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1 UNFIRED BRICK USING FLY ASH AND RED MUD BASED ON GEOPOLYMER TECHNOLOGY
1 UNFIRED BRICK USING FLY ASH AND RED MUD BASED ON GEOPOLYMER TECHNOLOGY Vu Huyen Tran 1 , Nguyen Thi Thanh Thao 2 , Nguyen Van Chanh 3 Department of Construction Material, University of Technology HCM City, Vietnam ABSTRACT Red mud is a waste material obtained from the aluminium extraction industry with the Bayer process and million of tons of red mud are produced annually. Fly ash is the finely divided residue that results from the combustion of pulverized coal in coal-fired electric and steam generating plants and a siliceous and aluminous material. The unfired brick resulting of the chemical reaction between red mud and fly ash is an amorphous to semi-crystalline polymeric structure and can be hardened in ambient air temperature. Alkaline activator is also added as a structure-forming element and increases structural stability of unfired brick. For mix proportion using 50-60% fly ash, 40-50% red mud, 6-8ml alkaline activator for 100gr powder and curing temperature is 70 o C, compressive strength in range of 130-150 kgf/cm 2 , compressive strength of dried sample to compressive strength of sample saturated by water ratio 0.8-0.9, water absorption 6.3-9.7% and high resistance to water. This paper reports about the physico- mechanical properties and manufacruring process of the unfired brick using fly ash and red mud through geopolymerization process with the aim of finding a new material that is appropriate to Vietnam situation. This work proved that this unfired brick has promising properties to be used as unfired materials in the construction. Keywords: Red mud, Fly ash, Geopolymer , Physico-mechanical properties. 1. GENERAL Red mud is a by-product of the Bayer process and disposed as a slurry. The liquid phase contains about 7g/l of Na 2 O and pH in the range of 13. This is a big obstacle to recycle use but great advantage to geopolymer process. Besides, red mud is also a very fine material in terms of particle size distribution. Typical values would account for 90 volume % below 75µm and the specific surface of red mud is around 10m 2 /g [1]. A chemical analysis would reveal that red mud contains silica, aluminum, iron, calcium, titanium , etc. The variation in chemical composition between different red muds is high. Figure 1. Red mud from Bayer process Figure 2. Fly ash 2 Fly ash contains mostly silicon (Si) and aluminium (Al) in amorphous form is a possible source material for the manufacture of unfired brick based on geopolymer technology. The physical and chemical characteristics of fly ash produced from the combustion of coal in electric utility or industrial boilers depend on the combustion methods, coal source and particle shape [2]. The particles of fly ash are generally spherical, finer than Portland, typically ranging in size between 10 and 100 micron. Therefore, fly ash is also a good mineral filler in hot mix asphalt (HMA) and improves the fluidity of flowable fill and grout [2]. The chemical compositions of various fly ashes show a wide range, depend on the type of coal. Fly ash consists primarily of oxides of silicon, aluminum, iron and calcium. Magnesium, potassium, sodium, titanium, and sulfur are also present to a lesser degree. Geopolymerization Process According to research of Glukhovsky in the 1950s, a general mechanism for the alkali activation of materials primarily comprising silica and reactive alumina involved stages: destruction–coagulation, coagulation–condensation, condensation crystallization. Afterthat, Glukhovsky theories were extended by different authors. In this theories [3], dissolution of the solid aluminosilicate source by alkaline hydrolysis produces aluminate and silicate species. The dissolution of solid particles at the surface results in the liberation of aluminate and silicate most likely in monomeric form into solution. This is the mechanism responsible for conversion of the solid particles during geopolymerization. Once in solution the species released by dissolution are incorporated into the aqueous phase, which may already contain silicate present in the activating solution. A complex mixture of silicate, aluminate and aluminosilicate species is thereby formed. Dissolution of amorphous aluminosilicates is rapid at high pH. This creates a supersaturated aluminosilicate solution, then the formation of a gel, as the oligomers in the aqueous phase form large networks by condensation. After gelation, the system continues to rearrange and reorganize, as the connectivity of the gel network increases, resulting in the three-dimensional aluminosilicate network com- monly attributed to geopolymers. Barbosa et al. (2000) proposed a new model for the molecular structure of geopolymer gel as shown in Figure 3 [4]. Figure 3. A semi-schematic structure for Na-PSS from Barbosa et al. (2000) 3 Davidovits (1999) proposed the possible applications of the geopolymer material depending on the molar ratio of Si to Al, as given in Table 1 [5]. Table 1. The possible applications of the geopolymer material Si/Al Application 1 Bricks, ceramics, fire protection 2 Low CO 2 cements, concrete, toxic water encapsulation 3 Heat resistance composites, fibre glass composites 2. EXPERIMENTAL Samples were prepared using red mud from Tan Binh Chemistry Factory and fly ash from Nhon Trach Dong Nai Power Station with ratio of red mud:fly ash was 20:80, 30:70, 40:60; 50:50 and 60:40. Fly ash provides initially the geopolymeric system with soluble Si and Al that are essential for the aluminosilicate oligomers formation and consequently, for the progress of the whole geopolymerization process [6] [7]. Alkaline activator comprising soluble silicon and sodium hydroxide was added. Mixing red mud in liquid form without drying with fly ash and alkaline activator at about 100 o C. Mixes were formed in cubic molds 50x50x50 mm and cured in a oven for 48 hours, temperature 80- 100 o C. After specimens were cured, tests in compressive strength, water absorption, resistance to water were carried out. 3. RESULTS AND DISCUSSION 3.1 Properties of red mud and fly ash Red mud According to the X-ray diffraction analysis (Figure 4), red mud is a crystalline material that comprises mainly the mineralogical phases of gibbsite, goethite… The chemical composition of red mud was detailed in Table 2. Fe 2 O 3 content is high so the colour of the unfired brick is almost similar to the clay brick. Table 2. Chemical composition of red mud Al 2 O 3 (%) Fe 2 O 3 (%) SiO 2 (%) TiO 2 (%) CaO (%) MgO (%) Na 2 O (%) K 2 O (%) Cr 2 O 3 (%) P 2 O 5 (%) SO 3 (%) Cl (%) 31.26 47.44 6.17 6.73 0.41 0.06 6.64 0.01 0.22 0.24 0.44 0.15 6055504540353025201510 55,000 50,000 45,000 40,000 35,000 30,000 25,000 20,000 15,000 10,000 5,000 0 -5,000 -10,000 -15,000 -20,000 -25,000 Sodalite 1.23 % Rutile 1.35 % Hematite 6.45 % Gibbsite 54.70 % Goethite 27.22 % Mullite 2:1 2.61 % Gypsum 7.80 % Anatase 1.66 % Titanomagnetite 2.33 % Perowskite 2.16 % Figure 4. XRD result for red mud 4 Fly ash The fly ash has dark grey colour. The chemical composition was determined by XRD analysis (Figure 6) and was given in Table 3. The molar Si-to-Al ratio of fly ash was about 2.6 and the calcium oxide content was low 6.3%. The particle size distributions of the fly ash was given in Figures 5. Particles smaller than 60 μm was 80%. Table 3. Chemical composition of fly ash 3.2 Physico-mechanical properties of unfired brick Compressive strength The compressive strength of unfired brick increases as content of alkaline activator or fly ash is increased. When alkaline activator content is increased from 8 to 10 ml/100g solid mixture, compressive strength increases significantly. The increase in Figure 7. The relationship between fly ash content and compressive strength Figure 8. The relationship between compressive strength and alkaline activator content with 60% fly ash 29_MAU_QUOC THO_5 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) 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) 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 Lin (Counts) 0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 2-Theta - Scale 11 20 30 40 50 60 70 80 d=5.39393 d=4.26195 d=3.43584 d=3.40314 d=3.35201 d=2.88432 d=2.69550 d=2.54964 d=2.46126 d=2.28569 d=2.21060 d=2.12612 d=1.82171 d=1.54423 d=1.52469 d=1.38295 d=1.37278 d=1.22551 Figure 6. XRD result for fly ash Figure 5. Particle size distribution of fly ash SiO 2 (%) 41 Al 2 O 3 (%) 23.1 Fe 2 O 3 (%) 11.2 CaO(%) 6.3 MgO (%) 3.2 K 2 O (%) 0.61 Na 2 O (%) 0.98 5 compressive strength after 5 day is similar to 14 days (Figure 8). After 14 days, with fly ash content is 60%, compressive strength of specimens that using 4 ml alkaline activator/100g solid mixture is 120 kG/cm 2 while compressive strength of specimens that using using 8, 9, 10 ml alkaline activator/100g solid mixture is 156, 158 and 158 KG/cm 2 . Figure 7 shows the relationship between fly ash content and compressive strength of specimes that using 6 and 8 ml alkaline activator/100g solid mixture. With 8 ml alkaline activator/100g solid mixture, fly ash content is increased from 40 to 80 %, compressive strength increases from 110 to 190 KG/cm 2 . Water absorption Water absorption of unfired brick decreases respectively as content of fly ash is increased. Figure 9 shows the relationship between fly ash content and water absorption with content of alkaline activator is 6 and 8 ml/100g solid mixture. After 14 days, with fly ash content is 60%, specimens get lowest water absorption 6.3% (Figure 10). However, content of alkaline activator is increased more than 8 ml/100g solid mixture, water absorption increases. Water resistance factor As content of alkaline activator is increased more than 7 ml/100g solid mixture, water resistance factors are more than 0.9. These results show the high resistance to water ability of this unfired brick (Figure 11). 3.3 Production process of unfired construction materials: [8] Figure 9. The relationship between fly ash content and water absorption with content alkaline activator is 8 ml/100g solid mixture Figure 10. The relationship between alkaline activator content and water absorption with fly ash content is 60% Figure 11. The relationship between alkaline activator content and water resistance factor with fly ash content is 60% 6 4. CONCLUSION Using red mud and fly ash based on geopolymer technology to play an important role in physico-mechanical properties of unfired brick. With red mud content is from 20 to 60 % and alkaline activator content, compressive strength obtains in range of 100 - 190 KG/cm 2 , water absorption gets 5.2–12.7% and 0.7– 0.95 is water resistance factor. These properties indicate this unfired brick is the promising unfired materials in the construction. REFERENCES [1]Y.Pontikes(2005).Redmud characteristics. http://www.redmud.org/Characteristics.html. [2] American Coal Ash Association. Technical report documentation FHWA-IF-03-091. [3] P. Duxson A. Ferna´ndez-Jime´nez J. L. ProvisG. C. Lukey A. Palomo J. S. J. van Deventer (2007). Geopolymer technology: the current state of the art. Advances in geopolymer science & technology, pp.3,9,12. [4] Barbosa,V.F.F., Mackenzie,K. J. D. and Thaumaturgo, C. (2000). Synthesis and characterisation of materials based on inorganic polymers of alumina and silica:sodium polysialate polymers. International Journal of Inorganic Materials. [5] Joseph Davidovits(1999). Geopolymers: inorganic polymeric new materials. Journal of Thermal Analysis, 37, 1633-1656, (1991). [6 ] Nguyen Van Chanh, Bui Dang Trung, Dang Van Tuan. Recent research geopolymer concrete. The 3rd ACF International Conference-ACF/VCA 2008. [7] Nguyen Van Chanh, Tran Quoc Tho. Inorganic composite materials for road surface utilizing Laterite, fly ash and red mud sluge waste in Vietnam. The 8 th International Conference on Civil and Environmental Engineering. Pukyong National University, Busan, Korea. October 2009. [8] Nguyen Van Chanh, Vu Huyen Tran, Nguyen Thi Thanh Thao . Geopolymer technology from fly ash and red mud for unfired brick making. The 4 th Conference on Science Technology – Vietnam Science and Technology Institute. Lam Dong-Vietnam 20- 21 August 2010. Fly ash Red mud Alkaline activator Water Mixing Mixing, 100 o C Molding Unfired construction materials Curing, 80-100 o C . 1 UNFIRED BRICK USING FLY ASH AND RED MUD BASED ON GEOPOLYMER TECHNOLOGY Vu Huyen Tran 1 , Nguyen Thi Thanh Thao 2. d=2. 210 60 d=2 .12 612 d =1. 8 217 1 d =1. 54423 d =1. 52469 d =1. 38295 d =1. 37278 d =1. 225 51 Figure 6. XRD result for fly ash Figure 5. Particle size distribution