UFC 3-250-03
15 May 2001
a. Advantages and disadvantages. The addition of stone increases the strength of the sand
mixture significantly. However, the addition of stone may increase the cost and in some cases produce
a loose aggregate problem resulting in broken windshields or foreign object damage.
b. Uses. Stone-filled sheet asphalt pavements have the same uses as sand-asphalt mixtures.
4.
PENETRATION MACADAM.
a. General. A penetration macadam surface course is constructed beginning with a layer of rolled
coarse aggregate followed by a pressure application of asphalt cement. Next, the surface voids in the
coarse aggregate layer are filled with fine aggregate to lock in the coarse aggregate followed by an
additional application of asphalt binder which is then covered with fine aggregate and rolled. A minimum
amount of equipment is required for construction, and for this reason the pavement is particularly
adapted for jobs in remote localities involving small yardage. Macadam surfacing is not generally
considered equal in quality to asphalt pavements produced by central paving plants. The surface course
is not as dense as plant-mixed asphalt pavements, and the possibility of loosely bound surface
aggregates prohibits the use of penetration macadams on airfield and heliport pavements. Penetration-
type surfaces may be considered for roads and streets not subjected to traffic by tracked vehicles. The
use of penetration macadam construction has greatly diminished over the years because of new and
better developments in equipment and construction techniques for other pavement types.
b. Materials.
(1) Asphalt materials. The binder specified for penetration macadam is an asphalt cement.
The asphalt may be either an 85 to 100 or a 120 to 150 penetration-graded or an AC-5 or AC-10
viscosity-graded asphalt cement.
(2) Aggregates.
(a) Only clean, uncoated, dust-free aggregate should be used in macadam construction.
The aggregate should be composed of hard, angular stone with a one-size (uniform) gradation. The
gradation should also be strong enough to resist crushing under the construction rolling and should be
polish-resistant under traffic. Flat and elongated aggregate particles and wet or dusty aggregate are
undesirable. Wet or dusty material can result in poor adhesion and stripping.
(b) Tables 6-1 and 6-2 give the recommended gradations for 50 millimeter (2 inch-) and
64 millimeter- (2-1/2 inch-) thick macadam, respectively.
c. Design. Tables 6-3 and 6-4 present the general application rates for placing one application of
coarse, two of key, one of fine aggregate, and three applications of bitumen. Table 6-3 is for
50 millimeter (2-inch)-thick macadam, and table 6-4 is for 64 millimeter (2-1/2-inch)-thick macadam.
d. Placement.
(1) Special attention must be given to each course of aggregate and binder to insure that the
desired application rates are applied, that the rolling is sufficient, and that the desired grade and
smoothness are obtained.
(2) For better control of application rates, an aggregate spreader and an asphalt distributor
should be used. The spreader and distributor must be calibrated and checked for the specified
application rate. ASTM D 2995 offers a method of determining the application rate of asphalt
6-2
Previous Page
