SYNTHESIS AND PROPERTIES OF HIGH CALCIUM FLY ASH BASED GEOPOLYMER FOR CONCRETE APPLICATIONS

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1 SYNTHESIS AND PROPERTIES OF HIGH CALCIUM FLY ASH BASED GEOPOLYMER FOR CONCRETE APPLICATIONS P. Kamhangrittirong*, Kasetsart University, Thailand P. Suwanvitaya, Kasetsart University, Thailand P. Suwanvitaya, Kasetsart University, Thailand P. Chindaprasirt, Khon Khen University 36th Conference on OUR WORLD IN CONCRETE & STRUCTURES: August 2011, Singapore Article Online Id: The online version of this article can be found at: This article is brought to you with the support of Singapore Concrete Institute All Rights reserved for CI Premier PTE LTD You are not Allowed to re distribute or re sale the article in any format without written approval of CI Premier PTE LTD Visit Our Website for more information

2 36 th Conference on Our World in Concrete & Structures Singapore, August 14-16, 2011 SYNTHESIS AND PROPERTIES OF HIGH CALCIUM FLY ASH BASED GEOPOLYMER FOR CONCRETE APPLICATIONS P. Kamhangrittirong *, P. Suwanvitaya, P. Suwanvitaya and P. Chindaprasirt * Department of Building Technology Kasetsart University 50 Nhamwongvan Road, Chathujak, Bangkok, Thailand <paramesacs@yahoo.com, archpmk@ku.ac.th> Keywords: Geopolymer, high calcium fly ash, sodium hydroxide, sodium silicate, compressive strength, thermal conductivity Abstract. Sustainable developments of technologies in industrial waste utilization to concrete construction areas have been given considerable worldwide attention. Among these waste products, fly ash from power plants has become a subject of growing interests. This research shows the progress of geopolymer synthesis based on high calcium fly ash. Two types of geopolymer product and three ratios of fly ash to alkali activators were experimented. Alkali activators for this fly ash based geopolymer consisted of sodium silicate and sodium hydroxide. The fly ash contents were 60, 65 and 70 percents by weight and the weight ratio of alkali activators was 1.0. Geopolymer products from fly ash were synthesized and investigated by universal testing machine and thermal conductivity tester for mechanical and thermal conductivity properties, respectively. Scanning electron microscope (SEM)/energy dispersive X-ray (EDX) was used to determine the effect of fly ash ratio on the properties and microstructure. Generally, the compressive strengths of geopolymer mortar specimens above 30 MPa were reached after curing at room temperature for 28 days. The results indicated that increasing the fly ash to alkali activators ratio significantly increased the compressive strength. Results also showed that thermal conductivity of geopolymer products were less than 0.30 W/m.K. The EDX results confirmed that major elements of microstructure consisted of Si, Al and O. It is expected that the geopolymer products will contribute to the success of waste management. It has high potentials for development in the area of precast concrete construction, thus promoting these products for extensive use. 1 INTRODUCTION There is a growing interest on a sustainable development technology of concrete by utilizing industrial waste materials. It is well known that fly ash can be added in concrete for workability Department of Civil Engineering, Kasetsart University Department of Environmental Engineering, Kasetsart University Department of Civil Engineering, Khon Khen University

3 and long term performance improvement. Moreover, the major chemical properties of fly ash, consisting of alumina (Al 2 O 3 ) and silica (SiO 2 ) could produce a geopolymer binder, when mixing with high alkali solutions in the room temperature. Geopolymers were first developed by Davidovits in France 1-3. These inorganic products consist of the SiO 4 and AlO 4 tetrahedra networks. The influences of alumino-silicate materials, such as metakaolin and low calcium fly ash, were investigated by many researchers 4-9. Their properties are suitable for reformed aggregate as ordinary Portland cement (OPC). Based on the past results, high calcium fly ash has been successfully used as a raw material in the geopolymer mixture The aim of this research is to development a geopolymer product for construction applications. High calcium fly ash from a power plant was selected as a geopolymer binder. An extensive experimental program was conducted to investigate properties of geopolymer products and agricultural waste combination for construction materials. 2 MATERIALS AND EXPERIMENT DETAILS 2.1 Materials Fly ash (FA) produced by Mae Moh power plant in the north of Thailand and rice husk ash (RHA) were used as the raw material in this investigation. The chemical compositions of the FA and RHA are presented in Table 1. Based on the chemical composition, FA was classifled as class C. Commercial grade sodium hydroxide and sodium silicate solution (Na 2 O=9.25%, SiO 2 =28.48%, H 2 O=62.27%) were used as alkali activators for the synthesis of the geopolymeric material. Chemical composition (mass %) Raw material Loss on SiO 2 Al 2 O 3 CaO Fe 2 O 3 MgO Na 2 O K 2 O Others ignition FA RHA Table 1: Chemical compositions of fly ash and rice husk ash 2.2 Experiment Details Geopolymer pastes were prepared by mixing of fly ash with the alkali solution. The geopolymer pastes were then divided into 2 parts. One part was used for the setting time investigation. The other part of the mix was poured into cube plastic mould (5 X 5 X 5 cm.) and stored in ambient temperature. At the ages of 7 and 28 days, specimens were taken from the storage room and test for compressive strength. Five specimens of each mix were tested. The small pieces of tested specimens were examined using scanning electron microscope (SEM)/ energy dispersive X-ray (EDX) to determine the composition and structure of reaction products. The mixture proportions and compositions of oxide mole ratio are given in Table 2. Mix no. FA Solution FA (gm.) Weight NaOH 10M (gm.) Na 2 SiO 3 (gm.) Oxide mole ratio of the reactant mixture (*M 2 O = Na 2 O+K 2 O) M 2 O SiO 2 SiO 2 Al 2 O 3 H 2 O M 2 O M 2 O Al 2 O 3 P P P Table 2: Mix proportions of geopolymer paste For geopolymer applications, the weight ratios of geopolymer binder were kept at All geopolymer mortars were made with sand to ash ratio of The mixtures were devided into 20 x 10 X 5 cm. mould for geopolymer block and 20 x 20 X 1 cm. mould for geopolymer tile, respectively. Compressive strength of geopolymer block and transverse strength of geopolymer tile were tested at the ages of 3, 7 and 28 days. Water absorbtion of geopolymer block and thermal conductivity of geopolymer tile were investigated to evaluate performance of geopolymer

4 applications at the age of 28 days. The mixture proportions of FA and RHA at differrent replacement are given in Table 2. Mix no. % FA Weight (gm.) replacement FA RHA NaOH Na 2 SiO 3 Sand M-1-R M-2-R M-3-R M-4-R Table 3: Mix proportions of geopolymer mortar 3 RESLTS AND DISSCUSSIONS 3.1 Properties of geopolymer paste The initial setting time and compressive strengths of geopolymer pastes at the ages of 7d and 28d are shown in Fig.1. In general, the initial setting time of the geopolymer paste decreases and the compressive strengths increase with the increase in fly ash content Compressive strength (MPa) Compressive strength (28d) Compressive strength (7d) Initial setting time P-1-60 P-2-65 P Initial setting time (min.) Figure 1: Compressive strength and initial setting time of geopolymer paste Figure 1 indicates that alumino-silicate contents from fly ash are beneficial for compressive strength of fly ash based geopolymer. For example, the compressive strength (28d) of specimens with fly ash to alkali solution weight ratio of 2.33 (SiO 2 /Al 2 O 3 ratio = 3.535) is 33.3 MPa. Meanwhile, the compressive strength of specimens with fly ash to alkali solution weight ratio of 1.50 (SiO 2 /Al 2 O 3 ratio = 3.268) is 19.2 MPa. These results indicate that the ratio of fly ash to alkali solution played an important role in the development of compressive strength. Thus, the increase of fly ash led to the compressive strength of fly ash based geopolymer increase.this phenomenon was also noticed by other authers that higher amount of fly ash in the mixture, the compressive strength was also increased. The effect due to the fly ash to alkali solution ratio also influence to the initial setting time of fly ash based geopolymer. It should be noted that the increase of H 2 O to M 2 O ratio led to the initial setting time increase. The result also aligns with previous study Figure 1 shows that fly ash to alkali solution weight ratio of 1.86 is very interesting choice for construction applications.

5 3.2 Microstructure of geopolymer binder The SEM images of fly ash and high calcium fly ash based geopolymers are presented in Fig. 2 and Fig. 3, respectively. Figure 2 shows the spherical particles of various sizes of fly ash used. The harden structure formed during alkali activation and partly attacked fly ash can be observed in Figure 3. Some appearance of rough surfaces on some fly ash spheres were thought to be the result of the attack by the alkali solution in the mix. Figure 3a-c show unreacted and partially reacted traces of fly ash were dominated by fly ash to solution ratio. Figure 2: SEM image of fly ash (5000x) (a) Si/Al = 3.15 x (b) Si/Al = 2.75 x

6 (c) Si/Al = 2.21 x Figure 3: SEM images of fly ash geopolymer paste (5000x) (a) Mix no. P-1-60 (b) Mix no. P-2-65 (c) Mix no. P-3-70 The results of the SEM/EDS analyses of the samples are shown in right column of Figure 3 (a-c) and indicated that the major elements were silica (Si), alumina (Al) and sodium (Na), with some calcium (Ca) also present. The presence of Na and Ca of this observation confirmed that fly ash based geopolymer structure have these ions in amorphous matrix. The composition atomic ratios of Si/Al in the matrix (areas marked X) were 3.15, 2.75 and 2.21 respectively, reflecting the increase in fly ash content from mix no. P-3-70 to mix no. P This indicates that the reactions of alumina in fly ash geopolymer are significantly different. The corresponding EDS results illustrated that increase in Si/Al was accompanied by the decrease in compressive strength of fly ash geopolymer. This was compatible with the findings from previous studies 8, Properties of geopolymer mortar products The compressive strength and water absorbtion of geopolymer block with different RHA replacements are shown in Table 4. The compressive strengths of geopolymer blocks decrease with the increase in RHA content from 2.5 to 7.5%. The water absorbtions of geopolymer blocks indicate that the high RHA content contributes to the high porosity of the geopolymer products. The high RHA content of geopolymer tile are also show a lower transverse strength than M-1-R0.0 mixture. This finding may be explained by the presence of the small amount of alumina content in RHA (Table 1). Mix no. Geopolymer block Geopolymer tile Compressive strength Water Transverse strength (MPa) absorbtion (MPa) 3 d 7 d 28 d 28 d (%) 3 d 7 d 28 d Thermal conductivity 28 d (W/m.K) M-1-R M-2-R M-3-R M-4-R Table 4: Compressive strength, water absorbtion, transverse strength and themal conductivity of geopolymer mortar Figure 4 and 5 illustrate the compresive strength of geopolymer block and transverse strength of geopolymer tile versus of fly ash replacement, respectively. The results show that both strength of geopolymer products trend to decrease as RHA amount increase. The rapid decrease in 28d compressive and transverse strength may be attributed to the high silica concentration in RHA. The test results also confirm that the alumino-silicate amount in raw material affects the mechanical properties significantly.

7 30.0 Compressive strength (MPa) d 7 d 28 d M-1-R0.0 M-2-R2.5 M-3-R5.0 M-4-R7.5 Figure 4: Compressive strength of geopolymer block 7.0 Transverse strength (MPa) d 7 d 28 d 0.0 M-1-R0.0 M-2-R2.5 M-3-R5.0 M-4-R7.5 Figure 5: Transverse strength of geopolymer tile From Table 4, one feature worth mentioning is the thermal conductivity of geopolymer products. The thermal conductivities of geopolymer mortars cured at room temperature are lower than normal concrete products. The amorphous structure of geopolymer binder, as evident by SEM images (Fig. 3a-c), results in a geopolymer mortar with high thermal resistance 13.This behavior can be very useful for the thermal insulation products. 4 CONCLUSIONS From the results of the study, the following conclusions can be made. The parameter affecting the setting time and compressive strength of fly ash geopolymer pastes was found to be the weight ratio of fly ash to alkali solution. The SEM images indicated the amount of alumina content in fly ash affacted the degree of reaction. The increase in Si/Al atomic ratio from EDS was accompanied by the decrease in

8 compressive strength, explaining the role of weight ratio of fly ash to alkali solution in the compressive strength results. The compressive strength of geopolymer mortar has a significant correlation with transverse strength that the increase of compressive strength led to transverse strength increase. Rice husk ash amount in the synthesis of geopolymer product was found to affect significantly the properties of geopolymer mortar. The increase of rice husk ash amount led to the compressive and transerve strength decrease and water absorbtion increase. Howover, it is also of interest to note for thermal conductivity of geopolymer mortar decreased as the RHA amount increased. In summary, it can be concluded that fly ash from Mae Moh power plant has potential to use as the raw material for manufacturing with high calcium fly ash based geopolymer. ACKNOWLEDGEMENT The authors would like to gratefully acknowledge the financial support from kasetsart university research and development institute (KURDI). REFERENCES [1] J. Davidovitz, Geopolymer chemistry and properties Applications, Geopolymer 88 international conference proceedings, Institut Géopolymère (1988), [2] J. Davidovitz, Geopolymers: Inorganic polymeric new materials. Journal of Thermal Analysis, Springer (1991), [3] J. Davidovits, Chemistry of Geopolymeric Systems Terminology. Proceedings: 2 nd International conference on geopolymere 99, Institut Géopolymère (1999), [4] H. Xu and JSJ. Van Deventer, The geopolymerisation of natural alumino-silicates, Proceedings: 2 nd International conference on geopolymere 99, Institut Géopolymère (1999), [5] A. Palomo, MW. Grutzeck and MT. Blanco-Varela, Alkali activated fly ashes: cement for the future, Cement and Concrete Research, Elsevier (1999), [6] H. Xu and JSJ. Van Deventer, Geopolymerisation of multiple minerals, Minerals Engineering, Elsevier (2002), [7] A.M. Fernandez-Jimenez, E.E. Lachowski, A. Palomo and D.E. Macphee, Microstructural characterization of alkali-activated PFA matrices for waste immobilization, Cement and Concrete Composites, Elsevier (2004), [8] T. Bakharev. Geopolymeric materials prepared using Class F fly ash and elevated temperature curing, Cement and Concrete Research, Elsevier (2005), [9] S. Andini, R. Cioffi, F. Colangelo, T. Grieco, F. Montagnaro and L. Santoro, Coal fly ash as raw material for the manufacture of geopolymer-based products, Waste Management, Elsevier (2008), [10] P. Chindaprasirt, T. Chareerat and V. Sirivivatnanon, Workability and strength of coarse high calcium fly ash geopolymer, Cement and Concrete Composites, Elsevier (2007), [11] A. Sathonsaowaphak, P. Chindaprasirt and K. Pimraksa, Workability and strength of lignite bottom ash geopolymer mortar, Journal of Hazardous Materials, Elsevier (2009), [12] D. Hardjito, D. M. J. Sumajouw and B. V. Rangan. On the development of fly ash-based geopolymer concrete, ACI Material Journal, American Concrete Insitute (2004), [13] T.W. Cheng and J.P. Chiu, Fire-resistant geoploymer producted by granulated blast furnace slag, Minerals Engineering, Elsevier (2003),

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