酸雨腐蚀对混凝土材料断裂特性的影响

为研究酸雨腐蚀环境下混凝土断裂性能的劣化情况而进行混凝土的实验室加速腐蚀实验，并通过三点弯曲试验及电测法获得了不同腐蚀程度混凝土的起裂荷载、最大荷载以及试件的弹性模量和断裂韧度的劣化情况，同时借助电镜扫描获取腐蚀混凝土裂尖的劣化样貌。在模拟酸雨环境下，混凝土裂纹尖端的腐蚀深度随着侵蚀时间的持续而逐渐增长，裂纹尖端混凝土将发生结构性的损伤，混凝土材料松弛并产生微裂隙，这将直接影响混凝土裂尖的抗裂能力。与水中浸泡试件相比，腐蚀试件的抗裂能力发生显著的退化；在不同pH值的模拟酸雨环境中，试件的起裂荷载与最大荷载都随着腐蚀时间的增加而呈现先增长而后降低的趋势；随着腐蚀程度的增加，起裂荷载则会加速劣化。混凝土断裂韧度随腐蚀时间先增大后减小；溶液pH值越低，断裂韧度的增长周期越短，最终的损失也越大。H⁺和SO₄^2-使裂尖混凝土发生复杂的物理化学变化，直接弱化混凝土的抗裂能力。混凝土断裂韧度劣化率随裂尖腐蚀深度呈现出抛物线式的发展态势。

Deterioration of Fracture Characteristics for Concrete Material Under Acid Rain Environment

Deterioration of fracture characteristics for concrete under acid rain attack was investigated by laboratory-accelerated corrosion tests, three-point bending (TPB) tests and scanning electronic microscopy (SEM). Elastic modulus, initial cracking load and maximum load of the corroded concrete with different corrosion periods were obtained and the deterioration of fracture toughness was analyzed. The corrosion depth increases with corrosion duration under simulated acid rain environment. The observation by scanning electron microscopy showed that the microstructures of crack tip are porous and loose due to acid corrosion, and many crisscross cracks appear at corrosion layer, which make the corresponding resistance stresses to crack propagation decrease. The experimental results of three-point bending tests showed that initial cracking load and maximum load of the corroded specimens increase in the initial stage of immersion, and decrease with the increase of immersion time. Beyond that, the deterioration of initial cracking load is accelerated with the increase of corrosion degree. The fracture toughness of concrete increases with corrosion time at the initial stage and then decreases, and the lower the pH value is, the shorter the duration of the strengthening phase is. Under the impact of acid corrosion, physical and chemical properties of the concrete change significantly around the crack tip, which is the main factor that results in the decrease of the mechanical properties for concrete. Also, the curves of fracture toughness versus corrosion depth were obtained in this study.