纤维协同效应下超高性能混凝土的弯曲性能

Flexural Properties of Ultra-high Performance Concrete Under Fiber Synergistic Effect

为研究钢-聚丙烯粗纤维对超高性能混凝土(UHPC)的弯拉性能影响,采用四点弯曲试验,得到不同掺量(钢纤维与聚丙烯粗纤维掺入体积分数分别为0、0.5%、1.0%、1.5%)组合下的荷载-挠度曲线,从试件破坏形态、抗弯强度、弯曲韧性等方面进行阐述,并且利用单掺纤维拟合公式引出一个可行性较高的评价模型,并利用该模型对混杂纤维的协同效应进行分析,最后结合扫描电子显微镜(SEM)对混杂纤维UHPC微观结构进行观测。试验结果表明:钢-聚丙烯粗纤维的掺入显著提高了UHPC的抗弯强度,提高幅度为17.8%~101.2%;同时利用提出的模型发现混杂纤维的协同效应在总纤维掺入体积分数为1.5%~2.0%时呈现正协同效应,并在钢纤维与聚丙烯粗纤维掺入体积分数为1.0%时取得最好的正协同效应;另外,与不掺纤维的试件相比,钢纤维与聚丙烯粗纤维的加入分别使基体试件的初裂韧度提升了51.8%~98.2%与33.9%~48.2%,同时在钢纤维掺入体积分数为1.0%和聚丙烯粗纤维掺入体积分数为1.0%的搭配比例下,对UHPC弯曲韧性的改善效果最优,进一步验证了纤维协同效应评价模型;最后在微观层面揭示了纤维混杂产生的协同作用及混杂纤维增强增韧机理。

To study the effect of steel-polypropylene crude fiber on the bending and tensile properties of ultrahigh performance concrete(UHPC),a four-point bending test was conducted to obtain different volume contents(the content of steel fiber and polypropylene crude fiber being 0,0.5%,1.0%,and 1.5%).The load-deflection curve under the combination is described from the failure form,flexural strength,flexural toughness,etc.,of the specimen,and a model with high feasibility is derived from the fitting formula of the single-doped fiber to analyze the synergistic effect of the hybrid fiber.Finally,the microstructure of the hybrid fiber UHPC was observed and analyzed by scanning electron microscopy(SEM).The test results show that the incorporation of steelpolypropylene crude fiber significantly improves the flexural strength of UHPC,with an increase range of 17.8%to 101.2%.At the same time,using the proposed method,it is found that the synergistic effect of hybrid fibers showed a positive synergistic effect when the total fiber volume content is between 1.5%and 2.0%,and the best positive synergistic effect is obtained in S10P10.In addition,compared with the specimens without fiber,the initial crack toughness of matrix specimens increases by 51.8%to 98.2%and 33.9%to 48.2%respectively with the addition of steel fiber and polypropylene crude fiber.When the content of steel fiber is 1.0%and the volume content of polypropylene crude fiber is 1.0%,the improvement to the bending toughness of UHPC is the best,which further verifies the evaluation model of fiber synergy effect.Finally,the synergistic effect and the toughening mechanism of the hybrid fiber are revealed at the micro level.