EARLY AGE CREEP OF SELF-COMPACTING CONCRETE USING LOW HEATCEMENT AT DIFFERENT STRESS/STRENGTH RATIOS

Krit Kangvanpanich
I.D. 1045025

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

Supervisor
Associate Professor Masashiro Ouchi

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

February 2002

Abstract
In this paper I will investigate the influence of different stress/strength ratios on the creep ofunsealed and sealed of self compacting concrete and normal concrete using Low Heat Cement
and the corresponding properties of Ordinary Portland Cement is outlined in this studied. The
results were compared with a similar mixture of Low Heat Cement and Ordinary Portland
Cement. The creep strain was measured at different stress/strength ratios of 10, 20, 30, 40 and 60
percent, for a maximum period of 7 days. All the tests were carried out in the room attemperature of 20°C and relative humidity of 50%. The study included forty mix proportions ofsealed and unsealed conditions with water -cement ratio equal to 0.3. Half of the mixes studied
were based on self -compacting concrete and the other half were based on normal concrete. Theage at loading of the concretes in the creep studied was carried out at 24 hours after casting.
Parallel studies were performed on strength (fc) and relative humidity (RH).
Creep of self-compacting concrete and normal concrete were found to vary linearly withlogarithm of time for both sealed and unsealed concrete. Also, creep of self-compacting concreteand normal concrete were found to be a linear function of stress/strength ratio between 10 and 60
percent.
The results show that the specimens subjected to air -dried curing exhibited higher creep
strains than sealed specimens; creep strains decrease with an increase in concrete compressive
strength at the time of loading.
KEYWORDS: Creep, Shrinkage, Self Compacting Concrete, Low heat cement, Stress/Strength
Ratios.

Acknowledgements
In preparation of this work, the generous contribution of many people is essential. The author
wishes to express my deep gratitude and sincere appreciation to my thesis advisor, Associate
Professor Masashiro Ouchi for his enthusiastic guidance, constructive, criticism valuablesuggestions and encouragement, which were of immeasurable value throughout the thesis study.
Profound is also extended to Professor Nobumitsu Fujisawa, Professor Hiroshi Shima andProfessor Mikio Kadota for their kindness, helpful recommendations.
Thanks also to Mr. Masaru Ueno for comment and suggestion in the process of laboratory
part. I would also like to thanks the Kochi University of Technology for providing on an
opportunity to undertake my graduated study and provide a full scholarship over duration thegraduate at Kochi University of Technology.
I would like to express the warm thanks of the faculty and staffs of Infrastructure System
Engineering Department during my study. My appreciation is also to dear seniors, friends oftheir goodwill, encouragement to contribute to this study.
Especially, I wish to express my deepest gratitude and indebted to my mother and father for
their infinite sacrifice, constant support. I would like to dedicate this thesis to them.

Contents
Abstract
Acknowledgements
Contents
List of Figures and Tables
1. INTRODUCTION
1.1 Objective and scope of study
LITERATURE REVIEW
1.2 General
1.3 The origin of creep
1.4 Factors Influencing Creep
1.5 Effect of Creep
1.6 Autogenous volume changes and expansion cements
1.7 Volume changes due to moisture changes
1.8 Effect of cement and water contents on shrinkage
1.9 Effect of microcracking
1.10Moisture diffusion in concrete
1.11 Basic equation of creep and shrinkage
1.12 Role of vapor pressure in hygral deformations of concrete
1.13 Summary of literature review and purpose of study
2. EXPERIMENTAL PROGRAM
2.1 Test variables
2.2 Material and mix proportions
2.3 Properties of fresh concrete
2.4 Specimen preparation
2.5 Experimental method
2.6 Experimental details and procedure
3. TEST RESULT AND ANALYSIS
3.1
Creep of self compacting concrete and normal concrete
3.1.1 Creep of normal concrete and self compacting concrete under unseal
condition
3.1.2 Creep of normal concrete and self compacting concrete under sealcondition
3.1.3 Effect of stress strength ratio on creep
3.1.4 Effect of powder content on creep
3.1.5 Effect of water-cement ratio on creep
3.1.6 Comparison of test result with codes
3.1.7 Relationship between sealed and unsealed condition of SCC andnormal concrete
3.1.8 Regression analysis
3.2
Relationship between shrinkage and creep
3.2.1 Effect of moisture loss on creep

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3.2.2 Effect of aggregate content on autogenous shrinkage
3.2.3 Relationship between autogenous shrinkage and drying shrinkage
3.2.4 Autogenous drying near the surfaces during seal conditions
3.2.5 Chemical shrinkage

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4. CONCLUSIONSRECOMMENDATIONS OF FURTHER STUDYREFERENCES
Appendix A
Appendix B

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List of Figures and Tables
Figure No.
2.2.1 Mixing procedure of self-compacting concrete
2.5.1 Geometry and size of test specimens
3.1.1 Normal concrete with unseal-load condition at 24 hours after casting
3.1.2 Normal concrete with seal-load condition at 24 hours after casting
3.1.3 Normal concrete at 24 hours after casting
3.1.4 SCC with unseal-load condition at 24 hours after casting
3.1.5 SCC with seal-load condition at 24 hours after casting
3.1.6 SCC at 24 hours after casting
3.1.7 Compare compressive strength of normal concrete andself-compacting concrete
3.1.8 Normal concrete with unseal-load condition at 24 hours after casting
3.1.9 Normal concrete with seal-load condition at 24 hours after casting
3.1.10 SCC with unseal-load condition at 24 hours after casting
3.1.11 SCC with seal-load condition at 24 hours after casting
3.1.12 SCC with seal-load,w/c=0.25 stress/strength ratio=0.3
3.1.13 SCC with unseal-load, w/c=0.25 stress/strength ratio=0.3
3.1.14 SCC with seal-load, w/c=0.5 stress/strength ratio=0.3
3.1.15 SCC with unseal-load, w/c=0.5 stress/strength ratio=0.3
3.1.16 SCC with seal-load, w/c=0.7 stress/strength ratio=0.3
3.1.17 SCC with unseal-load,w/c=0.7 stress/strength ratio=0.3
3.1.18 SCC with seal-load, stress/strength ratio=0.3 at 7days after casting
3.1.19 SCC with unseal-load, stress/strength rartio=0.3 at 7 days after
casting
3.1.20 Creep V.S. Age(Self compacting concrete)
3.2.1 Compare moisture loss of normal concrete and SCC with
unseal-load condition at 24 hours after casting
3.2.2 Comparison of modulus of elasticity of self-compacting concreteand self-compacting mortar
3.2.3 Comparison of self-compacting concrete and self-compacting mortar
3.2.4 Relationship between W/C and contribution of autogenous shrinkage

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3.2.5 Moisture distribution of underwater specimen
Table No.
2.2.1 Chemical composition
2.2.2 Specific gravity of materials
2.2.3 Mix proportion
2.2.4 Properties of each mix proportion
2.3.1 Type and specimen size
3.1.1 Creep ratios for unsealed of SCC compared with normal concrete
3.1.2 Creep ratios for sealed of SCC compared with normal concrete
3.1.3 Creep ratios for unsealed/sealed using SCC and normal concrete
3.1.4 Constants A and B and coefficient of correlation R for equations ofShrinkage versus age using normal concrete
3.1.5 Constants A nad B and coefficients of correlation R for equation of
Shrinkage versus age using self-compacting concrete
3.1.6 Constants A and B coefficient of correlation R for equations of creep
age using normal concrete
3.1.7 Constants A and B and coefficient of correlation R for equations ofcreep versus age using self-compacting concrete

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Chapter 1
INTRODUCTION

1.1 Objective and scope of study
During the hydration process, significant thermal and shrinkage gradient can cause stress that
could lead to cracking of concrete at early age. The presence of creep during the hydration
period, at an early age would have an effect of reducing this stress. During hydration whentemperature is increasing, tensile stress develops near the concrete surface where the temperature
is lower, and compressive stress develops at the center where higher temperature exists. In
addition, higher shr inkage strain occurs on the surface, which also causes tensile stress near thesurface and compressive stress at the center. During this phase the concrete has lower strength,
lower elastic modulus, and significant early-age creep. Although the tensile strength of theconcrete is low, the combined effect of low modulus and high creep will significantly reduce thetendency for surface cracking. When the center of the concrete starts cooling, the stress due tothermal gradient cause the reverse effect, wit h reduced compressive stress and perhaps eventensile stress due to thermal gradient cause the reverse effect, with reduced compressive stressand perhaps even tensile stress developing at the center of the concrete. During this phase theconcrete strength is higher, resulting in an increased modulus of elasticity and reduced creep.
Thus it is important to study the early age creep and shrinkage of concrete to accurately predictthe resulting stress due to heat of hydration.
Several researchers have studied from different aspects on the effect of admixtures in
concrete. However, very little information is available about the creep behavior at different
stress/strength ratios for unsealed and sealed concrete using low heat cement (Unsealed conditionmeans the moisture loss to the environment, put specimen in air dried condition and Sealedcondition mean wrap specimen with polyethylene, do not let the moisture loss to theenvironment). Moreover, from JSCE and ACI codes have some limitation on cement contents:
JSCE has limited the cement content to be less than 500kg/m3 and ACI has limit the strength of
concrete to be less than 1.3. The purpose of this study is to clarify whether JSCE or ACI codes
can predict creep when cement content above the codes limitation or not and this study will give
relationship between creep at the early age with vary water-cement ratios, stress-strength ratios
and powder contents when comparing with time. All of the specimen will be carried out at thecontrolled room temperature of 20°C and the relative humidity of 60%.
The distinction between sealed and unsealed concrete for the practical designer is clearly
illustrated by comparing mass and ordinary concrete structures. In mass concrete structures, suchas dams and pressure vessel walls that have a thickness of over 5 ft (152.4cm), moisture ispractically sealed within the concrete; while in ordinary structures that have a thickness of lessthan 5 ft. (152.4 cm), moisture within the concrete may evaporate into the atmosphere, dependingon the environmental conditions.

LITERATURE REVIEW
1.2 General
Concrete properties change rapidly in the few days following the mixing of water into thecement. Hydration is induced at the interface between pore water and particles of cement. CSH
gels form. This results in voids with diameters of a few decades of Å. The initial distribution ofvoid diameter is determined by the distribution of cement particles as well as the distribution of
aggregates in the mixture. The initial size of cement particles is almost the same as the initial
minimum pore size, which is almost 1 um. Next, CSH gel penetrates into voids and forms
smaller voids. CSH gel is said to have a size of 10~104 Å near unhydrated cement particles
separated with water, especially in the beginning. The water is called gel pore water or capillarypore water and can be vaporized. The existence of a pore system naturally affects the initialstress gradient if pore water pressure is somehow induced. Moreover, the initial concrete statealso effects behavior at a later age in terms of physical properties [4]. And this is especially
important for massive concrete structures; hydration heat can occur and thermal stress problems
may induce. Since concrete stiffness may be increased with the advanced of chemical hydration
at an early age, compressive thermal stresses may be mainly induced in the concrete. However, inthe few days after casting, the stress history reveals a contrary pattern and tensile stress may be
induced. At this stage, creep deformation may govern and may offset stress. However, theseeffects have not been clarified. If a deformational analysis of the creep problem is performed, thecreep function for hardened concrete may be interpolated. If the pore water has an effect,
however, it is the effect of size dependent. It is said that concrete creep is generally larger if amember size is smaller. However, creep is a material property and does not depend on size,
while pore water migration is a process of diffusion [7]. Moreover, the effect of creep ofcompression and tension is considered to be the same, while the effect of pore water in thecompressive stress state is quite different from that in tension. The time dependent behaviors ofconcrete at an early age can be assumed to be affected by pore water in the concrete. However, aclear mechanism is still being investigated.
Creep of concrete resulting from the action of a sustained stress is a gradual increase in strain
with time; it can be of the same order of magnitude as drying shrinkage. As defined, creep does
not include any immediate elastic strains caused by loading or any shrinkage or swelling causedby moisture changes. When a concrete structural element is dried under load the creep that
occurs is one to two times as large as it would be under constant moisture conditions. Adding
normal drying shrinkage to this and considering the fact that creep value can be several times aslarge as the elastic strain on loading, it may be seen that these factors can cause considerable
deflection and that they are of great important in structural mechanics [9].
Two mechanisms of creep in absence of drying may be distinguished: short-term creep andlong-term creep. Short-term creep is a consequence of redistribution of capillary water within the
structure of the hardened cement paste, and the long-term creep is a consequence of displacementof gel particles under load and, to a lesser extent, of creep of the gel particles. Simultaneous
drying further complicates the process because instantaneous plus creep deformation is largerthan the sum of creep and shrinkage deformations measured separately. The additional strain isnormally associated with drying creep. In analysis and design, creep is usually accounted for byusing a creep factor that is the ratio of creep strain at any time to instantaneous strain.
If a sustained load is removed, the strain decreases immediately by an amount equal to theelastic strain at the given age; this is generally lower than the elastic strain on loading since theelastic modulus has increased in the intervening period. This instantaneous recovery is followed
by a gradual decrease in strain, called creep recovery. This recovery is not complete because
creep is not simply a reversible phenomenon [12].
It is now believed that the major portion of creep is due to removal of water from between the
sheets of a calcium silicate crystallite and to a possible rearrangement of bonds between thesurfaces of the individual crystallites.
Extensive research has been carried out to study the phenomena of creep in concrete. These
investigations has been summarized by Neville, Dilger, and Brooks [5], Bazant and Wittmann [6]and CEB-FIP [3], factors influencing shrinkage and creep are concrete strength, water-cement
ratio, relative humidity, temperature, content of aggregate, member size and loading age.
Creep of concrete is a complex problem, especially at very early ages, due to the complexityof the material [1]. A limited amount of research has been conducted to study the creep ofconcrete during the early period of hydration, particularly for high strength concrete using low
heat cement. Byfors [7] studied the early-age creep of normal strength concrete with different
concrete compositions and water cement ratios. The age at the time of loading varied from about
8 hrs to 28 days with an applied stress-to strength ratio equal 0.3. All of the specimens weresealed and kept at a relative humidity of 80 percent and a temperature of 20°C. It was found thatspecific creep increases considerably due to very early loading. Data are presented for the first
100 hrs after load was applied. Since the properties of concrete change very rapidly during theearly period of hydration, this phenomenon is very complex and highly dependent on maturity(i.e., temperature and time) and moisture.
To account for the influence of moisture, creep of concrete is divided into basic creep anddrying creep. Basic creep of concrete is defined as creep in a sealed condition, whereas drying
creep, sometimes called the Picket effect, is the additional creep caused by moisture loss underconstant stress. It is typically assumed that creep and shrinkage are phenomena that do notinteract, and hence the total strain can be obtained by summing the elastic, creep and shrinkage
strains.
It is well known that earlier age loading results in higher elastic and creep strains. In
particular, very early loading may result in higher maturing creep due to the formation of cement
hydration products [5]. It is interesting to note that at very early ages the applied stress tostrength ratio actually decreases with time due to the hydration process (i.e., concrete strength
increases with time).

1.3 The Origin of Creep
The first observation is the importance of the viscous component in the beha vior of concrete.
The strain which is produced in the course of a creep test (after subtracting shrinkage) at the endof loading may be three or four times intensity of the initial (elastic) strain, which is utterly
exceptional for a mineral. The role of water content is very important here and is paradoxical; if
tests are conducted in which there is no exchange of water with the ambient environment (basic
creep) the lower the evaporation water content of the sample, the lower the creep strain, to theextent that it can become negligible. However, if the tests are conducted in a dry atmosphere, thegreater the drying the greater the creep- up to five times more than the basic creep of the concretewith the highest water content. [11]The water content of concrete plays an essential role in creep; concrete which has dried to thestate where evaporable water has been totally eliminated is not subject to creep. Twomechanisms are apparent from kinetic analysis of basic creep for pure cement pastes [12] which
are completely protected from desiccation. Both mechanisms are compatible with the mobility ofwater. The short characteristic time of the first mechanisms on the order of 7 days.[12] suggests
a stress-induced water movement towards the largest diameter pores (characteristic distance ofthe order of 0.1-1 mm). This short-term creep mechanism was first suggested by [11]: it may be
attributed to a change of the hygral equilibrium in the gas filling space which generates strain andstresses (and eventually microcracking), which results in the short-term component of creep. The
activation energy of this first mechanism could be that of permeation in the saturated capillarypores.
The second mechanism corresponds to an irreversible viscous behavior, and seems to be more
related to viscous flow in the hydrates (slippage between layers which is increasingly inhibitedover time, particularly if the hydrates start to lose water). This long-term creep occurs underalmost constant volume [13], which is consistent with a viscous slippage mechanism.
1.4 Factors Influencing CreepConcrete that exhibits high shrinkage generally also shows a high creep, but how the two
phenomena are connected is still not understood. The evidence suggests that the y are closely
related. When hydrated cement is completely dried, little or no creep occurs; for a given concrete
the lower the relative humidity and the higher the creep.
The strength of concrete has a considerable influence on creep, and within a wide range creep
is inversely proportional to the strength of concrete at the time of application of load. From this
it follows that creep is closely related to the water-cement ratio. There is no doubt also that themodulus of elasticity of aggregate controls the amount of creep that can be realized and concretes
made with different aggregates exhibit creep of varying magnitudes [12].
1.5 Effect of Creep
Creep affects strains, and deflections, also often stress distribution, but the effects of creep
vary with the type of structure.

Creep of plain concrete does not affect the strength although under very high stresses creep
hastens the approach of the limiting strain at which failure takes place; this applies only when thesustained load is above 85 or 90 percent of the rapidly applied static ultimate load [4].
The influence of creep on the ultimate strength of a simply supported reinforced concrete
beam subjected to a sustained load is not significant, but the deflection increases considerably
and may in many cases be critical consideration in design. According to Glanville and Thomas[10], there are two distinct neutral surfaces in a beam subjected to sustained loading; one of zerostress, the other of zero strain [8]. This arises from the fact that an increase in the strain in
concrete leads to an increased stress in the steel and a consequent lowering of the neutral axis
when an increasing depth of concrete is brought into compression. As a result, the elastic strain
distribution changes, but the creep strain is not cancelled out, so that at the level of the newstress-neutral-axis a residual tensile strain will remain. At some level above this axis, there is afiber of zero strain at any time although there is a stress acting [11].
With respect to reinforced concrete columns, creep results in a gradual transfer of load fromthe concrete to the reinforcement. Once the steel yields, any increases in load is taken by theconcrete, so that the full strength of both the steel and the concrete is developed before failure
takes place, a fact recognized by the design formula. However, in eccentrically loaded columns,
creep increases the deflection and can lead to buckling [14]. In statically indeterminate structures,
creep reduced internal stresses due to non-uniform shrinkage so that there is a reduction incracking. In calculation creep effects in structures it is important to realize that the actual timedependent deformation is not the free creep of concrete but a value modified by the quantity andposition of reinforcement.
On the other hand, with regarding to mass concrete, creep in itself may be a cause of cracking
when restrained concrete mass undergoes a cycle of temperature change due to the developmentof the heat of hydration and subsequent cooling. Creep relieves the compressive stress inducedby the rapid rise in temperature so that the remaining compression disappears as soon as somecooling take place. On further cooling of concrete, tensile stresses develop and, since the rate ofcreep is reduced with age, cracking may occur even before the temperature has dropped to theinitial value. For this reason, the rise in temperature in the interior of a large concrete mass must
be controlled by the use of low heat ce ment, a low cement content, precooling of mix ingredients,
limiting the height of concrete lifts, and cooling of concrete by circulating refrigerated water
through a network of pipes embedded in the concrete mass.
The loss of prestress due to creep si well known and, accounts for the failure of all earlyattempts at prestressing. It was only the introduction of high tensile steel, whose elongation isseveral times the contraction of concrete due to creep and shrinkage that made prestressing a
successful proposition [15].
The effects of creep may thus be harmful but, on the whole, creep, unlike shrinkage, isbeneficial in relieving stresses concentrations and has contributed very considerably to thesuccess of concrete as a structural material.

1.6 Autogenous Volume Changes and Expansion Cements
Before volume changes resulting from drying or wetting of hardened concrete are discussed,
autogenous volume changes should be mentioned because they occur where little or no change intotal moisture content is possible and are of particular importance in the interior of mass concrete.
Two opposing effects can be produced. As reaction between water and the unhydrated cement
proceeds, the actual volume of the solid increases. This causes stresses through the set structure
and results in expansion. At later ages, the water available for the reaction will decrease,resulting in self-desiccation of the cement paste and a shrinkage ranging from 0.001 to more than
0.015 percent [13].
1.7 Volume Changes due to Moisture Changes
Although the mechanism of volume change that occurs during moisture change is not fully
understood, much has been learned to provide useful information for engineering purposes.
When concrete is dried, the first water to be removed causes no changes in volume. This isconsidered to be free water held in rather large “pores”. With continued drying, shrinkage
becomes quite large and at equilibrium in 50 percent RH values in excess of 0.10 percent havebeen recorded for some concretes. Shrinkage values for neat cement paste have been observed inexcess of 0.40 percent; the difference of this value from that of concrete is due to various
restraints. A large portion of concrete is made up of relatively inert aggregate (from 3 to 7 times
the weight of cement) and this, together with reinforcement, reduces shrinkage. In addition tointernal restraints, some restraint arises from non-uniform shrinkage within the concrete member
itself [14]. Moisture loss takes place on the surface so that a moisture gradient is established.
The resultant differential shrinkage is associated with internal stresses, tensile near the surfaced
and compressive is the core, and the result in warping or cracking.
1.8 Effect of Cement and Water Contents on Shrinkage
Water content is probably the largest single factor influencing the shrinkage of paste andconcrete. Typical shrinkage values for concrete specimens with a 5 to 1 aggregate-cement ratio
are 0.04, 0.06, 0.075 and 0.085 percent for water-cement ratio of 0.4, 0.5, 0.6 and 0.7,
respectively. One of the reasons is that the density and composition of calcium silicate formed at
different water-cement ratios may be slightly different. In general, a higher cement content
increase s the shrinkage of concrete; the relative shrinkages of neat paste, mortar and concrete
may be of the order of about 5, 2, and 1. For given materials, however, and a uniform watercontent, the shrinkage of concrete varies little for a wide range of cement contents; a richer mix
will have a lower water-cement ratio and these factors offset each other [10].
1.9 Effect of microcracking
The drying creep strain sCd (t,t’,t o ), also called the stress-induced shrinkage, includes theeffects of microcracking (or cracking) and of pore humidity rate on the apparent creep viscosities,
both of which are almost equally important [1]. In a specimen under sufficient compression theobserved shrinkage is much closer to the true material shrinkage (free shrinkage of a smallelement) than in a load-free specimen. The reason is that the shrinkage observed on a load-free
specimen is significantly offset by microcracking.
This is true also of the final values, because microcracking is largely irreversible (thecrackings, once formed, cannot close completely). This phenomenon causes the average crosssection shrinkage to depend on stress, which is taken into account by the term sCd(t,t’,to ).
The microcracking can be enhanced by restraint which reduces the shrinkage strain; the terms Cd(t,t’,to ) is essential for realistic calculation of shrinkage stress in restrained concrete beams or
slabs [1].
1.10 Moisture Diffusion in Concrete
The moisture flux (J) is proportional to the gradient of the pore relative humidity, and isexpressed as Eq. 1 [1]:J = -k grad h(1)
Where h is the pore relative humidity, and k is the permeability. The specific water content (w)is the function of pore relative humidity (h) in the desorption isotherm, i.e.,w = w(h), so that the mass balance equation can be expressed as follows:∂w ∂w ∂h 1 ∂h==
= − divJ(2)∂t∂h ∂t c ∂t∂w
whereis the moisture capacity, which represents the slope of the desorption isotherm.
∂hEliminating w and J from Eqs. 1 and 2, the nonlinear moisture diffusion equation can be obtained
as follows:∂h= cdiv(k grad h) = div(D grad h)(3)∂twhere D is the moisture diffusion coefficient, and defined as ck. The moisture diffusion
coefficient is dependent on the relative humidity and temperature. In CEB-FIP(’90) model code,for isothermal conditions, the moisture diffusion coefficient is expressed as a function of the pore
relative humidity 0<h<1 according to Eq. 4:


1− α

D(h) = D1 α +(4)n 
1 + [(1 − h) /(1 − hc )] Where D 1 is the maximum of D(h) for h = 1.0, a = Do /D1 , Do is the minimum of D(h) for h= 0.0,
hc is the pore relative humidity at D(h) = 0.5D 1 , and n is an exponent. a = 0.05, hc = 0.08 and n =15 are approximately assumed [3]. D1 may be also estimated from Eq. 5:
D1, 0
D1 =
(5)
f ck / f cko
Where D1,0 = 3.6*10-6 m2 /h, fcko = 10 MPa, and the characteristic compressive strength fck may be
estimated by the mean compressive strength fcm , i.e., fck = fcm – 8 MPa.

As the boundary condition of moisture, it is necessary to correlate the surface moisture withthe humidity of the environmental atmosphere. On the exposed surface S, the boundary
condition is as follows: ∂h 
D   = f (hen − hs )(6) ∂n  s
Where f is the surface factor, hen is environmental humidity, and hs is the relative humidity on the
exposed surface. Bazant dealt with this problem by assuming an additiona l thickness to thespecimen, i.e., the equivalent surface thickness [4].
1.11 Basic equation of creep and shrinkage
When some load acts on the section consisting of steel and concrete, the initial elastic stresss co is generated in a concrete and a creep strain of concrete proceeds as time passes. This
relationship can be shown by the Dischinger’s basic equation regarding creep and shrinkage asfollows:
σ co
σ k + s (t) t σ k +s ( t ) dϕ (τ )×
ek+s(t) =⋅ ϕ (t ) ++ ∫+es(t)
(7)
Ec
dτ
Ec
Ec
0
Where: ek+s(t) = strain caused by creep and shrinkage; sk+s(t) = stress caused by creep andshrinkage; es(t) = strain of shrinkage; f(t) = creep coefficient; and Ec = Young’s modulus.
This equation can be rewritten as follows when considering the assumption (8) and very shorttime intervals:σ∆σ k + s∆ϕ∆ ε k +s = co ⋅ ∆ ϕ +(1 +) + ∆ε s
(8)
Ec
EC
2

For ACI creep equation:∆ ε k +s =σ co∆σ k +s⋅ ∆η ++ ∆ε sEϕEγ(9)where:
Ef =

Ec
∆ϕ
1+
2

∆η =

∆ϕ
∆ϕ
1+
2

(10)

If we divide the time ∆ t into very small intervals, we can obtain the generated strain to good
accuracy by using the numerical integration method from this equation, because both ∆ f and ∆ εcan be given as the increments during the very short time.
1.12 Role of Vapor Pressure in Hygral Deformations of Concrete
When concrete is exposed to drying, hygral equilibrium is upset and water will evaporate fromthe capillaries until the vapor pressure is reduced to the ambient value.[8] The tension in thecapillary water rises, and, to maintain equilibrium, the compression in the solid phase also
increases. Hydrostatic tension is only developed when a meniscus is formed in a capillary. The
capillary stress is given by the simple formula Ρ = 2γ / R , where γ is the surface tension of waterin a cylindrical capillary and r is the radius of meniscus.
The capillary tension is indicated by the internal vapor pressure; the higher the tension, thelower the vapor pressure. Using the Kelvin equation, Powers calculated that for vapor pressure in
the specimen equal to 50 percent of the saturated vapor pressure at the atmosphere pressure, theresult was 110 MPa [5]. The physical possibility of tension is accepted by Powers because ofcohesive forces between the solid and the water molecules. The mechanisms of increasing thetension can be that of increasing the menicus curvature by evaporation.
The vapor pressure controls not only capillary tension stress but also disjoining pressure.
When the specimen is saturated, the disjoining pressure in the gel is at maximum. It decreases as
the vapor pressure decreases, being proportional to the change in the logarithm of ambient
relative humidity (RH). Any change in the disjoining pressure also changes the surface tensionof the solid phase.
The water content of a capillary system depends on the moisture content of the surrounding
air. At 100 percent RH, all the capillary voids are filled with water, at 0 percent RH, they
become empty. At an intermediate RH, the quantity of capillary water is determined by the
moisture content of the air and the capillary structure (diameter) of the porous system.
To better imagine the role of vapor pressure in shrinkage phenomena, it can be helpful toconsider the following simplified scheme based only on the account of capillary tension stressdeveloped when a meniscus is formed. Let’s consider a single capillary of linear variable radiusthat reflect a variety of capillaries of different form and with different radii [4].
The contact angle between pure water, which has a tendency to wet surfaces, and the capillarywall is accepted as zero (as for clean glass capillary). The concave meniscus of the radius R,
dependent on RH of the air and vapor pressure, rises on contact between the liquid surface andsolid. Free water begins to evaporate when the relative humidity drops slightly below RH= 100
percent of saturated level [3]. The radius of the curvature R does not change until the meniscus of
the spherical form will be formed. That is why the removal of free water should not be
accompanied by shrinkage.
The capillary water can continue to be removed only if the radius of the meniscus will bedecreased by r<R, but this will result in capillary contraction and consequent shrinkage of thematerial. The capillary radius at which evaporation of capillary water commences is a directfunction of RH. For example, r = 0.1 um at RH=99 percent and 0.001 um at RH= 34.8 percent.
[9] The removal of the capillary water continues as long as there is no need for the further
decrease of meniscus radius and or the additional drop in vapor pressure [5].
When concrete is sealed, the vapor pressure increase quickly and changes the meniscus
curvature so that the level of liquid becomes flatter and the effective average (radius of meniscus

increases. The releases the capillary surface tension and immediately leads to capillary distention
and consequent swelling deformation. However , if the material is dried out to the other moisture
content that corresponds to the other value of meniscus curvature (r instead of R), it can be seenthat the previous capillary distention radius will cause a similar value of swelling deformation[6].
1.13 Summary of Literature Review and Purpose of Study
Self compacting concrete (SCC) is considered as a concrete which can be placed andcompacted under its self-weight with little or no vibration effort, and which is at the same timecohesive enough to be handled without segregation or bleeding. It is used to facilitate and ensure
proper filling and good structural performance of restricted areas and heavily reinforced
structural member. Self compacting concrete contain high amount of cement which cause highshrinkage (changed in strain due to loss of moisture) and can cause high creep(changed in strain
due to loading). There are many empirical formulas to predict creep of self compacting concretesuch as from JSCE codes or ACI codes or Dischinger’s equation, etc. However, those empiricalformulas have some limitation on the cement content such as the limitation of cement content for
JSCE and ACI codes must be less than 500kg/m3. But self compacting concrete contains theamount of cement higher tha n 500kg/m3 , then this study will clarify whether JSCE or ACI codes
can predict of self compacting concrete or not. And this study will find a relationship of creep ofself compacting concrete at the early age with vary water-cement ratios, stress-strength ratios andpowder contents.

Chapter 2
EXPERIMENTAL PROGRAM
2.1 Test Variables
To study the effect of creep using Self-Compacting Concrete (Low Heat
Cement) compared with Normal Concrete (Low Heat Cement), concrete were compressed withfive levels of stress to strength ratios: 10%, 20%, 30%, 40% and 60% with varying water tocement ratios of 0.25, 0.3, 0.5 and 0.7: vary powder content in 250, 400, 550 kg/m3 . In thisstudied unseal-load, seal-load, unseal-unload, and unseal-unload conditions were examined.
2.2 Material and mix proportions
The chemical composition and physical properties of Low Heat Cement (LH) and Ordinary
Portland Cement (OPC) are given in Table 2.2.1 and Table 2.2.2. Table 2.2.3 gives the mix
composition and strength characteristics of studied concrete.
Table 2.2.1 Chemical Composition
Chemical Analysis, percent

LH-Analysis Results

OPC-Analysis Results

Silica (SiO2)

25.4

21.69

Alumina (Al2O3)

3.5

5.89

Iron oxide (Fe2O3)

3.5

2.8

Calcium oxide (CaO)

62.5

63.15

Magnesium oxide (MgO)

1.1

1.87

Sulfur trioxide (SO3)

2.2

2.05

Available alkalikes as Na2O

0.22

0.5

K 2O

0.38

0.41

Physical Analysis

Analysis Results

Fineness (g/cm 2)

3248

3400

Compressive strength at 3 days MPa

11.6

27.5

Compressive strength at 7 days MPa

17

42.8

Compressive strength at 28 days MPa

40.5

63.8

Table 2.2.2 Specific gravity of materials
materials
Specific Gravity
Ordinary Portland Cement
Low Heat Cement
Limestone
Sea SandCrushed sandCoarse Aggregate

3.15
3.27
2.7
2.58
2.57
2.68

Fine Aggregate

2.64

Table 2.2.3 Mix Proportion
No.

Type

w/p

1 Normal 0.94
2 Normal 0.94
3 SCC 0.94
4 SCC 0.94
5 SCC 0.94
6 SCC 0.94%
replacement cement

w/c
0.3
0.5
0.25
0.3
0.5
0.7

0.5
36.7
0.5
22.6
36.7
53.6

Ls

water

sand

gravelSP(kg/m3) (kg/m3) (kg/m3) (kg/m3) (kg/m3) (kg/m3)
485
2
144
758
1039 4.877
291
169
144
758
1039 4.599
597
3
179
774
848
9.295
448
131
179
774
848
6.94
358
207
179
774
848
5.938
259
293
179
774
848
4.91

Sealed condition, Air-dried condition, Stress Strength Ratios of 0.1, 0.2, 0.3, 0.4 and 0.6 are allapplied to all mix proportions.
Table 2.2.4 Properties of each mix proportion
No.

Type w/p

Funnelspeed
Slump flow
(mm. X mm.) (sec.)

w/c

Box test
(cm.)

Temp.
(celcius)

Slump height(cm.)

1 Normal 0.94
2 Normal 0.94

0.3
0.5

-

-

-

23.8
22.8

13.9
18.4

3 SCC

0.94

0.25

650x640

11.3

32.2

22.1

-

4 SCC

0.94

0.3

668x670

15.4

31.5

22.8

-

5 SCC

0.94

0.5

670x663

15.9

32.3

22.3

-

6 SCC

0.94

0.7

658x660

15.2

31.2

23.2

-

Cement+Sand

Water(1)mixing 30 sec

Water(2)+Superplasticizer

mixing 90 sec

GravelEnd

mixing 30 sec mixing 60 sec

Figure 2.2.1 Mixing procedure of self-compacting concrete

2.3 Properties of fresh concrete
The slump of the control normal concrete was about 100-120 mm. The slump flow of theself-compacting concrete was in the range of 600-680mm, the funnel test flow times were in therange of 10-15 seconds and concrete can fill the box test up to 28-32 cm in height. All selfcompacting concrete mixtures presented a slump flow between 600-680 mm, which is anindication of a good workability.
2.4 Specimen preparation
As shown in Table 2.3.1, four types of concrete specimens were prepared for experiments on
moisture diffusion, self-desiccation. For measuring the internal relative humidity in concrete,
both drying specimens and sealed specimens were used. Another specimen was prepared formeasuring the total moisture loss of concrete during drying.

At the age of 1 day, the mould was removed from test specimens. After demoulded, test
specimens were exposed to a constant temperature of 20°C and constant relative humidity of60%.
A total of 42 specimens in the size of 10 cm x 10 cm x 40 cm in length, were studied. Double
layers of polyethylene sealed half the number of the specimens. No moisture loss was observed
from the sealed specimens during the study. The drying specimens were placed in thetemperature controlled room at 20°C and RH = 60 after 1 day of curing in a steel mold.
Table2.3.1 Type and specimen size

Specimen

Objective
Measure of relative humidity in concreteType of Specimen
Seal with unload specimen

size (cm)
10x10x40

Measure of moisture loss
Measure of relative humidity under loading condition

Unseal with unload specimen
Seal with load specimen

10x10x40
10x10x40

Measure of moisture loss under loading condition

Unseal with load specimen

10x10x40

2.5 Experimental Method
Both air-cured and sealed concrete were studied. The creep specimens were placed in a new
testing spring-loading device. The loading was 10%, 20%, 30%, 40% and 60% of the current
strength, and was applied by about 1Mpa/sec. From 24 hours’ age parallel studies were done on
shrinkage. The total strain in the creep studies was reduced by the shrinkage strain in order toobtain the creep strain. During the creep test the loading was held constant. The compressive
strength was obtained at 1, 3 and 7 days’ age, three cylinders of each concrete mix composition.
The creep and shrinkage measurement device was mechanical and calibrated.
Plane

10 cm

Jack

40 cm

10 cm

Cross Section

Load Cell

Steel Plate

Hand Pump

Data Logger

P.C

Figure 2.5.1 Geometry and size of test specimens2.6 Experimental details and procedure
As shown in Figure 2.5.1, the exposed volume of the drying specimen is 10x10x40 cm3 .
To measure the variation of moisture loss due to different stress to strength ratio, controlled
specimen and sealed specimens were also used.
The concrete was mixed in a laboratory pan mixer. Four specimens were cast at a time incast-iron molds. This procedure was chosen after some trial and error tests were performed forbest results. The next day after casting, the specimens were demoulded and their compressive
strength was determined from an average of 3 specimens to determine the required pressure to be
applied in the creep tests. Four specimens were loaded for each stress/strength ratio, two weresealed and the other two are unsealed. Creep strain was measured regularly every six hours up toa total period of 7 days.

Chapter 3
TEST RESULT AND ANALYSIS
3.1 Creep of self compacting concrete and normal concrete
In this part will focus on creep of self compacting concrete and normal concrete with varietiesof stress strength ratio, powder content and water-cement ratio. First, I will start with thecomparison of creep of self compacting concrete to normal concrete under sealed and unsealedconditions. Second part will be the comparison of creep of self compacting concrete under sealed,unsealed condition with vary stress-strength ratios. Third part will be the comparison of creep ofself compacting concrete under sealed, unsealed condition with vary powder contents. Fourthpart will be the comparison of creep of self compacting concrete under sealed, unsealed condition
with variety water-cement ratio. Fifth part will be the comparison of test result with JSCE andACI codes. And will end this part with the regression analysis.
3.1.1 Creep of normal concrete and self compacting concrete under unseal condition
Creep strain was taken to be equal to the total strain less shrinkage and the elastic strain
determined after unloading the specimens. Shrinkage was determined from companion
specimens made from the same mix as that used to determine the creep. The specimens were left
at the controlled room temperature of 20°C and the relative humidity of 60%. Shrinkage wasmeasured at the same time as the creep specimens. The shrinkage of the sealed specimens wasfound to be little when compared to the total creep as shown in Figure 3.1.3 and Figure 3.1.6
Figure 3.1.1 and Figure 3.1.4 show the comparison of creep of self compacting concrete andnormal concrete. As show in the graphs that creep of self compacting concrete is higher thannormal concrete due to the fact that normal concrete has higher compressive strength whencomparison to self compacting concrete. (Show in Figure 3.1.7)

3.1.2 Creep of normal concrete and self compacting concrete under seal condition
In Figure 3.1.2 and Figure 3.1.5 show the comparison of normal concrete and self compac tingconcrete under seal condition. The result still show that creep of self compacting concrete underseal condition has a higher creep value when comparison to normal concrete at every different
stress strength ratios(stress strength ratio vary from 0.1 to 0.6).

As shown in the graph, normal concrete in this study produced low creep when compared toself-compacting concrete. The reason is that first, this study used the low water to cement ratio
which make the strength of normal concrete a little higher when compared to self-compacting
concrete as shown in Figure 3.1.7. Second, the porosity in normal concrete is denser whencompared to self-compacting concrete.
The shapes of the curves for unsealed and sealed cases are similar. Creep was found toincrease as the stress/strength ratio increased. Creep of both self-compacting concrete and normal
concrete were found to vary linearly with an increase in stress/strength ratio. The increase instress/strength ratio will result in higher in creep of unsealed concrete.
3.1.3 Effect of stress strength ratio on creep
The creep versus stress/strength ratio for both concretes, self -compacting concrete and normal
concrete at the ages of 1, 3 and 7 days is plotted in Figure 3.1.8 to Figure 3.1.11. The higher
stress/strength ratios the higher creep will be obtained in a linear relationship.
The creep strain of SCC and normal concrete under unseal condition give higher value ofcreep when comparison to seal condition.

The value of creep strain in SCC (both of unseal and seal conditions) is higher than that ofnormal concrete as shown in the above figure. From the reason that shrinkage of SCC is higher
than normal concrete that give value of creep of SCC to be higher than normal concrete as
mentioned in 3.1.1 and 3.1.2
3.1.4 Effect of powder content on creep
Creep versus powder content by weight (%) of self-compacting concrete at the ages of 1, 3 and 7
days are plotted in Figure 3.1.12 to Figure 3.1.17. The higher powder content will result inhigher creep value will be obtained in a linear relationship.

The creep of SCC under seal load condition has a creep value lower than that of unseal loadconditions as shown in the Figure 3.1.14 to Figure 3.1.17 due to the moisture loss to theenvironment.

3.1.5 Effect of water-cement ratio on creep
Graphs in figure 3.1.18 and Figure 3.1.19, show the relationship between creep and powder
content by weight (%) and water to cement ratio. The higher powder content, water-cement ratio
will result in higher creep value. The creep value using the water to cement ratio of 0.50 is about
double of creep value of water to cement ratio of 0.25

The higher water-cement ratios will result in higher creep value in seal and unseal loadcondition of SCC. And the higher powder content will result in higher creep also in a linear
relationship.

3.1.6 Comparison of Test Result with Codes
From the test result above: The comparison of creep between test result and JSCE or ACI
codes are show below:

From the fact that JSCE and ACI codes have some limitation of the creep prediction such as for
JSCE code, cement content has to be less than 500 kg/m3 and for ACI code, creep coefficient of
concrete has to be less than 1.3. For the cement higher than the codes, the error does exist suchas comparison between test result with JSCE or ACI codes give the value different to be 13% and
15% respectively. Then for predicting creep by using JSCE or ACI codes can not be use in self
compacting concrete that has a cement content above the codes limitations.
3.1.7 Relationship between sealed and unsealed condition of SCC and normal concrete
Creep was found to vary linearly with an increase in stress/strength ratio, that is thestress/strength ratio increases, creep of concrete would also increase. A comparison was carriedout between the creep of concretes with self-compacting concrete and normal concrete as shownin Table 3.1.1 to Table 3.1.3 at different ages of 1,3 and 7 days.
Table 3.1.1 Creep ratios for unsealed of SCC compared with Normal Concrete
Age,
Stress/strength ratio, percent
days
1
3
7
Average

10
1.16
1.27
1.12
1.18

20
1.15
1.31
1.24
1.23

30
1.06
1.57
1.32
1.32

40
1.08
1.79
1.58
1.48

60 Average
1.1
1.11
1.99
1.6
1.74
1.4
1.61
1.37

Table 3.1.2 Creep ratios for sealed of SCC compared with Normal Concrete
Age,

Stress/strength ratio, percent

days
1
3
7

10
1.04
1.06
1.05

20
1.07
1.1
1.09

30
1.05
1.03
1.1

40
1.09
1.1
1.13

60 Average
1.1
1.07
1.14
1.09
1.2
1.15

Average

1.05

1.08

1.06

1.11

1.15

1.09

Table 3.1.3 Creep ratios for unsealed/sealed using SCC and Normal Concrete
Type

Age,

Stress/strength ratio, percent

days

60 Average

10

20

30

40

Low
heat

1
3

0.97
1.4

0.98
1.79

0.98
2.03

0.99
2.39

1.04
2.63

0.99
2.05

concrete

7

1.23

1.6

1.87

2.79

3.87

2.27

AverageOrdinary

1

1.2
1.07

1.46
1.05

1.63
0.97

2.06
0.98

2.52
1

1.77
1.02

portlandcement

3
7

1.7
1.17

1.84
1.5

1.91
1.82

2.01
2.6

2.2
3.38

1.93
2.09

1.31

1.46

1.57

1.86

2.19

1.68

Average

The ratio of creep of unsealed/sealed concrete at different ages of 1, 3 and 7 days are shown in
Table 3.1.3. It can be seen that the average value was found to be about 1.77 for SelfCompacting Concrete and 1.68 for Normal Concrete. This ratio tended to increase as age
increased for both concretes.
3.1.8 Regression Analysis
The empirical formula to predict creep of self compacting concrete that have a cement
contents above JSCE or ACI codes at difference water-cement ratios, stress -strength ratios andtime domains can be expressed in the Table 3.1.4 to Table 3.1.7
Regression analysis was carried out for drying shrinkage and autogenous shrinkage of both
concrete, normal concrete and self-compacting concrete, as a function of time using exponential,
logarithmic, and power function. A summary of the equations and their coefficients ofcorrelation are shown in Table 3.1.4 and Table 3.1.5. The logarithmic and power functions were
found to give the best fit for both concretes
Table 3.1.6 and Table 3.1.7 shows equations of creep as a function of time and theircoefficients of correlation using exponential, logarithmic, and power functions. The powerfunction and logarithmic functions were found to give the best fit for all curves.
Table 3.1.4 Constants A and B and coefficient of Correlation R for equations of shrinkage versus
age using normal concrete
Exponential
Logarithmic
PowerType I
R
A
B
R
A
B
R
A
B
Unsealed
0.87
2.77
0.022 0.99
109.3 32.51 0.98
0.008
2.1
Sealed0.87 1.997 0.0226 0.98
88.65
25.81 0.98
0.009 2.25

Exponential
Logarithmic
Power

S = A x eBt
S = A+B x LN(t)S = A x tB

S = Shrinkage strain x 10-6
A = S/S ; B = W/Ct = time (hours)R = Regression (best fit is R=1.00)
Table 3.1.5 Constants A and B and Coefficients of Correlation R for equation of shrinkage versus
age using self-compacting concrete
Exponential
Logarithmic
PowerType I
R
A
B
R
A
B
R
A
B
Unsealed
0.85 4.59
0.019 0.98
112
35.02 0.97
0.007 1.86
Sealed
0.86 2.69
0.0203 0.97
85.4
25.37 0.98
0.005 1.89

Table 3.1.6 Constants A and B coefficient of Correlation R for equations of creep versus age
using normal concrete.
Stress/strengthratio,
Exponential
Type I
percent
RA
B
R
10 0.87 4.11 0.023
Unsealed
20 0.83 8.06 0.022
and
30 0.88 121.6 0.007
Load
40 0.89 96.59 0.011

Logarithmic
Power
A
B
R
A
B
0.99
196
57.69 0.99 0.003
0.99351
131.53 0.99 0.003
0.99448
137.27 0.99 15.52
0.99
811
257.05 0.99 4.08

2.172
2.306
0.62
0.96

108 0.013

0.99

0.872
10 0.82 3.83 0.022
20 0.84 6.15 0.025
30 0.84 84.1 0.005
40 0.86 77.1 0.006
60 0.86 79.13 0.007

0.99
0.97
0.97
0.98
0.99
0.99

60
Average
Seal
and
Load
Average

0.89

0.844

1219
141
253
400
472
502

373.39

0.99

2.82

1.093

42.67
79.14
84.22
92.34
98.12

0.99
0.98 0.003
0.98 0.002
0.98 23.36
0.99 12.28
0.99 17.03

2.07
2.32
0.39
0.56
0.593

0.98

0.984

Table 3.1.7 Constants A and B and coefficient of Correlation R for equations of creep versus age
using self-compacting concrete.
Stress/strengthratio,
Exponential
Type I
percent
RA
B
R
10 0.87 4.11 0.023
Unsealed
20 0.83 8.06 0.022
and
30 0.88 121.6 0.007
Load
40 0.89 96.59 0.011
60 0.89 108 0.013

Logarithmic
A
B
0.99
196
0.99
351
0.99
448
0.99
811
0.99
1219

Average

0.99

Seal
and

0.872
10
20
30

0.82
0.84
0.84

3.83 0.022
6.15 0.025
84.1 0.005

0.97
0.97
0.98

Power
R
A
B
57.69 0.99 0.003
131.53 0.99 0.003
137.27 0.99 15.52
257.05 0.99 4.08
373.39 0.99 2.82

2.172
2.306
0.62
0.96
1.093

0.99
141
253
400

42.67
79.14
84.22

0.98 0.003
0.98 0.002
0.98 23.36

2.07
2.32
0.39

Load

40

0.86

77.1 0.006

0.99

472

92.34

0.99 12.28

0.56

60

0.86 79.13 0.007

0.99

502

98.12

0.99 17.03

0.593

0.844

0.98

Average

0.984

Exponential
C = A x eBt
Logarithmic
C = A + B x LN(t)Power
C = A x tB
R= Regression (best fit is R=1.00)

C = creep x 10-6
A=S/S ; B = W/Ct = time (hours)

From 3.2 to 3.6 will explained about the factors that cause concrete to creep such as moistureloss of concrete from autogenous shrinkage, drying shrinkage and chemical shrinkage.
3.2 Relationship between shrinkage and creep
3.2.1 Effect of moisture loss on creep
Moisture loss from concrete specimens to the surroundings is related directly to moisturediffusion and is not affected directly by self-desiccation. Figure 3.2.1 shows the moisture loss ofconcrete with various stress/strength ratios. In Figure 3.2.1 the moisture loss of the concrete isrepresented as moisture loss in weight per unit volume (g/cm3 ). The moisture loss of concrete
increase linearly as the stress/strength ratio increases. This is because concrete subjected tohigher stress gives higher creep strain.

Moisture Loss(g/cm3)

Figure 3.2.1Compare moisture loss of normal concrete and
SCC with unseal-load condition at 24 hours after casting
0.1
0.08
0.06

Normal Concrete

0.04

Self-Compacting
Concrete

0.02
0
0

10

20

30

40

50

60

70

Stress/Strength Ratio

3.2.2 Effect of aggregate content on autogenous shrinkage
The aggregate in the concrete restrained the shrinkage substantially compared with the freeshrinkage that occurred in cement paste.
Inclusion of aggregate leads to a reduction in autogenous shrinkage, as in the case of drying
shrinkage. This is due to the reduction in the cement paste content and to the elastic deformationof aggregate due to modulus of elasticity of self compacting concrete and self compacting mortar,which partly confines the shrinkage deformation of the paste as such, shown in Figure 3.3.1 andFigure 3.3.2

The test results show that increasing the cement content at constant water content or equivalently
decreasing the aggregate content increasing the creep strain.
3.2.3 Relationship between autogenous shrinkage and drying shrinkage
Drying shrinkage and autogenous shrinkage of concretes with extremely low water-cement
ratios are nearly the same. In other words, the shrinkage that has been regarded as the result ofdrying actually occurs independently of drying. Meanwhile, the weight does reduce, indicatingthat drying does not cause the shrinkage of such concretes with very low W/C. According to test
results, the drying shrinkage takes place about 0.0005g/cm3 for self-compacting concrete and0.0015g/cm3 for normal concrete, which are very low, negligible. Autogenous shrinkage takes
place about 0.042g/cm3 for self-compacting concrete and 0.023g/cm3 for normal concrete. The
difference between drying shrinkage and autogenous shrinkage increases as the water-cement
ratio increases as shown in Figure 3.2.4 [14].

Figure. 3.2.4 Relationship between autogenous shrinkage and drying shrinkage
3.2.4 Autogenous drying near the surfaces during seal curing
The magnitude of the autogenous shrinkage also was dependent on the type of the cement[14]. Low-alkali cement causes less autogenous shrinkage than normal alkali cement; a slow
hardening of cement has less shrinkage than a normal concrete using ordinary portland
cement[14].
Autogenous shrinkage occurs as the result of the chemical reactions that take place during
cement hydration. It can be significant in concrete with a very low water-cementitious materials
ratio. It is possible for such concrete to shrink without the loss of any water to the environment.
This is because, in general, it is accepted that the loss of water from the paste fraction of concretedue to external factors generates negative capillary pressures that cause the volume of the paste tocontract, hence the shrinkage.
The water content distribution as shown in Figure 3.2.5 [14] has been confirmed by several
sets of data measured on seal-cured specimens. The capillary water content is determined fromthe weight reductions of the samples ground in advance when they are dried to a constant weightin a room at temperature of 20°C and relative humidity of 50%.

Figure 3.2.5 Moisture distribution of underwater specimen
A comparison between self-compacting concrete and normal concrete showed that selfcompacting concrete obtained lower strength when compared to normal concrete. Also, the creep
coefficient of self-compacting concrete is higher when compared to normal concrete.
It is conceivable that a very low water-cement ratio tends to lead to discontinuous capillarywater. This is, however, a problem of balance between the volume of water transferred bycapillary tension and the absolute volume shrinkage due to hydration.
The very strong increase of the autogenous shrinkage at the beginning of the hardening
process can be related to the fact that at this early stage of the hardening process, the elastic
modulus has only developed minorly. The volumetric contraction of the microstructure will thenexperience hardly any restraint of the stiffness of the paste. Consequently, large def ormations
can easily occur. For higher water/cement ratios, this contraction force will be much smaller sothat the volumetric contraction of the microstructure will be less pronounced at that particular
stage of the hardening process.
3.2.5 Chemical Shrinkage
Chemical shrinkage is a volume reduction due to the fact that resulting volume of reaction
product formed by water/cement reaction is smaller than the volume of original constituents [19].
The chemical equations for each compound with coexisting gypsum are as follows;
2C2 S + 6H2O
C3 S2 H3 + 3Ca(OH)2(11)
2C2 S + 4H2O
C3 S2 H3 + Ca(OH)2(12)
C3 A + 3(CaSO4 2H2 O) + 26H 2 O
C3 A3CaSO4 32H2 O(13)
2C3 A + C3 A3CaSO4 32H2 O + 4H2 O
3[C3 ACaSO4 12H2 O](14)
C3 A + Ca(OH)2 + 12H2 O
C3 ACa(OH)2 12H2 O(15)
C4 AF + 3(CaSO4 2H2 O) + 27H2 O
C3(AF)3CaSO4 32H2 O + Ca(OH)2(16)
2C4 AF + C3 (AF)3CaSO4 32H2 O + 6H2 O
3[C3 (AF)CaSO4 12H2 O] + 2Ca(OH)2 (17)
C4 AF + 10H2 O + 2Ca(OH)2
C3AH6 – C3 FH6 (solid solution)(18)
At the earliest stage the reaction of C3 A will form ettringite as in equation (13) and at a laterstage it will transform into monosulfoaluminate as in (14) and C3 A remaining from the shortageof gypsum will follow equation (15). The absolute volumes of all compounds are decreased afterreaction, as is understood form each equation. An example of the shrinkage calculation as
follows:

WeightSpecific gravity
VolumeSum volume

2C2 S + 6H2 O
456.6 108.1
3.27
1.0
139.63 108.1
247.73C3 S2 H3 + 3Ca(OH)2
342.5
222.3
2.71
2.24
126.3899.24
225.62(19)

Chemical Shrinkage

 247 .73 − 225 .62  × 100 = 8.93%
247 .73

Densities of each compounds used in the calculation were adopted from [18]. The degrees ofhydration at each reaction time were adopted from DUCOM at early age of hydration. The total
shrinkage of cement paste at each reaction time was obtained from the sum of the shrinkage ofeach compound obtained from the mineral composition, the shrinkage ratio and the degree ofhydration of each compound. The volume change of gypsum was neglected in the calculation.
The results of the test show that, the autogenous shrinkage at 7 days is about 0.6%, and from[19] at the age of one year, autogenous shrinkage is about 1.3%. As time passed by the higher
value of autogenous shrinkage strain can be obtained, but the shrinkage strain value is quite low
when compared to chemical shrinkage.
The value of autogenous shrinkage strain compared to chemical shrinkage strain is lower fromthe reason that bleeding water takes effect. The water is absorbed in the cement paste after acertain period. If water is further fed on the top surface, the water continues to be absorbed,
providing that the level of bleeding water in set ceme nt is lower than the top surface[20]. The
amount of the absorbed water corresponds to the chemical shrinkage after some point of time
when the bleeding water disappears from the top surface, and is the volume change can bemeasured. When the water transfer is interrupted by a rubber film, the chemical shrinkage ismeasured while the bleeding water exists on the top surface, however, when the water level
becomes lower than the cement surface, autogenous shrinkage thereafter is measured. The time
when the level of bleeding water becomes lower than the top surface of water normally does notcoincide with the setting time. The Le Chatelier method determined the total of the hardening
shrinkage up to a very early age and the autogenous shrinkage after a certain point of time. In
this sense, the data after a certain point of time is technically of little use, because chemical
shrinkage at very early age is normally much larger than autogenous shrinkage.
In order to predict creep accurately, shrinkage that causes creep has to be investigate precisely.
There are many types of shrinkage such as drying shrinkage, autogenous shrinkage, chemical
shrinkage that are all explained in the above. Self compacting concrete contain high amount of
cement that can cause high shrinkage age and high creep. At this moment, the empiricalformulas that use to predict creep or shrinkage are still have some limitation such as JSCE or ACI
codes limit the amount of cement to be less than 500kg/m3 . However, self compacting conc retecontain the amount of cement more than 500kg/m3 , as a result JSCE or ACI codes can not use to
be predict creep of self compacting concrete as shown in 3.1. Moreover, creep of self
compacting concrete is higher than creep of normal concrete roughly about 1.4 times. One of themost important things that have to keep in mind about creep is that high amount of cement will
give higher creep value as an explained in this chapter.

Chapter 4
CONCLUSIONS AND DISCUSSIONSCreep tests of concrete must be rigorously standardized, because creep is a major factor of themechanical behavior of the concrete material. It depends on many factors, and is very sensitive
to air-dried conditions and environmental conditions. The need to establish robust and usable
data bases leads to fixing a certain number of the parameters of the test. From this study someconclusion can be made:1. The JSCE and ACI codes have limit the amount of cement content to be less than
500kg/m3 but in fact self compacting concrete contain the amount of cement higher than
500kg/m3 . Then as a result JSCE and ACI codes give creep value under estimation interm of creep value when compared to the test result by 13% and15% respectively.
2. The value of creep of self-compacting concrete is larger than JSCE or ACI codes design
value.
3. The higher water-cement ratios, stress-strength ratios, powder contents for self compacting
concrete will result in higher creep in linear relationship.
4. The creep of unsealed self -compacting concrete was found to be about 1. 4 times larger
than normal concrete.
5. The creep of sealed self -compacting concrete was found to be about 1. 1 times larger thannormal concrete.
.
RECOMMENDATIONS FOR FURTHER STUDY
1. Investigate the effect of cement replacement by fly ash, slag or the globalization is required.
2. Investigate the effect of applying light weight aggreagte, fiber aggregate in the selfcompacting concrete.

REFERENCES[1] Bazant, Z.P. and Chern, J.C., ‘Strain softening with creep and exponential algorithm’. J.
Engng Mech. ASCE 111 (EM5) (1985) 391-451[2] Bazant, Z.P. and Xi.Y, Mater. Struct. 27,3-14 (1994)[3] Comite Euro-International du Beton, ‘CEB-FIP Model Code 1990,’ 68-69 (1993)[4] Bazant, Z.P. and Najjar, L.J., Mater. Struct. 5,3-20 (1972)[5] Naville, a. M. andDilger, W. H and Brooks, J. J., Creep of Plain and Structural Concrete,
Construction press, Longman, 361 (1983)[6] Bazant, Z. P., and Wittmann, F. H., Creep and Shrinkage in Concrete Structures, John Wiley
andsons, 363 (1984)[7] Byfors, J., Plain Concrete at Early Ages, Swedish Cement and Concrete Institute, 465 (1990)[8] Freyssinet, E., Deformation of Concrete, Magazine of Concrete Research, V.3. No.8, 1951,
pp.49-56[9] Chernin, W., Cement Chemistry and Physics for Civil Engineers, Crossby Lockwood,
London, 1962, pp. 238[10] Glanville, W. H. and Thomas, F.G, Further Investigations on the Creep or flow of concrete
under load, Building Research Tech. No.21[11] Acker, P., Superficial shrinkage of Concrete,Lisbon, pp. 157-162[12] Hau, C., Analyses and models of the autogenous shrinbkage of hardening cement paste,
Cem. Con. Res. 25, 1457-1468[13] Ulm, F., Creep and shrinkage couplings, Cem. Con. Age. 26, 1687-1692[14] Tazawa, e., Miyazawa, S., Experimental Study on Mechanism of Autogenous Shrinkage ofConcrete. Cem. Con. Res. 25, 1633-1638[15] 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 StructuralEngineering & Construction, Taipei, Taiwan, 1998, pp. 1307-1312[16] Neville, A. M., Creep of Concrete: Plain, Reinforced, and Prestressed, North-Holland
Publishing Company, Amsterdam, 1970

[17] Tazawa, E. I. and Miyazawa, S., Effect of Self-Desiccation on Volume Change and Flexural
Strength of Cement Paste and Mortar. Report TVBM-3075. Div. Building Materials Lund
Institute of Technology. Lund, 8-14(1997).
[18] Tazawa, E. I. and Kasai, T., Chemical Shrinkage and Autogenous Shrinkage of Hydrating.
Cement Paste Cement and Concrete Research, Vol.25, No.2 pp.288-292(1995)[19] Persson, E., Experimental Studies on Shrinkage of High-Performance Concrete. Cement
and Concrete Research, Vol.28,No.7,pp. 1023-1036(1998).
[20] Bogue, R. H., The Chemistry of Portland Cement, Reinhold Publishing Corporation (1955)

Appendix A: Total Strain, unseal-load condition, seal-load condition unseal-unloadcondition and seal-unload condition

Appendix B: Creep Coefficient