Strength and deformation characteristics of recycled polyethylene fibre reinforced concrete
The main objective of this thesis is focused on the influence of recycled polyethylene fibres on the strength and deformation characteristics of a normal ordinary C30 concrete by both (i) adding to the concrete mix these above said recycled polyethylene fibres and (ii) maintaining the C30 plain concrete without the fibres for control purposes. Compressive strength tests were performed on twelve 150mm concrete cubes. The concrete cubes comprised a C30 plain concrete cube as control and C30 concrete cubes with fibre additions at volume fractions of 0.25%, 0.50%, and 1.0%. Flexural strength tests were also performed on twelve 100mm×100mm×300mm concrete prisms. The third parameter considered was the post crack toughness and the crack propagation and cracking behavior of normal strength concrete with 0.25%, 0.50%, and 1.0% polyethylene fibre addition and a reference concrete without the polyethylene fibre. This was done using twelve 150mm×200mm×2500mm reinforced concrete beams. The next parameter of interest was the water absorption and by extension the durability of concrete specimen containing 0.25%, 0.50%, and 1.0% polyethylene fibre and that of a reference concrete. Normal strength concrete cubes of dimensions 150mm were used in this case. The final parameter investigated was the surface abrasion resistance of the plain and polyethylene fibre reinforced concrete specimen. Twelve 100mm cubes were used for this investigation. All tests were conducted on 28 days old concrete but the compressive strength was determined at both 7 days and 28 days. The test results showed a significant reduction in compressive strength of polyethylene fibre reinforced concrete as the fibre content increased from 0.25% to 1.0%. Flexural tensile strength on the other hand increased by 2.5% for 0.25% fibre concrete compared to the reference concrete and by 14% and 27% respectively for 0.50% and 1.0% fibre concrete compared to the reference concrete. The control specimens possess a higher energy absorption capacity at I5, I10, and I30 compared to the 0.25% fibre concretes and the 0.5% fibre concretes. The 1.0% fibre concretes however showed a higher energy absorption capacity compared to the control specimens. Measurements of crack widths showed that the crack openings in the fibre reinforced beams were visibly smaller than the crack openings in the beams without fibres. Also the crack spacing in the fibre reinforced concretes beams were closer than the widely spaced crack pattern of the concrete beams without fibres. The 100mm concrete cubes containing 0.25% polyethylene fibres showed little surface wear compared to the plain concrete cubes. The 38% reduction in surface wear obtained is significant, tangible and worthwhile. The concrete cubes containing 0.5% and 1.0% polyethylene fibres however showed significant surface wear just like the plain concrete. Finally, the results also showed a reduction in water absorption of concrete as a result of addition of polyethylene fibres to concrete. The test results showed a reduction in water absorption of polyethylene fibre reinforced concrete from 9% to 20% as the fibre content increased from 0.25% to 1.0% respectively compared to the plain control concrete.
A thesis submitted to the Department of Civil Engineering, Kwame Nkrumah University of Science and Technology in partial fulfillment of the requirements for the degree of Master of Philosophy in Structural Engineering, 2016