Wearing of fine-grained aggregates in noise reducing pavements and generation of dust

Category Other
Group GSI.IR
Location International Geological Congress,oslo 2008
Author Torppa, Akseli۱; Rنisنnen, Mika۲; Mertamo, Matti۳
Holding Date 15 September 2008

Typical asphalt concrete is composed of ca. 90 vol-% of aggregate in a mixture of bitumen and other binder and filler materials. The relative amounts and properties of these components, e.g. the aggregate size, vary in different types of asphalts. The required physical and mechanical properties of asphalt aggregates are defined in national and international standards, and their testing is performed by standard test methods. For instance, the resistance to wear by abrasion from the studded tyres is determined by the Nordic abrasion test (EN 1097-9) which, according to the European standard, is performed on relatively coarse (11/16 mm) aggregate. However, it is well known that the mechanical properties of aggregates do not change linearly with the particle size and, thus, the test results cannot be directly extrapolated to substantially finer or coarser aggregate fractions. Consequently, there are no standard methods for determining the resistance to studded-tyre wear of, e.g., relatively fine aggregates such as those used in many noise reducing asphalt pavements. In the present study, we have applied the Nordic abrasion test method to test crushed rock aggregates in size fractions of 8/11mm and 4/8 mm. The tests were complemented by detailed petrographic study to examine how geological properties of aggregates contribute to the mechanical wearing of fine-grained asphalt pavements and, as a result, to the formation of urban dust. In the pilot part of the project, samples from three meta-volcanic formations and three granite formations in southern Finland were selected for investigation. In this data set, the volcanic rocks displayed much better wearing resistance than the granites and are therefore expected to produce less dust under abrasion. Also, the particle shape was observed to be an important variable in the test group of 4/8 mm aggregates. The results emphasize the importance of geological characteristics, i.e., the textural and mineralogical properties of rock, when producing asphalts that are largely composed of <8 mm aggregate. The detailed petrographical analyses of aggregates are particularly important in countries, where the widespread use of studded tyres in the winter sets requirements for the wearing resistance of asphalt pavements. In the forthcoming studies the scope will be extended to other rocks, such as gneisses and diabases, that are widely used as asphalt aggregate in areas of crystalline bedrock, e.g., Finland, Norway and Sweden.