chapter-2

Assessment of Soil Stabilization Using Fly Ash and Rice Husk Ash

CHAPTER-2

LITERATURE REVIEW

Of recent soil stabilization techniques using fly ash in construction of pavements

were successful. Since then quite a lot of research work has been done on the behaviour

of fly ash and different types of soils available locally. Some of earlier field trails are

Narendrakumaret.al., BHU, Varanasi(1996)in their research on USE OF FLY ASH IN

SOIL STABILIZATION FOR ROADS studied the effects of different mix proportions

of lime and fly ash on compaction,CBR. Atterberg limits and unconfined strength

properties Of the Local soil Varanasi to evaluate the suitability of fly ash-soil lime as

abase and sub base materials for the roads. The improvement in CBR values and

unconfined compressive strength compressive strength gives promising results.

The investigation using fly ash from OBRA thermal power station show that tests

gave good results when soil was stabilized with 15%of lime and fly ash proportions of

1:3 Different proportions enabled on increase in the CBR value from 4 to 20.7 and the

unconfined compressive strength from 134 kN/m2to 680kN/m2.

2.1 Sinhaet.al., CBRI. Roorkee (1998) have worked out the “BULK

UTILIZATION OF FLY ASH AS GEO-MATERAL FOR CONSTRUCTION OF

EMBANKMENTS.”In their laboratory investigations the selected soil samples having

maximum dry density ranging from 16 to 19 kN/m3 and OMC 35.8% and 29.25. the

results of homogeneously mixed soil- fly ash i.e. 20 to 45% by weight is found possible

to utilize as a geometrical for the construction of embankment depending on the type of

soil and quality of fly ash. Their conclusions are

The bulk utilization of fly ash as geometrical revealed an insight into construction of

earthen embankments admixing with fly ash in a large quantity and it may help to

consume large quantities of fly ash.

The compaction characteristics of soil-fly ash mixed homogeneously indicated the

utilization of 20 to 15% of fly ash by weight depending on type soil and quality of fly

ash.

DEPARTMENT OF CIVIL ENGINEERING Page 9 SVIST,KADAPA(YSR)


2.2 J Prabakar et.al.., SERC, Chennai (2004) has worked out on the

“INFLUENCE OF FLY ASH ON STRENGTH BEHAVIOR OF TYPICAL

SOILS.”

Construction of any infrastructure over a weak or soft soil is highly typical on the

geo-technical grounds as the soil undergoes differential settlements, poor shear strength

and high compressibility. Normally, the type of foundations varies depending upon the

availability of soil strata as well as cost involvement. Sometimes, it is essential to have a

high rise building over a weak soil, in such conditions, improvement of load bearing

capacity of soil is very much essential. In these aspects, improvement of load bearing

capacity of soil has been improved by adopting various techniques like spoil stabilization,

adoption of reinforcement etc. generally, admixing technique in soil has an effective

ground improvement because of its easy adaptability. Therefore, in this study its

describes the behavioural aspects of soils mixed with fly ash to improve the load bearing

capacity of soil. Three different types of soil have been considered using different

percentage of fly ash ranging from 9 to 46% by weight of soil. The main objectives of

this study is to assess the usefulness of fly ash as a soil admixture, and focused to

improve the engineering properties of soil to make it capable of talking more load from

the foundation structures. This study also benefits the effective use of fly ash and thus

cost effective method for improving the soil properties.

Specific gravity for soil-A ranging from 2.303 to 1.860, soil-B ranging from 2.23

to 1.96 and soil-C ranging from 2.30 to 1.83.maxim dry density is recording for soil free

from fly ash where it ranges from 1.775 to 1.760 g/cc and maximum dry density is lowest

in the case of 100% fly ash. The CBR values of pure soils are 4.7, 2.03 and 3.53: by

adding fly ash up to 46% the CBR value is increased up to 11.41.

Their conclusions are

Addition of fly ash reduces the dry density of soil due to the low specific gravity

and unit weight of soil. The reduction in dry density can be in the order of 15 to

20%.



The maximum value of cohesion is obtained as 0.39 in case of lorny soils and

0.66 kg/cm2 in the case of clayey soil.

The void ratio and porosity varies by the increasing amount of fly ash in soils.

Bye adding fly ash up to 46% the void ratios of soils can be increased by 25%.

CBR value of soil can be improved by the addition of fly ash as compared to pure

soil which would be beneficial especially for pavements etc. based on the

extensive experimental study carried out, it was noticed that the shear strength

and the angle of internal friction of soil admixed with fly ash gives hatter strength.

Introduction of fly ash in soil reduces swelling in the soil. Swelling is reduced by

increasing amount of fly ash. Further increasing amount of fly ash in soils leads to

further reduction in swelling. This is due to non- expansive characteristics of fly

ash, and the particle size and shape of fly ash, which leads to the conclusion that

the swelling behaviour of the soil can be effectively controlled by the addition of

fly ash.

From this study, the fly ash may be effectively utilized in soil to get improvement

in shear strength, cohesion and thus improvement in the bearing capacity. Fly ash

addition in soil can be effectively used the base materials for the roads, back

filling and improvement of soil bearing capacity of any structure.

2.3 ZaliheNalbantouglu, (2004) has worked out on the “EFFECTIVENESS OF

CLASS C FLY ASH AS AN EXPENSIVE SOIL STABILIZER”. Fly ash produced

in the combustion of sub-bituminous coals exhibits self – cementing characteristics and

can be used in wide range of stabilization applications. Fly ash treatments can be used in

wide range of stabilization applications. Fly ash treatment can effectively reduce the

swell potential of high plastics clays and prevent the swell beneath the smaller

foundation of expansive soils. These soils present problems in construction and possess a

variety of undesirable characteristics such as low strength , high plasticity, difficulty

compaction and high swell potential. Laboratory test results on these soils indicate that

fly ash is effective in ameliorating the texture and plasticity of the fly ash treated soils by

reducing the amount of clay size particles, plasticity index and the swell, potential.

Caution exchange is one of the important reactions responsible for the improvement in



the soil characterisitics. In the study, caution , exchange capacity (CEC) values have

been used to indicate the plasticity and water absorption potential. Their conclusions are

The fly ash treatment is effective in improving the plasticity of degirmenlik and tuzla

soils. The crossing of the A- line from the clayey region to the silty region occurred

in both soils.

The reduction in the swell pressure values of both soils indicates that the swelling of

the soils is prevented under smaller pressure values. Thus high swell potential values

are not expected beneath the smaller foundation pressures.

The reduced CEC values indicate that fly ash treatment causes changes in the

mineralogy of the treated soils and produces the new secondary reaction minerals.

The formation of these new pozzolanic reaction products causes the soils to became

more granular and result in less water absorption potential.

Utilization of fly ash as a stabilization material for soil appears to be of many viable

answers for handling the fly ash waste problem. Since there is much more fly ash

that is disposed of rather than utilized, making more productive use of fly ash would

have considerable environmental benefits, reducing land, air and water pollution.

2.4 AykutSenolet.al., (2006) has worked out on the “SOFT SUBGRADES

STABILIZATION BY USING VARIOUS FLY ASHES”. This publication presents

the results of research involving different types of self-cementing fly ashes without any

other activators for the stabilization of four different types of soft sub grades from various

road sites in Wisconsin, USA. The strength approaches were applied to estimate the

optimum mixture design and to determine the thickness of the stabilized layer. The

stabilized soil samples were prepared by mixing fly ash at different contents at varying

water contents. The performance of fly ash stabilized sub base depends both on the

specific source of fly ash and the engineering properties of soils. It is suggested that the

performance analysis of fly ash should be based upon the laboratory tests such as index

properties. Compaction, unconfined compressive strength and CBR tests of specific site.

This is suggested rather than using the study of the physical properties and chemical

composition of fly ash and soil. As disclosed in the literature, the strength gain due to

stabilization of fly ash and soil. As disclosed in the literature, the strength gain due to



stabilization depends up on three factors: ash content, moulding water content and

compaction dely. The samples were subjected to unconfined compression strength and

California bearing ratio (CBR) tests after 7 days curing time to develop water content-

strength relationship. To evaluate the impact of compaction delay that commonly occurs

in the field during construction, the sets of samples were compacted 2 hours later after

mixing with water. The unconfined compression strength and CBR tests were performed

and used to determine the thickness of the stabilized layer in pavement design. All of

these factors were taken into account throughout this research. Their objective of this

research was

To quantify the effect of fly ash stabilization on four different types of soft sub grades

encountered using locally available fly ash in Wisconsin.

The improvement in engineering properties of soft sub grades such as unconfined

compressive strength and CBR was investigated.

Soil-fly ash mixtures were prepared at different fly ash contents (10-20%) with the

specimens compacted at optimum water content and about 7% wetter than the optimum

water content.

Unconfined compression strength and CBR tests were then performed on these mixtures.

The fly ash stabilization increased both the unconfined compressive strength, and the

CBR values substantially for the mixtures tested and have the potential to offer an

alternative for soft sub-grade improvement of highway construction.

The research has shown that stabilizing the soft sub-grade at specified water contents and

minimizing compaction delay in the field could maximize the strength of fly ash-

stabilized soils.


chapter-2

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