AGENDA
1. Introduction 2. Materials 3. General Properties of Bitumen
4. Types of Bituminous Stabilization 5. Factors Affecting Bituminous Stabilization 6. Effect of Bitumen on Soil Property 7. Bituminous Material as Water Proofing Agent 8. Bituminous Material as Dust Controlling Agent
9. Case Study 10. Conclusion 11. Reference
________________________________________ What is soil stabilization? It is the alteration of any property of soil to improve its engineering performance. A technique aimed at maintaining or improving the stability, load carrying capacity or resistance to water absorption of soil. Stabilization can be done for surface and deep deposits of soil masses.
Methods used for stabilizing surface deposits : •Mechanical stabilization without addition of any material other than soil.
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________________________________________ Soil Stabilization(contd.) • Stabilization with special stabilizers such cement,lime,bitumen and various other chemicals. •Complex stabilization with more than one stabilizers. •Stabilization by heating. Deep soil deposits are stabilized by: Electrical method
Grouting method Heating or freezing,etc. 2
as
INTRODUCTION A process by which a controlled amount of bituminous material is thoroughly mixed with an existing soil or soil aggregate to form a stable base or wearing surface. Bitumen is a complex organic material possessing adhesive properties and substantially soluble in carbon disulphide.
Materials which are composed primarily of bitumen are bituminous materials. Bituminous materials include bitumen,bitumen emulsions and tars.
bitumen,
cutback
In non-cohesive soils,bitumen plays a role primarily of a binding agent. 3
In cohesive soils, its stabilization action consists mainly in preserving the strength by reducing the water absorption or by making the soil waterproof.
MATERIALS REQUIRED BITUMINIOUS MATERIALS Broadly classified as asphalts and tars. Asphalts, normally too viscous to be used directly for soil stabilization. They are used in the form of cut backs or emulsions which have a fluid consistency capable of direct incorporation into soil. Both cut back and tars may or may not require prior heating.
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MATERIALS REQUIRED…(Contd) SOIL Clays have been treated with both cutbacks and emulsions and performed adequately. The main use of bituminous stabilization is for sand and sand-gravels which lack cohesion and/or where a waterproofing action is required. Any non cohesive soil, sand or sand-gravel may be treated. WATER
Some water is necessary for compaction. Any water is acceptable but sea water should be avoided. 5
MATERIALS REQUIRED…(Contd) OTHER ADDITIVES There has been an extensive but somewhat haphazard search for additives such as coal fines, latex etc to improve the effectiveness of stabilization without marked success.
GENERAL PROPERTIES OF BITUMEN •Contain predominantly hydrocarbons with traces of sulphur, oxygen,nitrogen and metals.
•Soluble in carbon disulphide. •Colloidal in nature. 6
GENERAL PROPERTIES OF BITUMEN(contd.) •Thermoplastic. •Insoluble in water. •Chemically inert.
•Generally hydrophobic,but can be made hydrophilic by addition of surface active agents. •No specific melting point,boiling point or freezing point.
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TYPES OF BITUMINOUS STABILIZATION SOIL-BITUMEN STABILIZATION Used mainly in cohesive soil. Done mainly for water proofing. Best results are obtained with soils meeting the following requirements: Maximum Size
Less than one-third the compacted thickness of stabilized soil layer.
Passing 4.75 mm sieve
More than 50%
Passing 425 micron
35-100%
Passing 75 micron sieve
10-50%
Liquid Limit
Less than 40%
Plasticity Index
Less than 18
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TYPES OF BITUMINOUS STABILIZATION(contd.) SAND-BITUMEN STABILIZATION Used for non cohesive soils such as dune,pit or river sand. Sand particles are cemented together by means of bituminous materials.
More than 12% of material should not pass through 75micron sieve.In extreme cases, may be allowed up to 25%. Example-Arid desert region of Rajasthan.
WATERPROOF MECHANICAL STABILIZATION Refers to a well graded dense mechanical stabilized soils. 9
TYPES OF BITUMINOUS STABILIZATION(contd.) They are made waterproof by incorporating a small amount of bitumen into the soil. about 1-3% is sufficient. OIL-EARTH STABILIZATION
Refers to a surface which are made water and abrasion resistant by application of road oils. No mechanical mixing involved.
Stabilizer penetrates itself by a short distance into the soil layer. 10
FACTORS AFFECTING STABILIZATION Soil:
• Particle size, shape and gradation of soil influence the properties of mix. •Small proportion of fines in the soil preferred,but high clay content not desirable.
Types of bituminous materials: •Depends on soil type, climatic condition,equipments available,temperature,etc. •For stabilization in roads,highest grade that can be mixed with the soil at the time of construction is preferred. 11
FACTORS AFFECTING STABILIZATION(contd.) Amount of bitumen:
• Amount required should be optimum such that optimum compaction and strength characteristic and adequate resistance to water absorption is obtained. •For maximum stability,4 to 6% is normally adequate.
Mixing: •Improved mixing with low mixing period is preferred.
•To make mixing possible and to disperse the bitumen in fine particles,it is necessary to first mix the soil with water before adding the cutback. 12
FACTORS AFFECTING STABILIZATION(contd.) Compaction: • Better the compaction, higher will be the stability of the soil.
Curing: •By curing soil bitumen,the water and the volatiles(of the solvent used in cutback)are allowed to evaporate. •It allows the bitumen to be more effective to impart binding and waterproofing actions.
Additives: •Anti stripping and reactive chemical additives have been tried to improve the properties of the mixes.
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EFFECT OF BITUMEN ON SOIL PROPERTIES The immediate effect of addition of cutback bitumen on the properties of sandy clay soil.
On dry density: • Increasing amount of bitumen Causes the max. dry density to be progressively reduced while a corresponding increase in fluid content is observed. •Presumably due to greater viscosity
of the fluid films surrounding the particles.
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EFFECT OF BITUMEN (Contd.) The immediate effect of addition of cutback bitumen on the properties of sandy clay soil.
On strength • From the figure,unconfined Compressive strength of the specimens rises slightly until a binder content of 4% is reached. •In excess of 4% causes a decrease which may goes below than that
of the untreated soil.
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EFFECT OF BITUMEN (Contd.) The immediate effect of addition of cutback bitumen on the properties of sandy clay soil.
On water absorption •Fig.3 shows the amount of water absorbed in a capillary water absorption test on a sandy clay Soil specimen. •Addition of 2%bitumen causes an increase water absorbed after 28 days.
•But quantities of 4% and over causes a substantial reduction in water absorbed. 16
EFFECT OF BITUMEN (Contd.) EFFECT OF ADDITION OF STABILIZER •Reduces the need for water to be added for compaction.
•Maximum dry density will be reduced. •Advantageous in very dry condition. •For any compacted density,higher the bitumen content,the less the absorption and loss of strength on soaking compared to the untreated material.
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BITUMINOUS MATERIAL AS WATERPROOFING AGENT The soil-bitumen mixture does not absorb water so readily even when relatively small quantities of bitumen are used. The entry of further water is hindered by the resistance of bituminous film.
Presence of some wax in the bitumen enhances the waterproofing capability of the bitumen.
EFFECT OF MIXING ON ITS PERFORMANCE Fig.5 shows the variation of water absorption with mixing time for specimens of silty clay containing 3% of waterproofing oil. 18
EFFECT OF MIXING ON ITS PERFORMANCE(Contd.) Excessive mixing can reduce the waterproofing effect.
Waterproofing is due to coating of aggregates of soil particles by fairly thick film of bitumen. Too much mixing is due to breaking down of the soil aggregates into finer particles. Bitumen spread over a larger area
in thinner film.
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BITUMINOUS MATERIAL CONTROLLING AGENT
AS
DUST
For certain areas of the world such as middle east and mid western states of U.S.A,natural moisture content of silty and clay soils in dry season is low enough to permit the unsurfaced soil to carry traffic. They dust very easily and soften during rainy season. Can be stabilized by spraying the dry soil surface with an oil or medium curing cutback bitumen. Stabilizer is applied in two or three equal distributions totalling about 1 gal/sq.yard so that it penetrates ½ to 1 in. into the soil. 20
BITUMINOUS MATERIAL CONTROLLING AGENT(contd.)
AS
DUST
If the effects of traffic and weather is severe,stabilization is done to a greater depth.
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CASE STUDY The Shaybah Access Road is approximately 386 km long and runs from the main KSA-UAE highway near Batha to the Saudi Aramco Shaybah Facilities.
It is an asphalt pavement constructed in six months from recycling an unbound aggregate road with a mixture of foamed bitumen and cement slurry. The end result is a road with a smooth surface finish that can carry heavy goods vehicles travelling in excess of 80 km/h in the middle of the Arabian Desert. This foamed bitumen asphalt pavement was constructed using a computer controlled pavement recycler.The top 200 mm of the road was milled which was originally compacted marl surface.The recycler remixed in-situ,the milled material with foamed bitumen and cement slurry. Foamed bitumen is an effective binder that can be uniformly mixed with cement slurry and granulated material to form foamed bitumen asphalt. 22
CASE STUDY(Contd.) The re-mixed material was immediately profiled and compacted by graders and rollers following the recycler. The finished surface looked like a rolled dry lean concrete surface. The finish was smooth and hard and it was possible to run vehicles on the pavement almost immediately. The foamed bitumen asphalt was given a slurry seal finishing sealing the surface against the harsh environment, reducing wear on the surface and providing traction and skidding resistance. The performance of road was monitored over 3 year period by measuring material properties ,traffic flows,surface condition and pavement deflection at regular intervals. The overall assessment of the road‟s condition and its performance was that the foamed bitumen stabilized marl road performed well under the intense traffic and environment conditions.
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CASE STUDY(Contd.) SHAYBAH ACCESS ROAD
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CONCLUSION Bituminous stabilization has been used for many applications.
It has received its greatest use in bases for highway and air field pavements Stabilization with bituminous materials have been done in conjunction with cement in places such as parking areas and school playgrounds. Bitumen has been used in the form of „foam‟ and has been successful. It is used in replacing existing deteriorating roads,paving pipeline roads,improving the quality of marl sub bases.etc 25
CONCLUSION (Contd.) Bitumens are modified to enhance the effectiveness of binder. Examples are tar-bitumen mixtures,rubberized tar bitumen , polymer modified bitumen.
and
In general,bituminous stabilization is used in many applications with varying degree of success.
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REFERENCES ALAM SINGH “Soil Engineering(Theory and Practice)” Asia Publishing House,Bombay G.LEONARDS “Foundation Engineering” Mc Graw-Hill Book Company, New York KHANNA AND JUSTO “Highway Engineering” Nemchand and bros.,Roorkee L.R.KADYALI & N.B.LAL “Highway Engineering” Khanna Publishers,Delhi
O.G.INGLES & J.B.METCALF “Soil Stabilization(Design and practice)” Butterworths, Sydney 27
