Experimental Study On The Compressive And Fracture Behaviors Of PP Fibers Reinforced RAC After Exposure To Elevated Temperatures

In recent years, the quick urbanization in mainland China has led to increasing amount of the construction waste resulting from new constructions and demolition of old buildings; among the construction waste, about 40% is waste and/or old concrete. The conventional disposal method of the construction waste is landfilling, which not only occupies the land for urbanization but also leads to potential environmental problems. Recycled concrete aggregates, produced by recycling of the wasted or old concrete, can be used to fully or partially replace the nature aggregate in concrete and produce the recycled aggregate concrete (RAC). The use of RAC has important merit in terms of sustainable development of cities and environmental protection, as recycling the waste/old concrete only reduces the landfill but also saves the natural resources for producing natural aggregates. It is well established that polypropylene fibers (PP fibers) can be used to enhance the behavior of concrete by not only increasing its toughness in ambient temperature but also improving its spalling-resistance in high temperatures. Against the above background, this MSc research program investigated the compressive and fracture behavior of PP fibers reinforced RAC (with nature aggregates being fully replaced) after exposure to high temperatures. The research reported in this thesis include:1) High temperatures (200℃、400℃、600℃) exposure treatments were carried out for 60 concrete cylinders (diameter x height=150 mm x 300mm) and 60 notched small beams (width x height x length= 100mm x 100 mm x 515 mm). Surface changes, including color changes, spalling, cracking, were observed and/or measured, and mass loss was of each specimens was also measured. The test results showed that: apparent color changes were observed on the surfaces of specimens after exposure to higher temperature; higher exposure temperature usually leads to larger maximum crack width and mass loss.2) Axial compression tests were carried for the cylinders after exposure to high temperatures. During the tests, effects of exposure temperatures and amount of added PP fibers were investigated. The test results showed that although higher exposure temperature leads to increased deformation capacity, its decreases both the modulus of elasticity and cylinder compressive strength, and reduces the energy dissipation capacity (in terms of toughness) as well. However, the effects of amount of PP fibers on the compressive behavior of RAC cylinders are insignificant.3) Three-point bending tests were carried out for the small notched beams after exposure to high temperatures during which the effects of exposures temperature and the amount of PP fibers were investigated. The test results showed that although the inclusion of PP fiber significantly enhances the fracture behavior (fracture energy and toughness), it has marginal effect on the fracture behavior of notched beams after exposure to high temperatures (no less than 200℃).