Understanding the Mechanism and Kinetics of Pyrrhotite-induced Damage in Concrete

这项研究将提供必要的基础知识，以快速可靠地区分混凝土的耐用骨料和有害骨料。具体来说，它将侧重于磁黄铁矿在混凝土中引起破坏的机制和动力学，这种情况已经摧毁了美国北部的一些住宅社区。在确定和采购高质量和耐用的建筑骨料方面的挑战正在增加，因为高质量的原始骨料正在枯竭。自然资源的可持续管理需要一种经过深思熟虑的利用剩余资源的哲学。该项目将确定混凝土中磁黄铁矿反应性检测和定量的最佳方案。通过科学地选择骨料，可以降低修复过早退化和混凝土退化的成本。因此，社会和经济效益很高，并转化为设计可持续建筑环境的新知识和技术。该项目的成果将确保混凝土建筑物和结构的安全性、可维护性和持续使用，同时保护其所有者和居住者的健康和经济生计。混凝土中的磁黄铁矿损伤是由于磁黄铁矿（一种丰富的硫化矿物集合体）与水分和大气中的氧气接触氧化，在混凝土内部形成膨胀的氢氧化铁和硫酸而发生有害膨胀的结果。后者随后导致二次破坏，包括酸侵蚀、硫酸盐侵蚀和钢筋腐蚀。迄今为止，磁黄铁矿氧化仅在酸性矿井水（低pH值）的情况下进行了分析。本研究的新颖之处在于对磁黄铁矿在混凝土环境中的氧化进行了深入的研究。具体来说，pH值、温度、相对湿度和氧气水平对混凝土中反应的幅度和速率以及损伤演变的影响将被量化。将进行铁氧化物相的选择性溶解，并进行地球化学计算以计算磁黄铁矿反应性引起的体积变化。将创建集成的氧气传输和热力学模型，以快速可靠地评估和预测损坏。虽然是为磁黄铁矿相关的降解而开发的，但这种变革性的方法将适用于混凝土中各种集料引起的损伤。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This research will deliver fundamental knowledge necessary to rapidly and reliably distinguish durable from deleterious aggregates for concrete. Specifically, it will focus on mechanisms and kinetics of pyrrhotite-induced damage in concrete, a situation that has devastated some residential communities in the northern United States. Challenges in identifying and procuring high quality and durable construction aggregate are on the rise, as good quality virgin aggregates are being depleted. Sustainable management of natural resources requires a well-thought-out philosophy of using the remaining supplies. This project will lead to identifying optimal protocols for detection and quantification of pyrrhotite reactivity in concrete. By enabling science-driven selection of the aggregates, the costs of remediating premature deterioration and concrete degradation can be reduced. As such, societal and economic benefits are high and translate into new knowledge and technology to design sustainable built environment. The outcomes of this project will ensure safety, serviceability and continued use of concrete buildings and structures, along with protecting health and financial livelihood of their owners and occupants.The pyrrhotite damage in concrete is a result of deleterious expansions taking place when pyrrhotite (an abundant sulfide mineral in aggregates) oxidizes in contact with moisture and atmospheric oxygen, forming expansive iron hydroxides and sulfuric acid inside concrete. The latter subsequently leads to secondary damages, including acid attack, sulfate attack, and rebar corrosion. To date, pyrrhotite oxidation has been analyzed only in the context of acid mine drainage (low pH). The novelty of this research is in thorough investigation of pyrrhotite oxidation in concrete environment. Specifically, the effects of pH, temperature, RH, and oxygen level on the magnitude and rate of reaction and damage evolution in concrete will be quantified. Selective dissolution of Fe-oxide phases will be conducted and geochemical calculations executed to calculate volumetric changes resulting from pyrrhotite reactivity. Integrated oxygen transport and thermodynamic models will be created for rapid and reliable assessment and prediction of damage. While developed for pyrrhotite-related degradation, this transformative approach will be applicable to a wide array of aggregate-induced damages in concrete.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.