2.3 Stabilized Material
2.3 Stabilized Material
2.3 Stabilized Material
Chapter-2: Highway materials dispersive soils, organic soils, saline soil or presence of
saline water.
• These soils require special treatment before acceptance in
2.3 STABILIZED PAVEMENT MATERIALS pavement foundation so that they will be re-classified to fall into
one of the sub grade categories for the purpose of pavement
design.
Zeleke D.
zeladamtie@gmail.com
Feb, 2022
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• by blending two or more materials and improving particle size – stability and bearing capacity for sub grade, sub base, base, and low-
cost road surfaces.
distribution or
• Improve excessive sensitivity to change in moisture content
• by the use of stabilizing additives to meet the specified
– undesirable properties such as swelling, shrinkage, high plasticity
engineering properties.
characteristics, and difficulty in compaction, etc.
• ERA Manual define Soil stabilization as
• Improve durability
– The treatment of the materials used in the construction of – increase the resistance to erosion, weathering or traffic
• the road bed material, fill or pavement layers by the addition of a • Improve high permeability, poor workability, dust nuisance, frost
cementations binder such as lime or Portland Cement or the susceptibility
mechanical modification of the material through the addition of a soil
• To use Locally Available Materials
binder or a bituminous binder.
• To conserve Higher Quality Material
Concrete and asphalt shall not be considered as materials that have
• To recycle Existing Pavements/Bases
been stabilized.
• To reduce Thickness of Pavement
Soil stabilization is the treatment of natural soil to improve its
engineering properties.
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Cont’d Selection of Type of Treatment
• Many natural materials can be stabilized to make them suitable for road pavements
• The selection of the stabilizer is based on the plasticity and particle
but this process is only economical when
– the cost of overcoming a deficiency in one material is less than the cost of size distribution of the material to be treated. The appropriate
importing another material which is satisfactory without stabilization. stabilizer can be selected according to the criteria shown in Table
• The primary use for cement and lime stabilization in tropical countries like Ethiopia below.
has so far been with gravelly soils to produce road bases. Table 2.3.1: Guide to the Type of Stabilization Likely to be Effective
– The processes can also be used with more clayey soils to make the upper layer
of sub-bases.
• Soil stabilization methods can be divided into two categories. i.e. techniques of
stabilization commonly practiced in pavement construction are:
ii. Chemical stabilization: is blending of the natural soil with chemical agents
like Portland cement , asphalt binder, and lime. As a result, it is classified as
Cement stabilization, Notes. 1. The agent will have only a marginal effective
2. PP = Plasticity Product = PI x (percent passing 0.075mm sieve)
Lime stabilization, and
SOURCE : ERA, 2013
Bitumen stabilization.
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– Ease of application,
– Site constraints,
– climate,
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Cont’d Cont’d
Particle Size Distribution • When the pavement design relies on a relatively low permeability in the
• While maximum frictional strength does not necessarily coincide with pavement courses, the materials used should be of particle size
maximum density, the achievement of a high density will generally distribution within the limits established by substituting values of 0.50
provide a high frictional strength. i.e. High density will generally and 0.33 for ‘n’ in the Fuller equation. These limits are sufficiently wide
provide high frictional strength. to allow for variations that will inevitably occur in field mixing.
• However, if plant mixing is undertaken, more restrictive limits may be
– A particle size distribution that results maximum dry density, obtained set.
with the closest packing and minimum voids, has been shown – Where the value of the exponent ‘n’ is less than 0.33, the fines content of
experimentally to follow Fuller’s equation with the value of the the material may be excessive. A high fine content will result in reduced
exponent 'n' usually 0.45 to 0.50 for most soils. permeability, but may lead to the development of pore pressures and
• However, with some materials, e.g. consequent instability during compaction or in service.
– gravel-sand-clays, high densities can be achieved with ‘n’ – Where ‘n’ is greater than 0.5, the material tends to be harsh, and may be
values as low as 0.33. prone to segregation and ravelling and therefore more difficult to work.
– For materials with a maximum size of 19 mm, the amount of • The theoretical maximum density of aggregates is obtained when grain
fines passing the 75 m sieve will be 6 and 8 percent for ‘n’ size distribution follow the Fuller maximum density equation of the form:
• When the percentage of soil binder is low, as a rough rule, • However, conditions to be adopted for the test may be altered in respect of
• The permissible values depend on the use of the stabilized materials Pavement Minimum CBR values
High class, high traffic volume 100
and the climatic condition of the site. Rural roads, wet areas 80
Rural roads, dry areas 60
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pavement materials and situations. – Reduces the moisture susceptibility of soils - cement binds the
• Portland cement has been used particles greatly and reduces moisture induced volume change
– with great success to improve existing gravel roads, as well as to (shrinkage and swell) and it also improves strength & stability under
stabilize natural soils. variable moisture, and
– for base courses and sub bases of all types. – Develops inter-particle bonds in granular materials - increased
– in granular soils, silty soils, and lean clays, but it cannot be used in tensile strength and elastic modulus.
organic materials. Since soil cement shows strength gains over that of • Soil properties progressively change with increasing cement contents.
the natural material, it is very often used for base-course construction. • For practical reasons, two categories of cement stabilized materials
• Cement stabilization is widely used because:
• cement modified, and
1. cement is available at a relatively low price;
• cement bound materials.
2. involves less care and control than any other stabilizers;
– There are no established criteria to distinguish between modified and
3. more technical information is available on cement-stabilized materials;
bound materials, but based on arbitrary limit of Indirect tensile
and
strength of 80 kN or Unconfined compressive strength of 800 kPa
4. most pavement materials can be stabilized with cement (except those
after seven days moist curing.
with high organic matter or soluble sulphate contents)
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Cont’d Cont’d
• Cement modified materials:
• The most important factors influencing the quality of the cement-soil
Cement is used to reduce plasticity, volume-change, etc, without much increase in
interactions are:
elastic modulus and tensile strength. The material has weak cementitious bonds
between particles. – Nature and type of soil:
• clay content (max 5 %), plasticity of the soil (max LL of 45) , gradation (well-graded),
For design purposes, such materials are assumed to have the same elastic modulus as
content of organic materials (max 2 %), sulphate content (max 0.25 % for cohesive soils
an untreated material performing the same function , and to behave in the pavement as
and 1 % for non-cohesive soils).
an unbound material that does not have tensile strength and thus is not distressed by
fatigue cracking.
– Cement content : the quantity of cement to effectively stabilize soils vary with the
nature and type of soils. The criteria used are the compressive strength ( about 1.7 Mpa)
Such materials are evaluated as conventional unbound flexible pavement materials.
after 7 day. The quantity required for gravely soil is less than required for silty and clayey
• Cement bound materials: soils.
– cement is used to sufficiently enhance modulus and tensile strength.
– Moisture content: For hydration of cement to take place, to improve the workability, and
– Cement bound materials have practical application in stiffening the pavement. facilitate the compaction (increased density).
– Cement bound natural gravel and crushed rocks typically have elastic moduli in the – Curing temperature and time, mixing (in place & in plant), compaction, and
range 2000 – 20,000 MPa (versus 200 – 500 MPa for unbound materials), and 28-day degree of pulverization are important factors which affect the strength gained by cement stabilization.
unconfined compressive strengths greater that 4 Mpa. • the procedure of mix-in-place construction involves
– initial preparation of the subgrade,
– The bound material is relatively brittle and fail in tension under fairly low strain, and
– pulverization of the soil, spreading of the soil,
the critical strain normally reduces with increasing modulus. – dry-mix the soil and the cement,
– adding water and wet mix,
– Prevention of fatigue cracking is the main design concern for cement-bound bases and
– compact and finish, and
it is critical that they be properly constructed. – protect and cure (place a curing membrane to keep moist).
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Cont’d Cont’d
Table 2.3.4 General guidelines on cement requirement to stabilize soil • Since cement stabilized materials constitute in most cases the
main structural part of pavements, much attention is given to
Amount of cement (%) their mechanical characteristics such as:
Soil type By weight By volume
A-1-a 3-5 5-7 i. Tensile and compressive strength:
Granular A-1-b 5-8 7-9 i. Age:
Materials A-2 5-9 7-10
• cement stabilized materials gain strength with age
A-3 7-11 8-12
A-4 7-12 8-13 ii. Unconfined compressive strength:
Silt-Clay A-5 8-13 8-13
• it is used to determine strength of clay soil and stabilized
Materials A-6 9-15 10-14
materials, but has little direct application to pavement design.
A-7 10-16 10-14
iii. CBR and Triaxial tests:
A soil is regarded to be suitable for cement stabilization if • used to evaluate the strength of cement modified materials
% passing No. 200 sieve <35 % iv. Tensile strength:
% retained on No. 200 sieve > 55 % • important in the design of cement bound materials. Tensile
max. grain size < 75 mm strength is influenced by particle size distribution, moisture
content during compaction, cement content, and density.
LL <50
PL <25
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Cont’d
Cont’d ii. Deformation behaviour:
• In order to make proper stress-strain analyses, information on the elastic modulus of the
materials should be known.
• It is well known that clays, sands, and gravels show different elastic deformation behaviour
under repetitive loading.
• The addition of cement on these materials changes the elastic deformation properties, but
not completely.
• The parent material will have a great influence on the properties of the soil-cement mixture.
– have a different behaviour in compression (about 1.5 times of modulus) than in tension.
However, a more or less linear behaviour is observed up to 75 % of the failure load. The
material also exhibits some degree of permanent deformation under repeated loading and a
certain amount of creep under steady loads.
– exhibit a similar performance but permanent deformation and creep are less than in
cemented clayey soils.
• The less fines are present in the soil mixture the more the cement-treated soil behave like concrete.
iii. Fatigue characteristics:
Effect of age on strength • Cement stabilized materials cracks either due to hydration and drying shrinkage and fatigue at the
Variation of compressive result of repeated tensile stresses (strains).
strength of stabilized • Knowledge of fatigue characteristics of cement-treated materials is essential for design purposes.
materials • the durability test is normally used in the soil-cement mix design procedure.
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– As the proportion of cement in the mixture increases, so the strength – Calcium carbonate (CaCO3) – carbonate of lime.
increases. • Out of these, various forms of quick lime and hydrated lime have
• Strength also increases with time. been successfully utilized as a soil stabilizing agent.
• The choice of cement content depends on • In practice, the most commonly used products are
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Cont’d Cont’d
• Lime stabilization • Lime
– promotes long-term gain of strength through reactions with – is an effective stabilizing agent for clayey materials to improve both
workability and strength.
soil silica and soil alumina.
– is not effective with cohesionless or low cohesion materials without the
• When sufficient lime is added to a soil, addition of secondary (pozzolanic - fine materials which react with lime to form
– the pH of the soil-lime mixture increases to about 12.4. cementitious compounds i.e. cementitious silicate or aluminates) additives.
• The pH elevation increases the solubilities of silica and alumina. • Soil lime is a mixture of lime, water, and fine grained soil. If the soil contains silica
• The low pH value may retard the hydration process and affect the and alumina, pozzolanic reaction occurs , resulting in the formation of a cementing
hardening of stabilized soils making it difficult or impossible to type material.
compact. e.g. , clay minerals, quartz, and feldspar are all possible sources of silica and
• The soil-lime reaction can be described qualitatively as follows. alumina in typical fine grained soil.
• The cementitous products resulting from cement and lime stabilization are with
comparable behavior and follow fairly similar evaluation, and construction
considerations.
• The reaction between soil and lime are complex and still not completely
understood. Basically four different factors are involved in the soil-lime reactions.
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– Cation exchange, Flocculation, Pozzolanic reaction, and Carbonation
– It has been shown that the thickness of the water layer around the
clay particles decrease substantially due to cation exchanges.
– Under such conditions, flocculent structures are developed which
influence soil characteristics as
– plasticity, shrinkage and swell, workability and other normal clay-
Cation Exchange
Pozzalanic Reaction water interactions are distinctly inhibited, but not responsible for
rapid increase in strength.
– The effects of lime on the plasticity properties of soils are primarily due
to cation exchange reactions.
Al2o3 = A • An immediate reduction in plasticity results in an immediate increase
Cao = C
in shear strength.
Sio2 = S
Lime Cementation H2O = H – The effect of lime on clay minerals of high cation exchange capacity,
such as montmorillonite clays, is therefore more apparent than it is on
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pozzolanic in nature. 30
Cont’d Cont’d
• Lime cementing action in a soil is usually a slow process depending
on the type of pozzolans, it takes considerably more time than required
for hydration of Portland cement. This long term effect on strength,
causing continuing strength improvements with time, often called
pozzolanic reactions.
• However, presence of sulphur and organic materials may inhibit the lime
stabilization process. Sulphate (e.g. gypsum) will react with lime and swell, which
may have effect on soil strength.
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Effect of lime content and time on the CBR values of lime stabilized soil
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Cont’d Bituminous Stabilization
• Other factors that influence the soil-lime reaction are: • Bituminous materials are used as stabilizers to retard or completely stop moisture
– The presence of excessive quantities of organic carbon retards the lime-soil absorption by coating soil or aggregate grains in the soil-aggregate mixture.
reaction, • Bituminous Stabilization is used
– Moderately weathered and unweathered soils with high pH display good reactivity, – To introduce some cohesion into non-cohesive granular materials: the bitumen
– Poorly drained soils exhibit a higher degree of lime-reactivity than better drained adds cohesive strength;
soils, – To make cohesive materials less sensitive to increased moisture: the bitumen
– A minimum amount of clay, approximately 15 %, is required to ensure an adequate “waterproofs” and thus reducing loss of strength with increase in moisture
source of silica and/or alumina for the lime-soil pozzolanic reaction. content.
• The strength of lime stabilized materials is dependent on Both effects take place partly
• from the formation of bituminous film around the soil particles which bonds them
– the amount of lime, the curing time, curing temperature and compaction.
together and prevents the absorption of water, and
• In addition, the quality of water, type of stabilizing lime, and uniformity of mixing are important
• from simple blocking of the pores, preventing water from entering the soil mass.
factors affecting the quality of production as they are in cement stabilization.
– Because more care is necessary in bituminous stabilization to achieve
• Similar to cement-stabilization,
satisfactory mixing, its use has not been as widespread as cement and lime
– high lime content produce bound products; and
stabilization.
– less lime content produce modified materials. The later is more applicable to lime stabilized
• More successful with granular materials than with cohesive materials and used
materials.
primarily as bases and to lesser extent, sub-bases.
• The rate of gain in strength is considerably less than with cement stabilized materials, but will
continue with time provided curing is sustained. It is sensitive to curing temperature. • The amount of binder is considerably less than that for bitumen-bound pavement
• Soil-lime reactions are time and temperature-dependent and continue for long periods of time. materials.
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Cont’d Cont’d
• Bituminous materials: penetration grade bitumen, cutback bitumen and • Soils requirements: -
bitumen emulsion.
– Bituminous materials are used for the stabilization of both
– The characteristics of cutbacks depended on the particle size distribution of the
soil, the temperature of application, and the type of mix plant. cohesive and non-cohesive granular soils.
– The more viscous binders (penetration grade) are normally used for soils having
– Soils which can readily pulverized by construction equipment
only a small proportion of material passing the 0.075 mm sieve and for plant
mixes. are satisfactory for bituminous stabilization.
– The lighter binders (liquid bitumen) are used for mix-in-place methods and with
– Cohesive soils usually have satisfactory bearing capacity at low
soils containing a larger proportion of fines.
moisture content. The purpose of using bitumen as a stabilizer
– Emulsions are suitable for climates where rapid drying conditions occur, since
this is equivalent to adding water to the soil as well as bituminous binder. in such soils is to waterproof them as a means to maintain them at
– In the tropics, where the temperature is high,
low moisture contents and high bearing capacities.
• the use of emulsions may be an advantage since it helps to provide part of the
OMC for compaction thereby reduce amount of water required. – In the non-cohesive granular materials, bitumen serves as a
• Bituminous Materials: a wide range of materials may be stabilized with
bonding or cementing agent between particles.
bituminous materials, including gravels, sand, silty sand, sand clays and fine
crushed rock.
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Cont’d Cont’d
• Depending on the particle size distribution and physical properties of the available Table 2.3.5 Characteristics of soils empirically found suitable for bitumen stabilization.
soil materials and the function of the stabilizing bitumen, there are four types of Sieve size Percent passing
soil-bitumen mixtures in highway engineering. Soil-bitumen Water proofed granular stabilization
Sand-bitumen
– Soil - bitumen: A B C
1.5inch 100
• a mixture of cohesive soil and bitumen for waterproofing purposes.
1inch 80-100 100
• The bitumen requirements commonly range from 4 - 7% of the dry weight of the soil. 075inch 65-85 80-100 100
– Sand - bitumen: No. 4 >50 40-65 50-75 80-100
100
• sands such as beach, river, or existing roadway sand stabilized with bitumen if
No. 10 35-100 25-50 40-60 60-80
they are substantially free from vegetable matter, lumps or balls of clay. No. 40 15-30 20-35 30-50
No.100 10-20 13-23 20-35
– It is recommended that the sand contain < 12% of 0.075 mm.
No.200 10-50 8-12 10-16 13-30
– The required amount of bitumen content ranges from 4 -10 %, <12,<25
– The optimum should be determined by compaction, strength, and water Plasticity characteristics
LL <40
resistance testing and should not exceed the pore space of the compacted
PI <18 <10; <15 <10;<15 <10;<152
mineral mix.
Field moisture <201
– Waterproofed granular stabilization: Linear <51
• a soil material with good gradation from coarse to fine and high potential density shrinkage
1 lower value for wide and higher values for narrow gradation band sand
is waterproofed by uniform distribution of small amount (1-2 %) of bitumen.
– Oiled earth: 2 values between 10 and 15 permitted in certain cases
• This is a soil surface, consisting of silt-clay material made water and abrasion
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resistant by slow or medium curing bitumen cutbacks or emulsions.
Cont’d Cont’d
• The mechanism of stabilization with bituminous materials • Mix design procedure for bituminous stabilization of soil may
– Adding cohesive strength and – mix design for stability in non-cohesive material;
– reducing the percolation of water; no chemical interaction is taking – mix design for waterproofing in non-cohesive or cohesive materials;
place. – mix design for sand-bitumen mixes, and
• Waterproofing occurs by coating the surface of particles or aggregated – mix design for oiled earth roads.
lumps of particles or by blocking the pores of the soil mass. The
• For the first three types of mix, a series of tests should be made with
strength comes from the presence of a continuous film of bitumen,
varying bitumen contents and grades using hot bitumen, cutback and
giving cohesion.
emulsion, and the appropriate mix is selected giving due weight to the
– There are two opposing effects: need for stability or water resistance as required.
• the thinner the film of bitumen the stronger the material;
• Compaction, compressive, and water absorption test are normally used
however, thick films or filled pores are effective in preventing
to select the optimum amount of bitumen content.
ingress of water.
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