复合盐环境下疏浚砂混凝土梁断裂性能

Fracture characteristics of dredged sand concrete beams in composite salt environment

摘要

【目的】为实现长江疏浚砂就近用于入海口水工构筑物建设，【方法】定义疏浚砂占细骨料质量之比为掺量，设计5种掺量不同的混凝土小梁试件，将试件置于4种不同的盐环境(NaCl和Na_2SO₄溶液组成)中进行全浸泡侵蚀，对侵蚀时间为30 d、60 d、90 d及未侵蚀的试件开展非标准三点弯试验，研究其力学性能并结合声发射技术监测裂缝开展情况。【结果】结果显示：(1)随着掺量升高，混凝土抗裂性能逐渐降低，掺量每升高12.5%,断裂峰值荷载相应下降5%左右，当掺量大于或等于37.5%,断裂峰值荷载骤降30%以上；(2)离子浓度越高，侵蚀效果越明显，而加入Cl~-可缓解SO₄^2-对混凝土的侵蚀进程；(3)分析AF-RA值可知前期开裂以拉伸裂缝为主，剪切裂缝占比随裂缝扩展过程逐渐增大，掺量12.5%时剪切裂缝占比最小，此时裂缝发育最好；离子浓度越高剪切裂缝占比越大，裂缝发育越不完全。【结论】疏浚砂的掺入以及盐环境的侵蚀对混凝土的力学性能有明显的劣化作用，声发射累计振铃计数呈三阶段性，反映断裂破坏特性，验证了边界效应。研究成果为疏浚砂混凝土在盐环境下的水利水运工程应用提供了试验依据。

Abstract

[Objective] In order to realize that dredged sand from the Yangtze River can be used in construction of hydraulic structures near estuary, [Methods]proportion of dredged sand to the mass of fine aggregate was defined as the Content. 5 kinds of concrete trabecular specimens with different Content were designed, and the specimens were placed in 4 different salt environments(composed of NaCl and Na_2SO₄ solution) for full immersion erosion. Non-standard three-point bending tests were carried out on the specimens with erosion time of 30 d, 60 d and 90 d and those without erosion. The mechanical properties were studied and the crack development was monitored by acoustic emission(AE) technology. [Results] The results show:(1) Crack resistance of concrete gradually decreases with increase of the dosage. For every 12.5% increase, the peak breaking load decreases by about 5%. When the dosage is greater than or equal to 37.5%, the peak breaking load drops by more than 30%.(2) The higher ion concentration is, the more obvious erosion effect is, and addition of Cl~- can alleviate the erosion process of SO₄^2-.(3) The analysis of AF-RA values shows that tensile cracks are the main cracks in early stage, and the proportion of shear cracks increases gradually with the process of crack expansion. The proportion of shear cracks is the smallest when the content is 12.5%, and the fracture development is the best. The higher the ion concentration, the larger the proportion of shear fractures, the more incomplete the fracture development. The research result provide experimental basis for the application of dredged sand concrete in water conservancy and water transportation engineering under salt environment. [Conclusion] The addition of dredged sand and the erosion of salt environment have obvious deterioration effect on the mechanical properties of concrete. The accumulate counts of AE showed three stages, reflecting fracture characteristics and verifying boundary effect.

关键词

疏浚砂 / 断裂 / 复合盐侵蚀 / 声发射 / 混凝土 / 力学性能 / AF-RA值

Key words

dredged sand / fracture / composite salt corrosion / acoustic emission(AE) / concrete / mechanical properties / AF-RA

基金资助

国家自然科学基金项目(52379124)

中央高校基本科研业务费(B230204021)