Microwave Evaluation and Modeling of Rapid Chloride Ingress in Mortar

钢筋锈蚀和由此导致的钢筋混凝土结构劣化是基础设施损坏增加的主要原因之一。在联邦公路管理局(FHWA)所称的22.6万座钢筋混凝土桥梁中，钢筋锈蚀是造成大部分桥梁损坏的原因之一。1991年，美国交通部估计这些受损桥梁的修复费用为909亿美元。混凝土通常为钢筋提供足够的防腐保护。当钢筋被包裹在混凝土中时，由于混凝土的高pH值，在钢-混凝土界面上形成了一层保护性的氧化铁膜。然而，足够浓度的氯离子的存在可能会损害钝化层。在潮湿的情况下，钢会被腐蚀。开发一种可靠的测试方法来现场测量混凝土结构中氯离子的渗透深度和浓度，对混凝土和建筑业来说将是非常有价值的。从经济角度来看，准确测量混凝土结构中的氯化物浓度和渗透深度，将使各机构能够更有效地分配资金，用于修复有最关键需求的结构。因此，拟议调查的总体目标是更全面地了解接触氯化物溶液的水泥基材料的微波测量的基本影响。为了将微波测量与砂浆中的盐分含量和氯离子渗透深度相关联，提出了一种系统的研究计划。砂浆样品将在池塘中循环加入盐溶液。样品烘干后，将使用一种非常准确和灵敏的微波表征技术，使用四个独立的复反射和透射系数来评估它们的介电性能。然后，将该信息与离散的分层电磁模型和介电混合公式结合使用，以将关于盐体积含量的信息作为深度的函数呈现到样品中。这一过程被重复多次浸泡循环，给出关于盐分渗透梯度和总含量的信息，作为进入样品的深度、样品组成和浸泡周期的函数。这项拟议调查的预期结果是在评估钢筋混凝土结构中氯离子渗入的道路上取得的重大而全面的飞跃。

ABSTRACTSteel corrosion and the resulting deterioration of reinforced concrete structures is one of the primary causes of increasing damage to infrastructure. Corrosion of the reinforcing steel is implicated as a cause of damage to the majority of the 226,000 reinforced concrete bridges described by the Federal Highway Administration (FHWA) as deficient. In 1991, the United States Department of Transportation estimated rehabilitation costs for these damaged bridges at $90.9 billion. Concrete normally provides reinforcing steel with adequate corrosion protection. When steel is encased in concrete, a protective iron oxide film forms at the steel-concrete interface due to the high pH of the concrete. However, the presence of a sufficient concentration of chloride ions can compromise the passive layer. In the presence of moisture, the steel will corrode. Development of a reliable test method for in-situ measurement of the chloride ion penetration depth and concentration in concrete structures would be invaluable to the concrete and construction industry. From an economic standpoint, accurate measurements of the concentration of chlorides and penetration depth in concrete structures, would allow agencies to more effectively allocate funding for repair of those structures with the most critical needs. Thus, the overall objective of the proposed investigation is to gain a more complete understanding of the fundamental implications of microwave measurements of cement-based materials exposed to chloride solutions. A methodical research plan is proposed in order to correlate microwave measurements to the salt content and chloride penetration depth in mortar. Mortar samples will be cyclically ponded with salt solution. After the samples are oven dried, a very accurate and sensitive microwave characterization technique will be used to evaluate their dielectric properties using four independent complex reflection and transmission coefficients. This information is then used in conjunction with a discrete layered electromagnetic model and a dielectric mixing formula to render information about the salt volume content as a function of depth into the samples. This process is repeated for a number of soaking cycles, giving information about salt penetration gradient and total content as a function of depth into the sample, sample make-up and soaking cycle. The anticipated outcome of this proposed investigation constitutes a significant and comprehensive leap forward in the path to evaluating chloride ingress in reinforced concrete structures.