مقایسه ی ساختار های مواد بتن سبک با پلی اتیلن تصفیه شده و رس متراکم Comparison of material properties of lightweight concrete with recycled polyethylene and expanded clay aggregates

1. Introduction For the production of lightweight concrete various fillers with smaller density than a conventional gravel and crushed stone are used. Lightweight aggregates (LWA) differ in density, strength, water absorption, surface characteristics and shape. All these differences affect the mechanical and durability properties of the concrete. One of the problems in the production of lightweight concrete with porous LWA is that the rheological properties depend on sorption properties of such aggregates. Performed research of sorption properties of 14 expanded shale and expanded clay aggregates showed that 24h water absorption is from 6.0% to 30.5% [1]. If the aggregates are not pre-wetted, a lot of water can be lost through absorption during mixing and under the pressure of pumping concrete can lose workability. Meanwhile water absorption of most plastics is very small and these materials meet the requirements of density for production of lightweight concrete. The possible application of recycled plastic waste aggregates in concrete has been studied by many researchers [2,3]. State-of-the-art review in this area is presented by Siddigue [4]. It is stated that in Europe largest component of plastic waste is low density polyethylene (LDPE) at about 23% followed by 18.5% of polypropylene (PP), 17.3% of high density polyethylene (HDPE), 12.3% of polystyrene (PS/expanded PS), 10.7% polyvinyl chloride (PVC), 8.5% polyethylene terephtalate (PET) and 9.7% other types. About 40% of plastic waste is LDPE and HDPE, however most of the research is focused on use of polyethylene terephtalate (PET) waste [5] and low-density expanded polystyrene (EPS) beads [6]. Higher compressive strength lightweight concrete with EPS beads and cenospheres can be obtained using geopolymeric binder from fly ash, metakaoline, sodium hydrokside and sodium silicate solution. Geopolymeric binder materials applied with different aggregates, could result in low density concrete [7]. It was indicated that while the cenospheres has a tendency to absorb water almost as much as its own weight and conversely, EPS beads is hydrophobic and its water absorption is zero, water absorption of both concrete specimens is large and similar [7]. In order to increase cement mortar and plastic adhesion, surfaces of aggregates, produced from waste PET bottles and sand or ground blast furnace slag, were modified [8,9]. The use of polyethylene (PE) aggregates in concrete is not widely investigated. Ismail and AL-Hashmi [10] carried out a study on public plastic utilities which were made of 80% of polyethylene and 20% of polystyrene. Substituting 20% of sand by these waste resulted in significantly lower compressive strength in comparison with ordinary concrete. This could be explained by the decrease in adhesive strength between the surface of plastic waste and the cement paste. The present research focuses on investigation of the various shape of HDPE and LDPE plastic waste impact on the mechanical properties of concrete. The attained results are compared to the concrete with the same volumetric amount of expanded clay LWA. It is defined how the water absorption of the aggregates influence the water absorption of the concrete specimens.