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Highways and Engineering Conference - 2006
Soil-Cement Pavement Products from soil to
subgrade and more
Gregory E. Halsted, P.E. Pavements
Engineer Portland Cement Association
March 1, 2006 Billings, Montana
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• Applications
• Design
• Construction
• Testing
• Performance

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Cement-Based Pavement Materials
Roller-Compacted Concrete
Conventional Concrete
Soil-Cement
No Wearing Course
Cement Content
Cement- Treated Base
Wearing Course
Flowable Fill
Full-Depth Reclamation
Cast
Cement-Modified Soil
Rolled
Water Content
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Soil-Cement Materials in a Pavement Section
SURFACE COURSE

• BASE / SUBBASE COURSE
• Cement-Treated Base
• Full-Depth Reclamation

• TREATED SUBGRADE
• Cement-Modified Soil

UNTREATED SUBGRADE
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Cement-Modified Soil
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Reasons to Modify

• Improve the properties of the subgrade soil
• Reduce volume change caused by moisture
• Improve wet strength
• Improve compactibility
• Expedite construction by improving subgrade
  support in wet weather
• Eliminate muddy construction sites
• Create an all-weather work platform

It is important to remember that soil
modification is different than soil stabilization
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Solutions forPoor Subgrade Soils

• Excavate/replace with select fill
• Aggregate
• Soil
• Increase the base/pavement thickness
• Contain using
• fabrics or other geotextiles
• Modify soils with
• a calcium-based additive such as portland cement

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Benefits of Cement-Modified Soil

• Small addition of cement to soils to change
  properties
• Eliminates need for removal/replacement of
  inferior soils
• Low cost soil improvement
• Improves pavement support
• Forms weather-resistant work platform
• Provides permanent non-leaching modification

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By treating the soil with cement, the detrimental
properties of clay can be improved through the
following three processes

• Particle
• Restructuring
• Cement
• Hydration
• Pozzolanic
• Reaction

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Particle Restructuring
Unmodified clay particles
Clay particles after flocculation / agglomeration
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Cement Hydration
Cement Water Calcium Silicate Hydrate
(Cementitious Gel)
- plus
Calcium
Hydroxide
(Hydrated Lime)
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Pozzolanic Reaction
Hydrated Lime Silica Calcium Silicate Hydrate
Hydrated Lime Alumina Calcium Aluminate
Hydrate
Supplied by Cement Hydration
Clay Minerals
Cementitious Gel
Note Without silica or alumina-based clay
minerals, this process does not occur (e.g. sandy
or silty soils).
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Time of Modification Processes
Immediate to a few hours

• 1. Particle Restructuring
• 2. Cement Hydration
• 3. Pozzolanic Reaction

Largest strength gain between 1 day and 1 month
Slowly, over months and years
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Plasticity Index (PI)

• The range of moisture through which a soil
  deforms under loading
• The measure of a soils affinity to retain
  moisture
• Plasticity Index is the difference between the
  Liquid Limit and the Plastic Limit of a soil
• PI LL - PL

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Subgrades before and after CMS
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Primary Testing Requirements
A common gradation requirement is for 100 to
pass the 1.5-inch (38 mm) sieve and a minimum of
60 to pass the No. 4 (4.75 mm) sieve (ASTM C136).
A common density requirement is to be between 95
and 98 of the established laboratory standard
Proctor density (ASTM D558).
A common moisture requirement is to be within 2
of the laboratory established optimum moisture
content (ASTM D558).
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Secondary Testing Requirements
Thickness
Stability
Stiffness
Requirements for subgrade depths can vary from as
little as 6 inches (150 mm) up to 2 feet (0.6 m)
depending on governing agency.
Measures in-place engineering values using
structural layer stiffness, klbf/in (MN/m) and
Youngs Modulus of a material, kpsi (MPa).
Modified subgrade MUST be stable before next
pavement course is constructed! Proof-rolling is
the most commonly accepted practice.
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But what about strength?
The objective of CMS is to amend undesirable
properties of problem soils or substandard
materials so that they are suitable for use in
construction. The amount of cement added to the
soil is less than that required to produce a
hardened mass but is enough to improve the
engineering properties of the soil.
It is important to remember that soil
modification is different than soil stabilization
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CMS can be used as a base course for flexible
pavements or as a subbase for concrete pavements
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The final impact of CMS
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Cement-Treated Base
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Mixed-in-Place
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Plant Mixed
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What is Cement-Treated Base?

• Extremely dense
• Intimately blended
• Highly compacted
• Mixture of
• Aggregates or soil or combinations
• Portland cement
• Water
• Base or subbase for either concrete or bituminous
  surfacing

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Engineering Benefits

• Increased Rigidity
• Spreads Loads
• Eliminates Rutting
• Below Surface
• Reduced Moisture
• Susceptibility
• Reduced Fatigue
• Cracking
• Thinner Pavement
• Section

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Mix Design ProportioningMixed-in-Place

• Representative sample of material
• Pulverize to anticipated gradation
• 100 passing 25 mm (1)
• 80 passing 4.75 mm (4)
• Add estimated cement content
• Usually 4 to 10, by dry weight
• Run moisture/density curve
• Standard Proctor (ASTM D558)

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Mix Design ProportioningPlant Mixed

• Representative sample of material
• Gradation requirement
• 100 passing 50 mm (2)
• 55 to 90 passing 4.75 mm (4)
• 37 to 67 passing 2 mm (10)
• 0 to 30 passing 75 µm (200)
• Add estimated cement content
• Usually 3 to 6, by dry weight of materials
• Run moisture/density curve
• Standard Proctor (ASTM D558)

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Test for Strength

• Unconfined Compressive Strength Test
• Used by most State DOTs and FAA
• Simple
• Quick
• 7-day requirements range
• from 300 to 800 psi
• (2.1 MPa to 5.5 MPa)
• Strengths vary according
• to project requirements

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Inside a Rotary Mixer
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Pug Mill Layout
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Inside a Pug Mill
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Testing
Moisture
Gradation
Density
Thickness
Stability
Stiffness
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CTB creates an excellent base for either a rigid
or flexible pavement structure
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Full-Depth Reclamation
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Definition of Reclamation

• Method of flexible pavement reconstruction that
  utilizes the existing asphalt, base, and subgrade
  material to produce a new stabilized base course
  for an asphalt, chip seal, or concrete wearing
  surface.
• Alternative Terms
• Full-Depth Recycling (FDR)
• Cement Recycled Asphalt and Base (CRAB)
• Cement-Treated Base (CTB)
• Cement-Treated Existing Roadway Materials
  (C-TERM)
• Cement Stabilized Reclaimed Base (CSRB)

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Advantages of Reclamation

• Use of in-place materials
• Little or no material hauled off and dumped
• Maintains or improves existing grade
• Conserves virgin material
• Saves cost by using
• in-place investment
• Saves energy by reducing mining and hauls
• Environmentally friendly

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Engineering Benefits

• Increased Rigidity
• Spreads Loads
• Eliminates Rutting
• Below Surface
• Reduced Moisture
• Susceptibility
• Reduced Fatigue
• Cracking
• Thinner Pavement
• Section
• Retards Reflective
• Cracking!

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Retards Reflective Cracking
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Mix Design Proportioning

• Obtain representative samples of roadway material
• Typically up to 50 Reclaimed Asphalt Pavement
  (RAP)
• Meeting the gradation requirement is the key
• Pulverize to anticipated gradation
• 100 passing 75 mm (3)
• 95 passing 50 mm (2)
• 55 passing 4.75 mm (4)
• Estimate cement content
• Usually 4 to 6
• By weight of dry material
• Run moisture/density curve
• Standard Proctor
• (ASTM D558)

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Test for Strength

• Unconfined Compressive Strength Test
• Used by most State DOTs
• Simple
• Quick
• 7-day requirements ranging
• from 300 psi to 400 psi
• (2.1 MPa to 2.8 MPa)
• generally recommended

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Inside a Reclaimer
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Pulverization

• Pulverize mat to appropriate gradation
• Typically 1 or 2 passes

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Cement Spreading

• Cement is spread on top of roadway in measured
  amount

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Blending of Materialsand Moisture Addition

• Cement is
• blended into pulverized,
• reclaimed
• material and, with the addition of water, is
  brought to optimum moisture

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Grading and Compaction

• Material is graded to appropriate Plan line,
  grade, and cross-sections, and then compacted to
  95 to 98 minimum standard Proctor density

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Curing
Bituminous Compound
Water
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Testing
Moisture
Gradation
Density
Thickness
Stability
Stiffness
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FDR creates an excellent base for either a rigid
or flexible pavement structure
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Reclamation Costs
Note Costs are stated in U.S. dollars per
square yard
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The BIGGEST Advantage!

• Versatility through use of portland cement
• Stabilizes many materials
• old base
• asphalt surface
• granular or plastic subgrade
• blends

Portland Cement is probably the closest thing we
have to a universal stabilizer. Chemical
Stabilization Technology for Cold Weather United
States Army Corps of Engineers September 2002
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for additional information, please visit our
website at www.cement.org/pavements
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Thank You!
ghalsted_at_cement.org