14
ORIGINAL ARTICLE Long term deformations by creep and shrinkage in recycled aggregate concrete A. Domingo C. La ´zaro F. L. Gayarre M. A. Serrano C. Lo ´pez-Colina Received: 10 October 2008 / Accepted: 7 December 2009 / Published online: 15 December 2009 Ó 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 Sa ´nchez de Juan [3] and Go ´mez-Sobero ´n [4], who have worked previously in this line of investigation, presented several conclu- sions. Shrinkage values between 15 and 60% were obtained by Sa ´nchez de Juan et al. [3], higher in recycled aggregate concretes as compared to those containing natural aggregate. Go ´mez-Sobero ´n [4] A. Domingo C. La ´zaro ETSICCP, Polytechnic University of Valencia, Camino de Vera, s/n., 46071 Valencia, Spain F. L. Gayarre M. A. Serrano (&) C. Lo ´pez-Colina EPS Engineering, Dep. Construction, University of Oviedo, Campus de Viesques, 33203 Gijo ´n, Spain e-mail: [email protected] Materials and Structures (2010) 43:1147–1160 DOI 10.1617/s11527-009-9573-0

Long Term Deformations by Creep and Shrinkage in Recycled

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Page 1: Long Term Deformations by Creep and Shrinkage in Recycled

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: [email protected]

Materials and Structures (2010) 43:1147–1160

DOI 10.1617/s11527-009-9573-0

Page 2: Long Term Deformations by Creep and Shrinkage in Recycled

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

Page 3: Long Term Deformations by Creep and Shrinkage in Recycled

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

Page 4: Long Term Deformations by Creep and Shrinkage in Recycled

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

Page 5: Long Term Deformations by Creep and Shrinkage in Recycled

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

Page 6: Long Term Deformations by Creep and Shrinkage in Recycled

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

Page 7: Long Term Deformations by Creep and Shrinkage in Recycled

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

Page 8: Long Term Deformations by Creep and Shrinkage in Recycled

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

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

Page 9: Long Term Deformations by Creep and Shrinkage in Recycled

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

Page 10: Long Term Deformations by Creep and Shrinkage in Recycled

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

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

Page 11: Long Term Deformations by Creep and Shrinkage in Recycled

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

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

Page 12: Long Term Deformations by Creep and Shrinkage in Recycled

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

Page 13: Long Term Deformations by Creep and Shrinkage in Recycled

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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