylinder

underwent ultimate compressive

strength testing in accordance

with ASTM standards.

Figure 19: Strength test

cylinders were compressed to

failure. Each failure was then

classified under ASTM failure

mode specifications.


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Spancrete Standard Mix:o Batch 1: N-1B, N-1Do Batch 2: N-2B, N-2Do Batch 3: N-3B, N-3Do N-G1

(G began testing at 2 days of age, D at 12, and B at 32 days) Spancrete SCC Mix:

o Batch 1: S-1B, S-1Do Batch 2: S-2B, S-2Do Batch 3: S-3B, S-3Do S-G1

(G began testing at 2 days of age, D at 12, and B at 32 days) Spancrete SCC w/ slag Mix:

o Batch 1: SS-1B, SS-1Do Batch 2: SS-2B, SS-2Do Batch 3: SS-3B, SS-3Do

SS-G1(G began testing at 2 days of age, D at 12, and B at 32 days)

Strength and modulus tests: County Materials SCC Mix:

18 cylinders were taken, 6 cylinders for each batch,o Batch 1: C-1A, C-1B, C-1C, C-1D, C-1E, C-1Fo Batch 2: C-2A, C-2B, C-2C, C-2D, C-2E, C-2Fo Batch 3: C-3A, C-3B, C-3C, C-3D, C-3E, C-3F

(A cylinders were tested at 1 day of age, B at 7 days, C 28 days,D 90, and E and F 500 days)

Spancrete Standard Mix:o Batch 1: N-1A, N-1B, N-1Co Batch 2: N-2A, N-2B, N-2Co Batch 3: N-3A, N-3B, N-3Co N-G2

(A cylinders were tested at 1 day, B at 7, and C and G at 28 days;N-B cylinders were tested for strength, but not modulus)

Spancrete SCC Mix:o Batch 1: S-1A, S-1B, S-1Co Batch 2: S-2A, S-2B, S-2Co Batch 3: S-3A, S-3B, S-3Co S-G2

(A cylinders were tested at 1 day, B at 7, and C and G2 at 28 days;

S-B cylinders were tested for strength, but not modulus) Spancrete SCC Mix w/ slag:

o Batch 1: SS-1A, SS-1B, SS-1Co Batch 2: SS-2A, SS-2B, SS-2Co Batch 3: SS-3A, SS-3B, SS-3Co SS-G2


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(A cylinders were tested at 1 day, B at 7, and C and G2 at 28 days;

SS-B cylinders were tested for strength, but not modulus)

Creep Rig Setup: (cylinders placed in each rig)o Rig 1: S-1D, SS-3D, SS-2D, SS-1D

o Rig 2: N-1D, N-2D, N-3D, S-2D, S-3Do Rig 3: S-G1, SS-G1, N-G1, C-1B, C-3Bo Rig 4: S-2B, SS-2B, SS-3B, N-2B, N-3Bo Rig 5: N-1B, SS-1B, S-3B, S-1Bo Rig 6: C-1A, C-2A, C-3A, C-2B

Test Results:

Slump, Slump Flow, and J-ring Tests:

The following tables display the results of the tests performed at the Spancrete and

County Materials plants where batching and casting occurred.

Table 1: Spancrete Standard Mix Batching Information

Standard 3/4' aggregate mix (N) - Spancrete 4/13/2006

Slump Test Prisms 8 Cylinders (Times)

BatchTime of

Batching Time Slump (in)Temp

(F)Time ofcasting

LooseTime

2Creep

6 Strength &Modulus

1 13:05 13:10 7.75 74 13:15 14:45 13:15 13:162 13:35 13:38 8.5 74 13:40 14:45 13:41 13:39

3 13:57 14:01 8.5 73 14:03 14:45 14:01 14:03

Table 2: Spancrete SCC Mix Batching Information

Self-Consolidating Concrete 3/8 aggregate mix (S) Spancrete 4/13/2006

J-ring Test Slump Flow Test 73.3 F Prisms8 Cylinders

(Times)

BatchTime ofBatch

TimeDiameter

1 (in)Diameter

2 (in)Time

Diameter1 (in)

Diameter2 (in)

Timeof

casting

LooseTime

2Creep

6Strength

&Modulus

1 9:35 9:39 16.75 15.5 9:39 19.5 19 9:40 10:32 9:47 9:472 9:53 9:56 16.25 15.75 10:00 18 17.5 9:59 10:55 9:57 9:593 10:09 10:12 21.25 19.75 10:12 21.5 21 10:18 10:55 10:16 10:14


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Table 3: Spancrete SCC with slag Mix Batching Information

Self-Consolidating Concrete 3/8 aggregate with Slag mix (SS) Spancrete 4/13/2006

J-ring Test Slump Flow Test 69 F Prisms8 Cylinders

(Times)

BatchTime ofBatching

TimeDiameter

1 (in)Diameter

2 (in)Time

Diameter1 (in)

Diameter2 (in)

Timeof

casting

LooseTime

2Creep

6Strength&

Modulus

1 8:35 8:45 22 20 8:45 25.25 25.25 8:53 9:53 8:50 8:47

2 8:50 9:04 26.25 24.25 9:06 26.5 27.5 9:09 10:09 9:07 9:05

3 9:19 9:21 25.75 25.25 9:25 26.5 26 9:27 10:27 9:28 9:23

Table 4: County Materials SCC Mix Batching Information

Self-Consolidating Concrete mix (C) County Materials 8/31/2006

J-ring Test Slump Flow Test Prisms

8 Cylinders

(Times)

BatchTime ofBatching

TimeDiameter

1 (in)Diameter

2 (in)Time

Diameter1 (in)

Diameter2 (in)

Timeof

casting

LooseTime

2Creep

6Strength

&Modulus

1 10:50 11:00 21.5 20 11:05 22 21 11:10 11:30 11:00 11:00

2 11:40 11:47 25 23.5 11:52 25 23 11:50 12:20 11:50 11:50

3 12:00 12:10 26 24 12:15 25.5 25.5 12:12 12:30 12:10 12:10

Table 5: Spancrete Standard G Mix Batching Information

2-Day Standard Mix (NG) - Spancrete 5/10/2006

Slump TestTime of

Batching Slump(in)

Temp (F)AirContent(%)

UnitWeight(pcf)

9:40 7.75 74 2.3 154.8

Table 6: Spancrete SCC G Mix Batching Information

2-Day SCC Mix (SG) - Spancrete 5/10/2006

Slump Flow - 73 FTime of

Batching Diameter1 (in)

Diameter2 (in)

AirContent

(%)

UnitWeight(pcf)

9:20 22 22 5.6 144.2

Table 7: Spancrete SCC w/ slag G Mix Batching Information

2-Day SCC Mix with slag (SSG) - Spancrete 5/10/2006

Slump Flow - 71 FTime of

Batching Diameter1 (in)

Diameter2 (in)

AirContent

(%)

UnitWeight(pcf)

9:00 25.5 25.75 6.5 142.7


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Strength and Modulus Tests:

Modulus Test Results:

Sample

Modulus of Elasticity

"E" (based on 7.1 ofASTM C469-02) (psi)

Poisson's Ratio

"" (based on 7.2of ASTM C469-02)

SS2A 2466000 0.22

SS3A 2785000 0.12

S1A 3029000 0.14

S2A 2911000 0.14

S3A 2992000 0.18

N1A 4495000 0.12

N2A 4403000 0.21

N3A 4405000 0.25

C1A 4776000 0.18

C2A 4841000 0.13C3A 4376000 0.18

Table 8: 1-Day Modulus Test Results

SampleModulus of Elasticity"E" (based on 7.1 ofASTM C469-02) (psi)

Poisson's Ratio"" (based on 7.2of ASTM C469-02)

C1B 5089000 0.21

C2B 4975000 0.16

C3B 4681000 0.19



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Poisson's Ratio"" (based on 7.2of ASTM C469-02)

SS1C 3286000 0.22

SS2C 3904000 0.23SS3C 3668000 0.21

SSG2 4026000 0.01

S1C 3716000 0.22

S2C 3511000 0.21

S3C 3564000 0.21

SG2 4667000 0.31

N1C 6255000 0.14

N2C 5140000 0.21

N3C 5482000 0.25

NG2 5518000 0.28

C1C 5035000 0.12C2C 4986000 0.08

C3C 4822000 0.12



Poisson's Ratio ""(based on 7.2 ofASTM C469-02)

C1D 4350000 0.06

C2D 4994000 0.11

C3D 4887000 0.11



Poisson's Ratio ""(based on 7.2 ofASTM C469-02)

C1E 5910000 0.18

C2E 5474000 0.13

C3E 5238000 0.12

C1F 5404000 0.18

C2F 5890000 0.11

C3F 5127000 0.12



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Strength Test Results:

Strength Tests

SampleUltimateLoad (lb)

CompressiveStrength (psi)

SS1A 157950 5530SS2A 165400 5870

SS3A 168510 5940

S1A 179980 6380

S2A 185120 6500

S3A 179100 6360

N1A 241570 8470

N2A 230980 8140

N3A 226770 7950

C1A 199850 6970

C2A 198050 7000

1-DayStrength

C3A 193320 6840SS1B 184830 6530

SS2B 202400 7100

SS3B 204210 7210

S1B 201220 7040

S2B 216000 7560

S3B 209180 7360

N1B 272480 9620

N2B 273150 9660

N3B 265830 9420

C1B 223530 7880

C2B 222860 7850

7-DayStrength

C3B 208810 7280

SS1C 214410 7590

SS2C 219750 7780

SS3C 235720 8380

SSG2 230800 8150

S1C 228590 8031

S2C 245160 8690

S3C 224430 7940

SG2 208850 7400

N1C 284910 10077

N2C 297990 10440

N3C 299390 10500

NG2 293830 10230

C1C 246780 8650

C2C 245940 8560

28-DayStrength

C3C 239520 8450

Table 12: Strength Test Results


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SampleUltimateLoad (lb)

CompressiveStrength (psi)

C1D 280550 9920

C2D 286770 1004090-Day

Strength

C3D 273830 9650C1E 291310 10290

C2E 303310 10710

C3E 295360 10270

C1F 289240 10230

C2F 310180 10880

392-DayStrength

C3F 283700 10010

Table 13: Strength Test Results

Shrinkage Test Results:

The shrinkage data is plotted as decreasing length on the y-axis. Recall that the gagelength of the prisms was 11.25 inches on average.

Spancrete Standard Prisms - Shrinkage Strain

-0.000200

-0.000100

0.000000

0.000100

0.000200

0.000300

0.000400

0.000500

0.000600

0 100 200 300 400 500 600

Age (Days)

ShrinkageStrain

(in/in)

N1 N2 N3 N-G

Figure 20: Spancrete Standard Mix Shrinkage


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Spancrete SCC Prisms - Shrinkage Strain

-0.000200

0.000000

0.000200

0.000400

0.000600

0.000800

0.001000

0.001200

0 100 200 300 400 500 600

Age (Days)

Shrinkage

Strain

(in/in)

S1 S2 S3 S-G Figure 21: Spancrete SCC Mix Shrinkage

Spancrete SCC w/ Slag Prisms - Shrinkage Strain

-0.00020

0.00000

0.00020

0.00040

0.00060

0.00080

0.00100

0.00120

0 100 200 300 400 500 600

Age (Days)

Shrinkage

Strain

(in/in)

SS1 SS2 SS3 SS-G

Figure 22: Spancrete SCC with Slag Mix Shrinkage


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County Materials SCC Prisms - Shrinkage Strain

0.000000

0.000100

0.000200

0.000300

0.000400

0.000500

0.000600

0.000700

0 50 100 150 200 250 300 350 400

Age (Days)

Shrinkage

Strain

(in/in)

C! C2 C3

Figure 23: County Materials SCC Mix Shrinkage

Shrinkage Strain Averages

-0.00020

0.00000

0.00020

0.00040

0.00060

0.00080

0.00100

0.00120

0 100 200 300 400 500 600

Age (Days)

Strain(

in/in)

N S SS C G

Figure 24: Spancrete & County Materials Shrinkage Averages:

N=Spancrete normal, S=Spancrete SCC, SS=Spancrete SCC plus slag, C=County SCC

G=Spancrete SCC batch 2


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Creep Test Results:

The following plots show the results of readings taken directly on the creep cylinders. As

a result, the strain values represent the effects of both creep and shrinkage combined. The

separate creep values can be obtained by correcting for the shrinkage results shown in the

previous section since the cylinders and prisms were subjected to identical storageconditions. Note that the drop in strain at 28 days for the early loaded specimens was due

to the change in the applied stress level at that time.

Batch Results:

N-D loaded at 12 days - Creep + Shrinkage Strains

0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

0 100 200 300 400 500 600

Time (days)

Strain

(inch/inch)

N1 N2 N3 All in rig 2

Figure 25: Spancrete 12-Day loading Normal Mix Creep + Shrinkage


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N-B loaded at 32 days - Creep + Shrinkage Strains

0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

0.0014

0.0016

0.0018

0 100 200 300 400 500 600

Time (days)

Strain

(inch/inch)

N1-32 N2-32 N3-32 N1 is in rig 5; N2 & N3 in rig 4

Figure 26: Spancrete 32-Day loading Normal Mix Creep + Shrinkage

S-D loaded at 12 days - Creep + Shrinkage Strains

0.000000

0.000500

0.001000

0.001500

0.002000

0.002500

0 100 200 300 400 500 600

Time (days)

Strain

(inch/inch)

S1 S2 S3 S1 in rig 1; S2 & S3 in rig 2

Figure 27: Spancrete 12-Day loading SCC Mix Creep + Shrinkage


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S-B loaded at 32 days - Creep + Shrinkage Strains

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0 100 200 300 400 500 600

Time (days)

Strain

(inch/inch)

S1-32 S2-32 S3-32

S2 in rig 4; S1 & S3 in rig 5

Figure 28: Spancrete 32-Dayloading SCC Mix Creep + Shrinkage

SS-D loaded at 12 days - Creep + Shrinkage Strains

0.000000

0.000500

0.001000

0.001500

0.002000

0.002500

0.003000

0 100 200 300 400 500 600

Time (days)

Strain

(inch/inch)

SS1 SS2 SS3 All in rig 1

Figure 29: Spancrete 12-Day loading SCC w/Slag Mix Creep + Shrinkage


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Figure 30: Spancrete 32-Day loading SCC w/Slag

Mix Creep + Shrinkage

G loaded at 2 days - Creep + Shrinkage Strains

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0.0035

0.004

0 100 200 300 400 500 600

Time (days)

Strain

(inch/inch)

NG 2day SG 2day SSG 2day All in rig 3

Figure 31: Spancrete 2-Day G-Specimen Creep + Shrinkage

NG=normal mix, SG=SCC, SSG=SCC plus slag

SS-B loaded at 32 days - Creep + Shrinkage Strains

0

0.0005

0.001

0.0015

0.002

0.0025

0 100 200 300 400 500 600

Time (days)

Strain

(inch/inch)

SS1-32 SS2-32 SS3-32 SS1 in rig 5; SS2 & SS3 in rig 4


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C-A loaded at 2 days - Creep + Shrinkage Strains

-0.0004

-0.0002

0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

0.0014

0 50 100 150 200 250 300 350 400

Time (days)

Strain

(in/in)

C1 C2 C3 All in rig 6

Figure 32: County Materials 2-Dayloading SCC Mix Creep + Shrinkage

Note: The metals tabs were broken off during erection in the

University lab which explains the temporary flux in the

C1 creep readings during the first 30 days.

C-B loaded at 28 days - Creep + Shrinkage Strains

0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

0 50 100 150 200 250 300 350 400

Time (days)

Strain

(in/in)

C1 C2 C3 C1 & C3 in rig 3, C2 in rig 6

Figure 33: County Materials 28-Day loading SCC Mix Creep + Shrinkage


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Start day comparisons within mixes:

Spancrete Normal Mix - Creep + Shrinkage Strain

0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

0.0014

0 50 100 150 200 250 300 350 400 450 500

Days After Loading

Strain

(in/in)

N12 N32 NG-2

Figure 34: Spancrete Normal Mix, Creep + Shrinkage for 2, 12, and 32 day starts

Spancrete SCC Mix - Creep + Shrinkage Strain

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0.0035

0.004

0 50 100 150 200 250 300 350 400 450 500

Days After Loading

Strain

(in/in)

S12 S32 SG-2

Figure 35: Spancrete SCC Mix, Creep + Shrinkage for 2, 12, and 32 day starts


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Spancrete SCC Mix w/ Slag - Creep + Shrinkage Strain

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0 50 100 150 200 250 300 350 400 450 500

Days After Loading

Strain

(in/in)

SS12 SS32 SSG-2

Figure 36: Spancrete SCC w/Slag Mix, Creep + Shrinkage for 2, 12, and 32 day starts

County Materials SCC Mix - Creep + Shrinkage Strain

0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

0 50 100 150 200 250 300 350

Days After Loading

Strain

(in/in)

C2 C28

Figure 37: County Materials SCC Mix, Creep + Shrinkage for 2 and 28 day starts


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Group Average Comparisons:

Spancrete mixes loaded at 12 days - Creep + Shrinkage Strain

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0 100 200 300 400 500 600

Days after casting

Strain(inch/inch)

N S SS

3800psi up to 28 days, then 2000psi

`

Figure 38: Spancrete Mixes loaded at 12 days

N=normal, S=SCC, SS=SCC plus slag


0

0.0005

0.001

0.0015

0.002

0.0025

30 80 130 180 230 280 330 380 430 480 530

Days after casting

Strain

(inch/inch)

N S SS




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0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0.0035

0.004

0 100 200 300 400 500 600

Days after casting

Strain

(inch/inch)

N S SS



Note: Group averages for County Materials SCC mixes were shown in Figure 37


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Loaded at 28 days - Pure Creep Strain

0.00000

0.00020

0.00040

0.00060

0.00080

0.00100

0.00120

0.00140

0.00160

0.00180

0 50 100 150 200 250 300 350 400 450 500

Time (days)

Strain

(inch/inch)

N S SS C

Figure 41:Comparison: pure creep strains- loaded at 28 days

N=Spancrete normal, S=Spancrete SCC, SS= Spancrete SCC + slag, C=County SCC

Loaded at 2 days - Pure Creep Strain

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0 50 100 150 200 250 300 350 400 450 500

Time (days)

Strain

(inch/inch)

N S SS C

Figure 42: Comparison: pure creep strains- loaded at 2 days

N=Spancrete normal, S=Spancrete SCC, SS= Spancrete SCC + slag, C=County SCC


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Executive Summary:

Flowability:

All of the SCC mixes exhibited a high slump compared to the normal concrete mix

currently used in bridge girders. The normal mix had an average slump cone

measurement of 7.9 inches. Slump was measured in the SCC mixes using slump flowand the J-ring tests. The average flow diameters from the slump flow tests are shown in

Figure 43.

Figure 43. Slump flow measurements for the SCC mixes.

S=Spancrete SCC, SS= Spancrete SCC + slag, C=County SCC

Elastic Modulus:

SCC mixes from Spancrete had a lower elastic modulus in compression than the normalmix concrete, about 65% of the normal. Modulus values are compared in Figure 44.

Figure 44.Elastic modulus values for all the mixes.N= normal, S=Spancrete SCC, SS= Spancrete SCC + slag, C=County SCC


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Concrete Strength:

All of the SCC mixes showed similar strength values, which were lower than the strengthof the normal concrete mix. The SCC concrete appeared to reach strength at a slower rate

than the normal mix. The concrete strengths are shown in Figure 45.

Figure 45. Concrete strengths (note: log axis).N= normal, S=Spancrete SCC, SS= Spancrete SCC + slag, C=County SCC

Creep and Shrinkage:

The creep tests actually measured combined creep plus shrinkage. A comparison of total

creep plus shrinkage losses over a one year period is shown in Figure 46.

Figure 46.Combined creep plus shrinkage over one year.N= normal, S=Spancrete SCC, SS= Spancrete SCC + slag, C=County SCC

1-Year Creep + Shrinkage Strain

0

0.0005

0.001

0.0015

0.002

0.0025

0.003

0.0035

Strain(

in/in)

N S SS C

loaded at 2 days


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Shrinkage:

The Spancrete SCC mixes developed 75% more shrinkage than the normal concrete mixover the one year period. The County SCC mix had 20% more shrinkage than the normal

concrete in the one year period. Average shrinkage results are shown in Figure 47.

Figure 47.Shrinkage strain developed in one year.N= normal, S=Spancrete SCC, SS= Spancrete SCC + slag, C=County SCC

Creep:

A significantly earlier loading time can have an effect on the degree of creep strain

produced in the Spancrete SCC mix but not in the other mixes. The other mixes appearedto be less affected by time of loading or the higher initial loading that was used in the 2-

day loaded test.

The standard mix (N) used by Spancrete had considerably less creep and shrinkage thandid the Spancrete SCC mixes. The County SCC mix does not show substantially different

creep behavior from the normal mix. Creep results are shown in Figure 48.

Figure 48.Comparison of measured creep strains with loading at 2 and 32 days.

N= normal, S=Spancrete SCC, SS= Spancrete SCC + slag, C=County SCC


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Comparison with AASHTO predictions:

The AASHTO LRFD Bridge Design Specifications (2007)1provide a series of equations,

developed through a recent NCHRP project, that are suggested for prediction of creep

and shrinkage losses in prestressed concrete bridge girders. Those equations were used

with each of the concrete mixes tested in this program to compare existing creep

predictions with the amounts measured in this test program. Figure 49 shows the averagemeasured creep strain after one year for the specimens loaded at 2 days in comparison to

the AASHTO predicted amount of strain. The Spancrete SCC mixes exhibit substantially

higher creep than would be calculated in beam design using the AASHTO approach.

Figure 49.Comparison of measured and predicted creep.N= normal, S=Spancrete SCC, SS= Spancrete SCC + slag, C=County SCC

The creep data for the Spancrete normal mix (N) is shown in Figure 50a as compared to

the expected AASHTO predicted creep and in Figure 50b over an extended time period.

Creep Strain - Normal Concrete

0

0.0001

0.0002

0.0003

0.0004

0.0005

0.0006

0.0007

0.0008

0.0009

0 100 200 300 400 500 600

Time (days)

Strain

(inch/inch)

data AASHTO

Figure 50a. Comparison of normal concrete creep and AASHTO prediction.

1AASHTO LRFD Bridge Design Specifications, American Association of State Highway and

Transportation Officials, 4thEd., 2007

1-Year Creep Strains

-0.0005

0

0.0005

0.001

0.0015

0.002

0.0025

Strain(in/in)

AASHTO data

N S SS C

loaded at 2 days


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Figure 50b.Normal concrete creep data (to 365 days) shown with a logarithmic

trendline along with the AASHTO strain prediction.

Conclusions:

The objective of this study, as stated in the first section, was to determine whether SCC

mixes used by Spancrete and County Materials in precast, prestressed highway bridgegirders would act like ordinary portland cement concrete with 3/4inch aggregate. This

was to be done by proving that these mixes do not display a high degree of dimensionchange over long periods when under constant loading.

Based on the results and observations presented previously, it should be concluded thatthe SCC mixes from Spancrete do in fact exhibit high dimension change due to creep and

shrinkage. The creep and shrinkage in the County SCC mix was about the same as the

Spancrete normal mix.

Creep and shrinkage strains, approximately twice that of a normal mix, do constitute a

significant increase in the effects of creep and shrinkage which, in turn, would likelyresult in less than expected long term prestress in a girder after losses (if the higher loss

was not accounted for in design) and undesirable girder behavior.

The AASHTO LRFD (2007) prediction of shrinkage strain and creep strain in aWisconsin 54W girder at one year, assuming an initial stress of 3800 psi on the non-

composite girder followed by a stress 2000 psi in the composite girder would give values

of: sh~0.0003in/in, cr~0.0013in/in. These values compare very well with the average

Creep Strain - Normal Concrete

0

0.0002

0.0004

0.0006

0.0008

0.001

0.0012

0 5000 10000 15000 20000

Time (days)

Strain

(inch/in

ch)

data AASHTO data trendline


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values measured in the normal concrete: sh~0.0004in/in, cr~0.0008in/in. The increasedvolume change in the SCC concrete would appear to require a modification of the

AASHTO prestress loss prediction equations for bridge girders.

Further research on varying mixes may be warranted. Careful consideration should take

place to ensure the safety of the implementation of SCC in highway bridge girders byaccounting for the expected effects of shrinkage and creep in reducing the long term

prestress remaining in a bridge girder.

Structures and Materials Test

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