Assignment
on
CHEMICAL STABILIZATION OF SOIL
Submitted by:
Rahul Barman
18-21-417
M.Tech. (GEOTECHNICAL ENGG) 1st semester (2018-20)
Submitted on: 6th November,2018
DEPARTMENT OF CIVIL ENGINEERING
NATIONAL INSTITUTE OF TECHNOLOGY, SILCHAR-10
ASSAM
Chemical Stabilization of Soil
1. Introduction
For any structure, a strong foundation is very important to support the superstructure and thereby safely transfer the
loads to the soil. Hence the properties of the soil on which any structure is placed should be strong and stable. The
process of soil stabilization helps to achieve the required properties in a soil needed for the construction work. In India,
the modern era of soil stabilization began when there occurred a general shortage of petroleum and aggregates, it
became necessary for the engineers to look at means to improve soil other than replacing the poor soil at the building
site. Many areas of India consist of soils with high silt contents, low strengths and minimal bearing capacity . Soil
stabilization was used but due to the use of obsolete methods and also due to the absence of proper technique, soil
stabilization lost favor. With the availability of better research, materials and equipment, it is emerging as a popular
and cost-effective method for soil improvement. It is very expensive to replace the inferior soil entirely soil . The
stabilization process can result in higher resistance values, reduction in plasticity, lower permeability, reduction of
pavement thickness etc. Stabilization of expansive soils with admixtures controls the potential of soils for a change in
volume, and improves the strength of soils. Instead of borrowing a suitable soil from a long distance it was proposed to
use the locally available clay after stabilization with lime powder. On the other hand, in the world, lime production
amount was increased from 21.7 million tons to 51 million tons in 10 years. Increasing demand for Lime product rises
the generation of waste Lime material. The proportion of lime discharged as waste during block production at the
quarries is equal to 40-60% of the overall production volume. Large pieces of lime waste can be used as embankment
or pavement material. But only small portion of lime products are stored economically and most of them are stored on
lands. Increasing the usage of lime will eliminate the harmful effects on environment.
Soil stabilization can be accomplished by many methods all these fall into two main categories namely:
1) Mechanical stabilization.
2) Chemical stabilization.
2. Chemical Stabilization
Under this category, soil stabilization depends mainly on chemical reactions between chemical additives and
soil particles which then produce a strong network that bind the soil grains to achieve the desired effect. A chemical
stabilization method is the fundamental of this review since it produces better quality soil with high strength and
durability than mechanical and physical techniques and therefore, throughout the rest of this report, the term soil
stabilization will mean chemical stabilization. In chemical stabilization soil is stabilized by adding different chemicals.
The main advantage of chemical stabilization is that setting time and curing time can be controlled.
2.1. LIME
Lime has been used as a soil stabilizer for roads from olden days. Lime is produced from natural limestone,
The type of lime formed is based upon the parent material and production process. There are five basic types of lime:
High Calcium quicklime CaO
Dolomite quicklime CaO + MgO
Hydrated High Calcium Lime Ca(OH)2
Normal hydrated Dolomite Lime Ca(OH)2 + MgO
Pressure Hydrated Dolomite Lime Ca(OH)2 +Mg(OH)2
Hydrated lime (also called slaked lime) is the most commonly mused lime for soil stabilization. Lime is also
used in combination with other admixtures, like fly ash, cement, bitumen for soil stabilization.
2.1.1. Type of Soil
Best results are obtained with clayey soils (20 to 40% and even 70%).
2.1.2. Quantity of Lime
Adding 2 to 3% lime immediately provokes a lowering of the plasticity of the soil and fragments lumps. For
ordinary stabilization purposes, the amounts generally used range from 6 to 12%, i.e. equivalent to the amounts of
cement used, but it should be noted that in the case of lime, there is an optimum quantity to be used for each type of
soil.
2.1.3. Chemical Reactions
Two types of chemical reactions take place when lime is added to wet soil. The first one occurring almost
immediately is a colloidal-type of reaction involving any of the following : (i) ion exchange of calcium for the ion
naturally carried by the soil, ii) a depression of the double layer on the soil colloids because of the increase in cation
concentration in the pore water, and (iii) an expansion of the double layer of the soil colloids from the high pH of the
lime..The second reaction takes considerable time in a cementing action. The cementing action, also called pozzolanic
action, is not completely understood, but is thought to be a reaction between the calcium from the lime with the
available reactive alumina or silica from the soil. (Lambe, 1962).
2.1.4. Effects
Soil plasticity, density and strength ate changed by the addition of lime to soil. Lime generally increases the
plasticity index of low plasticity soils and decreases the plasticity index of highly plastic soils. Because of reduction in
the plasticity of plastic soils, due to addition of lime, the soil becomes more friable and easy for handling in the field.
Addition of lime causes a reduction in the maximum compacted density and an increase in the optimum moulding
water content. In general, lime increases the strength of almost all types of soil.
500 80
28 days 28 days
70
400
Liquid limit
Liquid limit
60
300
50
(%)
(%)
200
40
100 30
0 2 4 6 8 10 12 14 0 2 4 6 8 10 12 14
Lime content (%) Lime content (%)
Variation in liquid limit with lime content for expansive soil and residual soil
220 70
190 28 days 28 days
60
160
Plastic limit
Plastic limit
50
130
40
(%)
(%)
100
30
70
40 20
0 2 4 6 8 10 12 14 0 2 4 6 8 10 12 14
Lime content (%) Lime content (%)
Variation in plastic limit with lime content for expansive soil and residual soil
Unconfined compressive strength
3500 3000
Unconfined compressive strength
3 days 3 days
3000 7 days 2500 7 days
21 days 21 days
2500
28 days 2000 28 days
2000
1500
1500
1000 1000
(kPa)
500 500
(kPa)
0 0
0 2 4 6 8 10 12 14 0 2 4 6 8 10 12 14
Lime content (%) Lime content (%)
Variation in unconfined compressive strength with lime content
2.1.5. Construction Procedure
Construction procedure of lime stabilized soil bases are similar to those employed for soil-cement with a
difference that more time is allowed for placement operations for lime. This relaxation is possible as the lime-soil
cementation reaction is a relatively slow one. Adequate care should be taken to prevent carbonation of the lime. The
normal construction sequence for lime stabilized bases is as follows: (i) Scarify the base, (ii) Pulverise the soil, (iii)
Spread the lime, (iv) Mix the lime and soil (v) Add water if necessary to bring to optimum moisture content, (vi)
Compact the mixture, (vii) Shape the stabilized base, (viii) Cure-keep moist and traffic free for at least 5 days, and
(x) Add wearing surface.
2.1.6. Advantages of Lime Stabilization
(i)Soil becomes more workable. (ii)Strength is generally improved.(iii)Lime stabilization increases the
compressive strength sometimes as high as 60 times. (iv)It is effective for soils.
2.1.7. Disadvantages of Lime Stabilization
(i)Lime is produced by burning of lime stone in kilns, so that it is harmful for environment. (ii)It needs
more cost to burnt lime stone. (iii)It is not effective for sandy soils. (iv)There is limited percentage of amount of lime
required about 2 to 10% of the soil.
2.2. CALCIUM AND SODIUM CHLORIDES
Both calcium and sodium chlorides as soil stabilizer react in some what similarly. Salt has been used in
recent years as additive in the construction of granular stabilized road wearing and base courses. The effect of salt on
soils is from (i) causing colloidal reactions, and (ii) altering the characteristics of soil water. Although calcium and
sodium chlorides act as oil flocculants, they are not as effective as other chemicals such as ferric chloride.
Most of the beneficial actions of salt in soil are mainly due to the changes salt makes in the characteristics of the water
in the soil .pores. These changes reduce the loss of moisture from the soil and are explained by the fact that the salts
(especially calcium chloride) are deliquescent and hydroscopic and lower the vapour pressure of water. Frost heave in
soil is reduced due to addition of salt by lowering the freezing point of water. As most of the benefits of salt are due to
the presence of the salt in the soil pore fluid, any loss of salt concentration may reduce the strength of the stabilized
soil. Thus the performance of salt stabilised soil depends on the amount of ground-water movement. Salt addition
shows a slight increase of maximum compacted density and a slight reduction in the optimum moulding water content.
2.2.1. Discussion
(i) Compaction test : The relation between dry density and moisture content for different salts (NaCl, MgCl 2,
CaCl2) and different moisture percentages (2%, 4%, 8%). The addition of salts to the soil increased the dry density and
the optimum moisture content. They attributed this behaviour to the fact that at low moisture content the soil structure
(before compaction) tends to change from edge-to-face type of flocculation to face-to face flocculation (salt
flocculation) with the increase in salt concentration. Consequently under the influence of dynamic compaction, the clay
particles become more oriented and the compacted dry unit weight increases with the increase in salt content. The
decrease in the optimum moisture content as the salt content increased may be explained due to the higher the face-to-
face flocculation the lower is the amount of water required for lubrication.
(ii) Atterberg limits : The liquid limit, plastic limit and plasticity index decreased as the salts contend increased
due to the decrease in the thickness of the diffused double layer as the salt content increased.
(iii) Unconfined compression test : The unconfined compressive stress-strain relationships of specimens, with
different salts and different moisture percentages. It can be seen that the increased in salt contents leads to an increase
in the unconfined compressive strength. The addition of salt to the soil causes an increase in the ion concentration of
the pore water with concomitant reduction in the double layer thickness and this, in turn, causes a reduction in the
antiparticles repulsion and an increase in the attraction, resulting in the increase in cohesion. The compaction effort
also effect the strength of the cohesive soil. The unconfined compressive strength increase with the increase in the
compaction effort. The results indicate that the maximum shear strength is found in the soil treated with calcium
chloride. The addition of CaCl2 to the soil cause hardening and more strength as compared to the soil specimens
containing other salts additives.
2.3. LIGNIN
Lignin is available both in the powder form and in the form of sulphite liquid. Lignin in both the forms has
been in use as an additive to the soil. for many years. Lignin is water-soluble, hence its stabilizing effects are not
permanent. In an attempt to improve the action of lignin, the chrome-lignin process was developed and studied by
Smith (1952). An insoluble gel is formed when sodium bi-chromate or potassium bi-chromate is added to the sulphate
waste. The effect of lignin on the soil properties is based on the form of lignin and the type of soil treated. Lignin acts
as an acid if not neutralised. It is also reported that lignin also reduces from heave.
2.4. WATFRPROOFERS
Fine grained soils show considerable strength when they are chi and lose the strength when consumes more
water. Water proofers ie chemicals which prevent or reduce the deleterious attack of water on soils, have proved to be
highly useful in stabilization techniques. Water proofers function as follows (Lambe, 1982): one end of the water
proofer molecule becomes preferentially adsorbed to, and then reacts with the soil surface; the other end of the
molecule, being hydrophobic, repels water and thus makes the soil mineral non-wettable by water. Water proofers
which are recognised as soil stabilizers are alkyl chlorosilanes, siliconates, amines, and quaternary ammonium salts.
Water proofers do not increase the strength of soils but rather help them to retain the natural strength in the presence of
water.
2.5. NATURAL AND SYNTHETIC POLYMERS
Polymers are long-chained molecules formed by the linking, i.e., polymerizing of certain organic chemicals
called monomers. Natural polymeric materials (like resins) and synthetic polymeric materials (like polyvinyl alcohol
(PVA)) have been used as soil stabilizers. There are two ways of chemical incorporation. In the first method,- the
monomer along with a catalyst (to cause polymerisation) is added which react between the soil and monomer. In the
second method, performed polymer is added to the soil in the form of a solid, a solution, or an emulsion, causing
reactions between the polymer and the soil. Lambe (1962) has presented a few of the resins (both natural and
synthetic), which have been used for soil stabilization, along with their applicability and the same is given below:
A. Natural Resins
(i) Vinsol Resin : Imparts almost no strength to Boil, but appears to waterproof the fine-grained soils
(ii) Rosin : When added to a soil and then reacted with certain metal salts forms Insoluble gels which aid
stabilization.
(iii) Resin Stabilizer 321: A rosin derivative ; reduces the rate and amount of water adsorption and furnishes sodium
ions for ion exchange
(iv) Stabinol : A rosin derivative mixed with portland cement ; waterproofs the coarser soils.
(v) NSP-121 and NSP-252 : Materials made by National Southern Products Co. ; have given some water repellency
to certain soils.
(vi) NVX : A product of the Hercules Powder Co., has given some water repellency to certain soils.
(vii) Shellac : Set obtained by evaporation of a solution of an ester of shellac with maleic acid or by evaporation of
solvent from a solution of shellac in alcohol. Sand treated with shellac can have high strength, but practically all
this strength is destroyed by water immersion.
B. Synthetic Resins
(i) Aniline-furfural. Waterproofs and imparts strength to soil.
(ii) Polyvinyl alcohol (PVA) Forms tough, flexible films when evaporated from aqueous solutions. Films are
water-soluble, and to date attempts to make them insoluble have been unsuccessful.
(iii) Polyvinyl Acetate : Gives very high strength to sand, practically all of which is destroyed by water
immersion.
(iv) Resorcinol formaldehyde : Gives some strength to sand, but much of it is lost by water immersion.
(v) Others : Urea furfural and phenol-furfural resins Phenol-formaldehyde cornbinations ; Urea-formaldehyde
resins; Calcium sulfamate-formaldehyde resins; Ethocel ; Methoylol ureas and melamine.
Among the vast number of synthetic polymers, calcium acrylate is of interest to soil engineers as it is the forerunner to
stabilization with water-sensitive polymers.
2.6. AGGREGANTS AND DISPERSANTS
Aggregants and Dispersants are materials that, at low treatment levels, make relatively modest changes in
the properties of fine grained soils. The function of aggregants and dispersants is alteration of electrical forces between
soil particles. Like portland cement, aggregants and dispersants do not cement adjacent particles. This structure altering
character affect many soil properties such as plasticity, permeability and strength. Although aggregants and dispersants
have been widely used in different industries, it is not frequently made use of in soil stabilization These chemicals have
high potentials for use in situations where only a modest improvement in Boil behaviour is needed. Since these
chemicals are relatively cheap, are effective at low treatment levels, and can be relatively easily incorporated, they can
permit comparatively low cost soil stabilization (Lambe, 1962).
A. Aggregants : These, are the materials which are capable gf increasing the net electrical attraction between fine
grained soil particles tending to aggregation or flocculation of the soil mass. Aggregants are of two types, viz, in
organic salts such as calcium chloride or ferric chloride and polymeric materials such as Krilium. In general the
salts are cheaper than the polymeric materials.
When salts are dissolved in the pore water of a soil, they generate cations and anions which can participate in
one or rnore of the following reactions (Lambe, 1962) :
(i) Exchange with soil ions.
(ii) Because adsorbed on the particles.
(iii) Furnish ions that can link particles (e.g. K+ can fit within the lattices of two adjacent clay sheets upon drying
to bond the sheets permanently together).
(iv) Increase the ion concentration, thereby reducing the electric repulsion between particles.
Using the above reactions, polymeric materials can also link the adjacent soil particles since the ends of the long
chain polymeric molecules can become attached to soil particles. As the action of an aggregant is due to more than one
of the possible mechanisms, it is difficult to assess the contribution of each.
If attraction between soil particles is increased, aggregants cause them to stick and form larger particles. The
sticking particles tend to arrange themselves in a random loose array. This random arrangement of particles with a
loose structure make the aggregants to increase soil permeability. By the aggregants treatment an increase in
permeability in the range of two to twenty fold can be obtained. By altering the permeability characteristics of a soil,
aggregants can influence the frost-heave behaviour of the soil.
Aggregants improve soil strength by reducing the electric repulsion between soil particles. For example, a
leached quick clay can regain strength by the introduction of salt (an aggregant) into the pores of the clay.
B. Dispersants : These are the materials which are capable of reducing the cohesion between fine-grained soil
particles and tend to cause them to disperse by increasing the electric repulsion between adjacent soil particles. A
wide variety of materials are available to use as dispersants and the most common ones are the phosphates,
sulphonates and versanates. Practically there is no difference in the effectiveness of the various dispersants.
Dispersants reacting with soils adopt the following three mechanisms (Lambe, 1962):
(i) Sequestration. The polyanionic part of the dispersant removes and insolubilizes any monovalent exchangeable.
(ii) Ion exchange. The dispersant furnishes monovalent ions for exchange reaction with the soil.
(iii) Anion adsorption. The dispersant furnishes polyanionic groups for adsorption by the soil particles.
of the above three mechanisms, the anion adsorption is the most important.
Dispersants decrease the particle size, that is, break down aggregates and increase the fluidity of a soil-
water system. In a dispersed soil system, adjacent particles do not tend to cohere to form aggregates, but repel each
other so they can be easily moved relative to each other. Thus by mechanical work, they can be forced into a mass
of high density. Denser sediments and sediments with particles in a more nearly parallel array, (that is a more tortuous
path for flow of water), dispersants cause reduction in soil permeability. The permeability reduction is of the order of
one-fifth to one-fiftieth of the original value.
Dispersants can be added to the soil by physically mixing or by injecting. Because of reduction in permeability due
to dispersants, there will be a tendency for frost susceptibility also.
2.7. MISCELLANEOUS CHEMICAL STABILIZER
There are several chemicals which are used for soil stabilization merely based on the abundant availability or
based on some theoretical principles. Among these materials are (Lambe, 1962): (i) Tung oil, (ii) Linseed oil, (iii)
Cotton seed oil, (iv) Castor oil, (v) Rubber latex, (vi.) Plasticized sulphur, (vii) Molasses, (viii) Mineral oil, (ix)
Sodium carbonate, (x) Calcium carbonate, (xi) Paraffin, (xii) Hydrofluoric acid, (xiii) Ionic detergents. These
chemicals are nowadays very sparingly used. Two other chemicals, viz., sodium silicate and phosphoric acid have
some special properties.
Alkalic silicates, especially sodium silicate, belongs to a group of inexpensive and versatile compounds. They are
used in soil stabilization both as additives to conventional stabilizers (e.g., cement) and as primary stabilizers. Silicates
derive their benefits because of their cementitious components. The most widely used form of silicate stabilization is
by injection.
Phosporic acid has proved as a potent stabilizer. The solidification is attained only by the phosphoric acid.
However the reaction can be improved by the addition of fluorine compounds as cure accelerators or inorganic salts as
waterproofers. Soils containing strong basic components do not respond to phosphoric acid treatment.
REFERENCES
1.Monowar Hussain and Sujit Kumar Dash, “The Influence of Lime on Compaction Behaviour of Soils”
Environmental Geotechnics, ICE, U.K, 2016.
2.Sujit Kumar Dash and Monowar Hussain “Lime Stabilization of soils-Reappraisal” Journal of Materials in Civil
Engg, ASCE, Vol. 24, No. 6, June 1, 2012
3.Bowles, J. E. (1982). Engineering Properties of Soil. Vol.2. New York: McGrawHill
4.Lambe, T.W. (1958). The structure of compacted clay. Journal of Soil Mechanics and Foundation. 84, 55-70.
5.Ground Improvement Techniques by Purushothama Raj.
6.Bell, F. G. (1988). “Stabilization and treatment of clay soils with lime, Part 1—Basic principles.” Ground Eng.,
21(1), 10–15.
7.Bell, F. G. (1996). “Lime stabilization of clay minerals and soils.” Eng. Geol., 42(4), 223–237.
