dams with impervious membrane of asphalt concrete - Balwois

Binder Layer (BN)
Figure I.1. Types of impervious asphalt concrete membrane
a) The double lining membrane b) The single lining membrane,
Serves as a binding and leveling layer and foundation for the membrane. It is usually (4-10) cm thick and
should be placed only after a bituminous emulsion or hot bitumen is sprayed on the dam’s surface as a
tack coat. The functions of this layer are:
• Fixing the impervious layer by a good link of a aggregate,
• Transition between the bituminous concrete and the dam, in terms of deformability and
permeability,
• Leveling the irregularities of the dam’s surface,
• Bearing the capacity for the proper placing and compaction of the impervious layer.
Impervious Layer (I)
The next layer is well compacted impervious bituminous concrete layer (6-8) cm thick, which must be
watertight, stable and protected against stripping and aging.
The water-tightness results from the aggregate gradation, the percentage of asphalt-cement used and the
compaction of the mix. When the mix is compacted to a void content of 3 %, it is virtually impervious. The
compaction much beyond this point will cause the instability of the mix.
The stability is associated with the type and percentage of asphalt-cement binder and the voids content as
affected by compaction. The hot mix must be sufficiently stable to be placed and compacted on the slope
and then remain stable against creep at the service temperatures.
Stripping is an important consideration due to the constant contact between the membrane and the
reservoir. To prevent stripping, the asphalt cement content must be sufficiently high to coat all of the
aggregate particles.
BALWOIS 2008 - Ohrid, Republic of Macedonia - 27, 31 May 2008 4