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PHYSICAL AND GEOTECHNICAL PROPERTIES OF COAL ASH

Tony Kismoor Anak Sasak

Bachelor of Engineering with Honours (Civil Engineering)

2006

Faculty of Engineering

UNIVERSITI MALAYSIA SARAWAK

R13a BORANG PENGESAHAN STATUS TESIS

PHYSICAL AND GEOTECHNICAL PROPERTIES OF COAL ASH

SESI PENGAJIAN: 2005/2006

TONY KISMOOR ANAK SASAK Mengaku membenarkan tesis *ini disimpan di pusat Khidmat Maklumat Akademik, Universiti Malaysia Sarawak dengan syarat-syarat kegunaan seperti berikut: 1. Tesis adalah hakmilik Universiti Malaysia Sarawak. 2. Pusat Khidmat Maklumat Akademik, Universiti Malaysia Sarawak dibenarkan membuat salinan untuk tujuan pengajian sahaja. 3. Membuat pendigitan untuk mambangunkan Pangkalan Data Kandungan Tempatan. 4. Pusat Khidmat Maklumat Akademik, Universiti Malaysia Sarawak dibenarkan membuat salinan Tesis ini sebagai bahan pertukaran antara institusi pengajian tinggi. 5. ** Sila Tandakan ( ) di kotak yang berkenaan

Disahkan oleh (TANDATANGAN PENULIS) (TANDATANGAN PENYELIA) 721, Lrg 16, Tmn Desa Wira, Jalan Batu Kawa, 93250 Kuching, S’wak.

22nd May 2006

Judul:

Saya:

SULIT TERHAD TIDAK TERHAD

(Mengandungi maklumat yang berdarjah keselamatan atau kepentingan Malaysia seperti yang termaktub di dalam AKTA RASMI 1972).

(Mengandungi maklumat TERHAD yang telah ditentukan oleh organisasi/badan di mana penyelidikan dijalankan).

Alamat tetap:

Tarikh:

DR. PRABIR KUMAR KOLAY

Nama Penyelia Tarikh:

CATATAN * Tesis dimaksudkan sebagai tesis bagi Ijazah Doktor Falsafah, Sarjana dan Sarjana Muda. ** Jika tesis ini SULIT atau TERHAD, sila lampirkan surat daripada pihak berkuasa/organisasi berkenaan dengan menyatakan sekali sebab dan tempoh tesis ini perlu dikelaskan sebagai SULIT dan TERHAD.

The Following Final Year Project Report:

Title : PHYSICAL AND GEOTECHNICAL PROPERTIES OF

COAL ASH

Name : TONY KISMOOR ANAK SASAK

Matrix Number : 9264

has been read and approved by:

DR. PRABIR KUMAR KOLAY Date (Supervisor)

i

ACKNOWLEDGEMENTS

The author would like to thank the project supervisor, Dr. Prabir Kumar

Kolay for his guidance, support and precious knowledge along the implementation of

the project.

The author also takes this opportunity to thank the laboratory assistants of

Civil Engineering Program, Faculty of Engineering, Universiti Malaysia Sarawak and

the staffs of Sejingkat Thermal Power Plant for their supply of coal ash samples and

their cooperation very much appreciated.

The author is very grateful to his family, who are always give their countless

support and guidance that will always bear in mind.

Finally, not forgetting to the author’s friends Bertram, Domincie and Eugene

who are involved directly and indirectly in helping for the completion of this project.

iv

TABLE OF CONTENTS

CONTENTS PAGE

APPROVAL LETTER

APPROVAL SHEET

TITLE PAGE

ACKNOWLEDGEMENTS i

ABSTRACT ii

ABSTRAK iii

TABLE OF CONTENTS iv

LIST OF TABLES vii

LIST OF FIGURES viii

LIST OF NOMENCLATURES ix

CHAPTER 1 INTRODUCTION 1

CHAPTER 2 LITERATURE REVIEW

2.1 General 6

2.2 Physical properties 6

2.2.1 Particle Size Distribution (PSD) 7

2.2.2 Atterberg limits 9

2.2.3 Specific gravity (Gs) 11

2.2.4 Loss on Ignition (LOI) 12

2.3 Geotechnical properties 13

v

2.3.1 Compaction 13

2.3.2 Consolidation 15

2.3.3 Shear strength 16

2.4 Critical appraisal 18

2.5 Scope of study 19

CHAPTER 3 MATERIALS AND TEST PROCEDURE

3.1 General 20

3.2 Test materials 20

3.3 Test procedure 21





3.3.5 Compaction 24



CHAPTER 4 RESULTS AND DISCUSSION

4.1 General 26

4.2 Physical properties 26

vi





4.3 Geotechnical properties 31

4.3.1 Compaction 31



CHAPTER 5 CONCLUSION AND RECOMMENDATION

5.1 Conclusion 39

5.2 Recommendation 41

REFERENCES 42

APPENDIX

vii

LIST OF TABLES

TABLE PAGE

Table 1.1 Energy used in electric power plant in Malaysia 2

Table 2.1 Strength parameters from direct shear tests and effective

strength parameters from triaxial tests

18

Table 3.1 Designation of the coal ash sample collected from

thermal power plant

21

Table 4.1 Particle size distribution of coal ashes 28

Table 4.2 Specific gravity (Gs) of different types of coal ash 29

Table 4.3 Liquid limit for coal ash samples 29

Table 4.4 Loss on Ignition (LOI) for coal ashes 30

Table 4.5 Physical properties of different types of coal ash samples 31

Table 4.6 Optimum Moisture Content (OMC) and maximum dry

density for coal ashes

32

Table 4.7 Compression index (Cc) of coal ashes 34

Table 4.8 Strength parameters from direct shear test (peak values) 37

Table 4.9 Geotechnical properties of different types of

coal ash samples

38

viii

LIST OF FIGURES

FIGURE PAGE

Fig. 2.1 Size distributions of fly ash particles determined using (a)

Optical microscopy and (b) Sieving (Thipse et al., 2002)

8

Fig. 2.2 Comparison of liquid limit obtained by Ko stress method and

Cone penetration method (Sridharan et al., 2000)

10

Fig. 2.3 Standard Proctor compaction curve for the fly ash

(Gangadhara et al., 1998)

14

Fig. 2.4 Void ratio-pressure relationship for coal ash (Pandian, 2004) 15

Fig. 2.5 Consolidation pressure-void ratio curves for fly ashes

(Pandian and Balasubramonian, 1999)

16

Fig. 4.1 Grain-size distribution of different types of coal ashes 27

Fig. 4.2 Standard Proctor curve for different types of coal ashes 32

Fig. 4.3 Void ratio (e)-pressure (log P) relationship for coal ashes 33

Fig. 4.4 (a) Stress-strain characteristics for fly ashes 35

Fig. 4.4 (b) Stress-strain characteristics for pond ash 35

Fig. 4.4 (c) Stress-strain characteristics for bottom ashes 36

Fig. 4.5 Shear strength envelopes for coal ashes sample 37

ix

LIST OF NOMENCLATURES

µm micrometer

mm millimeter

Ko equilibrium water content at a known vertical stress

Gs specific gravity

D10 diameter corresponding to 10% finer



Cu uniformity coefficient

Cz coefficient of curvature

gm/cc gram per cubic centimeter

Cc compression index

cm/s centimeter per second

cm centimeter

mm millimeter

° degree

kPa kilo Pascal

ϕp peak angle of internal friction

cp peak cohesion

x

ϕ angle of internal friction

c cohesion

γd dry unit weight

ε strain

e void ratio

τ shear stress

P pressure (kN/m2)

ii

ABSTRACT

The present thesis aimed at studying the physical and geotechnical properties

of locally available coal ash. To accomplish this study, three types of coal ash (i.e.,

fly ash (FA-1 and FA-2), pond ash (PA) and bottom ash (BA-1 and BA-2)) have been

collected from Sejingkat Thermal Power Plant, Kuching, Sarawak, Malaysia.

Different physical and geotechnical tests have been conducted for these coal ash

samples and the results reveal that fly ash is silt-sized particle about 83.00 to 89.00%,

pond ash consist of silty-sand particle and bottom ash sand-sized particle about 83.50

to 84.50%. The specific gravity (Gs) of the coal ash tested ranges form 2.07 to 2.32.

The liquid limit and LOI for bottom ash is higher as compared to fly ash and pond

ash. The Optimum Moisture Content (OMC) and maximum dry density for coal ashes

vary from 17.50 to 36.50 % and 1.13 to 1.56 gm/cm3, respectively. The values of

compression index (Cc) for coal ashes vary from 0.049 to 0.113 and the bottom is

much more compressible than pond ash and fly ash. The shear strength parameters

(i.e., angle of internal friction (φ) and cohesion (c)) vary from 26.21 to 34.89° and

0.14 to 8.05 kN/m2, respectively and the fly ash has the higher value of angle of

internal friction and the cohesion value, followed by pond ash and bottom ash.

iii

ABSTRAK

Kajian ini adalah berkaitan dengan pengkajian tentang ciri-ciri fizikal dan

geoteknikal abu arang batu (coal ash). Untuk mencapai tujuan ini, tiga jenis abu

arang batu (contohnya, fly ash (FA-1 dan FA-2), pond ash (PA) dan bottom ash (BA-

1 dan BA-2)) telah diperolehi dari Stesen Janakuasa Sejingkat, Kuching, Sarawak,

Malaysia. Ujian fizikal dan geoteknikal yang berbeza telah dijalankan ke atas sampel

abu arang batu dan keputusan ujian menunjukkan bahawa fly ash terdiri daripada

partikel kelodak 83.00 ke 89.00%, pond ash terdiri daripada partikel kelodak-pasir

dan bottom ash partikel bersaiz pasir 83.50 ke 84.50%. Graviti tentu (Gs) untuk abu

arang batu ialah dalam lingkungan 2.07 ke 2.32. Had cecair dan nilai kehilangan

terhadap pembakaran (LOI) untuk bottom ash adalah tinggi jika dibandingkan dengan

fly ash dan pond ash. Kandungan lembapan optimum dan ketumpatan kering

maksimum abu arang batu masing-masing 17.50 ke 36.50% dan 1.13 ke 1.56g/cm3.

Nilai index mampatan (Cc) untuk abu arang batu adalah dalam lingkungan 0.049 ke

0.113 dan bottom ash lebih mampat daripada pond ash dan fly ash. Parameter

kekuatan ricih (nilai geseran antara zarah-zarah (φ) dan kejelekitan (c)) masing-

masing 26.21 ke 34.89˚ dan 0.14 ke 8.05kN/m2 dan fly ash mempunyai nilai geseran

antara zarah-zarah dan kejelekitan yang tinggi, dikuti pond ash dan bottom ash.

1

CHAPTER 1

INTRODUCTION

The growth in population with the resulting increase in energy consumption

and industrial development in any developing country needs a sustained supply of

electrical energy. In Malaysia this demand for energy is also met by electrical energy.

The major fuel used for producing electrical energy in Malaysia is crude oil and other

petroleum products. Malaysia’s energy policy (1980) for electrical energy production

focusing on four main sources of fuel namely petroleum, hydropower, natural gas and

coal, also aims at ensuring their reliability and security of supply. In addition, it also

aims to reduce the dependence on crude oil for energy production particularly after

the shocks of the oil crisis in 1980s though a fuel mix for power generation based on

the above four-fuel diversification policy. The trend towards the increased utilization

of coal is a practical approach in optimizing the fuel mix and reduces the over

dependence on a single fuel.

2

Coal utilization, mainly as fuel for power plants, is expected to increase

significantly from about 4.2 million tonnes in the year 2000 to about 13 million

tonnes in 2005 (Thaddeus, 2002). According to 8th Malaysia Plan, Malaysia used

about 11.2 million tonnes of coal per annum. This produces more than 2 million

tonnes of fly ash annually but only a small amount is utilized. Table 1.1 shows the

increasing amounts of coal used for electric power plant in Malaysia.

Table 1.1 Energy used in electric power plant in Malaysia

Year 1995 2000 2005 Fuel (%) 11.0 5.3 3.0 Coal (%) 9.7 7.9 30.3 Gas (%) 67.8 78.7 61.0

Hydro (%) 11.3 8.0 5.4 Others (%) 0.2 0.1 0.1

The use of coal results in the generation of enormous amount of the ash, as a

by-product, due to combustion of the pulverized coal. The ash is disposed of either by

sluicing to ponds or hauling to solid waste disposal areas. Disposal operations are

quite expensive and require the use of land that could be used for other purposes. Ash

generally exhibits a wide range in chemical and physical properties. The

characteristics of a particular ash are dependent on the coal source, coal preparation

procedures, boiler type and the ash collection device (Parker et al., 1977).

3

The mineralogical composition of the ash, which depends on geological

factor, related to the formation and deposition of coals, its combustion conditions etc.

could be established by X-ray diffraction (XRD) analysis. The dominant mineral

phases are quartz, kaolinite, illite, and sideraite. The less predominant minerals in the

untreated coals include calcite, pyrite and hematite. Quartz and mullite are major

crystalline constituents of low calcium ashes (Class F ashes) whereas the high

calcium fly ash consists of quartzite, C3A, CS, and C4AS (Mehta, 1989).

Chemical properties and composition provide the greatest variability to fly

ash. An acidic pH tends to discourage leaching of certain components. The primary

element of concern in leachate are usually As, Se, and B. Fly ash is composed of a

variety of elements such as (in order of decreasing abundance): Si, Al, Fe, Ca, C, Mg,

K, Na, S, Ti, P, and Mn. Most of the major elements are in the stable core, but trace

elements on the surface can cause the most problems. The major constituents in fly

ash are SiO2, Al2O3, Fe2O3, and CaO. The predominant mineralogy for fly ash is

amorphous, which is important since it gives fly ash its pozzolanic properties (Miller

et al., 1992). Based on the chemical composition of the fly ash it has been classified

according to ASTM C 618-94 (American Society for Testing and Materials) as

follows:

(i) CLASS F: The fly ashes produced from the combustion of anthracite or

bituminous coals belong to this class. For these ashes, the sum total of three major

oxides silicate (SiO2), iron (Fe2O3) and alumina (Al2O3) is greater than 70% and CaO

is less than 5%. These ashes exhibit pozzolanic properties. These ashes have high

4

contents of un-burnt carbon and are non-reactive and are also known as low calcium

ashes.

(ii) CLASS C

: The fly ashes produced from lignite or sub-bituminous coals

belong to this class. For these ashes the CaO is more than 20% and hence are known

as high calcium ashes. In addition to pozzolanic properties, these fly ashes exhibit

cementitious properties. These ashes have low contents of un-burnt carbon and are

highly reactive.

The size of ash particles may vary from several hundred micrometer to several

tenth of micrometer. It color varies from light tan to gray or black, depending on the

carbon content. Usually, ash consists of particles with different shapes such as

spherical, hollow (cenosphere), broken, plerosphere (i.e. a sphere within another

sphere), tubular and some other irregular shaped particles (Singh and Kolay, 2002).

The fly ash can be, and being successfully used, for different applications.

Some of these applications are: (a) as a stabilizer of sub-grade and sub-bases in

pavement construction, (b) as a filler material, specially for reclamation of low lying

waste lands and refuse dumps, filling of mines to foundation of soils, etc. (c)

treatment of pollutant water and soils unsuitable for agriculture (d) used as canal

lining etc. (Barnes, 2001).

5

However, not much attention has been paid locally to the characterization of

coal ashes in Sarawak. This study, therefore, aims to characterize the local coal ashes

for the investigation of its potential feasibility for different utilization.

6

CHAPTER 2

LITERATURE REVIEW

2.1 General

A review of existing literature on the physical and geotechnical properties of

coal ash has been discussed in this chapter. The first part of the literature review deals

with the physical properties of coal ash and the second part describe the geotechnical

properties of coal ash.

2.2 Physical properties

Physical properties help in classifying the coal ashes for engineering purposes

and some are related to engineering properties (Pandian, 2004). The properties

discussed are Particle Size Distribution (PSD), Atterberg limits, specific gravity (Gs)

and Loss on Ignition (LOI).

7

2.2.1 Particle Size Distribution (PSD)

Particle size distribution indicates whether the coal ashes are well graded,

poorly graded, fine or coarse and it also helps to classify the coal ashes. Coal ashes

are predominantly a silt-sized non-plastic material with some sand size fraction.

Leonard and Bailey (1982) reported the range of gradation for fly and bottom ashes,

which can be classified as silty sands, or sandy silts. Particle size distribution studies

by Mehta and Monterion (1997) shows that the particles vary from less than 1 µm to

100 µm in diameter with more than 50% under 20 µm.

There are many methods to determine the particle size distribution of fly ash.

Thipse et al., (2002) compared particle size distribution of fly ash by using optical

microscopy and sieve analysis. In optical microscopy measurement, the fly ash

sample was dispersed in oil on surfaces of microscope glass slide. A microscope was

coupled to a video camera and Snappy board was used to digitize the images for

further processing. Each particle on the image, identified by software as an object,

was converted into a perfect circle with the same area as the original particle. Each

image included 50 – 100 particles, and at least 10 images were collected and

processed for each ash sample to provide an acceptable quality size distribution. An

example of the representative size distribution for fly ash particles is shown in Figure

2.1(a).

8

(a)

(b)

Figure 2.1 Size distributions of fly ash particles determined using (a) Optical microscopy and (b) Sieving (Thipse et al., 2002)

In addition to the microscopic measurement, the fly ash particles were size-

classified using a set of four sieves with the 75, 150, 300 and 1000 µm opening sizes.

A sieve shaker was used and the results are shown in Figure 2.1(b), the results of

9

these measurements are in qualitative agreement with the size distribution determined

using optical microscopy. A more detailed comparison of the fly ash particle size

distributions determined by optical microscopy (Figure 2.1(a)) and by sieving (Figure

2.1(b)) indicates that the larger particles represent a greater mass friction according to

the optical microscopy. An explanation of this discrepancy could be that sieving

causes break-up of some of the loosely agglomerated particles that are counted as

single particles by the optical image processing software.

The particle size distribution of ash is depending on firing condition, initial

pulverization of coal and sedimentation in lagoons, which has the greatest influence

on the grading of fly ash (Singh and Trivedi, 2004).

2.2.2 Atterberg limits

The concepts of Atterberg limits for fly ash is related to the amount of water

that is attracted to the surfaces of the fly ash particles. Currently, two methods

Percussion cup and Falling cone methods are popular for determination of liquid limit

of fine-grained soils. In Percussion cup method, it is very difficult to cut a groove in

soils of low plasticity and the soils have tendency to slip rather than flow. Hence, this

method is not suitable for fly ash, which is non-plastic in nature. Even Cone

penetration method, there is a tendency for the fly ash in the cup to liquefy at the

surface. Further, there is also variation of water content at different depths in the cup

10

and it is difficult to get a smooth, level surface of the fly ash in the cup (Sherwood

and Ryley, 1970).

Sridharan et al., (2000) have proposed a new method for the determination of

liquid limit of soils from equilibrium water content under Ko stress. This method

consists essentially of finding the equilibrium water content at a known vertical stress

under the Ko condition in a conventional consolidation ring, which will be equal to

the liquid limit. They found that the vertical stress to be 0.9 kPa and the obtained

water content under the Ko condition correlates well with the conventional liquid limit

water content. The proposed method is simple, reasonably error free, less time

consuming and has good reproducibility. However, these methods only suitable for

Class F fly ash and not suitable for Class C fly ash that gains strength with time.

Figure 2.2 Comparison of liquid limit obtained by Ko stress method and cone penetration method (Sridharan et al., 2000)

11

However, according to Pandian (2004), the results obtained by using Ko stress

method show that fly ash have liquid limit water content ranging from 26% to 51%,

22% to 64% for pond ash and 45% to 104% for bottom ash. The liquid limit values

exhibited by coal ashes are not due to their plasticity characteristics but due to the

carbon content present in it.

2.2.3 Specific gravity (Gs)

The variation of specific gravity of the fly ash is the result of a combination of

many factors such as gradation, particle shape and chemical composition (Gray and

Lin, 1972). This low specific gravity of the fly ash results in low dry density. This is

because micro bubbles of air are entrapped in ash particles. The trapping of air

increases the surface area hence volume of the fly ash. The breaking of fly ash

particles increases specific gravity that may be because of release of entrapped gas

when ash grounded by mortar and pestle (Webb, 1973). According to Pandian et al.,

(1998) the low specific gravity could be either the presence of more hollow

cenospheres from which the entrapped air cannot be removed or the variation in the

chemical composition (in particular, iron content) or both.

In general, the specific gravity of coal ash lies around 2.0 but can vary to a

large extent (i.e., 1.6 to 3.1) (McLaren and Digioia, 1987). But, the investigation by

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