The Stripping of Penetration 85-100 Asphalt From Silicate Aggregate Rocks: A Laboratory Study

Report No: 71-R29

Published in 1972

About the report:

In Virginia stripping has occurred when certain of the acidic silicate rocks have been used as aggregate in bituminous paving. The purpose of this project was to discover which kinds of silicate aggregate would be most apt to remain well bonded in bituminous mixes and which would be more apt to have a poor bond and become stripped from their binders. 1. Neither the boiling test nor the classical static immersion test differentiated between the bonding abilities of the various types of acidic silicate rocks when used with a penetration 85-100 asphalt binder. 2. If a test which will so differentiate is needed, the heated static immersion test described in this report or one of the tests described in some of the more recent literature (9, 24) might be used for that purpose. 3.By means of the heated static immersion test it was determined that when one quarry is compared with another, the lighter colored, coarse grained aggregates, especially those whose composition is highly acidic and which contain little secondary mineralization, seem more apt to have a poor ability to remain bonded to penetration asphalt. Conversely, it was determined that aggregates which are darker colored and finer grained are more apt to have a good ability to remain bonded to bitumen. 4. Within a single quarry where the influence of secondary mineralization is the same throughout all the material, in all cases tested, the heated static immersion test showed the darker colored and fine grained material to have a better ability to remain bonded to bitumen than did the lighter colored and coarser grained material. 5. Whereas washing may improve the ability to remain bonded to bituminous coatings in the case of some aggregates (#28 and P-55), in the case of highly biotitic aggregates (P-1, P-10, P-51, and P-53) washing may lessen the bonding ability. 6.No exact correlation has been established between the specific mineralogic composition or textural type of a rock and its ability to retain bituminous coating. It is, therefore, recommended that each source of acidic silicate rocks be considered on its individual merits and no definite prediction of probable behavior in bituminous paving be made until representative samples of the aggregate have been subjected to empirical testing methods. 7. It is further recommended that whenever the run of aggregate from a quarry becomes more coarse grained or lighter in color that type of rock should be restricted to limited use.

Disclaimer Statement:The contents of this report reflect the views of the author(s), who is responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Virginia Department of Transportation, the Commonwealth Transportation Board, or the Federal Highway Administration. This report does not constitute a standard, specification, or regulation. Any inclusion of manufacturer names, trade names, or trademarks is for identification purposes only and is not to be considered an endorsement.

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Hollis N. Walker

Last updated: January 16, 2024

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