# Sand Rubber Mixtures under Oedometric Loading: Sand-like vs. Rubber-like Behavior
###### Abstract  
Each year, the number of scrap tires disposed of in huge piles across the world continuously increases. Consequently, new recycling solutions for these materials have to be proposed. Among them, one possibility consists of shredding tires and mixing the obtained tire chips with sand, which can be used as alternative soils in various geotechnical applications, such as backfilling for retaining structures, slope and highway embankment stabilization, road constructions, soil erosion prevention, and seismic isolation of foundations. Such types of mixtures are highly heterogeneous due to the important difference in elasticity and deformability between the two constituents, which leads to complex mechanical behavior. In this article, the one-dimensional loading/unloading behavior of sand-rubber mixtures is investigated by laboratory strain-controlled experiments performed for different packing densities, particle sizes, rubber contents, and sand/rubber size ratios. After a global analysis of the increase of the packing deformation with the rubber fraction and the stress level, a novel criterion to classify the behavior of the mixture as sand-like or rubber-like was proposed, based on the concavity of the void ratio--log of vertical stress curve. The concavity increased with the stress level and the rubber fraction, up to the limits where the saturation of the voids due to their filling with rubber induces a rubber-like behavior. A simplified phase diagram, limited to the range of this study, is proposed. The one-dimensional confined stiffness and the swelling behavior were also analyzed. s amd rubber mixture; granular materials; oedometric compression +
Footnote †: journal: Applied Sciences  
loading conditions [18; 19; 20; 21; 22; 23], and the monotonic strain-stress-strength behavior of various combinations of soils, rubber types, and particle size dimensions [24; 25; 26; 27; 28; 29]. Exploration of the small strain stiffness of sand-rubber composites has also been conducted [19; 30; 31; 32; 33; 34]. The applicability of the critical state framework to sand-rubber mixtures has been reported in [35; 36]. A simple model for predicting the isotropic compression behavior based on soft-rigid interactions at the particle scale has been developed in [37]. Particle-scale mechanisms that underlie the energy dissipation were observed in the sand-rubber mixtures under oedometer testing and have been previously reported [38]. An excellent summary of a range of experimental studies, including the physical characteristics of the mixture materials used as well as the testing conditions and main conclusions, can be found in [35; 36]. While, as equally emphasized by the same authors, comparison between different studies remains challenging, the examination of published results shows that the response of the sand-rubber composite mixtures is mainly controlled by the volume fraction of the components and the characteristic geometrical contrasts of the rigid/soft particles through either the aspect ratio (length over width) of fiber-type rubber inclusions, which encourages additional fiber-soil type internal interaction mechanisms [22; 26; 39; 40] or the rubber to sand particle size ratio, as shown by [19; 30; 41]. Based on a given set of these variables, the behavior of sand-rubber mixtures can vary from sand-like to rubber-like with a transitional state confinement stress-dependent. Large triaxial tests on sand-rubber mixtures and the behavior of mixtures as sand-like (for rubber contents < 34%) and rubber-like (rubber contents > 34%) have been reported in [42]. Further, [PERSON] et al. [43] proposed three different behavioral zones, viz. sand-like (rubber contents < 18%), rubber-like (rubber contents > 35%), and sand-rubber-like (18% < rubber contents < 35%). [PERSON] et al.