往复荷载下含孔洞缺陷衬砌混凝土的力学性能试验研究

通过添加不同含量的发泡聚苯乙烯(EPS)颗粒来预制目标孔隙率以模拟混凝土的不同孔洞缺陷,制备了不同孔隙率的C25和C30两种强度等级的混凝土试件,开展单调及往复荷载下含孔洞缺陷混凝土力学性能的试验研究,分析了混凝土试件破坏形态、强度、应变、弹性模量等随孔隙率的变化规律,探讨不同孔洞缺陷对混凝土力学性能的影响。试验结果表明:单调及往复荷载下,无预制孔洞缺陷的混凝土试件均表现为脆性破坏特征。但随着孔隙率的增加,混凝土试件的强度明显降低,应力-应变曲线逐渐趋于鱼肚状分布,试件由脆性向延性破坏转变,逐渐呈现多裂缝扩展特征,特别是对于往复加载情况。两种加载方式和两种强度等级条件下,试件主要力学参数随着预制孔隙率的增加均表现出一致的变化规律。峰值应力和弹性模量随孔隙率的上升呈指数下降,而峰值应变和应变极值呈线性增大。往复荷载下试件力学性能受孔隙率的影响程度均大于单调加载情况,而且,这种影响随混凝土强度的提高而减小。在往复加载过程中,孔隙率越大,峰值应力前试件的刚度比值越大,而峰后的刚度退化也愈严重。对于相同的孔隙率,混凝土强度等级越高,峰值应力前的刚度增长率及峰后的刚度退化程度越小。

Mechanical Properties of Lining Concrete with Hole Defects under Reciprocating Loading

The target porosity was prefabricated by adding different content of expanded polystyrene (EPS) particles to simulate different hole defects of concrete, and concrete specimens with different porosity levels of C25 and C30 were prepared to develop the mechanical properties of concrete with hole defects under monotonic and reciprocating loading. In the experimental study, the changes in the shape, strength, strain and elastic modulus of concrete specimens with porosity were analyzed, and the influences of different hole defects on the static and dynamic properties of concrete were discussed. The test results show that under monotonic and reciprocating loading, the concrete specimens without prefabricated hole defects show brittle failure characteristics. However, with the increase of porosity, the strength of concrete specimens decreases significantly, and the stress-strain curve gradually tends to distribute in a fish-maw shape. The specimens change from brittle to ductile failure and gradually show the characteristics of multi-crack propagation, especially for reciprocating loading. Under the two loading methods and two strength levels, the main mechanical properties of the specimens show consistent changes with the increase of the precast porosity. Peak stress and elastic modulus decrease exponentially with the increase of porosity, while peak strain and extreme strain increase linearly. The influence of porosity on the mechanical properties of specimens under reciprocating loading is greater than that of monotonic loading, and this effect decreases with the increase of concrete strength. In the reciprocating loading process, the greater the porosity, the greater the stiffness ratio of the specimen before the peak stress, and the more serious the stiffness degradation after the peak. For the same porosity, the higher the concrete strength grade, the smaller the stiffness growth rate before the peak stress and the less the degree of stiffness degradation after the peak.