Sand type effect on the behaviour of sand-granulated rubber mixtures: Integrated study from micro- to macro-scales

The mechanical behaviour of rubber mixed with different types of host sands is investigated from micro- to macro-scales. The change of the mobilized friction angle because of rubber inclusion is associated to the change of inter-particle friction angle and the friction angle due to particle rearrangement. The mobilized friction angles at the peak and critical states were obtained from triaxial testing data, and the inter-particle friction angles at different sand and sand-rubber interfaces were measured by means of grain-scale experiments. It is found that: (i) The peak friction angle decreases after adding rubber particles for all host sands, which is more significant for dilative sands. (ii) For smooth and non-breakable sands, adding rubber increases the friction angle at the critical state, due to the increasing inter-particle friction from sand-rubber interfaces, but the reduction of sandsand contacts weakens the interlocking, leading to easier particle rearrangement. For rough and breakable sands, adding rubber decreases the friction angle at the critical state, since the inter-particle friction of sand-rubber interfaces is lower than that of pure sand interfaces, but leads to less particle breakage and thus harder particle rearrangement. (iii) State parameter works well in assessing the effect of rubber inclusion on the peak strength.