b. Based on evaluation of current materials
following guidance is
provided for use of engineering fabrics or asphalt rubber.
(1) When overlaying asphaltic concrete, engineering fabric or asphalt
rubber can be used in Areas I and II. A E-inch minimum overlay is required in
Area I, and a minimum 3-inch overlay (at least two layers) is required in Area
I I . Neither asphalt rubber nor engineering fabric should be used when
overlaying asphaltic concrete in Area III.
(2) When overlaying Portland-cement concrete (PCC), asphalt rubber is
not effective as an interlayer and, therefore, should not be used.
Engineering fabric is effective when used in Areas I and II, but should not be
used in Area III. An engineering fabric strip is used to cover all joints
when overlaying PCC to minimize the material costs. A
is required in Areas I and II to ensure satisfactory performance.
(3) Recommended properties of fabrics are shown in table 1.
(4) When local experience has shown satisfactory performance
different from that described in the above guidance, local criteria should be
(5) Performance of new materials used in Area III will be monitored
and guidance`will be provided on favorable materials as they develop.
(6) The guidance in this ETL will be incorporated in the appropriate
road and airfield manuals.
6. Implementation. This letter will have routine application as defined in
ER 1110-345-100. This letter will have application to all
future civil works projects, except where local requirements govern otherwise.
FOR THE COMMANDER:
WILLIAM N. MCCORMICK, J .
Chief, Engineering Division
Directorate of Engineering