1 STRUCTURAL BEHAVIOUR OF BEAM WITH HDPE PLASTIC BALLS SUBJECTED TO FLEXURE LOAD Noridah Mohamad 1 , W.I.Goh 2* , A.A.A. Samad 3 , A. Lockman 4 , Josef Hadipramana 5 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