Recent Progress in Research on and Code Evaluation of

Journal of Advanced Concrete Technology Vol. 2, No. 2,133-140, June 2004 / Copyright © 2004 Japan Concrete Institute 133

Invited Paper

Recent Progress in Research on and Code Evaluation of Concrete Creep and Shrinkage in Japan Kenji Sakata1 and Takumi Shimomura2

Received 10 November 2003, revised 27 April 2004

Abstract This paper introduces the recent state of research on creep and shrinkage of concrete in Japan, focusing on several unique advances: new prediction models in design code, development of database, autogenous shrinkage and prediction of cracks in structural members. New prediction models for creep and shrinkage of concrete, which can be applied to high-strength concrete, were adopted in the JSCE standard specification for concrete structures in 2002. A creep and shrinkage database was developed and made available for international use. Thus Japanese researchers can be said to have made important contributions to research on autogenous shrinkage of concrete in the last ten years.

1. Introduction

Creep and shrinkage of concrete, as is well known, has been one of the major problems in cement and concrete engineering. It may affect either directly or indirectly various aspects of the performance of structures, such as reduction of effective prestress in prestressed concrete members, concrete cracking that lowers the durability of structures, and time-dependent deflection and redistri-bution of stress in structures under service load. Creep and shrinkage have therefore been significant issues for the practical design of structures, as well as in academic research around the world.

A fair amount of research on concrete creep and shrinkage has also been performed in Japan. Owing to the dedicated efforts by many researchers and engineers in this field, a number of unique and productive results have been obtained recently.

A recent example of the progress achieved in this field is that the adoption of new original prediction models for creep and shrinkage, which can be applied to high-strength concrete, in the JSCE (Japan Society of Civil Engineers) Standard Specification for Concrete Structures in 2002. To attain high strength and high du-rability, concrete with a low water-cement ratio has be-come widely used. The creep and shrinkage behavior of such concrete being known to differ from that of con-ventional concrete, models that can precisely predict creep and shrinkage behavior of such concrete were quickly developed and adopted in practical design specifications in Japan.

The speed with which this was done suggests that the domestic research committees on concrete creep and

shrinkage established by Japan’s various academic so-cieties have been working effectively. These committees have been addressing specific creep and shrinkage issues by collecting test data reliable enough to serve as the basis of prediction models, developing and maintaining a database, and preparing technical reports on concrete creep and shrinkage.

Autogenous shrinkage is another aspect whose im-portance has grown with the increasing use of high-strength concrete. Though known for many years, concrete shrinkage associated with the hydration of the cement in the concrete had not been regarded as a serious problem because, apart from drying shrinkage, it caused few defects in structural members made of conventional concrete. However, Tazawa et al. in 1992 emphasized that, in the case of concrete with a low water-cement ratio such as high-strength concrete, autogenous shrinkage is too large to be negligible and has various influences on structures. Since then, autogenous shrinkage of concrete has been widely studied both in Japan and abroad, and Japanese researchers have made important contributions in this field.

This paper reviews the recent state of research on concrete creep and shrinkage in Japan, focusing on as-pects unique to Japan, such as the development of pre-diction models, the creation of a database, and research on autogenous shrinkage.

2. Prediction models in JSCE specification

2.1 JSCE specification 1986 The JSCE (Japan Society of Civil Engineers) Standard Specification for Concrete Structures has served as a technical basis the design of concrete structures in civil engineering, such as bridges, dams, road structures, railway structures and power stations in Japan for more than 50 years. The Specification was revised several times, every five years in recent years, in order to keep up with technological advances.

Creep and shrinkage of concrete should be taken into

1Professor, Department of Built Environment, Okayama University, Japan. E-mail: [email protected] 2Associate Professor, Department of Civil Engineering Nagaoka University of Technology, Japan.

134 K. Sakata and T. Shimomura / Journal of Advanced Concrete Technology Vol. 2, No. 2, 133-140, 2004

account in various situations in design procedures for concrete structures. Therefore, similarly to other design codes in the world, the JSCE Specification includes practical prediction models for concrete creep and shrinkage. However, for a long time Japan did not have original prediction models for concrete creep and shrinkage. When the JSCE Specification was entirely revised in 1986 to adopt the limit state design, the pre-diction models in the CEB model code were imported (CEB-fip 1978). However, it is significant that at this time, the replacement of these borrowed prediction models with original ones was clearly set as an objective that would inform future research.

2.2 JSCE specification 1996 The 1996 revision of the JSCE Specification was note-worthy from the viewpoint of concrete creep and shrinkage because it was the first time that original Japanese prediction models were incorporated in the Specification (JSCE 1996).

A research project to develop original prediction models had been led by Sakata since the early 1980s. It resulted in the proposal of new prediction models for creep and shrinkage with high applicability to both Japanese and overseas data (Sakata 1993). The applica-bility of these models is demonstrated in Fig. 1. These were the models that were adopted in JSCE Specification 1996.

Shrinkage strain may be estimated using Eq. (1) for normal concrete with a compressive strength of up to 55 N/mm2, as follows.

( ) ( ){ }[ ] shoocs tttt εε ′⋅−−−=′ 56.0108.0exp1, (1)

where,

( )[ ]( )[ ] 210log5

log38100exp17850

SV

WRH

e

esh

−

+−+−=′ε (2)

shε ′ = final value of shrinkage strain (x 10-5)

( )ocs tt,ε ′ = shrinkage strain of concrete from age of to to t (x10-5)

Creep strain per unit stress ( ) cpocc ttt ',, σε ′′ for normal strength concrete having a compressive strength of up to 55 N/mm2 may be estimated using Eq. (3), when the concrete is subjected to drying and loading at effective ages of t and t’, respectively.

( ) ( ){ }[ ] crcpocc ttttt εσε ′⋅′−−−=′′′ 6.009.0exp1,, (3)

where,

dcbccr εεε ′+′=′ (4)

( ) ( ) ( ) 67.04.20.2 log15 −′+=′ tCWWC ebcε (5)

( ) ( ) ( )[ ]( ) 30.036.0

2.22.44.1

1001

10//log4500−

−

−

+=′

o

edc

tRH

SVCWWCε

(6)

crε ′ = final value of creep strain per unit stress (x10-10/(N/mm2))

bcε ′ = final value of basic creep strain per unit stress (x10-10/(N/mm2))

dcε ′ = final value of drying creep strain per unit stress (x10-10/(N/mm2))

Notations in Eqs.(1) to (6) are as follows. C = unit cement content (kg/m3) (260 kg/m3≤C≤500 kg/m3) W = unit water content (kg/m3) (130 kg/m3≤ W ≤230 kg/m3) W/C = water-cement ratio (40%≤W/C≤65%) RH = relative humidity (%) (45%≤RH≤80%) V = volume (mm3) S = surface area in contact with outside air (mm2)

0

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n -

µ

0 400 800 1,200

Calculated shrinkage strain - µ

Within limits

+40%

-40%

○ : JSCE data□ : RILEM data

(a) Shrinkage

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250

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- µ/

(N/m

m2 )

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Calculated specific creep strain - µ/(N/mm 2)

+40%

-40%

Number of data sets = 250

○ : RILEM data□ : CEB data◇ : JSCE data

(b) Creep

Fig. 1 Verification of prediction models in JSCE Specifi-cation 1986 (data: f’c<80N/mm2).

Exp

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train

- µ

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µ/

(N/m

m2 )

K. Sakata and T. Shimomura / Journal of Advanced Concrete Technology Vol. 2, No. 2, 133-140, 2004 135

V/S = volume -surface ratio (mm) (100 mm≤V/S≤300 mm) to, t’ and t = effective age (days) of concrete at the

beginning of drying, at the beginning of loading, and during loading, respectively; values corrected by Eq. (7) should be used.

for to, t’ and t ( )∑=

⎥⎦

⎤⎢⎣

⎡

∆+−⋅∆=

n

i oii TtT

t1

273400065.13exp (7)

it∆ = number of days when the temperature is T(°C) To = 1°C Just before JSCE Specification 1996 was published, a

technical committee on concrete creep and shrinkage, JSCE308, led by Chairman Sakata, was organized in the JSCE in 1995. This was the first domestic committee to deal with technical problems related to concrete creep and shrinkage, including the development of practical prediction models and a database, as well as fundamental research. Although the JSCE308 Committee was dis-continued in 2000, its activities were taken over and are being carried on by other organizations.

2.3 JSCE specification 2002 (1) General The prediction models for creep and shrinkage adopted in JSCE Specification 1996 were applicable to normal concrete with a compressive strength of up to 55 N/mm2. Meanwhile, the JSCE308 Committee was steadily working to develop original prediction models for creep and shrinkage of high-strength concrete. Experimental data on high-strength concrete, such as the example shown in Fig. 2, were collected and added in a database. Based on this data, new prediction models for creep and shrinkage of high-strength concrete were proposed in 2002 (JSCE308 2000).

(2) Shrinkage model It is generally known that autogenous shrinkage in high-strength concrete is greater than in conventional concrete. The ratio of autogenous and drying shrinkage in total shrinkage of concrete is schematically illustrated in Fig. 3.

In the case of conventional concrete, it is not a prob-lem if shrinkage is treated without distinguishing be-tween autogenous and drying shrinkage because the ratio of autogenous shrinkage to total shrinkage is not large in such concrete. On the other hand, in the case of high-strength concrete, autogenous and drying shrinkage should be distinguished because the ratio of these shrinkages to total shrinkage varies with respect to age when concrete is exposed to drying conditions. Therefore, in JSCE Specification 2002, shrinkage of high-strength concrete is evaluated as the sum of autogenous and dry-ing shrinkages, which are separately predicted.

( ) ( ) ( )000 ,,, tttttt asdscs εεε ′+′=′ (8)

where, ( )ocs tt,ε ′ = shrinkage strain of concrete from age of to

to t (x10-6) ( )ocs tt,ε ′ = drying shrinkage strain of concrete from

age to to t (x10-6) ( )oas tt,ε ′ = autogenous shrinkage strain of concrete

from age to to t (x10-6). The test data used for developing the prediction model

for drying shrinkage were obtained by subtracting the measured autogenous shrinkage from the measured total shrinkage. Based on these data, a prediction model for drying shrinkage was formulated as follows.

0

20

40

60

80

100

120

140

160

0 20 40 60 80 100

Strength at 28 days (N/mm2)

Num

ber o

f dat

a

Shrinkage

Creep

Fig. 2 Example of creep and shrinkage data in database.

Shrinkage

Concrete age

Total shrinkage after drying

Drying shrinkage

Start of drying

Autogenous shrinkage

(a) Conventional concrete

Shrinkage

Concrete age

Total shrinkage after drying

Drying shrinkage

Start of drying

Autogenous shrinkage

(b) High strength concrete

Autogenous shrinkage after drying

Fig. 3 Shrinkage in conventional and high-strength con-crete.


)()(),( 0

o

odsds tt

tttt−+−⋅′

=′ ∞

βε

ε (9)

β = term representing the time dependency of drying shrinkage

otSVW

7.0100/4

+=β (10)

∞dsε = final value of drying shrinkage strain (x10-6)

o

dsds t⋅+

=∞ ηε

ε ρ

1 (11)

⎭⎬⎫

⎩⎨⎧

′−+

−=

)28(500exp1501

)1001(

c

ds

f

WRHαε ρ

(12)

{ }Wfc 25.0))28(007.0exp(1510 4 +′= −η (13)

W = unit water content (kg/m3) (130 kg/m3≤W≤230 kg/m3) V/S = volume-surface ratio (mm) (100 mm≤V/S≤300 mm) RH = relative humidity (%) (40%≤RH≤90%)

)28(cf ′ = compressive strength of concrete at age of 28 days(N/mm2) ( )28(cf ′ ≤80 N/mm2)

α = coefficient representing the influence of the ce-ment type

ordinary or low-heat cement (α =11) high-early-strength cement (α =15) to and t = effective age (days) of concrete at the be-

ginning of drying and during drying, values cor-rected by Eq.(7) should be used. (1day≤t0≤98days, t0=98days for t0>98)

The accuracy of the prediction model for drying shrinkage is verified in Fig. 4.

The prediction model was found to have satisfactory applicability to the data including normal and high-strength concrete.

For autogenous shrinkage, the prediction model pro-posed by Tazawa and Miyazawa was adopted (Tazawa 1999).

( ) ( ) ( )oasasoas tttt εεε ′−′=′ , (14)

( ) ( ){ }⎥⎦⎤⎢⎣⎡ −−−∞

′=′ bsttaastas exp1εγε (15)

( )tasε ′ = autogenous shrinkage strain of concrete from the start of setting to age t (x10-6)

γ = coefficient representing the influence of the ce-ment and admixtures type (γ may be 1 when only ordinary Portland cement is used.)

∞′asε = final value of autogenous shrinkage strain (x10-6)

( ){ }CWas 2.7exp3070 −=′ ∞ε (16)

W/C = water-cement ratio ts = start of setting (days) a, b = coefficient representing the characteristic of

progress of autogenous shrinkage. Figure 5 shows a comparison between autogenous

shrinkage as predicted by Eq. (14) and actual test data (Tazawa 1999). (2) Creep model It had been known that the creep model in JSCE Speci-fication 1996 tends to overestimate creep strain of high-strength concrete if it is applied to high-strength concrete without any modifications. This tendency sug-gests that the nature of creep of high-strength concrete may be different from that of normal concrete because of the dense microstructure of high-strength concrete.

Based on the data in Fig. 2, the following prediction model for creep was formulated.

( ) ( ) ( )1log)(12

35010014,, +′−′′++−

=′′′ tttf

RHWttt ec

cpocc σε (17)

where, )(tfc ′′ = compressive strength of concrete at the loading age (N/mm2)

t’ and t = effective age (days) at the beginning of loading and during loading, respectively; values corrected by Eq.(7) should be used.

W = unit water content (kg/m3) (130 kg/m3≤ W ≤230 kg/m3) RH = relative humidity (%) (40% ≤ RH ≤ 90%) Figure 6 shows the accuracy of the new prediction

model for creep in high-strength concrete. The new model can predict with high accuracy creep in high-strength concrete as well as normal concrete.

It is also one of the characteristics of the new predic-tion model that it does not distinguish between basic creep and drying creep as the conventional model did. This results in a simple formula, as shown in Eq. (17). The reason why the model can reasonably predict ex-perimental results without distinguishing between basic and drying creep may be because drying creep of high-strength concrete is small compared with normal concrete.

3. Database for creep and shrinkage

Reliable test data are necessary in order to develop and verify prediction models for concrete creep and shrink-age. It is difficult for individual researchers to collect a large number of data covering various conditions. It is desirable, therefore, for a database to be systematically developed and continuously maintained by a task group in academic associations, as had been done by RILEM. Learning from the activities of their overseas counter-parts, Japanese technical committees JSCE308 (chair-man Sakata, 1995-2000) and JSCE320 (chairman Tsu-


baki, 2000-2003), developed a database for concrete creep and shrinkage. Most data in the database were collected from technical papers published in Japan and classified by type of standard specimen, member and structure. The database can be used for verification of prediction models, substitution of laboratory tests, and academic research. The computer display shown in Fig. 7 is the database developed by JSCE320 in 2003. Aiming to make this database accessible to overseas users, the database was translated into English and designed to be compatible with the databases of RILEM.

4. Autogenous shrinkage

Autogenous shrinkage has risen in importance with the increasing use of high-strength concrete. Though known about for a long time, concrete shrinkage associated with the hydration of cement had not been regarded very significant because, in practice, it caused less serious

0

250

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1,000

Expe

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- µ

0 250 500 750 1,000

Calculated shrinkage strain - µ

Number of data sets= 92

+40%

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+20 %

-20%

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0 250 500 750 1,000Calculated shrinkage strain - µ

Data : RILEM


+40%

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(a) Comparison with domestic data (b) Comparison with RILEM database

0

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Data : CEB


+40%

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1,250Ex

perim

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0 250 500 750 1,000 1,250Calculated shrinkage strain - µ

Data : JSCE


+40%

-40%

(c) Comparison with CEB database (d) Comparison with JSCE database

Fig. 4 Verification of new shrinkage model in JSCE Specification 2002. Fig. 5 Verification of prediction model for autogenous shrinkage (Tazawa 1999).

Exp

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Calculated shrinkage strain (µ)

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(µ)

Cement: Ordinary Portland Cement W/C: 20 – 56% Temperature: 20°C


problems in structures than drying shrinkage. However, it was emphasized by Tazawa et al. (Tazawa 1993) that, in the case of concrete with a low water-cement ratio such as high-strength concrete, autogenous shrinkage is too large to be negligible and has a negative influence on structures. Since then, autogenous shrinkage of concrete has been studied by many researchers throughout the world, and Japanese researchers have made important contributions in this field.

Domestic technical committees on autogenous shrinkage of concrete have been organized within JCI (chairman Tazawa, 1994-1998 and 2000-2002). They promoted research and systematized knowledge on autogenous shrinkage. The results of their activities were presented at the “AUTOSHRINK’98” internal workshop

on autogenous shrinkage of concrete held in Hiroshima in 1998 (Tazawa 1999).

5. Cracking in early age concrete

Cracking in early age concrete is one of the serious problems in structural members associated with concrete creep and shrinkage. Among the various types of crack-ing in early age concrete, thermal cracking in massive concrete structures due to cement hydration can now be successfully controlled. Since the early 1980s, the Technical Committee on Thermal Stress of Massive Concrete Structures within JCI (chairman Tanabe) has been working on the development of practical computer software for heat transfer and thermal stress analysis in

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/mm

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Number of data sets = 146

+40%

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Data : RILEM


+40%

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(a) Comparison with domestic data (b) Comparison with RILEM database

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Data : CEB


+40%

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/mm

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0 50 100 150


Data : JSCE


+40%

-40%

(c) Comparison with CEB database (d) Comparison with JSCE database

Fig. 6 Verification of new creep model in JSCE Specification 2002.

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(N/m

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structures. This software has been revised several times to reflect advances. Based on this technical innovation, the JSCE Specification adopted the systematic verifica-tion of thermal cracking in concrete structures in 1986.

On the other hand, although studies on shrinkage cracking in members have been carried out since 1950s, it is still difficult to rationally predict shrinkage cracking in members (Kawase 1991) (AIJ 2003). The occurrence of shrinkage cracking depends upon a complex combi-nation of factors consisting of the shrinkage characteris-tic of the concrete, its creep or relaxation characteristic, and the cracking criteria of the concrete. This is why, even for very simple members, theoretical prediction of cracking has not been available at the practical level. Hence, in the current JSCE Specification, cracking re-sistance of members is indirectly examined in terms of free shrinkage of concrete instead of cracking probability of the member.

Figure 8 shows the test specimen for examining shrinkage cracking resistance of concrete standardized by JIS (Japan Industrial Standard) in 2002. Figure 9 shows a typical experimental result obtained in this test: concrete stress induced by restrained shrinkage as a function of time. Concrete stress calculated from the measured strain of restraining steel plates is released when crack is generated. A great deal of effort had been made to collect experimental data with this test method before it was promoted as a standard test by JIS. The data and knowledge accumulated thus far can be efficiently used in quantifying creep characteristics and cracking strength of concrete under restraint shrinkage. The next target in this field of study is to establish a reasonable prediction method for shrinkage cracking in members under general conditions, as well as thermal cracking in massive concrete.

The International Workshop on Control of Cracking in Early Age Concrete was held in Sendai in 2000 (Mihashi and Wittmann 2002). A number of technical papers covering mathematical models, numerical simulation and experimental investigation on creep, shrinkage and

cracking problems in early age concrete were presented. The potential of Japanese researchers in this field has sufficiently grown for them to make important contribu-tion to worldwide research on creep and shrinkage (Maekawa 2003).

6. Conclusion

This paper outlined the state of Japanese research on concrete creep and shrinkage focusing on several unique aspects. Since experimental work takes a long time in general, rapid research results cannot be expected. The fact that several unique and promising advances, as

100mm

Restraining steel plates

Concrete specimen

Testing zone: 100x100x300mm

Anchoring zone

Fig. 8 JIS test specimen for cracking due to restrained drying shrinkage.

-1.0

0.0

1.0

2.0

3.0

0 10 20 30 40

Time (day)

Con

cret

e st

ress

(N/m

m2 ) Cracking

Fig. 9 Concrete stress induced by restrained shrinkage in JIS test specimen.

Fig. 7 Database developed by JSCE320.


presented in this paper, have already been achieved in this field indicates that such events are not accidental, but rather that research is headed in the right direction and that efforts are beginning to bear fruit.

However, there are still a number of problems that should be considered in the future, such as improvement of prediction models for creep and shrinkage and de-velopment of rational prediction methods for shrinkage cracking. Further study is likely again to produce meaningful results. References JSCE (1986). “Standard specification for design and

construction of concrete structures, part 1 [Design].” Tokyo: Japan Society of Civil Engineers.

JSCE (1986). “Standard specification for design and construction of concrete structures, part 1 [Construction].” Tokyo: Japan Society of Civil Engineers.

JSCE (1996). “Standard specification for design and construction of concrete structures, part 1 [Design].” Tokyo: Japan Society of Civil Engineers. (in Japanese).

JSCE (2002). “Standard specification for concrete structures, Structural performance verification.” Tokyo: Japan Society of Civil Engineers. (in Japanese).

JSCE308 (2000). “Creep and shrinkage of concrete II”, Tokyo: Japan Society of Civil Engineers. Concrete Engineering Series 39. (in Japanese).

Tazawa, E. and Miyazawa, S. (1993). “Autogenous shrinkage of concrete and its importance in concrete technology.” In: Z.P. Bažant and I. Carol, Eds. The fifth

international RILEM symposium on creep and shrinkage of concrete (ConCreep5), Barcelona 6-9 September 1993. London: E & FN Spon, 159-168.

Sakata, K. (1993). “Prediction of concrete creep and shrinkage.” In: Z. P. Bažant and I. Carol, Eds. The fifth international RILEM symposium on creep and shrinkage of concrete (ConCreep5), Barcelona 6-9 September 1993. London: E & FN Spon, 649-654.

JCI (1985). “Report of technical committee on thermal stress of massive concrete structures.” Tokyo: Japan Concrete Institute. (in Japanese).

Kawase, K. (1991). “Study for standardization of testing method on cracking of concrete due to restrained drying shrinkage – part 1.” Cement and Concrete, 532, 49-56. (in Japanese).

AIJ (2003). “Shrinkage cracking in reinforced concrete structures -Mechanisms and practice of crack control-.” Tokyo: Architectural Institute of Japan. (in Japanese).

Mihashi, H. and Wittmann, F. H. eds. (2002). “Control of cracking in early age concrete.” Lisse: A. A. Balkema Publishers.

Tazawa, E. ed. (1999). “Autogenous shrinkage of concrete.” London: E & FN Spon.

CEB-FIP (1978). “Model code for concrete structures, Vol. II, International system of unified standard codes of practice for structures.” Lausanne, Comité Euro-International du Béton.

Maekawa, K. Ishida, T. and Kishi, T. (2003). “Multi-scale modeling of concrete performance.” Journal of Advanced Concrete Technology, 1 (2), 91-126.

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Recent Progress in Research on and Code Evaluation of