Optimization of Frost Protection

混凝土通过添加表面活性剂（称为引气剂，AEA）来防止霜冻损坏，这种表面活性剂可以稳定空隙，在孔隙水冻结时调节体积膨胀，并在未冻结的孔隙水中产生吸力，抵消冰晶施加在孔隙壁上的压力。提出的工作目标是优化夹带空气空隙的性能。我们将研究商业AEA和其他表面活性剂与水泥浆体的相互作用，以获得有关AEA在气泡上吸附的速度和程度，以及在其表面形成的富石灰壳的生长速度和孔径的定量信息。吸附动力学将通过张力测定法来研究，该方法量化了溶液中表面活性剂浓度的变化。在近大气压力下的压缩率测量将量化壳在演化过程中的刚度。为了研究精细的早期水化产物的微观结构，我们将使用超临界干燥去除孔隙液体而不产生毛细压力。这将产生不变的结构，以供氮吸附和电子显微镜检查。研究结果将用于解释水泥浆和砂浆冻结时的膨胀曲线。冻结过程中的膨胀取决于成核行为，这将通过加入成核剂（三聚甲醛）来控制，以及空气空隙将冰限制在内部的能力，这取决于壳中的孔隙大小。该项目将为优化混凝土抗冻性能的化学添加剂的选择提供良好的依据，并为评价新型有机添加剂提供方法。通过提高混凝土的抗冻性，维护民用基础设施的成本将会降低，二氧化碳的排放将会减少，因为更换结构所需的水泥将会减少。引入研究空气夹带过程的新方法，以及制备用于分析的无人工制品样品，将开辟材料科学研究的新途径。评估空气空隙的张力法可以取代目前工业上使用的较少的定量方法。这项工作将有助于培养一名女研究生和博士后研究员，并将为本科生独立研究、高级论文和REU/RET项目提供主题。

Concrete is protected against frost damage by adding surfactants (called air-entraining agents, AEA) that stabilize air voids, which serve to accommodate the volume expansion as pore water freezes and to create suction in the unfrozen pore water that offsets the pressure exerted on pore walls by ice crystals. The goal of the proposed work is to optimize the performance of entrained air voids. We will study the interaction of commercial AEA and other surfactants with cement paste to obtain quantitative information about the rate and extent of adsorption of AEA on air bubbles, and the rate of growth and pore size of the lime-rich shells that form on their surfaces. The adsorption kinetics will be studied by tensiometry, which quantifies the change in concentration of the surfactant in the solution. Compressibility measurements at near-atmospheric pressure will quantify the rigidity of the shells as they evolve. To examine the microstructure of delicate early-age hydration products, we will use supercritical drying to remove the pore liquid without creating capillary pressure. This will produce unaltered structures for examination by nitrogen sorption and electron microscopy. The results will be used to interpret dilatometric curves obtained during freezing of cement paste and mortar. Dilatation during freezing depends on the nucleation behavior, which will be manipulated by incorporation of a nucleating agent (metaldehyde), and on the ability of the air voids to confine ice inside, which depends on the pore size in the shell. The project will provide a sound basis for choosing chemical additives that optimize the frost protection of concrete, and a methodology for evaluating new organic additives. By improving the frost resistance of concrete, the cost of maintaining the civil infrastructure will be reduced, and the emissions of CO2 will be decreased, because less cement will be required for replacement of structures. The introduction of new methods for studying the process of air entrainment, and for preparing artifact-free samples for analysis, will open new avenues of research in materials science. The tensiometric method for evaluating air voids could replace less quantitative procedures currently used in industry. This work will contribute to the education of a female graduate student and post-doctoral researcher, and will provide topics for undergraduate independent research, senior theses, and REU/RET projects.