Swell-shrink behavior of rubberized expansive clays during alternate wetting and drying

Abstract

The present study examines rubber’s capacity of improving the swell-shrink potential of expansive clays. Two rubber types of fine and coarse categories with different geometrical features were considered. The test program consisted of standard Proctor compaction and cyclic wetting- drying tests. Scanning electron microscopy (SEM) analysis was also performed to identify the soil- rubber amending mechanisms, and to observe the evolution of fabric in response to alternate wetting and drying. Cyclic wetting-drying led to the reconstruction of the soil/soil-rubber microstructure by way of inducing aggregation and cementation of the soil grains. The greater the number of applied cycles, the lower the swell-shrink features, following a monotonically decreasing trend, with the rubberized blends holding a notable advantage over the virgin soil. The tendency for reduction, however, was in favor of a larger rubber size, and more importantly the rubber’s elongated form factor; thus, predicating a rubber size/shape-dependent amending mechanism. The soil-rubber amending mechanisms were discussed in three aspects—increase in non-expansive content, frictional resistance generated as a result of soil-rubber contact, and mechanical interlocking of rubber particles and soil grains. The swell-shrink patterns/paths indicated an expansive accumulated deformation for the virgin soil, whereas the rubberized blends manifested a relatively neutral deformational state, thereby corroborating the rubber’s capacity to counteract the heave and/or settlement incurred by alternate wetting and drying.