Department of Transportation

Jar Slake Test

Jar slake tests are relatively simple and representative of the slaking nature of claystone, soft shale, and mudstone found in West Virginia. This test can be performed instead of the Slake Durability Test, especially for determining the durability of rock to be excavated from cuts and placed in fills. Most of the rock in the western portion of West Virginia tends to break down after being exposed. This rock can be problematic since it will continue to break down over a long period of time and will move or creep causing failures in our roadway and approach fills if not properly identified, placed, and compacted. For this purpose, we offer the Kentucky Method presented below to identify soft shale.

Under this testing, any rock that results in a category less than 6 (see below) should be considered as soft shale, which should be placed and compacted as random material per our standard specifications.

Kentucky Method 64-514-08
Revised 02/26/08
Supersedes KM 64-514-02
Dated 11/15/02

  1. SCOPE: The test is intended to assess the resistance to weathering of rock samples by a simple and quick procedure. The basis for the test is that weakly cemented or compacted argillaceous material absorb moisture when subjected to a very basic, simulated weathering process. This procedure supplements the Slake Durability Index (SDI) test.

    1. Drying oven capable of maintaining a temperature of 230° ± 9°F.
    2. Beakers of at least 250 milliliters capacity.
    3. Distilled water or tap water.

    1. Oven-dry an approximately 50-gram sample of material for at least 6 hours, then let it cool for 30 minutes at room temperature.
    2. Immerse the sample in a beaker of distilled or tap water at least half an inch below the surface.
    3. Observe at frequent intervals for the first half hour, noting the time with each observation; then at intervals thereafter for 24 hours.

  4. REPORT: Jar slake values shall be reported according to the following criteria:

    Category Behavior
    1 Degrades to pile of flakes or mud (Complete Breakdown).
    2 Breaks rapidly and/or forms many chips.
    3 Breaks slowly and/or forms many chips.
    4 Breaks rapidly and/or develops several fractures.
    5 Breaks slowly and/or develops few fractures.
    6 No change.