This paper presents the structural behavior of reinforced concrete beam embedded with high density polyethylene balls (HDPE) subjected to flexural load. The HDPE balls with 180 mm diameter were embedded to create the spherical voids in the beam which lead to reduction in its self-weight. Two beam specimens with HDPE balls (RC-HDPE) and one solid beam (RC-S) with dimension 250 mm x 300 mm x 1100 mm were cast and tested until failure. The results are analysed in the context of its ultimate load, load-deflection profile, and crack pattern and failure mode. It was found that the ultimate load of RC-HDPE was reduced by 32% compared to RC-S beam while the maximum deflection at its mid span was increased by 4%. However, RC-HDPE is noticed to be more ductile compared to RC-S beam. Both types of beams experienced flexure cracks and diagonal tension cracks before failur

Goh, Wan Inn

Hadipramana, Josef

Lockman, A.

Mohamad, Noridah

Samad, A.A.A.

English

UTHM Institutional Repository

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Structural behaviour of beam with HDPE plastic balls subjected to flexure load

This paper presents the structural behavior of reinforced concrete beam embedded with high density polyethylene balls (HDPE) subjected to flexural load. The HDPE balls with 180 mm diameter were embedded to create the spherical voids in the beam which lead to reduction in its self-weight. Two beam specimens with HDPE balls (RC-HDPE) and one solid beam (RC-S) with dimension 250 mm x 300 mm x 1100 mm were cast and tested until failure. The results are analysed in the context of its ultimate load, load-deflection profile, and crack pattern and failure mode. It was found that the ultimate load of RC-HDPE was reduced by 32% compared to RC-S beam while the maximum deflection at its mid span was increased by 4%. However, RC-HDPE is noticed to be more ductile compared to RC-S beam. Both types of beams experienced flexure cracks and diagonal tension cracks before failure

Goh, W. I.

A. Samad, A. A.

1  STRUCTURAL BEHAVIOUR OF BEAM WITH HDPE PLASTIC BALLS SUBJECTED TO FLEXURE LOAD Noridah Mohamad1, W.I.Goh2*, A.A.A. Samad3, A. Lockman4, Josef Hadipramana5  1,2,3,4,5 Department of Structure and Material Engineering, Faculty of Civil and Environmental Engineering Universiti Tun Hussein Onn Malaysia, Parit Raja, 86400 Batu Pahat, Johor, Malaysia *Corresponding author: wigoh@uthm.edu.my Abstract This paper presents the structural behavior of reinforced concrete beam embedded with high density polyethylene balls (HDPE) subjected to flexural load. The HDPE balls with 180 mm diameter were embedded to create the spherical voids in the beam which lead to reduction in its self-weight. Two beam specimens with HDPE balls (RC-HDPE) and one solid beam (RC-S) with dimension 250 mm x 300 mm x 1100 mm were cast and tested until failure. The results are analysed in the context of its ultimate load, load-deflection profile, and crack pattern and failure mode. It was found that the ultimate load of RC-HDPE was reduced by 32% compared to RC-S beam while the maximum deflection at its mid span was increased by 4%.  However, RC-HDPE is noticed to be more ductile compared to RC-S beam. Both types of beams experienced flexure cracks and diagonal tension cracks before failure.    Keywords: HDPE plastic balls, self-weight, structural behavior, flexural load, deflection 1.0 Introduction Concrete is the most consumed material for construction industries. However, the concrete weight penalty has become its weakness. This has created interest among researchers to look at possible ways to overcome this shortcoming by altering the mixture of material used in concrete casting.  The usage of lightweight materials in construction has become increasingly popular due to huge available of such materials either artificially made or from industrial and organic waste. Among the lightweight materials that have been used as materials in construction are extruded polystyrene, foamed concrete, lightweight aggregate, plastic bottle, aluminum, and even products from plantation such as peanut shells and rice husk. Studies have proven that certain materials mentioned above are viable to be used as building materials.  For example, polystyrene has been used as the insulation material enclosed between two outer skin layers in walls [1,2,3]. Recycled aggregate is proven to have lower density and mechanical properties slightly lower or similar to natural aggregate depending on the percentage it is used as replacement and also the type of curing [4, 5]. Meanwhile, alumina is proven to be viable as both skins and core layer in sandwich panel system [6,7].           One of the solutions to reduce the weight of the concrete is by using reinforced concrete with hollow plastic balls such as high-density polyethylene balls or HDPE. HDPE is created from ethylene through catalytic process. This material is higher in density and strength compared to low density polyethylene. HDPE is also good in impact resistance, light weight, low moisture absorption, and high tensile strength. HDPE can  be recycled where it has economically advantages due to lower costs of removing the waste and the reduction of pollution and contamination. This type of polymer wastes is suitable for non-structural use and more cost effective compared to normal concrete [8].          There are many investigations that have been conducted by previous researchers on HDPE; however, the study was limited to its performance in the slab. It has been proven that voided flat slab have lower stiffness than that of solid flat slabs with the reduction of stiffness is about 10% to 20%. It was also noticed that the stiffness of the voided flat slabs decreased as the thickness of the slab increased. By introducing spherical voids into flat plate slabs, the self-weight of the slabs can be reduced up to 32%. [9] Another investigation on slab with hollow plastic balls 2  subjected to flexure load has shown that the hollow slabs yield a satisfactory flexural behavior in term of crack pattern, and flexural strength, which is similar to that of conventional concrete solid slabs up to the ultimate state [10].         In this study, HDPE hollow plastic balls were used as a replacement for concrete at the center layer of the reinforced concrete beam to decrease the self-weight of the beam. The beam was strengthened with 12 mm steel bars as main reinforcement and 6 mm steel stirrups. The structural behavior of reinforced concrete beam with plastic balls was tested under flexure load. The results are analysed in the context of its ultimate load, load-deflection profiles, crack pattern and mode of failure. The results for reinforced concrete beam with HDPE plastic balls were compared with the results obtained for solid reinforced concrete beam. 3.0 Materials and Methods Total number of three (3) beam specimens were cast in this study; two specimens with HPDE hollow plastic ball and one specimen without the plastic ball which function as the control specimen. The proportion for the materials used to cast the concrete beam is presented in Table 1. The concrete’s strength targeted is 30 MPa with 2400 kg/m³ density. The proportion of these materials were measured by weight. Concrete cubes and cylinders were also cast and tested to determine the concrete’s compressive and tensile strength.  Table 1: Mixture of concrete materials Conrete Grade (MPa)   Cement Content (kg) Fine aggregates (kg) Coarse aggregates (kg) Maximum w/c ratio 30 29 57 113 0.5           The beam specimens were reinforced by the main bar and stirrups. The dimension of the specimens is 250 mm width x 300 mm depth x 1100 mm length. High tensile steel reinforcement bar of 12 mm diameter was used as the main reinforcement at top and bottom of the beam. Meanwhile, low tensile strength steel with 6 mm diameter was used as the stirrup along the span of the beam. HDPE plastic balls with diameter 180 mm are placed in the beam to create the hollow section.   3.1    Fabrication Process The fabrication process includes the preparation of formworks, mixing the concrete, placing the reinforcement and stirrup in the concrete and finally pouring the concrete. The formwork is made of plywood as shown in Figure 1. The process started with placing a few concrete cover blocks to make sure the steel reinforcement will be fixed in the formworks. The plastic balls and steel reinforcement were then placed in the formwork. Sufficient spacing with length of 180 mm was used to make sure the plastic balls can fit in between the stirrups. Steel wire was used to tie the stirrups to make sure the plastic balls will not float during the casting process. Figure 2 shows the arrangement of plastic balls in the steel reinforcement. The details of the dimension are as shown in Figure 3 and Figure 4 for its layout design and cross-section design, respectively.        Similar steps were taken in the fabrication of reinforced concrete solid beam but without plastic balls. The concrete mixture then poured into the formwork while using the vibrator to make sure all the voids in the formwork filled with concrete mixture. The specimens   underwent the normal curing at 20 °C for strength test for 28 days. Cubes and cylinders were cast and tested for its compressive strength at 7, 14 and 28 days. 3                            Figure 1: Formwork                       Figure 2: arrangement of plastic balls in                                                                                                        the steel reinforcement                     Figure 3: Layout design for reinforced concrete beam with plastic balls       Figure 4: Cross section design for concrete beam with plastic balls 3.2 Test Set-up Four point bending test was carried out to study the  behaviour of beam with HDPE plastic balls. In this experiment, reinforced concrete beams with plastic balls and the reinforced concrete solid beam as controlled specimen were tested under four point bending test to compare the behaviour obtained by  both beams. This test required a load cell to impose the applied load on the beam and  Linear Voltan Digital  Transducer (LVDT ) to measure the deflection of the specimen. Three LVDT were placed at various locations along the span of the  beam as shown in Figure 5 and    300mmmmmmmm 2T12 1100 mm 100mm 100mm 48 mm 48 mm 250 mm T12 Y6 50 mm 25 mm 300 mm 4  Figure 6.  Figure 5 shows a schematic design of reinforced concrete beam tested by four point bending test and Figure 6 shows the laboratory experimental set-up for the test. In this test, the ultimate load, deflection and modes of failure of the beam  specimens were analysed.  Figure 5: Schematic diagram of reinforced concrete beam  tested by four point bending test.  Figure 6: Reinforced concrete beam specimen were ready for testing 4.0 Results and Discussions 4.1 Mechanical Properties of Concrete 4.1.1 Compressive Strength. The compressive strength of the concrete has increased gradually and at the age of 28 days of maturity, the compressive strength of the concrete has achieved 38.9 MPa which is within the target range of compressive strength for normal concrete grade C30 with density of 2400 kg/m³. The compressive strength value has increased linearly when the curing period increased which is 25.7MPa for 7 days, 32.2 MPa for 14 days and 38.9 MPa for 28 days as shown in Figure 7. 5   Figure 7: Compressive Strength of concrete 4.1.2 Split Tensile Strength. From the split cylindrical tensile strength test conducted, the average value results for tensile strength of the concrete at 28 days  is 2.78 MPa. Table 1 shows the results recorded for both cylinder specimens Table 1: Split Tensile Strength of concrete Specimen Grade Age  Load (kN) Strength (MPa) C1 C30 28 days 203.04 2.89 C2 C30 28 days 195.11 2.67 Average stength (MPa) 2.78 4.2 Ultimate Load. From the results recorded, the average ultimate load of reinforced concrete beam with plastic balls has reached 143kN while the ultimate load of controlled specimen has reached 210kN before failure. The different in percentage for both specimens is almost 32%. The beam with HDPE plastic balls failed at 32% lower load compared to the control specimen.   Figure 7: Ultimate Load of reinforced concrete beam specimens 6  4.3 Load-deflection Profile. The maximum deflection at the mid-span for reinforced concrete beam with plastic balls is 5.91mm while the maximum deflection at the mid-span for reinforced concrete solid beam is 5.67 mm. However, the maximum deflection value recorded for reinforced concrete beam with plastic balls within the loading area at the left load is 4.12 mm compared to reinforced concrete solid beam which is 3.55mm. This difference recorded a greater percentage value of deflection which is almost 14%. The difference maximum deflection value near the loading area at the right was recorded at 2% for the two specimens.   Figure 8: Load-Deflection at the mid-span of reinforced concrete beam specimens  Figure 9: Load-Deflection at the (a) left  and (b) right  point load  of reinforced concrete beam specimens 4.4 Mode of Failure. Beam specimens were subjected to flexural load from four point bending test until failure. Cracks were recorded during the loading. The cracks for reinforced concrete beam with plastic balls (RC-HDPE) and solid reinforced concrete beam (RC-S) can be seen in Figure 10(a) and Figure 10(b), respectively. The failure load and crack load recorded for RC-HDPE are 143 kN and 89 kN, respectively.  The vertical flexural crack was  measured at 1.4 mm length within the loading area. The cracks were noticed to initially started from tension zone and propagate to the compression zone. Diagonal tension crack  measured at  0.35 mm and 0.5 mm length occured when the load reached 107 kN and 101 kN, respectively before the load reached 140kN. Vertical cracks of  1.9 mm and 2mm length also occured at the mid-span of the beam when the load reached 113 kN and 107 kN and the maximum deflection recorded at 3.55 mm.  7   Figure 10: (a) The crack patterns of reinforced concrete with plastic balls                                          (b)The crack patterns of reinforced concrete solid beam  As for the controlled specimen, the first crack took a longer time to occur and only appeared when the load reached 125 kN with crack length recorded at 1.1 mm. The crack propagated as tension crack at the bottom part of the beam. Compared to the reinforced concrete beam with plastic balls, the flexural cracks for reinforced concrete solid beam were recorded to occur at more locations along the beam’s span. This is due to the larger load it took before failure. Table 2 presents the values of first crack load, maximum deflection at mid-span, crack length, and mode of failure for both RC-HDPE and RC-S beams. All the values recorded for RC-HDPE beam are the average values recorded from two tested RC-HDPE specimens.    Table 2: Values of first crack load, maximum deflection at mid-span,  and the crack length of RC-HDPE  Specimen First Crack Load(kN) Maximum Deflection  (mm) Crack Length (mm) Mode of Failure RC-HDPE 89 5.91 1.4 Flexure cracks and Diagonal tension cracks RC-S 125 5.73 1.1 Flexure cracks and Diagonal tension cracks 5.0 Conclusions The ultimate load and first crack load recorded for RC-HDPE are lower compared to the RC-S beam. Maximum deflection and crack length of RC-HDPE beam is slightly higher compared to RC-S beam. However, from the load-deflection profile, it is noticed that RC-HDPE beam is more ductile compares to RC-S beam where it took longer time to fail after the first crack load. Acknowledgement The author would like to thank the Universiti Tun Hussein Onn Malaysia and Ministry of Higher Education Malaysia for their financial support for this project.    8  Reference [1]   N. Mohamad, W. Omar, R. Abdullah. Precast Lightweight Foamed Concrete Sandwich Panel (PLFP) Tested under Axial Load: Preliminary Results. Advanced Materials Research, Vols. 250-253, pp. 1153-1162. 2011. [2]   Md Azree Othuman Mydin. Potential of Using Lightweight Foamed Concrete in Composite    Load-Bearing Wall Panels In Low-Rise Construction . Concrete Research Letter. Vol. 2 (2), 2011.  [3]    N. Mohamad, H. M. Muhammad, "Testing of Precast Lightweight Foamed Concrete Sandwich Panel with             Single and Double Symmetrical Shear Truss Connectors under Eccentric Loading", Advanced Materials  Research, Vols. 335-336, pp. 1107-1116, 2011. [4]   Kang, T. H.-K., Kim, W., Kwak, Y.-K., & Hong, S.-G. “The choice of recycled concrete aggregates for flexural members.”  Proceedings of 18th International Association for Bridge and Structural Engineering Congress on Innovative Infrastructures, Seoul, Korea. 2012. [5]   Sato, R., Maruyama, I., Sogabe, T., & Sogo, M. “Flexural Behavior of Reinforced  Recycled Concrete   Beams.” Journal of Advanced Concrete Technology, 5, 1, 43–61. 2007. [6]    M. Kampner, R. M. Deacon, A. R. Marder. Failure analysis of an aluminum sandwich panel  skin from the   space shuttle Columbia. Journal of Failure Analysis and Prevention. Volume 6, Issue 1,  46-50. 2006 [7]   K.Kantha Rao, K. Jayathirtha Rao, A.G.Sarwade, B.Madhava Varma. Bending Behavior of  Aluminum Honey Comb Sandwich Panels . International Journal of Engineering and Advanced Technology (IJEAT) ISSN: 2249 – 8958, Volume-1, Issue-4, 2012. [8]  M.Mustafa Al Bakri, S. Mohammad Tamizi, A. R. Rafiza, Y. Zarina, Investigation Of HDPEPlastic Waste Aggregate On The Properties Of Concrete. Journal of Asian Scientific Research, 1(7), pp. 340-345, 2011 [9]   Saifee Bhagat , Dr. K. B. Parikh . Comparative Study of Voided Flat Plate Slab and Solid   Flat Plate Slab . Internatinal Journal of Innovative Reasearsch and Development. Vol. 3, Issue 3. 2014. [10] Lan Chung,  Sang-Hyun Lee,  Seung-Ho Cho, Sung-Sik Woo,  Kyoung-Kyu Choi Investigations on Flexural Strength and Stiffness of Hollow Slabs. Journal of Advances in Structural Engineering, Vol. 13, No. 4, 2009.      

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Structural behaviour of beam with HDPE plastic balls subjected to flexure load

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