Ijciet 10 01_020

http://www.iaeme.com/IJMET/index.asp 209 editor@iaeme.com
International Journal of Civil Engineering and Technology (IJCIET)
Volume 10, Issue 1, January 2019, pp.209–219, Article ID: IJCIET_10_01_020
Available online at http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=10&IType=1
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
©IAEME Publication Scopus Indexed
NUMERICAL INVESTIGATION OF THE
STRUCTURAL BEHAVIOR OF REINFORCED
CONCRETE BEAMS WITH CRUSHED
CONCRETE AGGREGATE
Ahmad L. Al-Mutairi
Faculty of Engineering, Cairo University, Egypt
AliK. Al-Asadi
College of Engineering, University of Sumer, Rifai, Iraq
Hany Ahmed Abdalla
Faculty of Engineering, Cairo University, Egypt
ABSTRACT
Recycling of waste materials produced from the construction and demolition
activities is becoming a demand for modern societies willing to achieve environmental
sustainability. To date, the use of crushed concrete aggregate (CCA) in replacement of
natural coarse aggregate to produce high quality concrete is very limited. This can be
attributed to the missing information on the properties of the original concrete before
crushing, the limited data that clarifies the influence of using CCA on the material
properties of the concrete mixture as well as the overall structural behavior of the
reinforced concrete element in which it is used. An experimental testing program has
been conducted on reinforced concrete beams to assess the influence of CCA
replacement ratio on their structural performance and the results have been briefly
discussed in this paper. The primary aim of the study presented herein is to
numerically evaluate the influence of the concrete compressive strength (fcu) and the
shear span to depth ratio (a/d) on the structural performance of reinforced concrete
beams casted with two different concrete mixtures incorporating 0% and 100% CCA.
Accordingly, ten beams have been modelled using ANSYS finite element software with
two control beams being validated with the experimental data. The results
demonstrate the increase of the load carrying capacity and ductility of beams with
100% CCA with increasing the fcu. On the contrary, increasing the shear span to depth
ratio leads to the reduction in the capacity of the beams casted with the two different
concrete materials. As a final conclusion, the results of the performed numerical
analysis designate undesirable structural performance of the concrete beams with
100% CCA. Therefore, it is not recommended to use concrete mixtures with full

Ahmad L. Al-Mutairi, AliK. Al-Asadi and Hany Ahmed Abdalla
http://www.iaeme.com/IJCIET/index.asp 210 editor@iaeme.com
replacement of natural coarse aggregate by CCA in casting concrete structural
members where ductile behavior is indispensable.
Keywords: Crushed Concrete Aggregate, Finite Element Analysis, Reinforced Beams,
Compressive Strength, Shear Span.
Cite this Article: Ahmad L. Al-Mutairi, AliK. Al-Asadi and Hany Ahmed Abdalla,
Numerical Investigation of The Structural Behavior of Reinforced Concrete Beams
with Crushed Concrete Aggregate, International Journal of Civil Engineering and
Technology (IJCIET), 10 (1), 2019, pp. 209–219.
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=10&IType=1
1. INTRODUCTION
Nowadays, there are global environmental concerns regarding the construction and demolition
of waste materials that tremendously increased due to the expansion of construction works
and the fast pacing population growth. Almost 50% of the natural resources are consumed by
the construction industry according to the European Commission Report (2001), [4].
Consequently, countries that aim to achieve environmental sustainability have serious moves
towards recycling demolished concrete.
Crushed concrete aggregate (CCA) has been used in geotechnical applications as a
pavement subbase material and backfilling material for embankments (Vieira and Pereira
2007; Santos and Vilar 2008), [11,9] after proven to have equivalent or even superior
properties over natural granular subbase materials (O’Mahony and Milligan 1991; Arulrajah
et al. 2013), [8,2].
Till this moment in time, the practical use of CCA in producing high quality concrete as a
replacement of natural coarse aggregate (NCA) is scarce. Such limitation of use can be
attributed to the uncertainty in the available data on the mix proportions and the mechanical
properties of the original concrete prior crushing, besides the lack of studies and experience
on the effect of concrete with CCA on the structural performance of reinforced concrete
members (Sato et al. 2007), [10].
Extensive research studies can be found in the literature focusing on investigating the
influence of replacing natural coarse aggregate with CCA on the mechanical properties of
concrete (Exteberria et al. 2007; Bravo et al. 2015), [5,3]. Exteberria et al. (2007), [5]
estimated a 35% reduction in the concrete compressive strength when the natural coarse
aggregate was totally replaced with CCA. Others, reported that concrete mixes with up to
75% CCA resulted in concrete with acceptable quality, however the high percentage of CCA
affected the durability of the mixture compared to the control specimens (Zega et al. 2014),
[12]. Additionally, the influence of CCA on the shear and flexural behavior of reinforced
concrete beams have been examined. Contradiction can be recognized in the reported
conclusions; some results showed insignificant effect of CCA on the shear and flexural
behavior of the beams (Gonza´lez-Fonteboa and Martı´nez-Abella 2007), [6], others indicated
the reduction of the shear capacity of the beams with increasing the replacement ratio of CCA
(Lee and Yun 2007), [7].
As the influence of CCA on the shear capacity of reinforced concrete structural members
is still controversial, experimental testing and numerical analysis have been conducted to
elaborate the influence of incorporating different proportions of CCA in concrete mixtures as
well as other parameters on the shear capacity of beams. The core of this paperis to discuss
the details of the numerical analysis and the obtained results, however, brief discussion of the

Numerical Investigation of The Structural Behavior of Reinforced Concrete Beams with Crushed
Concrete Aggregate
conducted experimental testing, whose details can be found elsewhere (Al-Mutairi 2018), [1],
will be included as well.
2. EXPERIMENTAL STUDY
2.1. Experimental Program
A series of flexural tests was conducted on 12 beams to experimentally evaluate the influence
of using CCA in concrete mixes and shear reinforcement on the shear capacity and cracking
pattern of reinforced concrete beams. The beams were casted using four different concrete
mixes with CCA replacement ratios (R) of 0% (control specimen), 50%, 75% and 100%. All
the tested beams had the same cross section of 250 mm width  300 mm thickness and length
of 2200 mm besides the same longitudinal reinforcement. The beams were split into 3 groups
based on their shear reinforcement with four beams in each group of the four beams, one was
casted using the control concrete mix, while the other three beams were casted using concrete
mixes with 50%, 75% and 100% CCA replacement ratios.
Each of the tested beams was simply supported with a constant spacing of 2000 mm
between the supports and was symmetrically loaded at two points as shown in Figure 1. Such
loading configuration results in subjecting the middle region between the applied loads to
pure bending without shear and is typically known as flexural test. A constant shear span (a)
of 700mm, which is the distance from the support to the point load on its same side, has been
set to attain a constant shear span to depth ratio (a/d) of 2.5 for all the tested beams.
Figure 1 Schematic of the tested beams (All dimensions are in mm)
2.2. Experimental Results
As the experimental study is not the primary objective in this paper, only the results of the
four beams of the first group will be discussed herein. The used designation for the tested
beams includes a combination of the group number and the CCA replacement ratio. For
example, beam B1-75% indicates the beam in group number 1 and casted with concrete mix
having 75% replacement ratio. Accordingly, the four beams of group one are B1-0%, B1-
50%, B1-75%, and B1-100%.
Visual inspection, in terms of crack patterns and propagation of cracks showed no
influence of CCA replacement ratio as the behavior of the four beams was almost the same.
Though, with increasing the CCA content, the critical load at which cracks start to develop
decreased, indicating earlier appearance of cracks. Furthermore, beams B1-50%, B1-75%, and
B1-100% exhibited reduction of the peak shear strength by 3.2%, 16.0% and 20.1%,
respectively compared to that measured forB1-0%.
Figure 2 elaborates the load-deflection curves at mid-span of the four beams. At early
stages of loading, the beams showed linear behavior, then gradually a transition to a non-
linear phase arose due to the non-linearity of the concrete material as well as the reduction in
stiffness accompanying the generation of cracks. Beam B1-50% revealed load-deflection
a
=

relationship almost equivalent to that measured for the control beam B1-0% with minimal
reduction in the flexural stiffness, peak load and ductility. Yet, the deleterious influence of
incorporating CCA was recognized with increasing the replacement ratio in excess of 50%.
Beam B1-75% showed semi-ductile behavior with small deflections recorded beyond the
linear phase and a recognized reduction in the peak load. Moreover, the most detrimental
behavior was displayed for the beam with full replacement of CCA (B1-100%) which showed
significant reduction in the peak load together with brittle mode of failure, see Figure 2.
Based on the experimental testing results, it was concluded that the optimum replacement
ratio of CCA is 50% by weight and higher percentages are expected to be deleterious for the
structural behavior of concrete elements.
Figure 2 Load-displacement curves for beams of the first group
3. NUMERICAL ANALYSIS
3.1. Modelling Details
Three dimensional (3D) non-linear finite element analysis (FEA) was conducted using
ANSYS software to assess the structural behavior of control reinforced concrete beams and
beams with 100% CCA under loading condition similar to that applied during the conducted
flexural tests in the experimental program previously described. Replacement ratio of 100%
was selected to demonstrate on the findings of the experimental study of its detrimental
influence.
ANSYS library provides a variety of finite elements to simulate 3D objects. Each of the
developed models consisted of a concrete part, steel reinforcement (RFT) and four plates as
presented in Figure 3. The concentrated loads were applied on the two plates on top of the
beam, while the two other plates were defined as the supports. An eight-node solid element,
SOLID65-3-D Reinforced Concrete Solid element, was used to model the concrete part. The
used solid element has three translational degrees of freedom (DOF) at each node without any
rotational DOF. SOLID 65 elements allow plastic deformation, cracking and crushing.On the
other hand, LINK180-3-D Finite Strain Spar element was used to model the steel
reinforcement. Link 180 element has two nodes with one translational DOF at each node and
a total of 2 DOF per element. All the plates were modelled using the eight-node SOLID 185-
3D Structural Solid element with fixed boundary conditions at their bottom surfaces.

Concrete Aggregate
Figure 3Details of the components of the reinforced concrete beam model
To account for the non-linearity of concrete properties and differentiate between the
behavior of concrete material with 0% CCA, named Concrete (R = 0%), and that with 100%
CCA, named Concrete (R = 100%), the stress-strain curves depicted in Figure 4 were
assigned for the two different concrete materials. These stress-strain curves simulate
multilinear isotropic behavior for the two types of concrete and wereidealized from the
experimental results. Concrete failure was defined through Von Mises failure criterion along
with William & Warnke model. Moreover, as the load-deflection behavior is of major
importance in this study, smeared crack model was used to predict the development of cracks.
For steel reinforcement, bilinear material model was assigned with Young’s Modulus (E) of
200 GPa, yield stress of 425 MPa and Poisson’s ratio () of 0.3.
The main objective of the developed numerical analysis is to investigate the structural
performance of reinforced concrete beams casted with concrete mixtures incorporating 0%
and 100% CCA. Furthermore, the study elaborates the influence of the concrete compressive
strength (fcu) and shear span to depth ratio (a/d) on the beams casted with the two different
concrete materials. In view of that, ten different beams, with the same cross sectional area and
steel reinforcement as that presented in Figure 1, were modelled using ANSYS software. The
ten beams are divided into two groups based on the defined concrete material and will be
referred to as groups G1 and G2from now on. Group G1 includes five beams casted with
Concrete (R = 0%), while group G2 includes five beams casted with Concrete (R = 100%).
The used beam designation for the modelled beams in this paper includes a combination of
the beam number and the CCA replacement ratio. For example, beam B3-100% indicates the
third beam casted with concrete mix having 100% CCA. Accordingly, the five beams of

group G1 are designated as B1-0%, B2-0%, B3-0%, B4-0%, and B5-0%. Similarly, the beams
of group G2 are designated as B1-100%, B2-100%, B3-100%, B4-100%, and B5-100%.
Figure 4Stress-strain relationship for the two defined concrete materials
Table 1 summarizes the details of the modelled beams. Beam B1 in each group(B1-0%
and B1-100%) is the control beam and it exactly simulates the corresponding tested beam in
the experimental study to verify the conducted models. Whereas the assigned concrete
compressive strength was altered to 25 and 35 MPa for beams B2 and B3, respectively, to
study the influence of fcu, maintaining all the other parameters. Similarly, the shear span to
depth ratio was changed to 2.0 and 3.0 for beams B4 and B5, respectively, to assess the
influence of a/d.
Table 1Details of the modelled beams
Group (G1) beams Group (G2) beams
Parameter B1-0%B2-0%B3-0%B4-0%B5-0%
B1-
100%
B2-
100%
B3-
100%
B4-
100%
B5-
100%
Material Concrete (R = 0%) Concrete (R = 100%)
fcu (MPa) 32.9 25.0 35.0 32.9 32.9 29.0 25.0 35.0 29.0 29.0
a (mm) 700 700 700 560 840 700 700 700 560 840
a/d 2.5 2.5 2.5 2.0 3.0 2.5 2.5 2.5 2.0 3.0
3.1. Results and Discussion
The results obtained from the developed numerical models will be discussed to elaborate the
influence of the concrete compressive strength and a/d on the structural behavior of concrete
beams casted with concrete having 0% and 100% CCA. The structural behavior is analyzed in
terms of the mode of failure, load-displacement curve and ultimate shear load capacity.
Figure 5 illustrates the visualized cracks at failure during the experimental testing of beam
B1-0% and the corresponding cracks induced in the numerical model. The numerical model
shows crack patterns adequately similar to that observed during the experimental testing. Such
result proves the ability of the developed model to simulate the generated cracks in concrete
under the applied loading condition, which is expected to highly influence the general
structural behavior. Moreover, Figure 6 presents the experimental and numerical load-
displacement curves for beams B1-0% and B1-100%. The experimental and numerical results
show the linear and non-linear phases previously described in the experimental results for

Concrete Aggregate
beam B1-0%. Although, the numerical results show slightly higher stiffness in the linear zone
compared to that experimentally measured, the obtained peak loads are almost alike with just
4.3% difference. Similar comparison can be reported for beam B1-100% with peak ultimate
loads of 301 and 284 kN from the experimental and numerical data, respectively, indicating a
5.6% difference. Therefore, the comparison delivered in Figure 6 demonstrates the reliability
of the developed models to simulate the structural performance of the reinforced concrete
beams subjected to the described experimental loading configuration.
(a) Experimental
(b) Numerical
Figure 5 Cracking patterns for beam B1-0% at failure
Figure 6 Comparison between the experimental and numerical load-displacement curves
The effect of the concrete compressive strength on the beams of groups G1 and G2 is
elaborated in Figures 7 and 8, respectively. For beams of group G1, it can be recognized that
decreasing fcu from 32.9 MPa for beam B1-0% to 25.0 MPa leads to the minimal reduction in
the flexural stiffness of the beam unlike the relatively noticeable reduction in the peak shear
load from 358 kN to 321 kN. Alternatively, increasing fcu to 35.0 MPa shows almost
negligible influence on the flexural stiffness of the beam and about 5% higher peak load. This
could be the reflect of the slight difference between the two values of fcu. It is worth to
mention that the load-deflection curves presented in Figure 7 indicate ductile failure of the
three beams as after exceeding the linear phase, deflection continues in the beam with slight
variations in the applied loads. For beams in group G2 with 100% CCA, increasing fcu from
25.0 MPa to 29.0 MPa to 35.0 MPa leads to increasing the shear load capacity from 260 kN to
284 kN to 300 kN, respectively, accompanied with slight increase in the flexural stiffness of
the beams. Furthermore, it can be noted that the displacement at which failure occurs
B1-0%

increases with increasing the concrete compressive strength, which means increasing the
ductility of the beam.
Figure 7Effect of fcu on the load-displacement of beams of group G1
Figure 8Effect of fcu on the load-displacement of beams of group G2
Figure 9 reveals the influence of the shear span to depth ratio on the beams of group G1. It
can be noticed that different load-deflection curves are obtained for exactly the same beam
when varying a/d. Beam B4-0% with reduced a/d compared to beam B1-0% exhibits 13.7%
increase in the ultimate load, while beam B5-0% with the highest a/d experiences 19%
reduction in the peak load relative to the control beam B1-0%. Likewise, failure occurres at
smaller displacement for beam B5-0% compared to the two other beams. Thus, the closer the
applied concentrated load to the beam support, the higher the load carrying capacity of the
beam. Similar outcome can be recognized in Figure 10 for beams in group G2. The estimated
peak load for the control beam in this group B1-100% (a/d =2.5) is 284.0 kN, while that for
beam B4-100% (a/d =2.0) is 328.4 kN, which signposts an increase of the load capacity by
15.6% when decreasing the shear span to depth ratio from 2.5 to 2.0. Alternatively, increasing
a/d to 3.0 for beam B5-100% leads to almost 15.5% reduction in the peak capacity compared
to the control specimen.

Concrete Aggregate
Figure 9 Effect of a/d on the load-displacement of beams of group G1
Figure 10Effect of a/d on the load-displacement of beams of group G1
Finally, it can be recognized from the results of the presented numerical study that all the
five beams of group G1 casted with concrete without CCA experiences ductile failure, unlike
the beams of group G2 with 100% CCA which experiences brittle behavior with the exception
of beam B3-100% with increased fcu. Therefore, the use of concrete mixtures with full
replacement of natural coarse aggregate with CCA is not recommended in the concrete
structural members where ductile behavior is a necessity.
4. CONCLUSION
This study focuses on numerically evaluating the structural performance of reinforced
concrete beams casted with two different concrete materials incorporating either 0% or 100%
CCA in their matrix. This numerical study is an extension of the experimental study that was
conducted on beams with different replacement ratios of CCA under the standard flexural test
loading conditions. Ten different beams were modelled to study the influence of the concrete
compressive strength and the shear span to depth ratio on the structural behavior of beams
casted with 0% and 100% CCA. Consequently, the modelled beams were equally split into
two groups G1 and G2. Group G1 represents beams casted with 0% CCA while G2 represents

those with 100% CCA. The control specimen in each group was verified against the
experimental data and the results established reliability in the developed model to simulate the
beams performance under the applied loading conditions. Out ofthe obtained results from the
numerical investigation it can be concluded that:
 Non-linear finite element modelling is capable of mimicking the cracks formation in
reinforced concrete structures, which is a governing factor that leads to the material non-
linearity and affects the overall structural performance.
 Decreasing fcu from 32.9 MPa to 25 MPa have smaller influence on the flexural stiffness
compared to the 10% reduction in the load carrying capacity of the beams with 0% CCA
(group G1). While increasing it to 35 MPa has almost insignificant influence.
 For beams in group G2 with 100% CCA, increasing fcu from 25.0 MPa to 29.0 MPa to 35.0
MPa leads to increasing the peak load from 260 kN to 284 kN to 300 kN, respectively,
accompanied with slight increase in the flexural stiffness of the beams
 Increasing fcu for beams with 100% CCA increases the ductility of the beams.
 Increasing the shear span to depth ratio from 2.5 to 3.0 leads to the reduction of the load
carrying capacity by 19.0% and 15.5% for the beams with 0% and 100% CCA, respectively.
 The closer the applied concentrated load to the beam support, the higher the load carrying
capacity of the beam.
 The five modelled beams of group G1 casted with concrete without CCA experienced ductile
failure, unlike the beams of group G2 with 100% CCA which experienced brittle behavior
with the exception of beam B3-100% with increased fcu.
 Finally, it is not recommended to use concrete mixtures with full replacement of natural
coarse aggregate with CCA in concrete structural members where ductile behavior is essential.
REFERENCES
[1] Al-Mutairi, A. L. Shear Behavior of Recycled Aggregate Reinforced Concrete Beams.
PhD Thesis, Cairo University, Egypt, 2018.
[2] Arulrajah, A., Piratheepan, J., Disfani, M. and Bo, M. Geotechnical and
Geoenvironmental Properties of Recycled Construction and Demolition Materials in
Pavement Subbase Applications.Journal of Materials in Civil Engineering, 25, 2013, pp.
1077–1088.
[3] Bravo, M., Brito, J., Pontes, J. and Evangelista, L. Mechanical Performance of Concrete
Made with Aggregates from Construction and Demolition Waste Recycling Plants.
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[4] European Commission. Competitiveness of the Construction Industry. A Report Drawn up
by the Working Group for Sustainable Construction with Participants from the European
Commission, Member States and Industry. European Commission, 2001.
[5] Exteberria, M., Vasquez, E. and Mari, A.R. Influence of Amount of Recycled Coarse
Aggregates and Production Process on Properties of Recycled Aggregate Concrete.
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[6] Gonza´lez-Fonteboa, B. and Martı´nez-Abella, F. Shear Strength of Recycled Concrete
Beams.Construction and Building Materials, 21(4), 2007, pp. 367–379.
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Concrete Aggregate
[9] Santos, E.C.G. and Vilar, O.M. Use of Recycled Construction and Demolition Wastes
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[10] Sato, R., Maruyama, I., Sogabe, T. and Sogo, M. Flexural Behavior of Reinforced
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[11] Vieira, C.S. and Pereira, P.M. Use of Recycled Construction and Demolition Materials in
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[12] Zega, C. J., Maio, A.A. and Zerbino, R.L. Influence of Natural Coarse Aggregate Type on
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