UNSW May 2011 lecture on AustStab template.ppt€¦ · •Able to remedy many types of pavement...
Transcript of UNSW May 2011 lecture on AustStab template.ppt€¦ · •Able to remedy many types of pavement...
The University of
New South WalesSchool of Civil and Environmental
Engineering Engineering
Pavement Engineering
******************************************
Insitu Stabilisation
Scott Young Stabilising Manager Downer
Greg White,
CEO AustStab
Aim
To introduce the fundamentals of stabilisation and show applications
2
stabilisation and show applications and advantages in pavement construction and rehabilitation.
Agenda
• Introduction• Types of stabilisation• Design outline• Binders used in stabilisation
3
• Binders used in stabilisation• Construction• Unsealed roads• Sustainability
Stabilisation is the introduction of
additional material to a pavement with
the purpose of improving the engineering the purpose of improving the engineering
characteristics.
The additional material can either be
aggregates or binders.
4
The process
5
The process
6
Failed Pavement
7
Types of Failure
8
Advantages of Stabilisation
•Re-use existing pavement materials, this reduces landfill and the
need to use diminishing quarry resources
•Strengthen existing pavements
•Improve the permeability of pavements, reducing the main
cause of pavement failure – water ingress
•Drastically reduce construction time and lane closures•Drastically reduce construction time and lane closures
•Reduce greenhouse gases and construction energy usage
•Reduce the cost of construction because of lower material
inputs, raw material transport and energy use
•Subgrade improvement in greenfields sites to long term strength
gains and wet weather construction access, and
•Improvement the wearing characteristics of unsealed pavement
9
Types of StabilisationCategory of
stabilisation
Indicative
laboratory
strength after
stabilisation
Common binders
adopted
Anticipated performance
attributes
Subgrade CBR>5%
(subgrades and
formations)
• Addition of lime
• Addition of
chemical binder
• Improved subgrade
stiffness
• Improved shear strength
• Reduced heave and
shrinkageshrinkage
Granular 40% < CBR <
+70%
(subbase and
basecourse)
• Blending other
granular materials
which are classified
as binders in this
context
• Improved pavement
stiffness
• Improved shear strength
• Improved resistance to
aggregate breakdown
10
Types of Stabilisation (continue)
Category of
stabilisation
Indicative
laboratory
strength after
stabilisation
Common binders
adopted
Anticipated performance
attributes
Modified 0.7 MPa < UCS<
1.0 MPa
• Addition of small
quantities of
cementitious binder
• Addition of lime
• Addition of
• Improved pavement
stiffness
• Improved shear strength
• Reduced moisture
sensitivity, i.e. loss of • Addition of
chemical bindersensitivity, i.e. loss of
strength due to increasing
moisture content
11
Category of
stabilisation
Indicative
laboratory
strength after
stabilisation
Common binders
adopted
Anticipated performance
attributes
Lightly Bound UCS 1.0 – 2.0 MPa • Addition of small
quantities of
cementitous binder
• Addition of lime
• Similar to Modified
Bound UCS > 2.0 MPa • Addition of greater • Increased pavement
Types of Stabilisation (continue)
Bound UCS > 2.0 MPa
(Basecourse)
• Addition of greater
quantities of
cementitious binder
• Addition of a
combination of
cementitious and
bituminous binders
• Increased pavement
stiffness to provide tensile
resistance
• Greatest stiffness and
hence load carrying capacity
12
Typical Pavements using Stabilisation
13
• Once the mix design (ie the percentage of what binder is to be added to the host material) has been determined, and the design strengths calculated (eg CBR, UCS
Pavement design
14
strengths calculated (eg CBR, UCS and/or Elastic Modulus), the pavement design commences.
• Common methods of pavement design include:
EmpiricalMechanisticFinite Element Modelling
15
Granular design chart
16
AustStab Design Guide for Cement Stabilised
Pavements for Lightly Trafficked Roads
17
Binders
Most stabilisation in Australia of pavement
materials uses the following binders
• Lime
• Cementitious• Cementitious
• Bitumen
• Dry Powdered Polymers
• Other granular material
18
Preliminary binder SelectionPrior to selection of a binder a pavement
material is tested for particle size distribution
and Atterberg limits.
19
Laboratory Testing
Reasons for laboratory testing
•Determine most appropriate binder
•Determine optimum binder content•Determine optimum binder content
•Provide the parameters required for
empirical or mechanistic pavement
design (Modulus, CBR, UCS,PSD)
20
Typical Testing
•Unconfined compressive strength (UCS)
•CBR
•Modulus
•Lime demand•Lime demand
•Particle size distribution
•Atterberg limits
21
Cementitious Stabilisation
Cementitious stabilisation is used to
• Strengthen existing pavements
•Improve low quality material to make
suitable for base and subbasesuitable for base and subbase
•Reduce need to increase base thickness to
achieve design strength
•Dry out wet pavements
22
Cementitious Stabilisation
Primary reaction is the binder reacts with water
in the soil to form cementitious material. This
reaction is independent of the type of soil.
Cementitious binder is made up of one or more
of the following constituents:
GP Cement Slag
GB Cement Lime
Fly Ash
23
Cement
Historically Portland Cement was used in stabilisation. Cement
is produced by mixing calcium carbonate, alumina, iron oxide
and silica and then calcining and sintering this mixture.
The product hydrates in the presence of water to form hydrated
silicates and aluminates and calcium hydroxide.silicates and aluminates and calcium hydroxide.
If there is clay present in the soil the Ca(OH)2 will react with it.
The hydrated cement via inter particle bonding produces a
strong and durable pavement.
GP cement is often blended with slag or flyash and is called
GB cement.
24
Problems with Cement
Cement gains strength quickly and has a
relatively high shrinkage
The resultant stabilised pavement is prone toThe resultant stabilised pavement is prone to
•Reduced working time in the field
•Higher shrinkage
•Block cracking
25
Cementitious Blends
In recent years the use of supplementary
binders has been the preferred option in
stabilisation.
Common Blends
•Slag/lime•Slag/lime
•Cement/flyash
•Slag/cement
•Cement/lime
•Triple blends
26
Supplementary materials
FlyAsh
By product of burning of coal in electricity generation
Recovered from flue gas.
Has high percentages of silica and alumina.
Granulated ground blast furnace slagGranulated ground blast furnace slag
By product of iron manufacture, these glass particles
react with water particularly in the presence of an
activator to form calcium-alumina-silica hydrate similar
to those produced in the hydration of cement.
Normally use an activator such as lime or cement.
27
Advantages of Cementitious Blends
•Increased working time
•Reduced shrinkage
•Minimal cracking•Minimal cracking
•Slower strength gain over time
•Cheaper cost
•Uses recycled products (slag/flyash)
28
Lime Stabilisation
Lime is produced by the calcining of
limestone.
Types of LimeTypes of LimeQuick lime CaO
Slaked lime Ca(OH)2
Agricultural lime Crushed limestone (<2mm)
29
Chemical reactions
�Burning: • CaCO3 + heat (>1000oC) -> CaO + CO2
�Hydrating: • CaO + H2O -> Ca(OH)2 + Heat
�Pozzolanic reaction:�Ca++ + OH - + Soluble Clay silica -> Calcium Silicate Hydrate (CSH)�CA++ + OH - + Soluble Clay Alumina -> Calcium Aluminate Hydrate (CAH)
30
Flocculation
Realignment of clay particles
31
Lime reacts with most clays
Clays have pozzolans that react with the
lime to form calcium silicates and
aluminates.aluminates.
For the reaction to be stable there must be
an alkaline environment (pH > 12.3)
32
Lime demand test
To determine minimum lime content the
lime demand test is used.
33
Strength gain using lime
34
Lime stabilisation of subgrades
In Australia there are many roads that are built
of poor subgrades often with CBR <3%
•Affected by water
•Can be expansive
•Poor compaction base•Poor compaction base
Result of lime stabilisation
•Dry out pavement
•Establish all weather working platform
•Reduces permeability
•Reduces pavement thickness35
Bituminous stabilisation
Bituminous stabilisation can be carried out
using bitumen emulsion or foamed bitumen
Current practice is to use foamed bitumen Current practice is to use foamed bitumen
due to
•Cost
•Temperature dependence
36
Behaviour of Bitumen Stabilised Material
37
Advantages of BSM
•Increase in strength of pavement (substitute
for asphalt)
•Improved durability and moisture sensitivity
•Lower quality aggregates can be utilised
•Environmental advantages•Environmental advantages
•Not sensitive to material variability
•Greatly reduced traffic delays
•Able to remedy many types of pavement
failures
•Reduces construction traffic
38
Foamed bitumen
39
Foamed bitumen coats fines
Often requires foaming agent
40
Expansion ratio vs half life
41
Lime as secondary binder
•Stiffens bitumen
•Anti-stripping agent
•Usually 1-2%
•Improves bond strength•Improves bond strength
•Reduces moisture sensitivity
•Assists dispersion of bitumen
42
Foamed Bitumen stabilisation –
particle size distribution
43
Granular stabilisationGranular stabilisation is the blending of one or more
materials with a pavement material to improve its
engineering properties.
Typical uses:
•Mixing of materials from various parts of a
source depositsource deposit
•Mixing imported material with insitu pavement
•Mixing in water
•On site mixing plant combining different off site
products
•Mixing recycled products with existing
pavement44
Design for granular stabilisation
The principle properties
affecting stability of base
and subbase are as for
quarry productsquarry products
•Internal friction –
particle size distribution
•Cohesion – from clay
fraction
45
Design targets for granular stabilisation
46
Example of blending two materials
47
Example of blending two materials
48
Dry Powdered Polymers (DPP)
DPP has been shown to “waterproof” the pavement material by finely coating the fine material.
49
Construction of Stabilised Pavements
Initial site preparation
•The full length of the pavement to be stabilised should be inspected and samples taken of different types of pavements.taken of different types of pavements.•Often the pavement will be premilled to break down existing seals and oversized material.•Remove thick bituminous or stabilised patches.•Search for and adjust services
51
Pre-milling
52
Spreading binders
• Use load calibrated mechanised spreaders
53
• Verify binder application
o Use trays or matso Load cell measurement
54
• For heavy applications two spreading passes are required to ensure uniform distribution and hence uniform strength gain.
If quicklime is used, slaking is required prior to mixing
55
Application of liquid binders
• Conventional water truck with spraybar• Preferably by direct pumping into the mixing chamber of the stabiliser
56
Adding water
Practise is to add water directly into the mixing chamber. Ensures proper mixing and accurate and even
57
mixing and accurate and even distribution of correct water content to facilitate compaction.
58
Two Pass Mixing
Two pass mixing is required to ensure the adequate mixing of binder. • First pass should be 75 – 90% of final depth.
59
Joints
Overlap at start of work by 1.5m.This is required due to size and shape of drum.
Transverse Joints
60
shape of drum.
Longitudinal Joints
• Overlap at least 100 mm• Joints should be clear of wheel path.
Compaction
•Commence as soon as possible after mixing•Completed within working time of
61
•Completed within working time of binder
First compaction
- Padfoot roller- Most effective for lower levels- Grader used to eliminate foot marks
62
Compaction (Continue)
Steel Drum
- Most effective for upper levels
63
Multi tyred roller
- Used as final run to knead the surface and close pores
Check Density
• Accelerometer attached to vibrating roller• Trial section to ascertain passes
64
• Trial section to ascertain passes required• Proof rolling• Devices such as clegg hammer• Nuclear densometer • Sand replacement
Levelling and Trimming
Trimming by grader will give correct levels and grades.
65
levels and grades.
Trimmed material should not be used to fill in low spots of compacted material, this will cause delamination.
Curing
Curing of any stabilised layer
•Light and frequent water spray•Bituminous surfacing
66
•Bituminous surfacing•Constructing next layer
Unsealed RoadsBinders - Cement blends
- Lime
- Polymers
Depth 150 mm
Results
67
Results
•Reduces maintenance by over 100%
•Reduces dust (loose material down by over
300%)
•Reduces effect of water
•Environmentally friendly
68
Before After
Sustainability Principles
•Source materials close to construction site•Avoid significant natural vegetation removal•Use gravel pits that do not affect native landscape•Reduce foot print of material source
69
•Reduce foot print of material source•Avoid encroachment on water table•Avoid possible erosion•Reduce use of water•Reuse materials as much as possible
Advantages of Stabilisation
•Direct cost benefits•Social benefits•Environmental
70
Direct cost benefits
Stabilisation is often the only practical means of rehabilitating an existing failed pavement.Fortunately the cost of stabilising is at least 30% often over 50% cheaper than the alternative - remove and replace with new
71
alternative - remove and replace with new material.Although whole of life costs should be used, it has been found that the life, maintenance costs and rehabilitation costs are similar for conventional pavements.
Social benefits
• Insitu stabilisation is much faster process with minimal excavation and little material brought in or taken away from site.•Less chance of rain disruption causing extended delays
72
extended delays•Lanes reopened on same day.
In higher trafficked countries road agencies often charge for downtime of road lanes. This is a real cost to the community.
Environmental Benefits
Existing failed pavements retain a very useful proportion of their asset value
73
Addition of approximately 5% of binder restores and often exceeds the pavement’s original engineering properties.
Primary Environmental Benefits
•Reduced energy in excavation and trucking to/from site•Not using ever rarer land fill sites with materials that have value
74
materials that have value•Reduces drastically need for increasingly rare quarry resources•Reduced gas emissions from these operations•Use of recycled products in binders
Total Costs
75
Summary
�Stabilisation can be used in one form or another in nearly every pavement construction or rehabilitation situation, giving:� Time and lack of disruption benefits� Benefits to the environment
77
� Benefits to the environment� Cost benefits
In addition to the environmental and time benefits, rehabilitation using stabilisation is usually the most economical alternative.