There are no unique and universally accepted procedures for the determination of the maximum and minimum void ratios, emax and emin. This issue is particularly pertinent in the characterisation of the alternative sustainable materials examined in this study: well-graded tyre-derived aggregate (TDA), recycled concrete aggregate (RCA) and their mixtures (RCA-TDA), with a rubber content by weight of ΧM = 11, 23 and 55%. Uniformly graded TDA–sand mixtures with ΧM = 0, 15, 27, 42, and 100% were also considered. The results from dry and moist samples were compared with void ratios obtained after Proctor compaction and static loading. It was found that, in contrast to vibration for sand and sand–TDA mixtures, the most efficient densification techniques involve impact compaction at the optimum water content for RCA and RCA-TDA and static loading for TDA. Inversion of dry RCA, TDA and RCA-TDA samples in a graduated cylinder was the most effective to consistently achieve emax but induced visible segregation. Unlike sand–rubber mixtures, well-graded RCA-TDA did not exhibit a threshold rubber content at which emax and emin fell below those of RCA and TDA alone, suggesting reduced segregation. The findings offer practical guidance for improving specimen preparation reproducibility in the laboratory.
Kowalska et al. (Thu,) studied this question.