United States Department of Transportation
i
Microscopic and X-Ray Examination of Rock for Durability Testing
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1976-12-01
[PDF-27.65 MB]
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Edition:Final Report
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Abstract:Study of quarry rocks, core, weathered rock, and road base aggregates from 12 sources in western Oregon reveals that degree and type of alteration and textural distribution of glass are the chief causes of degradation in basaltic aggregate used in road construction. Smectitic clays are the alteration products most responsible for breakdown. Sampling for testing should include weathered rock. Some standard tests for durability show a higher correlation than others with type and degree of alteration and with actual service records of basaltic rock. A standard petrographic microscopic test must precede . other testing. A stain test using benzidine to reveal the presence and textural distribution of montmorillonite and nontronite clays shows promise as a supplement to standard AASHTO tests. In very doubtful cases, tests using activation by thermal neutron irradiation may be used to detect sodium distribution in rocks. Scanning electron microscopy is of value to detect micro-fracturing.
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