内蒙古河套地区盐渍土环境下混凝土耐久性研究

The He Tao region of Inner Mongolia is located in upper Yellow river, demonstrate typical characteristic of the arid and semi-arid climatic zone, like high temperature in summer and severe cold in winter, temperature difference between day and night, high evaporation and serious soil salinization. The concrete materials are damaged and corroded due to harmful ion of carbonate (hydrogen) saline soil and many environmental factors, leading to the degradation of concrete structure and threatening the duration and safety of such concrete structures..In this research, the test conditions are designed according to the environment and climate features, the failure mechanism of concrete are analyzed in the different environment and soil conditions, the reduction laws of the concrete performance are revealed due to freeze-thaw cycles, dry-wet cycles, salt corrosion and the correlations are analyzed about the effect factors of duration to the mass or the dynamic elastic modulus of concrete. Based on the testing results, the gray correlation and rough set theories are applied to determine the correlation degree between influencing factors and concrete durability and the weight coefficients of factors. Furthermore, MATLAB program is used to establish the evaluation models and suitable conditions, so that attenuation rule of dynamic elastic modulus of concrete can be evaluated under different environment conditions. Finally, the field comparison tests are conducted to verify the effectiveness. The research target is offering the theoretic guarantee and practical basis for reducing the potential durability and security threats of concrete engineering in cold and arid area.

内蒙古河套地区处黄河上游，属于干旱半干旱气候区、高温高寒、昼夜温差大、蒸发强烈，土壤盐渍化严重。其境内碳酸（氢）盐渍土的有害离子与环境多因素耦合作用下对混凝土材料造成腐蚀或损伤，引起混凝土结构性能的劣化，严重威胁各类建（构）筑物的耐久性及服役期间的安全性。本课题结合该地区的气候条件与土壤环境因素设计试验工况，进行不同环境因素或土壤情况下对混凝土破坏机理分析与评价；揭示盐蚀、干湿、冻融等单一或多重因素作用下混凝土性能的衰变规律；分析混凝土耐久性的诸多影响因素与其质量或动弹性模量的关联度；在试验结果基础上，运用灰关联度与粗糙集理论分析，确定各影响因素分别与混凝土耐久性之间的关联程度以及各影响因素的权重；应用MATLAB程序建立对不同环境条件下混凝土质量损失率或动弹性模量的衰减评价模型，并通过野外对比试验对其有效性进行验证，为减少寒旱区盐碱土对混凝土工程耐久与安全的潜在威胁提供理论保障与实践依据。

内蒙古河套地区处黄河上游，属于干旱半干旱气候区、高温高寒、昼夜温差大、蒸发强烈，土壤盐渍化严重。其境内盐渍土的有害离子与环境多因素耦合作用下对混凝土材料造成腐蚀或损伤，引起混凝土结构性能的劣化，严重威胁各类建筑物的耐久性及服役期间的安全性。本项目研究内蒙古河套地区公路混凝土盐渍土环境下的劣化机理，进行春、秋季节实地调研，分别在国道和省道附近土壤采样，模拟环境工况制备单盐溶液（Na2SO4）、复合盐溶液（NaCl、Na2SO4、NaHCO3、Na2CO3），配制7种不同掺量配合比混凝土试件（基准混凝土；掺 10%、15%、20%粉煤灰混凝土；掺 10%、15%、20%偏高岭土混凝土）进行了混凝土耐久性试验研究。分别进行了单盐-干湿循环试验、复合盐-干湿循环试验、单盐-冻融试验、复合盐-冻融试验，强度指标评价干湿循环试验，相对动弹模量值和质量损失率指标评价冻融试验。结果表明，河套地区盐渍土以碳酸盐为主，春季土壤可溶液总量大于秋季，春季土壤 pH 值大于秋季土壤，春季pH值最高9.80，秋季pH值最高9.32；复合盐-干湿循环试验对混凝土破坏大于单盐-干湿循环试验，掺粉煤灰和掺偏高岭土可以增强混凝土抵抗干湿循环破坏的能力；复合盐-冻融试验对混凝土破坏大于单盐-冻融试验，掺偏高岭土混凝土抗冻能力优于掺粉煤灰混凝土，偏高岭土与粉煤灰的最佳掺合量介于10%～20%。并建立了多重耦合作用下混凝土抗压、相对动弹性模量劣化预测模型，本试验范围内，复合盐-干湿-冻融试验后混凝土抗压强度劣化预测模型关系数为90%，复合盐-干湿-冻融试验后混凝土相对动弹模量劣化预测模型相关系数为93%。预测模型中，掺量为20%的偏高岭土混凝土劣化较小，劣化速度最慢。为该地区混凝土材料耐久性提供了理论依据和实践指导。