Effects of macro fibers on crack permeability evolution of concrete under loading
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摘要: 为研究荷载作用下结构型钢纤维和结构型聚丙烯纤维对混凝土裂缝渗透率演化的影响,通过劈拉试验引入混凝土裂缝,同时利用真空渗水试验装置对不同裂缝宽度下混凝土裂缝渗透率进行实时测量和分析。借助激光扫描仪对混凝土裂缝表面形态进行信息采集和形态重构。对比分析了结构型钢纤维、结构型聚丙烯纤维及混杂纤维(包括结构型钢纤维和结构型聚丙烯纤维)对混凝土裂缝渗透率及裂缝表面形态的影响。研究表明:结构型纤维可通过增大裂缝表面粗糙程度降低混凝土裂缝渗透率,且随着纤维掺量的增高,混凝土裂缝渗透率随之减小。对比单掺纤维混凝土,混杂纤维混凝土具有更粗糙的裂缝表面,且展现出更显著的裂缝抗渗性能;随着裂缝的扩展,混凝土裂缝渗透率更接近于泊肃叶渗流模型;相比于泊肃叶渗流模型修正系数ξ,本文所用渗透率参数α更适合量化结构型纤维对混凝土裂缝渗透率的影响。Abstract: In order to study the effects of macro fibers on the crack permeability evolution of concrete under loading, the splitting test was adopted to generate cracks on the concrete specimens. The crack permeability of different crack widths was measured in real time using the vacuum permeability test. The laser scanning equipment was adopted for the measurement of information and the reconstruction of the topography of crack surface. The effects of macro steel fiber, macro polypropylene fiber and hybrid fiber(including macro polypropylene fiber and macro steel fiber) on the crack permeability of concrete and the topography of crack surface were analyzed and compared. The results show that the macro fibers increase the crack surface roughness of concrete and indirectly decrease the crack permeability of concrete. With the increasing of fiber content, the crack permeability decreases. Compared to mono fiber reinforcement, the crack surface of hybrid fiber reinforced concrete is rough and the crack permeability of hybrid fiber reinforced concrete is small. With the increase of crack width, the crack permeability is closer to the value predicted by the Poiseuille flow model. Compared to modified factor ξ of Poiseuille flow model, parameter α of permeability is suitable for quantifying the effect of macro fibers on the crack permeability of concrete.
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Key words:
- macro fiber /
- crack permeability /
- crack surface topography /
- Poiseuille flow model /
- roughness number
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表 1 混凝土基准配比
Table 1. Basic mix proportion of concrete
kg·m−3 Cement Fly ash Fine aggregate Coarse aggregate Water Superplasticizer 390 155 822 848 272.5 5.5 表 2 结构型SF和结构型PP的性能参数
Table 2. Properties of macro SF and macro PP
Type Length/mm Diameter/mm Aspect ratio Tensile strength/MPa E-modulus/GPa Number/(pieces·kg−1) Macro SF 35 0.54 65 1 345 200.0 14 500 Macro PP 30 0.67 45 490 3.9 96 000 表 3 结构型SF和结构型PP掺量
Table 3. Contents of macro SF and macro PP
Type Macro SF Macro PP NC — — SF20/NC 20 kg/m3 (0.25vol%) — SF40/NC 40 kg/m3 (0.50vol%) — SF60/NC 60 kg/m3 (0.75vol%) — PP6.9/NC — 6.9 kg/m3 (0.75vol%) SF40-PP2.3/NC 40 kg/m3 (0.50vol%) 2.3 kg/m3 (0.25vol%) 表 4 普通混凝土(NC)、结构型钢纤维增强混凝土(SF/NC)、结构型聚丙烯纤维增强混凝土(PP/NC)和混杂纤维增强混凝土(SF-PP/NC)的DCOD与Afeff的拟合曲线参数的对比
Table 4. Comparison of fitted parameter between DCOD and Afeff of normal concrete(NC), macro steel fiber reinforced concrete(SF/NC), macro polypropylene fiber reinforced concrete(PP/NC) and hybrid fiber reinforced concrete(SF-PP/NC)
NC SF20/NC SF40/NC SF60/NC PP6.9/NC SF40-PP2.3/NC 0.02906 (R2=0.99) 0.03256 (R2=0.99) 0.03551(R2=0.95) 0.04039 (R2 =0.98) 0.03016 (R2=0.96) 0.04237 (R2=0.97) Note: R2—Coefficient of determination. 表 5 NC、SF/NC、PP/NC和SF-PP/NC拟合曲线的参数
Table 5. Fitted parameters of curves of NC, SF/NC, PP/NC and SF-PP/NC
Parameter β Fitted parameter α NC SF20/NC SF40/NC SF60/NC PP6.9/NC SF40-PP2.3/NC 1.541 171 465.3(Cv=6.1%) 66 963.0(Cv=8.9%) 18 477.5(Cv=5.4%) 1 942.1(Cv=7.6%) 10 020.3(Cv=3.8%) 1 431.0(Cv=5.1%) Note: Cv—Coefficient of variation. 表 6 NC、SF/NC、PP/NC和SF-PP/NC裂缝粗糙度
Table 6. Crack roughness number of NC, SF/NC, PP/NC and SF-PP/NC
NC SF20/NC SF40/NC SF60/NC PP6.9/NC SF40-PP2.3/NC 1.133 (Cv=1.9%) 1.214 (Cv=3.6%) 1.299 (Cv=6.9%) 1.430 (Cv=4.7%) 1.304(Cv=3.7%) 1.480(Cv=4.1%) -
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