Superpave workshop 2004 -5th edition.pdf

SUPERPAVE Workshop – 2005 Prepared and Developed by: Advance Engineering Center

Page 1 (AdEC)

SUPERPAVE™ Mix Design Workshop ‡aT))aJatJ

SRp„J)a†[J)ÉR))‡‰JcSJ cT‚a„J Prepared and Presented by

Dr. Ibrahim Al-Dubabe

1

Fifth Edition – June, 2005

Session 1 – First Day - Getting Started


Page 2 (AdEC)

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



Page 3 (AdEC)

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

----



Page 4 (AdEC)

Session No 1

Getting Started 2




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

3

Monday, December 27, 2004

Add Notes and Ask Questions Below:


Page 5 (AdEC)

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.


Page 6 (AdEC)

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:



My 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.

5

Friday, October 01, 2004



Page 7 (AdEC)

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

6




Page 8 (AdEC)

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 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

7




Page 9 (AdEC)

Time is live …..


Page 10 (AdEC)

Assistance AdEC AdEC is is always always ready ready to to work work with with you you to to handle handle all all issues issues and and matters matters related related to to highway highway engineering engineering especially especially materials materials (PMA, …). (PMA, NA, NA, HMA, HMA, PCC, PCC, Soil, Soil,…). P.O P.O Box Box 8658 8658 Riyadh Riyadh 11492, 11492, Saudi Saudi Arabia Arabia Tel: Tel: 4567377 4567377 ,, Fax: Fax: 4548166 4548166 Mobile: Mobile: 0505814198 0505814198 Email: Email: [email protected] [email protected] 9





Page 11 (AdEC)

Workshop Program Day

8:10 -9:00

9:00 – 9:50

Sat.

Session 1: Getting Started

Sun.

Mon.

9:50 – 10:00

10:00 – 11:00

11:00-12:00

Session 2: Introduction

Session 3: Overview

Session 4: Mixture Criteria

Session 5: Selection of Binder

Session 6: Selection of Aggregate

Session 7: Design Aggregate Structure

Session 8: Design Asphalt Content

Session 9: Moisture Sensitivity

Brake

Lab. Work: RV, Gyratory Comp. and ITS Demo.

Tues .

Session 10: Solving Some SUPERPAVE Mix Design Problems.

Design Example: ePAVE Solution

Wed.

Exam

Review of the H/O

10


Add Notes Below:



Page 12 (AdEC)

Session No. 2 Session

Introduction 2


Thursday, September 30, 2004


Background... Importance of the Subject Internationally SHRP (1987 to 1993) Background

Locally MOT instructions “circular No. 2253” MOT second “circular No. 30789” Saudi Arabia Roads Accidents 1425

3

Session 2 – First Day - Introduction



Page 13 (AdEC)

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.


More Into it ... Why SUPERPAVE? Limitation of current grading systems Penetration Viscosity

No tests to simulate in-service aging

4




Page 14 (AdEC)

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.


More Into it ... Why SUPERPAVE? Consistency Pen. Vis. hard

A B C

Vis.

soft 25

60

135

Temperature ,C

5


Page 15 (AdEC)

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.

2. A & C have similar viscosity at low temperature but differ at high temperature 3. B & C have similar consistency at 60 C but differ at all other temperatures. Add Notes and Ask Questions Below:



C o n s is t e n c y ( p e n e t r a t io n )

More Into it ... Why SUPERPAVE? Asphalt A = Low temp susceptibility Asphalt B = Medium temp susceptibility Asphalt C = High temp susceptibility

A B C 25

Temperature ,C

6




Page 16 (AdEC)

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.


More Into it ... Why SUPERPAVE? 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 7




Page 17 (AdEC)

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.


More Into it … What is 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).

8




Page 18 (AdEC)

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


What is New in SUPERPAVE Performance based (PG) Integrated approach Specification Mix design method

Based on project’s climate & traffic Compaction simulate actual conditions

9




Page 19 (AdEC)

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


What is New in SUPERPAVE ?

SUPERPVAE Binder Properties are related to Performance Test

Performance property

Mode of failure

RTFOT & PAV

Ageing & Hardening

Cracking

RV

Handling & Pumping

Flow

DSR (HT)

Permanent Deformation

Rutting

DSR (IT)

Fatigue Cracking

Cracking Structural

BBR & DTT

Thermal Cracking

Low temp. Cracking

10




Page 20 (AdEC)

For example, the binder testing, evaluation and grading in SUPERPAVE, as shown conceptually on this slide, can be related to field performance by engineering principles. In addition, these tests are performed at temperatures that are encountered in the real life during the pavement service.


Page 21 (AdEC)

Session No. 3

SUPERPAVE Overview 2


Monday, November 22, 2004


SUPERPAVE Design Steps Step 4: Moisture sensitivity Step 3: Selection of DAC Step 2: Selection of DAS Step 1: Selection of materials (binder, agg., modifiers, etc.)

3

Session 3 – First Day – SUPERPAVE Overview



Page 22 (AdEC) This is an overview of the SUPERPAVE design 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 distinguishing it from the conventional design methods (Marshall and Hveem) is the optimization of the aggregate gradation in the DAS step before the designer searches for the optimum asphalt content in the DAC step. Note: DAS = Design Aggregate Structure.


Step 1: Selection of Materials Selection of materials

Binder

4

Aggregate

• Modifiers • Others …

Page 23 (AdEC)

The first step is to select the materials, starting by the asphalt binder. The selection process is based on the actual conditions of traffic and environment of the project location. SUPERPAVE has chosen four aggregate properties to be considered in the selection of the aggregate and labeled them as consensus aggregate properties. In SUPERPAVE, the aggregate must meet the consensus properties and optionally meet the agency requirements.


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).




Step 2: Selection of DAS Selection of DAS

Develop Trial Blends

5

Compact

Evaluate and select confirming blend




Page 24 (AdEC) The selection of Design Aggregate Structure (DAS) is a new introduction to the HMA design by SUPERPAVE. Before selecting the Design Asphalt Content (DAC), or the optimum asphalt content as refer to in Marshall Mix design method, the aggregate gradation (or structure) must be selected. Selection of the DAS is the most complex part of the method. To fully understand this part, the designer must place special attention and care. Selection of Design Aggregate Structure will be illustrated by solving manually a design project example.


Step 3: Selection of DAC Selection of DAC

Compact

6

Analyze

Select DAC

Nmax verification

Page 25 (AdEC) After selecting the DAS (i.e. by selecting the most promising aggregate blend), the Design Asphalt content (DAC) can be selected. Computation in DAC and DAS are similar. Select the DAC at 4.0 air voids and check to confirm that the other volumetric properties and Dust Proportion is within the requirements. Note: Preparation of specimens in DAS and DAC are gyratory compacted to Ndes only not Nmax.


To protect against maximum densification by traffic, specimens are gyratory compacted at the DAS and DAC to Nmax. Note: %Gmm @ Nmax must be less than 98%.




Step 4: Moisture Sensitivity Moisture Sensitivity

Select Nx

7

Compact

Evaluate




Page 26 (AdEC)

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%.


Page 27 (AdEC)

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

8


Good information is available in this internet website: http//:training.ce.washington.edu/WSDOT/Modules/03_materials/03-3_body.htm



Page 28 (AdEC)

Session No. 4

Design Parameters & Mixture Criteria 2


Monday, November 22, 2004


Design Parameters NMS

Page 29 (AdEC)

There are three basic design input required by SUPERPAVE, these are: 1. Nominal maximum size of the aggregate (NMS). 2. Project location.

SUPERPAVE Basic Design Parameters

Location

3. Traffic level in terms of Equivalent Single Axle Load (ESALs)

Traffic (ESALs)

4

Session 4 – First Day - Design Parameters & Mixture Criteria




Design Parameters NMS, Nominal Maximum Size is One sieve size larger than the first sieve to retain > 10%. Five Mixture Gradation NMS MS 37.5 mm 50.0 mm 25.0 mm 37.5 mm 19.0 mm 25.0 mm 12.5 mm 19.0 mm 09.5 mm 12.5 mm

5




Page 30 (AdEC) 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: 1. The contract documents 2. SUPERPAVE implementation guidelines issued by MRDTM.

SUPERPAVE Workshop – 2005 Prepared and Developed by: Advance Engineering Center Session 4 – First Day

6

NMS Example …… Sieve Size, mm

Sieve Size, in

% Passing

MS

25

1

100.0

NMS

19

¾

94.0

>10%

12.5

½

76.6

9.5

3/8

63.7

4.75

No 4

37.2

2.36

No 8

28.2

1.18

No 16

20.9

0.6

No 30

14.2

0.3

No 50

7.8

0.15

No 100

4.0

0.075

No 200

3.1



Page 31 (AdEC) 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 Prepared and Developed by: Advance Engineering Center Session 4 – First Day

Design Parameters

Location: 1. The geographical location of the project where the Hot Mix Asphalt (HMA) will be used. 2. The position of the layer within the pavement 6

Page 32 (AdEC) 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 (PG). This selection is based on: 1. High pavement design temperature at a depth of 20mm from the pavement surface and 2. Low pavement design temperature.

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




Position in Pavement …

Pavement Surface

Top 100 mm Bottom 100 mm Aggregate Base Coarse Note: if less than 25% of the layer is within the surface then consider in the bottom.

8




Page 33 (AdEC)

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.

SUPERPAVE Workshop – 2005 Prepared and Developed by: Advance Engineering Center Standard Axle … 8.2 ton (18,000 lb)

Page 34 (AdEC)

The third design input is the Traffic in terms of ESALs; the definition is as shown in the slide.

Tire Pressure = 75 psi

9


Design Parameters 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. 10

The agency, Ministry of Transport for example, should specify the design parameters in the project contract documents.


Design Parameters Ministry of Transport (MOT) has identified the following ESAL classes: Class ESAL Designation Range VL Less than 300,000

Traffic Description Very Light

Typical Applications Agricultural roads, local & city streets (no trucks) Feeders, collectors ...

L

300,000 to 3 million

Light

M

3 million to 10 million

Medium

Main Roads, city streets

H

10 million to 30 million

Heavy

Highways & Expressway

More than 30 million

Very Heavy

VH

11

Heavily trafficked highways, industrial areas ..




Mixture Design Requirements SUPERPAVEGyratory GyratoryCompactive CompactiveEffort Effort(SGCE) (SGCE) 1.1.SUPERPAVE

ESAL Class (million) VL (<0.3) L (0.3 to <3) M and H (3 to <30) VH (> 30)

Nini

SGCE Ndes Nmax

6 7 8 9

50 75 75 115 100 160 125 205

12 Session 4 – First Day - Design Parameters & Mixture Criteria Add Notes and Ask Questions Below:


Page 35 (AdEC)

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.


Mixture Design Requirements (100 –– Air Air Voids%) Voids%) 2.2. %% GGmm mm == (100 ESAL REQUIRED DENSITY (% Gmm @) Class (million) Nini Ndes Nmax VL (<0.3) < 91.5 L (0.3 to <3)

< 90.5

M (3 to <10) H (10 to <30) VH (> 30

<89.0

96.0

< 98.0

13 Session 4 – First Day - Design Parameters & Mixture Criteria

Add Notes Below:


Page 36 (AdEC)

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


Mixture Design Requirements VMA %% 3.3. VMA REQUIRED VMA %, minimum Nominal Maximum Size, mm

37.5 25.0 19.0 12.5 9.5 11.0 12.0 13.0 14.0 15.0 13 Session 4 – First Day - Design Parameters & Mixture Criteria Add Notes Below:


Page 37 (AdEC)

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 Requirements VFA %% 4.4. VFA ESAL Class (million)

VFA % NMS = 19.0

NMS = 9.5

NMS = 25.0

NMS = 37.5

and 12.5 mm

mm

mm

mm

VL (<0.3) 70-80 70-80 67-80 L (0.3 to <3) 65 – 78 65 – 78 64-80 73 -76 M (3 to <10) 65 -75 H (10 to <30) 65 -75 VH (> 30 15 Session 4 – First Day - Design Parameters & Mixture Criteria Add Notes and Ask Questions Below:


Page 38 (AdEC)

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


Mixture Design Requirements Dust toto Binder Binder Ratio Ratio (Dust (Dust Proportion Proportion DP) DP) 5.5. Dust Position of Gradation Line

DP Ratio

ARZ

0.6 – 1.2

BRZ

0.8 – 1.6

16 Session 4 – First Day - Design Parameters & Mixture Criteria Add Notes and Ask Questions Below:


Page 39 (AdEC)

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.


Page 40 (AdEC)

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?



Page 41 (AdEC)

Session No. 5 Selection of Binder

3

Session 5 – Second Day – Step 1: Selection of Binder



Before the Design …… Use the Design Parameters of your project: ESAL (Class Designation or millions) NMS Location (Geographical & within pavement)

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

4

Session 6 – Second Day – Step 1: Selection of Materials



Page 42 (AdEC)

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


Page 43 (AdEC)

Before the Design …… Identify the following SUPERPAVE criteria for your Hot Mix Asphalt : Asphalt binder grade Consensus properties requirements Number of gyration for Nini, Ndes and Nmax % Gmm at Nini, Ndes and Nmax %VMA %VFA DP ratio 5





Asphalt Binder . . . Basics

☺ Performance based binder specifications AASHTO M320 (Standard Specifications for Performance–Graded Asphalt Binder) For details see Asphalt Institute SP-1 Intended for Modified and unmodified asphalt

☺ Depends on environment, traffic & reliability

7




Page 44 (AdEC)

SUPERPAVE binder grading system is performance based.



☺ Property is constant but temperature varies ☺ Example PG 64-22 ☺ Every Grade is 6 C.

8




Page 45 (AdEC)

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



7




Page 46 (AdEC)

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.


Asphalt Binder ... Grade Selection ☺ ☺ ☺ ☺ ☺

Determine project weather data Select reliability Determine design temperatures Verify asphalt PG (grade bumping) Determine temp-vis relationship

6




Page 47 (AdEC)

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 Selection

Selection of Asphalt Binder Grade is Based on the Kingdom Temperature Zoning Map 7




Page 48 (AdEC)

For the local conditions of the Kingdom of Saudi Arabia, Dr. Hammad ALAbdullwahb, 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..



Page 49 (AdEC)


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

ESAL VL <0.3

Standing Slow Standard (<20 km/h) (20-70 km/h) (>70 km/h) optional

L(0.3-<3)

Two Grades

One Grade

M (3-<10) Two Grades

One Grade

H (10-<30) Two Grades

One Grade

optional

VH (> 30) Two Grades

One Grade

One Grade

12




Page 50 (AdEC)

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.


Asphalt 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 13




Page 51 (AdEC)

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


Asphalt Binder ... Mixing & Compaction Temperature Viscosity Relationship

V is c o s it y , P a .s

10 Compaction Range (0.28 Pa.s) Mixing Range (0.17 Pa.s)

1

0.1 100 110 120 130 140 150 160 170 180 190 200 Temperature, C

10




Page 52 (AdEC)

Use the measured viscosities to generate the viscositytemperature relationship in a semilog 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


Page 53 (AdEC) Example

Asphalt Binder ... Grade Selection Example Problem: Design a wearing coarse layer with thickness of 7.0 cm. A) General Design Data: 1. Location: Al-Madinah Area – Highway connecting Madinah with Yanbu 2. Design traffic: Assumed = 18.000.000 ESALs B) Materials Properties: 1) Asphalt from Riyadh refinery having the following data

Property

Value

Flash point

325 C

Specific Gravity

1.02

Rotational viscosity at 135 C

0.494 Pa.s

Rotational viscosity at 165 C

0.075 Pa.s

16

Tuesday, November 23, 2004





Asphalt Binder ... Grade Selection Example ☺ From the temperature zoning map of the Kingdom the fitted grade is PG 70-10 ☺ Adjusting the binder grade for traffic (grade bumping): for speed no effect because high speed for level increase grade one step, then the suggested grade for this project is PG 76-10

☺ Note: Locally produced asphalt (RT,RY,KW & BH) is PG 64-12 and -18, then we need polymer modification. 17






Asphalt Binder ... Grade Selection Example From my previous research, an asphalt from Riyadh refinery modified with 3% SBS meets PG 76-10 and has the following performance properties: Property

Results

SUPERPAVE Criteria Fresh Binder - original

Flash point

328

> 230 C

Rotational viscosity @ 135C

1.562

< 3 Pa.s

DSR G*/sin delta, 76C

1.495

> 1.0 kPa RTFOT Residue - Aged Binder

DSR G*/sin delta, 76C

> 2.2 kPa

4.085

PAV Residue – Aged Binder

19

DSR G* x sin delta, 25C

2.362

< 3000 kPa

BBR Stiffness, -12 C

156

< 300 MPa

BBR m-value, -12 C

0.305

> 0.300





Page 56 (AdEC)

Session No. 6 Selection of Aggregates

2




Aggregate . . . Physical Properties ☺ Aggregate: Consensus (SUPERPAVE) Requirements: Gradation Coarse agg. Angularity, (CAA) Fine agg. Angularity, (FAA) Flat and elongated particles (F&E) Clay content, (SE)

4

ASTM D5821 AASHTO T304 ASTM D4791 AASHTO T176


Aggregate . . . Physical Properties ☺ Aggregate: Source (MOT) Requirements: Toughness AASHTO T96 Soundness AASHTO T104 Clay lumps & friable particles AASHTO T112 Others

5




Page 57 (AdEC)

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.


Selection of Aggregate SUPERPAVE Aggregate Requirements ESAL L (<0.3) LM (0.3-<3) M (3-<10) MH (10-<30) H (> 30

16

CAA <100 55/ 75/ 85/80 95/90 100/100

>100 50/ 60/ 80/75 100/100

FAA <100 40 45 45 45

>100 40 40 40 45

Sand Eq. F&E 40 40 45 45 50

Tuesday, January 11, 2005



10 10 10 10

Page 58 (AdEC)

Test criteria for CAA, FAA, SE and F&E are shown here. Less than 100 or more than 100 is the location of the layer under the design from the pavement surface. For the CAA, the first figure is for one fractured face while the second is for two fractured faces. Note: (1) the fraction of the aggregate that must be considered in the test. (2) 85/80 = one fractured face/two fractured faces


Page 59 (AdEC)

Aggregate . . . Gradation Basis

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.

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

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.

100

% P a s s in g

80

60

40

20

Sieve Size Raised to the 0.45 Power Session 6 – Second Day – Step 1: Selection of Materials

20

Aggregate . . . Gradation Basis

100

% P a s s in g

80

Maximum Density Line

60

40

Maximum Size

20

19.0 mm Sieve Size Raised to the 0.45 Power

8



SUPERPAVE has added two important features to the 0.45power 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 Requirements 100

80

Maximum Density Line

% P a s s in g

Control Point 60

Restricted Zone Nominal Maximum Maximum Size Size

40

20

12.5 mm 19.0 mm

Page 60 (AdEC) 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 12.5mm 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.

Sieve Size Raised to the 0.45 Power

9


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.




Page 61 (AdEC)

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



Page 62 (AdEC)

Session No. No. 77 Session

Selection of Design Aggregate Structure

2




Step 2: Selection of DAS Selection of DAS

Trial Blends

Compact

Evaluate

A) Establish trial blends: Develop Three blends Determine combined aggregate properties

B) Compact trial blend samples: Estimate trial AB% Prepare mixture Gyratory to Ndes

C) Evaluation Analyze and select the most appropriate blends to be used to select DAC

5

Session 7 – Third Day - Step 2: Selection of DAS



Page 63 (AdEC)

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 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

6




Page 64 (AdEC)

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


A) Establish Trial Blends 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.

7




Page 65 (AdEC)

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).


A) Establish Trial Blends 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 Variable

Hot bin 1 Hot bin 2

Hot bin 3 Hot bin 4

Blending Percentage of aggregate from hot bin

B1

B2

B3

B4

Value of the property of aggregate from hot bin

P1

P2

P3

P4

8




Page 66 (AdEC)

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 blends Select % Trial Asphalt Binder (Pbi) using one of the following methods: Computation (AASHTO PP-28) Experience SUPERPAVE suggestions

9




Page 67 (AdEC)

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.


B) Compact trial blends 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 gravity C = Aggregate absorption factor is assumed 0.8 but for absorptive aggregate use 0.6 or 0.5 Gsa = Aggregate apparent specific gravity 10




Page 68 (AdEC)

Or by utilizing SUPEPRAVE suggested values shown below: NMS 37.5 25.0 19.0 12.5 9.5

Suggested % 3.5 4.0 4.5 5.0 5.5

The Computation method to estimate asphalt content for the three trial blends based on AASHTO PP28 is shwon.


B) Compact trial blends 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 binder Va = 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) 11




Page 69 (AdEC)

Computation method to estimate asphalt content for the three trial blends


B) Compact 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

12




Page 70 (AdEC)

Computation method to estimate asphalt content for the three trial blends


B) Compact 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) + Ws Ws = weight of aggregate Pbi = percent binder by weight of mix 13




Page 71 (AdEC)

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.


B) Compact trial blends 2) Prepare Hot Mix Asphalt ☺ Using: The trial blends Design Aggregate Structure The estimated initial trial asphalt binder (Pbi) The mixing and compaction temp. determined form the temp.-vis. relationship

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

17




Page 72 (AdEC)

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.


B) Compact trial blends 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

18




Page 73 (AdEC)

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.


C) Evaluate Trial Blends 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

19




Page 74 (AdEC)


B) Compact trial blends %Gmm @ any Nx = %Gmm @ Ndes x

HNdes HNx

Where: HNdes = Height of specimen at Ndes HNx = Height of specimen at any N 20




Page 75 (AdEC)

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 … Example Computation of % Gmm at any Nx

21

N

H, mm

% Gmm

5

129.0

85.1

Nini = 8

127.0

86.5

10

125.7

87.7

30

120.1

91.5

40

119.0

92.4

50

118.0

93.1

60

117.2

93.8

80

116.0

94.7

Ndes = 100

115.2

95.4

Gmb

2.445

Gmm

2.563




Page 76 (AdEC)

Design project example.


C) Evaluate Trial Blends 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)

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

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

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

22




Page 77 (AdEC)

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%


C) Evaluate Trial Blends 3. Calculate DP ratio Compute Pbe using: Pbe = - (Ps x Gb ) x (Gse – Gsb)/GsexGsb) + Pb,estimated

DP using: DP = P0.075 / Pbe

4. Summarize results and Compare with SUPERPAVE criteria and select the most confirming blend. 23




Page 78 (AdEC)


Page 79 (AdEC)

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?



Page 80 (AdEC)

Session No. No. 88 Session Selection of of Selection Design Asphalt Asphalt Content Content Design

2


Wednesday, November 24, 2004


Step 3: Selection of DAC Selection of DAC

Compact

5

Analyze

Select DAC

Nmax verification

Session 8 – Fourth Day - Step 3: Selection of DAC



Page 81 (AdEC)

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)


Step 3: Selection of DAC A. Compact samples of the selected blend i. Prepare mixture at four AB% ii. Compact to Ndes

B. Analyze i. mixture Volumetric properties ii. Generate graphs

C. Select DAC at 4.0% air voids D. Verify mixture densification at Nmax

6




Page 82 (AdEC)

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 Prepare HAM using four Asphalt Binder %s: 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

Measure Gmm Compact 2 specimens @ each AB% to Ndes Measure specimen height and Gmb

7




Page 83 (AdEC)

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


B) Analyze the results 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%

8




Page 84 (AdEC)

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) Analyze the results

9



10



11



Page 85 (AdEC)


C) Select DAC From the graphs @ 4.0 % air voids determine DAC and check: VMA and VFA and % Gmm @ Nini Compute DP at DAC

Compare with SUPERPAVE criteria and adjust your design as needed.

12




Page 86 (AdEC)

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.


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

14




Page 87 (AdEC)

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


Page 88 (AdEC)

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?



Page 89 (AdEC)

Session 9 Moisture Sensitivity Evaluation

2




Step 4: Moisture Sensitivity Moisture Sensitivity

Select Nx

5

Compact

Evaluate

Session 9 – Third Day - Step 4: Moisture Sensitivity



Page 90 (AdEC)

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.


Step 4: Moisture Sensitivity Select Nx 7 % air voids

Compact specimens 6 specimens Compact to Nx

Evaluate AASHTO T283 Tensile strength ratio is 80% minimum. Compare with SUPERPAVE criteria and adjust your design as needed.

6




Page 91 (AdEC)

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.


A) Select Nx Use the densification data of the Nmax verification step to determine the number of gyrations to achieve 7% air voids. Note: 7% air voids = %Gmm of 93.0

7




Page 92 (AdEC)

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


Determination of N to Achieve 7% voids

%Gmm @ any Nx = %Gmm @ N

max x

HNmax HNx

Where: HNmax = Height of specimen at Nmax HNx = Height of specimen at any N 8




Page 93 (AdEC)

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.


Example

Determination of N to Achieve 7% voids N

H, mm

% Gmm

5

129.0

85.1

8

127.0

86.5

10

125.7

87.7

30

120.1

91.5

40

118.1

93.0

70

117.2

93.8

100

116.0

94.7

160

115.2

95.4

50

9

92.4

119.0

50

93.0

118.1

Gmb

2.445

Gmm

2.563




Page 94 (AdEC)

Design Project Example Data.


Page 95 (AdEC)

B) Compact Samples

Prepare HAM using DAS and DAC Gyratory compact 6 specimens to Nx

10





Page 96 (AdEC)

C) Evaluate Three specimens are control (no conditioning) o

The other three is conditioned for 24 h at 60 C Test all specimens to determine maximum indirect tensile load at failure Load

11

Load





Page 97 (AdEC)

C) Evaluation Compute ITS Maximum allowable ITS loss is 20% Compare with SUPERPAVE criteria and adjust your design as needed.

12





Page 98 (AdEC)

Session No 10 Typical Problems in SUPERPAVE Mix Design

2


Sunday, December 12, 2004


Page 99 (AdEC) Session 10 – Fifth Day

Main Problems …………. Asphalt Binder:

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.

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

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

3 Add Notes and Ask Questions Below:



Asphalt ……


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

Solution: 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.




Asphalt ……


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

Solution: 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..




Asphalt ……


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

Solution: 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.




Aggregate ……


1.0 Problem: Inaccurate measurements of Specific Gravities. (Gsb, Gsa, Gmb, Gmm …)

Solution 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 needed specific 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.




Aggregate ……


2.0 Problem: Which method we should use to measure the FAA in AASHTO T304

Solution Use method A




Hot Mix ……


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

Solution The VMA is an aggregate property which depends on the packing characteristics of the aggregate. Gradation: 1. 2. 3.

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)

Surface texture: 1. 2.

Use particles with high angularity Use particles with rough surface texture.

3.

Increase manufactured sand

More ……..

9 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?



Page 106 (AdEC)

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.



Page 107 (AdEC)

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.



Hot Mix ……

Session 10 – Fifth Day

1.0 Problem Cont’d: What can I do to increase the VMA in my design?

Solution The VMA is an aggregate property which depends on the packing characteristics of the aggregate. Shape: 1. 2. 3.

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.

10

Page 108 (AdEC) 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

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



Page 109 (AdEC)

Hot Mix …… 2.0 Problem: What can be done if the designed mix fail in the moisture sensitivity testing (TSR is less than 80%). Solution 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: Material Requirement Portland Cement, Type I or II ASTM C-150 (AASHTO M204) Blended Hydraulic Cement, Type IP ASTM C-595 Lime, Type N or S ASTM C-207 (AASHTO M303) 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

11

Session 10 – Fifth Day Typical Problems in SUPERPAVE Mix Design




Others ……


Problems faced by the Participants from their experience:

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

.. .. .. .. .. ..



Superpave workshop 2004 -5th edition.pdf

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