纤维增强混凝土韧性及声发射特征分析

Toughness test and acoustic emission characteristics analysis of fiber reinforced concrete

针对地下开采所引发的建筑物开裂、破坏等问题,研制了具有较强抗变形能力的混凝土材料。对添加端钩形钢纤维、波浪形钢纤维、微丝镀铜钢纤维、仿钢纤维和丝状聚丙烯纤维5种不同纤维的纤维混凝土(FRC)进行抗压、劈裂、轴心抗压和四点弯曲试验,研究了FRC的抗压韧性评价指标和抗弯韧性评价指标变化规律。并通过声发射试验,对波浪纤维混凝土四点弯曲时裂缝的萌生和扩展进行监测,将声发射相关参数与混凝土的弯曲韧性联系起来,分析了FRC在整个弯曲破坏阶段的力学行为,基于现有弯曲韧性评价方法,提出了一种包含5个指标的新型弯曲韧性评价方法。该方法可以定量分析纤维混凝土的峰前、峰后弯曲性能。研究结果表明:微丝镀铜钢纤维对混凝土的抗压韧性改善最大,能有效抑制混凝土开裂剥落,端钩形钢纤维、波浪形钢纤维对C40和C50混凝土抗弯韧性改善最大,改变了裂纹生长方式。纤维的掺入减小了开裂宽度和早期微裂缝的产生,延长裂缝扩展的时间,拉伸裂纹向剪切裂缝的转变是FRC韧性提升和裂缝以不规则形式攀升的主要原因。声发射特征参数能够准确监测FRC裂缝萌生阶段、稳定增长阶段、失稳开裂阶段、残余破坏阶段与特定挠度下的特征点。由此改进的弯曲韧性评价方法,可以更直观反映FRC的弯曲性能。

Aiming at the problems of building cracking and damage caused by underground mining,a concrete material with strong deformation resistance is developed.The compressive,splitting,axial compressive and four-point bending tests of fiber reinforced concrete(FRC)with five different fibers including hooked steel fiber,wave-shaped steel fiber,microfilament copper-plated steel fiber,imitation steel fiber and filamentous polypropylene fiber are carried out.The variation rules of compressive toughness evaluation index and flexural toughness evaluation index of FRC are studied.The initiation and propagation of cracks in the wave-shaped fiber reinforced concrete during four-point bending are monitored through acoustic emission test.The mechanical behavior of FRC in the whole bending failure stage is analyzed by combining acoustic emission related parameters with the bending toughness of concrete.Based on the existing evaluation methods of concrete’s bending toughness,a new bending toughness evaluation method is proposed containing five new flexural toughness indexes.This method can quantitatively analyze the pre-peak and post-peak bending properties of fiber reinforced concrete.According to the experimental results,it can be concluded that the microfilament copper-plated steel fiber has the greatest improvement on the compressive toughness of concrete and can effectively inhibit the cracking and spalling of concrete.The hooked steel fiber and wave-shaped steel fiber have the greatest improvement on the flexural toughness of C40 and C50 concrete and change the crack growth mode.The addition of fiber reduces the crack width and the generation of early microcracks,prolongs the crack propagation time,and the transformation from tensile crack to shear crack is the main reason for the improvement of FRC toughness and the irregular rise of cracks.Acoustic emission characteristic parameters can accurately monitor the characteristic points of crack initiation stage,stable growth stage,unstable cracking stage,residual failure stage and the characteristic points of particular deflection value.The improved evaluation method of bending toughness can more intuitively reflect the bending performance of FRC.