| Based on the design requirement of segment with diameter of 10m of Wangjing tunnel, a steel fiber reinforced concrete segment was studied using a new type of steel fiber to partly or totaly substitute steel rebar. And then, the early strength of steel fiber reinforced concrete segment which has lowest compressive strength of 15MPa in 8 hours was prepared using sulphoaluminate cement in Portland cement. The residual flexural tensile strength and toughness, the effects of stray current and chloride ion erosion, key durability of complex service conditions, bending test of full size segment of SFRC been systematically investigated.Firstly, in this paper, the residual flexural tensile strength and toughness of SFRC with various fiber volume fractionswere studied to provide data for the design of the steel fiber reinforced concrete segment. The results show that the residual flexural tensile strength of steel fiber reinforced concrete of SFRC55P12-40 series is larger than the SFRC55P12-30 series. The residual flexural tensile strength increased by 20.6%,22.8%,17.6%,47.6% at the CMOD=0.5mm,1.5mm,2.5mm,3.5mm, respectively. The flexural toughness index, equivalent bending strength and flexural toughness ratio of steel fiber reinforced concrete of SFRC55P12-40 series are larger than SFRC55P1230 series. The crack resistance effect can be enhanced with adding steel fiber, especially the more steel fiber content, the more obvious effect.Compared with the traditional reinforced concrete segment, this study found that steel fiber reinforced concrete segment of ultra shallow section has obviously advantages, save up to 38.9%. The cost of steel fiber reinforced concrete segment of shallow buried section can save up to 4.7%. At the same time, the crack width of shallow buried segment decreased from 0.3mm to 0.14mm, reducing 53%; Deep buried segment crack width decreased from 0.24mm to 0.11mm, the crack width is reduced by about 50% in the design of increasing steel fiber and reducing the amount of steel reinforcement. The durability of segment can be significantly improved by reducing the crack width.Secondly, the conduct resistance, chloride diffusion coefficient, frost resistance, permeability resistance, high temperature resistance and drying shrinkage performance of the steel fiber reinforced concrete are researched in this study. Test results show that:(1) The resistivity of the steel fiber concrete is constant with the specimen's length of SFRC, while the resistivity was decreased with the increasing of the length of the specimen of steel rebar reinforced concrete. Because the steel fiber reinforced concrete segment has a higher conduct resistance than the reinforced concrete segment resistance value in reality, it is more difficult to conduct and has lower risk and rate of corrosion than SRRC. The resistance for stray current is more effective in SFRC. (2) The chloride ion diffusion coefficient of SFRC55P12-30 series and SFRC55P12-40 series of steel fiber concrete are smaller than average level, which is 2×10-12m2/s. it is satisfy for the design index 4×10-12m2/s and chloride ion diffusion coefficient with the volume fraction of steel fibers increase and reduce. (3) For SFRC55P12-30 series and SFRC55P12-40 series of steel fiber concrete, the relative dynamic elastic modulus are maintained more than 80% after 600 times of freeze-thaw cycle, the mass loss is less than 1%, and the frost resistance grade is higher than F600, and higher than the design requirements of the F300 frost resistance grade, exhibit good frost resistance. (4) For SFRC55P12-30 series and SFRC55P12-40 series steel fiber reinforced concrete, the anti-permeability grade is higher than P30, and higher than the design requirements of the P12 anti permeability grade. (5) For SFRC55P12-30 series and SFRC55P12-40 series of steel fiber concrete, the fireproof limit of the segment at is not less than 4h, the compressive strength loss rate is not higher than 40%, steel fiber concrete still has enough bearing capacity after heating at 600? for 4h. (6) the dry shrinkage of SFRC55P12-30 and SFRC55P12-40 series of steel fiber concrete at 28d is not exceed 200 mu epsilon, far less than the limit of the project requirement of 400 mu epsilon. All above, the steel fiber reinforced concrete has strong stray current corrosion resistance, chloride resistance, high temperature properties and durability, which can satisfy the requirements of the design of expressway tunnel segment.In addition, in order to make the steel fiber reinforced concrete segment to demould at early age, that is attained the strength of 15MPa in 6-8h at room temperature without steam curing, the early strength steel fiber concrete is further developed Based on the ordinary steel fiber reinforced concrete, using rapid hardening sulphoaluminate cement to replace Portland cement, the early strength steel fiber reinforced concrete with compressive strength of 15.9MPa in 8h and compressive strength of 19.5MPa in 10h is prepared. The residual flexural tensile strength, chloride ion diffusion coefficient and dry shrinkage property of the steam curing early strength steel fiber reinforced concrete is tested. The results show that the residual flexural tensile strength of early strength concrete with 40kg/m3 of steel fiber is similar to the ordinary steel fiber reinforced concrete with 30kg/m3 of steel fiber. The shrinkage of SAC-30 series is 231?? at 30d, the shrinkage of SAC-40 series is 189?? at 30d. The average chloride ion migration coefficient of SAC-30 series is 2.07×10-12 m2/s. The average chloride immigration coefficient of SAC-40 series is 2.89×10-12 m2/s. Durability properties are satisfying the requirements of design of the Wangjing tunnel.Finally, through the study of bending resistance of steel fiber reinforced concrete and full size segment composite with steel fiber, the cracking load, failure load and maximum crack width are obtained. The test results show that SFRC55P12-30 series of steel fiber reinforced concrete segment have the minimum cracking load and failure load minimum, are 11.3t and 17.6t respectively. SFRC55P12-30 series of composite reinforced segment cracking load and failure load, respectively 17.0t and 41.4t. SFRC55P12-40 series of segment cracking load and failure load are respectively 14.7t and 21.8t. Compared to the SFRC55P12-30 series and SFRC55P12-40 series of steel fiber concrete segment cracking load and SFRC55P12-30 with composite reinforced series of steel fiber concrete segment, and there is no obvious decline. So that the steel fiber reinforced concrete segment or steel fiber composite reinforced concrete segment instead of ordinary reinforced concrete segment for high iron shield tunnel segment is not only feasible, and more safety, durability and economy, and has significant technical, economic and environmental significance. |
PDF Full Text Request