The Wearing Characteristics of Mineral Aggregates in Highway Pavements

About the report:

Fifteen asphaltic concrete and seventeen portland cement concrete pavements located in Virginia were chosen for studies of aggregate wear and related wet pavement friction. Coarse aggregates from thirteen different geologic formations and quarry sources had been utilized in construction of the pavements. Field measurements of wet friction and pavement profiles and laboratory studies of aggregate petrography and surface microtexture were emphasized. The results of the research showed that aggregates can be classified into three categories based on their response to the wearing stresses of vehicle tires: (1) very homogeneous aggregates lacking significant zones and planes of weakness wear predominantly by abrasion; (2) aggregates marked by zones and planes of weakness wear predominantly by degradation or particle removal; and (3) aggregates of intermediate physical structure wear by a combination of abrasion and degradation. Polishing is most common with aggregates undergoing abrasion, the rate being dependent on the absolute hardness of the mineral constituents. Polishing removes micro-asperities and reduces the adhesion component of wet friction. The loss of macrotexture, or pavement relief, is common where degradation prevails. This loss, if excessive, retards water removal or drainage and adversely affects the hysteresis or tire deformation component of pavement friction. Optimum wet friction conditions are judged to prevail when a combination of abrasion and degradation creates an aggregate surface containing significant elements of both macro- and microtexture. It is concluded that careful petrographic study of aggregate mineralogy and texture will allow a high degree of prediction of the resulting surface configuration as aggregates wear under traffic.

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