Scientific significance Having argued and proved experimentally on the following issues: - The ability to make geopolymer from red mud depends on the amount ofsilicon oxide dissolved in
Trang 1MINISTRY 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
Trang 2THE 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 atInstitute of Building Science and Techonology, 81 Tran Cung street, NghiaTan, 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
Trang 31 Rationale of the Study
Red mud is the name of waste generated from bauxite hydrated alumina byBayer technology Tan Rai Aluminum Factory has the amount of red muddischarged into the environment during the operation process of 80÷90million m3, causing environmental pollution, significant impact onecosystems 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 compositionmay have radioactive substances very difficult to store and preserve.Utilizing the typical residual components, silicon oxide, aluminum oxide inred mud combined with the addition of silicon oxide from other wastesources such as fly ash and appropriate curing methods to fabricategeopolymer materials The demand for unbaked construction bricks inVietnam as well as environmental treatment is essential
2 Research subject and scope
The object of the dissertation is geopolymer using Tan Rai Lam Dong redmud 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 siliconoxide and aluminum oxide in raw materials Effect of materials, curingconditions on intensity, softening coefficient, pH and excess alkalinity ofgeopolymer 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 ofsilicon oxide dissolved in the alkaline solution, thanks to curing at highpressure and high temperatures or supplemented from materials such as flyash, silica fume
- Clarified the influence of material and technology parameters on theproperties of geopolymer from red mud From there set the technologicalparameters for production
4 Practical significance
- Based on the research results that have contributed to the market a newproduct, geopolymer unburnt bricks from Tan Rai red mud, meetingtechnical requirements for use in construction works
- Method of making geopolymer unburnt bricks from red mud by autoclavetechnology allows effective treatment of red mud waste, contributing toenvironmental protection
Trang 45 New contributions of dissertation
- Using red mud waste of Tan Rai Aluminum factory and fly ash of Tan Raiinternal thermal power plant, successfully manufacturing unbakergeopolymer bricks with autoclave technology to meet the requirements ofconstruction
- Clarifying the influence of several factors on the solubility ratio of siliconoxide in red mud and fly ash including alkaline solution concentration,temperature, pressure and curing time Under autoclave conditions, siliconoxide 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 andmixture of red mud and fly ash curing in autoclave conditions Whenautoclaving can improve the ratio of dissolved silicon oxide under lowalkaline concentration Thus, it is possible to improve the softeningcoefficient, 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 manufacturedusing Bayer technology (invented by Bayer in 1887) Red mud consists ofinsoluble, inert and quite stable components in weathering conditions such
as Hematite, Natrisilicat, Aluminate, Calcium-titanate, Mono-hydratealuminum and especially contains a amount of caustic soda, a type ofHighly 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 chemicalcomposition, minerals, particle size ;
+ Chemical composition: as reported by UNIDO, the solid phase chemicalcomposition of red mud includes Al2O3, SiO2, Fe2O3, Na2O, CaO, TiO2,L.O.I
+ Mineral composition: similar to the composition of bauxite and has twonew phases, namely Na2O.Al2O3.2SiO2.nH2O and compounds withoscillating components of CaO with Al2O3, Na2O and SiO2 components
Trang 5+ Particle size: red mud usually has a fine to very fine particle size Most ofthem 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 3components 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 intothe bottom of the river, seabed or partially blocked the bay to contain wastemud However, these measures have been banned Today, research focuses
on the following areas Agriculture: using red mud as arable land inagriculture Production of construction materials: cement, bricks, makinginorganic pigments Backfilling materials: roads Composite materials fromred mud Recovery of precious metals used in metallurgy, iron andaluminum Because of the red mud composition of aluminum hydroxides,iron hydroxides and iron oxide with very small particle size, it is possible touse unburnt bricks in the direction of geopolymerization is verymeaningful
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 4stages and these processes can take place in parallel and alternating so that
it is impossible to distinguish clear boundaries, namely: (1) Dissolvingsolid aluminosilicate in alkaline solution strong (2) Form the Si (Si) or Si-
Al (oligomer) base chain in the liquid phase (3) The polymerizationprocess stops the oligomeres forming three-dimensional silicate alunimonetwork (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 isnecessary to use additional raw materials containing active silica oxide totreat 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% alkalinemetakaolin NaOH and Na2SiO3 (glass water) for heat-resistant geopolymerreaching 400 ÷ 1000oC, compressive strength from 4÷9.5 MPa Use morelime and plaster Yang, using OPC steering port cement, fly ash, lime andgypsum to make geopolymer mortar, the intensity of 11.7÷29 MPa Kumaruses additional slag, curing 60oC for 24 hours compressive strength
Trang 664÷125 MPa Zang, using rice husk ash, NaOH 4M with red mud, intensity
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 ondeveloping and using unburnt bricks At the same time, issuing documentssuch as Circular 09/2012 / TT-BXD of the Ministry of Construction: 100%
of unburnt construction materials must be used from January 15, 2013; Inthe remaining areas, using at least 50% of unburnt construction materialsfrom 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 unburntbrick has set different technical requirements specified in the standarddepending on the characteristics and nature of that unburnt brick Unburntbricks from red mud are new products without technical requirements, so it
is necessary to set technical requirements for this type of products such asrequirements related to bearing resistance, relating to the use, soundproof,heat insulation
From research and practice of the dissertation, propose technicalspecifications of unburnt geopolymer bricks from Tan Rai red mud:compressive strength min 10 MPa; water absorption 8÷16%; waterpermeability 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
Trang 7When mixing Si and Al materials (such as fly ash) with alkali solution, ion of solution enters fly ash particles, causing Si-O-Si bond to be broken
OH-to form Si(OH)3O- Al(OH)4- is formed similar to Si The solubility of Siand 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 inthe composition of geopolymer fabrication material determines the bondformation and mechanical properties of the material Silicon has the ability
to bond directly with each other Si) or bond through oxygen globes O-Si) When bonded via oxygen globes, the polymer circuit can berepresented via coordinated polyhedrafts, creating a three-dimensionalspatial network The ions of the modified oxides such as Na2O, K2O, CaO,MgO do not create circuits, located in the holes of coordination polyhedra
(Si-1.4.2 Effect of temperature, pressure conditions on reaction process
When autoclave Si and Al materials will be dissolved more quickly andmore into NaOH caustic soda, speed curing and increase the efficiency ofgeopolymerization reaction In this soluble solution, depending on the pH,temperature and concentration of Si and Al solubility, groups of [SiO4]4-may exist independently (completely dissolved) or bound together to formpolymerization circuits (the oxygen globules create polymer circuits can bedenoted Q0, Q1, Q2, Q3 with 0,1,2,3 is the oxygen demand index in thestructure) According to Sani and Kani, the excess alkalinity is due to thehigh amount of alkalinity introduced, or the low level of activity of thematerial leading to an alkaline reaction The study of E N Kani usedpozzolan and NaOH, curing at different temperatures for 20 hours E.Najafi Kani and the study of chalk control phenomenon in Geopolymerproducts made from natural pozzolan also talked about this issue.Hydrothermal curing of N A M Sani (2008) is an effective way todevelop appropriate GP structure, the excess NaOH in geopolymerdecreases compared to non-curing heat and the lowest is 4.84% Kani withhis partners (2007) investigated the effect of autoclave on the strength development of geopolymer from blast furnace slag and natural pozzolan,concluding that the reaction is good, Al and Si components from rawmaterials are almost participants react almost completely in the autoclaveenvironment This is also consistent with Kriven's other research results,curing in autoclave at 1000 psi, 80 ° C for 24 h, and the author concludesthat autoclave curing makes the reaction more complete and complete.Bassel Hanayneh (2014) using kaolinite has also reaffirmed the advantages
Trang 8of autoclave maintenance A M Distillation of making an alkaline slagbinder with quartz powder, also confirms the role of curing autoclave.Through the above studies it can be seen that to improve the properties ofgeopolymer, scientists have cured: drying, hydrothermal and autoclave.Studies in the world about synthesis of geopolymer for autoclaving mainlyfocus on materials such as natural puzolan, slag, metakaoline, withoutany research on Bayer red mud technology With the aim of the researchtopic, using Tan Rai Lam Dong red mud to make unburnt geopolymer bricksystem Making full use of ingredients available in raw materials, excessalkali The dissertation conducted survey experiments and offered theoption of not adding more alkali to activate the reaction, but only addingwater to shape.
1.4.3 Scientific hypothesis
Geopolymer from red mud can only be formed by adding dissolved siliconoxide in the composition by using mineral additives or applying specialcuring at high pressure high temperature
1.4.4 Research objectives and missions
Objective: to make geopolymer unburnt construction bricks from Tan RaiLam Dong red mud under practical conditions of Vietnam
The task of researching and manufacturing geopolymer from red mudincludes the following issues:
- Determination of content of dissolving silicon oxide and aluminum oxide
- 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%; other3.27%; 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
Trang 94.2%; other 0.3%; L.O.I 3.85% Mullite mineral composition: Al6Si2O13:20%; Quartz: SiO2: 2%; amorphous 78%.
- Silicafume: Elkem Silicon Materials Volume density 360 kg/m3, density2.15 g/cm3, particle size 1.5 μm SiO2 chemical composition 94.5%; L.O.I2.74% The mineral content of 1% is Cristobalite SiO2, the remainingamorphous 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 Kaccording to the size of the test sample - Specific gravity: TCVN 4030:
2003 - Bulk density: TCVN 7572-6: 2006 - Softening coefficient: TCVN7572-10: 2006 - Humidity: TCVN 7572-10: 2006 - Chemical compositionand L.O.I of red mud and silicafume were determined according to TCVN141: 2008 standard, fly ash was determined according to TCVN 8262: 2009standard - Determination of pH: TCVN 9339: 2012 - Free excess alkalicontent: TCVN 6882: 2001, Na2Otd =% Na2O + 0,658 *% K2O
- Adhesion strength of mortar to brick substrate: TCVN 3121-12: 2013, inwhich, geopolymer board has natural moisture in the laboratory
- Testing of compressive strength of masonry: ASTM C1314 "Standard TestMethod for Compressive Strength of Masonry Prisms"
- Structural analysis: XRF, XRD, AAS, SEM, SEM-EDS
- Determine the soluble content of SiO2, 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/mm2, 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-dryforming, 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 excessalkali available in red mud (RM0) Samples added with 1M, 2M, 3MNaOH alkaline symbols with RM1, RM2, RM3, autoclave at 201oC, 1.6MPa 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
Trang 10alkaline (FA1) The sample is semi-dry pressed shape, after removing themold, autoclave curing: pressure 0.4; 0.8; 1.2; 1.6 MPa is equivalent to thepressure of 144oC, 170oC, 188oC, 201oC During 4 hours, 8 hours, 12 hoursand 16 hours After the autoclave was completed, it was rescued undernormal laboratory conditions for up to 28 days.
For samples of softening coefficient, saturated with water for 48 hours atthe time (from the 26th to the 28th day), up to 28 days of determination ofthe softening coefficient Autoclave time is constant time, constanttemperature, not including the stages of pressure rise and lower pressure.Turbocharging/lowering speed: 0.013 MPa/min (correspondingincrease/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 Al 2 O 3
in raw materials
The first stage in the synthesis of geopoymer materials is crucial to theprocess of geopolymerization and the properties of geopolymer materialsare the dissolution of SiO2 and Al2O3 In the study, the solubility of theseoxides in red mud and fly ash was assessed at different pressure andtemperature 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 SiO 2 , Al 2 O 3 dissolved curing at normal pressure
Heat mode Additional
NaOH solution concentration
Dissolved oxide ratio, mass (%)
Trang 11The results showed that SiO2 in red mud did not dissolve under normalpressure when adding NaOH 1M÷15M The dissolution process is also notactivated when the temperature increases from 80ºC to 200ºC Meanwhile,the ratio of dissolved SiO2 of fly ash after 24h at 80ºC increased sharplyfrom 2.33% to 15.21% when increasing the concentration of NaOHsolution from 1M to 15M The rate of dissolved Al2O3 is almost unchangedand does not depend on the concentration of NaOH Silica fume has anearly constant ratio of SiO2 at NaOH concentrations, the solubility reaches90.06% at 1M alkaline concentration, and reaches the highest value of90.32% 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 ofdissolved SiO2 of red mud after 10 h of autoclave increased from 0.34% to2.25% corresponding to an increase in pressure from 0.4 MPa to 1.6 MPa.Adding NaOH under autoclave conditions also increased the proportion ofSiO2 dissolved in red mud under curing conditions
Table 3.2 The ratio of SiO 2 and Al 2 O 3 dissolved when curing autoclave
Autoclave mode Additional
NaOH solution concentratio n
Dissolved oxide ratio, mass (%)
Trang 12mud, providing an additional source of dissolved SiO2 forgeopolymerization, improving the properties of the material Unlike SiO2,
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 andfly ash improved significantly The results of the solubility of SiO2 and
Al2O3 showed that it is possible to use the autoclave to activate thecomponents in the red mud to pave the way for the geopolymerizationreaction
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 Al2O3 To makegeopolymer under normal conditions, it is necessary to add dissolved SiO2content from the external source (such as fly ash, silica fume .) Thegradation 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
1 m3, (kg) Measured Geopolymer properties
Red
mud Flyash
NaOH solution
Density (kg/m3)
Dry comp.
strength, (MPa)
Water saturated comp.
strength, (MPa)
soft coeffi cient
pH Na2 O td (%) quan
tity
concen tratio n (M)
072BTN1 1601 245 369 1 1860 8,88 1,33 0,15 10,52 0,977 143BTN1 1294 462 351 1 1770 8,90 3,20 0,36 10,48 0,852 215BTN1 989 648 327 1 1650 8,02 3,29 0,41 10,42 0,805 072BTN2 1598 244 368 2 1870 11,00 2,86 0,26 10,79 1,120 143BTN2 1292 461 351 2 1780 13,84 6,23 0,45 10,75 1,050 215BTN2 988 647 327 2 1660 12,15 8,02 0,66 10,67 0,956 072BTN3 1608 246 371 3 1895 11,24 5,62 0,50 10,81 1,170 143BTN3 1297 463 352 3 1800 18,61 12,65 0,68 10,78 1,092 215BTN3 993 650 329 3 1680 17,63 14,10 0,80 10,74 1,062 072BTN4 1606 245 370 4 1905 12,39 7,56 0,61 10,90 1,238 143BTN4 1300 464 353 4 1815 23,54 18,13 0,77 10,82 1,188 215BTN4 995 652 330 4 1695 21,84 18,35 0,84 10,78 1,188 072BTN5 1613 246 372 5 1925 13,00 9,23 0,71 10,93 1,401 143BTN5 1306 467 355 5 1835 25,32 22,79 0,90 10,86 1,405 215BTN5 1004 658 332 5 1720 24,56 22,84 0,93 10,82 1,380 072BTN6 1621 248 374 6 1945 13,58 10,86 0,80 10,94 1,588 143BTN6 1313 469 356 6 1855 27,00 25,65 0,95 10,92 1,563 215BTN6 1007 660 333 6 1735 26,80 25,73 0,96 10,87 1,536
Trang 13Table 3.4 Addition parameter of soluble silica oxide by silica fume
Sampl
e
Amount of material using for
1 m3, (kg) Measured Geopolymer properties
Red
mud SF
NaOH solution
Density (kg/m3)
Dry comp.
strength, (MPa)
Water saturated comp.
strength, (MPa)
soft coeffi cient
pH Na2 O td (%) quan
tity
concen tratio n (M)
072BSN1 1864 42 381 1 1920 10,29 2,26 0,22 10,31 0,886 143BSN1 1810 80 378 1 1905 12,22 3,79 0,31 10,28 0,875 215BSN1 1763 118 376 1 1895 12,98 4,93 0,38 10,24 0,843 286BSN1 1714 152 373 1 1880 13,68 5,75 0,42 10,18 0,838 358BSN1 1670 185 371 1 1870 14,55 6,26 0,43 10,16 0,833 072BSN2 1869 42 382 2 1940 13,25 3,45 0,26 10,55 1,238 143BSN2 1816 80 379 2 1925 15,22 7,61 0,50 10,54 1,211 215BSN2 1768 118 377 2 1915 15,87 8,73 0,55 10,50 1,141 286BSN2 1724 153 375 2 1905 16,58 9,28 0,56 10,44 1,132 358BSN2 1680 186 373 2 1895 16,98 9,68 0,57 10,38 1,120 072BSN3 1880 42 384 3 1965 17,21 6,20 0,36 10,69 1,528 143BSN3 1827 81 382 3 1950 19,35 11,61 0,60 10,67 1,503 215BSN3 1779 119 380 3 1940 21,00 14,70 0,70 10,63 1,488 286BSN3 1734 154 378 3 1930 21,81 15,49 0,71 10,58 1,445 358BSN3 1691 188 376 3 1920 22,64 16,53 0,73 10,52 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, NaOH1M÷18 M activated alkaline solutions These gradients hardly solidifiedand decayed and lost their intensity when saturated with water This againconfirms that the red mud itself is not capable of curing itself Thegeopolymerization reaction does not occur because it does not containdissolved SiO2 under normal conditions The chart of the effect of theadditional fly ash ratio on the strength and softening coefficient ofgeopolymer is shown in Figure 3.1, Figure 3.2
From the results in Figure 3.1 shows that the addition of SiO2 contentdissolved by fly ash, the compressive strength of GP samples increased.The compressive strength of geopolymer is also proportional to theconcentration of NaOH alkaline solution used In the surveyed range,NaOH concentration from 1M÷6M, compressive strength of geopolymer
Trang 14reaches the highest value of 27 MPa at fly ash ratio of 26% with NaOH 6Mconcentration; lowest strength 8.88 MPa at NaOH 1M concentration.The above result (Figure 3.2) is in the state of water saturation, thecompressive strength of GP will be proportional to the amount of added flyash, or in other words, the higher the compressive strength when addingdissolved SiO2 from the fly ash The lowest compressive strength at fly ashratio of 13% and the highest of 40% In the survey range of fly ash, theoptimum 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 morereactive, creating more stable bonding products, so increasing NaOHconcentration makes the softening coefficient increase, water resistance ofgeopolymer increases The ratio of added fly ash greatly affects thesoftening coefficient in proportion to the fly ash content in the aggregatefrom 13÷26% The results also showed that the compressive strength andsoftening coefficients of geopolymer were directly proportional to thecontent of silica fume added to the mixture, ie the higher the dissolved SiO2ratio, the higher the compressive strength and the softening coefficient Thesample reaches the maximum compressive strength of 22.64 MPa, the softcoefficient 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 SiO2rate increases For fly ash samples, the higher the residual pH andalkalinity, the higher the NaOH concentration will be used and the greaterthe proportion of red mud in the mixture The more fly ash is added, themore the dissolved SiO2 is, the better the alkalinity will participate in thereaction, the alkaline ions will join the geopolymer network structure andbalance the charge at the network nodes, so the amount residual alkalinity
Trang 15will decrease This is shown by the specific result of the highest pH of10.94 (at fly ash ratio of 13%) and NaOH 6M concentration PH is at least10.42 (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 SiO2 dissolved by flyash, the compressive strength increases with the addition rate of fly ash inthe surveyed concentration of NaOH solution from 1M ÷ 6M Similarly, theamount of excess alkali decreases gradually with the addition of dissolvedSiO2, when the largest content of fly ash is used for the minimum residualalkalinity value
1M 1M Additio nal fly as h co ntent (% )
S- NaOH
1 M 2 M 3 M 4 M
Additio nal fly as h co ntent (% )
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 theeffect of the curing regimen of samples such as temperature, Autoclaveautoclave pressure, curing time to geopolymer properties The making ofgeopolymer from Tan Rai red mud is often required to add dissolved SiO2content from external additives In this study, supplementing dissolved SiO2
by activating SiO2 in red mud under high temperature and high pressure (inAutoclave)
Typical base for surveying different curing conditions to geopolymerproperties is shown in Table 3.5
Trang 16Table 3.5 Selected Geopolymer base for curing autoclave
Sample
symbols ratio S/A Molar
Added NaOH concentration (M)
Percentage of ingredients (%) Red mud Flying ash
Curing conditions parameters and results are presented in Table 3.6:
Table 3.6 Curing regime and experimental results when using fly ash
NaOH solution Density kg/m3
Dry comp.
strength (Mpa)
Water satura tion (Mpa)
Softening coefficient pH Na 2 O (%) quantit
y
Conc entra tion (M) RM0 1,6 201 16 2048 0 410 0 0 1896 10,60 7,00 0,66 9,55 0,229 RM1 1,6 201 16 2065 0 - 413 1 1936 10,62 7,33 0,69 9,79 0,364 RM2 1,6 201 16 2089 0 - 418 2 1964 10,86 7,60 0,70 10,55 0,665 RM3 1,6 201 16 2113 0 - 423 3 1989 10,95 7,77 0,71 11,45 1,435 FA0-1 0,4 144 10 1297 463 352 0 0 1760 7,36 4,49 0,61 9,58 0,231 FA0-2 0,8 170 10 1297 463 352 0 0 1760 10,61 7,75 0,73 9,52 0,202 FA0-3 1,2 188 10 1293 462 351 0 0 1755 12,68 10,65 0,84 9,22 0,152 FA0-4 1,6 201 10 1293 462 351 0 0 1755 14,16 12,89 0,91 9,09 0,139 FA0-5 - 50 10 1297 463 352 0 0 1760 6,11 2,38 0,39 9,91 0,419 FA0-6 - 100 10 1297 463 352 0 0 1760 6,22 2,49 0,40 9,90 0,416 FA0-7 - 150 10 1297 463 352 0 0 1760 6,38 2,68 0,42 9,90 0,400 FA0-8 - 200 10 1297 463 352 0 0 1760 6,85 3,15 0,46 9,88 0,396 FA0-9 1,2 188 4 1293 462 351 0 0 1755 11,04 8,28 0,75 9,39 0,167 FA0-10 1,2 188 8 1293 462 351 0 0 1755 11,98 9,10 0,76 9,23 0,159 FA0-11 1,2 188 12 1293 462 351 0 0 1755 13,88 11,94 0,86 9,18 0,150 FA0-12 1,2 188 16 1289 461 350 0 0 1750 15,28 13,75 0,90 8,99 0,138 FA1-1 0,4 144 10 1294 462 - 351 1 1770 11,26 6,98 0,62 9,75 0,347 FA1-2 0,8 170 10 1294 462 - 351 1 1770 14,65 11,13 0,76 9,68 0,329 FA1-3 1,2 188 10 1290 461 - 350 1 1765 17,36 14,76 0,85 9,58 0,232 FA1-4 1,6 201 10 1290 461 - 350 1 1765 19,08 17,55 0,92 9,48 0,200