Browsing by Author "Ibrahim, Kamoru Ademola"

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    Rheo-mechanical, hardened mechanical characterisation, and tensile creep of limestone calcined clay cement fibre-reinforced printed concrete (LC3-FRPC)
    (Stellenbosch : Stellenbosch University, 2023-10) Ibrahim, Kamoru Ademola; Babafemi, Adewumi John; Van Zijl, Gideon P. A. G.; Stellenbosch University. Faculty of Engineering. Dept. of Civil Engineering
    ENGLISH ABSTRACT: Concrete is a widely used and acceptable civil engineering construction material. It contributes significantly to infrastructural development and global economic growth. However, its major challenge is its vulnerability to environmental degradation, pollution, carbon emissions, and cracking, which have detrimental influence on the sustainability of its applications under high demand, low recycling rates, and loading. The scarcity of raw materials, caused by wastage, overuse, and environmental issues, threatens infrastructural development. Hence, research on an emerging technology named 3D printed concrete (3DPC) to reduce waste, but also time and cost associated with the construction of concrete infrastructure is imperative. 3DPC is an evolving construction method and has been proposed as an alternative and environmental-friendly construction method to traditional construction method. The high cement content required for the 3D extrusion process is being reduced by partial replacement with supplementary cementitious materials (SCMs) such as fly ash, slag, and silica fume. However, these SCMs are limited in volume and do not have global spread, implying an urgent need for alternatives, but also care for the longevity of infrastructure. Limestone calcined clay cement (LC3) is a suitable SCM for sustainable concrete because of its global availability and comparable early and later strength gain, as recommended by previous studies. When polypropylene fibres are added to the mix, control of plastic shrinkage cracks, increased toughness, and reduced brittleness of 3DPC can be achieved. The main goal of this study is to investigate the rheology, hardened mechanical properties, and tensile creep of fibre-reinforced 3DPC containing LC3 (LC3-FRPC) by quantifying its layer deformation, but also the orthogonal interlayer bond deformation at different stress levels under sustained loadings. To achieve the goal stated above, this research develops the material mix design satisfying 3DPC requirements for early strength and stiffness, shrinkage cracking resistance and mechanical properties, including interfacial bond. The rheology and hardened mechanical properties of LC3-FRPC were compared to that of the fly ash-based counterpart (FA-FRPC). The strategy for strengthening the interfacial bond of LC3-FRPC with effective microorganisms (EM), which enhances not only the bond strength but also improves mechanical capacities are presented. The mechanical responses were verified by microstructural analysis through scanning electron microscopy augmented by energy-dispersive X-ray spectroscopy and X-ray computed tomography to assess the hydration products of the blended binders and the self-healing action of LC3 and EM in FRPC. Then, the creep and shrinkage deformations in two orthogonal directions, and other parameters associated with creep responses, including creep fracture are also conducted experimentally on LC3-FRPC. The creep specimens were subjected to sustained stresses of 40, 60, and 80% of the direct tensile strength, and 40% of the flexural strength results obtained from the quasi-static tests. The results revealed that FRPC mixtures tested showed good rheological properties, with LC3-FRPC showing improved the workability, open time, and buildability by 1.7%, 15.4%, and 19%, respectively, compared to FA-FRPC. FA-FRPC outperformed LC3-FRPC in compression, tension, and flexure because of its lower water demand, but the bond strength between the interfacial layers is higher in LC3-FRPC than in FA-FRPC, with an increase of 8.1% for tension and 9.8% for flexure. EM-enhanced LC3-FRPC had significantly higher bond strengths than the reference LC3-FRPC in both direct tension (26.1%) and flexure (33.7%), thereby implying a lower level of anisotropy. The effects of the binders, particularly the LC3 and the EM on the strengths of FRPC and the macropores at the interfaces of printed concrete, improved the material by forming more calcite crystals. Finally, for the creep response under sustained loadings, none of the LC3-FRPC specimens fractured in tension and flexure. Instead, higher direct tensile and flexural strengths were recorded for the creep specimens after 225 days loaded at different stress levels.