Interim guide for the design of high modulus asphalt mixes ...€¦ · As part of the Sabita High...

Contract Report: CSIR/BE/IE/ER/2010/0042/B December 2010

Interim guide for the design of high modulus asphalt mixes and pavements in

South Africa

Restricted

Version: 1.1

Authors: E Denneman

JW Maina

M Nkgapele

Southern African Bitumen Association (sabita)

PostNet Suite 56, Private Bag X21

Howard Place 7450

CSIR Built Environment PO Box 395

Pretoria 0001

DOCUMENT RETRIEVAL PAGE Report No:

CSIR/BE/IE/ER/2010/0042/B

Title: Interim guide for the design of High modulus asphalt mixes and pavements in South

Africa

Authors: E Denneman, JW Maina, M Nkgapele

Client:

Sabita

Client Reference No:

Date:

December 2010

Distribution:

Restricted

Project No: 59E2085 ISBN:

Abstract:

As part of the Sabita High Modulus Asphalt (HiMA) technology transfer project, guidelines for the

design of HiMA mixes and the design of pavement structures containing HiMA layers will be

developed. The preliminary mix design guidelines presented in this document are based on best

international practise and the, at this stage, still limited local experience with HiMA materials. The

preliminary structural design guidelines were compiled by analysing typical South African pavement

structures including a base layer with HiMA material properties. The procedures in these guidelines

still need to be validated through accelerated pavement testing, before they can be disseminated to

industry.

(Note: this is a preliminary document awaiting the completion of laboratory testing, which

outcomes will feed into the development of structural design guidelines)

Keywords: High modulus asphalt, mix design, structural design

Proposals for implementation: The purpose of this document is to provide guidance to future

accelerated pavement testing of HiMA pavements

Related documents:

Nkgapele and Denneman (2010)

Anochie- Boateng et al (2010)

Signatures:

NOTE: This document is confidential to Sabita and CSIR, and may only be distributed with the written permission of the CEOs or their nominee.

HiMA interim design guide CSIR/BE/IE/ER/2010/0042/B

i

TABLE OF CONTENTS

1. INTRODUCTION ........................................................................................................................ 1

1.1 Background .............................................................................................................................. 1

1.2 Objective and scope ................................................................................................................. 1

1.3 Structure of the preliminary design guide ................................................................................ 1

2. HiMA MIX DESIGN .................................................................................................................... 3

2.1 Material selection ..................................................................................................................... 3

2.1.1 Binder selection.......................................................................................................... 3

2.1.2 Aggregate selection ................................................................................................... 4

2.2 Design grading ......................................................................................................................... 4

2.3 Layer thickness ........................................................................................................................ 7

2.4 Binder content requirements .................................................................................................... 7

2.5 Production of test specimens ................................................................................................... 8

2.6 Performance testing ................................................................................................................. 9

3. DESIGN OF HiMA PAVEMENT STRUCTURES ..................................................................... 11

3.1 Pavement types evaluated in this study ................................................................................. 12

3.2 Current pavement design procedure ..................................................................................... 15

3.3 Legal Damage (LDv): ............................................................................................................. 19

3.4 Total Damage (TDv) (= Load Equivalency Factor (LEFv) of Vehicle): .................................. 20

3.5 Total Additional Damage (TADv): .......................................................................................... 20

3.6 Summary of structural design ................................................................................................ 22

References ........................................................................................................................................... 23


ii

LIST OF FIGURES

FIGURE PAGE

Figure 1: HiMA mix design process ......................................................................................................... 2

Figure 2: Recommended initial grading and typical envelope for NMPS=13.2 mm ................................ 6

Figure 3: Eight road pavement structures and their material properties used for the mechanistic

analysis .......................................................................................................................................... 14

Figure 4a: HiMA layer in place of base and surfacing layers for eight road pavement structures

........................................................................................................................................................ 17

Figure 5b: HiMA layer in place of base and surfacing layers for eight road pavement structures ........ 18

Figure 6: Axle configuration of articulated six (6) axle single dual tyres. .............................................. 19

Figure 7: LEFv for all the eight pavement structures based on articulated six (6) axle vehicle. ............ 22


iii

LIST OF TABLES

TABLE PAGE

Table 1: Summary 10/20, 15/25 and 20/30 binder specifications (EN 13924 and EN 12591) ............... 3

Table 2: Aggregate selection criteria ....................................................................................................... 4

Table 3: Target grading curves and envelopes for HiMA base course (after Delorme et al, 2007) ........ 5

Table 4: Target grading curves and envelopes for HiMA base course (SA standard sieve sizes) ......... 5

Table 5: Target grading curves and envelopes for HiMA binder course ................................................. 6

Table 6: Target grading curves and envelopes for HiMA binder course (SA standard sieve sizes) ....... 7

Table 7: HiMA Layer thickness ................................................................................................................ 7

Table 8: Typical values for minimum binder content and target richness modulus ................................ 8

Table 9: Performance specifications ..................................................................................................... 10

Table 10: Minimum TSR criteria after (Taute, Verhaeghe, & Visser, 2001) .......................................... 10

Table 11: Pavement response parameters used in the mechanistic analysis ...................................... 11

Table 12: Standard and legal axle data used ........................................................................................ 16

Table 13: Summary of the eight abnormal vehicles (AVs) sorted according to their total load ............ 16


1

1. INTRODUCTION

1.1 Background

This guideline document forms part of the Sabita High Modulus Asphalt (HiMA) technology transfer

(T2) project. The project was executed in line with project proposal PP/2008/08/A1. The overall HiMA

technology transfer project consists of four phases:

• Phase 1: Preliminary assessment of viability;

• Phase 2: Preliminary guidelines on mix design and structural design;

• Phase 3: Validation of HiMA technology through APT, LTPP and laboratory studies;

• Phase 4: Drafting of guidelines and specifications for HiMA

The present report forms part of the deliverables for Phase 2. Initially, as part of Phase 2, mixes would

have been designed by Shell and Colas France using South African mix components. These mixes

would then have been evaluated using South African test methods and based on the results, a South

African mix design guideline would have been developed. However, the mix design attempts using

South African components failed to make the relevant French specifications for HiMA. The fatigue

performance of the proposed mix was below par. The project plan for the HiMA T2 was subsequently

revised to include a mix design improvement phase. The HiMA design developed in France was

replicated in the CSIR laboratories and used as a point of departure to improve the design. The

French test results were also used as a benchmark for their South African equivalents using local test

methods and equipment. The results obtained on the replicated mix are contained in Anochie-Boateng

et al (2010). Subsequently, several trial mixes were produced and measured against this benchmark

in order to improve upon the French design, particularly with respect to its fatigue properties. The

results of the mix design optimisation phase are reported by Nkgapele and Denneman (2010). The

mix design guidelines contained in this document are a conversion of the French design requirements

for HiMA, adapted for South African practice using the outcomes of the abovementioned mix

optimisation process.

1.2 Objective and scope

The aim of this document is to provide an initial guide for the design of HiMA mixes and pavement

structures in South Africa, based on international best practice and the, at this stage, still limited local

experience in the use of this type of material. The procedures in these guidelines still need to be

validated through accelerated pavement testing (APT) before they can be disseminated to industry.

1.3 Structure of the preliminary design guide

The report is divided into two parts: (a) a section on HiMA mix design, and (b) a section on the

structural design of road pavements containing HiMA layers. The steps involved in the HiMA mix


2

design process are shown in Figure 1. The preliminary HiMA mix design guide is structured in

accordance with the steps shown in the figure.

Select components

Formulate design grading

Select binder content

Compact gyratory specimens

Workability criteria met?

Durability criteria met?

Rut resistance criteria met?

Dynamic modulus criteria met?

Compact slab

Fatigue criteria met?

Implement!

YesNo

Yes

No

Yes

Yes

Yes

No

No

No

Figure 1: HiMA mix design process

The structural design guidelines contain design examples of pavement structures which incorporate

HiMA as a structural layer. These pavements are then compared with conventional pavement

structures using the South African Mechanistic Empirical design method.


3

2. HiMA MIX DESIGN

The HiMA mix design guidelines presented in this section are based on the French methodology for

the design of bituminous mixtures as described by Delorme et al. (2007), as well as on the preliminary

outcomes of the Sabita technology transfer T2 project. As part of the T

2 project, a HiMA mix design

based on South African mix components was developed in France using French specifications. The

performance of the mix in terms of the French criteria for HiMA is thus known. This mix design was

then used to produce test specimens at the CSIR laboratories in Pretoria. The specimens were tested

using South African test methods, allowing a comparison to be made between the French and South

African performance parameters.

The aim of the mix design procedure is to produce a HiMA mix that combines good workability with a

high dynamic modulus, a high resistance to permanent deformation, good fatigue performance and

low permeability.

2.1 Material selection

The characteristics that define a HiMA mixture are a high binder content of low penetration grade

bitumen combined with good quality, fully crushed aggregate, graded in a way that ensures good

workability and produces a mix with sufficient durability and low permeability.

2.1.1 Binder selection

In Europe, typically either a 10/20 or a 15/25 Pen grade binder, conforming to EN 13924, is used in

HiMA. However, the binder that has been used in the Sabita project to date is a 20/30 Pen grade

conforming to EN 12591. A summary of EN requirements for hard binders are shown in Table 1.

Table 1: Summary 10/20, 15/25 and 20/30 binder specifications (EN 13924 and EN 12591)

Property Test method Unit Penetration grade

10/20 15/25 20/30

Before RTFOT

Penetration at 25 °C EN 1426 0.1 mm 10-20 15-25 20-30

Softening point EN 1427 °C 58-78 55-71 55-63

Viscosity at 60°C EN12596 Pa.s >700 >550 >440

After RTFOT

Increase in softening point EN 1427 °C < 10 < 8 < 8

Retained penetration EN 1426 % - > 55 > 55

Mass change % < 0.5 < 0.5


4

2.1.2 Aggregate selection

In France, HiMA is typically produced using fully crushed fractured aggregate (Distin et al, 2008). In

the selection of an aggregate source, both angularity and surface texture are important. High

aggregate angularity and sufficient surface texture assist in the creation of voids in the mineral

aggregate (VMA). The VMA has to be such that it can accommodate a fairly high binder content. The

proposed aggregate selection criteria for HiMA are shown in Table 2 . The criteria are similar to those

recommended for HMA as contained in Taute et al. (2001). The particle index test provides a measure

of aggregate angularity and surface texture. The value for particle index is tentative. Generally

aggregates with a high particle pindex test result have a higher VMA. The flakiness index for HiMA

aggregate should preferably lie between 10 and 15 (Delorme et al, 2007).

Table 2: Aggregate selection criteria

Property Test Method Criteria

Hardness Fines aggregate crushing test: 10 %FACT TMH1, B1 ≥ 160

kN

Aggregate crushing value ACV TMH1, B1 ≤ 25%

Particle shape & texture Flakiness Index test SANS 3001 ≤ 25

Particle index test ASTM D3398 >15

Polished stone value SANS 3848 >50a

Water absorption Water absorption coarse aggregate

(>4.75mm)

TMH1, B14 ≤ 1.0 %

Water absorption fine aggregate TMH1, B14 ≤ 1.5 %

Cleanliness Sand equivalency test TMH1, B19 ≥ 50

a Only relevant if HiMA mixture is intended for a surfacing layer, which is not a typical application.

2.2 Design grading

The LPC bituminous mixtures design guide provides target grading curves and envelopes for HiMA

mixes (Delorme et al, 2007). It should be noted that these only provide a point of departure for the mix

design process and that they should not be used to impose a restriction on the grading as per the

current South African COLTO specifications. It should also be noted that the grading envelopes

provided by Delorme et al. (2007) of the Laboratoire Central des Ponts et Chaussées (LCPC) are

different from those contained in the report that deals with the implementation of HiMA in the United

Kingdom, produced by the Transport Research Laboratory (TRL) (Sanders & Nunn, 2005). Until more

experience is gained in South Africa, it is recommended that the envelopes published in the LPC

guideline be used instead.


5

The French guideline for grading curves cannot readily be translated into general South African

practice. This is due to the definition of the maximum particle size and the use of European sieve

sizes. In South Africa (SA), the nominal maximum particle size (NMPS) is defined as one sieve size

larger than the first sieve to retain at least 10% of aggregate. The French use the maximum stone size

D, with the requirement that 100 % of aggregate passes the sieve at 2D, 98-100% passes at 1.4 D

and 85-98% passes at D. In this document, the French definition of maximum aggregate size has

been maintained and the grading curves are plotted for both European and SA standard sieve sizes. It

is recommended that the customization of the LCPC grading guidelines be conducted once more local

experience with HiMA grading has been gained. The grading guidelines for HiMA base courses are

shown in Table 3 for European sieve sizes. These have been converted in Table 4 for SA standard

sieve sizes. For key sieve sizes, the table provides a target grading that can be used as a point of

departure, and also proposes typical grading envelopes. The values for the 13.2 mm maximum size

aggregate are plotted in Figure 2 for illustration purposes. Also shown is the maximum density line

(assuming a 5% binder content). The suggested target grading is fairly close to the maximum density

line for the smaller sieves. The grading includes a kink due to the relatively large percentage retained

on and above the 6 mm sieve.

Table 3: Target grading curves and envelopes for HiMA base course (after Delorme et al, 2007)

Percent

passing

sieve size

D = 10 mm D = 14 mm D = 20 mm

min. target max. min. target max. min. target max.

6.3 mm 45 55 65 50 53 70 45 53 65

4.0 mm 52 40 47 60 40 47 60

2.0 mm 28 33 38 25 33 38 25 33 38

0.063 mm 6.3 6.7 7.2 5.4 6.7 7.7 5.4 6.7 7.7

Table 4: Target grading curves and envelopes for HiMA base course (SA standard sieve sizes)

Percent

passing

sieve size

NMPS = 9.5 mm NMPS = 13.2 mm NMPS = 19 mm

min. target max. min. target max. min. target max.

6.7 mm 47 56 68 52 54 72 46 54 66

4.75 mm 53 43 49 63 42 49 62

2.36 mm 32 36 44 28 36 42 28 36 42

0.075 mm 6.4 6.9 7.4 5.5 6.9 7.9 5.5 6.7 7.9


6

0

10

20

30

40

50

60

70

80

90

100

0

Perc

en

tag

e p

ass

ing

Sieve size (raised to power 0.45) [mm]

SA sieve size envelope Target European sieve size envelope

0.0075 2.36 4.75 6.7 13.2

Figure 2: Recommended initial grading and typical envelope for NMPS=13.2 mm

The typical grading for HiMA intended for use as a binder course is shown in Table 5. The values are

converted for SA standard sieve sizes in Table 6. A binder course is the layer between the wearing

course and the base layer in European pavement structures. This type of mix design has not yet been

explored for use in South Africa.

The use of aggregate packing analysis techniques to optimize the mix design grading and mix

volumetrics, such as the Bailey method, is highly recommended.

Table 5: Target grading curves and envelopes for HiMA binder course (after Delorme et al, 2007)

Percent

passing

sieve size

D = 10 mm D = 14 mm

min. target max. min. target max.

10.0 mm 97 78

6.3 mm 45 57 68 47 52 58

4.0 mm 52 47

2.0 mm 27 34 39 25 31 35


7

0.063 mm 6.3 6.7 7.2 6.3 6.8 7.2

Table 6: Target grading curves and envelopes for HiMA binder course (SA standard sieve sizes)

Percent

passing

sieve size

NMPS = 9.5 mm NMPS = 13.2 mm

min. target max. min. target max.

9.5 mm 92 74

6.7 mm 47 61 71 49 55 60

4.75 mm 54 49

2.36 mm 31 37 45 28 34 40

0.075 mm 6.4 6.9 7.4 6.4 6.9 7.4

2.3 Layer thickness

The average and minimum specified layer thicknesses of HiMA are provided in Table 7. Since HiMA is

a structural layer, it is critical that the specified layer thicknesses are met during construction. It should

be noted that the average layer thicknesses of HiMA are generally thinner than those specified for

bitumen-treated base courses (BTBs) or large-aggregate mixes for bases (LAMBs). This is due to the

smaller stone size used in HiMA. Structurally, a thin HiMA layer may yield the same performance as a

thicker BTB because of the higher stiffness of HiMA. HiMA is also richer in binder which, compared to

conventional base courses, offers similar if not better resistant to fatigue cracking. Another attribute of

HiMA is that the mix is virtually impermeable, which may enable HiMA to be surfaced with a thin or

ultra-thin asphalt mix as suggested by Distin et al (2008), although this will require further

investigation.

Table 7: HiMA Layer thickness

D

[mm]

Average thickness

[mm]

Minimum thickness

[mm]

10 60 to 80 (base course)

50 to 70 (binder course)

50

14 70 to 130 (base course)

60 to 90 (binder course)

60

20 90 to 150 (base course) 80

2.4 Binder content requirements

Table 8 shows the minimum binder contents for different HiMA mix types, expressed as a percentage

by mass of total mix Pb. The French specifications allow for two classes of HiMA mixes: Class 1 for


8

‘light’ traffic, and Class 2 for heavy traffic. The mix tested in South Africa is a Class 2 HiMA. The table

is intended as a point of departure for selection of optimum binder content.

Table 8: Typical values for minimum binder content and target richness modulus

HiMA base course HiMA binder

course Class 1 Class 2

D (mm) 10,14,20 10,14 20 10 14

Pb min ρ= 2.65 g/cm3

3.8 5.1 5.

0

5.2 4.9

Pb min ρ= 2.75 g/cm3 3.8 4.9 4.

9

5.0 4.8

Richness modulus

K

2.5 3.4 3.

4

3.5 3.3

The richness modulus K shown in Table 8 is a proportional value related to the thickness of the binder

film coating the aggregate. It is akin to the film thickness calculation in the South African TRH 8. The

richness modulus K is a key design parameter used in the French asphalt mix design method. The

values in Table 8 should be adhered to. K is obtained from:

5Σ⋅= αKTLest (1)

Where:

TLest : is the binder content by mass of total aggregate. TLest can be converted to the binder content

by mass of total mix (Pb) generally used in South Africa using Equation 2

)100(

100

b

best

P

PTL

−= (2)

α: is a correction coefficient for the relative density of the aggregate (RDA)

RDA

65.2=α

Σ: is the specific surface area calculated from: fsSG 150123.225.0100 +++=Σ

Where:

G: is the proportion of aggregate retained on and above the 6.3 mm sieve,

S: is the proportion of aggregate retained between the 0.25 mm and 6.3 mm sieves,

s: is the proportion of aggregate retained between the 0.063 mm and 0.25 mm sieves,

f: is the percentage passing the 0.063 mm sieve

2.5 Production of test specimens

The mixing temperature for the binder shall be determined using the method in TMH1 C2. The

aggregates and binder are to be prepared in accordance with the protocols in TMH1. After mixing the


9

loose material is conditioned using a method known as “short term aging” to simulate the aging that

takes place during production in the plant and transport to site1. The short term aging conditioning

takes place by putting the loose mix back into the oven after mixing for four hours at the compaction

temperature. After this time period, the mix is removed from the oven and compacted.

Gyratory specimens are prepared in accordance with ASTM D6926-06. Slabs are compacted using

guidelines relevant to the equipment used. Specimens for performance testing shall be compacted to

an air void content of between 3% and 6%.

2.6 Performance testing

The preliminary design requirements for HiMA are shown in Table 9. The requirements were

developed based on the French performance specifications. The HiMA reference mix was first

assessed against the French specifications in a French laboratory. The HiMA reference mix was then

evaluated at the CSIR using South African test methods for a similar set of performance parameters.

The comparison of the results from the French and South African test methods was used to set

tentative specifications for the South African test methods. The performance specifications require

further validation through accelerated pavement testing.

1 Details on the background and development of the short term aging method can be found in (Von

Quintus et al (1991) and Bell et al (1994).


10

Table 9: Performance specifications

Property Test Method Performance requirements

HiMA base course HiMA binder course

Class 1 Class 2 Class 1 Class 2 Class 3

Workability Gyratory compactor, air voids

after 45 gyrations

ASTM D6926 ≤ 10% ≤ 6% 5 to 10 % for D = 10,

4 to 9 % for D = 14

Moisture

sensitivity

Modified Lottman ASTM D4867 Refer Table 10 Refer Table 10 Refer Table 10 Refer Table 10 Refer Table 10

Permanent

deformation

RSST-CH, 55°C, 30 000 reps AASHTO 320 ≤ 1.7% strain ≤ 1.7% strain ≤ 2.3% strain ≤ 1.7% strain ≤ 1.1% strain

Dynamic

modulus

Dynamic modulus test at 10

Hz, 15°C

AASHTO TP 62 ≥ 14 GPa ≥ 14 GPa ≥ 9 GPa ≥ 14 GPa ≥ 14 GPa

Fatigue Beam fatigue test at 10 Hz,

10°C, to 70% stiffness

reduction

AASHTO T 321 ≥ 330 µε for 10

E6 reps

≥ 430 µε for 10

E6 reps

≥ 360 µε for 10

E6 reps

≥ 330 µε for 10

E6 reps

≥ 330 µε for 10

E6 reps

Table 10: Minimum TSR criteria after (Taute, Verhaeghe, & Visser, 2001)

Climate Permeability

Low Medium High

Dry 0.60 0.65 0.70

Medium 0.65 0.70 0.75

Wet 0.70 0.75 0.80


11

3. DESIGN OF HiMA PAVEMENT STRUCTURES

A road or airport pavement, just like any other engineering structure, is designed to withstand traffic

loads, and more specifically the accumulation of all axle loads of vehicles that would be travelling over

the structure during its life cycle. For the design of the HiMA structures contained in this report, the

same structural analysis methodology than the one followed for the revision of TRH11 (1999-2000):

Recovery of Road Damage has been used (De Beer et al, 2008). It is based on a comparative

analysis of potential damage caused by abnormal vehicles (AVs) on pavement structures commonly

found in South Africa. The pavement damage is determined based on the South African Mechanistic

Design procedure (SAMDM) by considering the full axle/tyre configuration of a vehicle (i.e. tyre/axle

loading and its associated tyre inflation pressure) as input into the analysis. In this regard, no “fixed

equivalencies” are used per se. SAMDM takes into account factors relating to design strategy,

including road category, traffic volumes and structural design period, and considers material types,

environment, drainage, compaction and cost analysis. A summary of the different pavement response

parameters used, and their associated damages, are given in Table 11.

Table 11: Pavement response parameters used in the mechanistic analysis

Material Type and layer

Damage Criteria

Pavement Response Parameters used in the Analyses

Critical Position in Pavement Layer

Asphalt Surfacing

(20-75 mm thick)

(AC/AG)

Flexural Fatigue

Cracking hε

Bottom

Asphalt Base

(> 75 mm) (BC)

Flexural Fatigue

Cracking hε Bottom

Cemented Base and

Cemented Subbases

(C3, C4)

Crushing (Nc) zσ Top

Effective Fatigue, (Nef) hε Bottom

Shear Failure

(in equivalent

Granular (EG) phase)

1σ , 3σ Middle

Granular Base/Subbase/

Selected layer(G)

Shear Failure

(Factor of Safety)

1σ , 3σ

Middle

Subgrade (Soil) Rutting zε Top


12

Where:

zσ = Vertical Stress (used for estimation of crushing failure on the top of lightly cementitious (i.e.

stabilized) layers);

hε = Horizontal Tensile Strain (used for estimation of fatigue failure of bound layers);

zε = Vertical Compressive Strain (used for estimation of rutting (i.e. plastic deformation) of

unbound layers);

1σ , 3σ = Major Principal Stresses (used for estimation of shear failure of granular layers, leading to

rutting).

The pavement damage (or “additional pavement damage”) of the Abnormal Vehicle (AV), as used in

the TRH11 study, was directly estimated for nine typical pavement types found in South Africa. This

was done for both a relatively dry and a relatively wet pavement condition. In addition, a range of tyre

inflation pressures (TiP) ranging from 520 kPa to 1200 kPa was used. The mechanistic pavement

response parameters (i.e. stresses and strains) were directly related through the associated transfer

functions (TF) for pavement damage to layer life and hence “pavement life”. With this approach, the

pavement life is considered as being equal to the “critical layer life”, i.e. the life of the structural layer

with the lowest life in the pavement structure. This is fundamental to calculation of the Load

Equivalency Factors (LEFs).

The philosophy of “Equivalent Pavement Response - Equivalent Pavement Damage” (EPR-EPD) is

used instead of reducing a single Abnormal Vehicle to an ESWL (or ESWM), or to an equivalent axle

load of 80 kN (i.e. E80), all of which are based on the rather crude but well known 4th power law of

relative pavement damage.

3.1 Pavement types evaluated in this study

Eight typical flexible pavements found in South Africa were used for the mechanistic estimation of

relative pavement damage (or mechanistically based Load Equivalency Factors (LEFs)). The typical

flexible pavements were obtained from TRH 4 (1996) and are briefly described below (see Figure 3):

Pavement A: This is a heavy pavement with a granular base, basically representing relatively dry

conditions, Road Category A and design traffic class ES100. Structure: 50 mm asphalt surfacing,

150 mm G1 granular base, and two (2) 150 mm C3 cemented subbases on the subgrade.

Pavement B: This is a heavy pavement with a granular base, basically representing relatively

wet conditions, Road Category A and design traffic class ES100. Structure: the same as that of

pavement A but with different material properties owing to the wet conditions.


13

Pavement C: This is a light pavement with a granular base basically representing relatively dry

conditions, Road Category D and design traffic class E0.1. Structure: 15 mm surface treatment or

seal, 100 mm G4 granular base, 125 mm C4 subbase.

Pavement D: This is a light pavement with a granular base basically representing relatively wet

conditions, Road Category D and design traffic class E0.1. Structure: the same as that of Pavement C

but with different material properties owing to the wet conditions.

Pavement E: This is a heavy pavement with a bituminous base, Road Category A and design

traffic class ES30. Structure: 40 mm asphalt surfacing, 120 mm asphalt base, three 150 mm layers of

C3 (i.e. 450 mm of C3, built in 3 layers of 150 mm each) cemented subbase, and a 200 mm selected

layer on top of the subgrade.

Pavement F: This is a light pavement with a bituminous base, Road Category B and design

traffic class ES1.0. Structure: 15 mm surface treatment or seal, 80 mm asphalt base, 150 mm

cemented subbase.

Pavement G: This is a heavy pavement with a cemented base, Road Category B and design

traffic class ES10. Structure: 30 mm asphalt surfacing, 150 mm C3 cemented base, 300 mm C4

cemented subbase.

Pavement H: This is a light pavement with a cemented base, Road Category C and design traffic

class ES0.3. Structure: 15 mm surface treatment or seal, 100 mm C4 cemented base, 100 mm C4

cemented subbase.

Note that all the pavement structures are founded on selected layers or subgrade with assumed

material properties according to road category and traffic class. The Road Category and design traffic

class are defined in TRH 4, 1996 (CSRA, 1996). The particular pavement structures chosen are

considered to be a fair representation of many of the pavements found in South Africa and should

allow a pavement designer to correlate many typical cases to one of the pavements analyzed and

thereafter apply the findings in terms of LEF. In this study, the M-E analyses were done for both

relatively dry and relatively wet pavement conditions2.

2 The relatively “dry” and “wet” analyses options were selected in the mePADS Software as described

by Theyse and Muthen (2000). Note that this selection is strictly related to the life prediction of granular layers (i.e. safety factors against shear failure), and may not be sensitive for stabilised (or cementitious) layers.


14

50 AG*

150 G1*

150 C3*

150 C3

SUBGRADE

0.44

0.35

0.35

0.35

0.35

2000

250

2000

1500

90

1800

250

1700

120

90

1500

240

160

110

90

Pavement B:ES100

50 AG*

150 G1*

150 C3*

150 C3

SUBGRADE

Poisson's

Ratio Phase I Phase II Phase III

Elastic Moduli (MPa)

0.44

0.35

0.35

0.35

0.35

2000

450

2000

1500

180

2000

450

2000

550

180

1500

350

500

250

180

Pavement A:ES100

40 AG*

120 BC*

450 C3*

200 G7*

SUBGRADE

0.44

0.44

0.35

0.35

0.35

2500

3500

2200

300

150

2500

3500

1000

300

150

Pavement E:

ES30/ES50

S*

100 G4*

125 C4*

SUBGRADE

0.44

0.35

0.35

0.35

1000

200

1000

70

1000

180

120

70

Pavement D:

ES0.1

- - -

S*

100 G4*

125 C4*

SUBGRADE

0.44

0.35

0.35

0.35

1000

300

1000

140

1000

225

200

140

Pavement C:

ES0.1

- - -

30 AG*

150 C3*

300 C4*

SUBGRADE

0.44

0.35

0.35

0.35

2400

2000

1000

180

Pavement G:ES10

- -

S*

80 BC*

150 C4*

SUBGRADE

0.44

0.44

0.35

0.35

2000

2000

1000

140

1600

1600

300

140

Pavement F:ES1.0

- - -

S1*

100 C4*

100 C4*

SUBGRADE

0.44

0.35

0.35

0.35

2000

2000

1000

140

Pavement H:ES0.3

- -

* Classification according to TRH 14 (CSRA, 1985)

8 Pavement Structures-1.ppt

Poisson's



Poisson's

Ratio Phase I Phase II


Poisson's



Poisson's


Elastic Moduli (MPa) Poisson's



Poisson's



Poisson's

Ratio Phase I

Elastic Moduli (MPa)Poisson's

Ratio Phase I


1600

1500

300

200

140

Phase III

2000

1800

300

140

-

Phase II

1600

250

100

100

-

Phase III

1000

1500

300

140

-

Phase II

200

100

100

100

-

Phase III

50 AG*

150 G1*

150 C3*

150 C3

SUBGRADE

0.44

0.35

0.35

0.35

0.35

2000

250

2000

1500

90

1800

250

1700

120

90

1500

240

160

110

90

Pavement B:ES100

50 AG*

150 G1*

150 C3*

150 C3

SUBGRADE

Poisson's



0.44

0.35

0.35

0.35

0.35

2000

450

2000

1500

180

2000

450

2000

550

180

1500

350

500

250

180

Pavement A:ES100

40 AG*

120 BC*

450 C3*

200 G7*

SUBGRADE

0.44

0.44

0.35

0.35

0.35

2500

3500

2200

300

150

2500

3500

1000

300

150

Pavement E:

ES30/ES50

S*

100 G4*

125 C4*

SUBGRADE

0.44

0.35

0.35

0.35

1000

200

1000

70

1000

180

120

70

Pavement D:

ES0.1

- - -

S*

100 G4*

125 C4*

SUBGRADE

0.44

0.35

0.35

0.35

1000

300

1000

140

1000

225

200

140

Pavement C:

ES0.1

- - -

30 AG*

150 C3*

300 C4*

SUBGRADE

0.44

0.35

0.35

0.35

2400

2000

1000

180

Pavement G:ES10

- -

S*

80 BC*

150 C4*

SUBGRADE

0.44

0.44

0.35

0.35

2000

2000

1000

140

1600

1600

300

140

Pavement F:ES1.0

- - -

S1*

100 C4*

100 C4*

SUBGRADE

0.44

0.35

0.35

0.35

2000

2000

1000

140

Pavement H:ES0.3

- -

* Classification according to TRH 14 (CSRA, 1985)

8 Pavement Structures-1.ppt

Poisson's



Poisson's



Poisson's



Poisson's


Elastic Moduli (MPa) Poisson's



Poisson's



Poisson's

Ratio Phase I

Elastic Moduli (MPa)Poisson's

Ratio Phase I


1600

1500

300

200

140

Phase III

2000

1800

300

140

-

Phase II

1600

250

100

100

-

Phase III

1000

1500

300

140

-

Phase II

200

100

100

100

-

Phase III

Figure 3: Eight road pavement structures and their material properties used for the mechanistic analysis


15

3.2 Current pavement design procedure

The Mechanistic-empirical Pavement Analysis & Design Software (mePADS), developed by the CSIR,

was used for the preliminary structural analysis of the pavement structures listed in Section 3.1. The

procedure followed involved replacing the surfacing layers in each of the pavement structures with a

relatively thinner HiMA layer. The pavement information requires the material code, the thickness and

resilient properties to be entered for each of the layers in the pavement system. All loads are modeled

by a constant vertical stress, uniformly distributed over a circular contact area referred to as a load

patch. The load definition input requires the load magnitude (kN), the contact stress (kPa) and the X

and Y coordinates of the locations of the load patches under consideration. At least one load patch

must be defined. The load magnitude, contact stress and load patch location may be different for each

of the load patches provided.

mePADS, which implements multi-layer linear elastic (MLLE) analysis routines, was used to calculate

the stress-strain conditions within the pavement system in accordance with the South African

Mechanistic Pavement Design Procedure (SAMDM) (Theyse et. al, 1996). The stress-strain condition

was then used to calculate the bearing capacities of the individual layers and the pavement system.

The points where stress-strain conditions are computed (critical points) vary for different material types

as shown in Table 10 with the following descriptions:

• Asphalt layers. The horizontal tensile strain at the bottom of the layer controls the fatigue life

of the layer.

• Cemented layers. The horizontal tensile strain at the bottom of the layer controls the effective

fatigue life of the layer, while the vertical compressive stress at the top of the layer controls the

crushing life.

• Granular layers. The major and minor principal stresses at the middle of the layer controls the

shear potential of the layer.

• Soil (Subgrade) layers. The vertical compressive strain at the top of the layer controls the

rutting life of the subgrade.

The stress-strain responses at each of the critical points serve as input to the transfer functions for

each layer. The transfer functions then relate stress-strain conditions to the number of loads that can

be sustained by the layers before certain terminal condition is reached. The transfer functions are the

empirical components of the design procedure normally derived from field or laboratory test results.

The transfer functions correlate the number of repetitions at which a certain stress or strain level can

be sustained before a terminal conditions (failure) is reached. The layer that gives the minimum

number of stress or strain repetitions is then considered the critical layer and the number of repetitions

required to reach the terminal condition is consider the critical repetition (Ncritical) at that particular

load magnitude.


16

An important assumption in the analysis is that the fatigue performance of HiMA is at least equivalent

to that of a conventional bituminous base material. This assumption is based on the relative fatigue

performance of the HiMA material as reported by Anochie-Boateng et al (2010), compared to a

bituminous base material tested as part of the same study.

Figure 4a and 5b show how replacement of surfacing and base layers with thinner HiMA layers

ranging from 100 mm for heavy TRH4 pavement structures to 70 mm for lighter TRH4 pavement

structures. Table 12 shows the standard and legal axle data, whereas Table 13 presents details of the

eight AVs that were used in the analysis. Figure 6 shows an example of axle configuration of a six (6)

axle single dual tyres load combinations.

Table 12: Standard and legal axle data used

STANDARD AND LEGAL AXLES: Average Tyre Load (kN)Standard Deviation

(kN)

Total Load

(kN)Number of Tyres Average TiP (kPa)

Standard Deviation

(kPa)

Standard Axle (Std) 20.00 0.00 80.00 4 520.00 0.00

Legal Axle (Lg) 22.00 0.00 88.00 4 700.00 0.00

Table 13: Summary of the eight abnormal vehicles (AVs) sorted according to their total load

ABNORMAL VEHICLES (SORTED ON TOTAL

LOAD):Average Tyre Load (kN)

Standard Deviation

(kN)

Total Load

(kN)Number of Tyres Average TiP (kPa)

Standard Deviation

(kPa)

AV veh H - Abnormal Vehicle - 6 Axle Single tyres

(AVFS100077)25.41 4.76 559.00 22 727.00 86.78

AV veh A - Abnormal Vehicle - 6 Axle Single tyres

(AVGP105343)29.23 1.80 643.00 22 625.18 29.20

AV veh B - Abnormal Vehicle - 7 Axle Single Dual

tyres (AVNC100523)27.37 2.60 711.50 26 621.54 14.88

AV veh G - Abnormal Vehicle - 8 Axle Single Dual

tyres (AVKN300177)17.57 4.47 878.40 50 463.68 209.46

AV veh D - Abnormal Vehicle - 9 Axle Single Dual

tyres (AVKN300146)16.59 5.34 962.00 58 736.52 4.29

AV veh F - Abnormal Vehicle - 9 Axle Single Dual

tyres (AVGP305729)19.49 5.39 1130.60 58 494.66 162.10

AV veh C - Abnormal Vehicle - 9 Axle Single Dual

tyres (AVGP304803)20.88 5.58 1211.20 58 573.52 80.22

AV veh E - Abnormal Vehicle - 9 Axle Single Dual

tyres (AVGP305165)22.29 6.62 1292.80 58 624.48 1.14


17

Pavement A:ES100

Scenario 1 Scenario 2 Scenario 3

Phase 1 Phase 2 Phase 3 Phase 1 Phase 2 Phase 3 Phase 1 Phase 2 Phase 3

0.44 8000 5000 3000 0.44 15000 10000 5000 0.44 20000 10000 5000

0.35 2000 2000 500 0.35 2000 2000 500 0.35 2000 2000 500

0.35 1500 550 250 0.35 1500 550 250 0.35 1500 550 250

0.35 180 180 180 0.35 180 180 180 0.35 180 180 180

Poisson's

Ratio

Elastic Moduli (Mpa) Poisson's

Ratio


Ratio

Elastic Moduli (Mpa)

SUBGRADE

150 C3

150 C3*

100 HiMA

Pavement A:ES100

Phase 1 Phase 2 Phase 3

0.44 2000 2000 1500

0.35 450 450 350

0.35 2000 2000 500

0.35 1500 550 250

0.35 180 180 180

Poisson's

Ratio


SUBGRADE

150 C3

150 C3*

150 G1*

50 AG*

Pavement B:

ES100

Phase 1 Phase 2 Phase 3

0.44 2000 1800 1500

0.35 250 250 240

0.35 2000 1700 160

0.35 1500 120 110

0.35 90 90 90

Poisson's

Ratio


SUBGRADE

150 C3

150 C3*

150 G1*

50 AG*

Pavement B:ES100



0.44 8000 5000 3000 0.44 15000 10000 5000 0.44 20000 10000 5000

0.35 2000 1700 160 0.35 2000 1700 160 0.35 2000 1700 160

0.35 1500 120 110 0.35 1500 120 110 0.35 1500 120 110

0.35 90 90 90 0.35 90 90 90 0.35 90 90 90

Elastic Moduli (Mpa)Poisson's

Ratio


Ratio


Ratio

SUBGRADE

150 C3

150 C3*

100 HiMA

Replace the base

and surfacing with a

thinner HiMA layer

Vary the effective

elastic moduli based

on range of values

found in literature

Pavement C:ESO.1


Phase 1 Phase 2 Phase 1 Phase 2 Phase 1 Phase 2

0.44 8000 5000 0.44 15000 10000 0.44 20000 10000

0.35 1000 200 0.35 1000 200 0.35 1000 200

0.35 140 140 0.35 140 140 0.35 140 140

- - - - - - - - -

Poisson's

Ratio


Ratio


Ratio


SUBGRADE

125 C4*

70 HiMA

Pavement D:ESO.1



0.44 8000 5000 0.44 15000 10000 0.44 20000 10000

0.35 1000 120 0.35 1000 120 0.35 1000 120

0.35 70 70 0.35 70 70 0.35 70 70

- - - - - - - - -


Ratio


Ratio


Ratio

SUBGRADE

125 C4*

70 G1*

Thinner HiMA layer in place of base

and surfacing layers

Figure 4a: HiMA layer in place of base and surfacing layers for eight road pavement structures


18

Pavement E:ES30/ES50



0.44 8000 5000 0.44 15000 10000 5000 0.44 20000 10000 5000

0.35 2200 1000 300 0.35 2200 1000 300 0.35 2200 1000 300

0.35 300 300 200 0.35 300 300 200 0.35 300 300 200

0.35 150 150 140 0.35 150 150 140 0.35 150 150 140

Poisson's

Ratio


Ratio


Ratio


SUBGRADE

200 G7*

450 C3*

90 HiMA

Pavement F:ES30/ES50



0.44 8000 5000 0.44 15000 10000 0.44 20000 10000

0.35 1000 300 0.35 1000 300 0.35 1000 300

0.35 140 140 0.35 140 140 0.35 140 140

- - - - - - - - -


Ratio


Ratio


Ratio

SUBGRADE

150 C4*

50 HiMA



Pavement G:ES10



0.44 8000 5000 3000 0.44 15000 10000 5000 0.44 20000 10000 5000

0.35 1000 300 100 0.35 1000 300 100 0.35 1000 300 100

0.35 180 140 100 0.35 180 140 100 0.35 180 140 100

- - - - - - - - - - - -

Poisson's

Ratio


Ratio


Ratio


SUBGRADE

300 C4*

90 HiMA

Pavement H:ES0.3



0.44 8000 5000 3000 0.44 15000 10000 5000 0.44 20000 10000 5000

0.35 1000 300 100 0.35 1000 300 100 0.35 1000 300 100

0.35 140 140 100 0.35 140 140 100 0.35 140 140 100

- - - - - - - - - - - -


Ratio


Ratio


Ratio

SUBGRADE

100 C4*

50 HiMA



Figure 5b: HiMA layer in place of base and surfacing layers for eight road pavement structures


19

-2500

-2000

-1500

-1000

-500

0

500

1000

1500

2000

2500

-2500 0 2500 5000 7500 10000 12500 15000 17500 20000 22500 25000Y (m

m)

X (mm)

Figure 6: Axle configuration of articulated six (6) axle single dual tyres.

3.3 Legal Damage (LDv):

In this section, the potential basic formulations proposed for the quantification of the pavement

damage are defined. These include:

∑=

==

n

iV

AxlekPakNfromNcritical

AxlekPakNLegalfromNcriticalLDVehicleofDamageLegal

1 ) 520/ 80 (

) 700/ 88 (

Standard

×==

) 520/ 80 (

) 700/ 88 (


AxlekPakNLegalfromNcriticalnLDVehicleofDamageLegal V Standard

Where:

n = number of axles on Vehicle (v)

Ncritical from Legal 88 kN/700 kPa Axle = Minimum layer life of pavement under the loading of the

current Legal Axle of 88 kN and 700 kPa inflation

pressure on 4 tyres (i.e. 22 kN per tyre @ 700 kPa

contact stress (= inflation pressure)

Ncritical from Standard 80 kN/520 kPa Axle = Minimum layer life of pavement under the loading of the

current Standard Axle of 80 kN and 520 kPa inflation


contact stress (= inflation pressure)


20

3.4 Total Damage (TDv) (= Load Equivalency Factor (LEFv) of Vehicle):

∑=

===

n

i iVv

AxlefromNcritical

AxlekPakNfromNcriticalTDVehicleofDamageTotalLEF

1 ) (

) 520/ 80 (

Standard

Where:


Ncritical from Standard 80 kN/520 kPa Axle = Minimum layer life of pavement under the loading of the

current Standard Axle of 80 kN and 520 kPa inflation


contact stress (= inflation pressure).

Ncritical from Axlei = Minimum layer life of pavement under the loading of the Axlei of vehicle in

question.

3.5 Total Additional Damage (TADv):

∑ ∑= =

−

=

=

n

i

n

i ii

V


AxlekPakNLegalfromNcritical

AxlefromNcritical


TADVehicleofDamageTotal

1 1 ) 520/ 80 (

) 700/ 88 (

) (

) 520/ 80 (

StandardStandard

Additional

Where:


LDv = Legal Damage of Vehicle (v)

TDv = Total Damage of Vehicle (v) = LEFv.

As an example, results for a six of the eight pavements structures based on an LEFv of a six (6) axle

vehicle are shown in the following plots (Figure 7 – (A), (B), (C), (D), (G) and (H)). Except for scenario

1 on pavement H, all cases of HiMA replacement resulted in reduced LEFv, which is an indication that

HiMA replacement scenarios provided a better protection of pavement structures.

Pavement A

Pavement HiMA 1 A

Pavement HiMA 2 A

Pavement HiMA 3 A

1.05

0.17

0.05

0.05

Six axle vehicle LEFv for pavement type A Dry


21

(A)

Pavement B

Pavement HiMA 1 B

Pavement HiMA 2 B

Pavement HiMA 3 B

2.66

0.40

0.22

0.22

Six axle vehicle LEFv for pavement type B Dry

(B)

Pavement C

Pavement HiMA 1 C

Pavement HiMA 2 C

Pavement HiMA 3 C

4.47

1.12

0.60

0.61

Six axle vehicle LEFv for pavement type C Dry

(C)

Pavement D

Pavement HiMA 1 D

Pavement HiMA 2 D

Pavement HiMA 3 D

13.27

0.68

0.32

0.32

Six axle vehicle LEFv for pavement type D Dry

70 HiMA

(D)


22

Pavement G

Pavement HiMA 1 G

Pavement HiMA 2 G

Pavement HiMA 3 G

6.85

3.98

2.55

2.57

Six axle vehicle LEFv for pavement type G Dry

(G)

Pavement H

Pavement HiMA 1 H

Pavement HiMA 2 H

Pavement HiMA 3 H

8.14

9.25

1.78

1.80

Six axle vehicle LEFv for pavement type H Dry

(H)

Figure 7: LEFv for all the eight pavement structures based on articulated six (6) axle vehicle.

3.6 Summary of structural design

In this interim report, a mechanistically based methodology is proposed for the calculation of Load

Equivalency Factors (LEFs) for a given sample of Abnormal Vehicle (AV) combinations. The LEF

calculations were based on eight typical types of road pavement found in South Africa. These were

estimated at different positions under each of the outermost tyres, (per axle) and then summed for

cumulative damage, which is represented by the LEFv of the particular AV or Mobile Crane. The

analyses were expanded to include both relatively dry and relatively wet pavement conditions.


23

The findings from this interim study indicate that:

1. HiMA has a higher effective elastic modulus than normal asphalt with values ranging from 8

GPa to 25 GPa.

2. Comparative analyses with abnormal vehicles have shown that HiMA replacement protects

the pavement better against overloading for most of the pavement types.

3. Mechanistic analyses have shown that HiMA layers can reduce pavement base thicknesses

by approximately 30% of normal thicknesses without affecting the pavement structural life.

4. These are preliminary findings and should be used with care by the industry and associated

road authorities until field validation studies have been conducted.

References

Anochie-Boateng, J., Denneman, E., O'Connel, J., & Ventura, D. (2010). Level 1 Analysis report of High Modulus asphalt (reference mix). Pretoria.

Bell, C., Y., A. W., Cristi, M., & Sosnovske, D. (1994). Selection of Laboratory Aging procedures for Asphalt-Aggregate Mixtures. Corvallis: Oregon State University.

Delorme, J., De La Roche, C., & Wendling, L. (2007). LPC Bituminous Mixtures Design Guide. Director. Paris: Laboratoire Central des Ponts et Chaussees.

Distin, T., Sampson, L., Marais, H., & Verhaeghe, B. (2008). High Modulus Asphalt : Assessment of Viability Based on Outcomes of Overseas Fact Finding Mission. Asphalt. sabita.

Nkgapele, T., & Denneman, E. (2010). High modulus asphalt (HiMA) mix improvement project. Pretoria.

Sanders, P., & Nunn, M. (2005). The application of Enrobe a Module Eleve in flexible pavements. Industrial. doi: 10.1021/ie50052a020.

Taute, A., Verhaeghe, B., & Visser, A. (2001). Interim guidelines for the design of hot-mix asphal in South Africa. Pretoria.

Von Quintus, H., Scherocman, J., C.S., H., & Kennedy, T. (1991). NCHRP report 338: Asphalt-Aggregate mixture analysis system.. Austin: Brent Rauhut Engineering Inc.

Interim guide for the design of high modulus asphalt mixes ...€¦ · As part of the Sabita High...

Documents

Transcript of Interim guide for the design of high modulus asphalt mixes ...€¦ · As part of the Sabita High...