STRUCTURAL CONCRETE WITH INCORPORATION OF COARSE

RECYCLED CONCRETE AND CERAMIC AGGREGATES

- DURABILITY PERFORMANCE -

Marco Gomes1; Jorge de Brito1*

1 DECivil-IST, Technical University of Lisbon, Av. Rovisco Pais, 1049-001, Lisbon, Portugal

* corresponding author: Instituto Superior Técnico, Department of Civil Engineering and Architecture, Av. Rovisco Pais, 1049-001 Lisbon, Portugal; Tel. +351 218419709; Fax +351 218497650;

jb@civil.ist.utl.pt

ABSTRACT

The growing difficulty in obtaining natural coarse aggregates for the production of con-

crete, associated to the environmental issues and social costs that the uncontrolled ex-

traction of natural aggregates creates, led to a search for feasible alternatives. One of the

possible paths is to reuse Construction and Demolition Waste (CDW) as aggregates to

incorporate into the production of new concrete.

Therefore, a vast and detailed experimental campaign was implemented at Instituto Su-

perior Técnico, which aimed at determining the viability of incorporating coarse aggre-

gates from concrete and ceramic brick wall debris, in the production of a new concrete,

with properties acceptable for its use in new reinforced and pre-stressed structures. In

the experimental campaign different compositions were studied by incorporating pre-

determined percentages of recycled coarse concrete aggregates and recycled coarse ce-

ramic plus mortar particles, and the main mechanical, deformability and durability

properties were quantified, by comparison with a conventional reference concrete.

In this paper these results are presented in terms of the durability performance of con-

crete, namely water absorption, carbonation and chlorides penetration resistance.

KEYWORDS: concrete recycling, recycled aggregates, durability.

1

GLOSSARY

CBRA: coarse bricks recycled aggregates;

CCRA: coarse concrete recycled aggregates;

CDW: Construction and Demolition Waste;

CMBRA: coarse mortar and bricks recycled aggregates;

EU: European Union;

FCRA: fine concrete recycled aggregates;

IST: Instituto Superior Técnico (Technical University of Lisbon, Portugal);

LNEC: Portuguese National Laboratory of Civil Engineering (Lisbon);

NCA: natural coarse aggregates;

NFA: natural fine aggregates;

RAC: recycled aggregates concrete;

RC: reference concrete (without any recycled aggregates);

RCA: recycled coarse aggregates;

RFA: recycled fine aggregates.

1. INTRODUCTION

Building rubble from the demolition of degraded buildings keeps on growing in Europe.

The last data available stated that the amount of CDW produced in Europe is about 180

million tonnes per year (only 15 of the 27 EU countries were considered) with an in-

creasing trend. A major part of the rubble is concrete that usually is either dumped or

used as pavements sub-grade. The reuse as aggregates in high-grade concrete is up to

now restricted by absent standards and a lack of experience and knowledge. Concerning

this subject, various studies were carried out, particularly by Barra and Vásquez [1] and

2

Limbachiya et al [2].

The present paper presents the results of an experimental campaign developed at Institu-

to Superior Técnico (IST) [3] where the technical viability of replacing natural coarse

aggregates with coarse aggregates recycled from concrete and rendered ceramic parti-

tion walls was studied.

2. LITERATURE REVIEW

A few selected experimental researches mostly at IST concerning the properties of con-

crete with recycled aggregates analyzed in the present paper are briefly described.

2.1. Water absorption

Santos et al [4] tested a RC and two RAC, both without natural coarse aggregates

(NCA) and with RCA (recycled coarse aggregates) from concrete mixes with different

water / cement ratios, to determine their water absorption by immersion: 6.8, 9.6 and

9.8%, respectively. The corresponding porosity values were 15.2, 20.1 and 20.4%. The

authors concluded that the use of RCA instead of NCA increased the water absorption

and porosity but these properties did not seem to be significantly affected by the origi-

nal concrete source of the RCA.

Correia et al [5] determined the water absorption (by immersion and by capillarity) of a

RC and three RAC in which the NCA were replaced with 1/3, 2/3 and 3/3 of ceramic

coarse aggregates from crushed bricks (CBRA), with the same flow value and effective

water / cement ratio as the RC. The grading curve of the NCA and CBRA was also ex-

actly the same. A clear ascending trend with a very high correlation ratio was obtained

for the relationship water absorption by capillarity versus replacement ratio. The RAC

with only ceramic coarse aggregates (water absorption of 12%) presented water absorp-

tion 70% higher than the one of the RC with only limestone coarse aggregates (water

3

absorption less than 1%). A similar trend was obtained for the water absorption by im-

mersion with a corresponding increase of 62%.

In their experimental research, Evangelista and de Brito [6] produced a RC and five

RAC with 10, 20, 30, 50, and 100% replacement of natural fine aggregates (NFA) with

fine concrete recycled aggregates (FCRA), with the same flow value and effective water

/ cement ratio as the RC. Again, the grading curve of the NFA (water absorption of 1%)

and FCRA (water absorption of 13%) was exactly the same. The water absorption by

immersion versus replacement ratio relationship was practically linear with a maximum

increase of the concrete water absorption of 46%. The correlation coefficient for the

water absorption by capillarity versus replacement ratio relationship was lower (R2

equal to 0.70 instead of 0.87) even though a quasi-linear trend of increase could be de-

tected leading to maximum water absorption increases of between 150 and 200%.

Matias and de Brito [7] compared a RC with two RAC with the same flow value where

the NCA had been totally replaced by RCA, with exactly the same grading curve, and

two different superplasticizers had been used to compensate for the RCA’s drawbacks

(namely its much greater water absorption). In terms of water absorption by immersion,

the results were between 26 and 28% higher in the RAC than in the RC. As for water

absorption by capillarity, the RAC provided very similar results, around 80% above the

RC.

The Building Contractors Society of Japan [8] and Hansen [9] concluded that the higher

water absorption of the coarse aggregates is a result of the absorption of the old cement

mortar attached to the aggregate particles.

2.2. Carbonation penetration resistance

Matias and de Brito [7], in the same research program reported above, obtained very

similar results for the RAC carbonation penetration depth after 90 days in the carbona-

4

tion chamber as compared with the corresponding value of the RC (exactly the same for

the RAC with a last generation superplasticizer and 9% higher for a more conventional

superplasticizer). The authors concluded that the superplasticizers had a mixed perfor-

mance in terms of water absorption versus carbonation (much better in the second case).

Evangelista and de Brito [6], in the same experimental research quoted above, but with

only two RAC with 30 and 100% replacement of NFA with RFA (recycled fine aggre-

gates), obtained the following results concerning carbonation depth after 90 days in the

carbonation chamber: the 30% RAC had a performance 27% better than the RC’s and

the 100% RAC 35% worse. The authors considered the first result anomalous and pos-

sibly due to the limited number of specimens tested. However, the results were compat-

ible with the ones from the compression strength test where all the RAC mixes achieved

values very similar to the one of the RC.

In other studies [10], it is stated that the measured carbonation depth, mostly below 5

mm, increases with the amount of recycled aggregate content. However, the carbonation

rate when using RCA made from carbonated concrete was 65% higher than for control

groups [11].

2.3. Chloride penetration resistance

Evangelista and de Brito [6] performed the modified Luping test on the concrete mixes

referred above. The results, in terms of the average diffusion coefficient after 42 days,

were 12% higher in the RAC with 30% replacement of NFA with RFA and 34% higher

when the ratio went up to 100%. These results are consistent with the water absorption

tests and one of the results of the carbonation test. Clearly, it can be concluded that

more research is needed in terms of the use of RFA in structural concrete.

Using the same test procedure and apparatus, Matias and de Brito [7] obtained the fol-

lowing results in terms of average chloride diffusion coefficient after 42 days: the RAC

5

with superplasticizer had better performances than the RC’s by 1% and 16%. These

results are coherent with the ones reported in the carbonation test, i.e. instead of display-

ing a worse performance than the RC the RAC showed a similar or better performance

in terms of carbonation depth and chlorides penetration depth, proving that a feasible

way to improve the durability of RAC is through the use of superplasticizers.

Limbachiya et al [2] compared three sets (for 50, 60 and 70 MPA compressive strength)

of high performance concrete mixes each one consisting of a RC and three RAC with

30, 50 and 100% replacement ratios of NCA with RCA. In terms of chloride diffusion

coefficient, the results of the RAC were very similar with the ones of the corresponding

RC. It must be emphasized that, contrary to the other experimental campaigns described

above, in this one the parameter kept constant was the compression strength and not the

grading curve of the aggregates, the flow value and/or the effective water / cement ratio

and therefore these results are not in contradiction with those.

Kou and Poon [12] investigated the effects of fly ash on compressive strength, pore size

distribution and chloride-ion penetration of RAC (two series of concrete mixes were

prepared: series I with a water-to-binder ratio and a cement content of 0.55 and 410

kg/m3, respectively and series II with a water-to-binder ratio and a cement content of

0.45 and 400 kg/m3, respectively), and concluded that the compressive strength of con-

crete decreased as the recycled aggregate and fly ash contents increased. The total po-

rosity and average porosity diameter of concrete increased as the recycled aggregate

content increased. Furthermore, an increase in the recycled aggregate content led to a

decrease in the resistance to chloride ion penetration. Nevertheless, the replacement of

cement by 25% fly ash improved the resistance to chloride ion penetration and pore

diameters and reduced the total porosity of the RAC.

6

3. EXPERIMENTAL PROCEDURES

3.1. Selection of materials

The material designated as concrete rubble was obtained through the production in la-

boratory of prismatic concrete specimens, with a compression strength class of C30/37

and a maximum dimension of aggregate of 32 mm. At the age of 35 days these speci-

mens were crushed in a jaw crusher. The ceramic and mortar rubble was obtained from

the demolition of a partition wall, with an approximated age of six months, whose con-

stitution was current ceramic hollow bricks with two layers of cementitious mortar, with

a cement type of CEM II 32.5 R and an argyle sand. Both materials were crushed in a

jaw crusher, sieved and separated in sizes 2.38/4.76, 4.76/9.52, 9.52/12.7, 12.7/19,

19/25.4 mm.

3.2. Tests on the materials

All tests referred below were carried out for each size of recycled concrete and ceramic

plus mortar material. The aggregates tests consisted on the grading analysis, bulk densi-

ty, water absorption, specific density, abrasion (Los Angeles test), natural water content

and superficial water content, and particle shape (volumetric analysis). Since some of

these results are not paramount to the interpretation of the tests described in the present

paper, they are not presented except for the water absorption (2.21% and 2.29% for fin-

er and coarser NCA, 8.49% for CCRA, and 16.34% for CMBRA), the specific density,

in saturated dry surface conditions (2587 and 2573 kg/m3 for finer and coarser NCA,

2526 kg/m3 for CCRA, and 2301 kg/m3 for CMBRA) and oven-dry conditions (2565

and 2550 kg/m3 for finer and coarser NCA, 2448 kg/m3 for CCRA, and 2160 kg/m3 for

CMBRA) and the loss of material in the Los Angeles test (28.52% for NCA, 37.96% for

CCRA, and 65.47% for CMBRA).

7

3.3. Concrete mix design and procedure

The objective of the experimental campaign was to understand what would be the max-

imum replacement ratios that would lead to concrete properties within pre-defined limit

boundaries.

The following compositions were tested with different replacement ratios of natural

coarse aggregates (NCA) with recycled coarse aggregates (RCA):

- 12.5% (B12.5B), 25% (B25B), 50% (B50B), and 100% (B100B) for coarse con-

crete recycled aggregates (CCRA) only;

- 6.25% (B6.25C), 12.5% (B12.5C), 25% (B25C), and 50% (B50C) for coarse

mortar and bricks recycled aggregates (CMBRA) only;

- 6.25% CMBRA - 12.5% CCRA (B6.25C12.5B), 12.5% CMBRA - 25% CCRA

(B12.5C25B), and 25% CMBRA - 50% CCRA (B25C50B) for CCRA and CMBRA.

Every recycled aggregates concrete (RAC) mix was compared with a conventional ref-

erence concrete (RC) in terms of mechanical strength and durability.

In terms of aggregates, only the sand fraction 0/2 mm, natural river sand, was kept con-

stant in all the concrete mixes. The grading curve of the coarse aggregates was kept ex-

actly the same in every mix independently of their type (i.e. natural or recycled). As

stated below, this curve followed the theoretical design curve according to the Faury

method.

A pre-saturation method was implemented for the recycled aggregates during the mix-

ing procedure, due to its much higher water absorption when compared with natural

coarse aggregates, as a consequence of the larger porosity of the cementitious matrix

adhered to the recycled aggregates (and of the ceramic material of the bricks). The wa-

ter addition was determined in preliminary tests, where the absorption versus mixing

time curves for this type of aggregates was determined. The effective water / cement

8

ratio was the same in every concrete mix.

The pre-saturation process of the recycled aggregates in this experimental campaign

followed the following procedure:

1. Weighting of the different size fraction particles, in accordance with the concrete

design curve (Faury method for a strength class C30/37 and slump class S3);

2. Introduction of the coarse recycled aggregates inside the mixer;

3. Pre-saturation of the coarse recycled aggregates (additional water to compensate

the higher absorption of the recycled aggregates + one third of the mixing water) during

a period of 10 minutes for the recycled concrete aggregates and 15 minutes for the ce-

ramic and mortar aggregates;

4. Introduction of the sand fraction and mixing for an additional period of 3

minutes;

5. Introduction of the cement (Portland cement CEM II - 42.5R), slowly and care-

fully to prevent the cement powder from spreading;

6. mixing for another 2 minutes in order to homogenize all the mix contents in

terms of size, thus avoiding aggregates segregation;

7. Introduction of the last two thirds of water in the mix;

8. Finally, the concrete was mixed again for 5 minutes before the tests on fresh

concrete and the casting of specimens started.

The control mix with only natural aggregates (i.e. dense siliceous crushed stone) was

made in the same way. No plasticizers or any other admixtures were used in any of the

concrete mixes.

3.4. Tests on concrete

Fresh concrete was tested in terms of workability using the flow table and density. The

first of the campaign aimed at guaranteeing that every concrete mix had the same flow

9

value (85 ± 12 mm). The pre-saturation procedure led to successfully reaching this goal

and, at the same time, keeping the effective water / cement ratio constant at 0.43 (Tables

1 to 3). The difference between the w/c ratio and the effective w/c ratio is the extra wa-

ter that is added to the mix, in order to compensate the higher water absorption of the

recycled aggregates. Those values were determined experimentally by tracking the wa-

ter absorption curve for the recycled aggregates in time, adapting the procedures by

Leite for RFA [13] and applying the values obtained in the mix.

The second stage of the experimental campaign aimed at defining the boundary re-

placement ratios for each coarse recycled aggregate type whose inclusion in the con-

crete mix would still lead to acceptable values of various properties of the RAC relative-

ly to the same properties of the RC: concrete strength, shrinkage and water absorption

by immersion and capillarity.

In the third stage, a larger number of tests were performed on the RC and all the RAC

with replacement ratios within the boundaries defined in the second stage. Only the du-

rability related tests results are presented in this paper.

Comprehensive tests were performed on the hardened concrete mixes. The compressive

strength development was determined using 15 cm cubes. They were stored in a humid

chamber until the age of 28 days at 20 ºC and 65% relative humidity. The modulus of

elasticity was determined on cylindrical prisms of Ø150 300 mm high.

With regard to durability aspects, the aim of this paper, the capillary and immersion

water absorption was determined using 100 x 100 x 200 mm specimens and 100 mm

cubes, respectively. The carbonation and chloride penetration resistance were also de-

termined.

The absorption tests were performed according to the Portuguese National Laboratory

of Civil Engineering (LNEC) E393 and E394 specifications.

10

The measurement of the carbonation penetration depth was performed according to the

RILLEM CPC-18 recommendation. The specimens were previously inserted in a CO2

chamber (Figure 1 left), with a concentration of approximately 5%. Measurements (Fig-

ure 1 right) were made at the age of 7, 28, 56 and 90 days. Eight samples were made for

each concrete mix.

The determination of the chlorides diffusion constant was done according to Nordtest

NT Build 492 (Figure 2). For each type of concrete mix a sample of 3 specimens previ-

ously subjected to a curing period of 28 days was used.

4. RESULTS AND DISCUSSION

4.1. Mechanical properties

In order to determine the compressive strength of the various concrete mixes produced,

European Norm EN 12390-3 was used. Six specimens were used per mix, which had a

water-to-binder ratio and a cement content of 0.43 and 446 kg/m3, respectively.

The average results obtained at 28 days (after curing under controlled conditions) for

the 6 specimens tested per mix are presented in Table 4.

The results obtained showed that for the mixes with incorporation of CCRA (coarse

concrete recycled aggregates) the compressive strength is not affected by this change in

their composition. The same conclusion can be drawn for concrete mixes with simulta-

neous incorporation of CCRA and CMBRA (coarse mortar and bricks recycled aggre-

gates). The main reason for this is the high content in the recycled aggregates of cement

(hydrated and non-hydrated) with a high mechanical strength (CEM II 42.5R), that in-

creased the effective content of cement in the mix when compared with the theoretical

value. Another explanation to these results is linked to the concrete mix procedures,

which divide the mixing process into two parts and proportionally splits the required

11

water into two which are added at different times, allowing the cement slurry to enve-

lope the RA, providing a stronger interfacial zone by filling up the cracks and pores

within RA. The improvements of strength after adopting the two-stage mixing approach

have been proven by the works of Tam et al [14].

The tests to determine the modulus of elasticity were made according to norm LNEC E

397 - “Concrete: determination of the modulus of elasticity in compression”. Specimens

are cylinders with 150 mm diameter and 300 mm height.

The results showed that the module of elasticity of RCA are lower than the one of RC

and the more so the lesser the compactness of the recycled aggregates, i.e. the greater

the percentage of adhered cement paste in the recycled aggregates, which has lower

stiffness than natural stone. This is aggravated for ceramic aggregates due to their much

lower bulk density.

The modulus of elasticity is affected to a small degree by the incorporation of recycled

aggregates up to a maximum percentage of 50% CCRA and 25% CMBRA; this de-

crease is due to the lower compactness of these aggregates as compared with NCA and

the higher deformability of the adherent cement paste; for simultaneous incorporation of

CCRA and CMBRA up to a maximum ratio of 25% and 12.5% respectively, a reduction

of 16.2% in the modulus of elasticity was registered, a value that confirms the potential

of both of these types of recycled aggregates for structural concrete.

The stiffness losses to the RC of 10% for a maximum incorporation of 50% CCRA and

of 15.8% for a maximum incorporation of 25% CMBRA showed that their mechanical

capacity is affected to a limited degree unlike it is sometimes stated.

4.2. Concrete water absorption tests

Concrete’s water absorption is one of its properties more directly related with its dura-

bility, a fundamental characteristic for the evaluation of the maintenance of the initial

12

characteristics of the material throughout the service life of the structure.

The water absorption may be evaluated by immersion tests, which measure the open

porosity of the material, or by capillarity tests, which measure the capillarity absorption

by the differential of pressures occurred between the pressure of the liquid on the sur-

face of the concrete and the pressure inside the capillaries of the material.

First, the results obtained for the immersion tests are presented, where10 specimens per

composition were analysed for the evaluation of this parameter in the experimental

campaign. The average results obtained from all the compositions versus the ratio of

substitution of NCA with recycled coarse aggregates are presented in Figure 3.

The results obtained show that for the coarse concrete recycled aggregates (CCRA) and

coarse mortar and bricks recycled aggregates (CMBRA), the water absorption increases

approximately linearly with the increase of the incorporation ratio of recycled material

in the mix.

In what concerns concrete obtained from the incorporation of CCRA, the results

demonstrate that, for a full substitution of natural aggregates (B100B mix), a maximum

water absorption of 17.6% is obtained, which is 37.1% higher than the value obtained

for the reference concrete (RC). From the 50% substitution ratio on it is perceptible that

a steady value is reached for the water absorption near 18%, somehow questioning the

idea stated before that there is a linear correlation between water absorption and re-

placement ratio.

For the concrete mixes obtained from CMBRA, the values obtained in the water absorp-

tion tests are naturally higher than for RCA’s concrete mixes, which is easily explained

by the higher porosity of the material ceramic and mortar. In the graph presented for this

type of concrete it is visible that there seems to be no slowing down in the increase of

the water absorption for higher incorporation ratios of recycled material.

13

For the simultaneous application of CCRA and CMBRA (two parts of the former for

each part of the latter) in concrete mixes, the water absorption graph versus replacement

ratio was also determined and is presented in Figure 4.

It can be seen that from the 50% overall replacement ratio on a steady value is reached

for the water absorption, as seen for the RCA mixes, a value of approximately 19%.

In terms of water absorption by capillarity, Figures 5 to 7 present the results obtained

(average results of the experimental campaign) for the various concrete mixes after 72

hours: RAC with CCRA, RAC with CMBRA, and RAC with CCRA and CMBRA.

In terms of concrete mixes obtained from CCRA (Figure 5), the results point to a trend

of progressive increase of the water absorption coefficient with the replacement ratio

(reaching a maximum of 16.6% increase for the 100% replacement ratio versus RC),

probably caused by an increase in the density and length of the capillaries within the

concrete matrix, namely within the mortar adherent to the original natural aggregates.

A similar trend is found for the concrete mixes obtained from CMBRA (Figure 6),

reaching a maximum increase value of 71.3% for the 50% replacement ratio versus RC,

where anomalous results occurred for the 12.5% replacement ratio (which are overly

high). Since a similar situation occurred for the water absorption by immersion test with

the same concrete mix (not shown in Figure 1), it is concluded that an undetected flaw

occurred during the production of this particular mix.

As for the simultaneous application of CCRA and CMBRA (Figure 7), a 33.3% increase

of the 72 hours water absorption coefficient was detected for the 25% CMBRA plus

50% CCRA replacement ratio versus the RC value.

4.3. Concrete carbonation penetration resistance tests

Six specimens per composition were analysed (cylindrical specimens with 100 mm di-

ameter and height of 40 mm) at 7, 28, 56 and 90 days. The average results obtained for

14

the 4 mixes analyzed in the experimental campaign are presented in Figure 8.

Observing these results, it is possible to notice that the carbonation depth of the refer-

ence concrete (RC) and the concrete mixes with recycled aggregates (RAC) starts to

diverge from the beginning and this difference is emphasized between the 7th and the

28th day of age. From then on the performance of the different concrete mixes more or

less maintains its relative difference to the RC (with some fluctuations for the

B12.5C25B and B50B mixes).

It can be stated that there is an increase of the carbonation depth, for the same age, when

recycled aggregates are incorporated in the concrete matrix. Basheer et al [15] refer that

the carbonation resistance is directly dependent from the permeability to gases and the

latter is directly related with porosity, which presents a linear growth with the increase

of the incorporation of recycled aggregates in the mix. From the results obtained here

(Table 5), even though it is not possible to quantify precisely the decrease in terms of

carbonation resistance due to the presence of the various types of recycled aggregates, it

can be stated that the difference is relatively small for the concrete mixes (and respec-

tive replacement ratios) tested.

4.4. Concrete chloride penetration resistance tests

The degradation evolution of concrete exposed to sea water is a phenomenon widely

studied by the scientific community. The main related problem concerns the corrosion

of steel in reinforced or prestressed concrete structures. This degradation rate is in-

creased if the aggressive agents easily penetrate the micro-structure of concrete. In sea

water several types of salts are present, with a predominance of sodium chloride, which

initiates the concrete degradation, with the aggravating factor of installing an electric

potential, through the presence of CL- ions, which accelerates the corrosion process.

There are various laboratory tests to determine the penetration resistance of chlorides:

15

some in real time (extremely slow), that point out the CL- ions concentration found,

where the results can be extrapolated for future ages; others, accelerated tests, which

determine migration coefficients or diffusion coefficients, where one can empirically

estimate the evolution of the chloride concentration inside the concrete.

The laboratory test performed in this case aimed at the determination of the chloride

migration coefficient from non-steady state migration experiments, according to the

Nordtest NT Build 492. The results are expressed in Table 6, for the different concrete

mixes with recycled aggregates.

An increase of the chloride penetration depth in the concrete mixes with recycled ag-

gregates is detected by comparison with the reference concrete (RC). This difference is

due to the higher permeability of the concrete paste adhered to the recycled aggregates.

The new cement and natural fine aggregates introduced in the mix are not expected to

affect the results, since the effective water / cement ratio and the slump of the modified

concrete mixes have been kept constant.

Researchers such as Coutinho [16] and Evangelista and de Brito [6] state that the ions

penetration is strongly dependent on the porosity of the concrete mixes. A close correla-

tion can be expressed between the chloride penetration resistance and the water absorp-

tion (specifically by immersion). Therefore, a similar curve is presented in Figure 9, for

the different types of recycled aggregates.

Analysing Figure 9, it can be concluded that there is no linear relationship between the

two properties under analysis that is independent of the type and nature of the recycled

aggregates. Nevertheless, a trend can be detected in the relationship between these two

properties depending on the type of recycled aggregate, i.e. the slope of this relationship

increases from concrete mixes with CCRA to those with CMBRA, while the simultane-

ous use of CCRA and CMBRA is an intermediate stage between these two limits.

16

The migration coefficients in a non-steady state migration, obtained for each type of

concrete mix, are expressed in Table 7. The maximum variation found corresponds to

the B25C mix (7.50 × 10-11 m2/s), with an increase of 18.8% compared with the refer-

ence concrete (6.31 × 10-11 m2/s). The minimum is obtained for the B50B mix (6.66 ×

10-11 m2/s), with an increase value of 5.6%, which reveals a promising durability charac-

teristic for concrete using recycled aggregates up to a maximum of 50% RCA incorpo-

ration in the mix, in the same line with the values presented by Limbachiya [2] of 6.0 ×

10-11 m2/s for a 50 MPa compressive strength concrete.

5. CONCLUSIONS

The previous research programs on industrially processed crushed concrete from con-

struction and demolition works proved that the production of high-grade aggregate for

the reuse in low strength recycled concrete is possible. Still, few research works have

been made up till now for structural concrete with recycled aggregates, guaranteeing a

valid comparison with a reference concrete, as well as a constant effective water / ce-

ment ratio and slump.

From the results presented in this paper, the following are emphasized:

- The water absorption by immersion does exhibit a linear correlation with the in-

corporation ratio of recycled aggregate, for concrete with CCRA, CMBRA and the mix

of these two types. For CCRA and the mix of CCRA and CMBRA it is perceptible that

from a replacement ratio higher than 50% on there is almost no increase of the water

absorption. On the contrary, for concrete with CMBRA this characteristic seems to tend

to increase even after a replacement ratio of 50%;

- The water absorption by capillarity clearly point to an increase of the corre-

sponding coefficient with the replacement ration independently of the type of recycled

17

aggregates. However, the relative results (modified concrete mixes versus RC) obtained

after 72 hours are acceptable for concrete with CCRA(increase of the capillarity coeffi-

cient by less than 10%) and with CCRA plus CMBRA (33% increase) (within the limits

tested) and much worse for concrete with CMBRA (120% increase in the coefficient);

- The carbonation depth for concrete mixes with recycled aggregates does not ex-

hibit significant differences from the one observed for RC at the age of 90 days. For a

50% replacement ratio for CCRA, an increase of 10% was obtained. For a 25% re-

placement ratio for CMBRA, a 9% growth of carbonation deepness was obtained. These

results reveals that, up to these replacement ratios, very good concrete mixes can be

obtained in terms of their resistance to this phenomenon, as compared to the value ob-

tained by the Building Contractors Society of Japan [8], i.e. 65% higher carbonation

depth in a RAC than in the corresponding RC;

- Clearly the mixes with recycled aggregates showed a somewhat higher chloride

intrusion than the reference concrete. However, the highest value was reached for the

mix with 25% of coarse recycled ceramic and mortar aggregates. In all cases, for the

incorporation boundaries studied, the loss of resistance to the penetration of chlorides

was limited to about 6% for the concrete mixes with CCRA and 20% for concrete mixes

with CMBRA or a blend of CCRA and CMBRA.

Therefore, it is shown that, from a durability point of view, it is possible to make struc-

tural concrete with recycled aggregates, not by totally replacing the fraction 4-32 mm of

the natural aggregates, but only by the partial substitution of the coarse fraction, up to

the incorporation boundaries determined in this work. From the results from other re-

searchers, namely Evangelista and de Brito [17], and from a mechanical behaviour point

of view, it was also proved that it is possible to replace part of the fraction < 4 mm

(sand) with crushed concrete fines but again total replacement is not recommended.

18

‘Sustainable concrete construction’ is a key objective for the modern world society, and

demands many diverse approaches. Much progress has been made, particularly in de-

veloping the understanding of the issues involved. Areas where future research can

make particularly important contributions to the sustainable use of concrete are:

• Adaptable buildings;

• Robust tools for service life design and whole life costing;

• Design for deconstruction;

• Low energy cements;

• Innovative use of concrete to minimise energy in use.

6. ACKNOWLEDGEMENTS

The authors wish to thank Cimpor, S.A for providing the materials used as natural and

recycled aggregates in this work. The authors also thankfully acknowledge the support

of the ICIST Research Institute from IST, Technical University of Lisbon and of FCT

(Foundation for Science and Technology).

7. REFERENCES

[1] Barra M, Vásquez E (1998) Properties of concrete with recycled aggregates: influ-

ence of properties of the aggregates and their interpretation. In Sustainable Construc-

tion: Use of Recycled Concrete Aggregates, Thomas Telford, London, pp. 19-30.

[2] Limbachiya M, Leelawat T, Dhir R (2000) Use of recycled concrete aggregate in

high-strength concrete. Materials and Structures 33: 574-580.

[3] Gomes M (2007) Structural concrete with incorporation of concrete, ceramic and

mortar recycled aggregates. (in Portuguese) Masters in Construction Dissertation, IST,

Technical University of Lisbon, Lisbon, Portugal.

19

[4] Santos R, Branco FA, de Brito J (2002) Use of coarse recycled concrete aggregates

in the production of new concrete. (in Portuguese) Proceedings of Congress Structures

2002, Lisbon, Portugal, pp. 227-236.

[5] Correia JR, de Brito J, Pereira AS (2006) Effects on concrete durability of using

recycled ceramic aggregates. Materials and Structures 39(2): 151-158.

[6] Evangelista L, de Brito J (2004) Incorporation of fine recycled concrete aggregates

in the production of new concretes. (in Portuguese) Proceedings of Congress Construc-

tion 2004, Porto, Portugal, pp. 21-26.

[7] Matias D, de Brito J (2005) Influence of plasticizers on the performance of concrete

produced with concrete recycled aggregates. (In Portuguese) ICIST (IST Civil Depart-

ment Research Institute) Report DTC 03/05, Lisbon, Portugal.

[8] Building Contractors Society of Japan (1978) Study on recycled aggregate and recy-

cled aggregate concrete. Concrete Journal 16(7): 18-31.

[9] Hansen TC (1986) The second RILEM state of the art report on recycled aggregates

and recycled aggregate concrete. Materials and Structures 111(1): 201-246.

[10] Park C, Sim J (2006) Fundamental properties of concrete using recycled concrete

aggregate produced through advanced recycling progress. Transportation Research

Board, #06-0810, 13 p.

[11] ACI 555R-01 (2004) Removal and reuse of hardened concrete. ACI Committee

555R-04 Report, American Concrete Institute, Michigan, 26 p.

[12] Kou S, Poon CS (2006) Compressive strength, pore size distribution and chloride-

ion penetration of recycled aggregate concrete incorporating class-F fly ash, Journal of

Wuhan University of Technology 21(4): 130-136.

[13] Leite M (2001) Evaluation of the mechanical properties of concrete made with re-

cycled aggregates from construction and demolition waste. (in Portuguese) PhD Thesis

20

in Civil Engineering, Federal University of Rio Grande do Sul, Porto Alegre, 270 p.

[14] Tam WYV, Gao XF, Tam CM (2005) Micro-structural analysis of recycled aggre-

gate concrete produced from two-stage mixing approach, Cement and Concrete Re-

search 35(6): 1195-1203.

[15] Basheer L, Kropp J, Cleland DJ (2001) Assessment of the durability of concrete

from its permeation properties - a review. Construction and Building Materials 15: 93-

103.

[16] Coutinho AS (1988) Production and properties of concrete, Volume I. (in Portu-

guese) Portuguese National Laboratory of Civil Engineering (LNEC), Lisbon.

[17] Evangelista L, de Brito J (2007) Mechanical behaviour of concrete made with fine

recycled concrete aggregates. Cement and Concrete Composites 29(5): 397-401.

8. STANDARDS USED IN THE EXPERIMENTAL WORK

EN 12390-3, Committee European of Normalization, “Concretes, cement and concrete

technology, compressive strength, test specimens, failure (mechanical), compression

testing, mechanical testing”. Brussels, 2001.

LNEC E391, Portuguese National Laboratory of Civil Engineering standard, “Concrete:

determination of carbonation resistance”. (in Portuguese) Lisbon, 1993.

LNEC E393, Portuguese National Laboratory of Civil Engineering standard, “Concrete:

water absorption by capillarity”. (in Portuguese) Lisbon, 1993.

LNEC E394, Portuguese National Laboratory of Civil Engineering standard, “Concrete:

water absorption by immersion”. (in Portuguese) Lisbon, 1993.

LNEC E397, Portuguese National Laboratory of Civil Engineering standard, “Concrete:

determination of the modulus of elasticity in compression”. (in Portuguese) Lisbon,

1993.

21

NT Build 492, Nordtest method, “Concrete, mortar and cement-based repair materials:

chloride migration coefficient from non-steady-state migration experiments”, 1999.

22

FIGURES CAPTIONS

Figure 1 - Carbonation chamber (left) and measurement of the carbonation depth (right)

Figure 2 - Specimens positioned inside the diffusion cells (left) and measurement of the

chloride penetration depth (right)

Figure 3 - Water absorption by immersion versus replacement ratio (average results of

10 specimens) for concrete mixes with CCRA (blue) and CMBRA (red)

Figure 4 - Water absorption by immersion versus replacement ratio (average results of

10 specimens) for concrete mixes with the simultaneous use of CCRA and CMBRA

Figure 5 - Water absorption by capillarity versus replacement ratio (average results of 4

specimens) for concrete mixes with CCRA

Figure 6 - Water absorption by capillarity versus replacement ratio (average results of 4

specimens) for concrete mixes with CMBRA

Figure 7 - Water absorption by capillarity versus replacement ratio (average results of 4

specimens) for concrete mixes with the simultaneous use of CCRA and CMBRA

Figure 8 - Carbonation penetration depth evolution in the first 90 days (average results

of 6 specimens treated with a hyperbolic regression)

Figure 9 - Chloride migration coefficient (average results of 3 specimens) versus water

absorption by immersion (average results of 10 specimens)

23

Figure 1 - Carbonation chamber (left) and measurement of the carbonation penetration

depth (right)

Figure 2 - Specimens positioned inside the diffusion cells (left) and measurement of the

chloride penetration depth (right)

24

0.0 0.2 0.4 0.6 0.8 1.010

12

14

16

18

20

CCRA

CMBRA

Y= 0,0005x+0,1346R2=0,81

Y= 0,0013x+0,1272R2=0,95

Replacement ratio [%]

% W

ater

Abs

orpt

ion

Figure 3 - Water absorption by immersion versus replacement ratio (average results of

10 specimens) for concrete mixes with CCRA and CMBRA

0 20 40 60 8010

12

14

16

18

20

22

Y= 0,007x+0,1392R2=0,82

Replacement ratio [%]

% W

ater

Abs

orpt

ion

Figure 4 - Water absorption by immersion versus replacement ratio (average results of

10 specimens) for concrete mixes with the simultaneous use of CCRA and CMBRA

25

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0 12 24 36 48 60 72

Time [h]

Kc (

g/m

2 xh0.

5 )

RCB100BB50BB25BB12.5B

Figure 5 - Water absorption by capillarity versus replacement ratio (average results of 4

specimens) for concrete mixes with CCRA

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

0 12 24 36 48 60 72

Time [h]

Kc (g

/m2 xh

0.5 )

RCB50CB25CB12.5CB6.25C

Figure 6 - Water absorption by capillarity versus replacement ratio (average results of 4

specimens) for concrete mixes with CMBRA

26

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0 12 24 36 48 60 72

Time [h]

Kc (

g/m

2 xh0.

5 )

RCB6.25C12.5BB12.5C25BB25C50B

Figure 7 - Water absorption by capillarity versus replacement ratio (average results of 4

specimens) for concrete mixes with the simultaneous use of CCRA and CMBRA

0

1

2

3

4

5

6

7

8

9

0 20 40 60 80 100

Time (days)

Car

bona

tion

dept

h(m

m)

RCB50BB25CB12.5C25B

Figure 8 - Carbonation penetration depth evolution in the first 90 days (average results

of 6 specimens treated with a hyperbolic regression)

27

12.9%

16.9%

12.9%

15.6%

12.9%

16.3%

4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

8.0

0.10 0.12 0.14 0.16 0.18 0.20

Water absorption by immersion [%]l

Chl

orid

e m

igra

tion

coef

ficie

nt 1

0E-1

2 (m2 /s

)CCRA

CMBRA

CCRA andCMBRA

Figure 9 - Chloride migration coefficient (average results of 3 specimens) versus water

absorption by immersion (average results of 10 specimens)

28

TABLES CAPTIONS

Table 1 - Composition of the mixes with recycled concrete aggregates (CCRA) (/m3)

Table 2 - Composition of the mixes with recycled bricks and mortar aggregates

(CMBRA) (/m3)

Table 3 - Composition of the mixes with concrete, bricks and mortar recycled aggre-

gates (CCRA and CMBRA) (/m3)

Table 4 - Carbonation depth for the different mixes of concrete with recycled aggregates

at the age of 90 days

Table 5- Chloride deepness for the different mixes of concrete with recycled aggregates

Table 6 - Chloride migration coefficients obtained for the various concrete mixes of

concrete with recycled aggregates

29

Table 1 - Composition of the mixes with recycled concrete aggregates (CCRA) (/m3)

RC B12.5B B25B B50B B100B Replacement ratio (%) 0 12.5 25 50 100

Cement CEM II 42,5 R (kg) 446 446 446 446 446 Water (l) 192 194.5 197.0 202.1 212.3 w/c ratio 0.43 0.44 0.44 0.45 0.48

Effective w/c ratio 0.43 0.43 0.43 0.43 0.43 Fine aggregates (natural sand) (kg) 426 426 426 426 426

Natural coarse aggregates (kg) 1111.8 972.8 833.9 555.9 0 Recycled coarse aggregates (kg) 0 133.4 266.8 533.6 1067.3

Table 2 - Composition of the mixes with recycled bricks and mortar aggregates

(CMBRA) (/m3)

RC B6.25C B12.5C B25C B50C Replacement ratio (%) 0 6.25 12.5 25 50

Cement CEM II 42,5 R (kg) 446 446 446 446 446 Water (l) 192 197.2 202.4 212.8 233.6 w/c ratio 0.43 0.44 0.45 0.48 0.52

Effective w/c ratio 0.43 0.43 0.43 0.43 0.43 Fine aggregates (natural sand) (kg) 426 426 426 426 426

Natural coarse aggregates (kg) 1111.8 1042.3 972.8 833.9 555.9 Recycled coarse aggregates (kg) 0 58.9 117.7 235.4 470.9

Table 3 - Composition of the mixes with concrete, bricks and mortar recycled aggre-

gates (CCRA and CMBRA) (/m3)

RC B6.25C12.5B B12.5C25B B25C50B Replacement ratio (%) 0 25 50 100

Cement CEM II 42,5 R (kg) 446 446 446 446 Water (l) 192 199.7 207.4 222.9 w/c ratio 0.43 0.45 0.47 0.50

Effective w/c ratio 0.43 0.43 0.43 0.43 Fine aggregates (natural sand) (kg) 426 426 426 426

Natural coarse aggregates (kg) 1111.8 903.3 694.9 277.9 Recycled coarse aggregates (kg) 0 192.3 384.5 769

Table 4 - Carbonation depth for the different mixes of concrete with recycled aggregates

at the age of 90 days

Concrete mix Specimen 1 Specimen 2 Specimen 3 Specimen 4 Specimen 5 Specimen 6 Average ∆ (%) RC 7.50 7.50 8.00 6.00 6.00 6.00 5.13 -

B50B 7.50 7.50 6.50 6.50 9.00 8.00 5.63 10 B25C 9.00 8.00 7.50 7.00 6.50 6.50 5.56 9

B12.5C25B 7.00 12.00 8.50 8.35 8.70 8.00 6.57 28

30

Table 5- Chloride deepness for the different mixes of concrete with recycled aggregates

Concrete Specimen 1 Specimen 2 Specimen 3

Average 1st measure-ment

2nd meas-urement

1st measure-ment

2nd meas-urement

1st measure-ment

2nd meas-urement

RC 13.22 11.79 14.71 10.29 - - 12.50 B50B 12.29 13.29 14.29 11.71 14.36 13.36 13.21 B25C 22.51 22.32 26.58 25.80 - - 24.30

B12.5C25B 14.44 13.56 15.57 15.21 12.58 14.98 14.39

Table 6 - Chloride migration coefficients obtained for the various concrete mixes of

concrete with recycled aggregates

Dnssm (m2/s) ∆ (%)

RC 6.31 × 10-12 - B50B 6.66 × 10-12 5.6 B25C 7.50 × 10-12 18.8

B12.5C25B 7.26 × 10-12 15.1

31