Use of waste and low energy materials for construction
Yalley, Peter Paa-Kofi
Considerable work has been done on the mechanical properties of coconut-fibre enhanced concrete. The primary test variables were the fibres weight fraction, and fibres aspect ratio. The addition of coconut-fibres significantly improved many of the engineering properties of concrete, notably torsion, toughness and tensile strength. The ability to resist cracking and spalling were also enhanced. However, the addition of fibres did not improve the compressive strength, as expected, due to difficulties in compaction which consequently lead in increase of voids. When coconut fibre was added to plain concrete, the torsional strength increased (by up to about 25%) as well as the energy-absorbing capacity, but there is an optimum weight fraction (0.5% by weight of cement) beyond which the torsional strength started to decrease again. Similar results were also obtained for different fibre aspect ratios, where again results showed there was an optimum aspect ratio (125). An increase in fibre weight fraction provided a consistent increase in ductility up to the optimum content (0.5%) with corresponding fibre aspect ratio of 125. The second part of this research, reports on the investigation on cement stabilised soil block. A local soil was stabilised chemically by cement. A better compressive strength at the dry state and after two hours of immersion in water was obtained with chemical stabilisation at cement content of 5%. Blocks stabilised with 5% cement content by weight of soil has a dry and wet compressive strength of 6.64 and 2.27MPa respectively, and dry density of 1910 kg/m3 at an optimal water content of 12% by weight of cement. The highly decreased compressive strength after two hours of immersion in water, even with higher cement content, indicated that appropriate building design that would prevent stabilised soil blocks from coming into direct contact with rainwater was important. A newly proposed concept of a plastic carton soil blocks as masonry units for low-cost environmentally friendly construction is proposed in the final part of the thesis. A test system was designed to perform rigorous and comprehensive measurements on seven types of soil block specimens encased in thermoplastic cartons. The cartons were similar to "ice cream tubs" of dimensions 165x60x120mm, thus making a building block/brick of reasonable handling size. Some of the test specimens also had soil mixed with palm or plastic fibres. Thermoplastic carton soil blocks without the addition of fibres as an enhancement were measured with a minimum compressive strength of 17.5MPa. Even so it should be noted that 17.5MPa is still a very reasonable strength and over half that of a typical concrete block. In the case of the fibre enhanced soil block, the compressive strength increased with increase in fibre content. With fibre addition of 1.5% (by weight), the compressive strength of the thermoplastic cartons increased by 28.5% and 38% respectively for palm and plastic fibres, over the plain thermoplastic carton soil block without fibres. For increase in fibres content from 0.75% to 1.5% (i.e. a doubling of fibre content) the compressive strength increased by only about 20% to 23%. Additionally, stiffness is also greatly improved. A finite element model was constructed for the thermoplastic carton soil block geometry and input files were generated for non-linear static analyses in MSC Patran. Very good agreement was achieved between the numerical predictions and experimentally measured results in both size and shape of the stress-strain graphs.
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