Study on compressive, tensile and bond properties of used tire rubber reinforced concrete.

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Bwalya, Theresa
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The University of Zambia
Concrete is one of the most widely used construction material in the world and the construction industry is looking for ways of making concrete using greener methods so as to reduce ecological effects on the environment that come as a result of large scale exploitation of natural aggregates. The construction industry is also in need of finding cost-effective materials to enhance the properties of concrete. Cement and aggregate, which are the major constituents in concrete production are the vital materials needed in the construction industry. This has inevitably led to a continuous and increasing exploitation of natural materials to produce the constituents for concrete production. The result has been the depletion of virgin raw materials and increased effects of environmental degradation. Parallel to the need for the utilization of the natural resources emerges a growing demand to protect the environment and preserve natural resources such as the aggregates and stone for cement production, by use of alternative materials such as recycled or waste materials. In this research, a study was carried out on the use of recycled rubber tyres as a partial replacement for coarse aggregates in concrete production. Recycled waste tyre rubber is a promising material in the construction industry due to its reduced weight, elasticity, energy absorption, sound and heat insulating properties. However, literature suggests that there is a significant loss in the strength of rubberized concrete with increasing tyre content. Further, workability and bond properties have been reported to reduce as well. Therefore, it is necessary to lower or control this loss of strength and other parameters in concrete in the replacement process of natural aggregates. This research aimed at studying the compressive, tensile and bond properties of used tyre rubber reinforced concrete. The research also aimed at establishing whether the use of rubber reinforced concrete (rubberized concrete) is technically and economically viable in Zambia. Rubber modified concrete was compared to normal concrete produced from natural coarse aggregates and Portland cement. The research involved literature review, laboratory testing on natural raw materials and used rubber as aggregates (to determine their properties and suitability for use in concrete), concrete mix design, concrete trial mixes, and tests on both wet and hardened concrete. Test results from laboratory experiments enabled determination of mechanical, physical and durability properties, as well as establishment of the extent of substitution of normal aggregates with waste rubber as aggregate in concrete production. Three classes of concrete, C15, C20 and C25 were produced by substitution of selected percentages of aggrgates by treated chopped waste tire rubber. The chopped rubber, whose surfaces were first roughened by use a wire brush, was later soaked in clean water and then left to dry completely in the sun. This was done to increase the inter-phase bonding between the rubber particles and cement. The percentage replacement of coarse aggregates was 5, 15 and 25 per cent. The size of the chopped rubber aggregates varied from 20 mm to 19 mm. Slump, permeability and bulk density tests were conducted on fresh concrete mixes for both the normal and treated rubber modified concrete. Similarly, compressive strength, tensile splitting strength, bond test and durability against acid attack tests were conducted on hardened concrete. The research established that rubber modified concrete compares favourably with standard concrete, with up to 15 per cent replacement of coarse aggregate. At 15 per cent replacement, only 0.1 per cent loss of strength was established. There was observed reduction in properties with 25 per cent replacement. Rubber modified concrete performed better by gradual cracking at elevated temperatures. There is potential for rubber modified concrete products in Zambia which in turn mitigates adverse impacts resulting from over exploitation of natural aggregates and disposal of used rubber tires.
Thesis of Master of Engineering in Structural Engineering.