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Lime Stabilisation of Subgrades & Marginal Materials – South Western QLD
Characteristics, Properties, Design and Construction
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So Why LIME?
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1st is Expansive Clay Soils in QLD (in grey)
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Cracking & Rutting on the Warrego Hwy
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2nd is that Lime Reacts with Clay
• Lime is an effective additive for plastic soils improving both workability and strength
• Not effective in cohesionless soils or materials without the addition of pozzolanic additives.
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Benefits of Lime Stabilisation
• Modification of material.
• Reduced plasticity.
• Improved workability.
• Strength gain.
• Improved effective grading.
• Reduced sensitivity to moisture changes (shrinkage).
• Modification of compaction properties.
• Reduced permeability with sufficient lime.
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Uses for Lime Stabilisation in South Western Regions
• Improve subgrade materials into subbasematerials.
• Reduce overlying pavement depths.
• Improves Marginal Gravel Materials that have high plasticity (Lime blends)
• Provides moisture resistance, and Cracking (shrink/Swell).
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Lime Terminology
• Hydrated Lime
• Quicklime
• Limestone (Rock) CaCO3• No structural gain, used for acid sulphate soils etc
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Hydrated Lime vs Quicklime
Hydrated Lime Quicklime
Composition Ca(OH)2Calcium Hydroxide
CaOCalcium Oxide
Form Fine powder Granular
Equiv. CaO 1.32 1.00
Bulk density
(t/m3)0.45 to 0.56 0.9 to 1.3
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Construction ConsiderationsHydrated Lime and Quicklime
• Hydrated Lime• Susceptible to dusting
• Used in laboratory testing (specified in design)
• Spread and mix only
• Quicklime• Cheaper per quantity of active lime (direct cost
and transport)
• Involves the slaking process for strength gain
• Requires additional water for slaking
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Slaking of Quicklime - Considerations
• For heavy application rates, utilise multiple spreading passes
• Ensure adequate addition of water to ‘hydrate lime’
• Ensure uniform mixing of binder application
• Understand the potential consequences of non hydrated quicklime within the pavement!
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Lime Reactions
Two-Stage Reaction Process
• First Stage - Modification
• Second Stage - Strength Gain
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Lime Reactions
First Stage - Modification
• Promotes flocculation of the clay particles, immediately improving grading and handling properties.
• Base exchange - calcium ions displace sodium and hydrogen cations.
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Lime Reactions
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Lime Reactions
Second Stage - Strength Gain
• Dissolution of the clay, particularly at the edges of clay plates.
• Formation of calcium silicate and calcium aluminate hydrates.
• These cementitious products are similar in composition to cement paste.
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Lime Reactions - Considerations
• Occurs with higher lime addition rates
• Highly alkaline environment (pH > 12.4)
• Greater effect on montmorillonite clays than kaolinite clays
• Effect depends upon clay minerals/ pozzolanic material present
Therefore important to carry out adequate investigation and mix design!
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Investigation and Design
• Subgrade investigation
• Host material investigation
• Lime demand test
• Undertake mix design•CBR Method
•UCS Method
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Design – Lime Demand Test
Determine the binder application rate at which the pH reaches the ideal alkaline
environment of pH 12.4 for the host material
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Design – Effect on Basecourse Depth
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Construction Process- Mill and Sidecast
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Construction – Spreading Lime
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Construction - Mixing
First Mixing Pass
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Construction - Mixing
Second Mixing Pass
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Construction Process- Trim and Compact
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Construction Process- Reinstate Basecourse
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Core samples QDMR job Dalby
13 months after lime stabilising, black soil subgrade
(UCS 2.5 to 3.5MPa)
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LIME BLENDS
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Benefits of Lime Blends
• Can be Taylor made to suit most host Materials.
• Of use where there are Materials with a Plastic content eg Ridge Gravels
• Strength improvement in Marginal Gravels.
• Can be combined with Slag, Cement, or Fly Ash.
• Ideal when using top up gravel with existing pavement or subgrade incorporation.
• The other benefits of Stabilisation are efficient Mixing and Incorporation of Moisture!
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Balonne Hwy – Slag Lime Blend (85% Slag /15% Lime) @2%
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Moisture Conditioning
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Summary
Fixing the subgrade using lime stabilisation is easier than a lot of people think.
When done properly, the strength gain from lime stabilisation is permanent and on going, as with cement.
The benefits of: direct cost savings
speed and lack of disruption
environmental advantages
are SIGNIFICANT.
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Further Info & Technical References
• Auststab – Technical Work Tips, Stabilisation Guide
• QTMR – MRTS 07A & B
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Any Questions?