硫酸盐、镁盐双重因素下地铁混凝土耐久性试验

Experiment on durability of metro-concrete under action of double factors of sulfate and magnesium-salt

为研究地铁混凝土对SO_4^(2-)、Mg^(2+)的抗侵蚀性能,将3种水胶比和3种粉煤灰掺量共5种配合比的混凝土长期浸泡在5 000mg/L的硫酸镁溶液中,采用相对质量评价参数、相对动弹性模量评价参数及同时考虑质量和动弹性模量的综合损伤评价参数作为评价指标,并结合微观图像对不同浸泡时间下地铁混凝土试件表面的腐蚀形态及耐久性进行研究.结果表明:在腐蚀性环境下,SO_4^(2-)、Mg^(2+)和水化产物发生复杂的化学反应生成膨胀产物钙矾石、石膏晶体及无胶结性能的M-S-H凝胶,使混凝土出现严重的开裂、起皮、掉渣;水胶比0.35、粉煤灰掺量30%的混凝土表现出了最佳的抗腐蚀性能;综合损伤评价参数能够很好地反应混凝土在硫酸盐溶液中内部密实度及外部宏观质量的变化.

In order to study the corrosion resistance of metro-concrete to SO^2-4 and Mg^2+,concrete specimens with 5 kinds of mixture ratio of aggregates including 3 kinds of water-to-cement ratio and 3 kinds of fly-ash-to-content ratio were soaked in 5 000 mg/L magnesium sulfate solution.Taking the relative quality evaluation parameters,relative dynamic elastic modulus evaluation parameters,and comprehensive damage evaluation parameters,in which both the mass and dynamic elasticity modulus were simultaneously taken into account,as the evaluation indexes,and using microscopic image,the surface corrosion form of the concrete specimens and their durability after different soaking time were studied.The result shows that the SO^2-4,Mg^2+,and hydrated products will take part in a complex chemical reaction in corrosive environment to generate expansive products of ettringite,gypsum crystal,and bind-less M-S-H gel,making the concrete severe cracking,peeling and slagging.The water-to-cement ratio of 0.35 and fly-ash content of 30%will exhibit an optimal characteristic of corrosion resistance.Comprehensive damage evaluation parameters can well reflect the internal compactness of the concrete in sulfate solution and the change of its external macroscopic quality.