Masters Degrees (Civil Engineering)

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Browsing Masters Degrees (Civil Engineering) by Author "Ajayi, Babatunde Luke"

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    Mechanical properties of eco-friendly one-part metakaolin-based geopolymer concrete with Recycled Glass and Plastic (RESIN8) aggregates
    (Stellenbosch : Stellenbosch University, 2023-11) Ajayi, Babatunde Luke; Babafemi, Adewumi John; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering.
    ENGLISH ABSTRACT: The high demand for concrete in the construction industry is directly proportional to the demand for Portland cement (PC), which is the binding agent in concrete. However, PC production leads to the emission of its equivalent amount of carbon dioxide (CO2), resulting in global warming. Consequently, a one-part "just add water" geopolymer binder is developed, which is a potential sustainable binder that could substitute PC. Therefore, this study investigates and reports the mechanical performance, microstructural properties, and cost analysis of a one-part metakaolin-based geopolymer concrete (GPC) produced with anhydrous sodium silicate, sodium hydroxide, and calcium hydroxide as alkali reagents. The GPC materials were pretreated and investigated to assess their physical properties (such as water absorption, particle gradation, specific gravity, and moisture content of the aggregates) and the chemical composition and morphology of the precursors. The optimum GPC mix design was obtained using the Taguchi experimental design approach, and the materials were dry-mixed before water was added. Further, the natural sand was substituted by fine waste aggregate (FWG) and RESIN8 (recycled plastic waste containing Resins 1–7), respectively, at a 5% and 10% replacement level. The influence of the recycled aggregates on the fresh and hardened properties of the composite was investigated and reported. Furthermore, the effects of different curing methods, such as climate-controlled curing (CC), water-curing (WC), and ambient-curing (AC) conditions, were investigated on the compressive strength. The samples tested for splitting tensile and flexural strength were subjected to AC conditions. Adding 5% and 10% of FWG and RESIN8 as fine aggregate in concrete enhances its workability. However, the compressive strength of samples with 5% and 10% RESIN8 is reduced by 15.1% and 19% for CC, 15.7% and 24.1% for AC, and 14.7% and 22% for WC, respectively, compared to their respective control GPC samples after 28 days of curing. On the other hand, the addition of 5% FWG improved the performance of the matrices by 8.9%, 3.5%, and 5.3% for CC, AC, and WC, respectively. After 28 days of curing, the strength of CC sample was increased by 13.6% due to the addition of 10% FWG. In contrast, the strength of AC and WC samples decreased by 0.7% and 1.7%, respectively, when compared to the control GPC samples. The compressive strength of AC samples shows a 10.9% improvement, whereas WC samples show a 16.3% improvement compared to the 28-day CC GPC samples. Further, the compressive strength of CC GPC declined after 28 days of curing; hence, the choice of curing condition greatly influences the performance of GPC. The enhanced strength of the AC and WC samples can be attributed to the presence of water within the concrete matrix, which allows for a complete geopolymerisation reaction. In contrast, the CC sample only underwent hydration due to the consistent curing temperature of 24 °C. The inclusion of 5% and 10% RESIN8 led to a 60.6% and 78% reduction, respectively, in the elastic modulus (E-mod) of GPC, while 5% and 10% FWG inclusion led to a 21.2% and 30.3% reduction in the E-mod of 28-day AC GPC, respectively. Using 5% and 10% FWG reduced the cost of GPC by 0.13% and 0.27%, respectively, while 5% and 10% RESIN8 increased the cost by 0.07% and 0.13%, respectively. The increased cost of RESIN8 containing GPC is due to the high cost of producing RESIN8. Conclusively, structural GPC is obtained, and 5% RESIN8 content and up to 10% FWG content have the potential to substitute natural sand in an environmentally friendly one-part metakaolin-based structural GPC. In contrast, 10% RESIN8 could be used for a non-structural concrete component. The use of RESIN8 and FWG in GPC possesses economic benefits and is a viable solution to environmental pollution, protection of aquatic lives and preservation of natural aggregates.