疲劳荷载作用下道路混凝土硫酸盐侵蚀及防护

Sulfate Corrosion and Corrosion Protection of Road Concrete under Fatigue Load

目的解决疲劳荷载作用下道路工程结构混凝土硫酸盐侵蚀破坏严重的问题。方法采用自主研发的腐蚀疲劳试验装置,通过化学分析及强度测试,研究荷载类型(交变荷载和持续荷载)、硫酸盐种类(Na2SO4和Mg SO4)、硫酸盐浓度(5%和10%(均为质量分数)的Na2SO4)、应力水平(20%、40%和60%)、水灰比(0.35、0.38)对道路混凝土腐蚀龄期为180 d时的硫酸根离子分布及强度变化的影响规律;同时,采用硅烷对混凝土进行表面涂覆,对其抗疲劳腐蚀性能进行测试。结果承受腐蚀疲劳的道路混凝土表层的硫酸根离子侵入速度是承受持续荷载的试件的1.43倍。在腐蚀疲劳作用下,当硫酸盐浓度提高1倍时,混凝土表层硫酸根离子侵蚀速度提高近1倍;应力水平由0.2提高至0.6时,表层硫酸根离子质量分数由2.51%提高至4.62%;水灰比由0.38降至0.35时,表层硫酸根离子扩散速度降低17%。由于硫酸镁腐蚀生成的Mg(OH)2溶解度很低,混凝土表层硫酸镁腐蚀速度是硫酸钠的70%。此外,涂覆硅烷的混凝土抗弯拉系数较未涂覆试件提高了近40%。结论疲劳荷载加剧了混凝土中硫酸盐的侵蚀。在腐蚀疲劳环境中,可采用适当降低水灰比、硅烷涂覆表面的方法提高混凝土抗硫酸根离子侵蚀能力,延长混凝土服役周期。

Objective To solve the problem that the concrete structure of the road is seriously damaged under the interaction of the fatigue load and the sulfate corrosion. Methods In this paper,using self-developed corrosion fatigue device,we mainly studied the distribution of sulfate ions and the strength variation rule of road concrete subjected to corrosion for 180 d under the condition of different load types（ alternating load and static load）,different sulfate species（ Mg SO4 and Na2SO4）,different sulfate concentrations（ 5 wt.% and 10 wt.% Na2SO4）,different stress levels（ 20%,40% and 60%） and different water-cement ratios（ 0. 35 and0. 38） by chemical analysis and strength test method. At the same time,the surface of the concrete was coated with silane,and the anti-fatigue performance of the concrete was tested. Results The sulfate ion penetration speed of the road concrete subjected to corrosion fatigue was 1. 43 times as high as that of the specimen subjected to sustained loading. Under the effect of corrosion fatigue,the sulfate ion erosion rate increased by nearly 1 fold when the sulfate concentration increased by 1 fold; The sulfate concentration increased from 2. 51% to 4. 62% when the stress level increased from 0. 2 to 0. 6; The sulfate ion diffusion speed was reduced by17% when the water cement ratio fell from 0. 38 to 0. 35. Since Mg（ OH）2generated from magnesium has low solubility,the effect of magnesium sulfate on the surface layer of concrete was 70% of sodium sulfate; The flexural tensile coefficient of the coated silane concrete was increased by nearly 40% compared with that of the uncoated specimen. Conclusion The fatigue load exacerbated the sulfate corrosion of concrete; In the corrosion fatigue environment,appropriate reduction of the water cement ratio as well as the adoption of the silane coating technology could greatly improve the sulfate corrosion resistance of concrete and prolong the service period of concrete.