dư lượng Red Từ Quặng Bauxite - dự án tại Lâm Đồng, Việt Nam

Inorganic Composite Material based on Fly Ash, Red Residue
From Bauxite Ore for Road Building Projects in Lam Dong Vietnam
Nguyen Van Chanh, 2Mitsuhiro Shigeishi, 3Tran Quoc Tho

1

2

1Department of Civil Engineering HCM City University of Technology, Vietnam
Department of Civil and Environmental Engineering, Kumamoto University, Japan
3
Department of Civil Engineering, HCM City University of Technology, Vietnam
e-mail:

ABSTRACT
The paper present solidifying technology based on geopolymer theory of inorganic
composite materials from bauxite, red residue from bauxite ore, fly ash and activators for road
building projects in Vietnam.
This study describes physical properties and chemical compositions of bauxite, red residue,
fly ash and the effects of bauxite-red residue-fly ash-activator mixes on the geotechnical
properties of inorganic composite materials. Mixture design and testing procedures for
inorganic composite materials. For mix proportion using 10-20% fly ash, red residue/bauxite
ratio is 30/70, 6-8ml alkaline activator/100gr powder, maximum dry density 1.75-1.81 g/cm3
together with optimum water moisture 19-21%. Plastic limit of bauxite modified by fly ash in
range of 11-17%, liquid limit 19-25%, swelling of inorganic composite materials 0.5-1.0%,
water absorption gets 6.5-8.5%, compressive strength in range of 55-80 kgf/cm2, compressive
strength in dry condition/compressive strength in water-saturated condition ratio 0.85-0.90,
splitting tensile strength 13-19 kgf/cm2, modulus of elasticity 5800-8000 kgf/cm2. New
inorganic composite materials have high durability and ability to water resistance in dry-wet
cycle.
The presentation also show microstructure analysis of inorganic composite materials based

on bauxite residue, fly ash and activators by X-Ray CT Analysis, X-ray diffraction analysis,
differential thermal analysis/Thermogravimetric Analysis (DTA/TG), transmission electron
microscopy (TEM) display high density, modified microstructure of inorganic composite
materials. Construction method of road using inorganic composite materials will be presented.
Keywords: Bauxite; Red residue; Fly ash; Inorganic composite materials; Mix proportions;
Road construction; Geopolymer technology.
1. INTRODUCTION
Researching in composite materials from bauxite, red mud, fly ash and activators for
building up rural road of highland region in Vietnam. Research is based on the mechanism of
composite materials stabilization with bauxite, red mud, fly ash and alkaline activators. The
method of study is based on examining factors that influence in physico-mechanical properties
of composite materials. Since then, we find out the proper proportions of materials for rural
road construction.
Bauxite is an heterogeneous material composed mainly of aluminum hydroxide minerals
(gibbsite which is the trihydrate, diaspore and boehmite which are the monohydrates). The
principal impurities common to nearly all known deposits of bauxite are aluminum silicates
(clays), iron and titanium oxides. The quantity of impurities varies from one deposit to another
as does the proportion of trihydrate to monohydrates [1] [2].
Chemical composition of bauxite soil consist of much sesquioxide of ferrite and aluminum
and other compositions. Sesquioxide ratio is different from the layers. In some cases, ferrite is
up to 90%, while aluminum is less than 5%, in other cases, ferrite is less than 4%, while

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aluminum is up to 60%. Silica is in the chemically bound phase and is present in kaolinite [1]
[2].

Figure 1. Raw bauxite deposit in Vietnam [1] Figure 2. Chemical composition of bauxite [1]
Characteristics of red mud: The most noticeable impacts of bauxite mining and alumina

production is red-mud. Red mud is mainly a by-product of the Bayer process, composed of the
impurities in the bauxite that are not dissolved in the refining process. The amount that is
generated per ton of alumina produced varies between 0.3 tons to 2.5 tons, depending on the
grade of bauxite used [2][3].
It is a mixture of compounds originally present in the parent mineral, bauxite, and of
compounds formed or introduced during the Bayer cycle. It is disposed as a slurry having a
solid concentration in the range of 10-30%, pH in the range of 13 and high ionic strength.
A chemical analysis would reveal that red mud contains silica, aluminum, iron, calcium,
titanium, as well as an array of minor constituents, namely: Na, K, Cr, V, Ni, Ba, Cu, Mn, Pb,
Zn etc. Typical values would account: Fe2O3 = 30-60wt%, Al2O3 = 10-20wt%, SiO2 = 350wt%, Na2O = 2-10wt%, CaO = 2-8wt%, TiO2 = trace-25wt% [2] [3]
Mineralogically, red mud has a very high number of compounds present. The more frequent
addressed are: hematite (Fe2O3), goethite Fe(1-x)AlxOOH (x=0-0.33), gibbsite Al(OH)3,
boehmite AlO(OH), diaspore AlO(OH), calcite (CaCO3), calcium aluminum hydrate
(x.CaO.yAl2O.zH2O), quartz (SiO2), rutile (TiO2), anatase (TiO2), CaTiO3, Na2TiO3, kaolinite
Al2O3.2SiO2.2H2O, hydroxycancrinite (NaAlSiO4)6.NaOH.H2O, sodalites, aluminum silicates,
chantalite
CaO.Al2O3.SiO2.2H2O,
hydrogarnet
cancrinite
(NaAlSiO4)6.CaCO3,
Ca3Al2(SiO4)n(OH)12-4n [2] [3].
Red mud is a very fine material in terms of particle size distribution. Typical values would
account for 90 volume % below 75µm. The specific surface (BET) of red mud is around
10m2/g [3].
2. GEOPOLYMER ACTIVATION MECHANISM OF INORGANIC COMPOSITE
MATERIALS
The purpose of composite materials stabilization is: to create stable molecule structure like
inorganic materials in natural condition. If elements of material bind together through certain
methods or chemical reactions, materials will possess good property of natural stone.
With presence of fly ash (containing SiO2 and Al2O3) and bauxite, red residue (containing

Al2O3 and Fe2O3), Al and Si can combined together through coordination linkage with oxygen
when activated by alkaline and suitable temperature [5]. Polymerization reactions are
conducted as following:

2


Geopolymerization is a modification of microstructure in materials to form stable silicate
skeletons. Reaction conditions are presence of alkali catalyst and a temperature range 40100oC, atmospheric pressure condition [4].
Geopolymerization involves a chemical reaction of Al-Si materials under highly alkaline
conditions, yielding polymeric Si-O-Al-O bonds. Its chemical structure can be described by
Mn{-(SiO2)z – AlO2}n .wH2O, where “M” is a cation such as potassium, sodium or calcium,
“n” is a degree of polymerization, and “z” is 1,2 or 3 [4].
Depend on Si/Al ratio, lattices are formed as following: (-Si-Al-O-) poly(sialate), (-Si-OAl-O-Si-O-) poly(sialate-siloxo, (-Si-O-Al-O-Si-O-Si-O-) poly(sialate-disiloxo) [4].

Figure 3. Some lattices formed by polymerization [4]
3. EXPERIMENT ON PROPERTIES OF BAUXITE, RED RESIDUE AND FLY ASH
Bauxite and red residue after selection of bauxite ore were taken from Bauxite Company in
Lam Dong province, Vietnam.
Fly ash from Formosa Company, Dong Nai province.
Alkaline activator: Natri silicate solution, density of 1.440, Na2O = 10%, SiO2 = 28%,
concentration of 12M, modulus silicate of 2.4.
A. Chemical Composition Analysis of Bauxite and Red Residue
Bauxite and red residue have high content of Al2O3, respectively 37.6% and 34.2%. The
amount of SiO2 is rather low (9.8% and 16.7% respectively). Especially, Fe2O3 is high in
bauxite and red residue (44.3% and 41.9%, respectively).
TABLE 1. CHEMICAL COMPOSITION OF BAUXITE AND RED RESIDUE
Samples
Bauxite
Red

residue

Chemical composition (%)
Al2O3 SiO2 Fe2O3 TiO2 CaO L.O.I
37.60 9.80 44.30 7.00 0.05 1.25
34.20 16.70 41.90

6.00

0.10

1.10

3


B. X-Ray and Scanning Electron Microscopy of Bauxite

Figure 4. SEM of bauxite
The results in X-ray analysis of bauxite and red residue show that they have the same
mineral composition of gibbsite 54.70-45.15%, goethite 27.22-28.84%, hematite 6.45-10.08%,
quartz 1.52-1.08%.
Through SEM and TEM analysis, shape of minerals in bauxite exists in layer and flake,
condensed tube-shape.
Quartz
Rutile
Hematite
Gibbsite
Goethite
Mullite 2:1

Anatase
Titanomagnetite
Perowskite

70,000
60,000
50,000
40,000
30,000
20,000

1.52 %
1.35 %
6.45 %
54.70 %
27.22 %
2.61 %
1.66 %
2.33 %
2.16 %

10,000
0
-10,000
-20,000
-30,000
-40,000
10

15

20

25

30

35

40

45

50

55

60

Figure 5. X-ray diffraction of bauxite

Figure 6. TEM analysis of bauxite.

C. Sieve Analysis of Bauxite soil
Group of grading particles contribute compaction capacity of soil. Fine particles (less than
0.075mm) have properties such as: high specific surface area, water-retaining property, water
absorption, volume change and shrinkage, flexibility; these properties cause instability of
bauxite attacking to water [7].
100
90

Percent passing (%)

80
70
60

Red residue
Bauxite

50
40
30
20
10
0
10

1

0.1

0.01

0.001

Particle size (mm)

Figure 7. Grading curve of bauxite and red residue

4


D. Atterberg limit of bauxite and red residue
TABLE 2. ATTERBERG LIMIT OF BAUXITE AND RED RESIDUE
Atterberg limit, %
Sample

Liquid
limit

Plastic
limit

Plastic
Index

Density

Bauxite
Red residue

34.25
45

23.29
26.83

10.96
18.17

Bulk
density
(g/cm3)

2.51
-

1.52
-

E. Physico-Chemical and Mineral Composition Analysis of Fly Ash
Test results show that fly ash have high total content of SiO2 và Al2O3 (88.4%) and high
value of fineness passing 0.05mm screen is 93.5%, density 2.4 g/cm3, active index 90.7%.
Test result of X-ray analysis of fly ash proved the present of specific peak SiO2 in
unidentified form and peaks mullite, quartz.
TABLE 3. CHEMICAL COMPOSITION OF FLY ASH
SiO2 Al2O3 Fe2O3 CaO MgO K2O Na2O TiO2 P2O5
(%) (%)
(%) (%) (%) (%) (%) (%) (%)
53.9

34.5

4.0

0.4

0.7

0.3

1.7

0.06

d=3.35201

150

1.0

140

130

120

110

90

80

d=1.22551

d=1.38295
d=1.37278

d=1.82171

d=2.21060

d=2.12612

d=1.54423
d=1.52469

20

d=2.28569

d=2.88432

30

d=2.69550

40

d=2.54964

d=5.39393

50

d=2.46126

60

d=3.43584
d=3.40314

70

d=4.26195

Lin (Counts)

100

10

0
11

20

30

40

50

60

70

8

2-Theta - Scale
29_MAU_QUOC THO_5 - File: 29_MAU_QUOC THO_5.raw - Type: 2Th/Th locked - Start: 10.000 ° - End: 79.990 ° - Step: 0.030 ° - Step time: 1. s - Temp.: 25 °C (Room) - Time Started: 16 s - 2-Theta: 10.000 ° - Theta: 5.000 ° - Chi: 0.00
00-015-0776 (I) - Mullite, syn - Al6Si2O13 - WL: 1.5406 - Orthorhombic - a 7.54560 - b 7.68980 - c 2.88420 - alpha 90.000 - beta 90.000 - gamma 90.000 - Primitive - Pbam (55) - 167.353 - I/Ic PDF 1. - F30= 60(0.0135,37)
00-046-1045 (*) - Quartz, syn - SiO2 - WL: 1.5406 - Hexagonal - a 4.91344 - b 4.91344 - c 5.40524 - alpha 90.000 - beta 90.000 - gamma 120.000 - Primitive - P3221 (154) - 3 - 113.010 - I/Ic PDF 3.4 - F30=539(0.0018,31)

Figure 8. The result of X-ray diffraction analysis of fly ash
4. EXPERIMENT ON PHYSICO-MECHANICAL PROPERTIES OF INORGANIC
COMPOSITE MATERIAL
The method of study is based on examining factors that influence in physico-mechanical
properties of composite materials. The objective is to find out the proper proportions of
materials for rural road construction through parameters such as: compressive strength,
flexural strength and splitting tensile strength, water absorption and water resistance, Proctor
compaction test, modulus of elasticity [6], [8], [9].
After casting, specimen is kept in the ambient condition, then specimens are dried. Time for
drying : 6 hours. Drying temperature: 105oC. After drying, specimens are cured into air
condition and water saturated condition.

5


Figure 9. Sampling process in laboratory.
A. Moisture-Density relationships and Swell values
Figure 10 show considerable improvement on compaction properties of inorganic
composite materials with presence of fly ash.
Mix proportion using bauxite, 10-20% fly ash, 6-8% activators, max dry density 1.72-1.78
g/cm3, optimum moisture 21%.
8%Quicklime (Bauxite/Red residue =70/30)
1.8
1.85

1.6
1.4
Expansion (%)

DRY DENSITY (g/cm3 )

1.80
1.75

2

1.70
1.65

1.2
1
0.8
0.6
0.4

1

1.60
1.55
18.0

19.0

3

4
20.0

21.0
MOIS TURE (%)

22.0

0.2
0

23.0

24.0

Figure 10. Moisture-Density
relationships of bauxite + 20% fly ash
combined with (1) 4%, (2) 6%, (3) 8%
and (4) 10% alkaline silicate activators.

0

10

20

% Fly ash

Figure 11. Swell values of inorganic
composite materials

Incorporation of Class F fly ash reduced soil plasticity and reduced the potential for
swelling. Use of fly ash for stabilization could be sufficient to improve soil properties to
desired levels.
B. Compressive Strength and Splitting Tensile Strength
With an increase of 10-20% fly ash, 8-10% activators, compressive strength of inorganic
composite materials get 70-80 kgf/cm2, splitting tensile strength 10-20 kgf/cm2. Increasing in
strength is due to geopolymer activation mechanism of inorganic composite materials based on
bauxite and fly ash.

Figure 12. Compressive strength test and sample damaged

6


Figure 13. Splitting tensile strength and modulus of elasticity test.

18

3

5

16

2

4

14

12
10

1

8
6

2

20

4
2
2

3

4

5

6

7

8

9

10

(kgf/cm )

28 day compressive strength

28 day splitting tensile strength
2
(kgf/cm )

22

85
80
75
70
65
60
55
50
45
40
35
30
25

5
3

1

2

11

2
4

3

4

5

6

7

8

9

10

11

% Activators

% Activators

Figure 14. The relationship between activators and compressive strength, splitting tensile
strength (1/ 0% Fly ash +8% quicklime ; 2/ 10% Fly ash +8% quick lime; 3/20% Fly ash
+8% quicklime ; 4/10% Fly ash; 5/20% Fly ash)
Bauxite incorporated of class F fly ash and activators significantly improves the strength
very quickly. This benefit is particularly important because the heaviest loads to be placed on
the subgrade often occur during construction of the road and the development of associated
properties.
C. Modulus of Elasticity
2

28 day modulus of elasticity (kgf/cm )

9000
8000

3
4

7000
6000

5

1

5000
4000
3000
2000
1000

2

3

4

5

6

7

8

9

10

11

% Activators

Figure 15. The relationship between activators, fly ash and modulus of elasticity (1/ 0%Fly
ash +8% quicklime; 2/ 10% Fly ash +8%quicklime; 3/20%Fly ash+8%quicklime; 4/10% Fly
ash+; 5/20% Fly ash)
Presence of activator, fly ash influences in compressive strength. When using of 4-10ml
activator/100gr powder and 10-20% fly ash, modulus of elasticity (6000-8000 Kgf/cm2)
increase up to 20%.

7

D. Water absorption and water resistance factor:
5

0.92

4

0.90
0.88

2

3

0.86

Water absorption (%)

Water resistance factor

0.94

1

0.84
0.82
0.80
0.78

2

3

4

5

6

7

8

9

10

12
11.5
11
10.5
10
9.5
9
8.5
8
7.5
7
6.5

6
5.5
5

2

3
5
2

11

1

4

3

4

5

6

7

8

9

10

11

% Activators

% Activators

Figure 16. The relationship between activators and water absorption, water resistance factor
(1/ 0%Fly ash +8%quicklime; 2/ 10%Fly ash +8%quicklime; 3/20%Fly ash +8%quicklime;
4/10%Fly ash; 5/20%Fly ash
Mix proportion using bauxite combined with 10-20% fly ash, 6-8ml activator/100gr, water
absorption 6.5-8.0%. With an increase of fly ash and activator, water resistance factor increase
dramatically. Compressive strength of materials in water-saturated condition get 85-90%
compared to of materials in dry condition.
5. EXPERIMENT ON CHEMICAL COMPOSITION AND MICROSTRUCTURE
ANALYSIS OF INORGANIC COMPOSITE MATERIAL
A. X-ray diffraction and Infrared spectroscopy (IR)
Result of mineral composition of composite : quartz 9.48%, sodalite 1.23%, hematite
9.33%, gibbsite 40.76%, goethite 22.52%, mullite 5.52% (Figure 17).
Infrared spectroscopy (IR) can yield information concerning structural detail of the material
are show in figure 18.
Quartz
Sodalite
Hematite
Gibbsite
Goethite
Mullite 2:1
Gypsum
Titanomagnetite

Perowskite

35,000
30,000
25,000
20,000
15,000
10,000

9.48 %
1.23 %
9.33 %
40.76 %
22.52 %
5.52 %
7.80 %
1.71 %
1.66 %

5,000
0
-5,000
-10,000
-15,000
-20,000
10

15

20

25

30

35

40

45

50

55

60

Figure 17. X-ray diffraction result of composite
(red residue 22% + Bauxite soil 50% + lime 8%
+ fly ash 20% + alkaline activator 8%)

Figure 18. IR result of composite red
residue 22% + Bauxite soil 50% + lime
8% + fly ash 20% + alkaline activator

The intense bands occur at 420, 434, 473, 532, 558 cm-1 for mode of the O-Si-O, at 663,
735, 798 và 877 cm-1 mode of O-Si-O or Si-O-Al in zeolite. The intense bands occur at 9501000 cm-1 mode of gel aluminosilicat Si-O and Al-O, at 1400-1700 cm-1 for mode of
geopolymer Si-O-Al.
The absorbance band in between the wave number 950-1400 cm-1 in the IR spectrum of fly
ash – bauxite – alkaline activator composite represent the presence of substituted Al atoms in

the forms of silica frame work. Geopolymerization involves a chemical reaction of Al-Si
materials under highly alkaline conditions, yielding polymeric Si-O-Al-O bonds.
B. Transmission Electron Microscopy (TEM)
Important component of the binder phase is formed in the geopolymer process of the crystal
structure is nanoscale. Nano-crystalline aluminosilicate materials in the form of gel is
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amorphous in bauxite soil, red sludge also contributes to forming a binder with high
performance. Microstructure of geopolymer with inorganic nanometer level are given in
Figure 19.
C. X-ray CT Analysis
This method allows assessment of the extent of the compact structure and material
composition of each solid phase. Which can demonstrate the ability to create a compacted
form, the combination creates fusion materials compact structure, thereby enhancing the
physical properties of materials and capabilities for water resistence well improved.
In one section of composite materials (Figure 20), we can see the consistency of synthetic
soil material bauxite, fly ash. Xray diffraction diagrams corresponding CT has changed the
type of diffraction at a location containing fly ash is micro porous structure.

Figure 19. Microstructure of
inorganic composite materials
based on bauxite, red residue and
fly ash activated by alkaline
activator for at 105oC

Figure 20. X-ray CT analysis of inorganic
composite materials

6. EXPERIMENTAL CONSTRUCTION OF ROAD IN SITE USING INORGANIC

COMPOSITE MATERIAL
Preparing the base layer: Using motor grader to windrowing along the center of road, the
base layer need to be smooth, horizontal slope is as designed and the base is compacted with
compacting factor ≥0.95 [6], [10], [11].

Figure 21. Preparation of subgrade

Figure 22. Mixing process of materials for road

9


Figure 23. Grader for leveling work

Figure 24. Road roller for compaction

Fly ash, bauxite, red residue, dry quicklime, alkaline activator are mixed. Spread out the
mixture of the specific content into the thin layer by using grader. Using road roller and
watering during compacting. Finishing. After compaction is finished, the pavement is dried by
sun shining.
The compaction on a small area is carried out for compacting factor. Then, determine the
number of compaction of each roller to get the maximum compaction capacity. The required
compaction is 0.95 γ k max ( γ k max is maximum dry density, determined by Proctor compaction test)
[6] [10].
CONCLUSION
Residue from bauxite ore can be successfully solidified by the geopolymer technique by
blending fly ash as active filler with alkaline activator. The effective requirement of blending
fly ash is generally 20% and more. Inorganic composite materials based on bauxite, fly ash and
red residue have high strength and ability to water resistance. Geopolymerization involves a
chemical reaction of Al-Si materials, modifying structure of composite material with stable

skeleton based on formation of stable frameworks in materials with -Si-O-Al-O- geopolymer
sequence.
For mix proportion using 10-20% fly ash, red residue/bauxite ratio is 30/70, 6-8ml alkaline
activator/100gr powder, maximum dry density 1.75-1.81 g/cm3 corresponding with optimum
water moisture 19-21%. Plastic limit of bauxite modified by fly ash in range of 11-17%, liquid
limit 19-25%, swelling of inorganic composite materials 0.5-1.0%, water absorption gets 6.58.5%, compressive strength in range of 55-80 kgf/cm2, compressive strength in dry
condition/compressive strength in water-saturated condition ratio 0.85-0.90, splitting tensile
strength 13-19 kgf/cm2, modulus of elasticity 5800-8000 kgf/cm2.
Inorganic composite materials showed good properties for construction of road surface and
increased the durability of road.
ACKNOWLEDGMENT
We wish to thank Japan International Cooperation Agency (JICA) and Ho Chi Minh city
University of Technology for supporting to this research through SUPREM-HCMUT Program.
REFERENCES
[1] Vietnam National Coal – Mineral Industries Group – Vinacomin, Conference in
sustainable development of aluminum industry in highland, Vietnam, September (2009).
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[3] A. R. Hind, S. K. Bhargava, Stephen C. Grocott, "The surface chemistry of Bayer process
solids: a review", Colloids and Surfaces Physicochem. Eng.(1999), pp. 359–374
[4] Joseph Davidovits, “Geopolymer chemistry and applications”, (2008).
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[7] Vietnam Standard TCVN 4198-95, “Soil for construction, methods for determination of
grade curve, Atterberg limits of soil in laboratory”, (1995).

[8] Modified Proctor compaction Test AASHTO T180-90.
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University of Kansas, Lawrence, “Field performance of fly ash stabilised subgrades”,
Ground Improvement 9, No. 1, USA, (2005), pp.33–38.
[10] Department of the army, the navy, and the air force, “Soil stabilization for pavements”,
October (1994).
[11] M. A. Rahman, Department of Civil Engineering, University of Ife, “Effects of
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