Experimental Study On Tensile And Compression Properties Of Multi-scale Polypropylene Fiber Roller Compacted Concrete

Roller compacted concrete(RCC)has low flexural strength,tensile strength and toughness,and is prone to cracks under complex external loads,which affects the safety and service life of Engineering structures.However,the crack resistance and toughness of RCC can be effectively improved by means of "Fiber Reinforcement Technology".In the past,the mechanical properties of RCC were improved by mixing fine polypropylene fiber(PPF)with steel fiber.However,steel fiber have some shortcomings,such as high cost,poor corrosion resistance in adverse environments.Crude PPF,also known as special-shaped plastic steel fiber,have comparable reinforcing and toughening effects with steel fiber.And PPF have low price and excellent corrosion resistance.In view of those,based on the multi-scale structural characteristics of cement-based composites,the multi-scale polypropylene fiber roller compacted concrete(MPFRCC)is obtained by mixing different scales of crude and fine PPF.The influence of different scales of PPF content and mixing ratio on the tensile and compression properties of RCC is studied by means of laboratory tests and theoretical analyses.The main research contents and results are as follows:(1)By changing the content and mixing ratio of three scales of PPF,one plain RCC and eight polypropylene fiber reinforced roller compacted concrete(PFRCC)test groups were designed,and the compression strength and splitting tensile strength of PFRCC cubes at different ages were tested.The results show that fine PPF can significantly improve the splitting tensile strength of concrete matrix before seven days of curing age,and crude PPF plays a major role after seven days of curing age.Furthermore,based on the maturity theory,the relationship between cube compression strength and time is obtained.(2)The effect of blending ratio of PPF on the tensile properties of RCC was studied by axial tension test.The results show that PPF has little influence on RCC before tensile failure,and the incorporation of crude PPF can significantly slow down the downward trend of the stress-strain curve under axial tension,and make the tensile failure of the axis present ductile characteristics.Based on the measured tensile stress-strain curves,the constitutive equations of RCC under axial tension are obtained.(3)The effects of PPF blending method on the compression properties of RCC were studied by axial compression stress-strain curve test,modulus of elasticity andPoisson’s ratio test.The results show that PPF has little effect on the deformation properties of RCC before failure,but has a significant effect on the improvement of its toughness.The toughness of each group of specimens was ranked from high to low according to the way of fiber incorporation as follows: multi-scale PPF > single blending crude PPF > blending of crude and fine PPF > single blending fine PPF > no fiber.Due to the mutual support and complementation of three PPF in MPFRCC,which show better toughness and ductility,showing a positive hybrid effect.According to the measured stress-strain curves,the constitutive equation of concrete under axial compression is obtained.(4)According to the mechanical properties of each group of PFRCC under axial tension and compression,a "Multi-scale Fiber Hybrid Effect Function" was proposed.Through fitting and analyses,it is obtained that: compared with the coarse and fine PPF blending,the multi-scale PPF blending method can significantly improve the tensile strength and compression toughness of RCC,but has limited effect on the improvement of compression strength and tensile toughness;the formula can intuitively reflect the influence of "fiber mixing effect" on the axial tension and compression properties of RCC,moreover,it is easy to predict the optimal blending ratio of fiber according to the test data,which has guiding significance for the application of hybrid PPF in practical engineering.