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A Re-Examination Of Creep Mechanisms In Hydrated Cement Systems
1. A RE-EXAMINATION OF CREEP MECHANISMS IN
HYDRATED CEMENT SYSTEMS
J.J. Beaudoina
, B. Tamtsiab
and J. Marchandc
a
Institute for Research in Construction, National Research Council
of Canada, Ottawa, Ontario, Canada K1A OR6
b
Department of Civil Engineering, University of Ottawa,
Ottawa, Ontario, Canada K1N 6N5
c
Department of Civil Engineering, Université Laval,
Ste-Foy, Québec, Canada G1K 7P4
(Originally published in Proceedings, Materials Science of Concrete Workshop, April 27-29, 2000)
ABSTRACT
Mechanisms of creep of hydrated Portland cement paste are reviewed with
reference to the role of water. The coupling of an a.c. impedance analyzer with a
miniature loading system was used to follow real-time microstructural changes
due to sustained load.
Various pre-drying treatments (including use of solvent exchange methods) were
used to probe the sensitivity of the creep process to microstructural change and the
presence or absence of moisture. Characterization of the water in the paste was
carried out using a controlled environment differential thermogravimetric
technique. Evidence suggests that the presence of water is not an 'à priori'
condition for creep. A creep mechanism involving microsliding between C-S-H
sheets appears to be compatible with the experimental evidence.
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RÉSUMÉ
Cet article traite du rôle de l’eau dans le fluage de la pâte de ciment Portland hydraté. Un
analyseur d’impédance couplé à un système de chargement miniature a permis de suivre
en temps réel les changements de microstructure dus à la charge subie. On a utilisé
plusieurs traitements de pré-séchage (y compris des méthodes à échange de solvants) pour
vérifier l’influence des changements de microstructure ainsi que de la présence ou
absence d’humidité sur le fluage. La caractérisation de l’eau dans la pâte s’est faite par la
méthode thermopondérale en milieu contrôlé. Les résultats ont prouvé que la présence
d’eau n’était pas une condition préalable au fluage. En revanche, un microglissement
entre les couches de C-S-H paraît compatible avec les résultats expérimentaux.
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INTRODUCTION
Water is generally considered to have a seminal role in the majority of the hypotheses for
the creep behavior of hardened cement paste [1,2]. For example it is integral to the
seepage theory which describes time-dependent volume change due to applied load in
terms of changes in the internal vapor pressure and hence in the so-called gel water
content [3]. Variations of the seepage theory have been reported [4]. Other theories
dependent on some form of water interaction include: the viscous shear theory (creep
occurs through slip between C-S-H particles in a shear process in which water acts as a
lubricant) [5]; the thermal activation theory (water plays an indirect role through its effect
on disjoining pressure which, in turn, weakens interparticle bonds) [1]; microprestress-
solidification theory (microprestress is generated by the disjoining pressure of the
hindered adsorbed water in the micropores and by the very large and highly localized
volume changes caused by hydration or drying) [6]. Physico-chemical processes during
creep include: silica polymerization of C-S-H induced by loading or drying [7]; the
interlayer consolidation (creep is a manifestation of the gradual aging of a poorly
crystallized layered silicate material accelerated by drying or stress) [8]; microcracking
near non-shrinking calcium hydroxide crystals [9].
A detailed description of the theories referred to above is provided in an excellent review
by Neville [4]. There remains however, despite the various theories proposed, no
universally accepted theory or mechanism for creep of hardened cement paste.
The experiments discussed in this paper were specifically designed to re-assess the
importance of water and related volume change mechanisms in the creep process. Creep
data was obtained on miniature specimens under environmentally controlled conditions.
The monitoring of real-time changes in the microstructure of cement paste subjected to
sustained load through a coupled a.c. impedance loading system facilitated the
assessment.
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EXPERIMENTAL PROGRAM
Specimen Preparation and Characteristics
The Portland cement paste used to fabricate the creep specimens was prepared at a water-
cement ratio = 0.50 and hydrated for periods up to 30 years. The Portland cement had the
following composition in percent: SiO2 (20.7); Al2O3 (5.9); Fe2O3 (3.1); CaO (62.7);
MgO (3.5); SO3 (2.2) and the lime (0.2). The Bogue composition in percent was as
follows: C3S (46.5); C2S (24.6); C3A (10.4) and C4AF (8.3). Mixing details are provided
elsewhere [10].
The C3S paste samples were prepared at a water-solid ratio of 0.4. The procedure was
similar to that for fabrication of the Portland cement paste. These samples were hydrated
for 28 days. The C3S had the following composition in percent: CaO (73.9); SiO2 (26.2);
Al2O3 (0.08); free CaO (0.46).
"T" shaped specimens 25.4 mm long were cut from paste cylinders for the creep and
shrinkage measurements. They had a cross-section 7.00 mm deep with a flange width of
12.70 mm and flange and web thicknesses of 1.27 mm. Details of the fabrication process
are also given elsewhere [10].
Specimen Pre-treatment
Four series of test specimens were fabricated and conditioned to provide a wide variety of
microstructural treatment and pore structures for the creep and shrinkage tests.
Series I (All tests were performed in a saturated condition)
The "T" shaped Portland cement paste specimens were conditioned (prior to testing) as
follows:
(1) Untreated - samples were saturated surface dry and directly used for test
without any further treatment.
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(2) Drying at 37°C - samples were initially saturated surface dried, vacuum dried
at 37°C for 24 hours and then re-saturated (with synthetic pore solution) under
vacuum for 18 hours. Prior to the re-saturation process, the samples were
vacuum dried for 3 hours in a dessicator at 20°C and 1x10-4
mm Hg.
(3) Methanol exchange - samples were soaked in methanol for 48hours, vacuum
dried at 37°C for 24 hours, then re-saturated (with synthetic pore solution)
under vacuum for 18 hours. Prior to the re-saturation process the samples
were vacuum dried for 3 hours in a dessicator at 20°C and 1x10-4
mm Hg.
(4) Isopropanol exchange - samples were conditioned in a manner similar to that
for the methanol exchange process.
Series II (All tests were performed in a dry condition)
The "T" shaped C3S paste specimens were subjected to the following drying treatments.
(1) Reference state - the specimens were all dried to 11% RH for 30 days in a
dessicator and then re-saturated in lime-saturated water for 14 days. This was
followed by D-drying.
(2) Methanol exchange - the specimens prepared as described for the reference
specimens were exchanged with methanol after re-saturation with lime-water.
This was followed by D-drying.
(3) Isopropanol exchange - the specimens prepared as described for the reference
specimens were exchanged with isopropanol after re-saturation with lime-
water. This was followed by D-drying.
Series III (All tests were performed in the saturated state)
The "T" shaped Portland cement paste specimens were conditioned (prior to testing) as
follows:
(1) Reference state - specimens were tested in their original saturated state.
(2) Drying to 42% RH - reference specimens were dried to 42% RH and re-
saturated with lime-water.
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(3) D-drying - reference specimens were D-dried and then re-saturated with lime-
water.
The series III enables the evaluation of intermediate drying and D-drying on the creep of
saturated Portland cement paste.
Series IV (All tests were performed in a dry condition)
The "T" shaped Portland cement paste specimens were subjected to the following drying
treatments.
(1) D-dry - specimens were oven-dried at 105°C for 3 hours.
(2) Drying at 37°C - specimens were vacuum dried at 37°C for 24 hours.
(3) Methanol exchange - specimens were subjected to a methanol exchange
process and then vacuum dried at 37°C for 24 hours.
(4) Isopropanol exchange - specimens were subjected to a isopropanol exchange
process and then vacuum dried at 37°C for 24 hours.
It is important to distinguish the conditions for solvent exchange in the test series II from
those of the series I and IV. In series II all specimens are dried to 11% RH and then re-
saturated prior to exchange. Pore coarsening effects are therefore similar for all
preparations prior to exchange.
Thermal Analysis
Differential thermogravimetric Analysis (DTGA) was used to characterize the state of
water in the samples. The method provided information on the effect of the various pre-
treatments on the amount of water associated with the C-S-H phase. A Dupont 951
Thermal Analyzer placed in an environmentally controlled chamber was used for the
tests.
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Creep Measurement System
The a.c. impedance creep and shrinkage spectral responses were carried out by mounting
the "T" shaped specimens (two per frame) in a miniature creep frame linking the
specimens to a load cell through electrode interfaces which were connected to a Solatron
1260 frequency response analyzer. The creep frames were placed in environmentally
controlled cells. Modified Tuckerman optical extensometers were used for length change
measurements. They were mounted on the flanges of each of the two "T" shaped
specimens. Creep strain was monitored with an accuracy of about 1 µstrain. Details of
the measurement system are provided in reference 10.
RESULTS AND DISCUSSION
The total strain (creep + shrinkage) - time curves for the series I Portland cement paste
specimens (w/c=0.50, stress-strength ratio=0.30) under sustained load are presented in
figure 1. The total strain at 72 hours is 320, 450, 515 and 600 µ∈ for the control
specimens and those dried at 37°C, solvent exchanged with isopropanol and solvent
exchanged with methanol respectively prior to re-saturation with synthetic pore solution.
The strain recovery for the control specimens and those dried at 37°C or exchanged with
isopropanol prior to re-saturation with pore solution is about 100 µ∈. The value for the
methanol exchanged specimens is about 200 µ∈. The increase in total deformation of the
dried (37°C) or solvent exchanged specimens may be partly due to the pore coarsening
effect. Nevertheless the collapse of the C-S-H structure on drying (a form of hindered
aging) prior to re-saturation may occur to a lesser extent for pastes that have undergone
solvent exchange. This may account for the higher strain values observed. The drying
creep - time curves (not shown) display similar relative differences between the treated
and untreated control specimens.
The a.c. impedance spectra for the total strain measurements of methanol exchanged
specimens plotted in figure 2 are typical. The size of the high frequency arcs for the
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unloaded specimens (not shown) is significantly greater than the corresponding arcs (at
each specific time) for the loaded specimens.
The growth of the high frequency arc diameter (total strain conditions) for all the
specimens subjected to the four pre-treatments is plotted in figure 3. The size of the arc
at 72 hours is in the following order: untreated > isopropanol exchanged > methanol
exchanged > drying at 37°C. The total strain (figure 1) was in the following order:
methanol exchanged > drying at 37°C > isopropanol exchanged > untreated. These
results are consistent with the relative pore coarsening effects due to the pre-drying
treatments.
The smaller arc sizes for the total strain sequences (compared to shrinkage) suggests that
processes involving displacement (slipping and sliding) of C-S-H sheets induced by the
applied load are operative.
Previous work has shown that loading cement paste up to about 50 percent of the
maximum has a little effect on the size of the high frequency arc [11]. This suggests that
microcracking processes had little effect on the a.c. impedance response (stress/strength
ratio = 0.30) obtained in these experiments.
The differences in high-frequency arc diameter between the shrinkage and the total strain
impedance spectra (at corresponding times) generally increase with time. The differences
at 24 hours are in the following order: methanol exchanged > isopropanol exchanged >
untreated > pre-drying at 37°C. The large differences for the methanol and isopropanol
exchanged samples are consistent with the large relative creep observed for these
specimens.
The high-frequency arc is usually imperfect and depressed below the real axis by angle
expressed as αd.π/2 where αd is an indicator of the extent of the arc depression. The
depression angle parameter n (1-αd) is plotted against time for the cement paste
specimens in figure 4. The range of values of n are 0 < n < 1 where n = 1 represents a
perfect arc. The initial value of n is in the following order: untreated > methanol
exchanged > isopropanol exchanged > pre-drying at 37°C. The order remains the same
for the first few hours with the exception of n for the untreated specimen which decreases
rapidly between 2 and 6 hours reaching a value significantly lower than for the treated
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specimens. This suggests that initially the drying treatments perturb the surface. The
dependence of the arc depression has been linked to fractal characteristics of surfaces
[12]. The low values of drying creep for the untreated specimens may be related to the
low values of the depression angle parameter. The fractal nature of the surface may affect
the slipping-sliding behavior of the C-S-H sheets in cement paste under load.
Analysis of the specific total strain rate provides additional evidence for a slipping-sliding
mechanism. The specific total strain rate versus time is plotted as a log-log relation in
figure 5. Two straight lines describe the data. The line for the untreated control
specimens lies below a line representative of the other specimens. The co-linearity of
these type of curves (in other investigations) suggests that specific creep rate is
independent of loading time and degree of hydration [13]. It has been shown that the
long-term aging effect can be characterized by a decrease of the creep rate inversely
proportional to the material age. This would suggest that the rate determining mechanism
is associated with the behavior of the C-S-H sheets themselves, perhaps involving a
slipping and sliding process as suggested previously.
The C3S paste "T" shaped specimens (series II) were dried at 11% RH then re-saturated,
immersed in an organic solvent and D-dried prior to loading. The results are presented in
figure 6 in terms of specific basic creep i.e. micro-strain per unit stress. All specimens
exhibit significant creep in the dry-state. The results indicate that solvent exchange with
methanol before drying reduces creep. Methanol treated samples exhibit less specific
basic creep than both the isopropanol exchanged and the untreated control specimens. It
is especially important to note that the D-dried reference samples exhibit significant
creep. This suggests that the presence of water is not an 'à priori' condition for creep to
occur. Slipping and sliding of C-S-H layers may be an operative creep mechanism [10].
In these experiments all the specimens were initially dried at 11% RH (as indicated
above) and therefore experienced a similar degree of pore 'coarsening' and C-S-H
microstructural change prior to re-saturation and solvent exchange. Under these
conditions the removal of water by a solvent prior to D-drying may alter the
microstructural changes taking place in normal drying and therefore reduce the creep
capacity of the hydrated C3S paste. This is significantly different to what occurs when
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solvent exchange occurs prior to initial drying. In the latter case there appears to be a
'hindered' aging process that results in an increase of creep due to the exchange process.
The DTGA results (figure 7 gives results for the methanol exchange only) indicate that
immersion of C3S paste, treated as described above, may remove water from C-S-H and
therefore, bring the sheets into closer proximity once dried under vacuum. This may
explain the smaller magnitude of creep in such C3S paste specimens (series II)
particularly those immersed in methanol.
The magnitude of specific basic creep of saturated Portland cement paste specimens
(series III) is dependent on the previous drying history (figure 8). Samples dried at 42%
RH or D-dried have significantly greater creep at 25 days than the reference specimens.
Creep of the saturated reference specimens is greater than or similar to that of series IV
Portland cement paste specimens tested in the D-dry state (figure 9). The amount of
creep of dry specimens can be very large if the specimens are immersed in organic
solvents prior to the drying process. The removal of water by a solvent prior to vacuum
drying may reduce the microstructural changes taking place in normal drying (a form of
'hindered' aging) and therefore increase the creep capacity of hardened cement paste as
indicated by the results in figure 9 and the corresponding high surface area. The creep
result (methanol exchange) can also be explained by the formation of a new complex
from the reaction between the solvent and the cement paste.
Methanol has been shown to react with CH and C-S-H [14]. Such chemisorbed products
and/or complexes that possibly form may weaken the C-S-H surface resulting in an
increase in the sliding capacity between sheets.
Plots of the compliance (total deformation per unit stress) versus time (log-log scale) for
series III and IV were linear (as were the plots for the cement paste specimens series I that
were monitored by a.c. impedance spectroscopy described earlier, figure 5). The curves
are power functions that can be expressed as follows:
β
α )
(
)
,
(
o
t
t
dt
t
t
dJ o
−
=
11. NRCC 44012
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where J (t, to) is the compliance of hardened cement paste at age t loaded at to, α and β
are constants and (t - to) is the time elapsed under loading.
The range of variation for the β parameter in this study is small i.e. 0.71-0.94. The
assumption that α is the only variable seems reasonable [13]. The values of α for the
solvent exchanged specimens are more than 5 times those for the D-dried or vacuum
dried specimens (37°C for 24 hours) and approximately 4 times the values for the other
specimens tested in the saturated condition. This variation indicates that methanol and
isopropanol exchanged specimens behave quite differently than the others. The
comments referred to above concerning the independence of loading time and degree of
hydration on specific basic creep rate also apply to these experiments. The results
provide further evidence for the view that the rate determining mechanism is associated
with the behavior of the C-S-H sheets themselves, perhaps involving a slipping and
sliding process.
CONCLUSIONS
1. Creep of Portland cement paste subjected to drying is significantly affected by the
solvent exchange pre-drying treatment. This also applies to creep recovery.
2. A.C. Impedance spectroscopy can detect real-time microstructural changes in Portland
cement paste unloaded or subjected to a sustained load.
3. The observation of smaller high frequency arc sizes in the a.c. impedance spectra for
total strain measurements relative to the arcs obtained for shrinkage measurements
suggests that continuous processes involving slipping and sliding of the C-S-H sheets
are operative when cement paste is under sustained load.
4. The value of the high-frequency arc depression angle in the a.c. impedance spectrum
appears to reflect the relative creep potential of hardened cement paste.
5. The linear character of the log specific strain versus log time relation for Portland
cement paste subjected to a sustained load suggests that the rate determining
mechanism may be associated with slipping and sliding of the C-S-H sheets.
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6. The D-dried tricalcium silicate reference paste exhibits a significant amount of creep
confirming that creep mechanisms associated with water transport are not necessarily
dominant.
7. Methanol and isopropanol exchanges of tricalcium silicate paste (after drying to 11%
RH and re-saturation with water) reduce the magnitude of creep in the dry state. This
may be due to irreversible interactions of the solvent with C-S-H.
8. Portland cement paste dried to an intermediate humidity and re-saturated creeps
significantly more than saturated cement paste that has not been previously dried.
This is attributed to the pore coarsening effect due to drying and possible increase in
creep sites due to increased layering of C-S-H.
9. Specific basic creep can be expressed as a power function. The parameters depend on
the water content of the samples and/or on the drying condition and pre-treatment
history.
REFERENCES
[1] F. H. Wittmann, Influence of Moisture Content on the Creep of Hardened Cement,
Reol. Acta. 9 (2) (1970) 282-87.
[2] V.S. Ramachandran, R.F. Feldman and J.J. Beaudoin, Concrete Science, Heyden &
son, London, 1981, p427.
[3] T. C. Powers, Mechanisms of Shrinkage and Reversible Creep of Hardened
Portland Cement Paste, International Conference On the Structure of Concrete,
Cement and Concrete Association, London, England, 1968, pp. 319-44.
[4] A. M. Neville, Creep of Concrete: Plain, Reinforced and Prestressed, Chapters 10
and 11 (Mechanisms of Creep and Creep hypotheses), North Holland Publishing
Co, Amsterdam, 1970, pp. 258-309.
[5] W. Ruetz, A Hypothesis for the Creep of Hardened Cement Paste and the Influence
of Simultaneous Shrinkage, International Conference On the Structure of Concrete,
Cement and Concrete Association, London, England, 1968, pp. 365-87.
13. NRCC 44012
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[6] Z. P. Bazant, A. B. Hauggard, S. Baweja, F. J. Ulm, Microprestress-Solidification
Theory for Concrete Creep I: Aging and Drying Effects, Journal of Engineering
Mechanics, 123 (11) (1997) 1188-94.
[7] A. Bentur, R. L. Berger, Jr F. V. Lawrence, N. B. Milestone, S. Mindess, J. F.
Young, Creep and Drying Shrinkage of Calcium Silicates Pastes, III. A hypothesis
of Irreversible Strains, Cem Concr Res 9 (1) (1979) 83-96.
[8] R. F. Feldman, Mechanism of Creep of Hydrated Portland Cement Paste, Cem
Concr Res 2 (5) (1972) 509-20.
[9] O. Ishai, The Time-Dependent Deformational Behaviour of Cement Paste, Mortar
and Concrete, International Conference On the Structure of Concrete, Cement and
Concrete Association, London, England, 1968, pp. 345-64.
[10] B. Tamtsia and J.J. Beaudoin, Basic Creep of Hardened Portland Cement Paste: A
Re-Examination of the role of water, Cement and Concrete Research, in press.
[11] P. Gu, P. Xie and J.J. Beaudoin, Impedance Characterization of Microcracking
Behavior in Fiber-Reinforced Cement Composites, Cement and Concrete
Composites, 15 (3), 1993, pp. 173-180.
[12] T. Pajkassy and L. Nyikos, Impedance of Fractal Blocking Electrodes, Journal of
Electrochemical Society: Electrochemical Sci. and Tech., 133 (10), 1986, pp. 2061-
2064.
[13] F. J. Ulm, F. Le Maou, C. Boulay, Creep and Shrinkage Coupling: New Review of
Some Evidence, Revue Francaise de Génie Civil, 3 (3-4) (1999) 21-37.
[14] J. J. Beaudoin, Validity of using methanol for studying the microstructure of cement
paste, Materials and structures, 20 (115) (1987) 27-31.
14. NRCC 44012
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Figure 1 Total strain (Creep+Shrinkage) and strain recovery of hardened cement paste (w/c=0.5)
onditioned at about 96% relative humidity after resaturation from different drying
pretreatment.
0
100
200
300
400
500
600
0 20 40 60 80 100 120 140
time, in hours
microstrain,
in
µ
µ
µ
µ
m/m
Reference (untreated)
Dried at 37°C for 24 hours then resaturated with pore solution
Immersed in methanol, dried at 37°C then resaturated with pore solution
Immersed in isopropanol, dried at 37°C then resaturated with pore solution
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Figure 2. AC impedance spectra: total strain of hcp methanol soaked vacuum dried at 37°C and
resaturated with pore solution (w/c=0.5); specimens conditioned at about 96% relative
humidity for 0, 1, 2, 3.66, 6.5, 9, 12.66, 24, 48, and 72 hours
-12000
-10000
-8000
-6000
-4000
-2000
0
0 2500 5000 7500 10000 12500 15000 17500 20000 22500 25000 27500 30000
Real, in ohms
Imaginary,
in
ohms
96% RH Arc diameter increasing
w ith time under load : 0
1h
2h
3.66h
6.5h
9h
12.66h
24h
48h
72h
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Figure 3. High-frequency arc diameter R 2 (following re-saturation of cement paste (w/c=0.50) after
several drying conditions) during a total strain (Creep + Shrinkage) test at 96% RH
0
5000
10000
15000
20000
25000
30000
35000
40000
45000
0 10 20 30 40 50 60 70 80
time, in hours
semi-circle
diameter
R
2
,
in
ohms
untreated
dried at 37°C
methanol
isopropanol
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Figure 4. Depression angle parameter of high frequency arc following re-saturation of cement
paste (w/c=0.50) after several drying conditions
0.6
0.7
0.8
0.9
1
0 10 20 30 40 50 60 70 80
time, in hours
depression
angle
parameter,
n
=
(1-
α
d
)
Reference (untreated)
Dried at 37°C for 24 hours then resaturated with pore solution
Immersed in methanol, dried at 37°C then resaturated with pore solution
Immersed in isopropanol, dried at 37°C then resaturated with pore solution
18. NRCC 44012
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Figure 5. Specific total strain rate of hardened cement paste (w/c=0.50) conditioned at ~96%
relative humidity after re-saturation from different drying pre-treatments
[ R2
= 0.8311 ]
[ R2
= 0.8446 ]
0.1
1
10
0.1 1 10 100
time, in hours
specific
total
strain
rate,
in
µ∈
µ∈
µ∈
µ∈=
=
=
=
/
Mpa
/
h
Power
Power
Pre-drying (see text)
5512
.
0
)
(
4199
.
2
)
,
( −
−
= o
t
t
dt
o
t
t
dJ
7322
.
0
)
(
4145
.
5
)
,
( −
−
= o
t
t
dt
o
t
t
dJ
Control
Control
Pre-drying
19. NRCC 44012
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0
10
20
30
40
50
60
70
80
0 10 20 30 40 50 60 70 80
loading period, in days
Specific
basic
creep,
µ∈
µ∈
µ∈
µ∈
/Mpa
Reference
Methanol
Isopropanol
Figure 6. Specific basic creep of D-dried C 3 S paste (74% hydrated)after alcohol
exchange
20. NRCC 44012
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-0.05
0.05
0.15
0.25
0.35
0.45
0.55
0.65
0.75
0.85
100 150 200 250 300 350 400 450 500
temperature, in °C
d(TG
%mass)/dt
Unhydated
28 days (Control)
56 days (Methanol)
56 days (Control)
28 days (Methanol)
Figure 7. Effect of Methanol treatment on the dehydration of C 3 S blend (w/s=0.4)
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0
25
50
75
100
125
0 5 10 15 20 25 30
Loading period, in days
specific
basic
creep,
in
µ∈
µ∈
µ∈
µ∈
/MPa
Saturated (first state)
Dried at 42% r.h. then resaturated
D-dried then resaturated (second state)
Figure 8. Specific basic creep of cement paste (w/c=0.5) after resaturation from different
drying treatments
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0
40
80
120
160
200
240
280
320
360
400
0 10 20 30 40 50 60 70 80 90 100
Loading period, in days
specific
creep,
in
µ∈
µ∈
µ∈
µ∈
/MPa
D-dried
Dried at 37°C for 24 hours
Meth. then dried at 37°C for 24 hours
Isop. then dried at 37°C for 24 hours
0
45
90
135
180
0 1 2 3
Figure 9. Specific basic creep of cement paste (w/c=0.5) after different drying
treatments
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