Restabilising Stabilised
Pavements
What are the Options?
David Bell
Regional Manager
South Queensland
Background/Context
• Asset owners are continually faced with the task of
rehabilitating pavements that have failed or
reached their design life
• Many existing pavements are stabilised
• What options do I have when looking to
rehabilitate a previously stabilised pavement?
• How do I go about selecting a recycling treatment?
• What aspects do I need to consider in order to
recycle?
What are stabilised pavements?
• Existing stabilised pavements contain binder that
has been previously incorporated either exsitu (pug
mill) or insitu (reclaimer/stabiliser)
• Binders can include:
•
•
•
•
•
Cementitious
Lime
Bitumen
Polymer
Other
Typical Stabilised Pavements
Wearing course
Basecourse
General Blended Cements
Blends (slag/lime/cement)
Foamed Bitumen/Emulsion
Subbase
Subgrade
Quicklime
Hydrated Lime
Lime blends
Existing CTB /Stabilised Pavements
Excess Binder and
Insufficient Mixing Depth
Why look to restabilise?
Recycling
Lower carbon footprint
Minimal construction waste or use of virgin materials
Less truck movements on existing / adjacent road network
Faster Construction time with less disruption to residents
Cost Savings over remove & replace options of 30 - 50%
Case Studies and Further Technical Presentations Available
The Key Questions
Q:
A:
Can I restabilise a stabilised pavement?
Of course you can!
Q:
A:
How do I select a treatment and design?
The same process used to stabilise / design the
pavement in the first instance!
However…… there are various items to consider
What process do I undertake?
Structural Design
Mix Design
Site Investigation
Identify Potential Options
Material Sampling and
Insitu Data Collection
Model Structurally
Laboratory Testing
Selection of Mix Design
What are attributes to consider?
• Impact of residual binder
• Depth of treatment with respect to existing layer(s)
• PSD post treatment (retention of aggregate size
during mixing passes)
• Reclamation of bound pavement
Impact of Residual Binder…
Impact of Residual Binder….
Can contribute to strength gain when recycling again
Case Study 1
Location
Additive rates
Trench 1
Ch 102.683
Trench 1
Ch 102.683
Trench 3
Ch 103.293
Bitumen 3%
Lime 1.5%
Bitumen 3%
Lime 1.0%
Bitumen 3%
Lime 1.5%
Initial
(MPa)
3 day cured 3 day soaked
(MPa)
(MPa)
Retained
%
998
3518
2177
62
762
3846
2352
61
920
3288
1724
52
Impact of Residual Binder….
Can contribute to strength gain when recycling again
Case Study 2 - 2.5% Bitumen
Depth of treatment
A bound and cracked subbase can produce reflective cracking
In this instance, consideration should be given to full depth
mixing (incorporate all previously stabilised material) or
implement strain alleviating membrane
PSD Impacts During Treatment
Does the pulverising and mixing process break down
the stone size?
• Stone hardness
• Can determine preconstruction through Qld TMR
sampling method (Q061)
• Bobcat (replicate mixing action)
• 3 times (replicate mixing process)
• Addition of material
PSD Impacts During Treatment
Example PSD prior and during construction
*Central Coast Council, Showground Road
Reclamation of Bound Pavement
Spot the Difference?
•
•
•
•
Modified, bound, heavily bound
Potential limitations of reclaimer/stabiliser
Use of profiler
Construction staging/methodology
Case Studies
This is extremely common throughout LGA and SRA’s
throughout Australia
Many councils have been restabilising pavements at the
end of their design life for years
Some intriguing examples include:
• City of Gold Coast
• TMR - Naughtons Corner
• TMR - El Arish
City of Gold Coast
Upland Drive, Parkwood
Points of Interest
• LGA local to IPWEAQ conference
• First conscious attempt at restabilisation
• Existing bound pavement that has fatigued
• Originally stabilised in 1996, restabilised 2012
• Implemented the process as a trial study to ensure
a structured/considered approach
City of Gold Coast - Construction
City of Gold Coast – Learnings
#
• Pavement is performing well two years after
restabilisation (2014) with cored UCS of 3.2 – 3.7MPa
• Insitu pavement recycling could be successfully
completed for the second time
• Significant economic and environmental advantages
will be achieved by recycling the pavement more than
once. Cost savings up to 60% could be achieved
compared with total reconstruction methods
• A balanced laboratory and field testing program is
required to achieve improved field performance (e.g.
collecting soil samples using a Bobcat profiler to
replicate the insitu stabilisation process)
# Source – “Pavement Recycle 2 – Insitu Pavement Recycling Twice.
City of Gold Coast - 2014 AustStab Awards Submission
Transport and Main Roads
Bruce Hwy, Naughtons Corner
Points of Interest
• Initial pavement was cement stabilised under NDRRA
events 2011-2013
• Pavement fatigued due to high binder content and
insufficient layer thickness from previous treatment
• Flexible pavement was
preferred option
• Foamed Bitumen selected as
preferred treatment for mix
design testing (following
confirmation of PSD)
Transport and Main Roads
Bruce Hwy, Naughtons Corner
Location
Additive rates
Trench 1
Ch 102.683
Trench 1
Ch 102.683
Trench 3
Ch 103.293
Bitumen 3%
Lime 1.5%
Bitumen 3%
Lime 1.0%
Bitumen 3%
Lime 1.5%
Initial
(MPa)
3 day cured 3 day soaked
(MPa)
(MPa)
Retained
%
998
3518
2177
62
762
3846
2352
61
920
3288
1724
52
• 100% cement treated bases were reused, lime was reduced from
TMR’s typical 2% down to 1.5% (Northern) and 1.0% (Southern)
• Design thickness included 50mm and 30mm ‘bite’ into subbase to
ensure no rigid underlying pavement remained (reflective
influence)
Transport and Main Roads
Bruce Hwy, Naughtons Corner
Transport and Main Roads
Bruce Hwy, El Arish
Points of Interest
• Unsuccessfully foamed bitumen stabilised in 2007,
resulting in premature failure (multiple modes)
• Foamed bitumen was not uniform and issues occurred
in relation to achieving conforming foaming properties
• TMR conducted mix design testing and confirmed
pavement could be foamed bitumen stabilised again
• Construction methodology was a key part of tender
phase to ensure cross blending of non uniform
pavement materials
• Only known instance of refoaming foamed bitumen
Transport and Main Roads
Bruce Hwy, El Arish (Existing Failure Modes)
Transport and Main Roads
Bruce Hwy, El Arish (Construction Photos,
crossblending & additional material)
Transport and Main Roads
Bruce Hwy, El Arish (Finished Project)
Outcomes
• Mix design resulted in reduction
of bitumen application rate to
2.5%
• Restabilised in mid 2014
• Pavement is performing well
however there are some spray
seal defects (surface)
• A pioneering case study to
monitor with time
Potential Items for Further Study
Impact of residual binder
• Cementitious binders
• Refoaming, foamed bitumen
PSD Impacts
• Methods to replicate mechanics of mixing
Summary
• Restabilising stabilised pavements is a viable option
for rehabilitation
• Evaluation of treatment selection follows the same
process as stabilising an unbound pavement
• Items to consider include
•
•
•
•
Reclaiming bound pavement
Sampling and testing
PSD and stone hardness
Residual binder
• Many LGA’s throughout Australia have been
undertaking this practice over an extended period
Questions
www.stabilisedpavements.com