A NEW TESTING METHOD FOR CREEP BEHAVIOR OF
SELF-COMPACTING CONCRETE AT EARLY AGE

Krittiya Kaewmanee

A dissertation submitted to
Kochi University of Technology
in partial fulfillment of the requirements for
The Degree of Master of Engineering

Supervisor
Professor Hajime Okamura

Department of Infrastructure System Engineering
Kochi University of Technology
Kochi, Japan

January 2001

Abstract
Creep and shrinkage of concrete are known to have significant effects at early age of concrete.
To be able to simulate the behavior of creep and shrinkage during this stage, accurate andactual properties of concrete should be obtained from the test. However, by performing
normal creep testing, applying constant dead load to specimen, some important and necessary
parameters cannot be obtained. Furthermore, creep also has significant effects on loss ofprestress. Such normal test cannot clearly explain this kind of behavior well. Therefore, a new
testing method for creep test is proposed. From this testing method, the modulus of elasticity
of concrete (as a function of time) that is a useful parameter in estimating creep and reliablestrain value can be achieved. Concrete creep and shrinkage are affected by many parameters.
The factors investigated in this research were type of cement, cement content and w/c ratio,
age at loading/drying, and stress/strength ratio. The tests were performed on mortar of selfcompacting concrete. It was found that type of cement has slight effect on creep due to its
difference in chemical compositions. For the same day of loading and same stress/strength
ratio of applied load, the higher the w/c ratio the larger creep. Age at loading also has effecton creep such that the later age at loading, the smaller creep is. Stress/strength ratio hassignificant effect on creep. A new creep factor is proposed and it is found to give good
agreement with the conventional terms, which are specific creep and creep coefficient.

Acknowledgements
I would like to express my deepest gratitude to my advisor Professor Hajime Okamura for hiskind encouragement and valuable advice throughout the course of this study. I express myprofound gratitude to Assistant Professor Masahiro Ouchi for his guidance especially on selfcompacting concrete and his encouragement during the course of this study. My gratefulappreciation is extended to Professor Hiroshi Shima for his suggestions. It has been an honor
and a privilege to work with them for their outstanding examples of scientific dedication in
their field.
Grateful acknowledgements are also extended to Associate Professor Chiyo Myojin and
Associate Professor Masataka Takagi for their interest and serving as members of
examination committee.
Sincere words of gratitude are expressed to Mr. Masaru Ueno for his useful advice andsupport in experimental work.
I also would like to thank Mr. Supakit Swatekititham and Mr. Thammanoon Denpongpan, andThai juniors for their help, support and patience towards many of my problems during thecourse of the experimental work.

Contents

Abstract
Acknowledgements
Contents
List of Figures and Tables
1.

2.

i
ii
iii
iv

INTRODUCTION
1.1 Objective and scope of study

1

LITERATURE REVIEW
2.1 Definition of terms used
2.2 Conventional creep test
2.3 Factors affecting creep

2
3
4

3.
3.1
3.2
3.3
3.4

EXPERIMENTAL OUTLINE
Mix proportions of mortar
Geometry of specimens
Setup method
Measuring method for strain

6
7
8
8

4.1
4.2
4.3
4.4
4.5
4.6

ANALYSIS AND VERIFICATIONS
Analytical methods
Compressive strength and Young’s modulus
Effect of type of cement
Effect of w/c ratio
Effect of age at loading
Effect of stress/strength ratio

10
12
13
13
14
15

5.

CONCLUSIONS

17

6.

RECOMMENDATIONS OF FURTHER STUDY

18

4.

REFERENCES

Appendix A
Appendix B
Appendix C
Appendix D
Appendix E
Appendix F

Total strain, shrinkage strain, and elastic strain of all specimens
Creep strain of all specimens
Young’s modulus of all specimens
Specific creep of all specimens
Creep coefficient of all specimens
Creep factor of all specimens

List of Figures and Tables
Figure No.
2.1.1
2.2.1
3.1.1
3.2.1
3.2.2
3.3.1
3.4.1
4.1.1
4.1.2
4.1.3
4.1.4
4.1.5
4.1.6
4.1.7
4.1.8
4.2.1
4.2.2
4.2.3
4.3.1
4.4.1
4.5.1
4.6.1

Definition of terms
Different kinds of load systems for creep test
Mixing procedure of mortar in self-compacting concrete
Geometry of specimens for creep and drying shrinkage test
Point gauges and their positions on the test specimen
Setup method for creep test
Stages of creep test
Shrinkage strain versus time (log scale)
Creep strain versus time (log scale)
Modulus of elasticity versus time (log scale)
Elastic strain versus time (log scale)Specific creep versus time (log scale)
Creep coefficient versus time (log scale)
Creep strain and modulus of elasticity versus time (log scale)
Creep factor versus time (log scale)Compressive
Young’s modulus
Relationship between compressive strength and Young’s modulus
Effect of type of cement
Effect of w/c ratio
Effect of age at loading
Effect of stress/strength ratio

Table No.
3.1.1 Specific gravity of material
3.1.2 Properties of mortar
4.3.1 Mix proportion and environmental condition for the effect of type of
cement analysis
4.4.1 Mix proportion and environmental condition for the effect of w/c ratio
analysis4.5.1 Mix proportion and environmental condition for the effect of age atloading analysis
4.6.1 Mix proportion and environmental condition for the effect ofstress/strength ratio analysis

page
2
3
6
7
7
8
9
10
10
10
10
11
11
11
12
12
12
12
13
14
15
15-16

6
6
13
13
14
15

Chapter 1
INTRODUCTION
1.1 Objective and scope of study
The early age of concrete is known to have a significant control on the overall performance ofconcrete structures. During this stage, concrete may be subjected to severe internal actions
due to thermal and hygric gradients within concrete itself and at the same time it may beaffected by the external conditions of environment and loading. All these actions may lead todifferent deformations within the concrete that is just building its resistance and stiffness.
Important examples of harmful effects of creep are prestressed concrete member, where creep
causes loss of prestress, and mass concrete structures which undergo a heating-cooling cycle
due to the development of the heat of hydration and then the temperature drop to the ambient
temperature. During this cycle of temperature change, creep relieves the stress due tocompression induced by the initial rapid rise in temperature. Thus, on cooling, tensile stresseasily develop and cracking may easily occur. Creep and shrinkage of concrete are known tohave significant effect at early age of concrete. Thus, discussing the performance of thisyoung age concrete with special attention to the shrinkage and creep and time dependent
deformations is of interest by many researchers.
Self-compacting concrete is a kind of concrete that can be compacted into every corner of aformwork, purely by means of its own weight and without the need for vibrating compacting.
Nowadays, this type of concrete is widely used. Normally, in order to obtain high selfcompactability, the aggregate content is limited and the powder content is high. Due to thishigh powder content, creep and shrinkage of self-compacting concrete are significant.
The accurate and reliable information on properties of concrete at early age is very difficult toobtain. To be able to simulate the behavior of creep and shrinkage during this stage, accurate
and actual properties of concrete should be obtained from the test. However, by performing
normal creep testing, applying constant dead load to specimen, some important and necessary
parameters cannot be obtained. Furthermore, creep also has significant effects on loss ofprestress. Such normal test cannot clearly explain this kind of behavior well.
Therefore, a new testing method for creep test is proposed. The study focuses on creep of selfcompacting concrete at early age where creep is thought to be significant.

Chapter 2
LITERATURE REVIEW
2.1 Definition of terms used
Creep is defined as a deformation occurring under, and induced by, a constant sustained stresswhile shrinkage is termed changes in strain due to movement of water from or to the ambient
medium when no external stress is acting [1]. The common practice over many years has been
consider the two phenomena to be additive. The overall increase in strain of a stressed anddrying member is thus assumed to consist of shrinkage (equal in magnitude to that of a similar
unstressed member) and of a change in strain due to stress, i.e. creep. This approach has amerit of simplicity and is suitable for the many practical applications where creep andshrinkage occur together. The definition is, however, not correct because creep and shrinkage
are not independent phenomena to which the principle of superposition can be applied. In fact,
we know that the effect of shrinkage on creep is to increase the magnitude of creep. However,
it is possible to define creep as the deformation in excess of shrinkage. Such a definition
makes it possible to analyze the data of previous investigators who believed creep andshrinkage to be additive. Figure 2.1.1 shows the terms and definitions involved.

Figure 2.1.1 Definition of terms

It should be noted that, since the modulus of elasticity of concrete increases with time, theelastic strain decreases with time. Thus, creep should be reckoned as strain in excess of theelastic strain at the time considered and not in excess of the elastic strain at the time of
application of load. However, this parameter cannot be obtained from conventional creep
testing method.
2.2 Conventional creep test
The majority of creep tests are performed on compression specimens – prisms and cylinders –subjected to a uniaxial stress. General speaking, there are four loading methods: dead load,
spring-loaded, hydraulic, and stabilized hydraulic. Figure 2.2.1 show different types of loadsystems for creep test as mentioned above.

(a)

(b)

(c)

a) a spring-loaded creep frame b) a hydraulic load creep frame c) a stabilized hydraulic loadsystemFigure 2.2.1 Different kinds of load systems for creep test
The dead load system is hardly ever used because for the usual size of specimens it requires
large dead weight and is, therefore, cumbersome and often impractical.
The spring-loaded system, one or more heavy coil springs are held in a compressed position
against a suitable frame. This procedure improves the constancy of the applied load. The maindifficulties lie in the application of the proper load sufficiently rapidly so that no creep takes
place.
In the hydraulic system [2], high loads can be applied more easily and can be maintained to ahigh degree of accuracy. This system is compact and flexible. The application of the desiredload is simple and reliable. However, the maintenance of a sustained load is sensitive andoften there is an unavoidable small leakage of the hydraulic fluid.
The stabilized hydraulic loading system [3,4,5] can be used for a number of specimens at thesame time. This system solves the difficulties encountered in the hydraulic system.

However, the modulus of elasticity as a function of time couldn’t be obtained from the above
kinds of creep test. To be satisfactory, a loading system for creep tests should be able tomaintain a constant stress with a minimum of maintenance and manual adjustment, andshould ensure a uniform stress distribution over the cross-section of the specimen. It is also
desirable that the loading system be compact to make possible operation in a room with
controlled temperature and humidity.
2.3 Factors affecting creep
Cement is the most important factor in creep because the hydrated cement paste is the sourceof the phenomenon. The influence of cement is twofold: that arising from the physical andchemical properties of the cement, and that due to the variation in the amount of the hydrated
cement paste [6]. Creep seems to be inversely proportional to the rapidly of hardening of thecement used. The more hardened the paste the more rigid it is and the lower its creep potential
at a given applied stress.
The investigation [7] of the influence of the type of cement on creep lead to the establishmentof an approximate stress/strength ratio rule, which states simply that, for constant mix
proportions and same type of aggregate, creep is proportional to the applied stress andinversely proportional to the strength at the time of application of the load. From a wide rageof experimental results there exists a linear relationship between creep and the applied stress,
except in specimens loaded a very early age: 1 to 3 days. Iriya, K., Hattori, T., and Umehara,
H., [8] studied compressive creep at early age of mortar with w/c ratio of 55% by using 10x20
cm cylindrical specimen. The tests were carried out at control temperature of 30°C andrelative humidity of 100%. The specimens were loaded 3 days after casting and kept applying
load for 5 days and then unloaded for 3 days. Stress/strength ratio was varied by 4.4%, 20%,
29%, 49% and 60%. From the test, it can be concluded that final creep strain andstress/strength ratio has linear relationship up to stress/strength ratio of 20%. For the
stress/strength ratio more than 20%, the relationship becomes exponential. The equation toestimate final creep strain as a function of stress/strength ratio is shown in Eqn. (2.3.1).

ε cr = 109.91e 0.038( S / S )ε cr = 11.95( S / S )(20 ≤ S / S ≤ 60)( S / S ≤ 20)(2.3.1)

where εcr is final creep strain (µ) and S/S is stress/strength ratio (%), respectively.
Washa and Fluck’s [9] discussed the applicability of the stress/strength ratio rule such that thechange in strength while the concrete is under load, and hence a change in the value of thestress/strength ratio is a factor in creep.
Lorman [10] studied the effect of w/c ratio on creep and found that creep is approximately
proportional to the square of the w/c ratio. Iriya, K., Hiramoto, M., Hattori, T., and Umehara,
H., [11] studied compressive creep in concrete at early age. The important factors on thiscreep behavior in concrete at early age are loaded age, loaded stress level, and temperatureeffects. A creep model which is a function of stress/strength ratio, w/c ratio, quantity of
cement paste, loaded age was proposed as shown in Eqn. (2.3.2).

ε cr (t e , S / S ,W / C , P, τ e ) = FS / S ( S / S ) ⋅ FW / C (W / C ) ⋅ FP ( P) ⋅ FL (τ e ){⋅ 28.502(1 − e − 206.08e ) + 47.442(1 − e −1.747 te ) + 9.144t e}(2.3.2)

FS / S ( S / S , τ ) = C (τ e ) S / S
D(τ e )e 0.035 S / S
C (τ e ), D(τ e ) : loading age coefficients
C (τ e ) = 0.007(τ e − 1) + 0.036
C (τ e ) = 0.001(τ e − 3) + 0.050
C (τ e ) = 0.053
D(τ e ) = 0.069(τ e − 1) + 0.359
D(τ e ) = 0.014(τ e − 3) + 0.499
D(τ e ) = 0.524(0 ≤ S / S ≤ 20)(2.3.3)(20 ≤ S / S )(1 ≤ τ e ≤ 3)
(3 ≤ τ e ≤ 5)
(5 ≤ τ e )(1 ≤ τ e ≤ 3)
(3 ≤ τ e ≤ 5)
(5 ≤ τ e )FW / C (W / C ) = 1.69(W / C ) −2.43(2.3.4)FP ( P) = 1.58 ln( P ) − 7.85

(2.3.5)FL (τ e ) = 1.082(1 − e −0.86τ e )(2.3.6)

where εcr is final creep strain (x10-6), S/S is stress/strength ratio (%), τe is loading age (days),
te is time duration of loading (days), W/C is water to cement ratio (%), and P is quantity of
cement paste (cm3/ m3), respectively.
Moreover, creep is also affected by relative humidity and the temperature of the surrounding
environment, the aggregate content, and the use of admixture.

Chapter 3
EXPERIMENTAL OUTLINE
3.1 Mix proportions of mortar
In this research, normal Portland cement and low heat cement were used. Fine aggregateswere river sand and crushed sand. Table 3.1.1. shows specific gravity of materials used in thisresearch. Properties of mortar are shown in Table 3.1.2. Mix design and mixing procedure ofmortar in self-compacting concrete were done as suggested by Ouchi, M., Hibino, M., Ozawa,
K. and Okamura, H. [12] and Ouchi, M. and Edamatsu, Y. [13], respectively. Figure 3.1.1.
shows the mixing procedure of mortar in self-compacting concrete. Firstly, trial mixes of selfcompacting concrete were performed. From the properties of fine and coarse aggregates, theamount of coarse aggregate was selected to be 53% of solid volume and the amount of fineaggregate was chosen as 45% of mortar volume. Fine aggregate consisted of river sand andcrushed sand and the ratio was selected as 50% by volume. At the fixed aggregates content,
the superplasticizer dosage and water to powder ratio by volume are to be varied in order toachieve proper deformability and viscosity of mortar. From the trial mixes, the appropriate
water to powder ratio was 0.94. The mix proportion of mortar was then determined from themix proportion of concrete by taking out the amount of coarse aggregate. This is aimed tofurther study the effect of coarse aggregate on creep of self-compacting concrete. The water tocement ratio was varied by varying the percent replacement of limestone powder.
Table 3.1.1 Specific gravity of materials
Material
Ordinary Portland Cement
Low Heat Cement
Limestone
Sea SandCrushed Sand

Specific Gravity
3.15
3.27
2.70
2.60
2.58

Table 3.1.2 Properties of mortar
SP (%
by
%
weightSand
1-day f'c 3-day f'c
Type of W/P (by W/C (by Replacement Cement Waterof3
3
3
No. cement volume) weight) of limestione (kg/m ) (kg/m ) (kg/m ) powder) (kgf/cm2) (kgf/cm2)
1
LH
0.94
0.3
0
615
179
783
1.4
110
295
2
OPC
0.94
0.3
0
597
179
783
1.6
288
706
3
OPC
0.94
0.5
36.7
358
179
783
1.1
148
410
4
OPC
0.94
0.7
53.6
256
179
783
0.9
79
211

**(OPC = Ordinary Portland Cement and LC = Low Heat Cement)*Two types of sands were used: sea sand and crushed sand, with ratio 50:50 by volume

Powder + Sand

Water (1)

Water (2) + Superplasticizer

mixing 30 seconds mixing 120 seconds

end

mixing 120 seconds

Figure 3.1.1 Mixing procedure of mortar in self-compacting concrete

The specimens were cast in control room at temperature of 20°C and were demolded 16 hours
later after the setting time. Specimens were kept sealed until the day of loading or drying, i.e.
24 and 72 hrs after casting in this research. Three 10x20cm cylindrical specimens were tested
at the loading age to obtain compressive strength. Creep specimens were loaded atstress/strength ratio of 20%, 30%, 40% and 60%.
3.2 Geometry of specimens
This research is mainly concerned with young age concrete where the effect of shrinkage andcreep is significant. Therefore, two types of specimens were analyzed. The first group is
subjected to drying only to study the factors affecting the shrinkage behavior and the other issubjected to simultaneous drying and loading to study the drying creep behavior. Figure 3.2.1
shows the specimen used for creep and drying shrinkage test. The test specimen was chosen
as prism-shaped specimen of size 10x10x40cm. The creep specimen will be subjected toloading by applying pre-stress method. In order to do so, steel sheet was inserted at the centerof the specimen before casting for both creep and drying shrinkage specimen so that they are
subjected to the same condition except that creep specimen will be subjected to loading while
drying shrinkage specimen will not. Figure 3.2.2 shows gauge point and the position of thegauge points on the specimen. The gauge points are put at the centerline of all four surfaces at
10 cm equal interval. Gauge point type was selected instead of strain gauge because at earlyage strain gauges are not attached well to the specimen and as a result the values of strain
obtained are not reliable.
10 cm

40 cm

10 cm

Cross section

Steel sheet

Figure 3.2.1 Geometry of specimens for creep and drying shrinkage test

Plane
5 cm

10 cm

10 cm

10 cm

5 cm

5 cm
5 cm

Point gauges
φ2 mm

3 mm

10 mm
10 mm

Figure 3.2.2 Point gauges and their positions on the test specimen

3.3 Setup method
Figure 3.3.1 shows the setup method of the creep test. The tension steel attached with two
strain gauges was inserted into the creep specimen through a provided steel sheet. These strain
gauges were used to monitor if the applied stress was constant or not. The load cannot be used
to assured constant stress because for a while specimen undergo creep and increase in strain.
Load applied should be also increased to keep applying constant stress but we cannot
determine the magnitude. Two steel plates and nuts were placed on both sides of the specimen
and the jack and load cell placed on one side of the specimen.
Plane

10 cm

Jack

40 cm

10 cm

Cross Section

Load Cell

Steel Plate

Hand Pump

Data Logger

P.C

Figure 3.3.1 Setup method for creep test
Load was applied to the specimen by using a hand pump. The value of applied load and strainof steel were transferred from data logger to computer. Load should be applied very rapid
because if the load is applied slowly some creep takes place. As a result of rapid loading, theelastic strain can be determined from measurement of the change in strain under a fluctuatingstress of small magnitude. [14] The creep and drying shrinkage specimens were tested atcontrol temperature of 20°C and 50% relative humidity.
3.4 Measuring method for strain
In this research, the shrinkage and creep strains were recorded for 7 days from the starting of
the test. From the fact that, the change of shrinkage and creep strains is significant at early dayof test, strains were measured every 6 hours for the first 3 days and every 12 hours for thelater 4 days. To determine the shrinkage strain, the length change was measured using acontact gauge. Figure 4 shows the stages of creep test. The applied stress in this research wasselected as 30% of its compressive strength at the testing day.

Stress
b

e

load

c

reloadE
unloadaStraind

Total strain

Figure 3.4.1 Stages of creep test
The initial length was measured (point a). The specimen was first loaded from zero stress to acertain compressive stress level (a-b) and the applied stress was maintained. Next time ofstrain record (point c in Figure 3.4.1), the specimen was unloaded to zero stress (c-d). Again
the specimen was reloaded (d-e). The processes of unload and reload was performed
alternately and the length change at each stage was measured (point b, c, d, e,...). The strain ateach point is determined as ratio of length changes over initial length. The strain of creep
specimen at each elapse time is determined from the difference of strain at zero stress stage.
Since the applied stress is only 30% of the strength, the modulus of elasticity is simply
calculated as the difference of stress divided by difference of strain on the reloading path.

Chapter 4
ANALYSIS AND VERIFICATIONS
4.1 Analytical methods
From the test, we can calculate creep strain by subtracting shrinkage strain and elastic strain
from the total strain of creep specimen measured at zero stress as shown in Eqn. (4.1.1).

ε c = ε t − ε sh − ε e(4.1.1)

where εc is creep strain, εt is total strain, εsh is shrinkage strain, and εe is elastic strain,
respectively.
By plotting shrinkage strain and creep strain against log (t+1), where t is the time when drying
and loading start, a linear relationship can be obtained as illustrated in Figure 4.1.1 and 4.1.2,
respectively.

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Figure 4.1.1 Shrinkage strain versus time (log scale)Figure 4.1.2 Creep strain versus time (log scale)Moreover, from this kind of test the modulus of elasticity and elastic strain as a function oftime can be obtained. Figure 4.1.3 and 4.1.4 shows the modulus of elasticity and elastic strain
plotted against log (t+1), where t is the time when loading starts.

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Figure 4.1.3 Modulus of elasticity versus time (log scale)     
  (   )
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Figure 4.1.4 Elastic strain versus time (log scale)

To compare creep, it is common to express as specific creep or creep coefficient. Specificcreep is defined by creep strain per applied stress Eqn. (4.1.2) and creep coefficient is definedas creep strain per initial elastic strain Eqn. (4.1.3).

J=

εc
σ

(4.1.2)where J is specific creep (kgf/cm2)-1, εc is creep strain and σ is applied stress (kgf/cm2),
respectively.
Φc =

εc
ε ie

(4.1.3)where Φc is creep coefficient, εc is creep strain and εie is initial elastic strain, respectively.

     
  (   )
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
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

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     
  (   )
 * * *%&'($(  "Figure 4.1.5, 4.1.6 and 4.1.7 show the expression of specific creep, creep coefficient, andcreep factor of the test result against log (t+1), where t is the time when loading starts.

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Figure 4.1.5 Specific creep versus time (log scale)Figure 4.1.6 Creep Coefficient versus time (log scale)

However, those expressions are not quite correct since concrete undergoes strength
development simultaneously. Therefore, it had better express creep as creep strain per elasticstrain as a function of time. This parameter can only obtain from this newly introducing
simple test. Figure 4.1.7 shows the graph of creep strain and modulus of elasticity as afunction of time plotted against log (t+1), where t is the time when loading starts.

Creep strain∆εcModulus of elasticity
∆t
t

t+∆t

log t+1

Figure 4.1.7Creep strain and modulus of elasticity versus time (log scale)Thus, a new creep factor as a function of time can be expressed as Eqn. (4.1.4)

ε c (t + ∆ t ) − ε c (t )(4.1.4) ε e (t + ∆ t ) + ε e (t ) 


2


where εc(t+∆t) - εc(t) is difference of creep strain and [εe(t+∆t) + εe(t)]/2 is the average elasticstrain which can be calculated from modulus of elasticity at time (t+∆t) and t, respectively.
φ c (t ) = ∑ *

     
  (   )
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
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Figure 4.1.8 Creep factor versus time (log scale)Figure 4.1.8 demonstrates the creep factor as the summation of difference of creep strain per
average elastic strain from test result is plotted against log (t+1), where t is the time after startloading.
4.2 Compressive strength and Young’s modulus
Figure 4.2.1 and 4.2.2 show the variation of compressive strength and Young’s modulus ofmortar made with different limestone powder replacement. The replacement of Ordinary
Portland cement by limestone powder reduces the strength both at 1-day and 3-day age.
 / 0   $(  " * .  $(  "

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Figure 4.2.2 Young’s modulus/ 0   $(  "It is clear that Young’s modulus is directly proportional to the compressive strength as shownin Figure 4.2.3.
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Figure 4.2.3 Relationship between compressive strength and Young’s modulus

From the test results, the relationship between compressive strength and Young’s modulus
can be expressed as Eqn. (4.2.1).
E = (64165 ln f c' ) − 208637(kgf/cm2)(4.2.1)
4.3 Effect of type of cement
Table 4.3.1 Mix proportion and environmental condition for the analysis
No.
w/c
Cement type
Ambient conditions
case 130LC
RH = 50% after 1 daycase 230OPC
RH = 50% after 1 day(*LC = Low Heat Cement, OPC = Ordinary Portland Cement)
In this observation, only type of cement is different while the stress/strength ratio is 30% in
both cases. From the test results, as shown in Figure 4.3.1 (a), (b) and (c), mortar made withlow heat cement exhibits higher creep than mortar made with ordinary Portland cement. The
differences result from their differences in chemical composition of cement.


12
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12

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Figure 4.3.1 Effect of type of cement
4.4 Effect of w/c ratio
Table 4.4.1 Mix proportion and environmental condition for the analysis
No.
w/c
Cement type
Ambient conditions
case 230OPC
RH = 50% after 1 daycase 350
OPC
RH = 50% after 1 daycase 470
OPC
RH = 50% after 1 day(*OPC = Ordinary Portland Cement)

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15
10
2

y = 80.009x 411.87x + 943.21

5050
w/c ratio70

y = 80.009x 2 - 411.87x +943.2130

50
w/c ratio(a) Specific creep
creep strain at 7 days
(x10^-6)

1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0

y = 0.173x + 0.851

70(b) Creep coefficient

2

700
600
500
400

y = 0.2577x + 0.8627
1.5
y = 80.009x 2 - 411.87x +943.21

300
200
100
0

1
0.5

creep factor

30

700
600
500
400
300
200
100
0

creep coefficient20

y = 4.2382e0.468x

creep strain at 7 days
(x10^-6)

700
600
500
400
300
200
100
0

specific creep at 7days (x10^6/kgf/cm 2)

creep strain at 7 days
(x10^-6)

In this case, the w/c ratio is varied by varying percent replacement of Ordinary Portland
Cement by limestone powder. From the test results, it is clear that as w/c ratio increases, creep
also increases. This due to the fact that, as w/c ratio increases, the strength of mortar is
reduced thus results in higher creep. Figure 4.4.1 (a), (b) and (c) show graph plotted between
creep strain, specific creep, creep coefficient, and creep factor at 7 days of different w/c ratio.

0
30

50
w/c ratio

70(c) Creep factor

Figure 4.4.1 Effect of w/c ratio
4.5 Effect of age at loading
Table 4.5.1 Mix proportion and environmental condition for the analysis
No.
w/c
Cement type
Ambient conditions
case 130LC
RH = 50% after 1 daycase 1-3
30
LC
RH = 50% after 3 daycase 470
OPC
RH = 50% after 1 daycase 4-3
70
OPC
RH = 50% after 3 day(*LC = Low Heat Cement, OPC = Ordinary Portland Cement)
In this analysis, the tested specimens are studied under sealed conditions and thestress/strength ratio is kept constant so that just the effect of age development can be assessed.
Figure 4.5.1 (a), (b) and (c) show the analytical results for this case. It can be observed thatthe smaller creep, the larger the value of the age at loading is. This can be explained as mortar
loaded at different ages undergoes different growth in strength with creep being smaller thegreater the value of strength, which is the case in older age [15].

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(a) Specific creep
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' !" # "(c) Creep factor

Figure 4.5.1 Effect of age at loading
4.6 Effect of stress/strength ratio
Table 4.6.1 Mix proportion and environmental condition for the analysisNo.
s/s ratio
Cement type
Ambient conditions
case 1-20
20
LC
RH = 50% after 1 daycase 130LC
RH = 50% after 1 daycase 1-40
40
LC
RH = 50% after 1 daycase 1-60
60
LC
RH = 50% after 1 day(*LC = Low Heat Cement))%!

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 * , * *, %'($(  "In this case, the stress/strength ratio is varied from 20%, 30%, 40% and 60%. It is evident thatcreep is significantly affected by stress/strength ratio. The higher stress/strength ratio, thelarger creep. Figure 4.6.1 (a), (b) and (c) represent the effect of stress/strength ratio on creep.

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(c) Creep factor

Figure 4.6.1 Effect of stress/strength ratio
From the experimental results, creep depends on type of cement, w/c ratio, age at loading, andstress/strength ratio, or the other word, the strength at the time of the application of load andthe applied load. Due to lack of data, it cannot be definitely conclude that creep of selfcompacting concrete which contains high volume of cement exhibits high creep. Due to thefact that self-compacting concrete gains high strength even at early age, creep can be less. The
effect of cement content is found to be more pronounced on shrinkage. However, shrinkage
and creep are not independent phenomena. In fact, effect of shrinkage is to increase themagnitude of creep. In addition, it was found that high replacement of cement by limestone
powder results in lower compressive strength, thus creep is larger. It is suggested thatlimestone powder can act as filler in concrete. Filler is defined as a very finely-groundmaterial, of about the same fineness as Portland cement, which, owing to its physicalproperties, has a beneficial effect on some properties of concrete such as workability, density,
permeability, capillarity, and bleeding or cracking tendency. Non-reactive limestone filler is
not considered as an integral part of cement but rather as a replacement for a certain
proportion of aggregate. The filler effect is expected primarily through the reduction of thepaste porosity. It is of interest to study the filler effect of small replacement of limestone
powder, about 5, 10 and 15%, in self-compacting concrete. It may be possible that thestrength of self-compacting concrete made with small replacement of limestone powder is notmuch different from strength of self-compacting concrete made with no replacement, while
the reduction of the paste porosity can be enhanced and thus creep is reduced.
Moreover, some difficulties were encountered and result in errors of data. This is very
important because it is an interactive test where one factor affects the other. For example, forthe case of start drying at 24 hours after casting, it is found that the higher the cement content
the greater the shrinkage strain. However, when drying starts at 72 hours, ordinary Portland
cement gives the lowest shrinkage strain. There are two possible reasons to explain this result.
The first reason is that shrinkage itself is small. Second, it is possible that there occurs surface
cracking due to the great difference between pore water pressure of the inner core of specimen
and the outer surface, which is exposed to drying at 20°C and relative humidity of 50%. For
the corresponding creep specimen, crack may not be observed due to the applying stress. As
mention earlier, if shrinkage strain is wrong, creep strain would be also wrong due to theadoption of superposition method. Moreover, it is very hard to apply load very fast and at thesame time get the required stress. This also results in some errors of the value of the modulus
of elasticity as a function of time and elastic strain. Errors due to measuring contact gauge arealso found to be significant. It is also important to keep constant stress all the time. This kindof test requires skill work and good control.

Chapter 5
CONCLUSIONS
Based on the test results of mortar of self-compacting concrete, it was found that:
1. Creep depends on type of cement, w/c ratio, age at loading, and stress/strength
ratio, or the other word, the strength at the time of the application of load and theapplied load.
2. Replacement of cement by limestone powder about 36.7-53.6% results in decreasein strength, and thus increases creep at early age.
3. The new testing method proposed is beneficial in determining modulus ofelasticity as a function of time. However, good results are difficult to obtainbecause it is an interactive test and requires skill.
4. The new creep factor proposed is found to give good agreement with theconventional terms, which are specific creep and creep coefficient.

Chapter 6
RECOMMENDATIONS FOR FURTHER STUDY
1. Improvement on the testing method in order to reduce errors and obtain goodresults.
2. To study creep behavior of self-compacting concrete with small replacement oflimestone powder.
3. To study creep behavior of self-compacting concrete blended with pozzolanicmaterials, for example, fly ash, slag, and silica fume.
4. To study the effect of relative humidity, temperature, superplasticizer on creep ofself-compacting concrete at early age by performing the new testing method.
5. To study the differences in behavior of creep of mortar and concrete of selfcompacting concrete in order to simulate a model which can predict creep ofconcrete from mortar test.
6. To study the differences in behavior of creep of normal concrete, high strength
concrete, and self-compacting concrete by performing the new testing method.
7. To study tensile creep of self-compacting concrete.

REFERENCES
1. Neville, A. M., Creep of Concrete: Plain, Reinforced, and Prestressed, North-Holland
Publishing Company, Amsterdam, 1970, pp. 11,15.
2. L’Hermite, R., What do we know about the plastic deformation and creep of concrete?,
RILEM Bulletin No. 1, March 1959, pp. 21-51.
3. Ali, I. And Kesler, C.E., Rheology of concrete : a review of research, Engineering
Experiment Station, University of Illinois, Urbana, Bulletin 476, 1965, pp.101.
4. Meyers, B. L. and Pauw, A., Apparatus and instrumentation for creep and shrinkage
studies, Highway Research Record No. 34, 1963, pp. 1-18.
5. Best, C. H., Pirtz, D. and Polivka, M., A loading system for creep studies of concrete,
ASTM Bulletin No. 224, September 1957, pp. 44-47.
6. Neville, A. M., Creep of Concrete: Plain, Reinforced, and Prestressed, North-Holland
Publishing Company, Amsterdam, 1970, pp. 28.
7. Neville, A. M., Role of cement in the creep of mortar, ACI Journal, Proc. 55, 1959, pp.
963-984.
8. Iriya, K., Hattori, T., and Umehara, H., Study on characterization of compressive andtensile creep behavior for early aged concrete, Journal of Materials, Concrete Structures andPavements, JSCE, No. 599/V-40, August 1998, pp. 105-117.
9. Washa, G.W. and Fluck, P.G., Effect of sustained loading on compressive strength andmodulus of elasticity of concrete, ACI Journal, Proc. 46, 1959, pp. 693-700.
10. Lorman, W.R., The theory of concrete creep, ASTM Proc. 40, 1940, pp. 1082-1102.
11. Iriya, K., Hiramoto, M., Hattori, T., and Umehara, H., Study on compressive creep in
concrete at early age, Journal of Materials, Concrete Structures and Pavements, JSCE, No.
599/V-40, August 1998, pp. 1-14.
12. Ouchi, M., Hibino, M., Ozawa, K. and Okamura, H., A Rational Mix-Design for Mortar in
Self-Compacting Concrete, Proceeding of the Sixth East-Asia-Pacific Conference on
Structural Engineering & Construction, Taipei, Taiwan, 1998, pp. 1307-1312.
13. Ouchi, M. and Edamatsu, Y., A Simple Evaluation Method for Interaction between Coarse
Aggregate and Mortar Particles in Self-Compacting Concrete, the Proceedings of the RILEM
Symposium on Self-Compacting Concrete, Stockholm, Sweden, 1999.
14. Neville, A. M., Creep of Concrete: Plain, Reinforced, and Prestressed, North-Holland
Publishing Company, Amsterdam, 1970, pp. 17.
15. Neville, A. M., Creep of Concrete: Plain, Reinforced, and Prestressed, North-Holland
Publishing Company, Amsterdam, 1970.

Appendix A Total strain, shrinkage strain, and elastic strain of all specimens















              













! "##    
     

























%       $        
























 !             



























! "$         


























%! "$  $       


























%              




























































































%              

%&              &Appendix B Creep strain of all specimens















              













! "##    
     

























%       $        
























 !             




























! "$         



























%! "$  $       


























%              





























%              









































%&              &













Appendix C Young’s modulus of all specimens















              













! "##    
     

























%       $        
























 !             




























! "$         



























%! "$  $       


























%              





























%              









































%&              &













Appendix D Specific creep of all specimens















              













! "##    
     

























%       $        
























 !             




























! "$         



























%! "$  $       


























%              





























%              









































%&              &













Appendix E Creep coefficient of all specimens















              













! "##    
     

























%       $        
























 !             




























! "$         



























%! "$  $       


























%              





























%              









































%&              &













Appendix F Creep factor of all specimens















              













! "##    
     

























%       $        
























 !             




























! "$         



























%! "$  $       


























%              





























%              









































%&              &