Nghiên cứu chế tạo gạch xây không nung hệ geopolymer từ bùn đỏ tân rai lâm đồng tt

MINISTRY OF EDUCATION AND TRAINING

MINISTRY OF CONSTRUCTION

VIETNAM INSTITUTE OF BUILDING SCIENCE AND TECHONOLOGY
----------------------------------

QUANG LE VAN

RESEARCH ON MANUFACTURING GEOPOLYMER UNBAKED
BRICK BASED ON RED MUD OF TAN RAI LAM DONG
SUMMARY OF DOCTORAL THESIS

Specialization: Materials engineering
Code: 9520309

HA NOI-2019


THE DISSERTATION IS COMPLETED AT:
VIETNAM INSTITUTE FOR BUILDING SCIENCE AND TECHONOLOGY

Academic supervisor:
1. Doctor HOANG MINH DUC
INSTITUTE OF CONCRETE TECHONOLOGY - VIETNAM INSTITUTE FOR
BUILDING SCIENCE AND TECHONOLOGY

2 Associate Professor. Doctor DO QUANG MINH
HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY

Reviewer 1: Asso.Prof. Dr. Ngoc Nguyen Minh

Reviewer 2: Asso.Prof. Dr. Long Luong Duc
Reviewer 3: Dr. Dai Bui Danh

This dissertation is defended by Academy Doctoral Examination Boar at
Institute of Building Science and Techonology, 81 Tran Cung street, Nghia
Tan, Cau Giay District, Ha Noi at …… on the

day of

2019.

The dissertation may be read at:
- National Library of Vietnam
- Library of Vietnam Institute of Building Science and Techonology


INTRODUCTION
1. Rationale of the Study
Red mud is the name of waste generated from bauxite hydrated alumina by
Bayer technology. Tan Rai Aluminum Factory has the amount of red mud
discharged into the environment during the operation process of 80÷90
million m3, causing environmental pollution, significant impact on
ecosystems and society.
In the composition of red mud containing alkali, easy to soak into the soil,
polluting water sources, degradation of arable land or in the composition
may have radioactive substances ... very difficult to store and preserve.
Utilizing the typical residual components, silicon oxide, aluminum oxide in
red mud combined with the addition of silicon oxide from other waste
sources such as fly ash and appropriate curing methods to fabricate
geopolymer materials. The demand for unbaked construction bricks in

Vietnam as well as environmental treatment is essential.
2. Research subject and scope
The object of the dissertation is geopolymer using Tan Rai Lam Dong red
mud to meet the requirements for making unburnt bricks.
The scope of the study includes: properties of component materials. Effect
of alkaline concentration, curing conditions on the solubility of silicon
oxide and aluminum oxide in raw materials. Effect of materials, curing
conditions on intensity, softening coefficient, pH and excess alkalinity of
geopolymer. The properties of geopolymer and economic efficiency.
3. Scientific significance
Having argued and proved experimentally on the following issues:
- The ability to make geopolymer from red mud depends on the amount of
silicon oxide dissolved in the alkaline solution, thanks to curing at high
pressure and high temperatures or supplemented from materials such as fly
ash, silica fume.
- Clarified the influence of material and technology parameters on the
properties of geopolymer from red mud. From there set the technological
parameters for production.
4. Practical significance
- Based on the research results that have contributed to the market a new
product, geopolymer unburnt bricks from Tan Rai red mud, meeting
technical requirements for use in construction works.
- Method of making geopolymer unburnt bricks from red mud by autoclave
technology allows effective treatment of red mud waste, contributing to
environmental protection.
1


5. New contributions of dissertation
- Using red mud waste of Tan Rai Aluminum factory and fly ash of Tan Rai

internal thermal power plant, successfully manufacturing unbaker
geopolymer bricks with autoclave technology to meet the requirements of
construction.
- Clarifying the influence of several factors on the solubility ratio of silicon
oxide in red mud and fly ash including alkaline solution concentration,
temperature, pressure and curing time. Under autoclave conditions, silicon
oxide in red mud can be dissolved in alkaline solution and can participate
in geopolymerization reaction.
- Contributing data on the properties of geopolymer from red mud and
mixture of red mud and fly ash curing in autoclave conditions. When
autoclaving can improve the ratio of dissolved silicon oxide under low
alkaline concentration. Thus, it is possible to improve the softening
coefficient, reduce the excess alkalinity and the pH of geopolymer.
6. Structure of the dissertation
The dissertation includes introduction, five chapters (15 periods),
conclusions and recommendations, list of references and appendices .
CHAPTER 1. OVERVIEW OF RESEARCH ISSUES OF USING RED
MUD IN CREATING GEOPOLYMER
1.1. Red mud emission and treatment direction
1.1.1. The process of red mud emissions
Red mud is a waste of bauxite alumina production by Bayer technology.
Nowadays, there are about 90% of alumina in the world is manufactured
using Bayer technology (invented by Bayer in 1887). Red mud consists of
insoluble, inert and quite stable components in weathering conditions such
as Hematite, Natrisilicat, Aluminate, Calcium-titanate, Mono-hydrate
aluminum ... and especially contains a amount of caustic soda, a type of
Highly toxic alkaline excess from the manufacturing process..
1.1.2. Characteristics of the red mud
- Solid phase of red mud: characterized by main factors such as chemical
composition, minerals, particle size ...;

+ Chemical composition: as reported by UNIDO, the solid phase chemical
composition of red mud includes Al2O3, SiO2, Fe2O3, Na2O, CaO, TiO2,
L.O.I.
+ Mineral composition: similar to the composition of bauxite and has two
new phases, namely Na2O.Al2O3.2SiO2.nH2O and compounds with
oscillating components of CaO with Al2O3, Na2O and SiO2 components.

2


+ Particle size: red mud usually has a fine to very fine particle size. Most of
them have a grain grade of 100% <100 µm, red mud (Jamaican bauxite)
<44 µm, accounting for 90%.
- Liquid phase of red mud: characterized by the chemical composition of 3
components Na2Ot (NaOH + Na2CO3), Na2Oc (NaOH) and Al2O3.
1.1.3. Directions for handling red mud
In the past, lakes were built to store red mud or people pumped mud into
the bottom of the river, seabed or partially blocked the bay to contain waste
mud. However, these measures have been banned. Today, research focuses
on the following areas. Agriculture: using red mud as arable land in
agriculture. Production of construction materials: cement, bricks, making
inorganic pigments. Backfilling materials: roads. Composite materials from
red mud. Recovery of precious metals used in metallurgy, iron and
aluminum. Because of the red mud composition of aluminum hydroxides,
iron hydroxides and iron oxide with very small particle size, it is possible to
use unburnt bricks in the direction of geopolymerization is very
meaningful..
1.2. Research situation of using red mud in geopolymer production
1.2.1. Concepts and principles of geopolymer synthesis
"Geopolymer" is the term that French scientist Davidovits named in 1979.

Geopolymer is an inorganic polymer with a structural unit of tetrahedra
[SiO4]4- and [AlO4]5-. The mechanism of geopolymerization consists of 4
stages and these processes can take place in parallel and alternating so that
it is impossible to distinguish clear boundaries, namely: (1) Dissolving
solid aluminosilicate in alkaline solution strong. (2) Form the Si (Si) or SiAl (oligomer) base chain in the liquid phase. (3) The polymerization
process stops the oligomeres forming three-dimensional silicate alunimo
network. (4) Creating solid bonds between geopolymer frames and curing
in the whole system to form solid geopolymer structures..
1.2.2. Using red mud in manufacturing geopolymer
Studies in the world consider red mud as a subsidiary material, it is
necessary to use additional raw materials containing active silica oxide to
treat red mud by geopolymerization method. Using fluidized fly ash,
metakaolin for compressive strength 2÷13 MPa, using fly ash type C,
intensity of 7÷13MPa. Dimas uses 85% red mud and 15% alkaline
metakaolin NaOH and Na2SiO3 (glass water) for heat-resistant geopolymer
reaching 400 ÷ 1000oC, compressive strength from 4÷9.5 MPa. Use more
lime and plaster. Yang, using OPC steering port cement, fly ash, lime and
gypsum to make geopolymer mortar, the intensity of 11.7÷29 MPa. Kumar
uses additional slag, curing 60oC for 24 hours compressive strength
3


64÷125 MPa. Zang, using rice husk ash, NaOH 4M with red mud, intensity
of 3.2÷20.5 MPa.
In Vietnam, red mud replaced a part of clay for making bricks, baked at low
temperatures of 600÷800oC, geopolymer reached compressive strength over
5 MPa. Add fly ash, glass water intensity of 7.7÷18.7 MPa. Technology of
manufacturing iron ore concentrate and unburnt construction materials
from red mud and making geopolymer meet the unburnt brick standard
TCVN 6476:1999. Red mud and jelly, Ho Chi Minh City University of

Technology team, 30% alkaline liquid glass and 70% NaOH 10M. Curing
for 60oC to 28 days achieves compressive strength of 46.5 MPa. There are
also a number of studies on red mud binders replacing cement, making
porous bricks from red mud and diatomite.Domestic and foreign studies
show that it is impossible to make geopolymer when using the red mud
independently under normal conditions but must combine with other
materials containing silicon oxide components from outside sources.
1.3. Building materials using geopolymer from red mud
1.3.1. Trend of unbaked construction materials in Vietnam
Over the past years, Vietnam has paid much attention to researching on
developing and using unburnt bricks. At the same time, issuing documents
such as Circular 09/2012 / TT-BXD of the Ministry of Construction: 100%
of unburnt construction materials must be used from January 15, 2013; In
the remaining areas, using at least 50% of unburnt construction materials
from the effective date to the end of 2015, after using 100%.
1.3.2. Technical requirements for geopolymer building materials from
red mud
Currently there are many types of unburnt bricks, with each type of unburnt
brick has set different technical requirements specified in the standard
depending on the characteristics and nature of that unburnt brick. Unburnt
bricks from red mud are new products without technical requirements, so it
is necessary to set technical requirements for this type of products such as
requirements related to bearing resistance, relating to the use, soundproof,
heat insulation ...
From research and practice of the dissertation, propose technical
specifications of unburnt geopolymer bricks from Tan Rai red mud:
compressive strength min 10 MPa; water absorption 8÷16%; water
permeability max 16 l / m2.h; softening coefficient min 0.8 and pH max 9.5.
1.4. Scientific basis for manufacturing geopolymer from red mud as a
construction material

1.4.1. Scientific basis using red mud in geopolymer production
4


When mixing Si and Al materials (such as fly ash) with alkali solution, OHion of solution enters fly ash particles, causing Si-O-Si bond to be broken
to form Si(OH)3O-. Al(OH)4- is formed similar to Si. The solubility of Si
and Al from the starting material can be described by chemical equation
(1.1).
(SiO2.Al2O3) + 2MOH + 5H2O → Si(OH)2 + 2Al(OH)3 + 2M* (1.1)
Where: M is Na or K.
The role of silicon oxide is very important, the dissolved silicon oxide in
the composition of geopolymer fabrication material determines the bond
formation and mechanical properties of the material. Silicon has the ability
to bond directly with each other (Si-Si) or bond through oxygen globes (SiO-Si). When bonded via oxygen globes, the polymer circuit can be
represented via coordinated polyhedrafts, creating a three-dimensional
spatial network. The ions of the modified oxides such as Na 2O, K2O, CaO,
MgO...do not create circuits, located in the holes of coordination polyhedra.
1.4.2. Effect of temperature, pressure conditions on reaction process
When autoclave Si and Al materials will be dissolved more quickly and
more into NaOH caustic soda, speed curing and increase the efficiency of
geopolymerization reaction. In this soluble solution, depending on the pH,
temperature and concentration of Si and Al solubility, groups of [SiO 4]4may exist independently (completely dissolved) or bound together to form
polymerization circuits (the oxygen globules create polymer circuits can be
denoted Q0, Q1, Q2, Q3 with 0,1,2,3 is the oxygen demand index in the
structure). According to Sani and Kani, the excess alkalinity is due to the
high amount of alkalinity introduced, or the low level of activity of the
material leading to an alkaline reaction. The study of E. N. Kani used
pozzolan and NaOH, curing at different temperatures for 20 hours. E.
Najafi Kani and the study of chalk control phenomenon in Geopolymer
products made from natural pozzolan also talked about this issue.

Hydrothermal curing of N. A. M. Sani (2008) is an effective way to
develop appropriate GP structure, the excess NaOH in geopolymer
decreases compared to non-curing heat and the lowest is 4.84%. Kani with
his partners (2007) investigated the effect of autoclave on the strength deve
lopment of geopolymer from blast furnace slag and natural pozzolan,
concluding that the reaction is good, Al and Si components from raw
materials are almost participants react almost completely in the autoclave
environment. This is also consistent with Kriven's other research results,
curing in autoclave at 1000 psi, 80 ° C for 24 h, and the author concludes
that autoclave curing makes the reaction more complete and complete.
Bassel Hanayneh (2014) using kaolinite has also reaffirmed the advantages
5


of autoclave maintenance. A. M. Distillation of making an alkaline slag
binder with quartz powder, also confirms the role of curing autoclave.
Through the above studies it can be seen that to improve the properties of
geopolymer, scientists have cured: drying, hydrothermal and autoclave.
Studies in the world about synthesis of geopolymer for autoclaving mainly
focus on materials such as natural puzolan, slag, metakaoline, ... without
any research on Bayer red mud technology. With the aim of the research
topic, using Tan Rai Lam Dong red mud to make unburnt geopolymer brick
system. Making full use of ingredients available in raw materials, excess
alkali. The dissertation conducted survey experiments and offered the
option of not adding more alkali to activate the reaction, but only adding
water to shape.
1.4.3. Scientific hypothesis
Geopolymer from red mud can only be formed by adding dissolved silicon
oxide in the composition by using mineral additives or applying special
curing at high pressure high temperature.

1.4.4. Research objectives and missions
Objective: to make geopolymer unburnt construction bricks from Tan Rai
Lam Dong red mud under practical conditions of Vietnam.
The task of researching and manufacturing geopolymer from red mud
includes the following issues:
- Determination of content of dissolving silicon oxide and aluminum oxide
in raw materials;
- The influence of input materials on the properties of geopolymer. Adjust
the amount of dissolved silicon oxide by additions from an external source;
- Effect of autoclave curing parameters on geopolymer's properties. Adjust
the amount of dissolved silicon oxide by autoclave;
- Properties of geopolymer unburnt brick products;
- Practical application in masonry and calculation of economic efficiency..
CHAPTER 2. MATERIALS AND RESEARCH METHODS
2.1. Materials
- Red mud: Tan Rai alumina factory. Chemical composition: SiO2 7.4%;
Al2O3 13.65%; Fe2O3 56.05%; Na2O 3.63%; K2O 0.25%; CaO 3.1%; other
3.27%; L.O.I 12.5%. Where, alkaline dissolved according to TCVN 6882:
2011 symbol (Na2Otd) is 0.664%. Mineral content: Goethite: FeOOH:
21%; Hematite: Fe2O3: 14%; Gibbsite: Al(OH)3: 5%; amorphous 60%.
- Fly ash: 30MW of Tan Rai internal thermal power plant. Volume density
905 kg/m3, density 2.2g/cm3, particle size 48.2 μm. Chemical composition:
SiO2 47.74%; Al2O3 35.36%; Fe2O3 7.02%; Na2O 0.69%; K2O 0.41%; CaO
6


4.2%; other 0.3%; L.O.I 3.85%. Mullite mineral composition: Al 6Si2O13:
20%; Quartz: SiO2: 2%; amorphous 78%.
- Silicafume: Elkem Silicon Materials. Volume density 360 kg/m 3, density
2.15 g/cm3, particle size 1.5 μm. SiO 2 chemical composition 94.5%; L.O.I

2.74%. The mineral content of 1% is Cristobalite SiO 2, the remaining
amorphous phase.
- NaOH: 2M ÷ 18M. Bien Hoa chemical factory, Dong Nai province.
2.2. Experimental methods
- Compressive strength: TCVN 6016: 2011 and TCVN 6477: 2016 in the
study do not use the conversion of the effect of the shape factor K
according to the size of the test sample. - Specific gravity: TCVN 4030:
2003. - Bulk density: TCVN 7572-6: 2006. - Softening coefficient: TCVN
7572-10: 2006. - Humidity: TCVN 7572-10: 2006. - Chemical composition
and L.O.I of red mud and silicafume were determined according to TCVN
141: 2008 standard, fly ash was determined according to TCVN 8262: 2009
standard. - Determination of pH: TCVN 9339: 2012. - Free excess alkali
content: TCVN 6882: 2001, Na2Otd =% Na2O + 0,658 *% K2O.
- Adhesion strength of mortar to brick substrate: TCVN 3121-12: 2013, in
which, geopolymer board has natural moisture in the laboratory.
- Testing of compressive strength of masonry: ASTM C1314 "Standard Test
Method for Compressive Strength of Masonry Prisms".
- Structural analysis: XRF, XRD, AAS, SEM, SEM-EDS.
- Determine the soluble content of SiO 2, Al2O3: refer to TCVN 7572-14:
2006; TCVN 141: 2008, TCVN 9191: 2012, TCVN 7131: 2002.
2.3. Process of manufacturing sample
Making samples by semi-dry and static pressing method with the pressure
of 72 KN, corresponding to the pressure of 10 N/mm 2, with this pressure,
the semi-dry molding pattern is removed mold immediately after pressing.
General parameters liquid/solid ratio 0.2. Specimen size 90x80x40 mm.
a). Normal conditions: Base using red mud with added fly ash replacement
is 13%; 26%; 40%. NaOH concentrations surveyed were 1M, 2M, 3M, 4M,
5M, 6M. Additional gradations of replacement silica fume are 2%; 4%; 6%;
8%; ten%. NaOH concentration is 1M, 2M, 3M. Samples after semi-dry
forming, curing under normal conditions up to 28 days.

b). Autoclaved conditions: Base only uses independent red mud to make
geopolymer: Use 100% red mud in the aggregate. Utilizing the excess
alkali available in red mud (RM0). Samples added with 1M, 2M, 3M
NaOH alkaline symbols with RM1, RM2, RM3, autoclave at 201 oC, 1.6
MPa pressure for 16 hours. - Base use to add fly ash: 26% more fly ash,
just add water, do not add alkali (FA0) and samples added 1M NaOH
7


alkaline (FA1). The sample is semi-dry pressed shape, after removing the
mold, autoclave curing: pressure 0.4; 0.8; 1.2; 1.6 MPa is equivalent to the
pressure of 144oC, 170oC, 188oC, 201oC. During 4 hours, 8 hours, 12 hours
and 16 hours. After the autoclave was completed, it was rescued under
normal laboratory conditions for up to 28 days.
For samples of softening coefficient, saturated with water for 48 hours at
the time (from the 26th to the 28th day), up to 28 days of determination of
the softening coefficient. Autoclave time is constant time, constant
temperature, not including the stages of pressure rise and lower pressure.
Turbocharging/lowering
speed:
0.013
MPa/min
(corresponding
increase/decrease of about 2oC/min, to the set temperature).
CHAPTER 3. STUDY OF CREATING UNBAKED BRICKS BASED
GEOPOLYMER FROM RED MUD IN TAN RAI.
3.1. The influence of several factors on the solubility of SiO 2 and Al2O3
in raw materials
The first stage in the synthesis of geopoymer materials is crucial to the
process of geopolymerization and the properties of geopolymer materials

are the dissolution of SiO2 and Al2O3. In the study, the solubility of these
oxides in red mud and fly ash was assessed at different pressure and
temperature conditions. Curing regimen under normal pressure condition
(Table 3.1) and under pressure condition (Table 3.2).
3.1.1. Effect of alkaline concentration and temperature
Table 3.1. The ratio of SiO2, Al2O3 dissolved curing at normal pressure
Heat mode
T, (ºC)

τ, (h)

Additional
NaOH solution
concentration

80
80
80
80
80
80
80
80
50
100
150
200
50
100
150

200

24
24
24
24
24
24
24
24
10
10
10
10
10
10
10
10

1M
3M
5M
7M
9M
11M
13M
15M
1M
1M
1M

1M

Dissolved oxide ratio, mass (%)
Red mud
Fly ash
SiO2
Al2O3
SiO2
Al2O3
0.00
4,13
2,33
4,56
0.00
4,74
4,58
4,66
0.00
4,76
8,66
4,70
0.00
4,76
10,65
4,76
0.00
4,76
13,68
4,76
0.00

4,76
14,98
4,76
0.00
4,76
15,15
4,76
0.00
4,76
15,21
4,76
0.00
1,20
1,06
1,47
0.00
2,20
1,41
2,41
0.00
2,26
1,75
2,48
0.00
2,29
2,20
2,56
0.00
1,74
2,23

2,11
0.00
2,95
3,65
3,14
0.00
3,02
4,10
3,88
0.00
3,22
4,37
4,25

8


The results showed that SiO2 in red mud did not dissolve under normal
pressure when adding NaOH 1M÷15M. The dissolution process is also not
activated when the temperature increases from 80ºC to 200ºC. Meanwhile,
the ratio of dissolved SiO2 of fly ash after 24h at 80ºC increased sharply
from 2.33% to 15.21% when increasing the concentration of NaOH
solution from 1M to 15M. The rate of dissolved Al2O3 is almost unchanged
and does not depend on the concentration of NaOH. Silica fume has a
nearly constant ratio of SiO2 at NaOH concentrations, the solubility reaches
90.06% at 1M alkaline concentration, and reaches the highest value of
90.32% from 5M to 15M concentrations.
3.1.2. Effect of high pressure conditions
By pressure, the SiO2 in the red mud begins to dissolve. The ratio of
dissolved SiO2 of red mud after 10 h of autoclave increased from 0.34% to

2.25% corresponding to an increase in pressure from 0.4 MPa to 1.6 MPa.
Adding NaOH under autoclave conditions also increased the proportion of
SiO2 dissolved in red mud under curing conditions.
Table 3.2. The ratio of SiO2 and Al2O3 dissolved when curing autoclave
Autoclave mode
P, (MPa)

T, (ºC)

τ,
(h)

0,4
0,8
1,2
1,6
1,2
1,2
1,2
1,2
0,4
0,8
1,2
1,6
1,2
1,2
1,2
1,2

144

170
188
201
188
188
188
188
144
170
188
201
188
188
188
188

10
10
10
10
4
8
12
16
10
10
10
10
4
8

12
16

Additional
NaOH
solution
concentratio
n
1M
1M
1M
1M
1M
1M
1M
1M

Dissolved oxide ratio, mass (%)
Red mud
fly ash
SiO2

Al2O3

SiO2

Al2O3

0,34
1,05

2,18
2,25
1,46
1,95
2,22
2,71
1,28
1,87
2,38
2,89
1,95
2,08
2,44
2,98

3,87
5,65
7,22
8,12
5,74
6,25
7,48
8,35
4,25
6,25
7,98
8,45
6,42
7,02
8,33

9,03

1,94
6,75
7,58
8,18
6,86
7,08
7,84
8,94
8,34
9,69
11,65
13,72
10,33
11,46
13,00
18,25

5,22
8,25
13,65
16,58
8,69
11,88
15,88
16,87
6,25
10,25
16,35

20,25
10,33
13,65
17,98
20,33

Pressure deposition significantly increases the ratio of dissolved SiO 2 of fly
ash. The ratio of dissolved SiO2 increases with increasing pressure or
curing time. To achieve the same ratio of dissolved SiO 2, the autoclave
activated material allows the NaOH to be reduced. With a greater
proportion of dissolved SiO2, fly ash can be used to replace a part of red
9


mud, providing an additional source of dissolved SiO 2 for
geopolymerization, improving the properties of the material. Unlike SiO 2,
Al2O3 in red mud, fly ash can be dissolved in all curing conditions.
When curing autoclave, the level of Al2O3 solubility of both red mud and
fly ash improved significantly. The results of the solubility of SiO 2 and
Al2O3 showed that it is possible to use the autoclave to activate the
components in the red mud to pave the way for the geopolymerization
reaction.
3.2. The influence of several factors on the properties of curing
geopolymer under normal conditions
The common condition SiO2 in red mud is insoluble in alkaline solution,
while there is still a certain amount of dissolved Al 2O3. To make
geopolymer under normal conditions, it is necessary to add dissolved SiO 2
content from the external source (such as fly ash, silica fume ...). The
gradation parameters are shown in Table 3.3 and Table 3.4.
Table 3.3. Parameters when adding dissolved silicon oxide with fly ash

Sampl
e

Amount of material using for
Measured Geopolymer properties
1 m3, (kg)
NaOH
Water
solution
Dry comp. saturated
soft
Red
Fly
Density
concen
strength,
comp.
coeffi
pH
mud
ash
quan tratio (kg/m3)
(MPa)
strength,
cient
n
tity
(MPa)

Na2Otd
(%)

(M)

072BTN1
143BTN1
215BTN1
072BTN2
143BTN2
215BTN2
072BTN3
143BTN3
215BTN3
072BTN4
143BTN4
215BTN4
072BTN5
143BTN5
215BTN5
072BTN6
143BTN6
215BTN6

1601
1294
989
1598
1292
988

1608
1297
993
1606
1300
995
1613
1306
1004
1621
1313
1007

245
462
648
244
461
647
246
463
650
245
464
652
246
467
658
248
469

660

369
351
327
368
351
327
371
352
329
370
353
330
372
355
332
374
356
333

1
1
1
2
2
2
3
3
3

4
4
4
5
5
5
6
6
6

1860
1770
1650
1870
1780
1660
1895
1800
1680
1905
1815
1695
1925
1835
1720
1945
1855
1735

8,88

8,90
8,02
11,00
13,84
12,15
11,24
18,61
17,63
12,39
23,54
21,84
13,00
25,32
24,56
13,58
27,00
26,80

10

1,33
3,20
3,29
2,86
6,23
8,02
5,62
12,65
14,10
7,56

18,13
18,35
9,23
22,79
22,84
10,86
25,65
25,73

0,15
0,36
0,41
0,26
0,45
0,66
0,50
0,68
0,80
0,61
0,77
0,84
0,71
0,90
0,93
0,80
0,95
0,96

10,52
10,48

10,42
10,79
10,75
10,67
10,81
10,78
10,74
10,90
10,82
10,78
10,93
10,86
10,82
10,94
10,92
10,87

0,977
0,852
0,805
1,120
1,050
0,956
1,170
1,092
1,062
1,238
1,188
1,188
1,401

1,405
1,380
1,588
1,563
1,536


Table 3.4. Addition parameter of soluble silica oxide by silica fume

Sampl
e

Amount of material using for
Measured Geopolymer properties
1 m3, (kg)
NaOH
Water
solution
Dry comp. saturated
soft
Red
Density
concen
SF
strength,
comp.
coeffi
pH
mud
quan tratio (kg/m3)

(MPa)
strength,
cient
n
tity
(MPa)

Na2Otd
(%)

(M)

072BSN1
143BSN1
215BSN1
286BSN1
358BSN1
072BSN2
143BSN2
215BSN2
286BSN2
358BSN2
072BSN3
143BSN3
215BSN3
286BSN3
358BSN3

1864
1810

1763
1714
1670
1869
1816
1768
1724
1680
1880
1827
1779
1734
1691

42
80
118
152
185
42
80
118
153
186
42
81
119
154
188

381
378
376
373
371
382
379
377
375
373
384
382
380
378
376

1
1
1
1
1
2
2
2
2
2
3
3
3
3

3

1920
1905
1895
1880
1870
1940
1925
1915
1905
1895
1965
1950
1940
1930
1920

10,29
12,22
12,98
13,68
14,55
13,25
15,22
15,87
16,58
16,98
17,21
19,35

21,00
21,81
22,64

2,26
3,79
4,93
5,75
6,26
3,45
7,61
8,73
9,28
9,68
6,20
11,61
14,70
15,49
16,53

0,22
0,31
0,38
0,42
0,43
0,26
0,50
0,55
0,56
0,57

0,36
0,60
0,70
0,71
0,73

10,31
10,28
10,24
10,18
10,16
10,55
10,54
10,50
10,44
10,38
10,69
10,67
10,63
10,58
10,52

0,886
0,875
0,843
0,838
0,833
1,238
1,211
1,141

1,132
1,120
1,528
1,503
1,488
1,445
1,405

3.2.1. Effect of materials on the strength and softening coefficient of
geopolymer
In the study, a geopolymer sample was used only 100% red mud, NaOH
1M÷18 M activated alkaline solutions. These gradients hardly solidified
and decayed and lost their intensity when saturated with water. This again
confirms that the red mud itself is not capable of curing itself. The
geopolymerization reaction does not occur because it does not contain
dissolved SiO2 under normal conditions. The chart of the effect of the
additional fly ash ratio on the strength and softening coefficient of
geopolymer is shown in Figure 3.1, Figure 3.2.
From the results in Figure 3.1 shows that the addition of SiO 2 content
dissolved by fly ash, the compressive strength of GP samples increased.
The compressive strength of geopolymer is also proportional to the
concentration of NaOH alkaline solution used. In the surveyed range,
NaOH concentration from 1M÷6M, compressive strength of geopolymer

11


reaches the highest value of 27 MPa at fly ash ratio of 26% with NaOH 6M
concentration; lowest strength 8.88 MPa at NaOH 1M concentration.
The above result (Figure 3.2) is in the state of water saturation, the

compressive strength of GP will be proportional to the amount of added fly
ash, or in other words, the higher the compressive strength when adding
dissolved SiO2 from the fly ash. The lowest compressive strength at fly ash
ratio of 13% and the highest of 40%. In the survey range of fly ash, the
optimum proportion of additional fly ash ranges from 26÷40%.

Figure 3.1. Effect of additional fly ash
to GP dry compressive strength

Figure 3.2. Additional fly ash effect on
compressive strength of GP water
saturation

As NaOH concentration increases, making geopolymer products more
reactive, creating more stable bonding products, so increasing NaOH
concentration makes the softening coefficient increase, water resistance of
geopolymer increases. The ratio of added fly ash greatly affects the
softening coefficient in proportion to the fly ash content in the aggregate
from 13÷26%. The results also showed that the compressive strength and
softening coefficients of geopolymer were directly proportional to the
content of silica fume added to the mixture, ie the higher the dissolved SiO 2
ratio, the higher the compressive strength and the softening coefficient. The
sample reaches the maximum compressive strength of 22.64 MPa, the soft
coefficient KM = 0.73 at 3M NaOH concentration.
3.2.2. Effect of materials on pH and excess alkalinity in geopolymer
PH and alkaline content. The pH tends to decrease gradually when the SiO 2
rate increases. For fly ash samples, the higher the residual pH and
alkalinity, the higher the NaOH concentration will be used and the greater
the proportion of red mud in the mixture. The more fly ash is added, the
more the dissolved SiO2 is, the better the alkalinity will participate in the

reaction, the alkaline ions will join the geopolymer network structure and
balance the charge at the network nodes, so the amount residual alkalinity
12


PH Value

NaOH
concentration
11.00
10.90
10.8 0
10.70
10.6 0
10.50
10.40
10.30

10 15 20 25 30 35 40 45
Additio nal fly

1M
as h co ntent
1M (% )

Figure 3.3. Effect of fly ash addition
to pH of GP

Res idual alkali content, Na2O (%)

will decrease. This is shown by the specific result of the highest pH of
10.94 (at fly ash ratio of 13%) and NaOH 6M concentration. PH is at least
10.42 (at 40% fly ash ratio) with 1M NaOH concentration, corresponding
to the excess alkali content reaches the minimum value of 0.805%.
Thus, it can be seen that: when adding the amount of SiO 2 dissolved by fly
ash, the compressive strength increases with the addition rate of fly ash in
the surveyed concentration of NaOH solution from 1M ÷ 6M. Similarly, the
amount of excess alkali decreases gradually with the addition of dissolved
SiO2, when the largest content of fly ash is used for the minimum residual
alkalinity value.
S- NaOH
1.8 0
1.6 0
1.40
1.20
1.00
0.8 0
0.6 0
0.40

13

26

40

1
M
2
M

3
M
4
M

Additio nal fly as h co ntent (% )

Figure 3.4. Effect of additional fly
ash to Na2O residual of GP

The pH and the residual alkaline content of geopolymer from red mud with
silica fume supplementation have the same rules as the case of using fly
ash, excess alkalinity and pH decrease as the SiO 2 ratio increases, that is,
the addition of dissolved SiO2 the more the residual alkalinity and the lower
the pH.
3.3. The influence of several factors on the properties of geopolymer
when curing autoclave
From the results of section 3.2, we choose typical samples to study the
effect of the curing regimen of samples such as temperature, Autoclave
autoclave pressure, curing time to geopolymer properties. . The making of
geopolymer from Tan Rai red mud is often required to add dissolved SiO 2
content from external additives. In this study, supplementing dissolved SiO 2
by activating SiO2 in red mud under high temperature and high pressure (in
Autoclave).
Typical base for surveying different curing conditions to geopolymer
properties is shown in Table 3.5.

13

Table 3.5. Selected Geopolymer base for curing autoclave
Sample
symbols

Molar
ratio S/A

RM0
RM1
RM2
RM3
143BTN0
143BTN1

1,43
1,43

Added NaOH
concentration
(M)
0
1
2
3
0
1

Percentage of ingredients (%)
Red mud

Flying ash

100
100
100
100
74
74

26
26

Based on reference materials on curing support of autoclaved aerated
concrete (AAC) and specific preliminary tests on actual materials used, the
value range of variables to be investigated such as pressure, temperature
and curing time. In order to take advantage of the excess alkalinity in the
red mud, it is necessary to add a certain amount of dissolved SiO 2 from the
fly ash power plant materials, just add water to form without adding any
activating alkali differs from the outside.
Curing conditions parameters and results are presented in Table 3.6:
Table 3.6. Curing regime and experimental results when using fly ash
Curing conditions
Sample

RM0
RM1
RM2
RM3
FA0-1
FA0-2

FA0-3
FA0-4
FA0-5
FA0-6
FA0-7
FA0-8
FA0-9
FA0-10
FA0-11
FA0-12
FA1-1
FA1-2
FA1-3
FA1-4

The amount of material used
for 1 m3, kg

MPa Temper
Time,
Red
pressur ature,
(hours) mud
e
oC

1,6
1,6
1,6
1,6

0,4
0,8
1,2
1,6
1,2
1,2
1,2
1,2
0,4
0,8
1,2
1,6

201
201
201
201
144
170
188
201
50
100
150
200
188
188
188
188
144

170
188
201

16
16
16
16
10
10
10
10
10
10
10
10
4
8
12
16
10
10
10
10

2048
2065
2089
2113
1297

1297
1293
1293
1297
1297
1297
1297
1293
1293
1293
1289
1294
1294
1290
1290

The measured geopolymer properties

NaOH
solution

Fly ash water

0
0
0
0
463
463
462

462
463
463
463
463
462
462
462
461
462
462
461
461

410
352
352
351
351
352
352
352
352
351
351
351
350
-

Dry comp.

Conc Density strength
quantit entra kg/m3 (Mpa)
y
tion
(M)

0
413
418
423
0
0
0
0
0
0
0
0
0
0
0
0
351
351
350
350

0
1
2

3
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1

1896
1936
1964
1989
1760
1760
1755
1755
1760
1760
1760
1760

1755
1755
1755
1750
1770
1770
1765
1765

14

10,60
10,62
10,86
10,95
7,36
10,61
12,68
14,16
6,11
6,22
6,38
6,85
11,04
11,98
13,88
15,28
11,26
14,65
17,36

19,08

Water
satura
tion
(Mpa)

7,00
7,33
7,60
7,77
4,49
7,75
10,65
12,89
2,38
2,49
2,68
3,15
8,28
9,10
11,94
13,75
6,98
11,13
14,76
17,55

Softening
coefficient

pH

Na2O (%)

0,66
0,69
0,70
0,71
0,61
0,73
0,84
0,91
0,39
0,40
0,42
0,46
0,75
0,76
0,86
0,90
0,62
0,76
0,85
0,92

9,55
9,79
10,55
11,45

9,58
9,52
9,22
9,09
9,91
9,90
9,90
9,88
9,39
9,23
9,18
8,99
9,75
9,68
9,58
9,48

0,229
0,364
0,665
1,435
0,231
0,202
0,152
0,139
0,419
0,416
0,400
0,396
0,167

0,159
0,150
0,138
0,347
0,329
0,232
0,200


Curing conditions
Sample

FA1-5
FA1-6
FA1-7
FA1-8
FA1-9
FA1-10
FA1-11
FA1-12

The amount of material used
for 1 m3, kg

MPa Temper
Time,
Red
pressur ature,
(hours) mud
e

oC

1,2
1,2
1,2
1,2

50
100
150
200
188
188
188
188

10
10
10
10
4
8
12
16

1294
1294
1294
1294
1290

1290
1290
1287

The measured geopolymer properties

NaOH
solution

Fly ash water

462
462
462
462
461
461
461
460

-

Dry comp.
Conc Density strength
quantit entra kg/m3 (Mpa)
y
tion
(M)

351

351
351
351
350
350
350
349

1
1
1
1
1
1
1
1

1770
1770
1770
1770
1765
1765
1765
1760

8,96
9,34
9,59
9,56

15,17
16,86
18,66
20,06

Water
satura
tion
(Mpa)

4,57
4,95
5,37
5,45
11,53
13,49
16,05
18,25

Softening
coefficient

pH

Na2O (%)

0,51
0,53
0,56
0,57

0,76
0,80
0,86
0,91

10,40
10,39
10,38
10,38
9,59
9,58
9,56
9,52

0,505
0,486
0,475
0,464
0,299
0,231
0,215
0,202

3.3.1. Effect of curing pressure on geopolymer properties
For the independent red mud group, geopolymer has a intensity of 10.60
MPa with a soft coefficient of 0.66. When NaOH was added with the
concentration of 1M, 2M and 3M supplements, the geopolymer intensity
did not change much but the softening coefficient improved to 0.71. This
result shows that the process of geopolymerization took place using only
red mud without the addition of any materials except mixing water.

In subsequent experiments, additional dissolved SiO 2 was added by adding
26% of red mud to replace fly ash. The autoclave and properties of
geopolymer are shown in Table 3.6. The results show that pressure curing
has a great influence on the strength and softening coefficient of GP, the
pressure is almost linearly proportional to the intensity and softening
coefficient. The results also showed that at 1.2 MPa time of 10 hours, the
softening coefficients were both higher than 0.8 (FA0 samples were 0.84
and FA1 samples were 0.85) and further the pH of FA0 samples was 9.22
<9.5 The excess alkali content decreased to 69.11% compared to the
unreactive original sample. So we choose a pressure of 1.2 MPa
(corresponding to 188oC) to investigate the next conditions in the study..
3.3.2. The effect of temperature on geopolymer properties
The results showed that with the same fly ash ratio, raising the curing
temperature from 50ºC to 200ºC did not significantly increase the
compressive strength of geopolymer. The softening coefficient increases
very slowly, the FA0 sample has a softening coefficient of 0.39 ÷ 0.46 and
the FA1 sample reaches from 0.51 ÷ 0.57. The samples were not autoclaved
and cured, dried to 200oC with very low soft coefficient KM <0.6. The
residual pH and alkalinity of the FA0 and FA1 samples during drying
varied slightly and was almost constant. The FA0 sample had the lowest pH

15


of 9.88 excess Na2O of 0.396% and the FA1 sample had the lowest pH of
10.38 and the Na2O excess of 0.464%.
For curing samples in non-autoclave conditions, only drying to 200 oC of
FA0 and FA1 samples has low alkalinity content and is not qualified to
dissolve aluminosilicate components in raw materials.
3.3.3. Effect of curing time on geopolymer properties

Under the same conditions selected for the survey is a 1.2 MPa pressure
curing saturated steam with time changing from 4h ÷ 16h. The results
showed that the compressive strength and softening coefficient increased as
the curing time increased.
For pH and residual alkalinity content of geopolymer samples are also
greatly affected by curing time, pH and alkalinity correlated almost linearly
with curing time under autoclave conditions.
3.3.4. Effect of soluble silicon oxide on geopolymer intensity
Based on the mixing ratio of aggregate (74% red mud and 26% fly ash), the
content of SiO2 and Al2O3 dissolved in raw materials in the respective
curing regimes (Table 3.1 and Table 3.2) can calculate the total amount of
SiO2 and Al2O3 dissolved as well as the ratio between the two oxides for
each gradation in each curing regime. Using the least square method, the
regression equation described above relation has been identified for the
case of heating and autoclave. According to the results of the analysis, the
intensity of geopolymer is linearly and positively related to the total amount
of dissolved SiO2 in the mixture (Figure 3.5).
In this study, gradients with a ratio between red mud and fixed fly ash are
used. Converting the ratio of SiO2 to Al2O3 in the mixture will have a fixed
value of 0.93 (calculated by the total oxide). Curing heat or autoclave does
not change total oxide but only dissolved oxides.

Figure 3.5. The effect of dissolved SiO2 on the strength of geopolymer
16


The correlation equation for the two cases has nearly equivalent
coefficients. The regression equation based on data from both cases has the
following form:
R = 0.123 x (SiO2)atv + 5.967 (3.1)

Equation (3.1) with R² = 0.954 indicates that the above correlation reaches
statistical reliability. On that basis, Figure 3.5 can serve the selection of
geopolymer components according to compressive strength requirements.
3.3.5. Effect of curing conditions on the structure of geopolymer
Samples of geopolymer use only red mud: choose RM0 sample (samples
using only red mud with 20% more water). XRD spectrum shows no new
mineral in geopolymer. Therefore, eliminating the possibility of the
intensity formed by the mineral formation reaction. In Figure 3.6 the
typical pecks present in the red mud are gibbsite (at 2θ = 18.5), goethite (at
2θ = 21.2; 36.8) and hematite (at 2θ = 24.2; 33.1; 35 , 8; 40,5; 49,5; 54).
However, geopolymer samples from autoclaved red mud did not detect
peck gibbsite (at 2θ = 18,5) and peck hematite (at 2θ = 49,5). This confirms
that these minerals have been dissolved and involved in the
geopolymerization reaction.
The FA0-3 sample then selects 3 component analysis points at the selected
points by SEM - EDS method, as shown in Figure 3.7. With the results of
the analysis, it is possible to evaluate the chemical composition of point A
which is suitable for the un-reacted fly ash material. Point B is suitable for
red mud material.

Figure 3.6. XRD spectrum of
Figure 3.7. Figure SEM-EDS of
geopolymer RM0 model
geopolymer model FA0-3
Point C has a chemical composition unlike the original component of red
mud as well as fly ash, so maybe point C is the product of geopolymer. The
ingredient point C also contains 35.95% FeO so geopolymer products
17

containing Fe and iron are also dissolved and participate in the bond of
geopolymer.
3.4. Conclusion chapter
- The geopolymer intensity is also proportional to the content of added
silica fume. Using external additives to improve softening coefficient and
reduce excess alkalinity of the product.
- Autoclave support activated SiO 2 component in red mud, then it can be
used independently red mud to make geopolymer with compressive
strength of 10.6 MPa, soft chemical coefficient of 0.70.
- Geopolymer from red mud supplemented with 26% fly ash, autoclave at a
pressure of 1.2 MPa in 10 hours to achieve compressive strength of 12.68
MPa and soft coefficient KM = 0.84> 0.8; pH 9.22 <9.5; This result meets
the technical requirements of unburnt construction bricks as initially set by
the target.
- Curing regime has a great influence on the process of geopolymerization
as well as the properties of geopolymer materials using red mud. Different
from curing at normal pressure, the autoclave cure helps dissolve SiO2 in
red mud to contribute to geopolymerization.
- The structure of geopolymer expressed through XRD analysis method
does not appear any new crystalline minerals in the structure of the
material. From the results of SEM-EDS analysis, geopolymer products
containing Fe and iron were also dissolved in the activation process and
involved in the bonding of geopolymer.
CHAPTER 4. NATURE OF BRICKS USING GEOPOLYMER FROM
TAN RAI RED MUD
4.1. The physical properties
The properties of the selected geopolymer are: volumetric mass, water
absorption, water permeability and adhesion of mortar on brick substrate,
surveyed in both autoclave and normal laboratory conditions:
Sample of geopolymer curing autoclave at pressure of 1.2 MPa and 10-hour

time with sample code FA0-3. Sample of geopolymer curing in normal
laboratory conditions with concentrations of NaOH 4M solution with the
sample symbol 143BTN4.
- Samples of baked clay bricks and unburnt cement bricks with aggregate
dimensions of length x width x height: 180x80x40 mm as a control sample.
Test of adhesion of mortar on bricks, using M75 mortar using Ha Tien PCB
40 cement and Dong Nai yellow sand with actual compressive strength at
28 days of age to reach 9.8 MPa.

18


Some properties of geopolymer bricks and reference samples compared
with baked clay bricks, aggregate unburnt cement bricks are shown in Table
4.1.
Table 4.1. Results of some mechanical properties of bricks
No
1
2
3
4

Brick type /
symbol pattern
FA0-3
143BTN4
Burnt clay
XM
aggregates

1755
1815
1460

Water
absorption,
(%)
15,85
15,67
12,46

1880

9,25

Density,
(kg/m3)

Water
Adhesion,
permeability,

(L/m2/h)
0,88
0,66
0,27

(MPa)

18,42

0,20

0,19
0,18
0,16

Denssity of geopolymer bricks using the higher amount of activated alkali
will have a higher volume volume. The volume of geopolymer bricks is in
the average range between burnted clay bricks and aggregate cement
bricks.
Water absorption of geopolymer bricks is higher than that of baked clay
bricks or aggregate cement bricks and higher than the water absorption
requirement of aggregate cement bricks according to TCVN 6477:2016
(not permitted) larger than 14%), but still meeting the requirements of
water absorption of hollow clay bricks TCVN 1451:2009 (not greater than
16%).
Absorbent Geopolymer water permeability test and under normal
conditions have water absorption (15.85% and 15.67%) water permeability
(0.88 and 0.66 L/m2.h) are nearly equal.
4.2. Compressive strength development over time
Evaluation of compressive strength development over time at different age
days 3, 7, 14, 28, 60, 90 and 180 days, using geopolymer samples under
autoclave conditions and curing normal laboratory conditions, as follows:
- Sample of geopolymer for autoclaving with pressure of 1.2 MPa and 10hour time with sample code FA0-3.
- Sample of geopolymer curing under normal conditions in the laboratory
with different concentrations of NaOH 2M, 4M, and 6M with the model
symbol 143BTN2, respectively; 143BTN4 and 143BTN6.
The results also showed that when using low concentrations of NaOH
solution, the intensity of early development was slower than samples using

higher concentrations of NaOH, but at longer age, the sample had a higher
percentage. compared to R28 days higher. Form 143BTN6 uses NaOH 6M,
reaching the intensity values when comparing the days of age R3, R7, R14
with R28, respectively 28.3%; 59.4% and 85.1%. Compared to the old days
19


R60, R90 and R180 reached 106.2%; 109.5% and 112.1%. At this rate, it
can be said that geopolymer develops intensity slower than conventional
Portland cement.
For curing samples at high temperature in autoclave, the intensity almost
does not increase at different time points, even up to 180 days of age. This
shows that when the autoclave promotes the reaction, it is faster and more
thorough, shortening the time in the production process.
4.3. Study on the alkaline extraction of geopolymer under conditions of
sample immersion
4.3.1. The change in water soaked geopolymer brick samples over time
Geopolymer bricks (whole bricks) are soaked in water and monitored for
changes in water pH over time. From this, it is possible to evaluate the
residual alkalinity extraction of geopolymer in water over a period of 1 day,
7 days, 28 days, 90 days and 180 days, compared to the pH value when
grinding samples through sieve 0.09 mm. In the study, 3 samples of raw
bricks were immersed in water at 3 different levels. The first sample is
immersed in 1 liter of water, the second sample is immersed in 1.5 liters of
water and the third sample is immersed in 2 liters of water, the pH of the
original sample soaked water is 7.
Experimental geopolymer samples were selected under both autoclave and
normal laboratory conditions: - Autoclaved geopolymer samples at 1.2 MPa
and 10-hour time with the symbol FA0-3 .- Sample of geopolymer curing
under normal laboratory conditions with concentrations of NaOH 4M

solution with the sample symbol 143BTN4
The pH of the water soaked in geopolymer samples increases gradually
with the time of soaking and follows the logarithm rule. From the time the
sample was saturated with water (1 day) to 60 days, the pH continued to
increase rapidly, then increased gradually to 180 days with almost no
increase.
The pH of immersion geopolymer samples with the largest value of pH
9.83 is much smaller than the same geopolymer samples (pH 10.82) when
finely ground through the 0.09 mm sieve and tested according to standards.
Standards TCVN 9339:2012. Similarly for the autoclaved geopolymer, the
maximum pH of the immersion water reaches pH 8.64, much smaller than
the finely ground sample pH (pH 9.22). In fact, the geopolymer works in
water, the residual alkali remains washed away in the water for a long time.
4.3.2. The change in pH of water with soaked masonry over time
In order to make a more realistic assessment of the use of the material,
when plastered tiles are plastered, normally the plastered surface will be
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exposed to moist environment, so geopolymer bricks are plastered soaked
in water to monitor pH changes over time.
Geopolymer samples were plastered with M75 mortar of 10 mm thickness
on one side of the sample, the other sides were covered with impervious
paraffin.
These samples were soaked in water in 3 different levels, respectively 1
liter of water, 1.5 liters of water and 2 liters of water, for long periods of 1
day, 7 days, 28 days, 90 days and 180 days. The pH of the water when
immersed in these samples changes then it is possible to assess the ability
of alkali extraction in the long term exposure to water permeable to a 10
mm thick plaster.

Table 4.3. The pH of water soaked in geopolymer samples is plastered
with mortar
No
1
2
3
No
4
5
6

Normal GP
model
(143BTN4)
1L
1,5L
2L
Autoclave GP
Model (FA0-3)
1L
1,5L
2L

PH of water, timeline (days)
1

7

28

90

180

10,38
10,28
10,11

10,71
10,64
10,58

10,79
10,71
10,65

10,83
10,75
10,72

11,05
10,90
10,81

1

7

28

90

180

10,36
10,25
10,08

10,69
10,62
10,57

10,77
10,68
10,61

10,79
10,71
10,64

10,84
10,75
10,68

The pH of the water soaked in geopolymer samples increased rapidly at the
beginning and tended to decrease over time to 180 days. However,
compared to the non-plastered sample, the pH of the plastered sample was
much higher than that of the non-plastered geopolymer sample. This is
explained by the influence of alkaline plaster cement mortar in the form of
free lime Ca(OH)2 on water significantly increases the pH, so if based

solely on the measured pH value will not properly assess the ability of Na +
to extract alkali from water penetrating through the plaster.
To more accurately assess the pH due to Na + alkali extraction, it is
necessary to test the concentration of Na + and Ca2+ in water over time.
Water samples soaked in geopolymer bricks in autoclave and normal
conditions in 2L capacity bottles were selected to represent the results of
the concentration of alkaline ions, the results of the alkaline concentration
in water over time are shown in the Table 4.4.

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Table 4.4. Concentration of alkaline ions in water over time
No
1
2
3
4
5
6

Targets
Unautoclaved samples
Na+concentration
Ca2+concentration
pH
Autoclaved samples
Na+concentration
Ca2+concentration
pH

Unit
ppm
ppm
ppm
ppm
-

1
0,71
20,81
10,11
1
0,12
19,28
10,08

Value after sample soaking, day
7
28
90
5,61
12,22
40,81
58,62
64,87
73,22
10,58
10,65
10,72

7
28
90
0,45
2,46
5,22
59,25
65,25
70,19
10,57
10,61
10,64

180
62,65
76,26
10,81
180
8,35
74,55
10,68

The results shown in Table 4.4 show that the concentration of Ca 2+ ions
extracted into water in both samples is quite similar at all time points.
The amount of Na+ alkalinity was significantly different in the two
geopolymer samples tested. The age from 1 day to 28 days of Na + alkalinity
ability of both samples is relatively slow, in the long days of 90 days or 180
days, the concentration of Na+ alkaline increases significantly. This Na +
alkali extraction property is mainly due to the sample of geopolymer
material penetrating the outside plaster into the environment.

It is the difference of Na+ component in the two samples that has a great
influence on the pH of the water in the sample. At the beginning from 1 to
28 days when the amount of Na + extracted into the water environment was
low, the pH of the water was mainly decided by Ca 2+ alkaline due to the
plaster, so the pH of the two samples was nearly the same. But at larger
time points such as 90 days and 180 days, the amount of Na + alkaline
extraction soaked in non-autoclaved geopolymer samples (143BTN4) is
much higher than that of autoclaved samples (FA0-3), so the pH is also
higher.
4.4. Adhesion of mortar
The adhesion strength of the mortar on the masonry bricks, the panel used
in the experiment is the geopolymer unburnt building bricks with
dimensions Length x Width x Height: 90 x 80 x 40 mm. The adhesion
strength of mortar is influenced not only by the mortar but also by the
construction conditions, in which the moisture of the masonry and the
quality of the masonry surface have a great influence. In which the
moisture of the tiles is the humidity to be in a natural state in the laboratory.
Experimental samples prepared include geopolymer autoclaved sample,
labeled FA0-3; sample of non-autoclaved geopolymer 143BTN4; samples
of clay bricks and aggregate cement bricks.
The adhesion strength of the two geopolymer curing samples and
conditions is usually approximately the same, reaching 0.19 and 0.18 MPa
and still higher than that of baked clay bricks (0.16 MPa). Meanwhile,
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unburnt cement aggregate sample has the highest adhesion, reaching 0.20
MPa.
The results also showed that it is possible to use regular cement mortar to
make geopolymer bricks similar to the use of regular mortar for baked clay

bricks.
4.5. The strength of masonry prisms uses geopolymer bricks
The compressive strength of masonry prisms depends on the compressive
strength of brick, of mortar and the link between mortar and masonry
prisms. In the study of the dissertation, it is often used to build mortar with
sand and cement with grade of 7.5 MPa.
The strength of masonry using regular mortar can also be determined by
looking up the table in accordance with TCVN 5573: 2011 standard "stone
brick structure - design standard". Clay bricks, size 40 x 80 x 180 mm, are
used in experimental research according to TCVN 6355: 2009, actual
compressive strength 13.50 MPa, flexural strength 5.4 MPa and water
absorption 12.46%. Aggregate cement bricks, size 40 x 80 x 180 mm, used
in experimental research according to TCVN 6355: 2009, have
compressive strength of 14.70 MPa, flexural strength and water absorption
of 9.25% . M75 mortar using Ha Tien cement PCB 40, Dong Nai gold sand,
compressive strength at 28 days reaches 9.80 MPa.
Within the scope of the study, to prepare and conduct experiments
comparing 3 masonry groups with the following details:
- Sample geopolymer, using 4 masonry bricks (size 40 x 80 x 90 mm) built
with regular mortar with the thickness of mortar circuit being 10 ÷ 12 mm;
- Burnt clay bricks, using 4 masonry bricks (nail bricks of size 40 x 80 x
180 mm), which are built of ordinary mortar with a mortar thickness of 10
÷ 12 mm;
- Sample of unburnt cement aggregate brick, using 4 bricks (nail bricks of
size 40 x 80 x 180 mm), built with ordinary mortar with a thickness of 10 ÷
12 mm;
Actual strength of masonry is calculated based on the value of actual
destructive load, bearing area and conversion coefficient depending on the
ratio of height and thickness of masonry. Geopolymer sample reached 6.59
MPa; aggregate cement is 7.16 MPa and baked clay bricks is 6.5 MPa. The

destructive type is recorded according to ASTM C1314:2016, the height
effect factor (Correction Factor - hp / tp of all 3 types of masonry is 1.03).
The results showed that the actual compressive strength of fired clay bricks,
aggregate cement bricks and geopolymer bricks using mortar is often quite
similar and not much different. It is possible to use geopolymer-type
unburnt brick masonry blocks built with regular mortar.
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