Investigation of Mechanical properties of Ultra High Performance Fibre Reinforced Concrete with efficient cement and mineral admixtures uses Nima Mohammadian Tabrizi nima.mohammadian@cv.iut.ac.ir October,2020 Department of Civil Engineering Isfahan University of Technology, Isfahan 84156-83111, Iran Degree: M.Sc. Language: Farsi Supervisor: Davood Mostofinejad and Mohammad Reza Eftekhar dmostofi@cc.iut.ac.ir eft@cc.iut.ac.ir Ultra High-performance concrete is a new concrete with fine and homogeneous ingredient that has high compressive strength and extraordinary durability against aggressive and destructive environmental factors. Unlike the very high compressive strength of high performance concrete, the behavior of this concrete is very brittle during failure. In order to solve this problem and increase the ductility of uhpfrc, adding fibers to this concrete is common. Environmentally polluting materials such as high cement are commonly used to produce uhpfrc. In general, The sector of building materials is the third-largest CO2 emitting industrial sector world-wide and cement production represent 7% of the total greenhouse gas emissions. For this reason, in this study, to reduce the amount of cement used, from three levels of cement substitutes (microsilica + slag, microsilica + limestone powder + quartz powder and microsilica + slag + limestone powder + quartz powder) and to increase ductility, from Three types of synthetic fibers (steel, barchip and polypropylene) and the composition of these fibers have been used. In order to investigate the mechanical properties in this research, compressive strength and four-point bending tests have been used. Also, to achieve the desired compressive strength, wet and combined treatments were used. The obtained results show that compressive strength above 150 MPa was achieved by using combined treatment on all levels of cement substitutes. Also, except steel fibers, which increased the compressive strength compared to non-fibres samples; The use of barchip fibers and polypropylene reduced the compressive strength. In the bending test, all levels of the fibers used increased the flexural strength and ductility compared to the non fiber samples. In terms of ductility steel fiber and its hybrid composition with other fibers than other fiber levels. The results of the residual strength and endurance indices also prove that all levels of fiber have increased these indices, among which in this case the barchip fiber and the hybrid combination of macro fibers have provided closer result to steel fibers. Also, the use of combined treatment in bending test in reduction of flexural strength and ductility compared to wet treatment. Among all levels of cement replacement, the third level of cement replacement, the simultaneous use of microsilica, slag, limestone powder, and quartz powder, results between the other two different levels of cement replacement. according to the significant reduction of cement in this project and the replacement of about 50% of cement with slag and limestone powder, in terms of economic and environmental issues, the selection of this design is the most optimal design. Key Words: Ultra High Performance Concrete; Cement replacement materials; Synthetic Fibre; Curing; Mechanical Properties