基于气体稳态运动的高精度原位表层混凝土渗透性测试方法研究

The deterioration of concrete structures is a major problem in many countries throughout the world. This has prompted the search of techniques to expand service life of concrete structures. Due to a high cost benefit ratio, dense concrete with low water binder ratio (w/b) becomes a prevalent approach and has been being used in nearly all priority projects around the world. At present, one key issue is to develop suitable in situ techniques to estimate durability of these concretes in structures. Permeability of near surface concrete is generally used for this purpose and several in situ techniques are available to examine normal concrete. However, none are sufficiently sensitive to quantify and distinguish the difference between dense concretes with low w/b ratio. Furthermore, very few studies report the transport characteristics of fluid within concrete surface, which is the basis of interpretation of field test results. Against this background, a new in situ test method is proposed to determine air permeability of dense concrete with low w/b. To achieve this target, the working theory is extended on the basis of the steady-state flow theory. Air permeability coefficients are calculated according to analysis of 3-D simulated model. After this, effects of different parameters on sensitivity are investigated and approaches to improve performance are identified based on these findings. Meanwhile, reliability of the proposed test is validated by comparisons against the national standard laboratory-based test methods using regression analysis and requirements for site measurements are also investigated. The high sensitive field test method capable of determining air permeability is established on these grounds and will provide comprehensive performance criteria for dense concrete with low w/b.

混凝土结构耐久性是各国关注的热点问题。为延长结构使用寿命，低水胶比、高密实混凝土在世界范围内广泛使用。此类混凝土结构的耐久性评估成为当前困扰土木工程界的难题。在评价耐久性的诸多指标中，人们首先关注的是表层混凝土的渗透性。由于材性发生改变，现有原位测试方法已很难区分此类混凝土渗透性的差别。与此同时，混凝土渗透性的测评与所测介质的运动特性密切相关，但目前专门针对测试介质在表层混凝土运动特性的研究还很不够。为此，本项目提出“高精度原位表层混凝土渗透性测试方法研究”的课题，以建立气体稳态三维运动模型为切入点，以确立渗透系数求解方法、提高测试方法精度为主线，系统研究原位表层混凝土渗透性测试理论，明确提高测试方法精度和可靠性的措施，提出一套系统的、可操作性强的、能准确区分低水胶比、高密实混凝土渗透性的原位透气性测试理论与测试方法，为提升我国混凝土结构耐久性检测水平提供科学依据和技术支撑。

混凝土是现代土木工程中应用最普遍、最大量的建筑材料。混凝土结构的耐久性检测一直是世界工程界研究和讨论的热点问题之一。据统计，西欧发达国家平均每年应用于维护、修复基础设施的经费占国家建设总开支的50%以上。低水胶比、高密实度的高性能混凝土是提高混凝土结构耐久性关键技术。本项目以准确评估低水胶比、高密实混凝土的渗透性为目的，针对现有原位表层混凝土透气方法灵敏性差难以区分低水胶比混凝土渗透性差别、测试原理不清、原位测试方法适用性不明确等问题进行一系列相关研究，提出了气体在表层混凝土迁移方程，确立了透气系数求解方法，研究了测试时间、测试面积、测试腔体积和测试压力四个主要参数对表层渗透性测试方法敏感性的影响，利用SNR与DR评价了测试方法的误差与敏感性，提出了提高表层渗透性测试方法精度的技术手段，并建立了一套适用于混凝土试件透气性测试的预处理方法与相关评价准则，为进一步应用打下了坚实基础。