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.
