given by my sir

1. 01-Mar-19
1
GROUND
IMPROVEMENT
WITH
ADMIXTURES
Ground Improvement Methods
Dr. Shailen Deka
Tezpur University
SOIL ADMIXTURES
Anything that is added and mixed with soil to
modify some properties of soil:
 Mechanically and/or
 Chemically
The term means that the added material has to
be thoroughly mixed with the entire soil of layer
needed to be modified.
2

2. 01-Mar-19
2
INERT ADMIXTURES
 Chemically inert (relatively) admixtures are used if only
mechanical or physical properties are to be modified.
 The inert stabilizers do not react with the original soil
particles. They merely get evenly distributed in the
original soil matrix.
 They modify properties such as:
 Density
 Grain size distribution
 Porosity and permeability
 Shear strength and bearing capacity
3
INERT ADMIXTURES
A. Adding soil of different gradation to the original
soil. For example,
 Adding sand to gravels and cobbles – to fill up
the large voids, to increase density, to reduce
flow.
 Adding gravels to sand and silt – to introduce
large particles to increase shear strength.
 Adding clay to sand and gravels – to reduce
permeability.
 Etc.
4

3. 01-Mar-19
3
B. Adding industrial, municipal, or other waste.
1. Adding non-self-cementing fly ash (without lime
or without cement) or bottom ash
a. To coarse grained soil – to decrease pore volumes.
b. To clays – to reduce swell-shrink
2. Adding brick-bats or brick dust– to increase φ.
3. Adding coal dust or slags from burnt coal.
4. Adding ashes – wood ash, rice husk ash, etc.
INERT ADMIXTURES
5
5. Adding shredded tyre or tyre chips.
6. Adding plastic waste (hard) chips
INERT ADMIXTURES
Brick dustBrick bats Coal dust
Coal slag Rice Husk Ash Tyre chips
6

4. 01-Mar-19
4
 Chemical admixtures react with soil particles and
change the physical, engineering as well as chemical
properties of soil.
 Different types of chemical admixtures are:
 Lime
 Cement
 Industrial wastes like
 Coal Combustion Products (Fly Ash or Bottom Ash)
 Ground granulated blast furnace slag (GGBS)
 Phosphogypsum
 Cement kiln dust,
 Lime kiln dust, etc.
+ Combinations of two or more of the above
+ Other patented / marketed chemicals
CHEMICAL ADMIXTURES
7
LIME TREATMENT OF SOIL
 Lime treatment is done on clay soils or mix soils like clayey sand or clayey
silt.
 Both quick lime (CaO) and hydrated lime (Ca(OH)2) can be used.
 Generally 3-8% by weight of hydrated lime is mixed with the top layer of the
soil.
 Use of lime-soil mixture is not new. It is reported that the Greeks and
Romans used lime-soil mixtures.
 In modern times, lime was first used as a stabilizing agent of soil in 1924,
when some stretches of highways in the USA were strengthened by the
addition of hydrated lime.
 Now lime stabilization of clay soil is widely used throughout the world in
constructions such as
 subgrades and sub-bases for roads and airport pavements,
 embankments,
 as backfill for abutments and retaining walls,
 for improvement of soil beneath foundation slabs,
 in lime piles (deep treatment), etc.
8

5. 01-Mar-19
5
Lime helps to stabilise clay soil in the following ways:
 Modification of soil (Immediate)
► Heat of hydration (in case of quick lime): When quick lime comes in
contact with water, it hydrates to form hydrated lime. The reaction
produces heat, which vaporises some more water and reduces
moisture content of the soil.
► Cation exchange: Hydrated lime again dissociates in water to form
Ca2+ and OH- ions. Ca2+ ions replaces exchangeable cations like Na+
and K+ from between the clay plates. This produces stronger bonds
between the clay plates hindering expansion.
► Flocculation and agglomeration: Because of the Ca2+ ions, clay
particles form flocs and clusters increasing aggregate sizes.
 Stabilization (Long-term reactions)
► Pozzolanic reaction: The OH- ions increase the pH value of soil, which
starts pozzolanic reactions. It dissolves the silica (SiO2) and alumina
(Al2O3) particles and makes them react with Ca2+ ions to produce a
number of cementitious gels. Such gels sets (solidifies) as time
passes, binding the soil particles very strongly.
LIME TREATMENT OF SOIL
9
Clay structure before lime
treatment (dispersed)
Clay structure after lime
treatment (flocculated)
Cation Exchange:
In some clays, the inter-plate spaces are occupied by
cations (+ve ions) and water molecules. Exchangeable
monovalent cations like Na+ or K+ lodged between clay
plates are replaced by bivalent Ca2+ cations. This
increases the attraction between the plates and reduces
swelling.
LIME TREATMENT OF SOIL
10

6. 01-Mar-19
6
Results of soil modification with lime:
Modification reactions are immediate but reversible. Small
amount (1-3%) of lime is required for modification. In most clays
 Liquid limit decreases
 Plastic limit increases
 Plasticity Index decreases
 Swelling reduces
 Shear strength increases
 Optimum moisture content increases
 Maximum dry density decreases
 Clay becomes less sticky and more workable like granular soils.
 Permeability increases.
LIME TREATMENT OF SOIL
11
 Lime Stabilization (Pozzolanic Reaction): It continues for
months (and years). It is irreversible i.e. permanent.
 A pozzolan (or pozzolanic material) is a silicious or
aluminous material, which in itself possesses little or no
cementation value, but will, in finely divided form and in
the presence of moisture, chemically react with calcium
hydroxide at ordinary temperatures to form compounds
possessing cementitious properties.
 Most soils are compounds of silica or alumina or both,
and react with Ca(OH)2 solution.
 In sufficiently alkaline environment, SiO2 and Al2O3 get
dissolved from clay particles and react with Ca(OH)2
forming a series of complex compounds.
LIME TREATMENT OF SOIL
12

7. 01-Mar-19
7
POZZOLANIC REACTIONS OF CLAY
At pH>12,
Ca++ + SiO2 + H2O → Calcium silicate hydrate (CSH or C-S-H)
Ca++ + Al2O3 + H2O → Calcium aluminate hydrate (CAH or C-A-
H)
CSH and CAH are not chemical formulas, but the Cement
Chemists’ Notations (CCN) for some types of intermediate
materials, which with time combine with more water molecules
and set (or become hard). These are pozzolanic products.
Another type of pozzolanic product is Calcium aluminate
silicate hydrate (CASH).
13
Material CCN Notation
CaO C
SiO2 S
H2O H
Al2O3 A
Fe2O3 F
POZZOLANIC REACTIONS OF CLAY
CSH or CAH or CASH are gels, they surround and bind the
remaining soil particles. After solidification, the stabilized
material becomes very hard. It gives a lot of shear strength.
CSH or CAH or CASH are also formed when water is added to
cement.
CSH gels seen under electron microscope
14

8. 01-Mar-19
8
Lime Fixation Point or Initial Lime Consumption:
 Initial lime-soil reactions occur within about 1 hour of mixing.
 When lime is added to a clay soil, it must first satisfy the affinity of the
soil for lime, that is, ions are adsorbed by clay minerals and are not
available for pozzolanic reactions until this affinity is satisfied.
 Since the lime is fixed in the soil and is not available for other reactions,
the process has been referred to as lime fixation.
 The lime fixation point corresponds with the point where further addition
of lime does not bring about further changes in the plastic limit.
 This is the optimum addition of lime needed for maximum modification
of the soil and is normally between 1 and 3% of lime added by weight.
 Beyond this point lime is available to participate in the pozzolanic
reactions.
 Rule of thumb on the quantity of lime to be added: 1% by weight of lime
for each 10% of clay in the soil (Bell, 1996).
POZZOLANIC REACTIONS OF CLAY
15
Lime required for initiating pozzolanic reaction:
 The lowest percentage of lime that gives a pH of 12.4 is the
approximate lime percentage for stabilizing the soil. There may be
soils in which the pH is greater than 12.4. If this occurs select the
lowest percentage of lime where the higher pH value does not rise
for at least two successive test samples at increasing lime
percentages” (ASTM 6276).
 Lime may be added to soil at different percentages (e.g. 1%, 2%, so
on). For each sample, a slurry is to be made by adding 5 times water
by weight of soil. The pH value is tested by a pH meter after 1 hour
and a curve like the following is obtained. The lime percentage
beyond which there is no increase in pH value is the minimum
percentage of lime required to initiate pozzolanic reactions. More
lime than this is required to sustain the reaction.
POZZOLANIC REACTIONS OF CLAY
Lime (%)
pH
16

9. 01-Mar-19
9
Whether to modify or stabilize soil:
The choice depends on the purpose.
 Modification is chosen if the purpose of treatment is only to make
the soil workable, or to stop swelling, or increase permeability, and
NOT increase of strength and bearing capacity.
 Stabilization is adopted if increase in strength is essential. For
example, to increase the strength of subgrade for a road or airport
pavement.
 For stabilization, strength gain is measured by conducting
unconfined compression (UC) tests on lime-treated soil samples
cured for sufficient days.
 For stabilization, a strength gain of at least 350 kPa over the
original strength of soil is desirable for 5% lime addition and 48
hours curing.
CHOICE OF MODIFICATION OR STABILIZATION
17
STRENGTH GAIN FROM STABILIZATION
0
1000
2000
3000
4000
5000
6000
7000
8000
0 2 4 6 8
Unconfinedcompressivestrength(kPa)
Lime content (%)
1 day 7 days
30 days 90 days
The figure shows
strength gain of
lime-stabilized soil
obtained from
actual tests on a
particular soil.
• Strength
increases with
lime content.
• Strength
increases with
curing period.
18

10. 01-Mar-19
10
LIME APPLICATION IN FIELD
19
Steps in Lime Application:
• scarifying or partially pulverizing soil,
• spreading lime,
• adding water and mixing,
• compacting to maximum practical
density, and
• curing prior to placing the next layer or
wearing course.
Scarifying before lime appln
Lime spreading Scarifying after lime spreading
20
LIME APPLICATION IN FIELD
Adding water after lime application
Mixing soil, lime and water
thoroughly using rotary mixer
Initial compaction
using sheepfoot
or padfoot roller
Final compaction
using smoothwheel
roller

11. 01-Mar-19
11
ADVANTAGES AND DISADVANTAGES OF DIFFERENT LIME
APPLICATIONS
(Source – National Lime Association, USA)
The type of lime stabilization technique used on a project should be
based on multiple considerations, such as contractor experience,
equipment availability, location of project (rural or urban), and
availability of an adequate nearby water source.
Some of the advantages and disadvantages of different lime application
methods follow:
A. Dry hydrated lime:
Advantages: Can be applied more rapidly than slurry. Dry hydrated lime
can be used for drying clay, but it is not as effective as quicklime.
Disadvantages: Hydrated lime particles are fine. Thus, dust can be a
problem and renders this type of application generally unsuitable for
populated areas.
21
B. Dry Quicklime:
Advantages: Economical because quicklime is a more concentrated form of
lime than hydrated lime, containing 20 to 24 % more “available” lime oxide
content. Thus, about 3 % quicklime is equivalent to 4 % hydrated lime
when conditions allow full hydration of the quicklime with enough moisture.
Greater bulk density requires smaller storage facilities. The construction
season may be extended because the exothermic reaction caused with
water and quicklime can warm the soil. Dry quicklime is excellent for drying
wet soils. Larger particle sizes can reduce dust generation.
Disadvantages: Quicklime requires 32 % of its weight in water to convert to
hydrated lime and there can be significant additional evaporation loss due
to the heat of hydration. Care must be taken with the use of quicklime to
ensure adequate water addition, mellowing, and mixing. These greater
water requirements may pose a logistics or cost problem in remote areas
without a nearby water source. Quicklime may require more mixing than
dry hydrated lime or lime slurries because the larger quicklime particles
must first react with water to form hydrated lime and then be thoroughly
mixed with the soil.
22
ADVANTAGES AND DISADVANTAGES OF DIFFERENT LIME
APPLICATIONS

12. 01-Mar-19
12
C. Slurry Lime:
Advantages: Dust free application. Easier to achieve even
distribution. Spreading and sprinkling applications are
combined. Less additional water is required for final mixing.
Disadvantages: Slower application rates. Higher costs due to extra
equipment requirements. May not be practical in very wet
soils. Not practical for drying applications.
23
ADVANTAGES AND DISADVANTAGES OF DIFFERENT LIME
APPLICATIONS
LIME COLUMNS
Lime columns (or lime piles)
are insertions into soil, similar
to pile groups and SCP/GCP.
Boreholes are made into soil
in a rectangular grid, and
these are filled with lime,
usually CaO.
They are suitable for treatment
of compressible clay layers.
Unlike lime treatment of
surface soil, where the depth
of treatment is 300-600mm,
lime columns can treat clay
layers several meters deep.
24
 The method was
first used by Broms
and Bomans (1975,
1979).

13. 01-Mar-19
13
Installation:
25
LIME COLUMNS
Lime columns have the following effects on the
adjacent soil:
a) Consolidation / dewatering effect
Quick lime, CaO, absorbs water from the surrounding soil,
causing the lime to swell and forms slaked lime, Ca(OH)2 as
per the following chemical reaction
CaO + H2O → Ca(OH)2 + 15.6 Kcal/mol
b) Ion exchange effect
c) Pozzolanic effect
Ions travel from lime columns to the surrounding soil and cause
effects b and c.
26
LIME COLUMNS

14. 01-Mar-19
14
As a result of the above effects, the surrounding soil
→get consolidated faster,
→increase in density,
→gets modified and stabilized.
As consequences,
Shear strength increases
Bearing capacity increases
Future settlement reduces
The lime columns and the included soil behave as a
composite foundation system like pile group for load
transfer.
27
LIME COLUMNS
CHOICE OF ADMIXTURE FOR TREATMENT
A. For modification:
 Lime: For soils with PI ≥ 5% and more than 35% particles passing
through 75μ sieve.
 Fly ash and lime fly ash blends: For soils with 5% < PI < 20% and
more than 35% particles passing through 75μ sieve.
 Cement and/or Fly ash: For soils with PI < 5% and not more than
35% particles passing through 75μ sieve.
B. For stabilization:
 Lime: For soils with PI > 10% and clay content (2μ) > 10%.
 Cement: For soils with PI ≤ 10% and less than 20% particles through
75μ sieve.
28

15. 01-Mar-19
15
CEMENT TREATMENT OF SOIL
►Ordinary Portland cement (OPC) is used to stabilize soil
►Cement binds soil particles in the same way as lime does
through pozzolanic reactions.
►However, cement has less free lime compared to lime. So,
the variety of reactions is less in cement treatment of clay
soils. Lime treatment is therefore more effective than
cement treatment of clay soil. Moreover, clays which have
high affinity for water reduces water availability for cement
hydrations, so pozzolanic reactions may not be complete.
►Cement has shorter hydration and setting time than lime.
►Cement contains both lime and pozzolans (silica, alumina) in
it. Only water needs to be added for starting pozzolanic
reactions.
29
Typical constituents of Ordinary Portland cement
30
CEMENT TREATMENT OF SOIL
Constituent CCN Mass %
Calcium oxide, CaO C 61-67%
Silicon oxide, SiO2 S 19-23%
Aluminum oxide,
Al2O3
A 2.5-6%
Ferric oxide, Fe2O3 F 0-6%
Sulfate 1.5-4.5%

16. 01-Mar-19
16
Intermediary chemical components of OPC:
Cement Hydration Products: Similar to lime hydration products:
 CSH
 CAH
 CASH
31
CEMENT TREATMENT OF SOIL
Intermediary components CCN Mass %
Tricalcium silicate (CaO)3 · SiO2 C3S 45-75%
Dicalcium silicate (CaO)2 · SiO2 C2S 7-32%
Tricalcium aluminate (CaO)3 · Al2O3 C3A 0-13%
Tetracalcium aluminoferrite (CaO)4 ·
Al2O3 · Fe2O3
C4AF 0-18%
Gypsum CaSO4 · 2 H2O 2-10%
Cement treated soil is called Soil-Cement or cement
modified soil (CMS).
Soil cement is often used in preparation of pavement
subgrade, sub-base, base and shoulders.
Minimum cement required for modification: approx. 4%
by weight of soil.
Minimum cement required for stabilization: Depend on
the type of soil and type of road. For roads with light
traffic, it may be 3-5%. For high traffic and heavy axle
load, it may be 7-10% by weight of soil.
32
CEMENT TREATMENT OF SOIL