Stabilization of Silty Sand Using Combinations of Hydraulic Cements and Polymer Emulsions (05-1179)
Kent Newman, U.S. Army Engineer Research and Development Center
John F. Rushing, U.S. Army Engineer Research and Development Center

Polymer emulsion soil stabilization additives are being investigated as part of a research program for construction of contingency airfields for the US Army. Laboratory evaluations of several commercially available polymer emulsions have been performed to provide comparisons of these materials for stabilization of silty sand. Portland cement-stabilized specimens were prepared as a conventional stabilizer control. Additionally, blends of Type III Portland cement and select polymer emulsions were tested as potential soil stabilizers to increase strain properties and moisture resistance. Each of the additives were added to manufactured silty sand and compacted with a gyratory compactor at the optimum moisture content of 5% which was determined for the unmodified soil. Compacted specimens were cured in a controlled temperature and humidity environment (23°C and 50% relative humidity) a maximum of 28 days. Samples were prepared at equivalent emulsion solids contents of 2.75% (by weight of soil) to provide a baseline for comparative analysis. The emulsions reported here have percent solids contents of 40-50% such that 2.75% polymer solids content translates to 5-6% total weight of emulsion, including water. Portland cement was used at 2.75, 6 and 9% levels for the control specimens and at 3% for the samples containing polymer/cement combinations. Stress-strain measurements were performed to determine the unconfined compressive strength and toughness and under both “wet” and “dry” conditions. Results indicate that some emulsion polymers achieve compressive and retained wet strengths on the same order as the cement-stabilized soils at their lower additive levels. Further testing indicates that combinations of PCIII and polymer emulsions may create a synergistic effect and produce specimens capable of withstanding greater loads than cement alone. Toughness values reveal that some soil-polymers exhibit significantly higher values for both the wet and dry testing condition than soil-cements, indicating higher strains were attained at yield (defined as the point of maximum applied stress). Samples with polymer/cement also demonstrate the increase in toughness over those containing only cement. Cure time behavior of several soil-polymers indicates that these systems may not have reached ultimate physical properties even after 28-day cure times.