Effects of Aggregate Shape on the Stability of Bituminous Mixes

A laboratory study was made of the effects of crushed particles, both coarse and fine aggregate, on the stability of bituminous-aggregate mixtures. Crushed limestone and varying percentages of crushed and uncrushed gravel were used as the coarse aggregate while variation in the shape of the fine aggregate was obtained by using rounded natural sand and crushed-stone sand. These aggregates were used in three rep­ resentative bituminous mixes: a dense or surface mixture, an open or binder mixture, and an essentially one-size grading. The asphalt content of each mixture was either determined by Corps of Engineers’ design procedure or was that normally used by the State Highway Department of Indiana. Asphalt of 60-70 penetration was used throughout the study. Triaxial specimens with varying per­ centages of crushed coarse aggregate and different fine aggregates were molded by the double-plunger compaction method. These specimens were tested in triaxial compression apparatus at different confining pres­ sures. Resulting data were evaluated in terms of M ohr’s theory of strength, assuming a straight line M ohr’s rupture envelope. All data were analyzed statistically and the following results were indicated. With no variation in fine aggregate there was no significant differ­ ence in the strength, angle of internal friction and cohesion values for dense-graded mixtures with 0 and 100 per cent crushed gravel. A defl-