ISAP 2019High Modulus Asphalt

Enrobé à Module Élevé (EME)Asphalt Technology in South Africa

Steph Bredenhann13 October 2019

Sun City, South Africa

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Note: HiMA is a trademark (by Kraton) for Highly Modified Asphalt. This talk is on High Modulus Asphalt (EME) with a possible acronym HMA as used in USA. This can be confused with Hot-mix Asphalt in SA. In this presentation HIMA will be used for High Modulus Asphalt

Overview

• Background and Introduction• EME mix design (SABITA Manual 33)• Fatigue• Laboratory vs Field• EME Specification• Alternative High Modulus Asphalt• Highly modified asphalt• Construction• The future?

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Background

• EME developed in France since the 1990’s for use as mainly base layers on highways, airport runways and urban roads.

• Technology transfer to SA started in 2011• Initial designs done in France with SA Materials• Extensive testing at CSIR to establish design guide and specification

based on SA conditions• Real opportunities identified to apply technology in SA• Mix design differ from conventional asphalt as EME design is

strictly performance based

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EME Characteristics

• High binder content ≈ 6%• Hard bitumen: Pen 10-20• Low air voids content• High modulus > 14 GPa at 15°C, 10 Hz• High resistance against permanent deformation• Good fatigue resistance• Impermeable

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Aims set for SA Denneman RPF, 2011

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• Workability• Durability• Stiffness• Rut resistance• Fatigue

EME Implementation in SA

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Some projects so far

• Initial projects– OR Tambo (A380)– South Coast Road Durban (access to Durban Harbour – 60m E80s)

• Later projects– Mainly in KZN: N2, N3, Bus routes, M7– Cape Town: Jan Smuts Rd, N1 Huguenot Tunnel (crawler lane)– Gauteng: R104

• Total tonnage: approximately 350 000 tons

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Mix Design

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EME Mix Design Process (Manual 33)

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HWT - 4mmafter20 000 passes

Requirements for hard paving-grade bitumen

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10

100

0 2 4 6 8 10 12

Pen

@ 2

5 °C

(dm

m)

MSCR Jnr (kPa-1)

58 64 70

10/20

35/50

50/70

70/100

SHVE FAIL

Design grading

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It should however be noted that these gradings only provide a point of departure for the mix design process and should not be used to impose a restriction on the gradings adopted for optimal mix designs.

Binder content

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Binder content determined by Richness Modulus (K) 5

ppcBK

α=

∑

Bppc = mass of binder (%) including fillerΣ = specific surface areaα = correction factor for aggregate density

Performance Requirements

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Fatigue

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Definition of Fatigue

• Under repeated cyclic loading the fatigue life should correspond to the transition point between crack initiation and crack propagation

• Note: Fatigue is repeated/cyclic loading thing

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Fatigue considerations for EME

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Asphalt Fatigue EME

• Due to high modulus and higher order pavement - low strains can be expected

• Proposed fatigue specification Manual 33• Sinusoidal loading better results (Botes 2016)

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Test No of specimens

Method Requirement

Class 1 Class 2

4-pt Beam fatigue test at 10 Hz, 10°C to 50% stiffness reduction

9 AASHTOT321

≥ 106 reps@ 210 μξ

≥ 106 reps@ 260 μξ

Fatigue Sensitivity (binder)

• Recent (2014) N1 project (CAPSA 2019 paper)– EME binder content 5.7% - early rutting– EME binder content 5.4% - no early rutting

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Test Specification Binder content (%)

5.7 5.4

4-pt Beam fatigue test at 10 Hz, 10°C to 50% stiffness reduction

260 253 μξ 243 μξ

Fine balance required between high binder content (for high fatigue life) and low binder content (for low rutting)

BTB vs EME Denneman RPF 2011

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Note difference high and low binder content

EME Binder Nortje RPF 2011

• Reported on KZN trials– 5.7% best fatigue life– 5.2% lowest rutting

• Corresponds with previous results• More than 300 000 tons produced and placed in KZN so far,

performance good (telecon 2019)

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BTB vs EME Steyn, CAPSA 2015

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( )log 0.1782 log 3.5028t fNε = − +

Nf = 106

4-pt Beam fatigue test at 10 Hz, 10°C to 50% stiffness reduction

Effect of support layers on EME Fatigue Steyn, CAPSA 2015

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Recommended Experimental Design for EME Fatigue Testing Theyse 2014

• Strain levels– 100 μξ, 200 μξ, 300 μξ, 400 μξ

• Temperature– 0 °C, 10 °C, 20 °C

Thus 4x3 = 12 tests

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EME Laboratory vs Field

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See paper by Thomas, Jenkins & Rudman, CAPSA 2019

EME Laboratory vs Field

• On N1 project slabs were recovered from both top and bottom EME layers

• Dynamic modulus– At high temperatures lab higher than field

• Fatigue– Confirm that bottom layer with higher binder content has better

fatigue life– Fatigue lower for field than lab

• Flexural stiffness also lower field than lab

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Flexural Stiffness

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100

1000

10000

100000

1.E-06 1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00 1.E+01 1.E+02

Fle

xura

l Sti

ffne

ss (M

Pa)

Frequency (Hz)

S10-BC (Botes)

S11-BB (Botes)

2AAT (Thomas)

2BAB (Thomas)

Fatigue: Lab vs Field

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10

100

1000

10,000 100,000 1,000,000 10,000,000 100,000,000 1,000,000,000

Tens

ile S

trai

n (με)

Number of Load Cycles

W. Steyn (50% Fatigue)

M. Thomas (50% Fatigue)

Freeme 8000 MPa (50% Fatigue)

B. Botes** (50% Fatigue)

Freeme 5000 MPa (50% Fatigue)

EME Fatigue Specifications –Whereto from here

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Example Fatigue Results Chappat et al 2009

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Almost 50% of results fail! Should fatigue be specified?

OR: consider a compensation system?

Binder source: major role! Chappat et al 2009

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Fatigue Specifications?

• This aspect will be discussed in detail at a workshop at CAPSA 2019

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High Modulus Asphalt (HIMA) alternativesand Highly Modified Asphalt (HiMA)

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Asphalt Fatigue HIMA

• Where EME is manufactured with straight bitumen, HIMA allows modification

• Modulus generally lower than EME, not enough data available to confirm

• However, specification for EME can still be met• Thus, still high modulus and higher order pavement - low

strains can be expected

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HIMA Experience in SA

• Very little experience with HIMA in SA• Olard reported at CAPSA 2011 on Grave Bitume (GB), a French

HIMA mix, specifically GB5• De Beer reported at SATC 2017 of GB5 test trials in SA (done in

2014 in Durban)– Stone skeleton mix– 35/50 pen bitumen, 3% SBS polymer and cross-link– 20% reclaimed asphalt– Fatigue at 106 of 250 to 280 μξ reported

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Highly Modified Binder as an alternative

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Different binders age differently

Modification can increase SP but retain pen

Construction (N1 Cape Town)

• Mix design took long, delayed construction• Binder availability, especially when only small quantities required• Was warned against early “lock-up” below certain temperature.

Early “lock-up” was actually similar to normal mixes• Danger of over-compaction, not so; normal compaction• Layer flushes visibly, especially on roller overlaps; >95% MVD• Combination vibratory compactor plus heavy PTR. Initial rolling

with PTR was necessary• Compaction windows not entirely different, 90°C is lower limit• Implication of aggregate size on layer thickness critical

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The Future

• EME in SA seems to mature• Quite a few projects lined up for construction, mainly KZN• Approximately 400 00 tons of EME to be paved• Need to continuously interrogate methods and knowledge

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THANK YOU

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