Flexural properties and microstructure of recycled carbon fiber concrete with different morphologies
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摘要: 将回收碳纤维(RCF)掺入混凝土制备绿色环保材料是实现碳纤维增强复合材料固废回收利用的有效方式。为探究RCF对混凝土材料弯曲性能的影响,将三种RCF按不同掺量与长度掺入混凝土中,通过四点弯曲试验,分析了回收碳纤维混凝土(RCFC)破坏形态、荷载-挠度曲线和弯曲强度的变化规律;提出了新的初裂点确定方法并进行了弯曲韧性评价,结合SEM从微观层面解释内在原因;基于MIP测得的孔隙率提出了新的弯曲强度预测公式。结果表明:RCF可改善试件破坏形式,提升RCFC弯曲强度和韧性,弯曲强度最高提升38.67%,弯曲韧性指标I20最高提升70.14%;不同形态的RCFC试件弯曲强度、弯曲韧性指数、等效弯曲强度及弯曲韧性比的影响规律并不相同,这主要和RCF表观形貌有关,从弯曲韧性角度来看掺入1.5%长度12mm的RCF-A时性能最佳。本文研究结论和提出的计算方法可为RCFC的性能提升及推广应用提供参考。Abstract: Green materials can be prepared by incorporating recycled carbon fibers (RCF) into concrete, which is an effective way to realize the recycling of carbon fiber reinforced composite solid waste. In order to investigate the effect of RCF on the flexural properties of concrete, RCF from three different manufacturers were incorporated into concrete at different contents and lengths. Four-point bending tests were carried out to analyze the failure modes, load-deflection curves and flexural strength of recycled carbon fiber reinforced concrete (RCFC). A new method for determining the initial cracking point was proposed, and the flexural toughness was evaluated. The intrinsic causes were explained at the microscopic level in combination with SEM. A new bending strength prediction formula was proposed based on the porosity measured by MIP. The results show that RCF can improve the failure mode and improve the flexural strength and toughness, with a maximum increase of 38.67% in flexural strength and 70.14% in flexural toughness index I20. The effects of different forms of RCFC specimens on the flexural strength, flexural toughness index, equivalent flexural strength and flexural toughness ratio are not the same, which is mainly related to the apparent morphology of RCF. From the perspective of flexural toughness, the best performance is achieved when 1.5 wt% RCF-A with a length of 12 mm is incorporated. The research conclusions and calculation methods can provide reference for the performance enhancement and application of RCFC.
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Key words:
- recycled carbon fibers /
- flexural toughness /
- microstructure /
- porosity /
- flexural strength prediction
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表 1 回收碳纤维性能参数
Table 1. Properties of RCFs
Fiber Length/
mmRecycling
methodAdhesive
Yes or NoDiameter/μm Density/
(g·cm−3)Tensile
strength/MPaTensile
modulus/GPaCarbon
content/%RCF-A 6/12/18 Direct cutting Yes 5.83 1.78 3536 230 95.0 RCF-B 6/12/18 Heat treatment No 7.28 1.80 3474 230 91.3 RCF-C 6/12/18 Direct cutting Yes 7.28 1.79 2866 230 92.8 表 2 试件编号及配合比
Table 2. Number and mix proportion of specimens
Sample No. RCF parameter Sample No. RCF parameter Type Content/wt% Length/mm Type Content/wt% Length/mm NC — — — RCF-B0.5%-L12 B 0.5 12 RCF-A0.5%-L6 A 0.5 6 RCF-B1.0%-L12 B 1 12 RCF-A0.5%-L12 A 0.5 12 RCF-B1.5%-L12 B 1.5 12 RCF-A0.5%-L18 A 0.5 18 RCF-B1.5%-L6 B 1.5 6 RCF-A1.0%-L6 A 1.0 6 RCF-B1.5%-L18 B 1.5 18 RCF-A1.0%-L12 A 1.0 12 RCF-D0.5%-L12 C 0.5 12 RCF-A1.0%-L18 A 1.0 18 RCF-C1.0%-L12 C 1 12 RCF-A1.5%-L6 A 1.5 6 RCF-C1.5%-L12 C 1.5 12 RCF-A1.5%-L12 A 1.5 12 RCF-C1.5%-L6 C 1.5 6 RCF-A1.5%-L18 A 1.5 18 RCF-C1.5%-L18 C 1.5 18 表 3 参数拟合结果及RCFC弯曲强度预测情况
Table 3. Parameter fitting results and flexural strength prediction of RCFC
Parameter fitting results $ k $ $ \alpha \tau $ $ \beta $ $ \gamma $ 1.3078 84.7983 0.5816 0.9273 Measured and predicted values of bending strength No. Porosity/% Measured value/MPa Predicted value /MPa RCF-A1.5%- L 6 12.67 6.30 6.27 RCF-A1.5%-L12 12.26 6.26 6.32 RCF-A0.5%-L18 10.85 6.92 6.92 RCF-A1.0%-L18 12.38 6.35 6.35 RCF-A1.5%-L18 13.09 6.40 6.37 -
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