Using recycled concrete aggregates in precast concrete hollow blocks

Abstract

Among the construction waste that could be recycled, we can mention the aggregates resulting from crushed concrete. While the acquired knowledge about the use of recycled aggregates in new concrete mixes is fairly large, the use of such aggregates in the production of concrete blocks is very limited. This research aims to study the influence of the use of recycled aggregates in precast concrete hollow blocks on their compressive strength. Tests were carried out to determine the rate of recycled aggregates content to be used in the manufacture of concrete blocks in order to obtain blocks having suitable compressive strength. Tests were executed on several series of blocks whose composition includes recycled aggregates and on one series of reference blocks whose composition consisting exclusively of natural aggregates. Tests results have provided the maximum percentage of recycled aggregates that can be included in new concrete block mixes without affecting blocks compressive strength. Tests have shown that the use of recycled aggregates in concrete blocks could give a compressive strength similar to that of blocks manufactured without any recycled aggregates. It has been shown also that using recycled aggregates in the manufacture of concrete blocks without any natural aggregates is not economical at all because of the need to add a relatively high quantity of cement necessary to obtain the required compressive strength.

Full text

388
•
DOI
10.1002/mawe.201200970
Mat.-wiss.
u.
Werkstofftech.
2012, 43,
No
. 5
Using recycled concrete aggregates in precast concrete
hollow
blocks
Ober die Vewendung von wiederaufbereiteten Beton-Zuschlagstoffen
in
vorgeformten Beton-Hohlblocken
P.
Mata
~.
R.
El Dalati2
Among
the
construction
waste
that
could be recycled,
we
can
ment
ion
the
aggregates
resulting
fr
om
crushed
concrete
. While
the
acquired
knowledge
about
the
use
of
recycled
aggregates
in
new
concrete
mixes is fairly l
arge
,
the
use
of
such
aggregates
in
the
production
of
concrete
blocks is very limited. This
research
ai
ms
to
study
the
influence
of
the
u
se
of
recycled
aggr
egates
in p
recast
con
crete
ho
ll
ow
blocks on
their
compre
ssive
stre
n
gth
.
Te
s
ts
were
carried
out
to
determine
the
rate
of
recycled
aggregates
content
to
be
used in
the
manufacture
of
co
ncrete
blocks in
order
to
obtain
blocks having suitable compressive
strength
. Tests
were
executed
on
several
series
of
blocks w
hose
composition
includes recycled
agg
regates
and
on on
e
series
of
reference blocks
whose
composition
consisted
exclusively
of
natural
aggregates.
Tests
results
have provided t he maximum
pe
r
centage
of
recycled
aggregates
that
can
be
included in
new
concrete
bl
ock
mixes
without
affecting blocks compressive
strength
. Tests have
shown
that
the
use
of
recycled
aggregates
in
concrete
blocks could give a compressive
strength
similar
to
t
hat
of
blocks
manufactured
with
out
any
recycled
agg
r
egates
. It
has
been
shown
also
that
usi
ng
recycled
aggregates
in
the
manufa
ct
ure
of
conc
r
ete
blocks
without
any
natural
aggregates
is
not
econom
ical
at
all
because
of
the
need
to
add
a relatively high
quantity
of
cement
necessary
to
obtain
the
required
compressive
strengt
h.
Keywords:
recycl
ed aggregates I precast concrete hollow blocks I compressive strength I workability I
superplasticizer
Schliisselworter: wiederaufbereitete Zuschlagstoffe I vorgeformte Beton-Hohlblocke I Druckfestigkeit I
Umformbarkeit I F
lie
Bmittel
1 Introduction
While the acquired knowledge about the use
of
recycled aggre·
gates in new concrete mixes is fairly large (1-3),
the
us
e
of
such
aggregates in
the
production
of
concrete blocks is very limited
(4
,
5)
. This research aims to study
the
influence
of
the
use
of
recycled aggregates
in
precast concrete hollow blocks on their
compressive strength.
Concrete blocks containing recycled aggregates have a lower
strength than blocks with natural aggregates. This is
du
e to the
weaker
den
sity
of
recycled aggregates in comparison to natural
aggregates [
4)
.
Our
previous researches
[5)
showed
that
the use
of
recycled aggregates with a 10%
cem
ent
addition compared to
normally used cement quantity could allow the production
of
-
1
Lebanese
University,
Faculty
of
Engineering
.
Roumieh,
Ma
in
Road,
Lebanon
2
Leb
anese
University,
Faculty
of
Engineering,
Tripoli,
AI
Kobba,
Leba-
non
Corresponding author:
Pierre
Matar,
Lebanese
Univ
ersity, Faculty of
Engineering,
Branch
2,
Roum
ieh,
Main
Road,
Lebanon
E-mail
: pmatar@ul.edu.
lb
© 2012
WILE
Y-vCH
Verlag
GmbH
&
Co.
KGaA,
Weinheim
concrete blocks having
com
pressive strengths similar to those
of
concrete blocks with natural aggregates. Moreover, to assure the
workability
of
concrete which has been affected
due
to
the
addi·
tion
of
cement
and
the absorption
of
recycled aggregates, water
addition is needed. Since
the
principal responsible
of
the con-
crete deficiency is the addition
of
water, we aimed to substitute
in
some
mixes
the
addition
of
water by adding water-reducer super-
plasticizer.
This research represents tests carried out
on
blocks whose
composition includes natural
and
different percentage
of
recycled aggregates, as well as
on
blocks whose composition con-
sisted exclusively
of
natural aggregates. It shows
the
effect
of
the
per
centage
of
used recycled aggregates
on
the
compressive
strength
of
blocks, as well as the addition
of
cement
and
water
and
the addition
of
cement
and
superplasticizer.
The
objective
of
this research is to study
the
influence
of
recycled aggregates used in new concrete mixes for producing
precast concrete hollow blocks. This study aims to det
ermine
the
percentage
of
recycled aggregates to be used
in
the
manufacture
of
concrete blocks
in
order to obtain blocks having suitable phys·
ical
and
mechanical properties, i.e. workability
and
compressi
ve
strength.
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.wiley-vch.delhomelmuw

Mat.-wiss. u. Werkstofftech. 2012, 43, No.5 Using recycled concrete aggregates in precast concrete hollow blocks
Table 1. Concrete mixes
of
blocks
T
abelle
1. Zusammensetzung
der
Betonblticke
Constituents
Unit
1 2 3 4 5 6 7
RASO
RASO+C+W
RASO+C+SP
RA30 RA30+C+W RA30+C+SP NA
Cement
Addition
%(1)
-
10% 10%
-
10% 10%
-
NAQ-6mm
%(2)
100%
100% 100% 100% 100% 100% 100%
NA6-12
mm
%(
3)
50% 50%
50%
70% 70% 70%
100%
RA6-
12
mm
%
(3)
SO%
50%
SO%
30% 30% 30%
-
Water
Addition
%(4)
-
10%
- -
10%
--
Superplasticizer %(
S)
--
0.25%
--
0.25%
-
Table 2. Concrete mixes
of
blocks (by
weight
and volume)
Tabe
ll
e 2. Zusammensetzung
der
Betonblticke (Gewicht und Volumen)
Constituents
Unit
1 2 3 4 5 6 7
RA50
RA50+C+W RA50+C+5P
RA30
RA30+C+W RA30+C+5P NA
Cement kg/m3
144 158 158
144
158 158 144
NAQ-6mm
kg/m3
1435 1435 1435 1435
1
435
1435 1435
NA6-12
mm
kg/m3
359 359 359
503 503 503
718
RA6-12
mm
kg/m3
359 359
359
215 215 215
-
Water
l/m
3
144 158
-
144
158 -
144
a b c d e
Figu
re
1.
Production
of
precast concrete hollow blocks, a - mold;
b-
preparation
of
mix; c - block molding; d - block demolding;
e-
manufac-
tured blocks.
Bild 1. Herstellung
der
vorgeformten Beton-Hohlblticke, a - Form; b - Herstellung
der
Mischung; c - FUIIung
der
Form; d - Entformung; e -
hergestellte Blticke.
2 Test description
This research was carried out at the Laboratory
of
Civil
Engineer·
ing at the Lebanese University, except the compression tests
which were done at the Laboratory
of
Civil
Engineering at Notre
Dame University.
Six
series
of
three concrete blocks each were
prepared using natural and recycled aggregates,
and
one series
of
reference blocks without any recycled aggregates,
Tables
1
and
2. The used recycled aggregates were obtained from crushing
demolished structural concrete. The composition
of
concrete
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WILEY-VCH
Verlag GmbH &
Co.
KGaA,
Weinheim
required to produce blocks containing only natural aggregates
(mix
7)
was established based
on
the experience
and
tradition
of
local industry. The results presented
in
this paper correspond to
the mean value
of
3 specimens
of
hollow blocks
of
40
em
length x 20
em
height x
15
em
thickness. The different stages
of
blocks manufacture and the testing ofblocks,
Fig.
1,
Fig.
2.
Previous tests have shown that recycled aggregates absorb a
higher amount
of
water
than
natural aggregates
(4,
5]
. The water
demand is due to the porosity and angularity
of
recycled aggre-
gates. With the aim to avoid affecting concrete characteristics
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389

390
J
\
P.
Matar, R.
El
Dalati
Mat.
-wiss.
u.
Werkstofftech. 2012,
43
,
No
. 5
a b c d
Figure
2.
Testing of precast concrete hollow blocks,
a,
b,
c- preparation of blocks for testing;
d-
block during compression test.
Bild
2.
Untersuchung der vorgeformten Beton-Hohlblocke,
a,
b,
c-
Vorbereitung der
Blocke
zum Testen;
d-
Block
wah rend Druckversuch.
Ta
bl
e 3.
Density
and compressive strength of concrete b
locks
Tabe
ll
e
3.
Oichte u
nd
Druckfestigkeit
de
r Betonblocke
Constituents Unit 1 2
RA50
RA50+C+W
Density kg/m' 2259
2218
Strength
at
28 days
MPa
4.47 6.45
Standard Deviation
MPa
0.08 0.25
due
to
the
increase
of
water content,
the
water addition
in
some
mixes
was
substituted by
using
wat
er-re
ducer
superplasticizer.
All blocks
specimens
were
immersed
in
water
maintain
ed
at
a
temperature
of20
± 2 °C for 72
h.
The
air
humidity
was between
65%
and
75%.
The
compression tests were carried
out
after 7
days
from
the
date
of
manufacturing
using
a PERRIER compres-
sion
machine
with
a loading capacity
of
1500 kN
and
equipped
with
measurement
module
705.
The
load was applied
with
a con-
stant
speed
of
5 kNfs.
The
test
was considered complete
when
the
specimen
was
broken.
The
recorded
parameter
given by
the
testing
machine
dial pointer
was
the
concrete blocks compressive
strength.
The
standard
deviation values for all tests were
ranged
between 0.08
and
0.45 MPa.
3 Test results
Based
on
blocks tests,
the
density
and
the
28-day compressive
strength
of
each
block were
determined.
The
test results
are
pre-
sented
in
Table
3
and
Fig.
3 for each concrete mix.
3.1 Effect
of
recycled aggrega
tes
percentage
• Mixes
without
a
ny
addition
of
cement,
water
or
superplastici-
zer
(mixes 1
and
4):
Blocks
containing
30% recycled aggregates (RA30)
show
2.5% increase
of
strength
comparing
with
blocks containing
50% recycled aggregat
es
(RA50).
Comparing
the
test
results
for blocks with
natural
aggregates (NA),
the
strength
is
not
affected
at
all by
the
recycled aggregates;
it
even increases
in
comparison
with
the
strength
of
blocks
which
does
not
con-
tain
any
recycled aggregates.
This
increase
amounts
to
8.5%
for RA30
and
5.9% for RA50.
© 2012
WILEY-VCH
Ve
rlag
GmbH
&
Co.
KGaA,
Weinheim
3 4 5 6
RA50+C+SP
RA30
RA30+C+W
RA30+C+SP
2289
2269
2231
2366
6.27 4.58 6.62 6.75
0.45 0.13 0.26 0.17
•
CompressiveStre
..
th.
MPA
6.75
Figure 3. Compressive strength of concrete blocks.
B
il
d 3. Oruckfestigkeit der
Beton
-B
iocke.
7
NA
2352
4.15
0.18
• Mixes
with
addition
of
cement
and
water (mixes 2
and
5):
Blocks containing
300.16
recycled aggregates (RA30+C+W)
show
2.6% increase
of
strength
comparing
with
blocks con-
taining
50% recycled aggregates (RA50+C+W).
• Mixes
with
addition
of
cement
and
superplasticizer (mixes 3
and6):
Blocks co
ntaini
ng
30% recycled aggregates (RA30+C+SP)
show
7.7% increase
of
strength
comparing
with
blocks con-
taining
50% recycled aggregates (RA50+C+SP).
3.2 Effect
of
cement
and
water
addition
When
evaluating
the
effect
of10%
water
addition
in
mixes 2
and
5
comparing
with
mixes 1
and
4,
we
should
take
into
account
the
10
%
cement
addition
in
mixes 2
and
5. As stated
in
paragraph 1
above,
this
10%
cement
addition (compared
to
normally
used
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Mat.-wiss.
u.
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201
2, 43,
No.5
cement quantity) is necessary for
the
production
of
concrete
blocks with suitable compressive strength. Furthermore,
the
water addition is needed to maintain the workability
of
concrete
which will be affected
due
to addition
of
cement
and
to absorp-
tion
of
recycled aggregates.
• Mixes with 50%
RA
(mixes 1
and
2)
:
An
increase
of
44%
in
the
strength
of
blocks containing 50%
recycled aggregates (RA50+C+
W)
is observed when water is
added: comparing with blocks without any addition.
• Mixes with 30%
RA
(mixes 4
and
5):
The
percentage increase
of
strength
of
blocks containing 30%
recycled aggregates (RA30+C+W) is 45% when water is ad-
ded, comparing with blocks without any addition.
3.3 Effect
of
superplas
ticiz
er
When
evaluating
the
effect
of
superplastidzer comparing with
water addition, we
do
not
have to take into account
the
added
quantity
of
cement since such quantity is added with water too.
Test results show
that
the effect
of
superplasticizer is more
considerable for blocks containing 30% recycled aggregates
(RA30+C+SP) than for blocks containing 50% recycled aggre-
gates (RA50+C+SP).
The
positive effect
of
superplasticizer is
revealed by the 7.7% increase
of
strength as stated above.
• Mixes with 50%
RA
(mixes 1, 2
and
3)
:
An
increase
of
44%
in
the
strength
of
blocks containing 50%
recycled aggregates (RA50+C+
W)
is obtained when water is
added, while this increase is
of
40%
when
superplasticizer is
added (RA50+C+SP).
The
use
of
superplasticizer did
not
show any effect
on
the
blocks compressive strength.
• Mixes with 30%
RA
(mixes
4,
5
and
6):
The percentage increase in
the
strength
of
blocks containing
30% recycled aggregates (RA30+C+W) is 45% when water is
added, while
it
is 47%
when
superplasticizer is added
(RA30+C+SP).
The
superplasticizer addition provoked
minor
upgrading
of
blo~ks
compressive strength comparing with
water addition.
4 Conclusions and recommendations
The
obtained test results show that
the
compressive strength
of
the
concrete blocks manufactured with recycled aggregates
depends on:
e
the
percentage
of
recycled aggregates;
• the cement addition;
e the water addition;
e
the
use
of
superplasticizer.
For
the
manufacture
of
concrete hollow blocks containing
recycled aggregates, we can give the following conclusions
and
recommendations:
e Blocks containing 30% recycled aggregates have compressive
strength bigger than blocks containing 50% recycled aggrega-
© 2012
WILEY·VCH
Verlag
GmbH
&
Co.
KGaA,
Weinheim
Using
recycled
concrete aggregates
in
precast concrete
hollow
blocks
tes.
This
increase
of
strength is
the
same
for blocks without
any addition
of
cement, water
or
superplasticizer comparing
to
blocks with addition
of
cement
and
water (2.5 to 2.6%).
This increase is more considerable when comparing to blocks
with addition
of
cement
and
superplastidzer (7.7%).
e
We
can
use
up
to 50% recycled aggregates without affecting
blocks compressive strength as
long
as a small
cement
quan-
tity is added.
e
The
increase
of
concrete compressive strength
of
blocks with
addition
of
cement
and
water is satisfactory for blocks con-
taining 30% recycled aggregates (increase
of
45%)
and
for
blocks containing 50% recycled aggregates (increase
of
44%).
e
The
advantage
of
the
substitution
of
superplasticizer
use
for
water addition is somewhat remarkable for blocks containing
30% recycled aggregates.
Notes:
NA:
natural aggregates
RA:
recycled aggregates
C:
cement
W: water
SP: superplasticizer
t
tl:
percentage
of
cement addition comparing to
normal
quan-
tity (used
in
mixes 1, 4
and
7)
1
2l: percentage
of
0-6
mm
aggregates
tl
l: percentage of6-12
mm
aggregates
t
•l:
percentage
of
water addition compared to
normal
quantity
(used
in
mixes
1,
4
and
7)
t>l
: percentage
of
cement weight
5 References
[1]
T.C. Hansen, Recycling
of
demolished concrete
and
masonry,
RILEM
Rep., London,
UK,
1992.
[2]
J.D.
Merlet,
P.
Pimienta, Mechanical
and
physico-chemical
properties
of
concrete produced with coarse
and
fine
recycled concrete aggregates, presented at
the
Third
Interna-
tional
RILEM
Symposium
on
Demolition
and
Reuse
of
Con-
crete
and
Masonry,
London,
UK
, October
24-27,1993,
343
-
353.
[3]
R.
El
Dalati, P. Matar,
Materia!wiss.
Werkstofftech.
(Materials
Science
and
Engineering
Technology)
2011,
42,
398.
[4]
P.
Pimienta,
P.
Delmotte,
R.
Gregori, Utilisation des granu-
lats recycles
pour
la fabrication
de
blocs de construction,
CSTB
Report
drafted
on
request
of
Architecture
and
Construc-
tion
Plan,
1995, 30 p.
[
5]
P.
Matar,
R.
El
Dalati,
Phys.
Procedia,
2011, 21. 180, http:/ I
www.sciencedirekt.comfsciencefJoumalf18753892.
Received
in
final form: January
12th
2012
T970
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391