Experimental study on mechanical behavior of steel fiber recycled concrete under cyclic compression
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摘要: 为研究钢纤维再生混凝土在地震荷载作用下的力学行为,考虑了再生粗骨料取代率、钢纤维体积分数和加载速率3个变化参数,设计了52个圆柱体试件进行单轴循环受压试验。试验观察了钢纤维再生混凝土的破坏形态,获取了应力-应变全曲线及峰值应力、峰值应变、塑性应变等重要指标,深入分析了不同变化参数对其力学性能指标的影响规律。结果表明:循环荷载作用下钢纤维再生混凝土主要发生斜向劈裂破坏,随着钢纤维体积分数的增加,试件表面主裂缝宽度明显减小;钢纤维的掺入提高了再生混凝土的峰值应变和残余强度,但峰值应力有所下降;钢纤维体积分数为1.0vol%时再生混凝土峰值应力降低最小为5.9%,峰值应变增幅最大为15.9%,改性效果最好;采用了幂函数对归一化塑性应变与卸载点应变的关系进行了拟合,效果良好。最后,提出了钢纤维再生混凝土在循环受压作用下的应力-应变本构关系计算式。Abstract: In order to study the mechanics behavior of steel fiber recycled concrete under seismic load, 52 cylindri-cal specimens were designed for uniaxial cyclic compression test, three variation parameters including recycled coarse aggregate replacement rate, steel fiber volume fraction and loading rate were considered in the test. The failure modes of steel fiber recycled concrete were observed, and the stress-strain curve, peak stress, peak strain and plastic strain and other important indexes were obtained. The influence of different parameters on mechanical properties was deeply analyzed. The experimental results show that the steel fiber recycled concrete mainly occurs oblique splitting failure under cyclic loading. With the increase of steel fiber volume fraction, the width of main cracks on the specimens surface decreases obviously. The addition of steel fiber can enhance the specimens’ peak strain and the residual strength while reduce the specimens’ peak stress. When the volume fraction of steel fiber is 1.0vol%, the peak stress of recycled concrete decreases by 5.9% and the peak strain increases by 15.9%, the modified effect is the best. The relationship of the standardized plastic strain and the unloading point strain was fitted using the power function. Finally, the calculation of the stress-strain constitutive relationship of the steel fiber recycled concrete under the uniaxial cyclic compression was proposed.
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表 1 粗骨料的物理性能
Table 1. Properties of coarse aggregates
Aggregate Apparent density/(kg·m−3) Bulk density/(kg·m−3) Water absorption/% Crushing index/% Size/mm NA 2704 1499 0.43 17.2 5-20 RA 2296 1321 5.40 25.6 5-20 Notes: NA—Natural coarse aggregate; RA—Recycled coarse aggregate. 表 2 钢纤维再生混凝土(SF/RAC)试件设计参数
Table 2. Design parameters of steel fiber recycled aggregate concrete (SF/RAC) specimens
Specimen VSF/vol% r/wt% v/(mm·s−1) 0%SF/RAC(0%)-0.005 0.0 0 0.005 1.0%SF/RAC(0%)-0.005 1.0 0 0.005 1.0%SF/RAC(30%)-0.005 1.0 30 0.005 1.0%SF/RAC(50%)-0.005 1.0 50 0.005 1.0%SF/RAC(70%)-0.005 1.0 70 0.005 0%SF/RAC(100%)-0.005 0.0 100 0.005 0%SF/RAC(100%)-0.002 0.0 100 0.002 0.5%SF/RAC(100%)-0.005 0.5 100 0.005 0.5%SF/RAC(100%)-0.002 0.5 100 0.002 1.0%SF/RAC(100%)-0.005 1.0 100 0.005 1.0%SF/RAC(100%)-0.002 1.0 100 0.002 1.5%SF/RAC(100%)-0.005 1.5 100 0.005 1.5%SF/RAC(100%)-0.002 1.5 100 0.002 Notes: r—Replacement rate of recycled aggregate; VSF—Steel fiber volume fraction; v—Loading rate. 表 3 再生混凝土配合比及强度
Table 3. Mix proportion and strength of recycled aggregate concrete
r/wt% Cement/(kg·m−3) Water/(kg·m−3) Sand/(kg·m−3) NA/(kg·m−3) RA/(kg·m−3) Additional water/(kg·m−3) fcu/MPa 0 500 215 542 1153.0 0.0 0.0 45.1 30 500 215 542 807.1 345.9 7.5 43.8 50 500 215 542 576.5 576.5 12.5 38.3 70 500 215 542 345.9 807.1 17.5 35.5 100 500 215 542 0.0 1153.0 25.0 38.2 Note: fcu—Cube compressive strength. -
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