Date of Award
MS in Civil and Environmental Engineering
Civil and Environmental Engineering
A laboratory test program was undertaken to evaluate a series of engineering properties over a range of soil types; amendment types and addition rates; and moisture contents to enhance understanding of the engineering significance of polymer amendment. Four soils were manufactured and tested with varying ranges of fines and plasticity. A proprietary elastic copolymer was tested at addition rates of 0.5% to 2.5% (dry weight basis). Cement was tested at addition rates of 1% to 4%. Lime was tested at an 8% addition rate. Water addition rates ranged from 4% dry of optimum to 4% wet of optimum. Engineering properties determined throughout the test program included dry unit weight / moisture content relationships through compaction tests; shear strength through unconfined compression strength tests and direct shear tests; durability through freeze-thaw and wet-dry durability tests; and stiffness through resilient modulus tests and through interpretation of the unconfined compression and direct shear test results.
The addition of polymer altered the optimum moisture content of the soils. Change in optimum moisture content ranged from 0.51 to 1.27 times the control water demand. The dry unit weight of polymer amended specimens ranged from 0.97 to 1.01 times their respective control dry unit weight. The peak strength of polymer amended specimens ranged from 1.02 to 18.4 times the control strength. The peak wet-dry and freeze-thaw durability of polymer amended specimens ranged from 6.8 to 10.8 times the control durability. The addition of polymer increased the peak initial stiffness of specimens to approximately 3 times the control stiffness. However, the stiffness was reduced to 0.68 times the control stiffness with dynamic repeated loading through the resilient modulus test.
The polymer addition rate required to achieve peak engineering performance ranged from 0.5% to 2.5%, based on soil type. Polymer modified the engineering properties of soil through physical bonding. The amount of polymer required to modify the engineering properties was directly related to specific surface and soil particle coating thickness. It was determined that polymer amendment had an optimal addition rate that resulted in the greatest increase in engineering parameters. The addition rate was optimum when polymer was applied at rates high enough to sufficiently coat all soil particle surfaces, but at rates low enough that it did not cause additional particle separation.
Overall, polymer amendment of soil improved or maintained all tested engineering parameters, except the resilient modulus, of all soils. Polymer amended soils displayed a reduced performance compared to cement amended soils, and an improved performance compared to lime amended soils.