Geotechnical Properties of Clays Modified with Recycled Crumb Rubber

In the United States, nearly 300 million tires were discarded in 2003. Since rubber tires are not biodegradable and occupy a large portion of available landfill space, 35 states have banned whole tires from landfills, while 11 states have banned all tires from their landfills. As a result, many tires are improperly discarded posing several health and environmental concerns. Crumb rubber has been used in a variety of applications in geotechnical engineering including in highway pavements and backfills of retaining walls. In each of these applications, the rubber tire was used as an individual material, but the use of crumb rubber to modify soil may provide additional benefits. In this study, MH and CH types of soils were modified using different sizes and quantities of crumb rubber and used to evaluate the improvement in geotechnical properties. A Harvard miniature compaction apparatus was used to determine the maximum dry density and optimum moisture content for each sample that was, then, tested in an unconfined compression device to measure the undrained shear strength. Direct shear tests were also conducted on the soils modified with crumb rubber. Moreover, permeability and consolidation characteristics of the clay-tire mixtures were also evaluated for all mixtures. The results showed that for MH soils, the maximum dry density increased as the percentage of crumb rubber in the soil increased, while increasing the size of the crumb rubber increased the maximum dry density; no significant variation in the optimum moisture content was found with the addition of crumb rubber in the MH soil. In the CH soil, as the size of the crumb rubber increased, the maximum dry density of the modified soil increased with the highest maximum dry density when 2%-4% crumb rubber added. The optimum moisture content was found to increase as the size of the crumb rubber increased with the lowest optimum moisture content at 2% crumb rubber content. The highest strength was observed at 2-4% rubber in MH soils and at 4% rubber in CH soils. In general, the increase in strength was found to be larger when a larger size of the crumb rubber was used to modify the soil. Similar effect was observed in the coefficient of consolidation and permeability values. From this study, it is concluded that crumb rubber can be effectively used to improve the compaction and strength characteristics of weak soils.