HMA Design (Surface)
The surface course is the layer in contact
with traffic loads and normally contains the
highest quality materials. It provides
characteristics such as friction,
smoothness, noise control, rut and shoving
resistance and drainage.
4/13/2015
CEE 320
1
Steve Muench
Surface HMA
This top structural layer of material is sometimes
subdivided into two layers:
Wearing Course. This is the layer in direct contact with traffic
loads. It is meant to take the brunt of traffic wear and can be
removed and replaced as it becomes worn. A properly designed
(and funded) preservation program should be able to identify
pavement surface distress while it is still confined to the wearing
course. This way, the wearing course can be rehabilitated before
distress propagates into the underlying intermediate/binder
course.
Intermediate/Binder Course. This layer provides the
bulk of the HMA structure. Its chief purpose is to distribute load.
HMA Types
The three most common types of HMA pavement are:
Dense-graded HMA. Flexible pavement information in this Guide is
generally concerned with dense-graded HMA. Dense-graded
HMA is a versatile, all-around mix making it the most common
and well-understood mix type in the U.S.
Stone matrix asphalt (SMA). SMA, although relatively new in the
U.S., has been used in Europe as a material for years to support
heavy traffic loads and resist studded tire wear. Also known as
Gap Graded
Open-graded HMA. This includes both open-graded friction course
(OGFC) and asphalt treated permeable materials. Open-graded
mixes are typically used as wearing courses (OGFC) or
underlying drainage layers because of the special advantages
offered by their porosity.
Dense-Graded HMA
Stone Matrix Asphalt (SMA)
Open-Graded Mixes
0.45 Power Gradation
0.45 Power Gradation Curve Using 19.0-mm (0.75inch) Maximum Aggregate Size
Calculations for a 0.45
Power Gradation Curve
Using 19.0-mm (0.75inch) Maximum
Aggregate Size
0.45 Power Gradation Curve for Different Maximum
Aggregate Sizes
Typical Aggregate Gradations
and Permeabilities
FHWA gradation graph showing
representative gradations
No.200
¾-in
No.4
Open Graded
Dense Graded
% Passing
0.45
power
curve
Gap Graded
Restricted
Zone
Uniform Graded
0.075 mm
4.75 mm
Sieve Size
19 mm
Hot Mix Asphalt (Dense-Graded)
Hot Mix Asphalt (Open-Graded)
Hot Mix Asphalt (Gap-Graded)
HMA MIX DESIGN

Texas Gyratory Compactor (TGC). For
dense-graded hot mix asphalt

Superpave Gyratory Compactor (SGC).

Marshalls Method
HMA MIX DESIGN, Performance
Concerns







Resistance to Permanent Deformation
Resistance to Fatigue and Reflective
Cracking
Resistance to Low Temperature (Thermal)
Cracking
Durability
Resistance to Moisture Damage (Stripping)
Workability
Skid Resistance
Marshall Mix Design Procedure
The Marshall mix design method consists of 6
basic steps:
 Aggregate selection.
 Asphalt binder selection.
 Sample preparation (including compaction).
 Stability determination using the


Density and voids calculations.
Optimum asphalt binder content selection.
Marshall Mix Design Procedure

The Marshall Stability and Flow Test
Marshall Mix Design Procedure
Typical Marshall Design Criteria
.
Mix Criteria
Light
Traffic
(< 104
ESALs)
Medium Traffic
(104 – 106 ESALs)
Heavy
Traffic
(> 106
ESALs)
Min
.
Min.
Min
.
Max
.
Max.
Max
.
Compaction
(number of blows on each end
of the sample)
35
50
75
Stability (minimum)
2224 N
(500 lbs.)
3336 N
(750 lbs.)
6672 N
(1500 lbs.)
Flow (0.25 mm (0.01 inch))
8
20
8
18
8
16
Percent Air Voids
3
5
3
5
3
5
Bad Mix







blue smoke - blue smoke indicate that the
mix is too hot.
stiff appearance
mix slumped in truck.
lean, dull appearance - this indicates that the
mix has insufficient asphalt.
rising steam - too much moisture.
segregation.
contamination.