Hama, Mohammed Fadhil
(2024)
Assessing the viability of Tenera oil palm shells as fine and coarse aggregates in structural lightweight concrete: microstructure and mechanical properties.
PhD thesis, University of Nottingham.
Abstract
Oil palm shells (OPS), a significant waste product of the oil palm industry, have raised environmental concerns due to their abundance and disposal challenges. Researchers have explored the potential use of OPS as coarse aggregates in structural lightweight concrete (SLWC) to address these issues. However, most studies lack specific OPS variety information, although indications by the thickness and accompanying figures point to the prevalent use of Dura OPS. The emergence of Tenera, a hybrid oil palm variety with thinner OPS, has significant implications, as it offers a 57% reduction in OPS thickness and a 30% increase in palm oil production compared to Dura OPS. Over 90% of oil palm farmers in Malaysia have already switched to the Tenera fruit, suggesting that the Dura variety may be phased out in the future.
Concrete science acknowledges that changes to aggregate properties, such as size or thickness, can impact a concrete's mechanical property. Therefore, the primary focus of this study was to assess the mechanical properties of Tenera OPS when used individually as coarse and fine aggregates in SLWC, comparing them to normal weight concrete (NWC) of similar grade. Distinct mix designs and superplasticizers were employed, with a comprehensive analysis of density, permeable voids, and water absorption over time. Mechanical properties, including compressive strength, flexural tensile strength, modulus of elasticity, and drying shrinkage, were evaluated throughout a 365-day period in both cured and air-cured conditions. Microstructural analysis and ultrasonic pulse velocity testing were also performed.
A key finding is that the use of Tenera OPS as coarse aggregates in OPS concrete (coarse OPSC) results in a notable reduction in compressive strength compared to Dura OPS under similar mix designs. However, Tenera OPS exhibits more promising outcomes when employed as fine-sized aggregates in concrete (fine OPSC). Microstructural analysis reveals fewer void spaces in fine OPSC, attributed to the swelling and shrinking characteristics of OPS when exposed to moisture and drying. The favourable shape of fine-sized OPS contributes to better performance and reduced cement consumption. By utilizing OPS in a saturated surface dry (SSD) state, both coarse and fine OPS in concrete facilitate internal curing. In terms of mix designs, fine OPSC demands 263% less cement content to achieve equivalent 28-day compressive strength compared to coarse OPSC, and only 14% more cement content than NWC, which showcases potential economic and environmental advantages. Despite its higher coarse aggregate content, the density of fine OPSC meets lightweight concrete (LWC) requirements and exhibits lower permeable voids and water absorption compared to coarse OPSC. This suggests enhanced durability. Fine OPSC also demonstrates early strength development superior to both NWC and coarse OPSC and maintains superior strength at 365 days. In contrast, coarse OPSC displays the lowest flexural tensile strength in cured conditions but excels in air-cured conditions, indicating susceptibility to moist environments, which is beneficial for continued cement hydration. Unexpectedly, the deterioration of coarse OPS, likely due to white-rot fungi, affects specific mechanical properties when exposed to curing regimes, a phenomenon not observed in fine OPSC. Furthermore, fine OPSC exhibits comparable dynamic and static modulus of elasticity (MOE) values to NWC, while coarse OPSC exhibits significantly lower MOE values. Drying shrinkage values for fine OPSC are similar to or slightly lower than NWC, whereas coarse OPSC displays significantly higher drying shrinkage values, almost three times that of NWC and fine OPSC. While drying shrinkage almost ceases after 365 days for NWC and fine OPSC, it continues at a significantly higher rate for coarse OPSC.
This study offers critical insights and recommendations for future research, including strategies to mitigate OPS swelling and shrinking effects in concrete, refining mix designs, exploring additives to reduce cement content, examining performance under various environmental conditions, and conducting extended duration testing to further advance the utilization of OPS in sustainable construction practices.
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