Kuliah 11 (Chapter 13-Modifification by Admixtures)

7/24/2019 Kuliah 11 (Chapter 13-Modifification by Admixtures)

1/18

CHAPTER 13

MODIFICATION BY ADMIXTURES


2/18

Terminology, Con!r"#!ion Te#$ni%"e, &n'

Ty(i#&l UeThis chapter deals with modifying soils by the mechanical

addition of granular materials or chemical compounds such as

cement, lime, bitumen, and calcium chloride.

The purpose:Increase strength

Reduce deformability

Provide volume stability

Reduce permeability

Reduce erodibility

Increase durability

Control variability


3/18

Improving the engineering properties of a soil by admixtures is often referred

to as soil stabiliation.

!oil additives may help to:

"nhance subgrade or subbase properties in order to reduce the re#uired

overall pavement thic$ness.

Improve trafficability on construction sites

Prepare the ground for shallow foundations

!tabilie slopes by improving the soil%s shear strength

Reduce erosion by surface runoff or internal seepage &piping'

Construct emban$ments

(orm load)bearing columns &in situ'

Improve the wor$ability of borrow materials

Reduce traffic)generated dust

Contain haardous wastes

Rehabilitate polluted or mined ground

*ifferent ways of mixing additives with soil are illustrated in (igure +.+.


4/18

Fig"re 13)1 E*&m(le o+ ro"n' Mo'i+i#&!ion -i!$ A'mi*!"re


5/18

!tabiliation with admixtures is distinguished from

grouting by the fact that the in situ soil is at least

partially remolded during construction process. The additive is usually in the form of a pulveried solid

or thic$ slurry, rather than a viscous li#uid as in

grouting.

In-ecting grout increases the density of a soil by fillingits existing voidsor by displacing and compressing the

surrounding ground.

In contrast, mixing soil with additives li$e lime oftencreates additional voids nevertheless, chemical and

physical reactions still ensure increase ground strength

and reduced compressibility.


6/18

Ty(e o+ A'mi*!"re . T$eir E++e#! on Soil

Pro(er!ie

The most common artificial additives are: Portland cement

/ime

0itumen and tar


7/18

r&n"l&r A'mi*!"re

n

D

dp

=+11

where:

p 2 percentage passing the sieve with aperture d

* 2 maximum particle sie

n 2 exponent

(or most soils used in pavement construction, densest particle

pac$ing is achieved when 3n4 is in the range of 1.56 to 1.6well

graded soil.

The strength coarse)grained materials is largely related to their

density, which in turn depends significantly on the particle sie

distribution. 7aximum density is obtained in soils which have a

particle sie distribution which can be approximated by

&899!R9, +;


8/18

Por!l&n' Cemen!

!oil with cement admixtures are generally termed

cement)stabilied or cement)treated. 7itchell &+=


9/18

"ngineering 0enefits of Cement !tabiliation

L

fm

SSE =

@here:

!f 2 the strength of the soil mixed in the field

!/2 the strength of the soil mixed in the laboratory

>ood construction procedures may result in efficiencies in excess

of ;1A.

Typical cement contents in soil stabiliation range from ? to +1A.

7a-or gains in the cement treatment of soils are:Increased strength B stiffness

0etter volume stabilityIncreased durability

The mixing efficiency "m :


10/18

/ime

/ime is used in the form of #uic$lime, Ca, or hydratedlime, Ca&D'?. 9 third version of lime, CaC,, is used

for agricultural purposes only.

Ion CaEE 7gEE 8aE FaE.


11/18

Soil 0 /ime C&O2 Re!ion

!hort)term reactions include hydration &for #uic$lime'

and flocculation &ion exchange'. /onger)term reactions are cementation and carbonation.

Dydration: This drying action is particularly beneficial inthe treatment of moist clays.

(locculation: @hen lime is mixed with clay, sodium and

other cations &E ion' adsorbed to the clay mineral

surfaces are exchanged with calcium./ime causes clayto coagulate, aggregate, or flocculate. The clay%s

plasticity is reduced, ma$ing it more easily wor$able and

potentially increasing its strength and stiffness.


12/18

Cementation: The clay)lime reaction removes silica

from the clay mineral lattice to form products not

unli$e those of cement hydration. Cementation is the

main contributor to the strength of the stabilied soil.

Carbonation: Reaction of lime with carbon dioxide

&C?' in the open air or in voids of the ground forms

a relatively wea$ cementing agent.


13/18

Engineering Bene+i! o+ /ime S!&ili4&!ion

1) Im(ro5e' -or6&ili!y7

o.

@or$ability is improved because flocculation ma$esthe clay more friable.

o.The plasticity decreases, mainly because of an increase

in the plastic limit.

o.The // may increase or decrease, depending on the

type of soil &(ig. +.5'.

o./ime increases the optimum water content for

compaction. The maximum dry density achieved with aparticular compactive effort is reduced &(ig. +.6'. The

compaction curve for lime)treated clay is flatter, which

ma$es moisture control less critical and reduces the

variability of the density produced.


14/18


o In the first few hours after mixing, lime additives

cause a steady increase in strength, but a slower ratethan cement. The need for compaction immediately

after mixing is less critical for lime than cement &(ig.

+.


15/18


8) In#re&e S!reng!$7

/ime increases the strength of a clayey soil, typicallydemonstrated in term of unconfined compressive strength

or C0R test results.

3) In#re&e 9ol"me S!&ili!y7

Improved volume stability means reduce shrin$age andswell upon drying and wetting, respectively. 9 typical

result of a shrin$age and swelling test is shown in (ig.

+.=.

:) In#re&e (erme&ili!y7

It could mean better drainage and less pore pressure

buildup under load.


16/18

C&l#i"m C$lori'e

Calcium Chloride &CaCl?' has been used in highway

construction and maintenance since early ?1thcentury.

Today, CaCl?still has a variety of uses, but it isprobably

most appreciated as a dust palliative on highly traffic$ed

unpaved roads, such as haul roads in mining and onlarge earth)moving pro-ects.


17/18

Fly A$

(ly ash is a solid waste product created by the

combustion of coal.

nly +6 to ?1A of fly ash produced in the G!9 in +;

Kuliah 11 (Chapter 13-Modifification by Admixtures)

Documents

Transcript of Kuliah 11 (Chapter 13-Modifification by Admixtures)