硫酸盐侵蚀环境下混凝土双K断裂参数试验研究

为了评估硫酸盐侵蚀环境下混凝土的工作性能并为断裂分析提供依据,采用三点弯曲梁试验方法,研究在硫酸盐侵蚀和干湿循环双重作用下混凝土双K断裂参数等断裂性能的劣化规律.基于断裂力学理论,通过在裂缝尖端表面粘贴应变片来监测裂缝的起裂、扩展和失稳断裂情况,得到在不同硫酸盐侵蚀龄期下试件的P-CMOD曲线.以侵蚀系数为评价指标,采用混凝土双K断裂准则计算构件的失稳韧度和起裂韧度.结果表明:起裂荷载与最大荷载的比值PQ/Pmax大致分布在0.55～0.90,失稳韧度和起裂韧度在侵蚀初期均有较明显的增大,转折点分别为60和30d,之后随侵蚀龄期不断缓慢减小.与失稳韧度相比,起裂韧度受硫酸盐侵蚀因素的影响较敏感.

Experimental study on double-K fracture parameters of concrete exposed to sulfate environment

The deterioration regularity of double-K fracture parameters of concrete under sulfate attack and drying-wetting cycle environment was investigated by three-point bending beam test in order to assess the performance of concrete due to sulfate attack and provide references for fracture analysis.The initiation,propagation and unstable development of crack in the concrete were monitored by pasting some strain gauges onto the pre-crack tip based on the fracture mechanics.The load-crack mouth opening displacement(P-CMOD) curves under different sulfate attack periods were obtained by the experiment.Taking the erosion coefficient as an evaluation index,the unstable fracture toughness and the initial fracture toughness were calculated according to the double-K criterion.Experimental results indicated that the ratio of the initial cracking load to the unstable fracture load(PQ/Pmax) approximately varied between 0.55 and 0.90.Both unstable fracture toughness and initial fracture toughness obviously increased during the early stage of sulfate ingression,and reduced continuously and slowly with a turning point at 60 and 30 days respectively.The initial fracture toughness was more sensitive to sulfate attack than the unstable fracture toughness.