掺合料对纤维增强水泥基材料拉伸性能的影响

Effect of Admixtures on Tensile Behavior of Fiber Reinforced Cementitious Composites

为降低材料成本并探明掺合料对聚乙烯醇(PVA)纤维增强水泥基复合材料抗拉能力的改性效果,采用一定量的粉煤灰、硅灰和偏高龄土代替水泥,试验研究了改性前后水泥基复合材料的拉伸应变、开裂强度、极限强度以及裂缝发展规律,分析了各种掺合料对水泥基复合材料抗拉性能的影响机理.试验研究结果表明:用粉煤灰代替65.0%的水泥,材料的初始开裂强度和极限强度随着粉煤灰的掺入分别降低了25.5%和26.0%,但复合材料的变形能力提高了2倍;粉煤灰改善了复合材料的裂缝宽度和间距,使得多重开裂现象更易发生;用粉煤灰和硅灰分别代替50.0%和15.0%水泥,使得复合材料裂缝宽度略有减小,变形能力比单掺粉煤灰提高了7.6%;偏高岭土的掺入,使得材料具有更好的变形能力;在纤维体积掺量为2.0%的情况下,粉煤灰、硅灰、偏高岭土的复掺使得纤维增强水泥基复合材料的极限拉应变达到2.0%,极限强度达到3.99 MPa,材料在拉伸荷载作用下呈现出高延性和多裂缝开裂特性,材料自身对裂缝具有很强的可控性,其饱和状态最大裂缝宽度为175μm,平均裂缝宽度不超过115μm.

To reduce the material cost and understand the modification effects of admixtures on the tensile properties of polyvinyl alcohol fiber-reinforced engineered cementitious composites （PVA- ECCs）, PVA-ECCs were prepared with different mass percentages of silica fume （ SF）, fly ash （FA） and metakaolin （MK） for replacement of cement. Then, tensile tests were carried out to study the tensile properties of the PVA-ECCs before and after modification, including the ultimate tensile strain, the initial cracking load, the ultimate tensile strength, and the crack development. Furthermore, the influence mechanisms of the admixtures were discussed on the basis of the experiment. The resultsshow that the initial cracking load and the ultimate tensile strength of the composite modified by 65.0% of FA were decreased by 25.5% and 26.0% , respectively, but the deformation ability was twofold enhanced. In addition, fly ash improved the crack width and crack distance in the composite, causing the multiple cracking phenomenon happened more easily in the FA modified composite. For the composite admixed with 50.0% of FA and 15.0% of SF compound, the crack width decreased; however, the deformation ability was increased by 7.6% compared to the composite admixed with 65.0% of FA. When MK was incorporated into the composite, the modified materials had better deformation abilities. For the composites with the incorporation of FA, SF and MK and a moderate fiber volume fraction of 2.0% , an ultimate strain exceeding 2.0% as well as an ultimate strength of 3.99 MPa was achieved. In addition, the material exhibited a high ductility and multiple cracking characteristic. The cracks were controlled well by the material itself, in which the maximum crack width in saturation state was less than 175 μm and the average crack width was less than 115 μm.