| The rheological properties of the matrix in Steel Fiber Reinforced Concrete(SFRC)are an inherent factor in the working performance and fiber distribution changes of SFRC mixtures.This article is based on the existing mix proportions of plasticity,fluidity,high fluidity,and self compacting SFRC in the research group,and designs a mixture of paste and mortar with the same ratio to conduct experimental research on rheological properties,workability,and fiber distribution in the paste.The main research content and results are as follows:(1)Design and manufacture cement paste with different working performance,taking into account the influence of water cement ratio,water reducing agent type and dosage,and conducting rheological and flowability tests;Add a certain amount of steel fibers and make a center point pouring fiber paste circular cake specimen to study the distribution patterns of radial and normal fibers in different performance cement paste.The research results show that when the water cement ratio is 0.24,the corresponding yield stress within the range of fluidity120mm～350mm is 22.24Pa～1.78 Pa,and the plastic viscosity is 2.29 Pa·s ～0.51 Pa·s;When the water cement ratio is 0.3,the corresponding yield stress within the range of flowability from 100 mm to 350 mm is 4.13 Pa to 0.83 Pa,and the plastic viscosity is 0.63 Pa·s to 0.32 Pa·s;When the water cement ratio is 0.4,the corresponding yield stress within the range of fluidity175mm～350mm is 9.84Pa～0.4Pa,and the plastic viscosity is 0.85 Pa·s ～0.18 Pa·s;It can be concluded that the yield stress and plastic viscosity of the cement paste jointly affect the flowability of the paste,but the effect of yield stress on flowability is more significant than that of plastic viscosity.The flowability of cement paste with different water binder ratios increases at a similar rate as the yield stress decreases.(2)Design and manufacture cement mortar with different working performance,considering the effects of water cement ratio and water reducing agent dosage,and conduct rheological and flowability tests;Add a certain amount of steel fibers to make a central point pouring fiber mortar paste circular cake specimen,and study the distribution patterns of radial and normal fibers in different performance net paste.The research results indicate that within the scope of this experiment,the larger the amount of water reducing agent added,the better the workability of the mortar,and the smaller the rheological parameters.When the water cement ratio is 0.24,the yield stress corresponding to flowability in the range of100mm～350mm is 465.92Pa～7.95 Pa,and the plastic viscosity is 9.22 Pa·s ～7.66 Pa·s;When the water cement ratio is 0.3,the yield stress corresponding to the flowability in the range of100mm～350mm is 345.17 Pa～1.75 Pa,and the plastic viscosity is 5.51 Pa·s ～1.79 Pa·s;When the water cement ratio is 0.4,the yield stress corresponding to the flowability in the range of100mm～350mm is 248.46Pa～5.69 Pa,and the plastic viscosity is 2.77 Pa · s ～2.15 Pa · s.According to the results of the matrix paste and mortar tests,there is a good correlation between the working performance and rheological properties of the paste and mortar.The working performance of the mortar can be adjusted by testing the rheological properties of the paste.(3)A standard cube specimen was used to study the effect of mortar with different rheological properties on the settlement of a single fiber.The research results show that the yield stress in 0.24 water cement ratio mortar is 8.48Pa～21.42 Pa,and the plastic viscosity is within the range of 6.91 Pa·s ～7.66 Pa·s,and the fiber settlement phenomenon is observed.In the 0.3 water cement ratio mortar,the yield stress is 4.50Pa～37.75 Pa,and the plastic viscosity is within the range of 2.59 Pa·s ～3.29 Pa·s,and the fiber settlement phenomenon is observed.In the 0.4 water cement ratio mortar,the yield stress is 7.89Pa～26.85 Pa,and the plastic viscosity is within the range of 1.78 Pa·s ～2.06 Pa·s.Settlement phenomenon is observed in the fibers.From the experimental process,it can be seen that the smaller the rheological parameters,the smaller the effective lifting effect of the paste on the formation of fiber fibers.When the mix ratio is the same,the vertical fiber settlement changes more significantly than the horizontal fiber with the performance of the paste.(4)Make circular cake specimens,drill cores and slice them,and use manual statistical methods to study the distribution patterns of radial and normal fibers in different performance slurries and mortars.The research results indicate that the distribution rate of fibers along the gravity direction of the specimen is greatly influenced by the working performance,and its distribution uniformity mainly depends on the rheological parameters of the mixture.When the fluidity of the paste is 245 mm and the corresponding rheological parameters are 1.69 Pa and 0.48 Pa · s,the fiber distribution uniformity coefficient is the highest.The radial fiber distribution uniformity coefficient along the gravity direction is 0.40,and the normal fiber distribution uniformity coefficient is 0.38.When the fluidity of the mortar is 270 mm,the corresponding rheological parameters are 190.67 Pa and 4.57 Pa·s,and the fiber distribution uniformity coefficient is the highest.The radial fiber distribution uniformity coefficient along the gravity direction is 0.45,and the normal fiber distribution uniformity coefficient is 0.34.As the fluidity increases,the uniformity coefficient of fiber distribution decreases,indicating that low rheological parameters can lead to fiber settlement during pouring and molding processes.The uniformity coefficient of fiber distribution along the radial direction of the specimen decreases with the increase of fluidity,and the overall fluctuation amplitude is not significant.The uniformity coefficient of radial fiber distribution is greater than the uniformity coefficient of normal fiber distribution.. |
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