硫酸环境中混凝土摩擦桩耐久性能与承载力时变性研究

After the concrete pile foundation corroded by sulfuric acid, the cross-sectional area of the pile becomes smaller and the side surface of the pile becomes uneven. Furthermore, the corrosion products will remain around the pile. The durability of the pile foundation will be seriously affected and then the pile shaft mechanical properties and the shaft friction will be affected. There are hidden dangers in concrete pile foundation safety. Applicants have carried out the study of the effect of aggregate chemical composition on the durability and compressive strength of sulfuric acid corroded concrete specimens and the effect of sulfuric acid corrosion on the mechanical properties of the interface between concrete slab and sand (excluding the corrosion layer). However, concrete piles are often subjected to superstructure loads and groundwater pressure in service. The stress distribution on the cross-section of concrete piles is not uniform after the sulfuric acid corrosion and the root causes of the decrease of compressive ability of concrete piles are the reduction of the corrosion cross-sectional area and the degradation of mechanical properties of concrete in the corrosion zone. Moreover, pile-soil contact surface area and pile side frictional resistance will be changed by sulfuric aicd corrosion effects. The durability evolution and bearing capacity deterioration mechanism of concrete friction piles in sulfuric acid environment need to be studied urgently. This application intends to conduct research at the environment, materials and components levels to reveal the evolution of the durability and mechanical properties of concrete under coupling of load, water pressure and sulfuric acid corrosion, and to establish the stress-strain relationship of corroded concrete, and then to propose the frictional resistance revised calculation method for sulfuric aicd corroded concrete pile. The expected results of the study are of great significance for the design of the newly constructed concrete pile foundation and the evaluation of the existing concrete pile foundation in the sulfuric acid environment.

硫酸环境中混凝土桩基腐蚀后，截面积变小，桩侧变得凹凸不平，腐蚀产物停留在桩侧，严重影响桩基的耐久性，进而影响桩身和桩侧力学性能，桩基安全存在隐患。申请者已开展骨料成分对硫酸腐蚀混凝土耐久性和试件抗压强度的研究及腐蚀作用对混凝土板与砂土接触面（无腐蚀层）力学性能影响的研究，但未考虑到混凝土桩承受上部结构荷载和地下水压力作用，混凝土硫酸腐蚀后截面应力分布不均匀，桩体抗压能力降低的根源是腐蚀截面积减小以及腐蚀区混凝土力学性能退化，腐蚀作用改变了桩-土接触表面积及桩侧摩阻力，硫酸环境中混凝土摩擦桩耐久性能及承载力衰变规律亟待研究。本申请拟在环境、材料和构件三个层次上开展研究，揭示荷载、水压力、硫酸腐蚀耦合作用下混凝土的耐久性和力学性能演变规律，建立腐蚀区混凝土应力应变关系，提出硫酸腐蚀后混凝土桩侧摩阻力的修正方法，研究成果对硫酸环境中新建结构混凝土桩基的设计以及在役混凝土桩基的评估具有重要意义。

硫酸土壤环境中构筑物的混凝土桩基础，因硫酸对混凝土的腐蚀作用，其桩身的截面积、硫酸腐蚀混凝土的力学性能及桩土间的摩擦阻力具有时变性，桩基安全受到质疑，硫酸腐蚀土壤环境中混凝土桩的时变性亟需进行研究。项目从环境层次出发，开展了荷载、水压力作用下混凝土硫酸腐蚀性能研究；在材料层次上，开展了含4种骨料组合的混凝土试件在硫酸环境中的加速腐蚀试验，获得了加速腐蚀深度、质量损失、表面腐蚀形貌的分形维数、抗压强度、弹性模量等指标的时变规律，采用腐蚀深度或分形维数为“腐蚀当量”建立了实验加速腐蚀试验的结果与自然腐蚀环境中长期的实际结果之间的相关关系。在构件层次上，开展了大型接触面直接剪切试验来硫酸腐蚀作用对混凝土桩侧摩阻力的影响。硫酸环境中混凝土桩时变性研究是涉及环境、岩土、混凝土材料、混凝土构件、混凝土结构的综合课题。作为一项长期研究计划的一个重要组成部分，在本项目的资助下获得了丰硕的成果，对于正确评价硫酸环境中混凝土桩耐久性性能和工程安全都有重要的理论价值和实用价值。