In Situ Stabilization of Pavement Base Courses

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In Situ Stabilization of Pavement Base Courses
Roads Pavement Forum Thursday, May 17, 2001
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Introduction

• Clients
• Gautrans
• CCI
• SANRAL
• Laboratory and Heavy Vehicle Simulator results
  from R243/1
• One building block in a long-term process
• Focus on mechanical properties and structural
  bearing capacity

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Layout of presentation

• Purpose of the study
• Materials
• Experimental plan
• Results for each laboratory test
• Conclusions

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Purpose

• Assess the benefits of in situ stabilization in
  terms of improvements in the mechanical
  properties and structural bearing capacity of the
  treated material
• Mechanical properties
• Resilient modulus
• Compressive and tensile strength
• Flexibility
• Shear strength
• Bearing capacity
• Effective fatigue
• Permanent deformation

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Materials

• Basic material
• Ferricrete milled from HVS test site, including
  existing surfacing and upper portion of subbase
• Treatment processes
• Cement (Laboratory)
• 2 cement
• Foam and cement (Laboratory and HVS)
• 2 cement, 1.8 residual binder
• Emulsion and cement (Laboratory and HVS)
• 2 cement, 1.8 residual binder

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Materials Untreated

• Nominal maximum aggregate size 37.5 mm

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Materials Untreated

• Classification
• Grading G4
• Atterberg limits G5
• CBR G7

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UCS, ITS, Flexural Beam Test

• Treated materials only
• Foam and emulsion tested at 2 binder contents
• 1.8 residual binder content 2 cement
• 3.0 residual binder content 2 cement

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Flexural beam test

• Strain at crack initiation
• Indication of flexibility

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Triaxial Tests

• Untreated and treated materials
• 1.8 residual binder content, 2 cement
• Variables
• Density
• Saturation
• Confining pressure
• Stress ratio

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Triaxial tests

• Static triaxial tests
• Shear strength parameters
• Dynamic triaxial tests
• Resilient modulus
• Permanent deformation response

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Compressive strength UCS Results

• Cement-treated ferricrete has highest UCS
• Addition of binder reduces the UCS

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Tensile strength ITS Results

• Cement-treated ferricrete has highest ITS
• Addition of binder reduces the ITS

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Tensile strength ITS Results

• Samples dried to equilibrium MC at ambient temp
• 72 h in oven at 40º C

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Flexibility Flexural beam test

• Flexibility only increases at higher binder
  content

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Elastic stiffness (Mr) Dynamic triaxial tests

• Estimation of stiffness values
• Use regression model for untreated ferricrete
• Use ranges for treated materials

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Comparative results Average strain-at-break
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Comparative results Effective fatigue life

• SAMDM transfer functions
• Working strain of 125 ??
• ?bvalues from flexural beam test

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Comparative results Cohesion
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Comparative results Friction angle
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Comparative results Shear strength at ?3 50 kPa
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Comparative results Bearing capacity (9 PD)
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HVS tests Pavement structure

• 30 mm Asphalt
• 250 mm FTG / ETG
• - 1,8 residual
• bitumen
• - 2 cement
• In situ material
• In situ subgrade

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HVS tests Materials
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HVS tests Programme

• 2 x 100 m long experimental sections
• Foam-treated
• Emulsion-treated
• 1st Phase of HVS testing
• 80/100 kN tests (350 000/150 000 repetitions)
• Completed
• 2nd Phase of HVS testing
• 40 kN tests (750 00000 repetitions)
• In process

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HVS tests Deflection result
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Conclusions UCS, ITS and Flexibility

• Complex relationship between UCS, ITS and
• Percentage binder
• Cementation
• Curing procedure
• Flexibility
• No increase in flexibility at low binder content
• Increase in flexibility and effective fatigue
  life at higher binder content
• Strain-at-break slightly higher for
  foam-treatment at higher binder content
• Effective fatigue life models to be validated
  with HVS results

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Conclusions Resilient modulus

• Increase in resilient modulus with treatment
• Untreated ferricrete
• Resilient modulus influenced by
• Relative density and saturation
• Stress state
• Treated ferricrete
• Resilient modulus dictated by the stabilizing
  agent and largely insensitive to the above
  parameters
• No significant difference between stabilizing
  agents
• Resilient modulus values to be validated by HVS
  back-calculation results

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Conclusions Shear strength and plastic strain

• Shear strength increases with treatment
• Vastly improved bearing capacity in terms of
  permanent deformation
• Cement-treatment shows highest benefit
• No significant difference between foam- and
  emulsion-treatment
• Models need to be calibrated with HVS results

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Conclusions General

• Only considered mechanical properties
• Other properties to investigate
• Permeability and erodibility
• Workability
• Shrinkage cracking
• Time to opening the road early strength
• Improved understanding of mechanical properties
  and behaviour
• Properties of stabilized material significantly
  different from untreated material even at low
  binder content
• First structural design models for these types of
  materials