Road Construction with an Environmental Approach
Transcript of Road Construction with an Environmental Approach
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Road Construction with an Environmental Approach
Dr Bryan Pidwerbesky CPEng FIPENZ M.IPWEA General Manager – Technical
Fulton Hogan
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Outline of Presentation
• Fundamentals of pavement design & construction for local roads
• What’s important for good quality construction • Stabilisation • Sustainability in pavements:
– reduce total consumption of energy & virgin materials during construction & maintenance eg asphalt production (low energy/low emissions mix), sealing (emulsions), aggregates (recycling); recyclable materials – asphalt, glass, RCC, etc
– Change attitudes re performance of recycled materials • Vision for future pavements
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Pavement
Subgrade
Load, W
P0
P0
P1
P1
Fundamentals of pavement design & construction for local roads
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Pavement
Subgrade
Compression Tension
Load, WFundamentals of pavement design & construction for local roads
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Pavement Types
• Rigid pavements – Unreinforced concrete slabs – Reinforced concrete slabs – Continuously reinforced concrete slabs
• Flexible pavements
– Chip seal over granular and/or modified aggregates – Asphaltic concrete
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Flexible Pavement Types Description
Chip seal over unbound granular
Chip seal over unbound granular on cemented
Chip seal over cemented material
Chip seal over bitumen treated base over unbound
Full depth asphalt
Asphalt on unbound granular
Asphalt on unbound granular on cemented
Asphalt on cemented material
Asphalt on modified material
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Equivalent Standard Axle (esa)
Tyre & Axle Configuration
Single tyre - single axle Dual tyre - single axle
Dual tyre - tandem axle Dual tyre - tri-axle
• Number of standard axles
to cause same damage =
Reference Axle Load (kN)
53 80
135 181
Actual axle load 4 Reference axle load
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Simplified pavement design process for local roads
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Design Traffic Loading Calculations
Traffic Data Year of analysis
Current volume, AADT (vpd) 1,000 Annual Average Daily Traffic
Year of treatment
Current volume, AADT (vpd) 1,000 Annual Average Daily Traffic
Direction Factor, DF 0.5 Proportion of 2 way AADT travelling in design lane = 0.5 for a two-lane, two-way road with 50/50 directional split
%HV: 10.0% Heavy Commercial Vehicle content
HVAG / HCV 2.4 Average number of axle groups per heavy commercial vehicle (HCV). Presumptive value for NZ State Highways = 2.4 (2007 NZ suppl. 7.2.1)
ESA / HVAG 0.60 Average number of ESA per Heavy Axle Group Presumptive value for NZ State Highways = 0.6
Load Factor, ESA / HCV 1.44 Average ESA per Heavy Commercial Vehicle LDF 1.0 Lane Distribution factor - where there is unequal traffic distributed between
the lanes of multilane roads
Design Life (years), y 25 Years
Traffic Growth Rate, i 2.00%
Cumulative Growth Factor (CGF):
CGF (Geometric) 32.030 Geometric Cumulative Growth Factor = (((1+i)^y)-1)/I
CGF (Arithmetic) 31.000 Arithmetic Cumulative Growth Factor = y + ((y/2) * (y-1) * i) CGF (Average) 31.515
Design Traffic: Design Traffic, NDT NDT = 365 x AADT x CGF x DF x %HCV x LDF x NHVAG (APDG - Equation 7.1)
NDT 1.4E+06 HVAG
Design Equivalent Standard Axle, DESA = NDT x ESA / HVAG (APDG - Equation 7.4)
DESA 8.4E+05 ESA (use in Fig. 8.4)
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10
AUSTROADS Guide Figure 8.4
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Design Traffic (ESA)
103 104 105
Thic
knes
s of
Gra
nula
r Mat
eria
l (m
m)
0
100
200
300
400
500
Design chart for granular pavements with thin bituminous surfacing for lightly trafficked roads
Minimum Basecourse Aggregate Thickness Subgrade Strength (CBR
)
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Whole of Life Cycle Costing (WLCC)
Road authority costs: • Initial capital construction &
rehabilitation • Expected maintenance &
re-seal activities • Residual value of the
pavement
Road user costs: • Traffic delay during construction,
maintenance, re-sealing and rehabilitation
• Normal travel time • User operational costs (vehicle
operating costs, accidents & comfort) Intangibles & Externalities:
• air pollution • noise
• vibration • environmental impacts
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What’s important for good quality construction
• Subgrade bearing capacity – In field, measure with deflection, proof roll or Scala DCP
• Pavement materials – Good quality aggregates or mixes – Shear resistance & moisture susceptibility
• Compaction – Measure with nuclear densometer or deflection or proof roll – Check EVERY layer (subgrade, subbase, base)
• All seals & thin bituminous mixes are permeable – Reduce water ingress to pavement – Primers & surfacing selection/design
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Compaction – as per TNZ B/02 – plateau density testing & lab MDD
Degree of compaction
Sub-Basecourse Pavement Layer
Basecourse Pavement Layer
Mean Value ≥ 95 % ≥ 98 %
Minimum Value ≥ 92 % ≥ 95 %
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Plateau density - compaction
80
85
90
95
100
105
Pass 1 Pass 2 Pass 3 Pass 4 Pass 5 Pass 6
Density (% of Target)
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Deflection testing: uphill vs downhill
Benkelman Beam – uphill → higher deflections due to load transfer to rear axle on beam truck
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Moisture in the Pavement
A small amount is okay, and is beneficial Too much - disastrous!
Everything in Moderation!
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Pavement stresses Radius of contact
about 100 mm Pressure > 100 psi
Subgrade
Radius of stress about 500 mm
Pressure ≈ 4 psi
Radius of stress about 300 mm
Pressure ≈ 10 psi Granular layer(s)
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Pavement saturation
Numerous contact points each, under high stress in a well
compacted granular material
Aggregate particles
In a saturated system the applied load is transmitted equally in all directions, forcing the aggregate particles apart
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Primer
• specially formulated bitumen emulsion primer • is placed without chip • Should not be trafficked & a more substantial surfacing treatment
should be scheduled after the prime has dried. • Binds & penetrates surface of an unbound granular layer (typically 5
to10 mm) • Provides a bond onto which a subsequent bituminous surfacing can
adhere • Assists in waterproofing & protecting pavement
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First Coats • On new or rehabilitated pavements • Construction of a surface to which a first coat will
adhere must be a well-bound, relatively dry, smooth hard surface, with clean stones showing & no dust
• Benefits of priming unbound granular pavements
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Stabilisation
• when should one go for stabilisation? • Pros and Cons of cement Stabilisation and Lime
stabilisation? • Testing regime for Subgrade? Sub Base? • Improving a current CBR to a target CBR through
Roller passes, stabilisation, Foam bitumen etc?
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Base Course Stabilisation or
Pavement Recycling
• Improves long term durability &
shear strength of aggregates • Reduces moisture susceptibility
Modification and Stabilisation
Soil Modification and / or
Soil Stabilisation
• Unable to compact or unstable soil usually due to plasticity
• Insufficient bearing capacity
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Simplified representation of ion exchange during modification
Na+
Na+ Na+ Na+
Na+
Na+
Na+Na+
Na+
Na+
Na+
Na+
Na+Na+Na+
Na+
Na+Na+
Na+
Na+
Na+
Na+
Na+Na+ Na+Na+
Na+
Na+ Na+
Na+
Na+
Na+
Na+
Na+Na+
Na+Na+
Na+
Each Sodium ion can contain up to
79 water molecules
Clay
Ca++
Ca++
Ca++Ca++
Ca++
Ca++
Ca++
Ca++
Ca++
Ca++ Ca++
Ca++Ca++
Ca++
Ca++
Ca++Ca++
Ca++
Lime
+ NaCa++
Ca++
Ca++ Ca++
Ca++
Ca++Ca++
Ca++
Ca++
Ca++
Ca++
Ca++
Ca++
Ca++
Ca++
Ca++
Ca++
Ca++
Ca++
Ca++
NaNa
NaNa
Na
Na
Na
NaNa
Na
Na Na
Na
Na
Na
Na
Na
Na
Na
Na+
Na+Na+Na+
Na+Na+
Na+ Na+
Na+Na+Na+
Na+
Na+
Na+
Na+
Na+
Na+Na+
Na+
Ion Exchange
Ca++
Ca++
Ca++ Ca++
Ca++
Ca++
Ca++
Ca++
Ca++Ca++
Ca++
Ca++
Ca++
Ca++Ca++
Ca++
Ca++
Ca++Ca++
Ca++
Ca++
Ca++
Ca++Ca++
Ca++
Ca++
Ca++
Each Calcium ion can only contain up to 2 water molecules
Modified Clay
Soil Modification
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Lime
Quicklime Limestone + Heat → Quicklime + Carbon Dioxide CaCO3 + Heat → CaO + CO2 ↑ (gas)
Hydrated lime or slaked lime Quicklime + Water → Hydrated Lime + Heat CaO + H2O → Ca(OH)2 + Heat
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Soil modification
0 2 4 6
Com
pres
sive
Stre
ngth
(N/m
m²)
Cementitious binder added % by weight
Soil stabilisation
ICC - Initial consumption content
Certain amount of lime is required for modification Beyond the ICC - free lime for cementation
Soil Modification and Stabilisation
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foamed bitumen water
water cement foamed bitumen
Binding agents for basecourse stabilisation
cement water
Pulverise
lime
+
Add and Mix Stabilising Agent:
=
Compact and
Finishing
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Cement-only Stabilisation Process
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Supply trucks for water and cement are pushed by WR 2500 SK
Water tanker
Cement tanker
WR 2500 SK Recycler
Push bar Push bar
Water hose
Cement hose
Spreading of binders
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Foamed Bitumen and Cement / Lime can be added to the material in one pass
Addition of Foamed Bitumen and Cement
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Increased surface area makes it possible to mix hot bitumen with cold and damp aggregates
2 – 3 % water is mixed with 180 °C hot bitumen: bitumen expands 15 to 20 times its original volume
Foamed Bitumen
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Specifications for Modified & Bound Layers Produced In-Situ & In-Plant
Layer Binders In-Situ In-Plant
Modified Basecourse & Sub-base
Cement Lime
Foamed B. B. Emulsion
NZTA B/5 NZTA B/7
Bound Sub-Base
Cement Cement / Lime
NZTA B/6 NZTA B/8
Subgrade Lime
Cement NZTA B/9 N/A
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Sustainability in pavements
• Reduce total consumption of energy & virgin materials during construction & maintenance – asphalt production (low energy/low emissions mix) – sealing (emulsions) – aggregates (recycling) – recyclable materials – asphalt, glass, RCC, etc
• Main barrier: Attitudes re performance of recycled /
sustainable materials
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CoolPave with L.E.A (low emissions asphalt) • Biggest temperature reduction
– Produced between 95°C to 115°C – Before,165°C for HMA and 130°C for other warm mixes
• Lowest fuel usage • Biggest reduction in greenhouse gases
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• Compacts as easily as hotmix, similar roller patterns can be used
• Retains its workability for longer – More time for compaction – Good for long duration hand work, mix will retain workability
• Can be placed in colder temperatures • Can be carted further since temperature does not
reduce as quickly as hotmix • Improvement in longitudinal joints
Coolpave
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Opportunities for Recycling Materials
• Reclaimed asphalt pavement (RAP) • Recycled crushed concrete (RCC) • Crushed Glass • Melter slag • KOBM (Klockner Oxygen Blown Maxhutte)
– by-product of steel production • Fly ash • Crushed brick • Bitumen additives, extenders & replacements
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Materials Processing
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Asphalt: 98% RAP, 2% new binder, NO new aggregate
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Project Summary
• Excellent Technical Properties
• Savings obtained when whole of life costs are considered
• Encouraged sustainability of natural resources
• No environmental risks • Performed well for 7 years
until earthquakes!
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Christchurch Southern Motorway Sustainability
ZONE A ZONE B ZONE C
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Prince of Wales & Duchess of Cornwall on CSM Nov 2012 RCC Stockpile
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Materials & Design • Maximised use of RCC
– Trials to confirm optimum maximum size for stabilising – Tests confirmed optimum cement content to add for cemented
subbase • Maximised use of recycled asphalt (RAP)
– RAP sorting & storage methodology – 30% RAP in asphalt mix
• Maximised sustainable use of virgin aggregates – Maximised use of existing aggregate in Halswell Junction Rd – Broken faces as per B/5 spec in Zone B
• Trials of aggregate from 3 different quarries - Zone B – PSD vs moisture susceptibility
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Halswell Junction Road – Zone A
• Existing pavement well compacted & low deflections but low % broken faces
• Removed upper 100 mm • Placed 100 mm AP40 • Stabilised 150 mm deep
with 1.5% cement • Applied seal & SMA
Thickness (mm) Material40 SMA
First Coat Chip
Existing HJR Pavement
M/4 makeup metalNominal 100mm
HJR SH1 - SpringsChainage 0 - 2400
2.10E+07
Shands Road intersection – Bitumen Treated Basecourse
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Structural Asphalt – Zone C
Typical Design
40 OGPA 125 SAC
200 RCC+3.5% Cem
Membrane Seal
Curletts - Collins Chainage 7700 - 10300
4.00E+07
Subgrade CBR = 10%
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Recycling Crushed Glass
• Crushed glass is a viable replacement of virgin aggregate in basecourse
• Performance of pavements constructed at current specification levels (5%) identical to pavements with 100% virgin aggregate
• Extends life of both landfills and quarries • Incorporated into NZTA basecourse aggregate
specification
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Crushing Process
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Bitumen Additives, Extenders & Replacements
• Bitumen was a heavy residue “by-product” of petroleum refining
• Now, heavy residue can be cost-effectively refined to produce fuels & products with higher margins so no one wants to refine bitumen
• Australian refineries closing; those that continue, won’t produce bitumen
• NZRC Marsden Point – New Route bitumen • AUSTROADS project investigating common Aust/NZ
bitumen performance graded spec
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Recycling & Alternative Bitumen sources
• Crumb tyre rubber • Toner (from photocopiers) • Plastic milk bottles • Bio-binders
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4% SBS 3% HDPE Blend
Recycling Plastic Milk Bottles
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Bio-binders
• Superheat biomass (corn stalks, wood waste, etc) without oxygen
• Creates bio-binder, can be used with bitumen
• Trial of binder containing 5% bio-binder
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Noise reduction
Double layer porous asphalt Top: 25mm thick, 8mm max. aggregate, >20% air voids Bottom: 45mm thick, 16mm max. aggregate, 25% air voids, mod. binder
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Truck noise measurements
Surface Noise Levels from Trucks (dBA)
2005 2006 2007 2008
OGPA 88.8 89.9 91.8 90.4
∆ 2005 +1.1 +3.0 +1.8
WhispA™ 86.2 86.8 88.0 86.8
∆ 2005 +0.6 +1.8 +0.6
WhispA™ - OGPA -2.6 -3.1 -3.8 -3.6
Data from NZ Transport Agency & Opus Research
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Porous Pavements – Stormwater retention
Rai
n
Natural subgrade
Porous granular material
Porous surfacing Water passes through surfacing
Water temporarily retained
Water infiltrates into subgrade
Optional geotextile, woven filter fabric or sand blanket
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Porous Pavements
Auxiliary drain
Porous surface course Porous base Gap-graded granular sub-base (reservoir layer) Geofabric Subgrade
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Pavements as solar heat collectors Back
radiation Convection
Solar radiation
Atmospheric long wave radiation
Conduction
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Flexible pavements generate electricity
• Variety of systems: – rubber discs or
judder bars that compress, & kinetic energy converted to electricity
– Piezoelectric generators embedded in pavement