Meso-Scale Behavior Characterization of "Tunable" Clay-Polymer Composites

土壤是天然物质。因此，它们的属性在不同的位置可能会有很大差异。这种可变性使得很难预测或控制作为建筑材料的土壤的行为。减少这种变异性的一种方法是对土壤进行改造，使其以可预测的方式发挥作用。这笔赠款为研究“可调”粘土-聚合物复合材料提供了资金，在这种复合材料中，颗粒间和/或层间间距通过pH和离子浓度响应型聚合物来控制。这项研究将检验这一假设，即以前在颗粒水平上观察到的pH和离子浓度诱导的操纵也在中观尺度上表现出来。这项研究中使用的特殊聚合物是聚丙烯酰胺，这是一种广泛使用的廉价聚合物，经常用于水处理目的。粘土-聚合物复合材料的介观特性将包括：膨胀容量的测量；重复pH和离子浓度循环对滞后的影响；水力传导性随平均pH和离子浓度循环的变化；在选定的pH和离子浓度下的固结和剪切波速响应；以及在选定的pH和离子浓度条件下的剪切强度。这项工作的预期结果是：(1)所选择的pH和离子浓度环境之间的关系以及膨胀或收缩的程度；(2)所选择的pH和离子浓度环境与材料响应时间的关系；(3)所选择的pH和离子浓度的复合响应；(3)流体循环和任何潜在滞后；(4)通过水力传导性证明复合材料的“可调性”；(5)所选择的pH和离子浓度环境与复合材料的压缩性和剪切波速的关系；以及(6)复合材料在特定pH和离子浓度条件下的剪切强度特性。如果这项工作成功，这项工作的结果将有助于建立一个新的研究领域：使用功能聚合物的工程土壤。可调聚合物-粘土复合材料的发展将改善屏障系统、粘土衬里、过滤器和污染物去除系统的性能，其性能可以被修改以最大限度地提高其有效利用。这些工程土壤可以为特定应用而设计，并改善结构的性能，如过滤器、不透水屏障(水或气体)和污染物屏障。就其经济影响而言，生产这些粘土-聚合物复合土壤的总体成本可能相对较低，因为生产方法和聚合物都很便宜。如果化学稳定性和水力稳定性得到改善，那么在废物屏障系统中的应用可以减少渗滤液和渗透污染。聚合物-粘土复合材料也可能是稳定防渗系统应用的一种更可持续的材料。延长此类结构的使用寿命将减少与重建故障系统相关的能源需求。

Soils are natural materials. As such, their properties can vary greatly from location to location. This variability makes it difficult to predict or control the behavior of soil as a construction material. One approach to minimize this variability is to engineer a soil such that it performs in a predictable manner. This grant provides funding to investigate "tunable" clay-polymer composites in which the interparticle and/or interlayer spacings are controlled via a pH and ionic concentration-responsive polymer. This research will test the hypothesis that the pH- and ionic-concentration-induced manipulations previously observed at the particle level are also manifested at the meso-scale. The particular polymer used in this research is polyacrylamide, which is a widely available and inexpensive polymer often used for water treatment purposes. Meso-scale characterization of the clay-polymer composites will include measurement of swelling capacity; impact of repeated pH and ionic concentration cycling on hysteresis; changes in hydraulic conductivity with permeant pH and ionic concentration cycling; consolidation and shear wave velocity response under selected pH and ionic concentrations; and, shear strength under selected pH and ionic concentration conditions. The expected results from this work are: (1) a relationship between selected pH and ionic concentration environments and the degree of swell or shrink; (2) a relationship between selected pH and ionic concentration environments and response time of the material; (3) the composite response with selected pH and ionic concentration fluid cycling and any potential hysteresis; (4) demonstration of the "tunability" of the composites through hydraulic conductivity; (5) the relationship between the selected pH and ionic concentration environments and composite compressibility and shear wave velocity; and (6) shear strength properties of the composites when subjected to selected pH and ionic concentration conditions.If successful, the results of this work will contribute to the establishment of a novel field of research: engineered soils using functional polymers. The development of tunable polymer-clay composites whose properties can be modified to maximize their efficient use will improve the performance of barrier systems, clay liners, filters, and contaminant removal systems. These engineered soils can be designed for specific applications, and improve performance of structures such as filters, impervious barriers (water or gas), and contaminant barriers. In terms of their economic impact, the overall cost of producing these clay-polymer composite soils is likely to be relatively low since both the production method and the polymer are inexpensive. If improved chemical and hydraulic stability is shown, then application in waste barrier systems could lead to reduced leachate and infiltration contamination. Polymer-clay composites may also be a more sustainable material for stabilizing impervious system applications. Increasing the lifespan of such structures would reduce energy needs related to re-building failed systems.