| With the development of construction and building materials,especially various kinds of admixtures,preparation technology of steel fiber reinforced concrete(SFRC)has developed rapidly,and realized the extension of working performance from plasticity,fluidity and large fluidity to self-compacting SFRC.Due to the different fiber distribution in SFRC of various working performance,the fiber strengthening and toughening mechanism based on the assumption of three-dimensional chaotic distribution patterns of fibers in plastic SFRCS has significant limitations,and can not be directly extended to fluid,large fluid and self-compacting SFRC.Therefore,the changes of fiber distribution and mechanical properties caused by different working performance of SFRC have become the theoretical and technical bottlenecks to be solved urgently in the high efficiency upgrading of SFRC products.In this paper,seven groups of grade CF40 SFRC specimens were designed and manufactured based on the direct design method of mix proportion with SFRC proposed by our research team.The static flexural properties and flexural fatigue properties were tested,and the distribution of steel fibers on the damaged section of the specimen was statistically analyzed.Firstly,with steel fiber content of 0.8%,four kinds of SFRC specimens with working performance were designed: Plastic SFRC(slump is 10 mm～90 mm),flow SFRC(slump is 100mm～150 mm),large flow SFRC(slump is not less than 160 mm)and self-compacting SFRC(slump is not less than 240 mm,slump flow is not less than 550 mm).The influence of working performance on static load flexural property and flexural fatigue resistance were studied.Then,based on the self-compacting SFRC,four steel fiber volume fractions of 0%,0.4%,0.8% and1.2% were designed to study the influence of steel fiber content on static load flexural properties and flexural fatigue resistance.The specific research contents and conclusions are as follows.(1)150 mm×150 mm×550 mm beam specimen was used for bending performance test and fiber statistic of damaged section.The results show that the SFRC with different performance have different characteristics of flexural load-deflection curves.The peak load of selfcompacting and high-fluidity SFRC are larger and more full,and the bending toughness is significantly improved.The steel fiber content has a significant influence on the flexural loaddeflection curve after SFRC crack.The peak load not only increases with the increase of the fiber content,but also the number of fibers in the direction of the principal stress is an important factor affecting the flexural strength.The initial crack strength is positively correlated with the matrix,while the flexural strength,flexural toughness ratio and equivalent flexural strength are positively correlated with the content of steel fiber.(2)The beam type specimen of 150 mm×150 mm×550 mm was used,and the initial crack strength was taken as the initial load of the flexural fatigue test.The flexural fatigue test after SFRC crack was carried out.The results show that the flexural fatigue life of SFRC specimens after crack decreases with the decrease of working performance,which is attributed to the difference of fiber distribution morphology in SFRCS with different working performance.In self-compacting concrete,the flexural fatigue life of SFRC specimens after crack increases with the increase of fiber content.The fatigue strain curve of SFRC after crack presents the common characteristics of inverted S-shape with three stages of internal damage formation,stable expansion and instability development.Based on this,the fatigue life of SFRC specimens is analyzed and predicted.Weibull distribution theory model was used to check the fatigue life results of SFRC specimens.The results showed that the fatigue life of post-crack flexural specimens in this test complied with the two-parameter Weibull distribution model.(3)Based on the results of post-crack flexural fatigue test of SFRC,the damage variation rules of SFRC under different stress cycle ratios were obtained by the evolution model of bending fatigue damage of concrete from the point of damage mechanics,and the model was used to fit the fatigue test results,and the SFRC bending fatigue damage coefficient was obtained.The relationship between the stress level and the number of fibers on the failure surface and the damage coefficient was established.The regression curve obtained from the fatigue damage equation is in good agreement with the fatigue damage evolution curve,and the damage evolution law of SFRC conforms to the continuum damage model. |
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