干湿循环-硫酸盐侵蚀对钢纤维SCC弯曲性能的影响研究

Study on effect of sulfate attack on bending properties of steel fiber reinforced SCC

通过四点弯曲梁试验,研究了钢纤维体积分数(Vf)和30次干湿循环-硫酸盐侵蚀对钢纤维SCC荷载-挠度曲线(F-δ曲线)和特征参数的影响及作用机理。研究表明,随着Vf增加,F-δ曲线的饱满度增加,荷载软化阶段拐点的荷载和挠度明显提高。循环侵蚀前后钢纤维SCC的峰值挠度随Vf增加而增加,侵蚀后峰值挠度明显降低;Vf为1.00%时,侵蚀前后较基准SCC-0分别提高118%和58%,侵蚀后降低25%。侵蚀前SCC的等效弯曲强度fe随Vf增加而提高,侵蚀后则呈升高后降低的趋势,Vf为0.75%达到最高,均明显高于基准SCC-0,说明钢纤维有效改善了SCC的弯曲韧性;Vf不大于0.75%时,侵蚀后SCC的fe略有提高。侵蚀前后SCC断面SEM图片显示,未侵蚀SCC结构致密,经30次干湿循环-硫酸盐侵蚀后局部区域生成大量密集交错的针状AFt晶体束,部分区域可见疏松和多裂纹结构,说明侵蚀作用改变了SCC的水化产物和孔结构。

The effects of volume fraction(Vf) and 30 times of dry-wet cycle sulfate attacks on the SCC load-deflection curve(F-δ curve) and characteristic parameters of steel fibers were studied by a four-point bending beam test. The results show that with increasing of Vf, the fullness of the F-δ curve increases, and the load and deflection of the inflection point in the load softening stage increase significantly. The peak deflection of steel fiber reinforced SCC increases with the increase of Vfbefore and after cyclic attack, and decreases obviously after attack. When Vfis 1.00%, compared with SCC-0 before and after attack, the peak deflection increases by 118% and 58% respectively, and it decreases by 25% after attack. The bending toughness feof SCC increases with the increase of Vfbefore attack, but it first increases and then decreases after attack. When Vfis 0.75%, fereaches the maximum. They are all significantly higher than feof SCC-0, which indicates that steel fiber improves the bending toughness of SCC effectively. When Vfis no less than 0.75%, feincreases slightly after attack. SEM images of SCC sections before and after sulfate attack show that the structure of uneroded SCC is dense. After 30 times of dry-wet cycle sulfate attacks, a large number of dense and staggered acicular AFt crystal beams are staggering in local regions, and loose, porous, and multi-crack structures are visible in some regions, which indicates that sulfate attack changes the hydration products and pore structure of SCC.