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ORIGINAL ARTICLE
Long term deformations by creep and shrinkage in recycledaggregate concrete
A. Domingo • C. Lazaro • F. L. Gayarre •
M. A. Serrano • C. Lopez-Colina
Received: 10 October 2008 / Accepted: 7 December 2009 / Published online: 15 December 2009
� RILEM 2009
Abstract The main aim of this work was to deter-
mine creep and shrinkage variations experienced in
recycled concrete, made by replacing the main fraction
of the natural aggregate with a recycled aggregate
coming from waste concrete and comparing it to a
control concrete. It was possible to state that the
evolution of deformation by shrinkage and creep was
similar to a conventional concrete, although the results
after a period of 180 days showed the influence of the
substitution percentage in the recycled aggregates
present in the mixture. In the case when 100% coarse
natural aggregate was replaced by recycled aggregate
there was an increase in the deformations by creep of
51% and by shrinkage of 70% as compared to those
experienced by the control concrete. The substitution
percentages of coarse natural aggregate by coarse
recycled aggregate were 20, 50 and 100%. Fine natural
aggregate was used in all cases and the amount of
cement and water–cement ratio remained constant in
the mixture.
Keywords Creep � Shrinkage � Recycled concrete �Recycled aggregate concrete
1 Introduction
Under the National Plan of Construction and Demo-
lition Waste (PNRCD 2001–2006) carried out in
Spain, different studies were made with the purpose
of being able to reuse construction waste in concrete
production.
Currently in Spain several groups of researchers
are working jointly in the development of specific
rules that regulate the use of these materials in
concrete production [1, 2]. Following these objec-
tives, with the support of the Spanish Ministry of
Environment and coordinated by the Structures and
Materials Head Office Laboratory of the Cedex
(Training and Experimentation Center for Public
Works), the experimental project of regulatory con-
text RECNHOR was developed. Our work team
participated in this project together with three Span-
ish universities and more specifically was in charge of
evaluating the influence of recycled aggregate on the
deferred properties of the concrete. It was important
to determine these parameters in order to confront the
design of reinforced concrete elements prepared with
recycled aggregates in a safe way.
The Spanish researchers Sanchez de Juan [3] and
Gomez-Soberon [4], who have worked previously in
this line of investigation, presented several conclu-
sions. Shrinkage values between 15 and 60% were
obtained by Sanchez de Juan et al. [3], higher in
recycled aggregate concretes as compared to those
containing natural aggregate. Gomez-Soberon [4]
A. Domingo � C. Lazaro
ETSICCP, Polytechnic University of Valencia,
Camino de Vera, s/n., 46071 Valencia, Spain
F. L. Gayarre � M. A. Serrano (&) � C. Lopez-Colina
EPS Engineering, Dep. Construction, University of
Oviedo, Campus de Viesques, 33203 Gijon, Spain
e-mail: serrano@uniovi.es
Materials and Structures (2010) 43:1147–1160
DOI 10.1617/s11527-009-9573-0
concluded that due to a higher absorption of recycled
aggregate, the shrinkage and creep of the recycled
concrete increased. Similar values to the ones
obtained for concretes made with aggregates coming
from slag were presented [5]. Other study carried out
by Kishore [6] reveal creep and shrinkage strains in
the range of 14–33, and 3–30%, respectively. Poon
[7] concluded that shrinkage in steam curing recycled
concretes diminishes when the percentage o recycled
aggregate increases. For concretes prepared with
recycled aggregates, Sato [8] obtained values for the
autogenous shrinkage 40% lower than those of
conventional concrete for a 28 days period, never-
theless the drying shrinkage was the same for both
types of concretes for the longer period of 100 days.
2 Experimental program
2.1 Components
The cement considered for the preparation of the
concretes in this work was: CEM I 42.5 N/SR. The
natural aggregates presented a calcareous origin with
three different possibilities: coarse aggregate CNA
(10/20 mm), coarse aggregate CNA (4/10 mm) and
fine aggregate FNA (0/4 mm). All the recycled
coarse aggregates RCA (4/20 mm) considered came
from concrete waste. The additive Sikament 500�
was used as superplastifying.
The coarse recycled aggregate, whose rocky
matrix is also calcareous, is similar in appearance
to the natural crushed aggregates although its texture
is rougher due to adhered mortar waste [9, 10],
presenting a greater absorption than natural aggre-
gates (Table 1). Another important factor is the lower
density of recycled aggregates due to the presence of
mortar adhered to the aggregates [9, 10].
Recycled aggregates generally fulfil adequate
granulometric analysis for concrete production [10].
This granulometric analysis was carried out accord-
ing to the European Code UNE-EN 933-1. Figure 1
shows the granulometric analysis and the granulo-
metric modulus of the aggregates used.
The aggregates used in the study show a contin-
uous granulometric curve, and the percentage of
declassified material present in the coarse recycled
aggregates is lower than 5%, making them suitable
for use.
The most important property that differentiates
natural aggregates from recycled ones is the percent-
age of adhered mortar, determined according to the
test procedure established in [11]. This method
involves applying stresses to the adhered mortar in
order to cause its detachment from the rocky matrix.
The sample is weighed and immersed in water. Next,
the sample is heated up in a furnace and, subse-
quently, a thermal crash is produced by dipping it
again into cold water. Finally, the sample is sieved
using a 2 mm sieve. The mortar that is still adhered is
removed by hitting the sample with a rubber mallet.
Once the cleaning has been done, the sample is
weighed again. The weight difference represents the
adhered mortar.
It can be observed (Table 1) how a greater
percentage of adhered mortar is concentrated in the
finest fractions.
2.2 Mixtures
The dosage rate of the tested concretes can be
observed in Table 2. A control concrete with 40 MPa
of compressive strength was used. The recycled
concrete was produced by substituting 20, 50 and
100% of the natural coarse aggregate with the
recycled aggregate.
Table 1 Densities,
absorption and L.A. wear
coefficient of aggregates
Material Dry density
(kg/m3)
Density SSD
(kg/m3)
Absorption
24 h (%)
L.A.
coefficient (%)
Adhered
mortar
CNA (10/20 mm) 2647 2673 0.98 27.8
CNA (4/10 mm) 2622 2659 1.42 31.96
RCA (4/8 mm) 2338 2460 6.08 43.54 31.5%
RCA (8/20 mm) 2338 2460 5.19 40.22 18%
FNA (0/4 mm) 2460 2540 3.22
1148 Materials and Structures (2010) 43:1147–1160
Two mixtures (A and B) were prepared for each
percentage. Each one was cured in a different way in
order to study the behaviour of its mechanical
properties. The mixture was prepared according to
the following procedure: first, the coarse aggregates
and 1/3 of the water were added, giving the mixer a
few turns. Later the sand, the cement and another
third of the water was added, mixing it for 3 min and
leaving the mixture to rest for another 3 min,
covering it to avoid evaporation. Finally, the remain-
ing third of the water and the additive were added,
mixing it for 2 more minutes, after which the mixture
was ready.
The consistency of the concrete was measured by
the Abrams cone method, according to the code
UNE-EN 12350-2: 2006, obtaining results (Table 3)
that show how a greater presence of recycled
aggregate decreases the workability of the concrete.
That is the reason why it is necessary to use saturated
recycled aggregate [12] or a greater amount of
superplastifying additives.
Following the European Code UNE-EN 12390-2
to carry out the strength tests, samples in cylindrical
specimen of 15 9 30 cm unmolded the following
day were prepared so as to be cured for 7 days in a
chamber at a constant temperature of 20�C and a
humidity of over 95%. On the 18th day, the
specimens of mixture A were left in the humidity
chamber until day 28, whereas the specimens of
mixture B were taken to a climatic chamber that
0
10
20
30
40
50
60
70
80
90
100
1 2 3 4 5 6 7 8 9 10 11
Sieve size (mm)
% P
AS
SIN
G
CNA (10/20 mm) CNA (4/10 mm) FNA (0/4 mm) RCA (4/20 mm)
CNA (10/20 mm) CNA (4/10 mm) FNA (0/4 mm) RCA (4/20 mm)7.32 6.32 2.85 6.65
MaterialGranulometric modulus
Fig. 1 Aggregates
granulometric analysis
Table 2 Mixture
compositionMaterial Coarse recycled aggregate substitution
0% 20% 50% 100%
Cement (kg) 380 380 380 380
Water (kg) 190 190 190 190
FNA (0/4 mm) (kg) 713.90 744.45 709.54 714.56
CNA (10/20 mm) (kg) 882.20 665.28 414.06 0
CNA (4/10 mm) (kg) 121.59 91.69 57.07 0
RCA (4/20 mm) (kg) 0 189.24 471.12 874.04
w/c ratio 0.5 0.5 0.5 0.5
Additive 0.7% 0.7% 0.7% 1.4%
Materials and Structures (2010) 43:1147–1160 1149
presented a drying atmosphere of 65% RH and a
temperature of 23�C, where the creep and shrinkage
tests were carried out.
2.3 Hardened concrete
Tests on three samples were carried out for both
mixtures following the codes UNE-EN 12390-3 and
UNE-EN 83316 in order to determine the compres-
sive strength and the elastic modulus, respectively.
2.4 Test preparation
The test was carried out according to ASTM C512-02
[13]. In order to carry it out, rigid frames with a
capacity to withstand a nominal load of up to 500 kN
were designed. The frames made it possible to test
simultaneously three cylindrical specimens of
150 9 300 mm arranged in series (Fig. 2). The
frames with the specimens were introduced in a
climatic chamber at a controlled temperature of
23 ± 1�C and RH of 65 ± 10%. Since the specimens
are not sealed, the deformations measured are
Ta
ble
3P
hy
sica
lan
dm
ech
anic
alp
rop
erti
eso
fth
ere
cycl
edan
dco
ntr
ol
con
cret
es
Mix
ture
iden
tifi
cati
on
Per
cen
tag
e
recy
cled
Slu
mp
(cm
)
Den
sity
7d
ays
(kg
/dm
3)
Den
sity
28
day
s
(kg
/dm
3)
f c7
day
s
(MP
a)
Co
effi
cien
to
f
var
iati
on
(%)
f c2
8d
ays
(MP
a)C
oef
fici
ent
of
var
iati
on
(%)
Ela
stic
mo
du
lus
(MP
a)
Co
effi
cien
to
f
var
iati
on
(%)
H4
0A
01
72
.36
2.3
63
9.5
1.6
04
5.2
51
.83
33
,30
80
.71
20
14
2.3
52
.35
41
.51
.54
47
.40
2.0
43
2,3
60
1.4
2
50
52
.34
2.3
44
0.4
2.1
44
7.3
2.2
03
3,5
16
1.7
3
10
01
92
.31
2.3
24
7.3
1.8
85
4.8
02
.34
30
,33
71
.59
H4
0B
01
72
.37
2.3
44
5.8
51
.90
36
,22
31
.1
20
15
2.3
42
.32
47
.70
2.1
32
,36
01
.83
50
52
.35
2.3
25
0.2
02
.30
34
,07
22
.14
10
01
82
.31
2.2
95
4.1
02
.51
30
,99
52
.21
Fig. 2 Frame and test equipment
1150 Materials and Structures (2010) 43:1147–1160
shrinkage (autogenous and dried) and creep (basic
and dried).
The frame designed to conduct the test included a
hydraulic manual-action jack, making it possible to
test concretes up to 80 MPa with a 0.35 fc load level.
This load is maintained over long periods of time by
means of a hydro pneumatic accumulator of 1.5 dm3
nominal capacity and nitrogen preload of 110 bar.
The measurement system was made up of elec-
tronic devices that measure and register the defor-
mation, load, temperature and humidity values. The
deformation measurement due to creep and shrinkage
was made by means of three strain gauges, arranged
in three equidistant generatrix. The load in the creep
tests was measured by means of pressure transducers
with a capacity up to 400 bar. Inside the chamber an
electronic transducer measured the humidity and
temperature. All the instruments were connected to
data acquisition modules, with eight channels per
module, so as to periodically register the measure-
ments in real time.
The total extended deformation in a specimen
under compression stress r along with the tempera-
ture increase DT(t) for a period of time t is
determined using the superposition principle in the
equation:
e tð Þ ¼ esh t; t0ð Þ þ J t; t0; t0ð Þ � rþ a � DT tð Þ ð1Þ
The creep function that defines the total elastic
deformation of the concrete under a uniform com-
pression load after 28 days is expressed by:
J t; t0; t0ð Þ ¼ 1þ / t; t0; t0ð ÞE0
ð2Þ
where / is the creep coefficient defined by the
relation between the creep deformation and the initial
deformation. Since the temperature remained con-
stant during the test, its effects were not taken into
consideration.
3 Experimental results
The mortar present in recycled aggregate also causes
a greater wear rate in the Los Angeles machine
(Table 1). Comparing the natural coarse aggregate
to the recycled one, a wear increase between 26%
for the CNA (4/10 mm) and 44% for the CNA
(10/20 mm) was observed.
As it was indicated above, Table 1 shows the
results of the tests for adhered mortar in the recycled
aggregates.
Table 3 shows that the density of the samples
decreases when the substitution level of recycled
aggregate in the mixture is increased, and that the
curing process in the climatic chamber causes a slight
decrease in density due to the drying process of the
samples. The density of the concrete was obtained by
testing three samples following the procedure estab-
lished in the European Code UNE-EN 12390-7.
Table 3 also shows the compressive strength
values for the different substitution percentages and
curing times. In the case of mixture B only the test
after 28 days was carried out.
For all substitution levels, it was observed that
strength after 7 days exceeded 80% of the compres-
sive strength reached by mixture A on day 28. It was
also noted that when the substitution level of recycled
aggregate was increased, an increase in the compres-
sive strength was obtained, contrary to what was
established in other studies. This was possibly caused
by the fact that greater absorption of recycled
aggregates produced a smaller effective water–
cement ratio, although it could also have been caused
by the effects of the additive used.
On the other hand, the elastic modulus obtained
experimentally showed a clear decrease (Table 3) as
the substitution percentage of recycled aggregates
was increased. These results were in agreement with
other studies carried out [14].
The results obtained for the elastic modulus are
acceptable, with levels of substitution between 20 and
50% of the coarse aggregate, if they are compared
(Fig. 3) with those given by the proposed equation in
[14].
Nevertheless, when the substitution level exceeded
50% there was a decrease in the value of the elastic
modulus. In these situations the experimental results
disagree with those proposed by [14]. From these
values the influence of the recycled aggregates can be
observed. Their higher porosity caused an important
decrease in the elastic modulus when the replacement
level was 100%.
In order to verify whether indeed the compressive
strength was higher as a result of the greater
absorption of recycled aggregates, it was decided to
prepare a group of mixtures in which the effective
water–cement ratio remained constant, that is to say,
Materials and Structures (2010) 43:1147–1160 1151
adjusting the amount of water in the mixture to take
into account absorption. Table 4 shows the obtained
values of consistency, compressive strength and
elastic modulus for mixture A.
It was observed that when the effective water–
cement ratio was maintained constant, the slump, the
compressive strength and elastic modulus values
were the same, so the substitution of natural aggre-
gate by recycled aggregate did not have a significant
effect. The recycled aggregate used in the study
presented very good quality.
3.1 Shrinkage
Shrinkage began to be measured after 7 days of
curing, registering values (Fig. 4) that clearly showed
the influence of the percentage of recycled aggre-
gates. There was greater deformation by shrinkage as
E28
20.000
22.500
25.000
27.500
30.000
32.500
35.000
37.500
40.000
42.500
45.000
47.500
50.000
0% 20% 40% 60% 80% 100%
E (
MP
a)
REPLACEMENT PERCENTAGE
Fig. 3 Elastic modulus
versus Japanese
Architecture Institute
estimation
Table 4 Concrete properties, correcting the mix water by
effect of aggregate absorption for mixture A
Percentage recycled Slump (cone cm) fc (MPa) E (MPa)
0 21 42.78 32,153
20 21 42.70 31,178
50 21 41.30 31,204
100 21 41.80 31,589
0
25
50
75
100
125
150
175
200
225
250
275
300
325
350
375
400
0 14 28 42 56 70 84 98 112 126 140 154 168 182 196 210 224 238
ST
RA
IN (
μ m
/m)
AGE (Days)
SHRINKAGE STRAIN H40 RECYCLED CONCRETE EXPERIMENTAL
0%
20%
50%
100%
Fig. 4 Shrinkage
deformation versus concrete
age
1152 Materials and Structures (2010) 43:1147–1160
the percentage of recycled aggregate substitution
increased.
Shrinkage in the recycled concrete with a substi-
tution percentage of 50% was around 20% higher
than that of the control concrete, whereas with a
substitution percentage of 100% the shrinkage
increase reached 70% after a period of 180 days.
The evolution of shrinkage with the time for the
recycled concretes analysed was similar to that
showed by conventional concrete but approximately
50% higher for a period of 120 days.
It could also be observed that increases in the
chamber’s relative humidity caused the shrinkage to
diminish. In Fig. 4, it can be seen that the shrinkage
curves fell after around 77 days, coinciding with the
maximum values of relative humidity in the chamber
(Fig. 5).
The original mechanism of the shrinkage defor-
mations is in the cement paste of concrete. The
adhered mortar in the recycled aggregate causes an
increase in the volume of cement paste in recycled
aggregate concrete. This causes a higher drying
shrinkage because the ratio w/c, that has an important
influence in drying shrinkage, was uniform. The
volume of pores confined in the cement paste leads to
drying shrinkage because, when a humidity gradient
between concrete and ambient is present, as porosity
increases, the loss of water in the cement paste
increases too. On the other hand, when the natural
aggregate is substituted by the recycled one, the ratio
aggregate/cement in recycled concrete diminishes,
since the substitution is done taking into account
volume percentages and the recycled aggregate
includes cement paste adhered to its rocky matrix.
The increase in cement paste causes a rise in the
shrinkage of recycled concrete. Furthermore, due to
the adhered cement paste of the recycled aggregates
the density of concrete decreases and porosity
increases. This growth also contributes to a higher
drying shrinkage than in the reference concrete.
3.2 Creep
Creep mechanisms in concrete are quite complex and
they are still not completely known. Among all the
approaches there is a wide agreement on the impor-
tance of viscous flow, water leakage from C–H–S gel
and micro-cracking.
The original mechanism of creep can be explained
in a simple way by the loss of water of cement paste
due to the applied loads. Since creep happens in the
cement paste, those concretes with a higher volumet-
ric content of aggregates show lower strains caused by
creep.
When the natural aggregate is substituted by the
recycled one, the actual volume of aggregates is
reduced due to the old cement paste present in the
recycled aggregates. This implies a lower ratio
aggregate/cement in recycled concretes than in con-
ventional ones. Also the elastic modulus in recycled
aggregates coming from waste concrete is lower than
in natural aggregates due to the adhered mortar
present in recycled aggregates These effects cause an
increase in creep of the recycled concrete. On the
0
10
20
30
40
50
60
70
80
90
100
0 28 56 84 112 140 168 196 224 252TE
MP
ER
AT
UR
E (
°C)
-RE
LAT
IVE
HU
MID
ITY
(%
)
DAYS
TEMPERATURE AND HUMIDITY DATA IN THE CLIMATIC CHAMBER
Humidity Temperature
Fig. 5 Temperature and
humidity data in the
climatic chamber
Materials and Structures (2010) 43:1147–1160 1153
other hand the higher porosity of recycled concrete
causes an increase in creep.
Figures 6, 7 and 8 show how the deformation in
concrete rises when the substitution percentage of
natural coarse aggregate with recycled aggregate
increases.
Creep data (Fig. 6) were obtained by deducting the
deformation due to shrinkage and instantaneous
deformation caused by the compression load from
the total deformation. It can be observed that the
creep deformation of recycled concrete with a 20%
substitution percentage was found to be 35% higher
than that of the control concrete. For a 50%
substitution level, the creep deformation was 42%
higher, whereas for the 100% substitution level the
increase in the creep deformation was 51%.
When the total creep deformations are compared
with the elastic deformations under the applied load,
the creep coefficients may be obtained (Fig. 7). It is
of great importance to know these coefficients as they
are very useful when estimating the extended deflec-
tions in concrete structures.
The obtained results made it possible to determine
the total deformation, but they did not allow a profound
comparison of the creep potential in the different
mixtures since the recycled concretes and the control
0
100
200
300
400
500
600
700
0 14 28 42 56 70 84 98 112 126 140 154 168 182 196
DE
FO
RM
AT
ION
(μ
m/m
)
LOAD TIME (Days)
CREEP DEFORMATIONS H40 RECYCLEDEXPERIMENTAL
0%
20%
50%
100%
Fig. 6 Total deformation
due to creep effect
0
0,2
0,4
0,6
0,8
1
1,2
1,4
φ
LOAD TIME (Days)
CREEP COEFFICIENT H40 RECYCLED CONCRETE
0%
20%
50%
100%
0 14 28 42 56 70 84 98 112 126 140 154 168 182 196
Fig. 7 Creep coefficients
1154 Materials and Structures (2010) 43:1147–1160
concrete showed different compressive deformation
values. In addition, the load applied to each one was
different in order to maintain the 35% compressive
strength level. For that reason it is better to carry out the
comparison with the specific creep (Fig. 8).
The substitution percentage of recycled aggregate
also affected the creep deformations. The specific
creep of recycled concrete with a 20% substitution
percentage was found to be 25% higher than that of
the control concrete. In recycled concrete with a 50%
substitution level, the creep deformation was 29%
higher and for concrete with a 100% substitution
level the increase in the creep deformation was 32%.
This behaviour considerably exceeds the estimations
that could have been made according to Sanchez de
Juan [3], who concluded that the increase in creep
deformation was already taken into account in the
decrease of the elastic modulus.
4 Result analysis and contrast with prediction
models
4.1 Control concretes
The experimental results were compared with the
values obtained analytically by using prediction
models such as the ACI [14], the CEB-FIP [15], the
one recommended by Rilem [16] and a model
developed by Gardner and Lockman [17].
The variables used in the models are those related
to the control mixture, and the parameters of each
model are those recommended by their authors, since
there were no specific deformation values for the
aggregates used.
Figure 9 shows the total deformations anticipated
by different models and by the control concrete. It
can be observed that after 7 days the drying process
subsequent to the curing process started and, as a
consequence, deformations by shrinkage appeared.
At 28 days a uniform compressive load was
applied to the specimen, causing an instantaneous
elastic deformation and later creep deformations
appeared as the concrete got older. The values of
the shrinkage and creep deformations for the control
concrete can be observed in Figs. 10 and 11,
respectively, for comparison with the results from
their prediction models.
As can be seen in the previous figures, the values
obtained experimentally for both types of deforma-
tions are overestimated by the prediction models.
This trend suggests that the control concrete in fact
presents less extended deformations than predicted
and that estimations based on these models would be
conservative.
4.2 Concrete with recycled aggregates
A comparison of the experimental results was also
carried out for the recycled concrete in order to
evaluate whether use of the prediction models was
possible and thus to be able to predict the extended
deformations of this concrete. If the comparison is
not appropriate, an adjustment of the parameters is
0
5
10
15
20
25
30
35
40
( μm
/m)
/ MP
a
LOAD TIME (Days)
ESPECIFIC CREEP DEFORMATION H40 RECYCLED CONCRETE
EXPERIMENTAL
0%
20%
50%
100%
0 14 28 42 56 70 84 98 112 126 140 154 168 182
Fig. 8 Specific creep
deformation versus load
time
Materials and Structures (2010) 43:1147–1160 1155
0
100
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
0 7 14 21 28 35 42 49 56 63 70 77 84 91 98 105 112 119 126 133 140 147 154 161 168 175 182 189 196 203
DE
FO
RM
AT
ION
(μ
m/m
)
AGE (days)
EXTENDED DEFORMATIONS H40 -0%
PREDICTION MODELS (DRYING AFTER 7 DAYS AND LOAD SET UP TO 28 DAYS)
ACI 209
CEB-FIP
B3
GL2001
Fig. 9 Extended deformations predicted by models
0
50
100
150
200
250
300
350
400
450
500
0 7 14 21 28 35 42 49 56 63 70 77 84 91 98 105 112 119 126 133 140 147 154 161 168 175 182 189 196 203 210 217 224 231 238 245 252 259
DE
FO
RM
AT
ION
(
μ m
/m)
AGE (days)
SHRINKAGE H40 -0%PREDICTION MODELS -EXPERIMENTAL DEFORMATION
ACI 209 GL2001 B3 CEB-FIP 0% Experimental
Fig. 10 Experimental shrinkage versus prediction models for H40 control
1156 Materials and Structures (2010) 43:1147–1160
needed so as to know their influence on creep and
shrinkage when aggregates with special characteris-
tics are included.
It was observed that extended deformations
measured for recycled concrete with a 20% substi-
tution level (Fig. 12), although higher than those
0
5
10
15
20
25
30
35
40
45
50
0 7 14 21 28 35 42 49 56 63 70 77 84 91 98 105 112 119 126 133 140 147 154 161 168 175
SP
EC
IFIC
DE
FO
RM
AT
ION
(μ
m/m
) / M
Pa
LOAD TIME (Days)
CREEP H40 -0%FORECAST MODELS -EXPERIMENTAL DEFORMATION
ACI 209 CEB-FIP B3 GL2001 0% Experimental
Fig. 11 Specific experimental creep versus prediction models for H40 control
0
200
400
600
800
1000
1200
1400
1600
1800
0 14 28 42 56 70 84 98 112 126 140 154 168 182 196
DE
FO
RM
AT
ION
(μm
/m)
AGE (Days)
EXTENDED DEFORMATIONS H40 -20% FORECAST MODELS -EXPERIMENTAL DEFORMATIONS
GL2001
B3
ACI 209
CEB-FIT
20% EXPERIMENTAL
Fig. 12 Extended deformations of H40-20% concrete compared with prediction models
Materials and Structures (2010) 43:1147–1160 1157
predicted for the control concrete, were overesti-
mated by the prediction models used. Nevertheless,
when the substitution level of the recycled aggregate
was 50% (Fig. 13), the extended deformations
basically matched the values predicted by the
CEB-FIP model.
Finally, for 100% substitution levels, the models
used in the comparison usually reflect the behaviour
0
200
400
600
800
1000
1200
1400
1600
1800
DE
FO
RM
AT
ION
(μm
/m)
AGE (Days)
EXTENDED DEFORMATIONS H40 -50%
PREDICTIONS MODELS -EXPERIMENTAL DEFORMATIONS
GL2001
B3
ACI 209
CEB-FIT
50% EXPERIMENTAL
0 14 28 42 56 70 84 98 112 126 140 154 168
Fig. 13 Extended deformations of H40-50% concrete compared with prediction models
0
200
400
600
800
1000
1200
1400
1600
1800
2000
DE
FO
RM
AT
ION
(μm
/m)
AGE (Days)
EXTENDED DEFORMATIONS H40 -100%
FORECAST MODELS -EXPERIMENTAL DEFORMATIONS
GL2001
B3
ACI 209
CEB-FIT
100% EXPERIMENTAL
0 14 28 42 56 70 84 98 112 126 140 154 168 182 196
Fig. 14 Extended deformations of H40-100% concrete compared with prediction models
1158 Materials and Structures (2010) 43:1147–1160
of the concrete tested better than in previous com-
parisons (Fig. 14). It is, however, interesting to point
out that in some cases (after 150 days), the deforma-
tions actually reached were slightly underestimated,
which could be detrimental when applied to the
global behaviour of the structure.
The authors did not aim in this work to propose a
modified model. However, this is one of their main
objectives in the next research by increasing the
number of tests, since the codes do not include the
type of aggregate used in the concrete as a parameter.
5 Conclusions
Based on the experimental tests carried out, it is
possible to conclude that the recycled aggregate used
in this study presents a high quality, without signif-
icant differences of behaviour when compared to
equivalent mixtures with natural aggregates.
The texture and greater absorption characteristics
of recycled aggregates result in an increase in their
consistency. In order to maintain their workability,
the content in superplastifying additives should be
increased just in case the substitution percentage is
100%.
The effective water/cement ratio diminishes, when
completely dried recycled aggregates are used, due to
their higher absorption rate, and the compressive
strength of the recycled concrete increases. Besides
the superplastifying additive used contributes to
increasing the compressive strength of the recycled
concrete. These two factors cause the compressive
strength of the elaborated recycled concretes to
increase slightly as the substitution percentage of
recycled aggregates rises.
Due to the greater porosity of the recycled
aggregate the elastic modulus of the elaborated
recycled concretes diminishes as the substitution
percentage increases.
The shrinkage in the recycled concretes increased
after 28 days. The recycled concretes elaborated with
a substitution level of 20% showed a similar shrink-
age to the conventional concretes in the early stages.
For a period of 6 months, the shrinkage in these
recycled concretes was 4% higher. In the case of a
substitution level of 50%, the shrinkage increase was
12% greater than that of the conventional concrete
after 6 months.
Those concretes elaborated with a substitution
level of 100% showed a shrinkage and a creep which
were considerably higher than those of conventional
concretes, being, respectively, 70 and 51% higher for
a period of 180 days.
The shrinkage trend in the recycled concretes
elaborated with substitution levels of the coarse
aggregate lower than 50% is similar to that shown by
the conventional concrete.
Derived from the experimental results it can be
concluded that the prediction models used in this
research to determine the deferred deformations in
the recycled concrete can be considered conservative
with the exception of the CEB-FIP model for
substitution levels higher than 20%.
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