superpave workshop 2004 -5th edition.pdf

SUPERPAVE Workshop 2005 Page 1 Prepared and Developed by: Advance Engineering Center (AdEC)

1 Session 1 First Day - Getting Started

SUPERPAVESUPERPAVEMix Design WorkshopMix Design Workshop

aT))aJatJcTaJSJ)Jc)a[J)R)SRpJ

Prepared and Presented byDr. Ibrahim Al-Dubabe

Fifth Edition June, 2005


Workshop on the new SHRP technology for the

design of asphalt concrete hot mixes

SUPERPAVE

Superior Performing Asphalt Pavements

Based on the Asphalt Institute Mix Design Method as outlined in

SUPERPAVE Series No. 2 (SP-2) Third Edition 2001 Printing



Table of Content

Session Title Page

Session 1 Getting Started 4

Session 2 Introduction 12

Session 3 SUPERPAVE Overview 21

Session 4 Mixture Criteria 28

Session 5 Selection of Binder 41

Session 6 Selection of Aggregate 56

Session 7 Selection of Design Aggregate Structure 62

Session 8 Selection of Design Asphalt Content 80

Session 9 Evaluation of Moisture Sensitivity 89

Session 10 Solving Some SUPERPAVE Mix Design Problems

98

Appendix ePAVE User Manual ----




Session No 1

Getting StartedSession No 1

Getting StartedGetting Started



AdEC welcomes the reader and participant in this workshop. We will start by setting-up some norms to our meetings. First, let us know each other and strengthen the line of communication by answering the questions in the second page. Details of the remaining items shown will come in the next slides.

3 Monday, December 27, 2004

WELCOMEWELCOME

Icebreaking My Specialty Handouts & Software Participation & Quizzes Time Management Assistance (AdEC to them)

Add Notes and Ask Questions Below:



Quiz No (1) 1. What is your? Name: ________________________________________________ Company: _____________________________________________ Degree: _____________________________________________ Years in materials: 2. Define the following: Air voids: _____________________________________________ VMA: ________________________________________________ VFA: 3. Do you know SUPERPAVE? What does it stand for? 4. Connect the points below using four connected lines without passing twice over any line:



5 Friday, October 01, 2004

My SpecialtyMy Specialty

Interaction and continues evaluation. Participation is root of Success. If you teach me then you know it ??!! Continues Process Improvement (CPI). Quizzes during process not after the fact ! All are TQM Fundamentals.


Total Quality Management (TQM) relays heavily in many concepts one of which is participation and teamwork. That is, also, so important in the learning process. As others usually leave evaluation at the end of the process, we will incorporate it within the process to have the chance to improve as we proceed not after the fact.




Handouts and SoftwareHandouts and Software

H/O are unique Software (ePAVE) is developed by AdEC ePAVE Available upon request


ePAVE, AdEC development, was designed to:

1. Do the SUPERPAVE computation and decisions.

2. Be a user friendly 3. Produce a design

report. 4. Give some hints

for the designers to solve some design problems.




Time ManagementTime Management

Workshop for five days (Sat. to Wed.) Start 8:10 sharp End the sessions 12:00 sharp No late arrivals will be allowed Questions and comments are open If lab. work needs, group continue after 12:0


Time is live ..




Assistance Assistance

AdEC is always ready to work with you to handle all issues and matters related to highway engineering especially materials (PMA, NA, HMA, PCC, Soil,).

P.O Box 8658Riyadh 11492, Saudi Arabia Tel: 4567377 , Fax: 4548166

Mobile: 0505814198Email: [email protected]

AdEC is always ready to work with you to AdEC is always ready to work with you to handle all issues and matters related to handle all issues and matters related to highway engineering especially materials highway engineering especially materials (PMA, NA, HMA, PCC, Soil,(PMA, NA, HMA, PCC, Soil,).).

P.O Box 8658P.O Box 8658Riyadh 11492, Saudi Arabia Riyadh 11492, Saudi Arabia Tel: 4567377 , Fax: 4548166 Tel: 4567377 , Fax: 4548166

Mobile: 0505814198Mobile: 0505814198Email: [email protected]: [email protected]





Workshop ProgramWorkshop Program

Session 4:Mixture Criteria

Session 3:Overview

Session 2:Introduction

Session 1:Getting Started

Sat.

Lab. Work:RV, Gyratory Comp. and ITS

Demo.

Session 9:Moisture

Sensitivity

Session 8:Design Asphalt

ContentMon.

Design Example:ePAVE Solution

Session 10:Solving Some SUPERPAVE Mix

Design Problems.

Tues.

Session 5:Selection of

Binder

9:00- 8:10

Brake

9:50 10:00

Session 7:Design Aggregate Structure

Exam

Session 6:Selection of

Aggregate

9:00 9:50 11:00-12:00

Review of the H/OWed.

Sun.

10:00 11:00Day

Add Notes Below:



2

IntroductionIntroduction

Thursday, September 30, 2004

Session No. 2Session No. 2



3

Session 2 First Day - Introduction

BackgroundBackground... Importance of the Subject... Importance of the Subject

InternationallySHRP (1987 to 1993) Background

LocallyMOT instructions circular No. 2253

MOT second circular No. 30789 Saudi Arabia Roads Accidents 1425


This workshop is important because MOT wants to use SUPERPAVE in the design of asphalt mixes and stop using other methods. SUPERPAVE method is not simple and needs a good understanding to correctly use it and benefit from its power.



4

Friday, October 01, 2004

More Into it ... Why SUPERPAVE?More Into it ... Why SUPERPAVE?

Limitation of current grading systemsPenetrationViscosity

No tests to simulate in-service aging


The problem statement simply was "the roads met all specifications and yet perform bad". Rutting and cracking is always happening. We need to improve our specifications and design methods.





60

Pen.Vis.

Vis.

ABC

Consistency

Temperature ,C25 135

hard

soft


2. A & C have similar viscosity at low temperature but differ at high temperature

3. B & C have similar consistency at 60 C temperatures.

Three asphalts (A), (B) and (C) are having the same penetration and viscosity grades but note the following:

1. A & B have similar line slope hence similar temperature susceptibility but have different consistency at the range of temperature encountered in the real life.

Fifth Edition June, 2005 but differ at all other


Here again; A, B and C have the same consistency at 25 C (i.e. penetration), but have completely different temperature susceptibility and hence performance.



A

BC

Con

sist

ency

(pen

etra

tion)

Temperature ,C25

Asphalt A = Low temp susceptibilityAsphalt B = Medium temp susceptibilityAsphalt C = High temp susceptibility




The main part of the Hot Mix Asphalt (HMA) design technology was the selection of the materials and the selection of the proportions. The current practices in both parts have not given us a good performing mix.

7

Friday, October 01, 2004


Drawbacks of current design practices:Marshall Impact compaction. Shear strength of HMA is not adequately estimated.Hveem Important volumetric properties are not determined. Expensive and not portable.

pavements Unsatisfactory performance




8 Session 2 First Day - Introduction

More Into it More Into it What is What is SUPERPAVE?SUPERPAVE?

The final product of the SHRP Asphalt Research Program is the SUPERPAVE mix design system for new construction and overlays. This system employs a series of new performance based specifications, test methods

and practices for material selection, accelerated performance testing, and mix design (1994).


SUPERPAVE is defined as a "Hot Asphalt Mix design system that includes both the design method and the mixture specifications".



9

Session 2 First Day - Introduction

Performance based (PG) Integrated approach

SpecificationMix design method

Based on projects climate & trafficCompaction simulate actual conditions

What is New in SUPERPAVEWhat is New in SUPERPAVE


SUPERPAVE researchers have introduced new:

1. Binder grading system

2. Aggregate selection

3. Design method A unique feature of the SUPERPAVE is that it is performance-based specification. The tests and analysis is directly related to field performance



10 Session 2 First Day - Introduction

What is New in SUPERPAVE ?What is New in SUPERPAVE ?SUPERPVAE Binder Properties are related to Performance

Test Performance property Mode of failure

RTFOT & PAV

RV

DSR (HT)

DSR (IT)

Ageing & Hardening

Handling & Pumping

Fatigue Cracking

Permanent Deformation

Cracking

Flow

Rutting

Cracking Structural

BBR & DTT Thermal Cracking Low temp. Cracking


For example, the binder

E, as y on

l

ce.

testing, evaluation and grading in SUPERPAVshown conceptuallthis slide, can be relatedto field performance by engineering principles. In addition, these tests are performed at temperatures that are encountered in the realife during the pavement servi



2 Monday, November 22, 2004

Session No. 3

SUPERPAVEOverview


SUPERPAVESUPERPAVEOverviewOverview



3 Session 3 First Day SUPERPAVE Overview

SUPERPAVE Design StepsSUPERPAVE Design StepsStep 4:

Moisture sensitivity

Step 1:Selection of materials(binder, agg., modifiers, etc.)

Step 2:Selection of DAS

Step 3:Selection of DAC


This is an overview of the SUPERPAVE design

it

l

system showing the main steps needed to accomplish the mission. There are four steps to design a hot mix asphalt. A main feature of the SUPERPAVE design method distinguishingfrom the conventional design methods (Marshaland Hveem) is the optimization of the

Fifth Edition June, 2005 in the

Design Aggregate tructure.

aggregate gradationDAS step before the designer searches for the optimum asphalt content in the DAC step. Note: DAS =S


The first step is to select

osen

t the y

the materials, starting by the asphalt binder. The selection process is basedon the actual conditions oftraffic and environment of the project location. SUPERPAVE has chfour aggregate properties to be considered in the selection of the aggregate and labeled them as consensus aggregate properties. In SUPERPAVE, the aggregate must meeconsensus properties andoptionally meet the agencrequirements.


Step 1:Step 1: Selection of MaterialsSelection of Materials

Selection of materials

Binder Aggregate Modifiers Others

dd Notes and Ask Questions Below:

Finally select the modifier, in case it is needed, to upgrade the locally available binder to meet the selected binder grade based on traffic and environment for the project location. Carefully follow the modifier producer recommendations for the production of PMA (polymer modified asphalt - PMA).

A




Step 2:Step 2: Selection of DASSelection of DAS

Selection of DAS

Evaluate andselect

confirming blendCompactDevelop Trial Blends


A

The selection of Design S)

efore

C), or

election of the DAS is the

t, the ial

will be

ject

Aggregate Structure (DAis a new introduction to the HMA design by SUPERPAVE. Bselecting the Design Asphalt Content (DAthe optimum asphalt content as refer to in Marshall Mix design method, the aggregategradation (or structure)must be selected. Smost complex part of the method. To fully understand this pardesigner must place specattention and care. Selection of Design Aggregate Structure illustrated by solving manually a design proexample.


SUPERPAVE Workshop 2005 Page Prepared and Developed by: Advance Engineering Center (AdEC)


Step 3:Step 3: Selection of DACSelection of DAC

Selection of DAC

Compact Analyze Select DACNmax

verification


25


A

After selecting the DAS t

phalt

in

the

ote: Preparation of

nly not

To protect against maximum densification by traffic, specimens are gyratory an compacted at the DAS and DAC to Nmax. Note: %Gmm @ Nmax must be less th

98%.

(i.e. by selecting the mospromising aggregate blend), the Design Ascontent (DAC) can be selected. Computation DAC and DAS are similar. Select the DAC at 4.0 air voids and check to confirmthat the other volumetric properties and Dust Proportion is within requirements. Nspecimens in DAS andDAC are gyratory compacted to Ndes oNmax.


Finally, for protection against water effect, evaluate the moisture sensitivity of the HMA using AASHTO T 283. This can be achieved by compacting six specimens using the gyratory compactor for a number of gyrations enough to produce a specimen with 7% air voids (%Gmm = 93); then testing them after conditioning to determine the indirect tensile strength. The ITS loss should be less than 20%.


Step 4:Step 4: Moisture SensitivityMoisture Sensitivity

MoistureSensitivity

EvaluateCompactSelect Nx





http://training.ce.washington.edu/WSDOT/Modules/03_materials/03-3_body.htm

Good information is available in this internet website:

http//:training.ce.washington.edu/WSDOT/Modules/03_materials/03-3_body.htm



2 Monday, November 22, 2004

Session No. 4 Session No. 4 Session No. 4 Design Parameters &

Mixture CriteriaDesign Parameters & Design Parameters &

Mixture CriteriaMixture Criteria



There are three basic design input required by SUPERPAVE, these are: 1. Nominal maximum size of the aggregate (NMS). 2. Project location. 3. Traffic level in terms of Equivalent Single Axle Load (ESALs)

4 Session 4 First Day - Design Parameters & Mixture Criteria

Design ParametersDesign Parameters

SUPERPAVE Basic Design Parameters

Location

NMS

Traffic (ESALs)






NMS, Nominal Maximum Size is One sieve size larger than the first sieve

to retain > 10%.Five Mixture Gradation

NMS MS37.5 mm 50.0 mm25.0 mm 37.5 mm 19.0 mm 25.0 mm12.5 mm 19.0 mm09.5 mm 12.5 mm


The first design parameter that is needed by the SUPERPAVE method is the nominal maximum size of the aggregate comprising the mixture. The definition of the nominal maximum size is as given here, and, consequently, the maximum size is one sieve larger than the NMS in the standard SUPERPAVE sieve group. Five NMSs have been included in the SUPERPAVE. The selection of the Nominal Maximum Size for a specific location must be based on engineering judgment with the following considerations:

Fifth Edition June, 2005 1. The contract documents

2. SUPERPAVE implementation guidelines issued by MRDTM.


6

Session 4 First Day

NMS Example NMS Example

No 200

No 100

No 50

No 30

No 16

No 8

No 4

3/8

1

Sieve Size, in

0.075

0.15

0.3

0.6

1.18

2.36

4.75

9.5

12.5

19

25

Sieve Size, mm

3.1

4.0

7.8

14.2

20.9

28.2

37.2

63.7

76.6

94.0

100.0

% Passing

NMSMS

>10%


3. The Layer thickness requirements using the general formula outlined in MOT specifications stating that the target or design thickness equals three (3) times the nominal maximum size.

4. The nominal

maximum size should increase with depth.

In this example, the Maximum Size (MS) is 25.0 mm, the Nominal Maximum Size (NMS) is 19.0 mm and the Sieve that retains more than 10% is 12.5 mm.


SUPERPAVE Workshop 2005 Page 32 Prepared and Developed by: Advance Engineering Center (AdEC) Session 4 First Day


Location:

1. The geographical location of the project where the Hot Mix

A

The second parameter is the location. This parameter covers two types, the first is the geographical location of the project; the second is the position of the layer within the pavement. The project location is needed by SUPERPAVE to allow the designer to select the binder asphalt grade

FAsphalt (HMA) will be used.

2. The position of the layer

(PG). This selection is based on:

1. High pavement design temperature 6

within the pavement


For the local conditions of the Kingdom of Saudi Arabia, Dr. Hammad AL-Abdullwahb, Dr. Ibrahim Al-Dubabe and other coworkers have developed temperature zoning map of the Kingdom in KACST project "Adaptation of SHRP Performance Based Binder Specifications to the Gulf Countries"1996

at a depth of 20mm from the pavement surface and

2. Low pavement design temperature.

ifth Edition June, 2005


For the position of the layer, SUPERPAVE specifies two levels; the layer is either < 100 mm or > 100 mm from the surface. If less than 25% of a layer is within 100 mm of the surface, the layer may be considered to be below 100 mm for mixture design purposes.


Position in Pavement Position in Pavement

Note: if less than 25% of the layer is within the surface then consider in the bottom.

Aggregate Base Coarse

Bottom 100 mm

Top 100 mmPavement Surface




The third design input is the Traffic in terms of ESALs; the definition is as shown in the slide. The agency, Ministry of Transport for example, should specify the design parameters in the project contract documents.


Standard Axle Standard Axle

8.2 ton (18,000 lb)

Tire Pressure = 75 psi



Traffic is the anticipated project traffic level in terms of ESALs expected on the design lane over a 20-year period regardless of the actual design life of the

roadway.



Class ESAL Traffic Typical Designation Range Description Applications

VL Less than 300,000 Very Light Agricultural roads, local & city streets (no trucks)

L 300,000 to 3 million Light Feeders, collectors ...

M 3 million to 10 million Medium Main Roads, city streets

H 10 million to 30 million Heavy Highways & Expressway

VH More than 30 million Very Heavy Heavily trafficked highways, industrial areas ..

Ministry of Transport (MOT) has identified the Ministry of Transport (MOT) has identified the following ESAL classes:following ESAL classes:



The following slides in the reminder of this session will illustrate the mixture requirements based on the design parameters. This slide shows the gyratory compactive effort or number of gyrations needed for the design. SGCE selection is exclusively based on the traffic levels.


1. SUPERPAVE Gyratory Compactive Effort (SGCE)1. SUPERPAVE Gyratory Compactive Effort (SGCE)

NmaxNdesNini

20516011575

1251007550

9876

VH (> 30)

M and H (3 to


The compacted specimens at the GCE must meet the criteria of the density as shown here at varying traffic levels and SGCE.


Mixture Design RequirementsMixture Design Requirements2. % Gmm = (100 Air Voids%)2. % Gmm = (100 Air Voids%)

< 90.5 < 98.096.0



Mixture Design RequirementsMixture Design Requirements3. VMA %3. VMA %

14.0 15.011.0 13.012.0

12.5 9.519.025.037.5Nominal Maximum Size, mmREQUIRED VMA %, minimum

Add Notes Below:

The Voids in the Mineral Aggregate (VMA), is a property of the aggregate structure. The VMA criteria is based on the nominal maximum size of the aggregate.




Mixture Design RequirementsMixture Design Requirements4. VFA %4. VFA %

VFA %

The Voids Filled with Asphalt (FVA) criteria is based on the traffic level and the NMS.

64-80

65 -75

65 7867-80

73 -76

70-80

65 -75

65 7870-80

NMS = 37.5

mm

NMS = 25.0

mm

NMS = 9.5

mm

NMS = 19.0

and 12.5 mm

VL (


The Dust Proportion is the ratio of the passing 0.075 mm sieve to the effective asphalt content. The DP ratio criteria is general for all mixes and will vary as shown depending on the gradation line position with respect to the restricted zone. Note: ARZ = Above the restricted zone. BRZ = Below the restricted zone.


Mixture Design RequirementsMixture Design Requirements5. Dust to Binder Ratio (Dust Proportion DP)5. Dust to Binder Ratio (Dust Proportion DP)

0.6 1.2ARZ

0.8 1.6BRZ

DP RatioPosition of

Gradation Line




Quiz No (2)

1. State three reasons for the importance of this subject? a) b) C) 2. How does SUPERPAVE protect against: Rutting: Fatigue Cracking: 3. What are SUPERPAVE mix design steps? Step 1: Step 2: Step 3: Step 4: 4. Define: NMS: ______________________________________________ Location: ____________________________________________ Traffic: 5. What GCE we must use to prepare DAS specimens? 6. Why do we need to perform the Nmax verification?



3 Session 5 Second Day Step 1: Selection of Binder

Session No. 5Selection of Binder

Session No. 5Session No. 5Selection of BinderSelection of Binder



4 Session 6 Second Day Step 1: Selection of Materials

Before the Design Before the Design

Use the Design Parameters of your project:

to identify the required SUPERPAVE criteria for your Hot Mix Asphalt.

ESAL (Class Designation or millions)NMSLocation (Geographical & within pavement)


In preparation for the design, the designer needs to identify the design parameters from the contract documents.




Before the Design Before the Design

Identify the following SUPERPAVE criteria for your Hot Mix Asphalt :

Asphalt binder gradeConsensus properties requirementsNumber of gyration for Nini, Ndes and Nmax% Gmm at Nini, Ndes and Nmax%VMA%VFA DP ratio





SUPERPAVE binder grading system is performance based.

Asphalt Binder . . . BasicsAsphalt Binder . . . Basics

AASHTO M320 (Standard Specifications for PerformanceGraded Asphalt Binder) For details see Asphalt Institute SP-1

Intended for Modified and unmodified asphalt

Performance based binder specifications

Depends on environment, traffic & reliability




PG x-y Where:

x is the average seven-day maximum pavement temperature y is the minimum pavement design temperature



Property is constant but temperature variesExample PG 64-22Every Grade is 6 C.





SUPERPAVE binder grading system is unique. Rheological values are fixed but temperatures to meet these values vary. This made the specifications very sensitive to temperature because behavior asphalt is really highly dependent on temperature.





Use of engineering judgment in selecting the appropriate grade is crucial to handle the boarder lines and protect against the dominating failures encountered in the area.


Asphalt Binder ... Grade SelectionAsphalt Binder ... Grade Selection

Determine project weather dataSelect reliabilityDetermine design temperaturesVerify asphalt PG (grade bumping)Determine temp-vis relationship




For the local conditions of the Kingdom of Saudi Arabia, Dr. Hammad AL-Abdullwahb, Dr. Ibrahim Al-Duabe and other coworkers have developed temperature zoning map of the Kingdom in KACST project "Adaptation of SHRP Performance Based Binder Specifications to the Gulf Countries"1996..



Selection of Asphalt Binder Grade is Based on the Kingdom Temperature Zoning Map




The selection of the binder grade based on the temperature-zoning map is basic and needs to be adjusted for the special project conditions for traffic load and speed. The designer must make grade bumping according to the table shown in this slide.



Grade Bumping for speed and loading of traffic; Increase the selected PG based on the map by the grade equivalents as shown below:

One GradeOne GradeTwo Grades

One GradeTwo Grades

One GradeTwo Grades

One GradeTwo Grades

VH (> 30)

optionalH (10-



Asphalt Binder ... Mixing & CompactionAsphalt Binder ... Mixing & Compaction

To determine laboratory mixing and compaction temperatures use Rotational Viscometer ASTM D 4402 and AASHTO T 316.

Mixing Temp @ 0.17 Pa.s ()Compaction Temp @ 0.28 Pa.s ()

Sample

Spindle

Sample Chamber


The laboratory compaction and mixing temperatures are determined by measuring the rotational viscosity at two different temperatures (say 135 and 165 C).




Temperature Viscosity Relationship

0.1

1

10

100 110 120 130 140 150 160 170 180 190 200

Temperature, C

Visc

osity

, Pa.

s

Mixing Range (0.17 Pa.s)

Compaction Range (0.28 Pa.s)

Asphalt Binder ... Mixing & CompactionAsphalt Binder ... Mixing & Compaction


Use the measured viscosities to generate the viscosity-temperature relationship in a semi-log paper (or using ePAVE). The designer must determine the:

1. Mixing temperature at 0.17 + .02 Pa.s

2. The compaction temperature at 0.28 + .03 Pa.s



Example

16 Tuesday, November 23, 2004

Asphalt Binder ... Grade Selection ExampleAsphalt Binder ... Grade Selection Example

Problem:

A) General Design Data:1. Location:

2. Design traffic:

B) Materials Properties:1) Asphalt from Riyadh refinery having the following data

Design a wearing coarse layer with thickness of 7.0 cm.

Al-Madinah Area Highway connecting Madinah with Yanbu

Assumed = 18.000.000 ESALs

0.075 Pa.sRotational viscosity at 165 C0.494 Pa.sRotational viscosity at 135 C

1.02Specific Gravity325 CFlash pointValueProperty




Example



From the temperature zoning map of the Kingdom the fitted grade is PG 70-10Adjusting the binder grade for traffic (grade

bumping):

Note: Locally produced asphalt (RT,RY,KW & BH) is PG 64-12 and -18, then we need polymer modification.

for speed no effect because high speed for level increase grade one step, then the suggested

grade for this project is PG 76-10






From my previous research, an asphalt from Riyadh refinery modified with 3% SBS meets PG 76-10 and has the following performance properties:

> 0.3000.305BBR m-value, -12 C< 300 MPa156BBR Stiffness, -12 C

PAV Residue Aged Binder< 3000 kPa2.362DSR G* x sin delta, 25C

RTFOT Residue - Aged Binder

Fresh Binder - original

> 2.2 kPa4.085DSR G*/sin delta, 76C

> 1.0 kPa1.495DSR G*/sin delta, 76C< 3 Pa.s1.562Rotational viscosity @ 135C> 230 C328Flash point

SUPERPAVE CriteriaResultsProperty

Example





Session No. 6Selection of Aggregates

Session No. 6Session No. 6Selection of AggregatesSelection of Aggregates



The aggregate requirements in SUPERPAVE are in two groups:

1. The consensus properties

2. The Source properties

The proposed aggregate for the project must meet the consensus requirements according to SUPERPAVE criteria. However, the source properties are agency specific (i.e. MOT); no requirements in SUPERPAVE were specified for them.


Aggregate:

Aggregate:

Consensus (SUPERPAVE) Requirements: GradationCoarse agg. Angularity, (CAA) ASTM D5821Fine agg. Angularity, (FAA) AASHTO T304Flat and elongated particles (F&E) ASTM D4791 Clay content, (SE) AASHTO T176

Aggregate . . . Physical PropertiesAggregate . . . Physical Properties

Aggregate . . . Physical PropertiesAggregate . . . Physical Properties


Source (MOT) Requirements:Toughness AASHTO T96Soundness AASHTO T104Clay lumps & friable particles AASHTO T112Others




16 Tuesday, January 11, 2005

SUPERPAVE Aggregate Requirements

100>100 30

MH (10-


SUPERPAVE specifies gradation using the 0.45-power gradation chart. The x-axis is an arithmetic scale of sieve size in mm raised to the power 0.45 as shown in the upper figure on the left. An important feature of the 0.45-power chart is that the maximum density gradation line plots as a straight line from the origin to the maximum aggregate size. As shown in the middle figure in the left. SUPERPAVE has added two important features to the 0.45-power chart these are the control points and the restricted zone. Control Points. Control points function as master ranges through which gradations must pass. Control points are placed at the nominal maximum size, an intermediate size (2.36 mm), and the smallest size (0.075 mm). The control point limits vary depending on the nominal maximum aggregate size of the design mixture.


Aggregate . . . Gradation BasisAggregate . . . Gradation Basis

Aggregate . . . Gradation BasisAggregate . . . Gradation Basis

% P

assi

ng

Sieve Size Raised to the 0.45 Power

Example:4.75 mm Sieve Plots at (4.75)0.45 = 2.02

100

80

60

40

20


% P

assi

ng


100

80

60

40

20

19.0 mm

Maximum Density Line

Maximum Size




Aggregate Aggregate Gradation Gradation RequirementsRequirements

% P

assi

ng


100

80

60

40

20

19.0 mm

Maximum Density Line

Maximum Size

NominalMaximum

Size

12.5 mm

Control Point

Restricted Zone


In most cases, a humped gradation indicates an over-sanded mixture and/or a mixture that possesses too much fine sand in relation to total sand. This gradation often results in tender mix behavior, which is manifested by compaction problems during construction. These mixtures may also offer reduced resistance to permanent deformation (rutting) during their performance life. The restricted zone prevents a gradation from following the maximum density line in the fine aggregate sieves. Gradations that follow the maximum density line often have inadequate VMA to allow room for sufficient asphalt for durability. These gradations are typically very sensitive to asphalt content and can easily become plastic with even minor variations in asphalt content.

Restricted Zone. The restricted zone resides along the maximum density gradation between the intermediate size (either 4.75 mm or 2.36 nun) and the O.3-mm size. Figure 3.10 shows the control points and restricted zone for a 12.5-mm SUPERPAVE mixture (12.5-mm nominal maximum and 19.0-nun maximum size). The restricted zone forms a band through which it is generally recommended that the gradation not pass. Gradations that pass through the restricted zone from below the zone have often been called "humped gradations" because of the characteristic hump in the grading curve that passes through the restricted zone.



Quiz No (3) 1. In SUPERPAVE, What are the bases for selecting? GCE Density VMA% VFA% D/P ratio 2. Which statement is correct? A) ___ B) ___ A) In the binder specs. temperature is fixed and property varies B) In the binder specs. temperature varies and property is fixed 3. How can we determine compaction and mixing temperatures ? 4. What are SUPERPAVE requirements for the aggregates? 5. Does CAA and FAA criteria vary with depth of layer?

YES_____ No: _____ 6. Define Maximum Size and Nominal Maximum Size? MS NMS




Session No. 7

Selection of Design Aggregate StructureSelection of Design Selection of Design

Aggregate StructureAggregate Structure




5 Session 7 Session 7 Third Day Third Day -- Step 2:Step 2: Selection of DASSelection of DAS

Step 2:Step 2: Selection of DASSelection of DAS

A) Establish trial blends:

B) Compact trial blend samples:

C) Evaluation

Develop Three blends Determine combined aggregate properties

Estimate trial AB% Prepare mixture Gyratory to Ndes

Analyze and select the most appropriate blends to be used to select DAC

Selection of DAS

Trial Blends Compact Evaluate


After selecting the materials, the designer must start the process of selection of the design aggregate structure (DAS). DAS comprises three main steps as shown in the adjacent slide.




A) Establish Trial BlendsA) Establish Trial Blends

1) Establish trial blends based on: Hot bin gradations Blending % to meet SUPERPVAVE Criteria Control points for the design NMS Restricted zone for the design NMS Minimum of three blends are selected


In order to establish the trail blends, the designer must consider the shown items.




2) Compute combined aggregate properties Estimate mathematically the combined

aggregate properties based on the blending percentages and the aggregate properties.

For the selected blend verify the combined properties by testing.



SUPERPAVE requires developing a minimum of three blends from the available hot bins samples in the project site. The blending percentages are selected using ePAVE so that the resulted gradation line: 1 is away from the maximum density line. 2. is within the control points. 3. is outside the restricted zone (strong recommendation).




Use the following formula to Compute combined aggregate properties :

Property of the Combined Aggregate = B1 x P1 + B2 x P2 + B3 x P3 + B4 x P4


P2

B2

Hot bin 2

P3

B3

Hot bin 3

P4P1Value of the property of aggregate from hot bin

B4B1Blending Percentage of aggregate from hot bin

Hot bin 4Hot bin 1Variable


Once the gradation of the trial blends are selected, the designer must compute the combined properties for each blend using the blending ratios and the original properties of the individual aggregates from the hot bins.




B) Compact trial blendsB) Compact trial blends

Select % Trial Asphalt Binder ( ) using one of the following methods:

Pbi

Computation (AASHTO PP-28) Experience SUPERPAVE suggestions


To compact specimens from the three blends, we need to estimate asphalt content. The design can select and use any one of the shown methods. By computation which will be shown in details in the next slides. By the designer experience which can help in identifying the initial asphalt binder content based on the historical information applicable to the project and aggregate used.





1) Estimate Trial Blend (% AB) By Computation:a. Estimate the effective specific gravity of the

blends (Gse) using:Gse = Gsb+ C x (Gsa Gsb)

Gsb = Aggregate bulk specific gravityC = Aggregate absorption factor is assumed 0.8 but for absorptive aggregate use 0.6 or 0.5Gsa = Aggregate apparent specific gravity


Or by utilizing SUPEPRAVE suggested values shown below: NMS Suggested % 37.5 3.5 25.0 4.0 19.0 4.5 12.5 5.0 9.5 5.5 The Computation method to estimate asphalt content for the three trial blends based on AASHTO PP28 is shwon.




b. Estimate the volume of asphalt binder (Vba) absorbed into the aggregate for each blend using:

Ps x (1-Va )Vba = x(1/Gsb 1/Gse) x 100

(Pb)/Gb (Ps/Gse)Vba = volume of absorbed binderVa = volume of air voids (assumed 0.04)

Pb = percent of binder (assumed 0.05)Ps = percent of aggregate (assumed 0.95)Gb= Sp. Gr. Of binder (assumed 1.02)



Computation method to estimate asphalt content for the three trial blends




c. Estimate volume of the effective binder (Vbe) of the trial blends using:

Vbe = 0.081 -0.02931 x ln (Sn)Where:

Sn = the nominal maximum size of the aggregate blend in inches



Computation method to estimate asphalt content for the three trial blends




d. Finally estimate the initial AB% (Pbi) for each trial blend using:

Ps x (1-Va)Ws =

(Pb/ Gb + Ps / Gse)

Gb x (Vbe + Vba)Pbi =

(Gb x (Vbe + Vba) + WsWs = weight of aggregatePbi = percent binder by weight of mix



Computation method to estimate asphalt content for the three trial blends Design project example data. Hand computation is not recommended; use of ePAVE simplifies the process and guarantees the accuracy of the results.





2) Prepare Hot Mix Asphalt Using:

Apply the Short Term Oven Ageing (AASHTO PP2)Measure Gmm

The trial blends Design Aggregate Structure The estimated initial trial asphalt binder (Pbi) The mixing and compaction temp. determined form

the temp.-vis. relationship


After doing the computation, the designer must compact two specimens using the gyratory compactor for each blend using the estimated asphalt content and the gradation that was selected for each blend. STOA is the Short Term Oven Aging.





3) Compact 2 specimens for each blend to Ndes (determined for the ESAL of your project); then for each specimen: Measure Gmb Measure the specimen height at Nini & Ndes


Refer to the slide on page 34 to define the Ndes for your project based on the ESAL. After compaction, determine the compacted mixture properties as shown here.




1. Determine %Gmm @ Ndes by dividing the Gmb by Gmm x

100 %Gmm @ any Nx by multiplying %Gmm @ Ndes

by the ratio of the height at Ndes to the height at Nx from the gyratory compaction data.

Air voids & VMA using:% Air voids = 100 - % Gmm @ Ndes % VMA = 100 (% Gmm @ Ndes x Gmm x Ps) / Gsb

C) Evaluate Trial BlendsC) Evaluate Trial Blends






%Gmm @ any Nx = %Gmm @ Ndes xHNdes

HNx

HNdes = Height of specimen at Ndes

HNx = Height of specimen at any N

Where:


To determine the % Gmm at any N (gyratory compactor rotation) use the shown formula. Note that the gyratory compactor will give you only the height of the sample at each gyration (N).




Selection of DAS Selection of DAS ExampleExample

Computation of % Gmm at any Nx

2.563Gmm

95.4115.2Ndes = 1002.445Gmb

94.7116.08093.8117.26093.1118.05092.4119.04091.5120.13087.7125.71086.5127.0Nini = 885.1129.05

% GmmH, mmN


Design project example.




2. Estimate @ 4% air voids (96% Gmm @ Ndes): Asphalt content % using:

Pb,estimated = Pbi (0.4(4-Va)

VMA using:% VMAestimated = %VMA initial + C(4-Va)

VFA using:% VFAestimated = 100 x (%VMAestimated - 4.0)/% VMAestimated

% Gmm @ Nini using:% Gmm estimated @ Nini = % Gmm @ Nini (4.0 Va)


Note:C = 0.1 if Va < 4.0C = 0.2 if Va > 4.0


IMPORTANT SUPERPAVE system design the mixes by determining the aggregate gradation (DAS) and asphalt content percentage (DAC) for the HMA at a level of Air Voids of 4.0%




3. Calculate DP ratio

4. Summarize results and Compare with SUPERPAVE criteria and select the most confirming blend.

Compute Pbe using:Pbe = - (Ps x Gb ) x (Gse Gsb)/GsexGsb) + Pb,estimated

DP using:DP = P0.075 / Pbe





Quiz No (4) 1. What are the bases for the selection of the NMS? 2. Define: Control points: Restricted zone: 3. Why we have to do the short term oven aging? For how long? 4. How can we compute %Gmm @ any Nx? 5. What is the air void percentage at which we estimate the mix properties in the selection of the potential blend? (Step 2: Selection of DAS)? 6. How can we estimate the combined aggregate properties?



2 Wednesday, November 24, 2004

Session No. 8Selection of

Design Asphalt Content

Session No. 8Session No. 8Selection of Selection of

Design Asphalt ContentDesign Asphalt Content



5 Session 8 Fourth Day - Step 3:Step 3: Selection of DACSelection of DAC

Selection of DAC

Compact Analyze Select DACNmax

verification

Step 3: Selection of DAC


The selection of the optimum asphalt content (Design Asphalt Content DAC), is performed after selecting one blend from the three potential blends (i.e. the aggregate blend that has conformed to SUPERPAE criteria)




A.

Compact samples of the selected blend

Analyze

Select DAC at 4.0% air voidsVerify mixture densification at Nmax

i. Prepare mixture at four AB%ii. Compact to Ndes

B.i. mixture Volumetric propertiesii. Generate graphs

C.D.

Step 3: Selection of DAC


The selection of the optimum asphalt content (Design Asphalt Content DAC), is performed after selecting one blend from the three potential blends (i.e. the aggregate blend that has conformed to SUPERPAE criteria)




Prepare HAM using four Asphalt Binder %s:

Measure GmmCompact 2 specimens @ each AB% to NdesMeasure specimen height and Gmb

X X - 0.5 X + 0.5 X + 1.0%

Where: X = Estimated binder content from step 2

at 4.0 air voids for the selected blend

A)A) Compact SamplesCompact Samples


Eight specimens are compacted by the gyratory compactor to Ndes using the selected blend and four asphalt content parentages computed as shown in this slide




Use the same formulas in the selection of DAS to compute: % Gmm @ Ninitial and Ndes Volumetric properties (Air voids, VMA, VFA) DP ratio Generate graphs for each property vs. AB%

B)B) Analyze the resultsAnalyze the results


For the selection of the DAC, the designer shall use the computational formulas of the volumetric properties, the D/P and other properties that were used in the DAS step. The results of the computation will be used to generate graphical relationships between the AV%, VMA% and VFA and the asphalt binder content.




B) B) Analyze the resultsAnalyze the results








From the graphs @ 4.0 % air voids determine DAC and check:

Compare with SUPERPAVE criteria and adjust your design as needed.

VMA and VFA and % Gmm @ Nini Compute DP at DAC

C)C) Select DACSelect DAC


The control of the design is to select the DAC at 4.0% air voids, then perform a check by determining the other properties at this DAC and comparing them with SUPERPAVE criteria; if they meet then proceed to the next step, otherwise adjust your design as needed.



This step in the selection of DAC, is to verify the mix properties at Nmax. Specifying a maximum density at Nmax prevents designing of a mixture that will compact excessively under traffic, become plastic and produce permanent deformation (Rutting). Since Nmax represents a compactive effort much grater than Ndes


D)D) NNmaxmax VerificationVerification

Gyratory compact 2 specimens to Nmax Compute %Gmm @ Nmax Compare the results with SUPERPAVE criteria and adjust your design as needed.




Quiz No (5) 1. What is SUPERPAVE suggested asphalt binder content percentages to start the selection of DAC process?. 2. Why we need to verify the mixture properties after selection of DAC? What is the SGCE we must use to compact the specimens? 3. Define : Nmax: Ndes: 5 State some suggestions to improve your VMA% if your design does not confirm to the VMA criteria?




Session 9Moisture Sensitivity

Evaluation

Session 9Moisture Sensitivity

Evaluation



5 Session 9 Third Day - Step 4:Step 4: MoistureMoisture SensitivitySensitivity

Moisture SensitivityMoisture Sensitivity

MoistureSensitivity

EvaluateCompactSelect Nx

Step 4:Step 4:


The last step in the SUPERPAVE design method is to evaluate the mixture of the selected blend and selected asphalt content for the effect of water.




Moisture SensitivityMoisture Sensitivity

Select Nx7 % air voids

Compact specimens6 specimensCompact to Nx

EvaluateAASHTO T283Tensile strength ratio is 80% minimum.Compare with SUPERPAVE criteria and adjust your design as needed.

Step 4:Step 4:

9

99

999


Six specimens are prepared at a level of compaction to yield an air voids % of 7%. Then the specimens are tested according to AASHTO T 283 to determine the stability loss.




Select NxSelect Nx

Use the densification data of the Nmaxverification step to determine the number of gyrations to achieve 7% air voids.

Note: 7% air voids = %Gmm of 93.0

A)A)


Follow the standard test procedure to conduct the moisture evaluation and MOT SUPERPAVE Implantation Guidelines.




Determination of N to Achieve 7% voids Determination of N to Achieve 7% voids

%Gmm @ any Nx = %Gmm @ Nmax xHNmax

HNx

HNmax = Height of specimen at Nmax

HNx = Height of specimen at any N

Where:


The specimens are prepared at a level of compaction (i.e. Gyratory compactor rotations) to yield an air voids % of 7%. The designer must use the Nmax densification data to determine the N at which the specimen has air voids of 7% using the shown formula.




Determination of N to Achieve 7% voids Determination of N to Achieve 7% voids

2.563Gmm

95.4115.2160

2.445Gmb

94.7116.0100

93.8117.270

93.0118.150

92.4119.040

91.5120.130

87.7125.710

86.5127.08

85.1129.05

% GmmH, mmN

ExampleExample

50 118.1 93.0


Design Project Example Data.




Compact SamplesCompact SamplesB)B)

Prepare HAM using DAS and DAC

Gyratory compact 6 specimens to Nx

9

9





EvaluateEvaluateC)C)

Three specimens are control (no conditioning)The other three is conditioned for 24 h at 60 oCTest all specimens to determine maximum

indirect tensile load at failure

999

Load Load





EvaluationEvaluationC)C)

Compute ITS Maximum allowable ITS loss is 20%Compare with SUPERPAVE criteria and adjust

your design as needed.

999




2 Sunday, December 12, 2004

Session No 10Session No 10Typical Problems in

SUPERPAVE Mix DesignTypical Problems in Typical Problems in

SUPERPAVE Mix DesignSUPERPAVE Mix Design



3

Session 10 Fifth Day

Main Problems Main Problems ..

Asphalt Binder:

Aggregate:

Hot Mix:

Binder PG selection in case the project crosses two zones PG adjustments for speed and ESAL PMA lab testing results are different from the manufacturer recommendations.

Inaccurate measurements of Specific Gravities. (Gsb, Gsa, Gmb, Gmm ) FAA method selection in AASHTO T304.

Low VMA. The designed mix fail in the moisture sensitivity testing (TSR is less than 80%).



SUPERPAVE Workshop 2005 Page 100Prepared and Developed by: Advance Engineering Center (AdEC)

4


Asphalt Asphalt

1.0 Problem:

Solution:What binder PG must be selected in case the project crosses two zones?

Select the highest PG Split the project in to two PG or more. Use engineering judgment to select the PG based on the historical performance

of the project or similar in the area.




5


Asphalt Asphalt

2.0 Problem:

Solution:

How can we adjust PG for speed and ESAL in a project where these factors are different in some of the project locations?

Select the highest ESAL and the lowest speed (check cost ?) Use more than one PG. Use engineering judgment to select the PG based on the historical performance

of the project or similar in the area..




6


Asphalt Asphalt

3.0 Problem:

Solution:

What shall we do if the PMA lab testing results are different from the manufacturer recommendations?

Check PMA production instructions as given by the manufacturer for mixing mechanism, time and temperature.

Check the polymer content. If everything is OK, use your results, since the PMA physical and rheological

properties are asphalt source dependent.




7


Aggregate Aggregate

1.0 Problem:

SolutionInaccurate measurements of Specific Gravities. (Gsb, Gsa, Gmb, Gmm )

The volumetric properties are the heart of the SUPERPAVE mixture design system , which depends on the specific gravities of the materials; hence, high caution must be practiced in the measurements of the neededspecific gravities.

Read the standard procedures carefully and make sure they are applicable to your case.

Check all of your laboratory equipment for calibration, damage and errors. Do some self training and education. Follow the standard procedure carefully.




8


Aggregate Aggregate

2.0 Problem:

SolutionWhich method we should use to measure the FAA in AASHTO T304

Use method A




9


Hot Mix Hot Mix

1.0 Problem:

Solution

Move gradation away from the maximum density line.Gap-grade the gradation (reduce the amount between two sieves) Reduce the amount passing 0.075 mm sieve (No 200)

Use particles with high angularityUse particles with rough surface texture.

Increase manufactured sand

What can I do to increase the VMA in my design?

The VMA is an aggregate property which depends on the packing characteristics of the aggregate.

Gradation:1.2.3.

Surface texture:1.2.

3. More ..

How to Increase Voids in Mineral Aggregate Guidelines to Increase VMA of SUPERPAVE Mixtures (1)

Introduction The heart of the SUPERPAVE mixture design system is aggregate properties and volumetric properties. If all the requirements are met, the resulting mix design should have: A strong aggregate skeleton for permanent deformation resistance. Sufficient asphalt binder for fatigue and asphalt binder aging resistance. Sufficient air voids space to hold plastic properties at bay and prevent permanent

deformation. Problem An issue which has been experienced is the difficulty of obtaining adequate voids in the mineral aggregate (VMA). Although the number of mixtures which have experienced difficulty is in the minority, the mix designers have become frustrated. Problem mixes typically will have low VMA and will be non-responsive to changes in gradation. For example, a 19.0 mm nominal maximum size mixture calls for 13.0% VMA. Say a mix designer who is trying to design below the restricted zone finds the estimated VMA in trial blends to be in the low 12's. Further, he finds that if the gradation is varied within the range available below the restricted zone that the VMA varies from the low 12's to the high 12's, 13.0% seems unachievable. The designer knows that adding additional sand will open up the mixture. But what about the restricted zone? What to do?



First, the designer should realize that the packing characteristics of aggregate particles and hence VMA is dependent on three factors: 1. gradation 2. surface texture 3. shape In the example, the designer has investigated the effect of gradation within the limits below the restricted zone but has not yet considered surface texture or shape. The mix designer is correct that additional fine aggregate will increase VMA but the specifications prevent adding sand because of the weakening effect which will occur in the aggregate skeleton. If the contract allows mixtures above the restricted zone the designer can investigate such mixes, although other problems will be faced, in particular, meeting density requirements at N initial. Two competing demands are occurring during the mix design. Sufficient inter-particle space must be available for a minimum amount of asphalt binder and the aggregate must have a sufficiently strong skeleton to carry the traffic loads. SUPERPAVE specifications demand that adequate VMA be obtained without weakening the aggregate skeleton. Gradation Effect Changing the gradation (particle size distribution) of a mixture will influence the amount of space in the aggregate skeleton. The effect of gradation is separated from shape and surface texture effects if all sized particles have the same shape and texture. Research published by Nijboer in the 1940's, Goode and Lufsey in the 1960's and the Asphalt Institute in the 1980's provide a basis for the 0.45 power chart. Nijboer investigated aggregate gradations plotted as the log percent passing versus log particle size. He showed a maximum packing density for both gravel and crushed aggregates when the slope was 0.45. Goode and Lufsey reconfirmed Nijboer's results on gravel aggregates. Hence, the basis of the 0.45 power chart. Work by the Asphalt Institute evaluated the drawing of maximum density lines on a 0.45 power chart for both gravel and crushed limestone mixtures. Lower the Minus 0.075 mm Content Lowering the dust content in a mixture will increase the VMA. This effect may not be entirely from the effect of gradation, but never the less it has one of the stronger effects on VMA. Reducing dust content to the lower end of the specification will maximize the amount of VMA which can be obtained. If the dust content is coming from mineral filler adjusting the gradation can be simply a matter of reducing the amount being used. If the dust is coming predominately from one of the aggregate stockpiles, say screenings, try to reduce the amount of that stockpile. If the screenings are the only manufactured fines coming into the mix it may be necessary to wash them or blend them with a washed screening. But first check out other easier ways of increasing VMA. Make sure to add baghouse fines during the mix design if the fines are going to be added back into the mix during production. These fines will reduce VMA of the produced mixture. If friable aggregate particles are used, a greater quantity of dust should be used during the design since they tend to create more dust during construction. Including baghouse fines in the mix will make the design more accurate and reduce the amount of "VMA collapse" which occurs from design to production.



Gap-Grade the Gradation Try to blend the aggregates to give a gap grade. If the amount of material between two sieves can be reduced, the mixture will have a higher VMA. The reason has to do with packing. Smaller particles fill space in between larger ones. By gap grading the mixture the amount of a coarse sieve is increased and the amount of material between the next two sieves is decreased. Hence the mixture can not compact together as tightly, that is, VMA is increased. Re-screen the Stockpiles If the stockpiles contain a broad range of sizes it may be necessary to re-screen the piles into different sized products and re-blend them together at different percentages. For example, with a mobile plant where the aggregate for a single project is to be crushed in a gravel pit, the aggregate may need to be split into more than two stockpiles. If the stockpiles already exist when the mix design is being done, one of the piles may need to be re-screened on the 9.5 mm (3/8 inch) screen. Part of the sand may be excess. The mix design may not be able to use all of the sand which is present in the pit. Even if the mix design is using manufactured aggregate products there may be instances where splitting a stockpile and using different percentages in the design may be necessary. If VMA can not be obtained with a set of stockpiles the option of splitting one of them may be more desirable than obtaining an alternate stockpile from a different source. Surface Texture Effect The way in which aggregate particles pack together for any given gradation is influenced by the surface texture of the particles. Rougher textures generate more friction between aggregate particles and resist compaction. Therefore, under a standard compactive effort, say a design number of gyrations, the mixture will not compact as much and VMA will be higher. Typically crushed faces have more texture than non crushed faces. In the case of gravel aggregate, the more of the particle surface which has a crushed face, the more surface texture will be available. Usually the more crushed a particle is, the more surface texture it will have but not always. Some aggregates fracture with very smooth faces so crushing may not always increase texture Increase Manufactured Sand If manufactured sand and natural sand are being used together in a mix design the manufactured sand portion can be increased to increase surface texture. Switching out 20% natural sand for a washed manufactured sand with good "bite" can increase VMA by 2%. Good bite? Squeeze a handful and feel the way the particles bite into one another. Be aware of any offsetting gains in surface texture caused by increased dust. For example, if the natural sand is clean and the manufactured sand has a high minus 0.075 mm content, the benefit of increased surface texture may be offset or completely erased by increased dust content. Increase Crush Count Surface texture of the coarse aggregate can be increased by increasing the crush count, particularly crushed-two-face particles.



Shape Effect For any given gradation the density to which aggregate particles will pack is influenced by the shape of the particles. Cubical particles will not pack as tightly as flat "potato chip" particles. In the gyratory compactor, as under traffic, the flat particles lay down flat, one on top of the other. Therefore, there is not much space between them. The VMA is low. Under traffic, particles are flattened out. They roll down. The same effect occurs in a gyratory compacted specimen 10


Hot Mix Hot Mix

1.0 Problem Contd:

Solution

Use aggregate with low flat and elongated particles (1:3 instead of 1:5) Examine crunching operation (feed rate, cone setting,)VSI crushers tend to produce more cubical particles than cone crunchers.

What can I do to increase the VMA in my design?

The VMA is an aggregate property which depends on the packing characteristics of the aggregate.

Shape:1.2.3.

Under Marshall compaction the particles are not so free to rotate. In fact, flat particles tend to bridge in a Marshall mold and give high VMA. Therefore, be aware of the influence of particle shape when comparing Marshall specimens to SUPERPAVE specimens. Evaluate Flat and Elongated Particles If a mix design is giving low VMA measure the flat and elongated particles. SUPERPAVE specifications limit the percentage of particles with a ratio 5:1. Measure the percentage of particles which exceed a 3:1 or 2:1 ratio. If the percentages are high, say greater than 40%, try adding a coarse aggregate which has a lower percentage. It may be possible to change just one of the coarse aggregate stockpiles for another which is more cubical. Adding an intermediate sized coarse aggregate with cubical shapes will disturb the larger particles from lying flat, one on top of the other. The VMA will increase. The crushing operation can make a difference. Examining the feed rate, cone settings, etc. is beneficial. Vertical shaft impact (VSI) crushers tend to produce more cubical particles than cone crushers. Conclusion Obtaining adequate VMA in a SUPERPAVE mixture is an important part of the mix design which must be met. VMA is only one parameter, aggregate skeleton strength is another. The challenge to SUPERPAVE mix designers is to select aggregates which will give the proper amount of VMA without weakening the skeleton. Many mixtures meet the SUPERPAVE requirements without difficulty, others require more design work. This guidelines are intended to help mix designers with the decision of which materials to use.

(1) Source: "How to Increase Voids in Mineral aggregate Guidelines to increase VMA of SUPERPAVE Mixture" prepared by Ad Hoc Mix Design Task Group, Presented to the FHWA SUPEPEVE Mixtures Expert Task Group., 1996



11 Session 10 Fifth Day

Typical Problems in SUPERPAVE Mix Design

Material RequirementPortland Cement, Type I or II ASTM C-150 (AASHTO M204)Blended Hydraulic Cement, Type IP ASTM C-595Lime, Type N or S ASTM C-207 (AASHTO M303)

Hot Mix Hot Mix What can be done if the designed mix fail in the moisture sensitivity testing (TSR is less than 80%).

1. Compact another six (6) specimens replacing part of the filler with an approved mineral fillers according to item 4.05.2.3 of MOT General Specifications. Mineral fillers shall be either Portland cement, blended hydraulic cement or lime conforming to the following requirements:

2.0 Problem:

Solution

or chemical anti-stripping agents according to item 4.05.2.4 of MOT General Specifications

If this procedure fails, redesign the mix. No effort must be done to increase the DAC




12


Others Others

Problems faced by the Participants from their experience:

1. ..2. ..3. ..4. ..5. ..6. ..



superpave workshop 2004 -5th edition.pdf

Documents

superpave workshop

started session

superpave overview

superpave series

design of asphalt

superpave mix design

hot mixes superpave

selection of aggregate