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The Bricks from Recyclables team is dedicated to designing and constructing an eco-friendly concrete brick that incorporates plastic to tackle the issue of plastic waste in the environment. The sponsor, Samadhi Yoga Retreat, plans to use this innovative product as a building material on-site to recycle and repurpose plastic, thereby eliminating the impracticality of transporting plastic waste to a recycling center in the remote location.
The team conducted tests on four essential subsystems: shredder, mixer, mold, and brick. The shredder tests involved evaluating the shredder's capability and speed. The capability test demonstrated that the shredder could process both PET and HDPE plastic effectively into appropriate sizes, with HDPE producing slightly more of the targeted size. The speed test demonstrated that the shredder could process five bottles of both plastic types in under five minutes. These tests showed that the shredder adhered to the shredder functionality working criteria.
The mixer test evaluated whether the mixture could produce a visually uniform blend in less than five minutes. All mixtures created in the mixer successfully met the criteria. However, the team recommends using a larger mixer for producing full-size bricks.
The mold functionality test evaluated the effectiveness of the molds utilized to fabricate the coupons. The 3-D printed molds demonstrated excellent performance, with easy ejection of coupons and convenient cleaning and reusability. However, the melamine coupon mold proved less efficient due to being hand-manufactured and requiring the application of messy silicone for sealing. To accommodate the size limitations of the 3-D printers available to the team, the full-size mold comprises a combination of melamine and 3-D printed components. This test showed that the 3D printed mold adhered to the mold functionality working criteria.
The brick tests included a compression test to determine the optimum plastic-concrete formulation and a weather resistance test to assess the brick's water resistance. The compression test showed that pure Quikrete achieved a compressive strength of over 1900 psi for water ratios ranging from 7-7.5%. The team selected 7.5% water as it retained plastic particles more effectively. PET outperformed HDPE in compression tests. However, none of the coupons with plastic ratios ranging from 1 to 15 percent plastic on a mass basis, or 1.54 to 23.11 percent on a volume basis, met the 1900 psi requirement mandated by ASTM C90 . The team recommends longer curing times as a way to increase compressive strength.
The final phase of compression testing was anisotropic tests, which tested the bricks' performance in a more consistent orientation with how full-size bricks will be loaded. The results indicated that an increase in plastic particle size resulted in an increase in compressive strength. The rough surfaces of the coupons, caused by molds designed for testing in the other orientation, led to some of the lower fatigue stresses. This test demonstrated that modifying the mold's orientation could increase the compressive strength and potentially lead to a formulation that meets the 1900 psi requirement. The team recommends further research and testing on the anisotropic orientation.
The weather resistance test evaluated the water absorption capacity and the formation of salt deposits as the bricks/coupons dried. All specimens underwent both tests and successfully passed. To meet the requirements of the absorption test, the bricks/coupons needed to absorb less than 20% of their original weight. The full-size ASTM C90 bricks performed better, with a range of 6-7%, compared to the coupons, which had a range of 8.8-14.9%.
Mittleman, Miranda; Sarbah, Arvin; Scannell, Shane; and Sharpe, Joshua, "Final Project Report for Bricks from Recyclables" (2023). Engineering Senior Design Reports. 59.