| Recycled concrete aggregate can effectively solve the environmental pollution problem caused by waste concrete,and at the same time avoid the over extraction of natural resources.By adding steel fibers,the mechanical properties of recycled aggregate concrete could be significantly improved,which enables the potential wide applications in engineering industry.Recycled concrete aggregate shows significant dispersion in mechanical properties compared with the natural aggregate and thus the size effect of the concrete incorporated with the recycled aggregate may differ with the concrete with the natural aggregate.Therefore,this paper aims at investigating the influence of steel fiber content and recycled aggregate replacement ratio on the uniaxial compression performance and size effect of concrete,with the employment of experimental research,theoretical analysis and numerical simulation methods.The main work of the paper is as follows:(1)Uniaxial compression test was carried out on 36 recycled aggregate concrete cubes and 24 prisms in various specifications.The test results showed that the destruction mode of recycled aggregate concrete without steel fibers was similar to normal concrete,but with a stronger brittle destruction characteristic.The addition of steel fibers imparted plastic destruction characteristics to the recycled aggregate concrete.The compressive strength of the concrete with 100% recycled aggregate was14.6% lower than that of the control group;the peak strain was increased by 28.5%;and the elastic modulus was decreased by 25.5%.By adding steel fibers,the compressive strength of recycled aggregate concrete could be increased by up to 10%and the peak strain increased by 18.6% with barely any influence on elastic modulus.The size effect of the uniaxial compression performance of concrete showed an increasing trend with the increase of the replacement level of recycled aggregate and the increase of the steel fiber content.The size effect in terms of compressive strength,axial compressive strength and peak strain of 100% recycled aggregate concrete were1.4,1.44 and 2.19 times respectively of that of the normal concrete;and they were1.43,1.46 and 1.36 times respectively for the recycled aggregate concrete with additional 1% steel fibers.The size effect in terms of elastic modulus of steel fiber reinforced recycled aggregate concrete is comparatively weak.(2)The compressive strength data of the steel fiber reinforced recycled aggregate concrete were fitted and analyzed using the Bazant size effect theory and Carpinteri size effect theory.An empirical formula for calculating the parameters of the compressive strength scale law was proposed.Critical strength and critical dimensions of different specimens are calculated accordingly.(3)The mesoscopic analysis model of random aggregate in recycled concrete is established and the mechanical properties of corresponding phases are determined.Moreover,the size effect of recycled concrete in views of compressive strength is analyzed adopting the analysis model mentioned above.It is observed that i)the axial compressive strength of the prismatic recycled concrete with 100% recycled aggregate is about 15% lower than that of the normal concrete;ii)the size effect of the recycled aggregate concrete is obvious and the axial compression resistance of the specimen with 500 mm side length in cross section was about 77% of that of the concrete with 100 mm side length.Besides,the critical dimension and critical strength of the numerical specimen are calculated. |
