Accelerated Weathering of Tough Shales: Final Report

About the report:

The purpose of this study was to find or develop a test that would identify a very tough but relatively rapid weathering type of shale that has caused problems when used in embankments as rock. Eight shales, including the problem shale, were collected and tested by the slake, slake durability, and modified sulfate soundness tests, and a new sulfuric acid test that was thought to simulate the type of weathering that takes place in the field. Quantitatively, the slake and slake durability tests did not differentiate between the shales very well. However, observations of the physical condition of the shales after testing did provide some useful information. The relatively rigorous modified sulfate soundness test and the new sulfuric acid test did differentiate between the shales, and the orders of responsiveness of the shales to the tests compared quite favorably. The clay mineral chlorite was dissolved from the shales by the sulfuric acid and the shales underwent considerable physical distress. Thus, it is recommended that dark colored shales should be checked first for the presence of iron sulfide; if it is found to be present, then the shales should be checked for chlorite. If both minerals occur in the same shale, that shale should be considered to have the potential for relatively rapid weathering. The variability determined by the more rigorous tests for shales that appeared to be of the same toughness suggests the need for a classification system for Virginia shales.

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