Post on 25-Feb-2023
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.
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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).
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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.
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‘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