Experimental Study On Mechanical Properties And Toughness Of Fiber-reinforced Geopolymer Concrete

Concrete is the most widely used structural material in bridge engineering,and cement is one of the main raw materials for concrete preparation.The manufacturing process of cement causes great environmental pollution and energy consumption,as well as produces a large amount of waste.Ordinary cement concrete has already been not in line with the development requirements in recent times.Many studies are looking for alternatives to ordinary cement concrete.Geopolymer concrete is a kind of environment-friendly building material that takes industrial waste materials such as fly ash or blast furnace slag as the gel material,with the preparation process of low pollution,low energy.It makes industrial waste materials recycling,and has high strength,high temperature resistance,good corrosion resistance and other advantages.It is one of the preferred building materials to replace ordinary cement concrete in the future.However,geopolymer concrete has some shortcomings similar to ordinary concrete,such as high brittleness,low bending tensile strength,poor crack resistance and low strain capacity,which is not favorable for the further popularization and application of this new green building material in bridge engineering.Therefore,in this thesis,fly ash-slag based geopolymer concrete was used as the base material.The steel fiber,the basalt fiber and the short polyethylene-based polypropylene fiber were selected as the reinforcement fiber,and they were used as the base fiber,respectively mixed with long polyethylene-based polypropylene fiber as the hybrid reinforcement fiber for experimental research,in order to keep the basic mechanical properties of geopolymer concrete unchanged or improved,and improve the toughness of the purpose.The main work and achievements of this thesis are as follows:(1)The mix ratio test of fly ash-slag based geopolymer concrete was carried out,which provides the basis for the following test.(2)The cubic compressive strength and splitting tensile strength of fiber-reinforced geopolymer concrete were tested.The variation rule of the compressive strength and splitting tensile strength of geopolymer concrete with single and mixed fibers of different fiber content as well as the optimal fiber content were revealed.The experimental results of each group were compared comprehensively,and the relationship between the compressive strength and the splitting tensile strength was analyzed.(3)According to SEM microscopic morphology analysis,steel fiber and polyethylene-based polypropylene fiber mainly expend energy through fiber extraction from the matrix,basalt fiber expends energy through fiber extraction and pull-off to improve the toughness of geopolymer concrete.Compared with the SEM images of fiber-reinforced concrete,the synergistic cooperation between fiber and geopolymer concrete matrix is better.(4)Four-point bending tests of fiber-reinforced geopolymer concrete were carried out.The variation law of flexural strength and flexural toughness of geopolymer concrete with single and mixed fibers of different fiber content were revealed,and the optimal content was discussed.Meanwhile,the test results of each group were compared comprehensively,and the load-deflection curves were analyzed..(5)Three-point bending tests on notched beams of fiber-reinforced geopolymer concrete with fiber were carried out.The change rule of fracture toughness and fracture energy of geopolymer concrete with single and mixed fibers of different fiber content were revealed,and the optimal content was discussed.At the same time,the test results of each group were compared comprehensively,and the load-deflection curve and load-CMOD curve were analyzed.