Transcript MODULE 4 ASPHALT MIX DESIGN

MODULE 4
ASPHALT MIX DESIGN*
What’s it all about?
(*) Information taken from Asphalt Institute’s MS-2 manual, 6th Ed.
SCOPE
 What is a mix design?
 Would you recognize one if it
walked up to you and asked for
spare change?
 Basically, its just a recipe for
making hot mix.
 What are the ingredients?
SCOPE
 Well first you need a binder:
That would be the asphalt cement.
 What’s being bound together?
That would be the aggregate.
 The objective of the design process is
to “determine the proportions of asphalt
cement and aggregate that will give long
lasting performance as part of the
pavement structure”
(Asphalt Institute, MS-2)
SCOPE
 the percent asphalt cement is in terms
of the total mix mass in this course
 in order to get the right balance
between aggregate and binder we need to
know some properties of these materials
 the basic property of the aggregate is
its grain size distribution or gradation
 this, more than any other property will
affect the performance of the mix
OBJECTIVES
Objective 3.01
“to determine a cost-effective blend and
gradation of aggregates and asphalt
(cement) that yields a mix having:
1. sufficient asphalt (cement) to ensure a durable
pavement
2. sufficient mix stability to carry traffic without
distortion or displacement
3. sufficient voids in the total compacted mix to allow
for a slight amount of asphalt expansion due to
temperature increases without flushing, bleeding
and loss of stability
OBJECTIVES
Objective 3.01
4.a maximum void content to limit the
permeability of harmful air and moisture
into the mix
5.sufficient workability to permit efficient
placement of the mix without segregation
and without sacrificing stability and
performance
6.for surface mixes, proper aggregate
texture and hardness to provide sufficient
skid resistance in unfavourable weather
conditions”
(Asphalt Institute, MS-2)
MIX TYPES
Objective 3.02
The Asphalt Institute (MS-2) identifies
4 different types of asphalt paving
mixtures based on their functions
within the pavement:
1. Surface Course Mixtures (fine MPS*)
(*) MPS = Maximum Particle Size
2. Binder Course Mixtures (medium MPS)
3. Base Course Mixtures (coarsest MPS)
4. Sand-Asphalt Mixes (finest MPS)
Surface Course Mixtures
 for wearing surfaces, so fine aggregate
needed to give a smoother texture
 must still have sufficient stability and
durability for traffic loads
Maximum Particle Sizes range between
9.5 mm and 19 mm (⅜” to ¾”)
open-graded friction course (OGFC), a.k.a.
porous friction course or popcorn mix used to
reduce hydroplaning and increase skid
resistance
Objective 3.02
Binder Course Mixtures
intermediate layer between surface and base
larger Maximum Particle Sizes 19 mm - 38 mm
(¾” – 1 ½”)
can be used as a base course or as a surface
course where heavy wheel loads and tight
radius power steering turns are involved such
as is port facilities, logging yards and
industrial loading docks
Objective 3.02
Base Course Mixtures
can be placed directly on compacted subgrade
or over a granular base
Maximum Particle Sizes range up to 75 mm
(3”)
larger particle sizes result in higher stability
in dense-graded mixes and facilitate drainage
in open-graded mixes
Objective 3.02
Sand-Asphalt Mixes
Objective 3.02
produce tightest surface texture and with
proper aggregate type (hardness and shape)
can be highly skid resistant
minimum lift thickness is 15 mm (0.6”) which
is useful as overlay padding (scratch course,
leveling course)
Maximum Particle Sizes range between
4.75 mm and 1.18 mm (No. 4 to No. 16)
a.k.a. plant mix seal or sheet asphalt
MIX TYPES
Objective 3.02
The percent asphalt cement required for
mixes with the required properties
varies among these mix types according
to the maximum particle size:
1. Sand-Asphalt Mixes (highest %AC)
2. Surface Course Mixtures (lower % AC)
3. Binder Course Mixtures (lower % AC)
4. Base Course Mixtures (lowest % AC)
MIX DESIGN PROCESS
The Marshall mix design method involves
preparing and testing mix specimen at
trial % AC contents.
The steps that we will be covering are:
1. Sieve analyses of stock aggregates (stone, sand, mineral filler)
2. Proportion stock aggregates to produce a blend that meets specs
3. Measure specific gravities of stock aggregates and asphalt cement
4. Laboratory compaction of trial mix specimens (6 trial % AC’s)
5. Stability (or strength) and volumetric testing of each specimen
6. Analysis of results (determination of mix properties and optimum %AC)
Objective 3.02
Objective 3.02
Tests on Asphalt Cement
Test/Property
ASTM Designation
AASHTO Designation
Penetration
D5
T 49
Absolute Viscosity
D 2171
T 202
Kinematic Viscosity
D 2170
T 201
Flash Point
D 92
T 48
Thin Film Oven Test
D 1754
T 179
Rolling Thin Film Oven Test
D 2872
T 240
Ductility
D 113
T 51
Solubility
D 2042
T 44
Specific Gravity
D 70
T 228
Objective 3.02
Tests on Mineral Aggregates
Test/Property
ASTM Designation
AASHTO Designation
Los Angeles Abrasion
C 131 or C 535
T 96
Unit Weight
C 29
T 19
Sieve Analysis (Aggregates)
C 136
T 27
Sieve Analysis (Filler)
D 546
T 37
Specific Gravity (Coarse)
C 127
T 85
Specific Gravity (Fine)
C 128
T 84
Specific Gravity (Filler)
D 854 or C188
T 100 or T 133
Sulphate Soundness
C 88
T 104
Sand Equivalent
D 2419
T 176
Particle Shape
D 4791
-
Objective 3.02
Tests on Paving Mixture
Test/Property
ASTM Designation
AASHTO Designation
Asphalt Content
(Extraction)
D 2172
T 164
Asphalt Content (Nuclear)
D 4125
T 287
Recovery of Asphalt
D 1856
T 170
Density and Voids Analysis
See next slide
Maximum Specific Gravity
D 2041
T 209
Bulk Specific Gravity
D 1188 or D 2726
T 166
Steps for Voids Analysis
(T is AASHTO Test and D or C is ASTM Test)
1. Measure bulk specific gravities of coarse aggregate (T 85
or C 127) and fine aggregate (T 84 or C 128).
2. Measure specific gravity of asphalt cement (T 228 or D 70)
and of mineral filler (T 100 or D 854).
3. Calculate the bulk specific gravity of the aggregate
combination in the paving mixture.
4. Measure maximum specific gravity of loose paving mixture
(D 2041).
5. Measure bulk specific gravity of compacted paving mixture
(D 1188 or D 2726).
6. Calculate the effective specific gravity of the aggregate.
7. Calculate the asphalt absorption of the aggregate.