10/05/2013 1 Performance of Recycled Concrete Aggregate as a Base Course Material in Road Pavements Recycled demolition aggregates as a base course for roads • Recycled demolition material may be made up of: – straight crushed concrete – comingled demolition materials containing: • brick and tile • asphalt • other unbound aggregates • It should not contain any significant amounts of: – plaster or other friable material – timber – organics – asbestos or other hazardous materials
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10/05/2013
1
Performance of Recycled Concrete Aggregate as a Base Course Material in
Road Pavements
Recycled demolition aggregates as a base course for roads
• Recycled demolition material may be made up of:
– straight crushed concrete
– comingled demolition materials containing:
• brick and tile
• asphalt
• other unbound aggregates
• It should not contain any significant amounts of:
– plaster or other friable material
– timber
– organics
– asbestos or other hazardous materials
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Welshpool Road
• Four different pavement profiles were constructed:
– 250 mm of CDRB subbase and 150 mm of CGRB base
– 400 mm of CDRB base
– 250 mm of size 50 mm CDRB subbase and 150 mm of CCRB base
– 400 mm of CCRB base.
Basic observations
• The maximum dry density (MDD) of the CDRB and CCRB materials was slightly lower than the MDD of the conventional roadbase (CGRB)
– CDRB & CCRB: 1.95 t/m3
– CGRB: 2.21 t/m3
• The optimum moisture content (OMC) of the CDRB and CCRB materials was considerably higher than the OMC of the CGRB
– CDRB & CCRB: 11%
– CGRB: 6%
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Basic observations
• CDRB
– very easy to work and finish
– compacted easily with no spongy sections
– very resistant to raveling from traffic
• CCRB
– slightly harder to work and finish
– required little more effort to compact & some spongy sections
– very resistant to raveling from traffic
• CGRB
– very easy to work and finish
– compacted easily with some spongy sections
– not resistant to raveling from traffic
FWD Test results
Base Subbase Mean Curvature (mm)
150mm CGRB (Conventional roadbase)
250mm CDRB (Recycled comingled)
0.21
150mm CDRB (Recycled comingled)
250mm CDRB (Recycled comingled)
0.15
150mm CCRB (Recycled Concrete)
250mm CDRB (50mm Recycled comingled)
0.13
150mm CCRB (Recycled Concrete)
250mm CCRB (Recycled Concrete)
0.15
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EfromD3 analysis
Base Subbase Calculated Modulus (MPa)
Base Subbase
150mm CGRB (Conventional roadbase)
250mm CDRB (Recycled comingled)
641 722
150mm CDRB (Recycled comingled)
250mm CDRB (Recycled comingled)
1024 678
150mm CCRB (Recycled Concrete)
250mm CDRB (50mm Recycled comingled)
1275 505
150mm CCRB (Recycled Concrete)
250mm CCRB (Recycled Concrete)
1042 527
Welshpool Road findings
• Recycled base is stiffer than new granite roadbase
• Lower curvature values increase asphalt fatigue life
• Possibility of excessive stiffness in recycled materials
• Possibility of long term shrinkage cracking
• Recycled materials resist ravelling from traffic
• Recycled materials are easy to work
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Cost comparisons
Material Base price ($/t)
Transport Cost ($/t)
Insitu Cost ($/m3)
Actual Adjusted for
backload
Actual Adjusted for
backload
Limestone 6.60 5.50 5.50 22.38 22.38
Roadbase 10.80 3.14 3.14 30.80 30.80
Recycled Roadbase
8.80 2.36 1.18 21.76 20.58
Gilmore Ave Trials
• 1500m section south of Wellard Road
• 2 x 400m trial sections
– common 30mm DGA surface
– common 150mm Limestone subbase
– variable 125mm Base course – CGRB and CDRB?
• Constructed by Town of Kwinana in April 2003
• Technical assistance from MRWA.
• 20 year design traffic 4.5 x 106 ESA.
• Subgrade design CBR of 12%
Source: Adapted from Cheema (2004).
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Gilmore Ave – grading curves
AS 1152 sieve size (mm)
MRWA Spec 501 specified limits (% passing)
Average grading (% passing)
Min. Max. CDRB CGRB
26.5 100 100 100 100
19 95 100 97 100
9.5 60 80 70 94
4.75 40 60 49 85
2.36 30 45 38 63
1.18 20 35 29 45
0.6 13 27 22 31
0.425 11 23 17 23
0.3 8 20 12 20
0.15 5 14 6 17
0.075 5 11 4 13
Source: Adapted from Cheema (2004).
Gilmore Ave – CBR & MDD test results
• CBR test results
– CDRB: 5 tests ranging 165% to 200%
– CGRB: 4 tests ranging 130% to 170%
• MDD test results
– CDRB: 1.989t/m3 @ 11.4% OMC
– CGRB: 2.362t/m3 @ 5.8% OMC
Source: Adapted from Cheema (2004).
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Gilmore Ave – UCS test results
• Limited UCS testing was undertaken on CDRB
• Results were variable but typically <1.0MPa
• Conclusion reached that:
– 15% brick could be used in subbase
– 5% brick in basecourse material
– limited to <5 x 106 ESA
Source: Adapted from Cheema (2004).
Gilmore Ave – Benkelman Beam test results
Material
Mean Curvature values (mm)
May-03 Oct-03 Jun-04 Sep-04 Oct-10
CGRB 0.15 0.10 0.10 0.14 0.12
CDRB 0.07 0.07 0.03 0.05 0.09
Source: Adapted from Cheema (2004).
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Transport South Australia – Resilient modulus
Source: Andrews (1998).
Curtin testing – Unconfined compressive strength
Supplier UCS 1 day cure (kPa)
UCS 28 day cure (kPa)
Capital Demolition
668 1625
C&D Recycling 220 474
All Earth 541 1323
Day UCS (kPa)
1 625
7 979
28 1023
Additional testing – All Earth
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Curtin modulus results at 80% OMC
0
200
400
600
800
1000
1200
0 50 100 150 200 250 300
Re
sili
en
t M
od
ulu
s (M
Pa
)
Mean Normal Stress (MPa)
Resilient Modulus at 80% OMC
All Earth
Capital
C&D
Cemex
Boral
Curtin modulus results at 60% OMC
0
200
400
600
800
1000
1200
1400
0 50 100 150 200 250 300
Re
sili
en
t M
od
ulu
s (M
Pa
)
Mean Normal Stress (MPa)
Resilient Modulus at 60% OMC
All Earth
Capital
C&D
Cemex
Boral
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Curtin testing – Axial modulus with curing
y = 16.276x0.5826
R² = 0.9784
y = 19.586x0.5694
R² = 0.9751
y = 13.145x0.642
R² = 0.9625
200
400
600
800
1000
0 200 400 600 800 1000
Resilie
nt
Mo
du
lus M
r (M
Pa)
Bulk stress (kPa)
VARIATION OF MODULUS WITH TIMEAll Earth Material
dry back 1 day
dry back 7 days
dry back 28 days
Advantages of Recycled Pavement Materials
• Environmental
– reduced drain on new resources
– reduced habitat destruction
– energy savings in processing
– reduced landfill area
– reduced fuel usage by backloading
• Economic
– savings in material costs
– savings in fuel costs and vehicle costs
– reduced road wear
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Further definition for recycled materials
• Based on composition of source material
– CGRB – conventional new roadbase manufactured from virgin granite rock
– CCRB(S) – crushed concrete roadbase containing only concrete sourced mainly from structural grade concrete
– CCRB(N) – crushed concrete roadbase containing only concrete sourced mainly from non-structural grade concrete
– CDRB(x) – crushed demolition roadbase containing a mix of predominantly concrete with clay brick, tile and sand containing approximately x% concrete.
Possible applications
• Application of specific class roadbase
– CCRB(S) may be suitable under thick layers of asphalt, or as a subbase for heavy trafficked pavements.
– It may not be suitable for a heavy trafficked pavement with thin asphalt due to possible fatigue cracking.
– CCRB(S) can be blended with clay brick or tile to form CDRB(90), ie 90% concrete with 10% foreign material to limit potential cracking under thin asphalt.
• Research is proceeding
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Conclusion
• Recycled materials can be successfully used in road construction
• There are considerable environmental and economic benefits in using recycled materials
• Recycled materials can be used with confidence as a base in light traffic roads and sub-base in heavy traffic roads
• Recycled materials are likely to be suitable as a base in heavy trafficked roads.
Completed Recycled Concrete Base
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Completed Recycled Concrete Base
Completed Commingled Recycled Base
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Gilmore Ave – CGRB section
Gilmore Ave – CGRB section
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Gilmore Ave – CGRB section
Gilmore Ave – CDRB section
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Gilmore Ave – CDRB section
Gilmore Ave – Source material
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Warton Road – CCRB
Warton Road – CCRB
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Asbestos
• Asbestos raised as an issue
– Reasons:
• vested interests
• more vested interests
• any other vested interest
– But no sound basis
– Asbestos testing for Gt Eastern Hwy showed no asbestos
– There is background asbestos everywhere
– There are multiple asbestos ducts and pipes under many urban roads
– Process control minimises risk
Why does it crack (sometimes)
City of Gosnells City of Canning
Single coat primer seal 1.3l/m² 60%CRS Double coat primer seal 2.5l/m² 60%CRS
Base only around 175mm Base and subbase around 400mm
Dryback period? Dryback period generally weeks
Conventional construction methods Conventional construction methods
High stiffness High stiffness
Cracks occur No cracks have occurred
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