Lesson 1/Learning Event 1
Learning Event 1
ADVANTAGES AND LIMITATIONS OF BITUMINOUS SURFACING
INTRODUCTION
All bituminous materials are composed largely of bitumen, a black solid that gives bituminous
binders their black color, cementing ability, and waterproofing properties. Even though all
bituminous materials are black in color and are composed mainly of bitumen, their physical
properties differ greatly. Bituminous materials are classified into two main groups by origin:
Asphalts and Tars. These are the two bituminous materials used in the construction of roads and
airfields.
Bituminous surfaces are composed of compacted aggregate and bitumen (binder). The aggregate
transmits the load from the surface to the subgrade, takes the abrasive wear of the traffic, and
provides a nonskid surface. The functions of the binder are twofold. It binds the aggregate
together, thus preventing the displacement and loss of the aggregate. The binder also provides a
waterproof cover for the base and keeps surface water from seeping into and weakening that
material.
Pavements constructed with bituminous materials are economically, easily, and quickly, placed.
For this reason, these materials have gained tremendous importance to the military engineer in
the construction of roads and airfields.
Remember, the bituminous surface of a road or airfield is an important part of construction. Do
it right the first time.
Advantages
Bituminous surfaces are particularly adaptable to stage construction. Additional courses can be
added to existing pavements to provide further reinforcement if the loads or density of traffic
increases. The flexibility of bituminous surfaces permits slight adjustment caused by settlement
of the subgrade without detrimental effect. Bituminous wearing surfaces provide a resilient,
waterproof medium that protects the base course from water and traffic. Properly designed
bituminous wearing surfaces, when compared with concrete, are less affected by temperature
strains. Bituminous surfaces resist wear, weathering, and deterioration from aging with only
minimal maintenance.
While it is true that bituminous materials are highly versatile, and serve admirably in temporary,
expedient, and light traffic situations (where concrete is not justifiable), it is equally true that
thicker bituminous pavement designed for heavy and continuing duty are fully comparable to
concrete designed for the same service, consisting of heavy volumes of traffic or heavy wheel
loads. This is true not only for highways, roads and streets, but also for airfields.
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