Compactness of Scrap Tyre Rubber Aggregates in Standard Proctor Test

Scrap tyre derived aggregates (TDA) have been used in civil engineering since 1990-ties, mainly in the USA. The material may be used in various forms and sizes - from powder, through granulates, tyre shreds, chips. The TDA applications include: lightweight fills in embankments over soft soils, lightweight backfills behind retaining walls, insulation and drainage layers etc. In most of the works the material needs to be compacted to decrease the void ratio of the aggregate and reduce future settlement. This paper presents a study on compactness of four different fractions of scrap tyre rubber (A: 0.1 - 1 mm, B: 0.5 - 2 mm, C: 2 - 5 mm and D: 10 - 40 mm) in the standard Proctor test. The results in the form of dependency of dry and bulk density on water content are compared also with adequate results obtained for a clean uniform medium sand. It turns out that the optimum moisture content can be clearly estimated only in the case of the finest fraction (sample A) and it is equal to about 40%. The variability of dry density is however small - it changes from 0.54 to 0.61 g/cm³. Coarser TDAs behave more like self-draining materials - they retain much less water and the maximum moisture content equals to about 18%, 23% and 38% in case of tyre chips (D), 2 - 5 mm grains (C) and 0.5 - 2 mm grains (B) respectively. The dry densities for samples B, C and D possible to be obtained with standard Proctor energy have been estimated as: 0.61, 0.60 and 0.59 g/cm³ respectively.