Bases, Subbases, & Low Cost
Surfaces
Dr. TALEB M. AL-ROUSAN
Soil Stabilized Roads
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Soil stabilization: Combination and
manipulation of soils, with or without
admixtures, to produce a firm mass that is
capable of supporting traffic in all weather
conditions.
 Stable stabilized soil must have sufficient
shearing strength to withstand traffic loadings
in all weather conditions without excessive
deformations.
 If stabilized soil is to be used as wearing
surface, then it must be capable of
withstanding the abrasive effects of traffic.
Soil Stabilized Roads Cont.
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Purpose: Effective utilization of local materials
in order to decrease construction cost.
Used when natural soil has unfavorable
characteristics and require modification.
Primary use of stabilized soil is in base and
subbase construction.
Stabilized base and subbase support thin
wearing surfaces for light traffic.
Stabilized base and subbase may function as
base for high type pavements with heavy
traffic.
Classes of Stabilization
1.
2.
3.
4.
Soil-Aggregate Roads and Granular
Stabilization.
Bituminous Soil Stabilization.
Soil-Cement Roads
Stabilization by addition of Salt, lime,
and various other chemicals.
Soil-Aggregate Roads and
Granular Stabilization
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1.
2.
3.
Consist of a substantial layer of a properly
proportioned and blended mixture of soil and
aggregates compacted to form a road.
AASHTO : Known as (dense-graded
aggregates) It’s a natural or prepared mixture
consisting predominantly of stone, gravel, or
sand and containing silty clay.
Construction procedure:
Road mix construction
Traveling plant construction
Central plant construction
Soil-Aggregate Roads and
Granular Stabilization Cont.
Calcium Chloride is used some times to
expedite the compaction process by
slowing the rate of evaporation from the
mixture.
 Calcium Chloride might increase density
and maintain moisture in wearing
surfaces for desired max stability which
will prevent raveling of the surface and
reduce dust.
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Bituminous Soil Stabilization
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1.
2.
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Bituminous materials are used in conjunction with
aggregates and soil-aggregate mixture for two
purposes:
Supply cohesion to the stabilized soil mixtures (Like
in Sand stabilization).
Waterproofing
Mostly used for base construction.
Used with : well-graded soils, sands, and clays.
Finer soils require more bitumen for waterproofing.
Very fine plastic soils can not be stabilized
economically with bituminous materials because of
difficulties of pulverization and mixing.
Bituminous Soil Stabilization
Cont.
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1.
2.
3.
4.
Choice of bitumen depend on local
experience and comparative cost.
Use 4 – 7% bitumen
Types of bitumen:
RC: use for sandy soil or soils with min. clay
or silt.
MC : used for soils with higher clay or silt
particles (give more homogenous mixes)
SC: used for soils with 30 -40% silt & clay.
MS & SS emulsified asphalt (Table 18-3).
Bituminous Soil Stabilization
Cont.
 Oiled
earth surfaces: Liquid bitumen
is applied at properly prepared
natural soil surface.
 Prevent dust and provide a thin
stabilized surface that support
limited number of light vehicles.
 See Construction method in Text.
Soil-Cement Roads
Incorporating Portland cement (7 – 14%
volume of compacted mixture) with
naturally occurring or artificially created
soils or soil-aggregate mixtures.
 Used for bases in city street
constructions, driveways, shoulders,
parking areas, and some airport
runways.
 Also known as cement-treated base.
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Soil-Cement Roads Cont.
Nearly all subgrade soils may be
stabilized with cement except those soils
that contain high percentage of organic
materials.
 Silt and clay require large percentage of
cement for successful stabilization.
 Sandy and gravelly soils with 10 – 35%
silt and clay have most favorable
characteristics.
 See construction method in Text.
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Stabilization by Addition of Lime
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Incorporating small amounts of hydrated lime
improves certain plastic clay soils.
 Used to reduce plasticity, shrinkage, and swell
of clay soils and increasing their bearing
capacity.
 improve workability of plastic soil (easy to
pulverize).
 Waterproof soil to some extent and allow it to
dry quickly when saturated to expedite
construction.
Stabilization by Addition of Lime
Cont.
Use 3 – 6%.
 Depth of treatment around 6 inches.
 Subgrade soil is scarified and pulverized,
then lime is spread mechanically, water
is added (+ 5% above opt.), then allowed
to cure for (1 -7days). Mixing and
compaction is then applied.
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Macadam Roads
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Road surface or base in which crushed or broken
stone was mechanically keyed or locked by rolling and
cemented together by the application of stone
screening and water.
 Later, bitumen macadam roads were built using
bitumen material as binder.
 Water-bound macadam: broken stone bound together
by stone dust and water applied during construction
(Seldom Constructed).
 Bituminous macadam: crushed stone base or wearing
surface in which fragments are bound together by
bituminoius material; the aggregate layer is compacted
and bituminous material is applied to the surface
(Known as penetration macadam).
Bituminous Macadam
Construction
1.
2.
3.
4.
Spreading and rolling of coarse
aggregates.
Initial application of bituminous
material.
Spreading and rolling of key
aggregates.
Application of seal coat
Prime Coats
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1.
2.
3.
Application of liquid bituminous material to
previously untreated base or wearing
surface.
Bituminous material penetrate surface and
completely absorbed
Purpose:
Promote adhesion “bond” between base and
wearing surface.
Consolidate the surface on which the new
treatment is to be placed.
It may function as a deterrent to the rise of
capillary moisture into the wearing surface.
Prime Coats Cont.
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Use low viscous asphalt or tar.
Asphalt preferred to have high penetrated
qualities and should leave high viscosity
residue in the void spaces.
MC-30 and MC-70 widely used for dense
tightly bond surfaces, and surface with more
opened texture.
Slow setting emulsified asphalts are
recommended for penetrable surfaces.
Recommended quantity (0.9 – 2.3 L/m^2).
Tack Coats
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Single application of bituminous material to an
existing bituminous, Portland cement concrete,
brick, or block surface or base.
 Purpose: Provide adhesion between the
existing surface and the new bituminous
wearing surface.
 RC-70 through RC-250 are frequently used.
 Quantity required for application is small (0.19
to 0.38 L/m^2).
Seal Coat
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Very thin single surface treatment that
is usually less than (½ in) thick.
Single Surface treatment = single
application of bituminous material that
is covered by a light spreading of fine
aggregate or sand (spread
mechanically) then compacted with
pneumatic tired rollers.
Applied as final step in many types of
bituminous wearing surfaces.
Seal Coat Cont.
 Purpose:
1. Waterproof
or seal the surface.
2. Rejuvenate or revitalize old
bituminous wearing surfaces.
3. To nonskid slippery surfaces.
4. Improve night visibility.
Slurry Seal Coat
Mixture of well-graded, fine aggregate,
mineral filler (if needed), emulsified
asphalt, and water.
 Use principally for the resealing of old
bituminous wearing surfaces.
 Very thin (1/8” to ¼”).
 See Figure 18-6.
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