JANUARY 2008
STRUCTURES AND MATERIALS
TEST LABORATORY
SELF CONSOLIDATING
CONCRETE:
CREEP AND SHRINKAGE
CHARACTERISTICS
BY
PROF. M.G. OLIVA
PROF. S. CRAMER
CIVIL ENGINEERING
COLLEGE OF ENGINEERING
UNIVERSITY OF WISCONSIN
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
i
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 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.
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 bridge
girders. 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 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 likely
result 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.
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 the
project including Paul Georgieff, Dominique Piette, Jeff Barker, Han Ug Bae, and Tung
Doan.
ii
Table of Contents
Abstract .............................................................. i
Acknowledgements ............................................ ii
Problem Definition ............................................. 1
Objectives .......................................................... 1
Scope .................................................................. 1
Tests and Testing Procedures ..............................
1. Shrinkage tests ..........................................
2. Creep tests .................................................
3. Other tests .................................................
2
2
4
7
Test Specimen Matrix ........................................ 9
Test Results ........................................................ 11
Slump, Slump Flow, and J-ring Tests ............ 11
Strength and Modulus Tests ........................... 13
Shrinkage Test Results ................................... 16
Creep test Results ........................................... 20
Executive Summary ............................................ 30
Flowability ..................................................... 30
Elastic Modulus ............................................. 30
Concrete Strength ........................................... 31
Creep and Shrinkage Combined .................... 31
Shrinkage ....................................................... 32
Creep .............................................................. 32
Comparison with AASHTO .......................... 33
Conclusions ......................................................... 34
iii
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 in
prestressed 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 evaluate
whether they are acceptable for use in precast, prestressed concrete highway bridge
girders.
Estimating accurate prestress loss in girders due to shrinkage and creep is critical to
ensure 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 was
accomplished 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 used
for production of highway girders and comparing with the new SCC mixes.
Three basic concrete mixes were examined (with the designations in parenthesis):
ƒ Standard ¾” aggregate mix currently being used in highway girders (N)
ƒ 3/8” SCC concrete mix developed by Spancrete (S)
ƒ SCC mix developed by County Materials (C)
A fourth alternate mix was also examined for possible future use:
ƒ 3/8” Spancrete SCC concrete mix that includes ground granulated blast furnace
slag (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.) Jring flow measurement.
1
Samples from three different batches were obtained for each of the three different
concrete 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 to
the University.
Specific details of the tests performed are described in the following sections for each
type of test.
Tests and Testing Procedures:
Test procedures generally following ASTM standard procedures with some exceptions as
noted 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 this
test program since the primary purpose was to compare the behavior of the SCC concrete
with the normal ¾” 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 for
this 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 for
judgment 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
2
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 prestress
loss in the highway bridge girders.
The initial length readings were taken subsequent to the immersion. ASTM C-157
specifies 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 from
ASTM 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 ¼“ 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.
3
Figure 2: The HM-250D
Length Comparator with
digital indicator was used to
measure shrinkage at the
University.
Figure 3: Shrinkage prism
readings were performed in
accordance with ASTM C-157.
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 the
requirements 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 were
subjected 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 accommodate
6 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 set
of 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
4
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 and
another 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 were
simulating 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 age
were 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 initial
compression 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 was
loaded 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.
5
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.
Figure 6: Chucks were placed
around each tension strand to
sustain the desired compressive
load on the creep rigs.
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 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.
6
Figure 10: After assembly and loading,
the creep rigs were hung vertically on a
steel suspension system for storage.
Figure 11: A Soiltest multi-length
strain gauge set was used to take
creep readings from the metal tabs.
3. Other tests:
The remaining tests (strength, modulus, slump [ASTM C1611/C1611M-05] and
J-ring [ASTM WK7552]) were conducted at various time intervals. Figures 12
through 19 show the tests being conducted at the plant and lab.
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.
7
Figure 14: In addition to Jring tests, slump flow tests
were also performed on every
batch at the Spancrete and
County Materials plants.
Figure 15: Slump flow was
measured in accordance with
ASTM C1611 standards.
Modulus and Strength Tests
Figure 16: Both modulus and strength
tests were performed in the STML Lab
at the University with a SATEC
machine following ASTM standards.
8
Figure 17: An HM-131
Compressometer/Extensometer
was attached to the loaded
cylinders to obtain vertical and
radial displacements
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.
Test Specimen Matrix:
Three batches (1, 2, and 3) per mix were used to ensure random sampling of concrete
with 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,
ƒ County Materials SCC Mix: C-1, C-2, C-3
ƒ Spancrete Standard Mix: N-1, N-2, N-3, N-G
ƒ Spancrete SCC Mix: S-1, S-2, S-3, S-G
ƒ 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,
ƒ County Materials SCC Mix:
o Batch 1: C-1A, C-1B
o Batch 2: C-2A, C-2B
o Batch 3: C-3A, C-3B
(“A” cylinders were tested starting at 2 days age, the “B” at 28 days)
9
ƒ
ƒ
ƒ
Spancrete Standard Mix:
o Batch 1: N-1B, N-1D
o Batch 2: N-2B, N-2D
o Batch 3: N-3B, N-3D
o 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-1D
o Batch 2: S-2B, S-2D
o Batch 3: S-3B, S-3D
o 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-1D
o Batch 2: SS-2B, SS-2D
o Batch 3: SS-3B, SS-3D
o SS-G1
(“G” began testing at 2 days of age, “D” at 12, and “B” at 32 days)
• Strength and modulus tests:
ƒ 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-1F
o Batch 2: C-2A, C-2B, C-2C, C-2D, C-2E, C-2F
o 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)
ƒ Spancrete Standard Mix:
o Batch 1: N-1A, N-1B, N-1C
o Batch 2: N-2A, N-2B, N-2C
o Batch 3: N-3A, N-3B, N-3C
o 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)
ƒ Spancrete SCC Mix:
o Batch 1: S-1A, S-1B, S-1C
o Batch 2: S-2A, S-2B, S-2C
o Batch 3: S-3A, S-3B, S-3C
o 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)
ƒ Spancrete SCC Mix w/ slag:
o Batch 1: SS-1A, SS-1B, SS-1C
o Batch 2: SS-2A, SS-2B, SS-2C
o Batch 3: SS-3A, SS-3B, SS-3C
o SS-G2
10
(“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-3D
o Rig 3: S-G1, SS-G1, N-G1, C-1B, C-3B
o Rig 4: S-2B, SS-2B, SS-3B, N-2B, N-3B
o Rig 5: N-1B, SS-1B, S-3B, S-1B
o 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
Batch
1
2
3
Standard 3/4' aggregate mix (N) - Spancrete
Slump Test
Prisms
Time of
Temp
Time
of
Loose
Batching
Time
Slump (in)
(F)
casting
Time
13:05
13:10
7.75
74
13:15
14:45
13:35
13:38
8.5
74
13:40
14:45
13:57
14:01
8.5
73
14:03
14:45
4/13/2006
8 Cylinders (Times)
2
6 Strength &
Creep
Modulus
13:15
13:16
13:41
13:39
14:01
14:03
Table 2: Spancrete SCC Mix Batching Information
Self-Consolidating Concrete 3/8’ aggregate mix (S) – Spancrete
J-ring Test
Batch
1
2
3
Time of
Batch
9:35
9:53
10:09
Slump Flow Test – 73.3 F
Prisms
Time
Diameter
1 (in)
Diameter
2 (in)
Time
Diameter
1 (in)
Diameter
2 (in)
Time
of
casting
Loose
Time
9:39
9:56
10:12
16.75
16.25
21.25
15.5
15.75
19.75
9:39
10:00
10:12
19.5
18
21.5
19
17.5
21
9:40
9:59
10:18
10:32
10:55
10:55
11
4/13/2006
8 Cylinders
(Times)
6
2
Strength
Creep
&
Modulus
9:47
9:47
9:57
9:59
10:16
10:14
Table 3: Spancrete SCC with slag Mix Batching Information
Self-Consolidating Concrete 3/8’ aggregate with Slag mix (SS) – Spancrete
J-ring Test
Batch
1
2
3
Time of
Batching
8:35
8:50
9:19
Slump Flow Test – 69 F
Prisms
Time
Diameter
1 (in)
Diameter
2 (in)
Time
Diameter
1 (in)
Diameter
2 (in)
Time
of
casting
Loose
Time
8:45
9:04
9:21
22
26.25
25.75
20
24.25
25.25
8:45
9:06
9:25
25.25
26.5
26.5
25.25
27.5
26
8:53
9:09
9:27
9:53
10:09
10:27
4/13/2006
8 Cylinders
(Times)
6
2
Strength
Creep
&
Modulus
8:50
9:07
9:28
8:47
9:05
9:23
Table 4: County Materials SCC Mix Batching Information
Self-Consolidating Concrete mix (C) – County Materials
J-ring Test
Batch
1
2
3
Time of
Batching
10:50
11:40
12:00
Slump Flow Test
Prisms
Time
Diameter
1 (in)
Diameter
2 (in)
Time
Diameter
1 (in)
Diameter
2 (in)
Time
of
casting
Loose
Time
11:00
11:47
12:10
21.5
25
26
20
23.5
24
11:05
11:52
12:15
22
25
25.5
21
23
25.5
11:10
11:50
12:12
11:30
12:20
12:30
Table 5: Spancrete Standard “G” Mix Batching Information
2-Day Standard Mix (NG) - Spancrete
Slump Test
Air
Time of
Content
Slump
Batching
Temp (F)
(%)
(in)
9:40
7.75
74
2.3
5/10/2006
Unit
Weight
(pcf)
154.8
Table 6: Spancrete SCC “G” Mix Batching Information
2-Day SCC Mix (SG) - Spancrete
Slump Flow - 73 F
Air
Time of
Content
Batching Diameter Diameter
(%)
1 (in)
2 (in)
9:20
22
22
5.6
5/10/2006
Unit
Weight
(pcf)
144.2
Table 7: Spancrete SCC w/ slag “G” Mix Batching Information
2-Day SCC Mix with slag (SSG) - Spancrete
Slump Flow - 71 F
Air
Time of
Content
Batching Diameter Diameter
(%)
1 (in)
2 (in)
9:00
25.5
25.75
12
6.5
5/10/2006
Unit
Weight
(pcf)
142.7
8/31/2006
8 Cylinders
(Times)
6
2
Strength
Creep
&
Modulus
11:00
11:50
12:10
11:00
11:50
12:10
Strength and Modulus Tests:
•
Modulus Test Results:
Sample
Modulus of Elasticity
"E" (based on 7.1 of
ASTM C469-02) (psi)
Poisson's Ratio
"μ" (based on 7.2
of ASTM C469-02)
SS2A
SS3A
S1A
S2A
S3A
N1A
N2A
N3A
C1A
C2A
C3A
2466000
2785000
3029000
2911000
2992000
4495000
4403000
4405000
4776000
4841000
4376000
0.22
0.12
0.14
0.14
0.18
0.12
0.21
0.25
0.18
0.13
0.18
Table 8: 1-Day Modulus Test Results
Sample
Modulus of Elasticity
"E" (based on 7.1 of
ASTM C469-02) (psi)
Poisson's Ratio
"μ" (based on 7.2
of ASTM C469-02)
C1B
C2B
C3B
5089000
4975000
4681000
0.21
0.16
0.19
Table 9: 7-Day Modulus Test Results
13
Sample
Modulus of Elasticity
"E" (based on 7.1 of
ASTM C469-02) (psi)
Poisson's Ratio
"μ" (based on 7.2
of ASTM C469-02)
SS1C
SS2C
SS3C
SSG2
S1C
S2C
S3C
SG2
N1C
N2C
N3C
NG2
C1C
C2C
C3C
3286000
3904000
3668000
4026000
3716000
3511000
3564000
4667000
6255000
5140000
5482000
5518000
5035000
4986000
4822000
0.22
0.23
0.21
0.01
0.22
0.21
0.21
0.31
0.14
0.21
0.25
0.28
0.12
0.08
0.12
Table 10: 28-Day Modulus Test Results
Sample
Modulus of Elasticity
"E" (based on 7.1 of
ASTM C469-02) (psi)
Poisson's Ratio "μ"
(based on 7.2 of
ASTM C469-02)
C1D
C2D
C3D
4350000
4994000
4887000
0.06
0.11
0.11
Table 11: 90-Day Modulus Test Results
Sample
Modulus of Elasticity
"E" (based on 7.1 of
ASTM C469-02) (psi)
Poisson's Ratio "μ"
(based on 7.2 of
ASTM C469-02)
C1E
C2E
C3E
C1F
C2F
C3F
5910000
5474000
5238000
5404000
5890000
5127000
0.18
0.13
0.12
0.18
0.11
0.12
Table 12: 392-Day Modulus Test Results
14
•
Strength Test Results:
Sample
Strength Tests
Ultimate
Compressive
Load (lb)
Strength (psi)
1-Day
Strength
SS1A
SS2A
SS3A
S1A
S2A
S3A
N1A
N2A
N3A
C1A
C2A
C3A
157950
165400
168510
179980
185120
179100
241570
230980
226770
199850
198050
193320
5530
5870
5940
6380
6500
6360
8470
8140
7950
6970
7000
6840
7-Day
Strength
SS1B
SS2B
SS3B
S1B
S2B
S3B
N1B
N2B
N3B
C1B
C2B
C3B
184830
202400
204210
201220
216000
209180
272480
273150
265830
223530
222860
208810
6530
7100
7210
7040
7560
7360
9620
9660
9420
7880
7850
7280
28-Day
Strength
SS1C
SS2C
SS3C
SSG2
S1C
S2C
S3C
SG2
N1C
N2C
N3C
NG2
C1C
C2C
C3C
214410
219750
235720
230800
228590
245160
224430
208850
284910
297990
299390
293830
246780
245940
239520
7590
7780
8380
8150
8031
8690
7940
7400
10077
10440
10500
10230
8650
8560
8450
Table 12: Strength Test Results
15
90-Day
Strength
392-Day
Strength
Sample
Ultimate
Load (lb)
Compressive
Strength (psi)
C1D
C2D
C3D
C1E
C2E
C3E
C1F
C2F
C3F
280550
286770
273830
291310
303310
295360
289240
310180
283700
9920
10040
9650
10290
10710
10270
10230
10880
10010
Table 13: Strength Test Results
Shrinkage Test Results:
The shrinkage data is plotted as decreasing length on the y-axis. Recall that the gage
length of the prisms was 11.25 inches on average.
Spancrete Standard Prisms - Shrinkage Strain
0.000600
Shrinkage Strain (in/in)
0.000500
0.000400
0.000300
0.000200
0.000100
0.000000
0
100
200
300
400
-0.000100
-0.000200
Age (Days)
N1
N2
N3
N-G
Figure 20: Spancrete Standard Mix Shrinkage
16
500
600
Spancrete SCC Prisms - Shrinkage Strain
0.001200
0.001000
Shrinkage
Strain (in/in)
0.000800
0.000600
0.000400
0.000200
0.000000
0
100
200
300
400
500
600
500
600
-0.000200
Age (Days)
S1
S2
S3
S-G
Figure 21: Spancrete SCC Mix Shrinkage
Spancrete SCC w/ Slag Prisms - Shrinkage Strain
0.00120
Shrinkage Strain (in/in)
0.00100
0.00080
0.00060
0.00040
0.00020
0.00000
0
100
200
300
400
-0.00020
Age (Days)
SS1
SS2
SS3
SS-G
Figure 22: Spancrete SCC with Slag Mix Shrinkage
17
County Materials SCC Prisms - Shrinkage Strain
0.000700
Shrinkage Strain (in/in)
0.000600
0.000500
0.000400
0.000300
0.000200
0.000100
0.000000
0
50
100
150
200
250
300
350
400
Age (Days)
C!
C2
C3
Figure 23: County Materials SCC Mix Shrinkage
Shrinkage Strain Averages
0.00120
0.00100
Strain (in/in)
0.00080
0.00060
0.00040
0.00020
N
S
SS
C
G
0.00000
0
100
200
300
400
500
600
-0.00020
Age (Days)
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
18
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 storage
conditions. 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
0.0012
0.001
Strain (inch/inch)
0.0008
0.0006
0.0004
0.0002
0
0
100
200
300
400
500
Time (days)
N1
N2
N3
All in rig 2
Figure 25: Spancrete 12-Day loading Normal Mix Creep + Shrinkage
19
600
N-B loaded at 32 days - Creep + Shrinkage Strains
0.0018
0.0016
0.0014
Strain (inch/inch)
0.0012
0.001
0.0008
0.0006
0.0004
0.0002
0
0
100
200
300
400
500
600
Time (days)
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
0.002500
Strain (inch/inch)
0.002000
0.001500
0.001000
0.000500
0.000000
0
100
200
300
400
500
Time (days)
S1
S2
S3
S1 in rig 1; S2 & S3 in rig 2
Figure 27: Spancrete 12-Day loading SCC Mix Creep + Shrinkage
20
600
S-B loaded at 32 days - Creep + Shrinkage Strains
0.003
0.0025
Strain (inch/inch)
0.002
0.0015
0.001
0.0005
0
0
100
200
300
400
500
600
Time (days)
S2 in rig 4; S1 & S3 in rig 5
S1-32
S2-32
S3-32
Figure 28: Spancrete 32-Dayloading SCC Mix Creep + Shrinkage
SS-D loaded at 12 days - Creep + Shrinkage Strains
0.003000
0.002500
Strain (inch/inch)
0.002000
0.001500
0.001000
0.000500
0.000000
0
100
200
300
400
500
Time (days)
SS1
SS2
SS3
All in rig 1
Figure 29: Spancrete 12-Day loading SCC w/Slag Mix Creep + Shrinkage
21
600
SS-B loaded at 32 days - Creep + Shrinkage Strains
0.0025
Strain (inch/inch)
0.002
0.0015
0.001
0.0005
0
0
100
200
300
400
500
600
Time (days)
SS1-32
SS2-32
SS1 in rig 5; SS2 & SS3 in rig 4
SS3-32
Figure 30: Spancrete 32-Day loading SCC w/Slag
Mix Creep + Shrinkage
G loaded at 2 days - Creep + Shrinkage Strains
0.004
0.0035
Strain (inch/inch)
0.003
0.0025
0.002
0.0015
0.001
0.0005
0
0
100
200
300
400
500
Time (days)
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
22
600
C-A loaded at 2 days - Creep + Shrinkage Strains
0.0014
0.0012
Strain (in/in)
0.001
0.0008
0.0006
0.0004
0.0002
0
-0.0002
0
50
100
150
200
250
300
350
400
-0.0004
Time (days)
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
0.0012
Strain (in/in)
0.001
0.0008
0.0006
0.0004
0.0002
0
0
50
100
150
200
250
300
350
400
Time (days)
C1
C2
C3
C1 & C3 in rig 3, C2 in rig 6
Figure 33: County Materials 28-Day loading SCC Mix Creep + Shrinkage
23
•
Start day comparisons within mixes:
Spancrete Normal Mix - Creep + Shrinkage Strain
0.0014
0.0012
Strain (in/in)
0.001
0.0008
0.0006
0.0004
0.0002
0
0
50
100
150
200
250
300
350
400
450
500
Days After Loading
N12
N32
NG-2
Figure 34: Spancrete Normal Mix, Creep + Shrinkage for 2, 12, and 32 day starts
Spancrete SCC Mix - Creep + Shrinkage Strain
0.004
0.0035
Strain (in/in)
0.003
0.0025
0.002
0.0015
0.001
0.0005
0
0
50
100
150
200
250
300
350
400
450
Days After Loading
S12
S32
SG-2
Figure 35: Spancrete SCC Mix, Creep + Shrinkage for 2, 12, and 32 day starts
24
500
Spancrete SCC Mix w/ Slag - Creep + Shrinkage Strain
0.003
0.0025
Strain (in/in)
0.002
0.0015
0.001
0.0005
0
0
50
100
150
200
250
300
350
400
450
500
Days After Loading
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
0.0012
Strain (in/in)
0.001
0.0008
0.0006
0.0004
0.0002
0
0
50
100
150
200
250
300
350
Days After Loading
C2
C28
Figure 37: County Materials SCC Mix, Creep + Shrinkage for 2 and 28 day starts
25
•
Group Average Comparisons:
Spancrete mixes loaded at 12 days - Creep + Shrinkage Strain
0.003
0.0025
Strain (inch/inch)
0.002
0.0015
`
0.001
0.0005
0
0
100
200
300
400
Days after casting
500
600
3800psi up to 28 days, then 2000psi
N
S
SS
Figure 38: Spancrete Mixes loaded at 12 days
N=normal, S=SCC, SS=SCC plus slag
Spancrete mixes loaded at 32 days - Creep + Shrinkage Strain
0.0025
Strain (inch/inch)
0.002
0.0015
0.001
0.0005
0
30
80
130
180
230
280
330
380
Days after casting
N
S
SS
Figure 39: Spancrete Mixes loaded at 32 days
N=normal, S=SCC, SS=SCC plus slag
26
430
480
530
Spancrete mixes loaded at 2 days - Creep + Shrinkage Strain
0.004
0.0035
Strain (inch/inch)
0.003
0.0025
0.002
0.0015
0.001
0.0005
0
0
100
200
300
400
500
600
Days after casting
N
S
SS
Figure 40: Spancrete Mixes loaded at 2 days
N=normal, S=SCC, SS=SCC plus slag
Note: Group averages for County Materials SCC mixes were shown in Figure 37
27
Loaded at 28 days - Pure Creep Strain
0.00180
0.00160
0.00140
Strain (inch/inch)
0.00120
0.00100
0.00080
0.00060
0.00040
0.00020
N
S
SS
C
0.00000
0
50
100
150
200
250
300
350
400
450
500
Time (days)
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
0.003
0.0025
Strain (inch/inch)
0.002
0.0015
0.001
0.0005
0
0
50
100
150
200
250
300
350
400
450
500
Time (days)
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
28
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 flow”
and 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 normal
mix 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
29
Concrete Strength:
All of the SCC mixes showed similar strength values, which were lower than the strength
of 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.
1-Year Creep + Shrinkage Strain
loaded at 2 days
0.0035
0.003
Strain (in/in)
0.0025
0.002
0.0015
0.001
0.0005
0
N
S
SS
C
Figure 46. Combined creep plus shrinkage over one year.
N= normal, S=Spancrete SCC, SS= Spancrete SCC + slag, C=County SCC
30
Shrinkage:
The Spancrete SCC mixes developed 75% more shrinkage than the normal concrete mix
over 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 appeared
to be less affected by time of loading or the higher initial loading that was used in the 2day loaded test.
The standard mix (N) used by Spancrete had considerably less creep and shrinkage than
did 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
31
Comparison with AASHTO predictions:
The AASHTO LRFD Bridge Design Specifications (2007)1 provide 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 average
measured 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.
1-Year Creep Strains
loaded at 2 days
0.0025
Strain (in/in)
0.002
0.0015
0.001
0.0005
0
N
-0.0005
SS
S
AASHTO
C
data
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
0.0009
0.0008
Strain (inch/inch)
0.0007
0.0006
0.0005
0.0004
0.0003
0.0002
0.0001
0
0
100
200
300
400
500
600
Time (days)
data
AASHTO
Figure 50a. Comparison of normal concrete creep and AASHTO prediction.
1
AASHTO LRFD Bridge Design Specifications, American Association of State Highway and
Transportation Officials, 4th Ed., 2007
32
Creep Strain - Normal Concrete
0.0012
Strain (inch/inch)
0.001
0.0008
0.0006
0.0004
0.0002
0
0
5000
10000
15000
20000
Time (days)
data
AASHTO
data trendline
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 bridge
girders 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 dimension
change over long periods when under constant loading.
Based on the results and observations presented previously, it should be concluded that
the 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 likely
result 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 a
Wisconsin 54W girder at one year, assuming an initial stress of 3800 psi on the noncomposite girder followed by a stress 2000 psi in the composite girder would give values
of: εsh~0.0003in/in, εcr~0.0013in/in. These values compare very well with the average
33
values measured in the normal concrete: εsh~0.0004in/in, εcr~0.0008in/in. The increased
volume 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 by
accounting for the expected effects of shrinkage and creep in reducing the long term
prestress remaining in a bridge girder.
34