Browsing by Author "Oosthuizen, Jandré Daniel"

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    3D printing of eco-friendly concrete incorporating recycled plastic waste (RESIN8) as fine aggregate
    (Stellenbosch : Stellenbosch University, 2022-12) Oosthuizen, Jandré Daniel; Babafemi, Adewumi John; Walls, Richard Shaun; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH BSTRACTS: Plastic waste is a massive environmental issue worldwide which cannot be solved in a simple manner. Sand being a natural resource is limited in nature in contrast to the abundance of waste plastics in our environment. This study, therefore, investigates the suitability of creating an eco-friendly 3D printable concrete where recycled plastic waste, in the form of Resin8, is incorporated by replacing different percentages of fine aggregates. Replacement values of 5%, 10% and 15% of natural sand by volume are investigated, which are further characterized by varying Resin8 particle sizes. Particle sizes of Resin8 included are sub-5 mm, sub-1 mm and a combination of the two by mixing them by equal proportions (50/50). The concrete incorporating recycled plastic waste (Resin8) was compared to, and tested against a reference concrete mix which is the standard 3DPC mix at Stellenbosch University. Samples of each concrete mix were also mould cast into 160 x 40 x 40 mm prisms from the same concrete mix that were used for printing to investigate the effect the printing process had on the mechanical properties of the concrete. The rheology, slump flow (workability), buildability, air content and density are some of the fresh properties that were investigated. The mechanical properties of the different concrete mixes were investigated by means of flexural (4-point bending) and compression tests. Due to the anisotropic nature of 3DPC, the printed samples were tested in two different directions; D1 and D3. Porosity analysis by means of Computed Tomography (CT) scans were done on printed and cast samples of the reference mix as well as all sub-1 mm Resin8 printed samples to compare and investigate the effect of Resin8 on the microstructure of the printed concrete. Scanning Electron Microscopy (SEM) analysis was conducted on sub-5 mm and sub-1 mm Resin8 particles used in this study, as well as on the 3D printed samples of the reference mix and all replacement percentages of the combination Resin8 mixes after 28 days. All mixes containing Resin8 performed adequately for use in 3DPC based on characterisation of its fresh properties. It was observed that mixes containing Resin8 were more flowable, which has been validated by an increase in slump flow value when compared to the reference mix, while the buildability was negatively affected by the increased flowability. A lower density was obtained as the percentage of Resin8 replacement increased as expected due to the lower relative density of Resin8 compared to sand. Both the flexural and compressive strength decreased as the Resin8 replacement increased. However, an increase in interlayer bond strength was observed in all Resin8 mixes compared to the reference mix, which could possibly be as a result of excess pore water at the interlayer region due to the hydrophobic nature of plastics. The printing process had little effect on the performance of the 3DPC mixes based on similar flexural and compressive strength results achieved for orientation D3 and the mould cast samples, while orientation D1 yielded the best results. Considering the results obtained in this research, the addition of Resin8 into 3D printable concrete is a feasible option and could potentially lead to great reductions of waste plastics in our natural environment even for low replacement volumes.