1 Influence of Amount of Recycled Coarse Aggregates and Production Process
1 Influence of Amount of Recycled Coarse Aggregates and Production Process
1 Influence of Amount of Recycled Coarse Aggregates and Production Process
Abstract
In this study recycled coarse aggregates obtained by crushed concrete were used for concrete production. Four different recycled aggregate
concretes were produced; made with 0%, 25%, 50% and 100% of recycled coarse aggregates, respectively. The mix proportions of the four
concretes were designed in order to achieve the same compressive strengths. Recycled aggregates were used in wet condition, but not saturated,
to control their fresh concrete properties, effective w/c ratio and lower strength variability. The necessity to produce recycled aggregate concrete
with lowmedium compressive strength was verified due to the requirement of the volume of cement. The influence of the order of materials
used in concrete production (made with recycled aggregates) with respect to improving its splitting tensile strength was analysed. The lower
modulus of
elasticity of recycled coarse aggregate concretes with respect to conventional concretes was measured verifying the numeral models proposed by
several researchers.
2007 Elsevier Ltd. All rights reserved.
Keywords: Mixture proportioning; Workability; Mechanical properties; Aggregates; Recycled aggregates; Recycled aggregate concrete
1. Introduction
To obtain good quality concrete using recycled aggregate it
is necessary to follow the minimum requirements defined by
the BCSJ [1], RILEM [2], DIN 4226.100 [3], and
prEN
13242:2002 [4]. Acceptable properties of aggregates are an
elemental base for concrete quality, however adequate mix
proportions and concrete production methods are highly
important in concrete quality too. Recycled aggregates are
composed of original aggregates and adhered mortar. The
physical properties of recycled aggregates depend on both
adhered mortar quality and the amount of adhered mortar. The
adhered mortar is a porous material, its porosity depends upon
the w/c ratio of the recycled concrete employed [5]. The
crushing procedure and the dimension of the recycled
aggregate
have an influence on the amount of adhered mortar [69]. The
density and absorption capacity of recycled aggregates are
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workability of the mentioned concretes. This depends on
The high percentage of clean aggregates (without adhered
which type of crusher is used [19].
mortar) suggests that the original concretes (from which the
With respect to compressive strength, concrete made with
recycled aggregates were obtained) had low strengths. The
100% of recycled coarse aggregate with lower w/c ratio than
quantity of adhered mortar was approximately 20% for fraction
the conventional concrete can have a larger compression
10/25 mm and approximately 40% to 4/10 mm fraction. The
strength. When the w/c ratio is the same the compression
density, absorption and shape index of raw and recycled
3
strength of concrete made with 100% of recycled aggregate is
aggregates were respectively, density 2.67 kg/dm and 2.43
3
lower than that on conventional concrete [20].
kg/ dm , absorption 0.886% and 4.445%, and shape index 25%
In case of recycled aggregate concrete it will be necessary
and
to add more cement in concrete made with 100% of recycled
28% determined in accordance with EN specifications.
aggregate in order to achieve the same workability and
CEM I 52.5R, a high quality, high strength rapid-hardening
compression strength as conventional concrete. The employPortland cement was used in all four mixes.
ment of different qualities of recycled aggregate in concrete
In order to achieve the same workability in all four different
production brings about an increase in the compressive
concretes, Glenium C313, superplastificizer was used.
strength variation coefficient [21]. Any variation in concrete
production or in the properties of the constituents used
2.2. Experimental details
produces a variation of strength in the resultant concrete.
This paper examines the difficulty of obtaining the same
2.2.1. Dosage system and workability of fresh concrete
high compressive strength in concrete with high percentages
The Bolomey dosage method [23,24] was used in the
of recycled aggregates and conventional concrete. Four
mixing of both concretes, the dosage calculations began
different dosages were employed in the production of the
with the cement quantity and w/c ratio required. The
four mixes. The first concrete mix was a control concrete
aggregates percentage in each dosage was calculated by
(CC), in this case raw, fine and coarse aggregates were used.
the Bolomey analytical method (determining the volume of
In the second concrete mix, (RC25) 25% of the coarse raw
each fraction). The weight of each fraction employed in the
aggregates were replaced by recycled coarse aggregates, in
concrete mix was calculated by its density. The humidity of
the third concrete mix (RC50) 50% of the coarse raw
the aggregates was measured and their absorption capacity
aggregates were replaced by recycled coarse aggregates and
considered at the moment of concrete production. The
in the fourth one (RC100) 100% of the raw coarse
water content or the humidity of the aggregates was
aggregates were replaced by recycled coarse aggregates.
measured according to EN
Limestone sand (S) was used as fine aggregate in all
1097-5:2000. The mass of water content is the difference
concrete mixes. The utilization of recycled sand was avoided,
between the material mass in the situation of using and the dry
due to its absorption capacity, which would no doubt
mass. The humidity of recycled aggregates reduces the water
produce a shrinkage effect [21]. The quantity of adhered
absorption capacity of them and they were used with 3.5% of
mortar increases with the decrease of size of the recycled
humidity. In the case of limestone sand (which has a fastest
aggregates [22]. Once a similar compressive strength had
capacity for water absorption) it was imperative to calculate
been reached in the four concrete mixes by mix design, the
the amount of water to be added to the mix, so as not to affect
tensile strength and modulus of elasticity of the recycled
the effective w/c ratio and maintain the concrete's plasticity.
aggregate concrete were measured. The experimental values
Due to its high absorption capacity recycled coarse
of modulus of elasticity were compared with different
aggregate must be wet before its employment in making
numerical proposals. The influence of recycled aggregate
concrete. If the recycled coarse aggregate is not humid, it
content on variability of compressive strength was also
would absorb water from the paste thus losing both its
determined.
workability in the fresh concrete, and also the control of the
effective w/c ratio in the paste.
2. Materials and experimental details
In this study, recycled coarse aggregates were wetted by a
sprinkler system the day before they were used and they were
2.1. Materials
covered with a plastic sheet in order to maintain their high
humidity. A recommended level of humidity could be 80% of
The recycled aggregates employed to produce the concrete
the total absorption capacity, however the most important
were taken from a waste recycling area. They were obtained
factor is that the aggregates employed are wet in order to
by crushing unknown waste concrete by use of an impact
reduce their absorption capacity. In this case the mechanism
crusher. The composition of recycled aggregates determined
could be that recycled aggregate that had a moderate initial
by visual inspection were defined as 92.1% crushed concrete
moisture content absorbed a certain amount of free water and
(49.1% of original aggregate plus adhered mortar and 43% of
lowered the initial w/c in the ITZ at early hydration.
original aggregates), 1.6% of ceramic aggregates and 5.3% of
Newly formed hydrates gradually filled the region processes
Bituminous and 0.8% of other. Recycled and natural coarse
effectively improved the interfacial bond between the
aggregates, named RA and A respectively, had the same
aggregates and cement [25]. One should note, however, that
fraction size, 4/10 mm (1),
the recycled aggregates should not be saturated, as that would
10/16 mm (2) and 16/25 mm (3). Aggregates sieve
probably result in the failure of an effective interfacial
distribution was determined in accordance with code UNE-EN
transition zone between the saturated recycled coarse
933-1,2.
aggregates and the new cement paste. Barra
Table 1
Mix proportions of control (CC) and recycled aggregates concrete (RC
100)
S
A1
A2
A3
Cement Additive Water Effective
3
(kg)
(kg)
(kg)
(kg)
(kg/m
) (%)
(kg)
w/c
CC
RC100-1
RC100-2
RC100-3
RC100-4
RC100-5
660.7
613.9
586.8
586.8
660.7
422.2
433.7
448.5
448.5
422.2
300.7
296.8
298.0
298.0
300.7
383.9
378.9
380.3
380.3
383.9
325
345
365
365
325
2
2
2
2
0.58
178.7
189.7
186.5
186.6
178.7
0.50
0.43
0.40
0.4
0.52
S: Sand; A1, A2 and A3: natural coarse aggregate 4/10 mm, 10/16 mm and 16/
25 mm, respectively.
3. Experimental results
3.1. Production stage 1. Mix proportions for HC and HR100
Five dosages were used for 100% recycled aggregate
concrete to get the compressive strength of CC, see Table 1.
Table 2
Definitive dosage for control concretes (CC), 25% recycled aggregate concrete (RC25), 50% recycled aggregate concrete (RC50) and 100% recycled aggregate
concrete (RC100)
CC
RC25
RC50
RC100
A1
765.1
765.1
739.0
683.2
332.7
249.5
172.1
RA1
72.8
150.6
425.8
A2
295.1
221.3
147.4
RA2
64.6
129.2
306.4
A3
579.2
434.4
289.4
RA3
Cement
Additive %
Effective w/c
128.3
256.6
391.2
300
300
318
325
0.97
0.79
0.84
1.38
165
165
165
162
0.55
0.55
0.52
0.50
S: Sand; A1, A2 and A3: natural coarse aggregate 4/10 mm, 10/16 mm and 16/25 mm, respectively. RA1, RA2 and RA3: Recycled coarse aggregate 4/10 mm, 10/
16 mm and 16/25 mm, respectively.
Aggregates, cement and water are given in mass (kg) for 1 m3 of concrete.
Table 3
Mechanical properties of cubic test elements at 28 days of curing
Density
Compressive
Tensile
Modulus of
Fig. 2. Definitive concretes strengths at 7 and 28 days in cubic tests elements.
RC100
2.34
28
2.72
27,764.0
Table 4
Mix proportions for industrial volume
CC
RC25
RC50
RC100
A1
765.1
765.1
739.0
683.2
332.7
249.5
172.1
AR1
72.8
150.6
425.8
A2
295.07
221.3
147.4
AR2
64.6
129.2
306.4
A3
579.2
434.4
289.4
AR3
Cement
Additive (%)
Water
Effective w/c
128.3
256.6
391.2
300
300
318
325
1.40
1.66
1.90
1.90
165
165
165
162
0.55
0.55
0.52
0.50
The w/c ratio is an effective value in the paste. Aggregates, cement and water are given in mass (kg) for 1 m3 of concrete.
S: Sand; A1, A2 and A3: natural coarse aggregate 4/10 mm, 10/16 mm and 16/25 mm, respectively. RA1, RA2 and RA3: Recycled coarse aggregate 4/10 mm, 10/
16 mm and 16/25 mm, respectively.
Table 5
Properties of cylinder test specimens at 28 days and 6 months
CC
RC25
RC50
RC100
Compressive strength
(MPa) 28 days
Compressive strength
(MPa) 6 months
Tensile strength
(MPa) 28 days
Tensile strength
(MPa) 6 months
Modulus of elasticity
(MPa) 28 days
Modulus of elasticity
(MPa) 6 months
35.53
38.79
39.42
38.26
42.54 (+ 19%)
46.28 (19%)
44.4 (13%)
38.66 (1%)
2.84
3.01
3.36
2.79
3.64 (28%)
3.88 (29%)
3.65 (8.6%)
3.28 (18%)
32,129
32,840
32,505
28,635
32,437
31,427
29,758
27,063
Ravindrarajah [33]
Modulus of elasticity
E = 4.63f
cy
E = 6.6f
cy
E = 5.31fcy0.50 + 5.83 for conventional concrete
E = 3.02fcy0.50 + 10.67 recycled concrete
Kakizaki [34]
Ec 2:1
ds
2:3
1:5
fc
200
0:5
4. Conclusions
In accordance with the experimental phase carried out in
this study, the conclusions obtained are with respect to;
4.1. The properties of recycled aggregates
Concrete crushed by an impact crusher achieves a high
percentage of recycled coarse aggregates without adhered
mortar.
Fig. 6. Standard deviation of different type of concretes. RC100-1 and RC100-5: mix proportions of stage 1. CC; RC25 (1) and RC25 (2) the same mix proportions;
and RC50: mix proportions of stage 2.
Acknowledgements
The work presented in this paper is part of the Doctoral
Thesis developed by the first author, who obtained a
predoctoral scholarship from the Government of Catalonia,
Spain. The authors also want to thank the Environmental
Research Program of the Technical University of Catalonia
for the financial support provided.
References
[1] BCSJ, Proposed Standard for the Use of Recycled Aggregate and
Recycled Aggregate Concrete Building Contractors Society of Japan
Committee on Disposal and Reuse of Construction Waste, 1977.
[2] RILEM TC 172-EDM/CIB TG 22, Environmental Design Methods in
Materials and Structural Engineering, 1999.
[3] DIN 4226-100, Mineral Aggregates for Concrete and MortarPart 100:
Recycled Aggregates, 2000 (in German).
[4] PrEN 13242, Aggregates for Unbound and Hydraulically Bound
Materials for Use in Civil Engineering Work and Road Construction,
European Committee for standardization, 2002.
[5] S. Nagataki, Properties of Recycled Aggregate and Recycled Aggregate
Concrete, International Workshop on Recycled Concrete, 2000.
[6] T.C. Hansen, Elasticity and drying shrinkage of recycled aggregate
concrete, ACI journal 82 (5) (September 1985) JL82-52.
[7] T.C. Hansen, H. Narud, Strength of recycled concrete made from
crushed concrete coarse aggregate, Concrete InternationalDesign and
Construc- tion 5 (1) (January 1983) 7983.
[8] S. Hasaba, M. Kawamura, K. Torik, K. Takemoto, Drying shrinkage and
durability of the concrete made of recycled concrete aggregate, Transactions of the Japan Concrete Institute 3 (1981) 5560.
[9] Japanese researchers in BCSJ, Study on recycled aggregate and recycled
aggregate concrete, Building Contractors Society of Japan Committee o
disposal and reuse of concrete construction waste, summary in Concrete
Journal, Japan, vol. 16, no. 7, july 1978, pp. 1831 (in Japanese).
[10] EHE, Instruccin del hormign Estructural (Spanish Concrete Structural
Code), Ministerio de Fomento, Madrid, Spain, 1999.
[11] M. Kikuchi, T. Mukai, H. Koizumi, Properties of concrete products
containing recycled aggregate, Demolition and Reuse of Concrete and
Masonry: Reuse of Demolition Waste, Chapman and Hall, London,
1988, pp. 595604.
[12] T. Mukai, H. Koizumi, Study on reuse of waste concrete for aggregate of
concrete, Paper Presented at a Seminar on Energy and Resources
Conservation in Concrete Technology, JapanUS Co-operative Science
Programme, San Francisco, 1979.
[13] A.D. Buck, Recycled concrete, Highway Research Record 430 (1973).
[14] S. Frondistou-Yannas, Waste Concrete as aggregate for New Concrete,
ACI Journal (August 1977) 373376.
[15] V.M. Malhotra, Use of recycled concrete as a new aggregate, Proc. of
Symposium on Energy Ad Resource Conservation in the Cement and
Concrete Industry, Report, vol. 76-8, CANMET, Ottawa, 1978.
[16] T.C. Hansen, H. Narud, Strength of recycled concrete made from
crushed concrete coarse aggregate, Concrete InternationalDesign and
Construc- tion 5 (1) (January 1983) 7983.
[17] R.S. Ravidrarajah, T.C. Tam, Properties of concrete made with crushed
concrete as coarse aggregate, Magazine of Concrete Research 37 (O.
130) (March 1985).