Comparison of Deep Lift Asphalt & Foamed Bitumen Treatment Options for Heavily Trafficked RoadsScott Young BE (Hons), RPEng (Civil), RPEQ

Technical Manager, SPA

PREAMBLE

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This paper was prepared to explore the technical, commercial,

environmental and performance characteristics of foamed

bitumen stabilised pavements in direct comparison to deep lift

asphalt pavements, specifically for heavily trafficked roads.

AGENDA

1. Background2. Defining a Heavily Trafficked Pavement3. Foamed Bitumen Theory & Construction4. Design Considerations5. Resilience to Moisture6. Foamed Bitumen Performance7. Current Research & Development8. Case Study - Tilley Rd, Chandler

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BACKGROUND

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Treatment Selection

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Rehabilitation treatments are often limited by a few materials that can adequately withstand

high cyclic loading.

Full depth/thick asphalt treatments are a common and easy ‘go to’ treatments where design,

construction and performance characteristics are reasonably well understood in Australia.

Treatment Selection

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Adopting foamed bitumen materials as the structural element of a pavement in lieu of thick asphalt has been

successfully implemented in many parts of Australia for many decades.

There continues to be a lack of appreciation in some parts of the local government sector of the design

considerations, construction aspects and long term performance of these materials.

DEFINING A HEAVILY TRAFFICKED PAVEMENT

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2

How do we determine

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Road Classification:

*** Sub arterials – Arterials - Highways – Motorways – Industrial Sites – Bus Routes ***

Input variables:

*** Annual Average Daily Traffic (AADT) - % heavy vehicles - design period - cumulative growth factor ***

Design Equivalent Standard Axle (DESA) loading of 1.0E+06 or greater

FOAMED BITUMEN THEORY & CONSTRUCTION

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Foamed Bitumen

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Host Material Suitability

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Suitable PSD Envelopes for Foamed Bitumen Host Materials

Asphalt v FB

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Construction - Insitu

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Insitu Mixing Supplementary Binder (top); Insitu Mixing Foamed Bitumen (bottom)

Construction - Exsitu

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Exsitu Foamed Bitumen Mixing (L) and Placement (R)

DESIGN CONSIDERATIONS

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Structural Design

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Vb = usually 7% for foamed bitumen; typical range of 10-14% for asphalt

E = capped at 2,500MPa for foamed bitumen (soaked modulus), multiple range for

asphalt, depending on temperature, mix type, binder, design speed

Thickness Delta

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Design Speed: 80km/hr

WAMPT: 32oC

Project Reliability: 95%

Wearing Course: 50mm AC14 (E=2600MPa)

Structural Base: Variable thickness, AC20 (E=2900MPa) or Foamed Bitumen (E=2500MPa)

Subbase: 150mm Unbound Granular (E=150MPa)

Deep Lift Asphalt v Foamed Bitumen (Wearing Course + Base Thickness)

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Mix Design

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Laboratory Testing

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Basecourse Modulus Limits

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RESILIENCE TO MOISTURE

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Cyclone Debbie

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Mt Lindsey Highway at Cable Camp Rd

During Construction

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Bruce Highway, Ingham to Innisfail

TMR Experience

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- ‘…millions of dollars saved through more resilient pavements’

- ‘The Bruce Hwy (Sandy Gully) near Bowen showed no evidence of damage despite heavy

rainfall’.

- ‘…pavement construction in Warrill View, south of Ipswich, was able to continue without

delay, after the unsealed foamed bitumen pavement was inundated.’

- ‘…Yeppen floodway in Rockhampton has emerged from the deluge with a clean bill of health.’

TMR Experience

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- ‘…the department is not only saving on the cost of construction – foamed bitumen costs less per

cubic metre than asphalt – but also on the cost of maintaining and rehabilitating roads after

natural disasters like ex-Tropical Cyclone Debbie.’

- ‘Adding to its better long-term performance, foamed bitumen stabilised pavements also exhibits

comparable (and in some cases superior) fatigue properties to asphalt...’

FOAMED BITUMEN PERFORMANCE

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The TMR Perspective

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City of Gold Coast

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Coghill Dr, Currumbin Waters(200mm, 3.5% Bitumen, 1.5% Lime)

Kimberley Rd, Burleigh Waters(250mm, 3.5% Bitumen, 1.5% Lime)

Smith St Motorway

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Smith St Motorway

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Smith St Motorway

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CURRENT RESEARCH & DEVELOPMENT

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AP-T336-18

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• improvements to existing mix design methods

• moduli determined during the mix design phase is conservative compared to cured moduli obtained from the field

• confirmation that fatigue life based on use of thicknesses derived from the existing asphalt fatigue equation are well reflected in the field.

AP-T343-19

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• similar early life and long term performance of the

two crushed rock stabilised materials

• high proportions of RAP have little impact

• both foamed bitumen stabilised test sections showed

superior deformation resistance than the asphalt

control section at elevated temperatures.

CASE STUDY – TILLEY RD, CHANDLER

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The Site

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Suitability for Foamed Bitumen

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Material Thickness (mm) Proportion (%) PI (%) LS (%)

Imported Type 2.1-C Grading 50 20 <6 <3.5

Existing AC (RAP) 75 30 N/A N/A

Existing Gravel 125 50 7 4

TOTAL 250mm 100%

Design Input Parameters

Full Depth Asphalt and Foamed Bitumen Trialed for the Structural Elements

o Design subgrade CBR of 5%o 20 year design periodo Traffic loading, DESA = 4.5E+06o Project reliability of 95%o Design speed of 50km/hro WAMPT of 32oCo A 50mm AC14 (M1000) wearing course was modelled as a constant layer for both options

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Design Comparisons

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-300

-250

-200

-150

-100

-50

0

50

100

150

Full Depth Asphalt Insitu Foamed Bitumen Stabilised Base

Des

ign

Th

ickn

ess

(mm

)

Key Metrics Comparison

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Deep Lift Asphalt Mill & FillInsitu Foamed Bitumen

Stabilisation

Foamed

Bitumen SavingMill 100mm & dispose

Place 185mm AC in 3 layers

Import & Place 50mm Gravel

Stabilise 250mm

Place Single Coat Seal &

50mm AC

Construction Period 4 days 4 days 0%

Material Out 846 Tonnes 0 100%

Material In 1,709 Tonnes 1,027 Tonnes 40%

Total Truck Movements 468 240 49%

Construction vehicle network

coverage17,368 km 7,794 km 55%

Total Fuel Consumption 9,726 Litres 4,365 Litres 55%

CO2-e Emissions 442 Tonnes 274 Tonnes 38%

Capital Cost per SQM $91.87 $68.02 26%

SUMMARY

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KEY TAKEAWAYS

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✓ Foamed bitumen to stabilise pavement materials is proven technology

✓ It is underpinned by national design guidelines

✓ Current and future research continues to develop performance relationships

✓ Permanent deformation performance exceeds an equivalent full depth asphalt pavement for the same design life

✓ TMR have used this technology on >600km of roads in the last 20 years

✓ Particularly suited to high trafficked and moisture sensitive environments

✓ Local Councils in SEQ have benefited from adopting foamed bitumen solutions in lieu of thick asphalt treatments

KEY TAKEAWAYS

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The BCC case study highlights and quantifies the advantages of a foamed bitumen treatment compared to a thick

asphalt treatment for a 20 year design period.

Savings included:

- a 26% reduction in capital cost

- a 38% reduction in carbon footprint

- a 55% reduction in construction traffic causing damage to other parts of the network

- 100% reuse of the existing pavement materials