Experimental research on the mechanical properties of fiber-reinforced autoclaved aerated concrete under cyclic loading
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摘要: 为研究纤维增强蒸压加气混凝土(FAAC)循环受压力学行为，共设计11组棱柱体试件进行单调及循环受压试验，分析纤维种类(玄武岩纤维，BF；碳纤维，CF)和纤维掺量对FAAC破坏形态、应力-应变全曲线特征、塑性应变、刚度退化率、应力退化率等力学性能指标的影响规律。研究结果表明：循环荷载作用下FAAC的破坏模式主要为剪切破坏和竖向劈裂破坏，随纤维掺量增加，试件破坏模式由剪切破坏转向竖向劈裂破坏；纤维掺量为0.4%时，FAAC的峰值应力增幅最大，BF/AAC的单调加载曲线和循环加载曲线峰值应力分别增加了24.29%、29.16%，CF/AAC的单调加载曲线和循环加载曲线峰值应力则分别增加了31.45%、37.81%；纤维掺量为0.5%时，FAAC的峰值应变增幅最大，BF/AAC的单调加载曲线和循环加载曲线峰值应变分别增加了28.12%、28.77%，CF/AAC的单调加载曲线和循环加载曲线峰值应变则分别增加了37.17%、41.50%；两种纤维均小幅度增加了AAC的累积塑性应变，但纤维掺量与卸载刚度及应力退化率之间未表现出明显的规律。基于试验结果，采用幂函数对FAAC标准化塑性应变与卸载点之间的关系进行拟合；提出应力退化率及加、卸载曲线双折线简化模型；最后，建立了循环荷载作用下FAAC的应力-应变曲线计算方程。Abstract: In order to investigate the compressive mechanical properties of fiber-reinforced autoclaved aerated concrete (FAAC) under cyclic loading, a total of 11 sets of prismatic specimens were designed for uniaxial monotonic and cyclic compression tests. The effects of fiber types (basalt fiber, BF, carbon fiber, CF) and fiber content on the mechanical performance indicators of FAAC such as failure mode, stress-strain curve characteristics, plastic strain, stiffness degradation rate, and stress degradation rate, were analyzed. The research results indicate that the failure mode of FAAC under cyclic loading contains oblique shear failure and vertical splitting failure, and with the fiber content increasing, the failure mode of FAAC turns from shear failure to splitting failure. When the fiber content is 0.4%, the peak stresses of FAAC reach their maximum values, the peak stresses of BF/AAC under monotonic and cyclic loading increase 24.29% and 29.16%, respectively, while that of CF/AAC increase 31.45% and 37.81%, respectively. When the fiber content is 0.5%, the peak strains of FAAC reach their maximum values, the peak strains of BF/AAC under monotonic and cyclic loading increase 28.12% and 28.77%, respectively, while that of CF/AAC increase 37.17% and 41.50%, respectively. Both BF and CF slightly improve the cumulative plastic strain of AAC, but there is no significant relationship between fiber content, unloading stiffness, and stress degradation rate. Based on the experimental results, a power function is used to fit the relationship between the standardized plastic stain and unloading strain. Simplified double line models for stress degradation rate, unloading and reloading curves are proposed. Finally, the stress-strain curve calculation equation for FAAC under cyclic loading is established.
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Key words:
- autoclaved aerated concrete /
- fiber /
- cyclic loading /
- stress-strain curve /
- plastic strain /
- calculation equation
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图 3 循环荷载作用下FAAC破坏过程
Figure 3. Failure process of FAAC under cyclic loading
$ {\varepsilon }_{\mathrm{c}} $, $ {\sigma }_{\mathrm{c}} $, and $ {\varepsilon }_{\mathrm{p}} $ are the peak strain, peak stress, and plastic strain of the curve, respectively; $ {\varepsilon }_{\mathrm{u}\mathrm{n}-1} $ and $ {\sigma }_{\mathrm{u}\mathrm{n}-1} $ are the unloading strain and unloading stress of the previous level unloading curve, respectively; $ {\varepsilon }_{\mathrm{u}\mathrm{n}} $ and $ {\sigma }_{\mathrm{u}\mathrm{n}} $ are the unloading strain and unloading stress of the next level unloading curve
图 5 循环荷载作用下FAAC最终的破坏现象
Figure 5. Final failure phenomenon of FAAC under cyclic loading
图 6 单调及循环荷载作用下FAAC应力-应变曲线
Figure 6. Stress-strain curves of fiber-reinforced AAC under monotonic and cyclic loading
图 10 单调荷载作用下FAAC的归一化应力-应变曲线
Figure 10. Normalized stress-strain curve of FAAC under monotonic loading
图 11 纤维掺量与单调加载曲线拟合参数之间的关系
Figure 11. Relationship between fiber content and fitting parameters of stress-strain curve under monotonic loading
图 12 卸载、再加载曲线简化模型
Figure 12. Simplified model for unloading and reloading curves
$ {\sigma }_{\mathrm{u}\mathrm{n},\mathrm{r}} $—Stress of the point on reloading curve whose strain is equal to that of unloading strain of previous unloading curve
图 13 FAAC试验曲线与简化计算方程对比图
Figure 13. Comparison between test curve and calculation equation
表 1 纤维基本物理力学性能
Table 1. Basic physical and mechanical properties of fiber
Fiber Density/(g·cm−3) Length/mm Diameter/μm Tensile strength/MPa Melt point/℃ Elastic modulus/GPa CF 1.75 3 7 4900 800-900 230 BF 2.63-2.65 3 7-15 3000-4800 1050 91-110 Notes: CF—Carbon fiber; BF—Basalt fiber. 
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表 2 试件配合比
Table 2. Mix proportion of AAC
Tailing sand/wt% Lime/ wt% Cement/wt% Gypsum/wt% Aluminum powder/wt% Water/solid materials 58.3 12.9 25.8 3 0.08 0.50
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表 3 试件参数
Table 3. Specimen design parameters of AAC
No. Fiber Fiber content/wt% No. Fiber Fiber content/wt% AAC - - AAC - - BF/AAC-0.1 BF 0.1% CF/AAC-0.1 CF 0.1% BF/AAC-0.2 0.2% CF/AAC-0.2 0.2% BF/AAC-0.3 0.3% CF/AAC-0.3 0.3% BF/AAC-0.4 0.4% CF/AAC-0.4 0.4% BF/AAC-0.5 0.5% CF/AAC-0.5 0.5% Notes: AAC—Autoclaved aerated concreter; BF/AAC-n—Basalt fiber reinforced autoclaved aerated concrete with fiber content of n%, n varies from 0.1 to 0.5; CF/AAC—Carbon fiber reinforced autoclaved aerated concrete with fiber content of n%, n varies from 0.1 to 0.5.
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表 4 单调及循环荷载作用下FAAC试件的峰值应力及峰值应变
Table 4. Peak stress and peak strain of FAAC under monotonic and cyclic loading
No. Monotonic loading Cyclic loading No. Monotonic loading Cyclic loading $ {\varepsilon }_{\mathrm{c}} $/×10−3 $ {\sigma }_{\mathrm{c}} $/MPa $ {\varepsilon }_{\mathrm{c}} $/×10−3 $ {\sigma }_{\mathrm{c}} $/MPa $ {\varepsilon }_{\mathrm{c}} $/×10−3 $ {\sigma }_{\mathrm{c}} $/MPa $ {\varepsilon }_{\mathrm{c}} $/×10−3 $ {\sigma }_{\mathrm{c}} $/MPa AAC 3.958 1.968 3.945 1.883 AAC 3.958 1.968 3.945 1.883 BF/AAC-0.1 4.268 2.056 4.293 2.015 CF/AAC-0.1 4.327 2.194 4.418 2.152 BF/AAC-0.2 4.385 2.178 4.477 2.170 CF/AAC-0.2 4.545 2.341 4.490 2.246 BF/AAC-0.3 4.773 2.310 4.840 2.347 CF/AAC-0.3 5.089 2.518 5.020 2.454 BF/AAC-0.4 4.805 2.446 4.831 2.432 CF/AAC-0.4 5.343 2.587 5.496 2.595 BF/AAC-0.5 5.071 2.357 5.080 2.282 CF/AAC-0.5 5.429 2.444 5.582 2.399 Notes: $ {\varepsilon }_{\mathrm{c}} $—Peak strain of the curve; $ {\sigma }_{\mathrm{c}} $—Peak stress of the curve.
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