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Synthesis of geopolymer from indonesian kaolin and fly ash as a green construction material
Synthesis of geopolymer from indonesian kaolin and fly ash as a green construction material
Synthesis of geopolymer from indonesian kaolin and fly ash as a green construction material
Synthesis of geopolymer from indonesian kaolin and fly ash as a green construction material
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Synthesis of geopolymer from indonesian kaolin and fly ash as a green construction material

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The cement industry is a substantial contributor to the global greenhouse gases emissions, accounting for approximatley 6% of the total global CO2 emission. Geopolymer, an inorganic polymer consisting …

The cement industry is a substantial contributor to the global greenhouse gases emissions, accounting for approximatley 6% of the total global CO2 emission. Geopolymer, an inorganic polymer consisting primarily of Si-Al-O covalent chains, is an attractive alternative to the conventional portland cement due to its much smaller carbon footprint. This research is an early work aimed at elucidating the techno-economic feasibility of geopolymer production in Indonesia, utilizing domestic aluminosilicate minerals and waste materials as feedstocks. Kaolin from the Belitung island and Class F coal fly ash from an electric powerplant in East Java were selected as the geopolymer precursors. The kaolin was initially calcined at 750 oC for 6 hours to convert it to the much more reactive metakaolin phase. Besides the type of aluminosilicate raw materials, the type of alkali solution was also varied between NaOH and KOH. The aluminosilicate materials were each reacted with 10.0 M alkali hydroxide solution at a solid-to-liquid mass ratio of 1.2 and 2.8 for the case of metakaolin and fly ash, respectively. The effect of these variables was evaluated on mortars prepared by using the obtained geopolymers, which involved the measurement of settling time in accordance to an Indonesian standard Vicat apparatus method, and compressive strength according to the ASTM C 109-80 method. The setting time of fly ash - KOH/NaOH geopolymer mortars is shorter than those obtained using metakaolin, due to the higher reactivity of the amorphous fly ash. The higher reactivity of fly ash also promotes better crosslinking of the Si-Al-O bonds, resulting in a higher compressive strength compared to the metakaolin-based geopolymer samples.

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  • 1. Proceeding for "Moving towards the New Chapter in Chemical Engineering amongst ASEAN Region ",the 5thRegional Conference on Chemical Engineering, 7 – 8 February 2013, PATTAYA, THAILANDSynthesis of Geopolymer from Indonesian Kaolin and Fly Ash as aGreen Construction MaterialTjokorde Walmiki Samadhi1, Pambudi P. Pratama11: Chemical Engineering Program, Bandung Institute of Technology (ITB), Bandung, Indonesiatwsamadhi@che.itb.ac.idAbstract—The cement industry is a substantial contributor tothe global greenhouse gases emissions, accounting forapproximatley 6% of the total global CO2 emission. Geopolymer,an inorganic polymer consisting primarily of Si-Al-O covalentchains, is an attractive alternative to the conventional portlandcement due to its much smaller carbon footprint. This research isan early work aimed at elucidating the techno-economicfeasibility of geopolymer production in Indonesia, utilizingdomestic aluminosilicate minerals and waste materials asfeedstocks. Kaolin from the Belitung island and Class F coal flyash from an electric powerplant in East Java were selected as thegeopolymer precursors. The kaolin was initially calcined at 750oC for 6 hours to convert it to the much more reactive metakaolinphase. Besides the type of aluminosilicate raw materials, the typeof alkali solution was also varied between NaOH and KOH. Thealuminosilicate materials were each reacted with 10.0 M alkalihydroxide solution at a solid-to-liquid mass ratio of 1.2 and 2.8for the case of metakaolin and fly ash, respectively. The effect ofthese variables was evaluated on mortars prepared by using theobtained geopolymers, which involved the measurement ofsettling time in accordance to an Indonesian standard Vicatapparatus method, and compressive strength according to theASTM C 109-80 method. The setting time of fly ash -KOH/NaOHgeopolymer mortars is shorter than those obtainedusing metakaolin, due to the higher reactivity of the amorphousfly ash. The higher reactivity of fly ash also promotes bettercrosslinking of the Si-Al-O bonds, resulting in a highercompressive strength compared to the metakaolin-basedgeopolymer samples.Keywords-geopolymer; metakaolin; fly ash; green chemistryI. INTRODUCTIONIn recent years, global warming has become a majorresearch and development focus, especially in the context ofanthropogenic greenhouse gases emissions. As much as 65% ofthe total global greenhous gas emissions is contributed by CO2.From the overall CO2 emission, approximately 6% originatesfrom the cement industry [1], in which each ton of Portlandcement produced emits approximately 1 ton of CO2 to theatmosphere [2]. Considering the massive consumption ofPortland cement and other similar civil construction materials,greenhouse gases emissions reduction in this industrial sectorwill likely to give a substantial impact on global warmingmitigation.Geopolymer is a term coined for a class of inorganicpolymers consisting mainly of Si-Al-O chains obtained byreacting aluminosilicate solids with alkali solutions [3].Development of this material initated in the 1970s as aconstruction binder that can supplement or replace ordinaryPortland cement (OPC). Due to the low temperaturerequirement for the hardening reactions, geopolymers consumemuch less energy to manufacture compared to OPC, whichtranslates to a much smaller carbon footprint. As reviewed byvan Deventer, Provis, and Duxson [4], the replacement of OPCby geopolymers may reduce the equivalent CO2 emission by asmuch as 80%. For Indonesia, motivations for the developmentof geopolymer not only stems from the abundance of severalclasses of aluminosilicate raw materials, but also from thecommitment of the nation to reduce greenhouse gasesemissions by 26% by 2020 in accordance to the UNFCCCframework stated in 2009 [5].The objective of this research is to measure the effects ofaluminosilicate source type, alkali type, and curing temperatureon key engineering characteristics of geopolymer as aconstruction binder material. Domestically available rawmaterials are utilized, namely Belitung island kaolin and coalfly ash obtained from a large base-load powerplant in East Javaprovince. This raw materials selection is aimed at maximizingthe impact of the research to include not only the reduction ofgreenhouse gases emissions, but also the reuse of industrialwaste materials in Indonesia.The term geopolymers represents solid materials with achemical composition similar to zeolites, but which structurallyconsist of macromolecular chains consisting of silicon,aluminum, and oxygen atom. These silica-aluminamacromolecules incorporate polysialate groups, which arethemselves chains and rings of tetrahedrally coordinated Si4+and Al3+ions and oxygen atoms, the structure of which isamorf to semi-crystalline. This macromolecule is representedby the following empirical formula [6]:n(−(SiO2)z−AlO2)n wH2OIn the above formula, z has a value of 1 to 32, M representsmonovalent cations such as K+or Na+, and n expresses thedegree of polycondensation. Polysialate bonds in geopolymersare further classified into 3 types, namely polysialate (-Si-O-Al-O-), polysialate-siloxo (-Si-O-Al-O-Si-O-), and polysialate-disiloxo (-Si-O-Al-O-Si-O-Si-O-) [3]. In the gepolymersynthesis process, the dissolution of aluminosilicate byconcentrated alkali solution produces Si(OH)4 and Al(OH)4monomers, which subsequently undergo polycondensation toform an alkali-aluminosilicate polymer with three-dimensionalcrosslinking [3].
  • 2. Proceeding for "Moving towards the New Chapter in Chemical Engineering amongst ASEAN Region ",the 5thRegional Conference on Chemical Engineering, 7 – 8 February 2013, PATTAYA, THAILAND3.137.926.7111.635.6311.7912.0016.888.5415.5402468101214161820Init. Final Init. Final Init. Final Init. Final Init. FinalOPC FA+NaOH FA+KOH MK+NaOH MK+KOHSettingtime,hoursThe synthesis of geopolymers may virtually consume anyaluminosilicate solid material, encompassing raw naturalminerals to inorganic waste materials. Xu and van Deventer [7]classified these raw materials as: (1) calcinedaluminosilicates,such as fly ash ,metakaolin, slag, construction residues, etc. (2)non-calcinedaluminosilicates, such as kaolinite, feldspars, minetailings, etc. Calcinedaluminosilicates tend to produce higherearly compressive strength due to faster reactions with thealkali solution [8]. Conversely, non-calcinedaluminosilicatesexhibit higher increase in strength in the later stage ofgeopolymerization [9].II. METHODOLOGYDue to the scarcity of geopolymer research in Indonesia,this preliminary study is aimed primarily at proving thetechnical feasibility of utilizing several domestically abundantaluminosilicate materials in geopolymer synthesis. As such, asimple 22factorial experiment is performed, withaluminosilicate source type and alkali solution type selected asexperimental variables.Calcinedaluminosilicates, namely Class F coal fly ash andmetakaolin, are selected in this study to ensure faster reactionsin the initial stage of geopolymerization. The fly ash is a wastematerial from the Paiton base-load powerplant in East Javaprovince, while the metakaolin is obtained by calcining aBelitung kaolin sample at 750 oC for 6 hours. Table 1 outlinesthe oxide compositions of the raw kaolin and fly ash used inthis study, as measured by the X-ray fluorescence (XRF)method. Two types of alkaline solutions are selected, namelyNaOH and KOH solutions at a fixed concentration of 10.0 M.These solutions are prepared by dissolving solid alkalihydroxide flakes. Purity of the NaOH flakes is 97-98%, whilethat of the KOH flakes is in the 90-95% range.TABLE I. OXIDE COMPOSITION OF ALUMINOSILICATE SOURCESOxide BelitungkaolinFly ashSiO2 48.1 40.1Al2O3 36.1 30.7Fe2O3 0.6 35.7CaO 0.014 18.7MgO 0.016 5.4Na2O 0.04 0.59K2O 0.33 2.1Geopolymer cement pastes are prepared by first hand-mixing the aluminosilicate powder into the alkaline solution ina steel bowl. The metakaolin – alkali solution mass ratio is 1.2,while the fly ash – alkali solution mass ratio is 2.8. The mixtureis then transferred to a planetary mixer, where it is mixed atlow speed until a smooth, sticky consistency is obtained. Timerequired to achieve such consistency is approximately 3minutes. The geopolymer paste is then shaped into a small ballby hand and inserted into the sample chamber of the Vicatapparatus. The setting time is then measured in accordance tothe Indonesian SNI 15-3500-2004 standard method, which isbased on the measurement of the force required to pull out astandard needle from a setting cement paste specimen.Aside from geopolymer cement pastes, mortar samples arealso prepared according to the ASTM C 109-80 method, inwhich reference OPC mortars are prepared by mixing cement,water, and sand at a cement – sand ratio of 0.36 and water –cement ratio of 0.485. For the geopolymer mortars, a cement –sand ratio of 0.74 is selected. The geopolymer mortars are castinto 50 x 50 x 50 mm cubic specimens, vibrated to removetrapped air, then cured at 60 oC in an electric oven for 24 hours.Following this curing step, the specimens are subjected tocompressive strength measurement by uniaxial loadingaccording to the ASTM C 109/109M-02 method, and surfacemorphology characterization by scanning electron microscopy(SEM).III. RESULTS AND DISCUSSIONFigure 1 presents the initial and final setting times of thefour geopolymer paste specimens as measured by the Vicatapparatus. As a comparison, data for the reference OPC pasteare included. Each paste formulation is tested in 8 replicates toenable proper statistical analysis of the data. Average valuesand error bars of the setting times at a 95% confidence level areincluded in the graph.Figure 1. Initial and final setting times of geopolymer pastesmeasured by the Vicat apparatus (FA = fly ash, MK = metakaolin)Overall, the setting times of the geopolymer pastes aresignificantly longer than the OPC paste, both in the initial andfinal stage of polymerization, despite the use of calcinedaluminosilicates [8]. The shortest setting time of thegeopolymer paste is slightly less than twice the setting time ofthe OPC paste. For the same alkali type, fly ash exhibits asignificantly faster setting than metakaolin. On the other hand,for the same aluminosilicate source type, KOH produces afaster initial setting. However, the effect of alkaline typebecomes much less pronounced at the final stages. This isespecially true for fly ash, in which the alkaline type does notinfluence the final setting time in a statistically significantmanner. As the fly ash undergoes fusion during its generationin powerplant boilers, it is expected to be more amorphous thanthe semi-crystalline metakaolin, hence its higher reactivitytowards the alkaline solution.Figure 2 presents the compressive strength of thegeopolymer – sand mortars after curing at 60 oC for 24 hours.
  • 3. Proceeding for "Moving towards the New Chapter in Chemical Engineering amongst ASEAN Region ",the 5thRegional Conference on Chemical Engineering, 7 – 8 February 2013, PATTAYA, THAILAND29.6128.0439.989.3614.2301020304050OPC FA+NaOH FA+KOH MK+NaOH MK+KOHCompressivestrength,MPaThe figure clearly indicates that all geopolymer samples exhibitlower compressive strength than OPC, with the exception of flyash – KOH geopolymer mortar, which has a 35% higheraverage strength than the OPC mortar. This observation is inagreement with the setting time measurement (see Figure 1), inwhich the fly ash – KOH geopolymer exhibits the fastest initialsetting among all geopolymer samples.For both fly ash and metakaolin, KOH produces asignificantly higher compressive strength than NaOH. KOHhas a higher basicity compared to NaOH due to the largercationic radius of K+, enabling it to dissolve silicate at a higherrate than Na+does [10]. This behavior is also confirmed byYao, Zhang, Zhu, and Chen using an isothermal calorimetrymethod [11]. It is also argued that the larger cationic radius ofK+favors the formation of larger silicate oligomers in thegeopolymer gel phase, resulting in a higher degree ofpolycondensation compared to Na+[12].Figure 2. Compressive strength of geopolymer mortars aftercuring at 60 oC for 24 hoursFigure 2 also indicates that, for both alkaline solutions,metakaolin geopolymer mortars exhibits much lower strengththan fly ash geopolymer mortars. The finer particles of themetakaolin demands lower solid to liquid ratio during thepreparation of the geopolymer phase, which compromises thestrength of the cured product as observed by Kong, Sanjayan,and Sagoe-Crentsil [13]. In addition, these authors also arguethat fine pores formed as relics of reacted hollow fly ashmicrospheres may act as channels for moisture diffusion duringcuring at elevated temperatures, thereby resulting in lessinternal development and higher strength at high ambienttemperatures [13].Figures 3 and 4 presents the SEM images of the metakaolin- KOH and fly ash - KOH geopolymer mortars, respectively,both taken at 5000x magnification. The platelet-like relics ofthe metakaolin is still visible in Figure 3. However, the figurealso suggests that the metakaolin has reacted extensively withthe alkaline solution, as indicated by the extensive formation ofinterparticle bridges. Figure 4 clearly indicates severalunreacted fly ash particles, and the finer microstructure of thephase surrounding the spherical particles. The finermicrostructure suggests a better condensation or crosslinking ofthis sample compared to the metakaolin geopolymer mortar.The sphere on the right hand side of the figure is partiallyreacted, revealing the hollow nature of these spheres. Work iscurrently in progress which addresses the impact of high-temperature exposure on the microstructure of these metakaolinand fly ash geopolymer mortars.Figure 3. SEM image of metakaolin - KOH geopolymer mortar at5000x magnificationFigure 4. SEM image of fly ash - KOH geopolymer mortar at5000x magnificationIV. CONCLUSIONSThe preliminary technical feasibility of utilizing kaolin andfly ash from domestic resources in Indonesia to synthesizegeopolymeric construction materials has been proved, whichmay potentially contribute to the reduction of greenhouse gasesemission from the cement industry. Overall, fly ash producesgeopolymer with setting time and compressive that arecomparable to OPC. The use of KOH as the alkaline activator
  • 4. Proceeding for "Moving towards the New Chapter in Chemical Engineering amongst ASEAN Region ",the 5thRegional Conference on Chemical Engineering, 7 – 8 February 2013, PATTAYA, THAILANDin the geopolymerization increases the setting rate and earlycompressive strength. However, its higher price compared toNaOH may offset the better mechanical properties.Highersolids loading of the fly ash geopolymer provides it with ahigher compressive strength than the metakaolin geopolymer.Extensive reaction between the aluminosilicate solids andalkaline solutions is evident in microstructure of thegeopolymer mortars. Partially reacted hollow microspheres areobserved in the fly ash geopolymer microstructure, which arelikely to disappear at elevated temperatures.ACKNOWLEDGMENTThis research is partially funded by the 2013 ITB ResearchGroup Research and Innovation (Riset dan Inovasi KelompokKeahlian ITB 2013) program.REFERENCES[1] R. McCaffrey, “Climate Change and the Cement Industry”, GlobalCement & Lime Magazine, pp. 15-19, 2002.[2] J. Davidovits, “Global Warming Impact on the Cement and AggregateIndustries”, World Resources Review, vol.6 no.2, pp. 263-278, 1994.[3] J. Davidovits, “Geopolymers: Inorganic Polymeric New Materials”, J.Therm. Anal., vol. 37, pp. 1633-1656, 1991.[4] J.S.J. van Deventer, J.L. Provis, and P. Duxson, “Technical andCommercial Progress in the Adoption of Geopolymer Cement”, Miner.Eng., vol. 29, pp. 89-104, 2012.[5] M. Hilman (ed.), Indonesia Second National Communication under theUnited Nations Framework Convention on Climate Change (UNFCCC),Republic of Indonesia Ministry of Environment, 2010.[6] J. Davidovits, “Properties of Geopolymer Cements”, First InternationalConference on Alkaline Cements and Concretes, Kiev, Ukraine, 1994,pp. 131-149.[7] H. Xu and J.S.J. van Deventer, “Effect of Source Materials onGeopolymerization”, Ind. Eng. Chem. Res., vol. 42, pp. 1698-1706,2003.[8] A. Usherov-Marshak, L. Pershina, and P. Krivenko, “CalorimetricStudies of Hydration of Cementitious Materials Varying in Basicity”, J.Therm. Anal. Calorim., vol. 54 no. 1, pp. 57-61, 1998.[9] H. Xu and J.S.J. van Deventer, “The Geopolymerization of Alumino-Silicate Minerals”, Int. J. Miner. Process., vol. 59 no.3, p. 247, 2000.[10] J.W. Phair and J.S.J. van Deventer, "Effect of Silicate Activator pH onthe Leaching and Material Characteristics of Waste-Based InorganicPolymers", Miner. Eng., vol. 14, pp. 289-304, 2001.[11] X. Yao, Z. Zhang, H. Zhu, and Y. Chen, "Geopolymerization Process ofAlkali-Metakaolinite Characterized by Isothermal Calorimetry",Thermochim. Acta, vol. 493, pp. 49-54, 2009.[12] J.W. Phair and J.S.J. van Deventer, "Effect of the Silicate Activator pHon the Microstructural Characteristics of Waste-Based Geopolymers",Int. J. Miner. Process., vol. 66, pp. 121-143, 2002.[13] D.L.Y. Kong, J.G. Sanjayan, and K. Sagoe-Crentsil, "ComparativePerformance of Geopolymers Made with Metakaolin and Fly Ash AfterExposure to Elevated Temperatures", Cement Concrete Res., vol. 37, pp.1583-1589, 2007.

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