Analysis of Oil Palm Shell Concrete-A Review
Many researches have been conducted on to use oil palm shell (OPS) as the light weight material in last three decades. It is an agricultural waste normally generated from palm oil industry. This industry is normally situated in Malaysia, Indonesia, Thailand, and some other countries. There are many products being made from OPS. The use of OPS as lightweight aggregate in making concrete mix is the main project of many companies in different countries including Malaysia that was first introduced by Abdullah in 1984. Malaysia playing an important role in manufacturing of different oil palm products as it gives out 51% of palm oil production and exports of many products to other countries. Due to a large number of plantations of Palm trees, OPS waste is generated as lignocelluloses in large quantity (Yep et al., 2014)..
Many solid wastes are harmful to the surrounding environment; OPS waste is also one of these harmful elements for the environment. Research studies are going on to use such wastes as OPS, POFA and palm oil clinker in other products. These studies provided a decrease in the dangerous factor created by these materials for appropriate controlling measures (Yep et al., 2014).
The high water content used by OPS might be dangerous while using polyvinyl alcohol (PVL) on OPS reduced the water usage up to 4% as compared to uncoated one that used up to 25% that could be a good concern to take into consideration. Application of PVL provides increased durability to OPSC while preparing OPS aggregates. Yew et al., 2014, studied the effect of temperature on oil palm shell (OPS) on coarse aggregates that were found to be the best component for high strength light weight concrete (HSLWC). When oil palm shell (OPS) was heated to a temperature between 60 0C and 150 0C for the period of about half an hour/ or about 1 hour, they observed a reduction in the density of OPS within the range of HSLWC by adding a freshly heated mixture of coarse aggregates. They found that working capability of oil palm shell concrete (OPSC) could increase by raising temperature, and it is associated with the heating time duration of mixture. The figure1shows the surface characteristic of OPS with and without heat treatment and figure 2 presented the behavior of OPSC associated with temperature. In order to achieve good or maximum strength of OPS, the mixture must be heated for about 28 or 90 days that give strength up to 49 and 52 Mpa. Similarly, by applying high velocity materials like UPV (Ultra Sonic Pulse Velocity) the strength or working capability could be achieved within 3 days of time. They determined average elasticity modulus for OPS is to be 15.9 GPa, which is a higher quantity as compared to the values mentioned earlier.
Figure 1: Surface characteristics of oil palm shell aggregate: with (a) and without (b) heat treatment (Yew et al., 2014).
Figure 2: Temperature &Duration of heat on OPS VS Density. (Yew et. al., 2014)
Many experiments have been performed by using water reducers and pozzolans and the overall strength of HSLWAC can be obtained between 34 and 69MPa.Water to the cement ratio in HSLWAC is less than 0.45 and air density of less than 2000 kg/m3. There are many theories that showed the hardened density and compressive strength of OPSC could decrease the weight of concrete mix within the range of 1690-1910 kg/m3 and 14-17 MPa which is a good way of cost saving when it is reduced up to 17-20%. Using OPS as coarse aggregate is very useful in density viewpoint as there is a reduction in the density up to 30% is achieved in the OPSC. (Mo et al., 2014; Yep et al., 2014)
For the improvement of mechanical and ductility aspect of concrete, hybridization of steel-polypropylene is required. Yap et al., 2014 conducted research to evaluate the effect of steel, polypropylene (PP) and steel-PP hybrid fibers in the context of the compressive strength, tensile strength, ductility and flexural toughness of oil palm shell fiber reinforced concrete (OPSFRC). They also constituted a study related to oil palm shell concrete. The experimentation was carried out on 0.9% of steel and 0.1% of polypropylene fibers. They found an increase in the strength of OPS about 50 MPa and it is the highest amount noted in the history of OPSC. PP fiber quantity must be kept in limit, otherwise, if it goes beyond 0.1%, conditions could go deteriorated and low quantity fibers of polypropylene (PP) with value less than 0.1% can increase the crack bridging effect. However, the splitting tensile and flexural strengths of OPS increased up to 83% and 34% respectively. The use of 1% PP fibers can affect the tensile and compressive strengths of OPS. Flexural deflection and toughness of OPSC can be increased by the addition of fibers while there is a definite evidence of steel fiber on the toughness and crack flexural deflection of OPSC. Figure 3 and 4 presenting load-deflection characteristics of palm oil shells (Yap et al., 2014).
Figure 3: Load-Deflection behavior of un-crushed palm oil shells
Figure 4: Load VS Deflection characteristic of crushed oil palm shells (Yep et al., 2014)
Moreover, all mixes gain high compressive strength in the beginning. Adding silica fumes increases the cohesiveness of concrete and decreases the induction of micro cracks. Using crushed OPS increases compression and tensile strength of OPS and OPSFRC. The addition of fibers could increase the mechanical properties of concrete mix including compressive, tensile and flexural strength. The highest splitting tensile and flexural strength were found 5.81 and 7.49 MPa. Splitting tensile and flexural strength can be increased up to 83% and 34% by adding mixtures like 0.9% steel fiber and 0.1% PP hybrid fiber (Yep et al., 2014)
According to study result of Yep et al., 2014, advanced heat treatment and heat treating techniques, could create a decrease in the strength of OPS. So, proper heat treatments must be used to utilize full strength of OPS. They concluded that increased temperature up to 150 C at the time rate of 1 hour, the working aspect of OPS can be increased up to 20%. Increase in temperature and time duration decreased density when air-dry and oven-dry density for OPSC is kept between 1973–1988 kg/m 3and 1928–1948 kg/m 3.In addition, they pointed out that applying more heat, OPS- HSLWC with 28 days, compressive strength of about 49 MPa can be produced easily.
The use of OPS as light weight creates a good amount of OPSC with a decrease in the density of about 15-33% compared to the density of a normal weight concrete (NWC) 2400 kg/m3. This reduction in density simply increases the strength to density ratio of concrete allowing the decrease in fabrication cost reduces transportation and gives good flexibility to the design of OPS. Most of the lightweight concrete is lower in tensile strength. Similarly, the higher brittleness compared to the NWC of the same strength. Shafigh et al., 2011, took several steps in this matter by doing lot of experiments and increasing the strength of OPSC with the variation of size of OPS and made a good content cement of 500 kg/m3, but this increase could be cut down if brittleness is increased up to 6-10. The brittleness method could become dangerous if not controlled in an effective way which can easily harm the surrounding environment and can be dangerous for the environment (Mo et al., 2014).
According to Mo et al., 2014, addition of a specified quantity of fiber steel increased the tensile capacity of fiber reinforced concrete due to its non-ductility. De-bonding and pulling out of fibers from FRC required lot of heat which increases toughness and ductility of concrete. Many houses are built using these OPS concretes. A low aggregate impact value (AIV) implies high resistance. OPS could also be used in crash batteries and road blocks due to AIV. They examined physicals properties of OPS including bulk density, specific gravity and water absorption Research showed that the ductility of reinforced OPSC beam was about 2 times higher than the corresponding reinforced NWC beam. The AIV and the OPS were found 2 times lower than the crushed granite aggregate. The splitting tensile test is an indirect and easier method to find out the concrete tensile strength. The determination of concrete tensile strength is required to get the information on the maximum tensile load to sustain cracking. In the study, it was found that tensile/fiber greatly improved the splitting tensile strength of the concrete. The addition of 0.5% to 1.0% of steel fiber volume enhanced the splitting tensile strength up to 93% to 173%.
Figure 5: Relationship B/W Compressive Strength and Tensile Stress
Figure 6: Load-Deflection Curve of SFOPSC under Point Bending (Mo et al., 2014)
The homogeneity of the concrete could not be affected by the addition of steel fibers due to the presence of UPV value. The UPV values more than 4.00 km/s for the mixes with steel fiber could provide quality concrete. Moreover, fracture energy, fracture toughness and characteristic length consisting of SFOPSC increased due to the addition of steel fibers.
In short, application of heat treatment could produce a life friendly and good amount of OPSLWC. The required effectiveness of OPSC can be achieved by adjusting accurate temperature and the period within which the mixture is heated in order to gain the desired results.
References
Mo K.H., Yap, K.K.Q., Alengaram, J.U, & Jumaat M.Z, 2014. ‘The effects of steel fibers on the enhancement of flexural & compressive toughness and fracture characteristics of oil palm shell concrete’, Construction and Building Materials, Vol.55, pp.20-28.
Shafigh P., Mahmud, H. Jumaat M.Z.2011 ‘Effect of steel fiber on the mechanical properties of oil palm shell lightweight concrete’ Jr. of Material Des,Vol.32(7),pp.3926-3932.
Yap, S.P., Bu C.H., Alengaram, U.J., Mo K.H., & Jumaat, M.Z. 3014. ‘Flexural toughness characteristics of steel–polypropylene hybrid fiber-reinforced oil palm shell concrete’. Materials and Design, Vol.57, pp.652-659.
Yew, M.K, Mahmud, B.H., Ang B.C., & Yew M.C. 2014., ‘Effects of heat treatment on oil palm shell coarse-aggregates for high strength lightweight concrete’ Materials and Design, Vol.54, pp. 702-707.
