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 http://www.iaeme.com/IJMET/index.asp 209 editor@iaeme.com Ahmad L. Al-Mutairi, AliK. Al-Asadi and Hany Ahmed Abdalla 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 http://www.iaeme.com/IJCIET/index.asp 210 editor@iaeme.com 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. a = 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%, B150%, 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 nonlinear 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 http://www.iaeme.com/IJCIET/index.asp 211 editor@iaeme.com Ahmad L. Al-Mutairi, AliK. Al-Asadi and Hany Ahmed Abdalla 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 1853D Structural Solid element with fixed boundary conditions at their bottom surfaces. http://www.iaeme.com/IJCIET/index.asp 212 editor@iaeme.com Numerical Investigation of The Structural Behavior of Reinforced Concrete Beams with Crushed 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 http://www.iaeme.com/IJCIET/index.asp 213 editor@iaeme.com Ahmad L. Al-Mutairi, AliK. Al-Asadi and Hany Ahmed Abdalla 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 Parameter B1-0% B2-0% B3-0% B4-0% B5-0% Material fcu (MPa) a (mm) a/d 32.9 700 2.5 Concrete (R = 0%) 25.0 35.0 32.9 700 700 560 2.5 2.5 2.0 32.9 840 3.0 B1100% 29.0 700 2.5 Group (G2) beams B2B3B4100% 100% 100% Concrete (R = 100%) 29.0 25.0 35.0 700 700 560 2.5 2.5 2.0 B5100% 29.0 840 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 loaddisplacement 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 http://www.iaeme.com/IJCIET/index.asp 214 editor@iaeme.com Numerical Investigation of The Structural Behavior of Reinforced Concrete Beams with Crushed 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. B1-0% (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 http://www.iaeme.com/IJCIET/index.asp 215 editor@iaeme.com Ahmad L. Al-Mutairi, AliK. Al-Asadi and Hany Ahmed Abdalla 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. http://www.iaeme.com/IJCIET/index.asp 216 editor@iaeme.com Numerical Investigation of The Structural Behavior of Reinforced Concrete Beams with Crushed 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 http://www.iaeme.com/IJCIET/index.asp 217 editor@iaeme.com Ahmad L. Al-Mutairi, AliK. Al-Asadi and Hany Ahmed Abdalla 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 nonlinearity 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] [2] [3] [4] [5] [6] [7] [8] Al-Mutairi, A. L. Shear Behavior of Recycled Aggregate Reinforced Concrete Beams. PhD Thesis, Cairo University, Egypt, 2018. 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. Bravo, M., Brito, J., Pontes, J. and Evangelista, L. Mechanical Performance of Concrete Made with Aggregates from Construction and Demolition Waste Recycling Plants. Journal of Cleaner Production, 99, 2015, pp. 59–74. European Commission. Competitiveness of the Construction Industry. 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