Overview of Foam Bitumen Contracts Undertaken in Far North Queensland

Craig Gordon – Cairns Office

RTA Northern Region

17th March 2010

SCOPE

• Fundamentals of Foam Bitumen Pavements• Projects Undertaken• Construction Methods Used

Foam Bitumen Stabilised Pavements

• What is Foam Bitumen Stabilised Pavements.– It is a mixture of gravel, lime or cement, air, water and bitumen– When air, water and bitumen are mixed with each other the

mixture expands greater than 10 times its original volume and forms a fine mist or foam

– This foam is sprayed into the drum where it coats the fine particles

– As the foam collapses most of the water is lost through steam– The residual bitumen then has properties similar to its original

state and is well dispersed through the matrix in very small droplets

– The bitumen droplets are attracted to and coat the finer particles, forming a uniform matrix that effectively binds the mixture together.

Foam Bitumen Stabilisation

Where to Use the Foam Bitumen Process

• A pavement that has been repeatedly patched to the extent that pavement repairs are no longer cost effective

• A weak granular base overlays a reasonably strong subgrade

• Granular base is too thin to consider cementitious binders

• Alternative to full depth asphalt in moderate to high trafficked roads

• Unfavourable wet cyclic conditions• To complete the rehabilitation quickly to prevent

disruption to businesses, residents and public

Foam Bitumen Stabilisation

Contracts Undertaken

• Within the Peninsula District of North Queensland, a number of Foam Bitumen contracts have been carried out. The majority of these projects have been on the Bruce Highway where the roads have been affected by flood damage.

• The district is now also including foam bitumen pavements in new pavements / reconstructed pavements.

• Foam Bitumen Pavements appear to be the desired choice for the major highways in the District, Bruce, Palmerston, Captain Cook.

• The Cairns Regional Council has also done some minor works with Foam Bitumen Stabilisation.

• Mackay Regional Council have also awarded DEW a foam bitumen contract which we are currently undertaking.

Contracts Undertaken

• Department of Main Roads, Queensland (since November 2008 to current)– Bruce Highway – approximately 2.5km (El Arish)– Bruce Highway – approximately 3.5km (Mourilyan)– Bruce Highway – approximately 3.5km (Cardwell)– Palmerston Highway – approximately 5km – Palmerston Highway – approximately 2km– Palmerston Highway – approximately 0.7km– Palmerston Highway – approximately 3.5km

• Other Projects– Mackay Regional Council Flood Damage Package 7 (Various

council roads)

Foam Bitumen

• Basic design of the pavements is to incorporate an overlay, with 2% lime or 1.5% of cement and 3.5% of bitumen.

• An overlay is only used when required and generally consists of between 50mm and 100mm of Type 2.1 Gravel.

• The use of the overlay was for shape correction and also to increase the quality of the pavement material, ie gradings.

Foam Bitumen

• Design Considerations employed by Main Roads:– Design period– Design Traffic– Subgrade Material Properties– Pavement Material Properties– Environmental Influences– Construction and Maintenance Procedures– Drainage

Benefits and Limitations

Benefits:– Increased strength over granular pavement materials– Relatively quick construction method– Lower costs than Reconstruction– Trafficked immediately (in the right conditions)– Can be trafficked without a seal– Decreased susceptibility to moisture during

construction.– Can be reworked several days after final trimming

without extra binder

Benefits and Limitations

Limitations:– Requires a suitable grading of fines in the

pavement material– Purpose built equipment and experienced

operators are required– Cost is greater than cement stabilisation– Not suitable for all pavements (some pavements

show low strength gain, slow strength gain an unsuitable grading)

Secondary Stabilising Agent and Foaming Agent

• Secondary Stabilising Agent:– Usually consists of cement or lime, lime is the preferred

option, although cement is cheaper– Specified working time (4 hours) commences upon

incorporation, although bitumen is then required to be incorporated within the next 1.5 hours

– Incorporated 50mm above the target depth.– Purpose for secondary stabilising agent:

• Assist in strength increase• Assist in dispersion of bitumen throughout mix• Improves mix workability• Reduces the plasticity Index

Lime spreading

Lime mixing

Lime mixing

Secondary Stabilising Agent and Foaming Agent

• Foaming Agent– A proprietary product is used– Used to combat the anti foaming agent that has been put

into bitumen for transport reasons– A maximum of 2% by mass should be added– Generally we have found 0.5% is adequate to achieve half

life and expansion ratios– Assists in the dispersion of bitumen to coat each particle of

the pavement– Essential to be used, as bitumen will naturally foam when hit

with water, although the dispersion is still not as adequate without the foaming agent

Half life/foaming

Things to consider with Foamed Bitumen Stabilisation

• Safety is paramount when working in any environment, especially under traffic and when using hot bitumen binder

• Typical application rates of foam bitumen are between 2-4% bitumen with the addition of a binder i.e. lime or cement, around about the 2% mark

• Sufficient pavement testing including testing of the subgrade is crucial when determining mix design and potential for using foam bitumen. Testing can cost approx. $3000 - $4000 per test, although the bitumen savings it could produce are considerable

• Sealing rates over foam bitumen pavements are usually reduced by at least 10% compared to normal pavements, common problems are bleeding of seals and potential instability of asphalt layers.

• A foaming agent is a must when foaming bitumen

Things to consider with Foamed Bitumen Stabilisation

• Construction times are very important• Moisture content of the pavement is important, and

generally in the range 60-80% of optimum• Experienced construction teams are essential when

undertaking foam bitumen• Although method is less susceptible to wet weather

than other pavements, work in wet weather should be avoided as moisture can become trapped in lower layers of pavement causing problems with compaction

• Allowing traffic on the surface prior to primer sealing is not desirable, as the fines on the surface contain bitumen, which will in turn get stuck to cars.

Bitumen hookup

Construction Methods

• Plant and Labour Crew– Traffic Control– Project Manager– Supervisor– Wirtgen WR2000 or WR2500 (Foam Bitumen Capabilities)– Additional Mixer if required for pulverisation, cement / lime

incorporation– Grader– Loader (If Overlay)– Trucks (If Overlay)– Bitumen Tankers (Capable of attaching to the mixers bar)– Watercarts– Rollers (18t for up to 250mm, 21 tonne up to 300mm) include Pad

foot, Smooth Drum and Multi Tyred Rollers– Generally also require 3-4 additional laborers on the ground for

Quality Assurance checks and day to day tasks

Construction Methods

• Methodology– Generally, traffic control is set up to close 1 lane approx

500m in length– Place Overlay– Pulverize pavement– Spreading of lime / cement– Mixing of lime /cement and water– Incorporation of foamed bitumen– Final Trimming of Pavement– Sealing works

Production rates

• Indicative production rates achieved (daily/10 hr day) on a 250 mm pavement with 50 mm overlay, 8 kg/m2 cement and 18.4 kg /m2 bitumen.

• 1200 m2 to 2,400 m2 per day (under one lane traffic).• Production constraints• Supply of materials i.e. gravel, bitumen, powder,

aggregates and additives.• Stockpiles sites if required• Traffic• Weather• Machine breakdowns

Foam Bitumen Stabilised Pavements.

Questions Relating to the Construction Activities.