CE 3700 Final Exam Study Guide
Lecture 7
Mineral Aggregate for HMA
Any hard or inert minerals used for mixing in graduated particles or fragments
-Sand
-Gravel (crushed stone)
-Slag
-Rock dust (powder)
*93-95% by weight or 75-85% by volume
*Responsible for load supporting capacity of pavements
*Pavement performance is influenced directly by the aggregate used
Aggregate classification by size
Course aggregate – retained on No. 4 Sieve
Fine aggregate – passes through the No. 4 Sieve
Mineral filler – at least 70% pass the No. 200 Sieve
Types of Aggregates desired for HMA mixtures
-Cubical aggregate
-Rounded aggregate
*The shape of the aggregate affects the shearing behavior of the aggregate under
load
Properties considered in the evaluation of aggregate for HMA mixtures
-Internal angle of friction
Round: Low angle of friction
Cubical: High angle of friction
-Particle shape
Flat, elongated
-Cleanliness
Clean, dirty
-Toughness
Resistance to abrasion
-Durability
-Absorption
Consensus/Source Aggregate Properties
Consensus
-Course aggregate angularity (CAA)
-Based on fractured faces, the fractured surface must be larger than
25% of the aspect ratio
-Fine aggregate angularity (FAA)
-Based on the air voids in a loose sample, the more angular the
aggregate the higher the void content
-Natural sands <45
-Manufactured sands >42
-The minimum value is 45%, (rounder particles pack tighter leaving
less air voids)
-Flat, elongated particles
-Based on the dimensional ratio of particles
-Elongated, ratio of length to width
-Flat, ratio of width to thickness
-Measured using a Flat, Elongated particles apparatus set on the 1:5
pivot point
-Maximum value is 10%
-Clay content
-Based on the sand equivalency value (SE)
-Minimum value is 45%
-Clay on aggregate particles reduces binder adhesion
Source
-Toughness
-Durability
-Cleanliness
Lecture 8
Composition of compacted HMA
Asphalt cement (binder)
5-8% by weight
15-25% by volume
Aggregate
93-95% by weight
75-85% by volume
Air
Bituminous Materials
Asphalt cement
-Naturally occurring
-Produced by petroleum distillation
-Excellent adhesive
-Waterproof
Tar
-Produced from burning coal
-Hazardous to health
-Fuel resistant
Types of Asphalt Cement (2-types)
Natural
Petroleum-based
Types of Asphalt
Asphalt cements-generally a refinery-produced material
-Distilled from crude oil
-At a high temperature it’s a liquid and easily mixed to adhere to
aggregate
-Has an adhesive and waterproof characteristic
Cutbacks-Asphalt cements “cut” with petroleum solvents
-Classified based on rate of solvent evaporation
-Rapid cure (Naphtha, Gas)
-Medium cure (Kerosene)
-Slow cure (Low viscosity oil)
Emulsions-Mixture of asphalt cement, water, and emulsifying agents
-Anionic
-Negative charge, Aggregate has positive charge (limestone)
-Cationic
-Positive charge, Aggregate has negative charge (silica gravel)
Asphalt Grading Systems
-Penetration Grading
-Viscosity Grading
-Aged Residue Viscosity Grading
-Performance Grading
This grading system is based on climate
PG 64-22
PG=performance grading
64=average 7-day max pavement temperature
-22=minimum pavement temperature
Asphalt Binder Testing Equipment
Rolling Thin Film Oven (RTFO)
-Simulates binder aging (hardening) during production and
construction
-Resistance to aging during construction
Pressure Aging Vessel (PAV)
-Simulates binder aging during service life
-Resistance to aging during service life
Rotational Viscometer (RV)
-Measures binder properties at high construction temperatures
Dynamic Shear Rheometer (DSR)
-Measures binder properties at high intermediate service
temperatures
-Resistance to permanent deformation and fatigue cracking
Bending Beam Rheometer (BBR)
-Measures binder properties at low service temperature
-Resistance to thermal cracking
Direct Tension Tester (DTT)
-Measures binder properties at low service temperatures
-Resistance to thermal cracking
Lecture 9
Purpose of Mix Design
It is the selection of an optimum amount of asphalt cement content that is
required to satisfy a prescribed criteria
Criteria
Volumetrics
VTM (voids in total mix), VMA (voids in mineral aggregate), VFA
(voids filled with asphalt)
Densification
Stages during the compaction process
The Steps in Mix Design
1) Material Selection
-Aggregate, Asphalt
2) Design Aggregate structure
-Select the aggregate gradation
3) Design asphalt content
-Optimum asphalt content
4) Evaluate mixture
-Moisture susceptibility
Objectives in Mix Design
Resist
-Permanent deformation
-Fatigue cracking
-Low temperature cracking
-Moisture induced damage
-Skid
Workabilty
Specific Gravities used in volumetric computation
Aggregate specific gravity (3-types)
-Bulk specific gravity Gsb
-Effective specific gravity Gse
-Apparent specific gravity Gsa
Mixture specific gravity (2-types)
-Mixture bulk specific gravity Gmb
The mass of a unit volume of mix compared to a unit volume of water
(Compacted sample)
-Mixture maximum specific gravity Gmm
Mass per volume of material containing no air voids, compared to a
unit volume of water (Loose sample)
Mixture Volumetrics properties
VTM ranges between 3% and 5%
VMA ranges between 11% and 14%
VFA ranges between 65% and 75%
Mixture total asphalt content
-Mass concentration of total asphalt binder, % by mass of total mix
Lecture 10
Criteria of Mix Design
Volumetric
VTM, VMA, VFA
Densification
Stages during sample compaction process
Primary consolidation
%Gmm at Ninitial (construction), (related to density)
Secondary consolidation
%Gmm at Nmax (end of life performance), (related to density)
N = # of gyrations
Related to the amount of expected traffic loading
Asphalt concrete mix design methods
1) Marshal mix design
2) Hveem mix design
3) Superpave mix design
What Superpave stands for:
Superior Performing Asphalt Pavement
*All volumetric computations are computed using Ndesign
*All calculations stem from a Gsb value that’s either calculated or given
Gsb=weight of OD sample/(weight of SSD sample – weight of submerged SSD
sample)
γw=1.0 g/cm3
γw=62.4 lb/ft3
Rolling thin film oven
-simulates binder aging
during construction
-resistance to aging
during construction
Rotational Viscometer
-measures binder
properties at high
temperatures
Pressure Aging Vessel
-simulates binder aging
during service life
-resistance to aging
during service life
Dynamic Shield
Rheometer
-measures binder
properties at high service
temperatures
-resistance to permanent
deformation and fatigue
cracking
Bending Beam
Rheometer
-measure binder
properties at low service
temps
-resistance to thermal
cracking
Direct Tension Tester
-measures binder
properties at low service
temps
-resistance to thermal
cracking