Use of residual diatomaceous earth as a silica source in geopolymer production

The use of binders as an alternative to Portland cement has gained importance in recent years. Among them, geopolymeric binders, developed by the reaction between an aluminosilicate precursor and a high alkalinity solution, have become one of the most promising alternatives. The activating solution generally comprises waterglass and sodium hydroxide. Since waterglass is the most expensive material and has a high environmental impact, using alternative silica sources will lead to more sustainable binders. Previous studies have successfully used rice husk ash (RHA) as a silica source. This research aims to assess the possibility of using diatomaceous earth (or diatomite) as an alternative silica source, like the previous studies with RHA. Diatomite is a sedimentary rock with a high amorphous silica content formed by fossilized diatom remains. In this work, the geopolymer was obtained using a fluid cracking catalyst residue as the precursor and six different activating solution types prepared with commercial products, residual diatomite (from beer and wine industries) and RHA. The results open a new possible route for the reuse and recovery of diatomaceous earth residue, although the compressive strength results of the mortars were slightly lower than those for mortars prepared with RHA or commercial reagents

Microscopic chemical characterization and reactivity in cementing systems of elephant grass leaf ashes

[EN] Many agrowastes are being used for energy production by combustion in power plants. This process generates huge amounts of ash, which has a potential pozzolanic activity for blending with Portland cement or hydrated lime. In this paper, the ash obtained from elephant grass (Pennisetum purpureum Schum var. purple) leaves (EGLs) was studied, including the silicon content and its distribution, the presence of other compounds, and in addition, the presence of silica bodies (phytoliths). Combustion temperatures of 450 and 650°C produced an unaltered inorganic skeleton (spodogram), whereas at 850°C, there is a sintering process because of high potassium content in the ash. Phytoliths and different types of hairs were identified, and they contained high percentages of silica. Magnesium (mainly as periclase) was distributed in the most porous parts in the interior of the leaves. The silica can react with calcium hydroxide (pozzolanic reaction) forming calcium silicate hydrates (observed by field-emission scanning electron microscopy and thermogravimetric analysis). Fixed lime percentages at 28 curing days (63%) indicated the high reactivity of EGL ashes in calcium hydroxide pastes due to the pozzolanic reaction. This study demonstrates the possibility of the reuse of ashes from EGLs for the production of environmental-friendly cements.Rosello Caselles, J.; Soriano Martinez, L.; Savastano, H.; Borrachero Rosado, MV.; Santamarina Siurana, MP.; Paya Bernabeu, JJ. (2018). Microscopic chemical characterization and reactivity in cementing systems of elephant grass leaf ashes. Microscopy and Microanalysis. 24(6):593-603. https://doi.org/10.1017/S1431927618015192S59360324

Compressive strength and microstructure of alkali-activated blast furnace slag/sewage sludge ash (GGBS/SSA) blends cured at room temperature

In the present work, ground granulated blast furnace slag (GGBS) and sewage sludge ash (SSA) blends were assessed for the production of alkali-activated pastes and mortars. Percentages of SSA to substitute GGBS ranged from 0–30 wt.% and sodium concentrations of 6–10 mol.kg-1 were used for the activating solutions. Pastes and mortars were cured at 20 ºC for up to 90 days. Raw materials were characterised by granulometric analysis, XRF, XRD, FTIR and SEM techniques. The replacement percentage of GGBS by SSA and the sodium hydroxide concentration of the alkaline activator were optimised to produce mortar with compressive strengths close to 30 MPa after 28 curing days at room temperature. Best results were obtained in samples blended with 20 wt.% SSA activated with 6 mol.kg-1 NaOH solutions which, according to the XRD, FTIR and microscopic results, contained higher amounts of (N,C)-A-S-H gel. The potential use of SSA for the development of alternative cementitious materials at room temperature has been demonstrated

Morteros aligerados con cascarilla de arroz: diseño de mezclas y evaluación de propiedades

En el presente trabajo se analiza la posibilidad de utilizar la cascarilla de arroz con y sin pretratamientos, como una adición en la fabricación de morteros ligeros. Se estudiaron diversos pretratamientos de la cascarilla, tales como el lavado con agua destilada, baño en disolución ácida durante 24 horas, baño en disolución básica durante 24 horas, así como combinaciones y variaciones de los anteriores pretratamientos. Se determinaron propiedades como la densidad, la resistencia a flexión y la resistencia a compresión de los morteros realizados. Finalmente se sometieron a análisis de microscopia electrónica tres de las muestras más representativas. Los resultados muestran que se obtuvieron morteros de muy baja densidad y elevada porosidad que los convierten en candidatos para elaborar materiales de construcción para aislamiento térmico y acústico, pero no para fabricar elementos portantes debido a su baja resistencia mecánica. Se concluye que el tratamiento químico de la cascarilla con reactivos alcalinos y la adición de cloruro cálcico como acelerante del fraguado, son dos propuestas efectivas para la reutilización de estos residuos en morteros aligerados

Effect of silicoaluminous pozzolans on the hydration process of the Portland cement cured at low temperatures

The aim of this paper is to study hydration processes in cement pastes and mortars, blended with either metakaolin (MK) or a catalyst used in catalytic cracking (FCC), and cured at low temperature. The amounts of hydrates and portlandite in pastes have been determined for 3¿28 days curing at 5¿20 C. Microstructural study, using thermogravimetric analysis of the pastes, has shown that FCC acts mainly as a pozzolan at low temperatures (5¿10 C), whereas MK also accelerates Portland cement hydration. Mechanical strengths of a control mortar, and mortars made with 15% replacement of cement by these two pozzolans, have been measured. Both mortars containing pozzolans exhibited a relative increase in compressive strength when cured at 5 C. A limestone filler (LF) has been used to compare the effects of adding inert or pozzolanic materials. Finally, mortars were prepared by partially replacing aggregates with either MK, FCC or LF. The MK and FCC are effective materials even for low curing temperatures, especially when they are used to replace a fraction of the aggregates in mortarsAuthors thanks to Ministerio de Ciencia and Tecnologia of Spain the financial support of project MAT2001-2694 and FEDER funding.Soriano Martinez, L.; Monzó Balbuena, JM.; Bonilla Salvador, MM.; Tashima, MM.; Paya Bernabeu, JJ.; Borrachero Rosado, MV. (2013). Effect of silicoaluminous pozzolans on the hydration process of the Portland cement cured at low temperatures. Cement and Concrete Composites. 42:41-48. doi:10.1016/j.cemconcomp.2013.05.007S41484

Evaluation of the long-term compressive strength development of the sewage sludge ash/metakaolin-based geopolymer

[EN] This paper aimed to evaluate the long-term compressive strength development of the sewage sludge ash/metakaolin (SSA/MK)¿based geopolymer. SSA/MK¿based geopolymeric mortars and pastes were produced at 25ºC with different SSA contents (0 - 30 wt.%). Compressive strength tests were run within the 3-720 curing days range. A physicochemical characterisation (X-ray diffraction and scanning electron microscopy) was performed in geopolymeric pastes. All the geopolymeric mortars presented a compressive strength gain with curing time. The mortars with all the SSA evaluated contents (10, 20, 30 wt.%) developed a compressive strength over 40 MPa after 720 curing days at 25ºC. The maximum compressive strength of the mortars with SSA was approximately 61 MPa (10 wt.% of SSA), similarly to the reference mortar (100% MK-based geopolymer). The microstructure analyses showed that the SSA/MK¿based geopolymer presented a dense microstructure with N-A-S-H gel formation.This study was financed partly by the Coordenacao de Aperfeicoamento de Pessoal de Nivel Su-perior -Brasil (CAPES) -(Finance Code 001 and CAPES/DGU n. 266/12), and the National Council of Scientific and Technological Development -Bra-sil (CNPq) -(n. 14/2013, process 478057/2013-0 and 309015/2015-4). The authors would like to thank Programa Institucional de Internacionalizacao - CAPES -PrInt. The authors acknowledge the Scanning Electron Microscopy Service of FEIS/UN-ESP, Servico Municipal Autonomo de Agua e Es-goto (SEMAE) from the Sao Jose do Rio Preto city -SP, Brazil and Diatom Mineracao Ltda. The authors would like to thank Programa Institucional de Internacionalizacao CAPES -PrInt.Istuque, D.; Soriano Martinez, L.; Borrachero Rosado, MV.; Paya Bernabeu, JJ.; Akasaki, JL.; Melges, JLP.; Tashima, MM. (2021). Evaluation of the long-term compressive strength development of the sewage sludge ash/metakaolin-based geopolymer. Materiales de Construcción. 71(343):1-10. https://doi.org/10.3989/mc.2021.13220S1107134

Pozzolanic reactivity studies on a miomass-derived waste from sugar cane production: sugar cane straw ash (SCSA)

"This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Sustainable Chemistry & Engineering, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://pubs.acs.org/doi/abs/10.1021%2Facssuschemeng.6b00770.”Biomass has gained in importance as an energy source in recent years. One of the crops that presents interesting opportunities with regard to biomass is sugar cane. In Brazil, sugar cane production is increasing for alcohol and sugar manufacture. Some by-products, such as sugar cane straw, also are obtained during harvesting. Due the calorific value of the sugar cane straw, its use as biomass is increasing. After the straw is burned to produce energy, an ash is obtained: sugar cane straw ash (SCSA). This waste needs an appropriate destination and, since the recent publication of successful studies using biomass derived-ashes as pozzolanic material, the present study aimed to assess the pozzolanic reactivity of sugar cane straw ash. The pozzolanic activity was assessed using a new and simple recently proposed method: evaluation of the electrical conductivity of calcium hydroxide (CH) and pozzolan suspensions, in which solid CH is initially present. These results were compared to those of two other well-established techniques: Fourier transformed infrared spectroscopy and thermogravimetric analysis. The evaluation by all three techniques is similar and shows that sugar cane straw ash is a good pozzolanic material: high lime fixation values for CH:SCSA mixes were determined by thermogravimetric analysis and unsaturation respect to CH in 3.5:6.5 CH:SCSA suspension was achieved at 60ºC. According to this behaviour, a bright future for SCSA as a replacement for Portland cement is expected.We thank CNPq (processo no. 401724/2013-1) and the "Ministerio de Education, Cultura y Deporte" of Spain ("Cooperacion Interuniversitaria" program with Brazil PHB-2011-0016-PC). Thanks are also due to the Electron Microscopy Service of the Universitat Politecnica de ValenciaMoraes, J.; Melges, JLP.; Akasaki, JL.; Tashima, MM.; Soriano Martínez, L.; Monzó Balbuena, JM.; Borrachero Rosado, MV.... (2016). Pozzolanic reactivity studies on a miomass-derived waste from sugar cane production: sugar cane straw ash (SCSA). ACS Sustainable Chemistry and Engineering. 4(8):4273-4279. https://doi.org/10.1021/acssuschemeng.6b00770S427342794

Mineralogical evolution of cement pastes at early ages based on thermogravimetric analysis (TGA)

[EN] Ordinary thermogravimetric analysis (TG) and high-resolution TG tests were carried out on three different Portland cement pastes to study the phases present during the first day of hydration. Tests were run at 1, 6, 12 and 24 h of hydration, in order to determine the phases at these ages. High-resolution TG tests were used to separate decompositions presented in the 100¿200 C interval. The non-evaporable water determined by TG was used to determine hydration degree for the different ages. The effect of particle size distribution (PSD) on mineralogical evolution was established, as well as the addition of calcite as mineralogical filler. Finer PSD and calcite addition accelerate the hydration process, increasing the hydration degree on the first day of eaction between water and cement. According to high-resolution TG results, it was demonstrated that ettringite was the only decomposed phase in the 100¿200 C interval during the first 6 h of hydration for all studied cements. C-S-H phase starts to appear in all cements after 12 h of hydration.Funding was provided by Colciencias (Grant No. Convocatoria 567-2012).Gaviria, X.; Borrachero Rosado, MV.; Paya Bernabeu, JJ.; Monzó Balbuena, JM.; Tobón, J. (2018). Mineralogical evolution of cement pastes at early ages based on thermogravimetric analysis (TGA). Journal of Thermal Analysis and Calorimetry. 132(1):39-46. https://doi.org/10.1007/s10973-017-6905-0S39461321Benboudjema F, Meftah JM, Torernti F. Interaction between drying, shrinkage, creep and cracking phenomena in concrete. Eng Struct. 2005;27:239–50.Holt E. Contribution of mixture design to chemical and autogenous shrinkage of concrete at early ages. Cem Concr Res. 2005;35:464–72.Darquennes A, Staquet S, Delplancke-Ogletree MP, Espion B. Effect of autogenous deformation on the cracking risk of slag cement concretes. Cem Concr Compos. 2011;33:368–79.Slowik V, Schmidt M, Fritzsch R. Capillary pressure in fresh cement-based materials and identification of the air entry value. Cem Concr Compos. 2008;30(7):557–65.Evju C, Hansen S. Expansive properties of ettringite in a mixture of calcium aluminate cement, Portland cement and ß-calcium sulfate hemihydrates. Cem Concr Res. 2001;31:257–61.Bentz DP, Jensen OM, Hansen KK. Olesen, Stang, H. Haecker, C.J. Influence of cement particle-size distribution on early age autogenous strain and stresses in cement-based materials. J Am Ceram Soc. 2001;84(1):129–35.Barcelo L, Moranville M, Clavaud B. Autogenous shrinkage of concrete: a balance between autogenous swelling and self-desiccation. Cem Concr Res. 2005;35(1):177–83.Bouasker M, Mounanga P, Turcry P, Loukili A, Khelidj A. Chemical shrinkage of cement pastes and mortars at very early age: effect of limestone filler and granular inclusions. Cem Concr Compos. 2008;30(1):13–22.Bentz DP. A review of early-age properties of cement-based materials. Cem Concr Res. 2008;38(2):196–204.Ozawa T. Controlled rate thermogravimetry. New usefulness of controlled rate thermogravimetry revealed by decomposition of polyimide. J Therm Anal Calorim. 2000;59:375–84.Ramachandran VS, Paroli RM, Beaudoin JJ, Delgado AH. Thermal analysis of construction materials. Building materials series. New York: Noyes Publications; 2003.Zanier A. High-resolution TG for the characterization of diesel fuel additives. J Therm Anal Calorim. 2001;64:377–84.Tobón JI, Payá J, Borrachero MV, Restrepo OJ. Mineralogical evolution of Portland cement blended with silica nanoparticles and its effect on mechanical strength. Constr Build Mater. 2012;36:736–42.Singh M, Waghmare S, Kumar V. Characterization of lime plasters used in 16th century Mughal Monument. J Archeol Sci. 2014;42:430–4.Majchrzak-Kuçeba I. Thermogravimetry applied to characterization of fly ash-based MCM-41 mesoporous materials. J Therm Anal Calorim. 2012;107:911–21.Silva ACM, Gálico DA, Guerra RB, Legendre AO, Rinaldo D, Galhiane MS, Bannach G. Study of some volatile compounds evolved from the thermal decomposition of atenolol. J Therm Anal Calorim. 2014;115:2517–20.Rios-Fachal M, Gracia-Fernández C, López-Beceiro J, Gómez-Barreiro S, Tarrío-Saavedra J, Ponton A, Artiaga R. Effect of nanotubes on the thermal stability of polystyrene. J Therm Anal Calorim. 2013;113:481–7.Yamarte L, Paxman D, Begum S, Sarkar P, Chambers A. TG measurement of reactivity of candidate oxygen carrier materials. J Therm Anal Calorim. 2014;116:1301–7.Borrachero MV, Payá J, Bonilla M, Monzó J. The use of thermogravimetric analysis technique for the characterization of construction materials. The gypsum case. J Therm Anal Calorim. 2008;91(2):503–9.Tobón JI, Payá J, Borrachero MV, Soriano L, Restrepo OJ. Determination of the optimum parameters in the high resolution thermogravimetric analysis (HRTG) for cementitious materials. J Therm Anal Calorim. 2012;107:233–9.Kuzielova E, Žemlička M, Másilko, J, Palou, M.T. Effect of additives on the performance of Dyckerhoff cement, Class G, submitted to simulated hydrothermal curing. J Therm Anal Calorim. Accepted 29 Oct 2017Genc M, Genc ZK. Microencapsulated myristic acid–fly ash with TiO2 shell as a novel phase change material for building application. J Therm Anal Calorim. Accepted 24 Oct 2017.Singh M, Kumar SV, Waghmare SA. The composition and technology of the 3–4th century CE decorative earthen plaster of Pithalkhora caves, India. J Archeol Sci. 2016;7:224–37.Liu L, Liu Q, Cao Y, Pan WP. The isothermal studies of char-CO2 gasification using the high-pressure thermo-gravimetric method. J Therm Anal Calorim. 2015;120:1877–82.Majchrzak-Kuce I, Bukalak-Gaik D. Regeneration performance of metal–organic frameworks TG-vacuum tests. J Therm Anal Calorim. 2016;125:1461–6.Ion RM, Radovici C, Fierascu RC, Fierascu I. Thermal and mineralogical investigations of iron archaeological Materials. J Therm Anal Calorim. 2015;121:1247–53.Rupasinghe M, San Nicolas R, Mendis P, Sofi M, Ngo T. Investigation of strength and hydration characteristics in nano-silica incorporated cement paste. Cem Concr Compos. 2017;80:17–30.Esteves PL. On the hydration of water-entrained cement–silica systems: combined SEM, XRD and thermal analysis in cement pastes. Thermochim Acta. 2011;518:27–35.Riesen R. Adjustment of heating rate for maximum resolution in TG and TMA (MaxRes). J Therm Anal. 1998;53:365–74.Lim S, Mondal P. Micro- and nano-scale characterization to study the thermal degradation of cement-based materials. Mater Charact. 2014;92:15–25.Gill PS, Sauerbrunn SR, Crowe BS. High resolution thermogravimetry. J Therm Anal. 1992;38:255–66.Mounanga P, Khelidj A, Loukili A, Baroghel-Bouny V. Predicting Ca(OH)2 content and chemical shrinkage of hydrating cement pastes using analytical approach. 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Design and properties of 100% waste-based ternary alkali-activated mortars: blastfurnace slag, olive-stone biomass ash and rice husk ash

[EN] Alkali-activated cements (AACs) technology is being widely investigated as a replacement for ordinary Portland cement (OPC) for environmental benefits. Blast furnace slag (BFS) is one of the most well known precursors used in AACs, having comparable properties to those of traditional OPC-based materials. AACs require alkali solutions, which are commonly based on a combination of sodium or potassium hydroxides with sodium or potassium silicates in high concentration. These alkali solutions represent the use of chemical reagents, and thus can have major environmental, health and economic impacts. Olive-stone (also known as olive pits) biomass ash (OBA) is a residue mainly composed of calcium and potassium oxides. Rice husk ash (RHA) is a rich silica residue from the combustion of rice husk. The combination of both residues can produce a good activating reagent for BFS-based AACs. In the present work, 100% waste-based ternary alkali-activated mortars (TAAM) based on BFS activated by OBA and RHA were developed. The mortars were assessed in terms of their dosage, curing treatment and time evolution. Finally an eco-friendly 100% waste-based TAAM with 67.39 +/- 0.44 MPa after 90 days of curing at 20 degrees C is obtained and a complete microstructural characterization shows a dense and compact matrix with binding gel products labelled as C(K)-S(A)-H and C(K)-S-H.Font-Pérez, A.; Soriano Martinez, L.; Pinheiro, SMDM.; Tashima, MM.; Monzó Balbuena, JM.; Borrachero Rosado, MV.; Paya Bernabeu, JJ. (2020). Design and properties of 100% waste-based ternary alkali-activated mortars: blastfurnace slag, olive-stone biomass ash and rice husk ash. Journal of Cleaner Production. 243:1-11. https://doi.org/10.1016/j.jclepro.2019.118568S111243Adesanya, E., Ohenoja, K., Luukkonen, T., Kinnunen, P., & Illikainen, M. (2018). One-part geopolymer cement from slag and pretreated paper sludge. Journal of Cleaner Production, 185, 168-175. doi:10.1016/j.jclepro.2018.03.007Andrew, R. M. (2018). Global CO<sub>2</sub> emissions from cement production, 1928–2017. Earth System Science Data, 10(4), 2213-2239. doi:10.5194/essd-10-2213-2018Beltrán, M. G., Barbudo, A., Agrela, F., Jiménez, J. R., & de Brito, J. (2016). Mechanical performance of bedding mortars made with olive biomass bottom ash. Construction and Building Materials, 112, 699-707. doi:10.1016/j.conbuildmat.2016.02.065Bernal, S. A., Rodríguez, E. D., Mejía de Gutiérrez, R., & Provis, J. L. (2015). Performance at high temperature of alkali-activated slag pastes produced with silica fume and rice husk ash based activators. Materiales de Construcción, 65(318), e049. doi:10.3989/mc.2015.03114Bouzón, N., Payá, J., Borrachero, M. V., Soriano, L., Tashima, M. M., & Monzó, J. (2014). Refluxed rice husk ash/NaOH suspension for preparing alkali activated binders. Materials Letters, 115, 72-74. doi:10.1016/j.matlet.2013.10.001Cheah, C. B., Part, W. K., & Ramli, M. (2015). The hybridizations of coal fly ash and wood ash for the fabrication of low alkalinity geopolymer load bearing block cured at ambient temperature. Construction and Building Materials, 88, 41-55. doi:10.1016/j.conbuildmat.2015.04.020De Moraes Pinheiro, S. M., Font, A., Soriano, L., Tashima, M. M., Monzó, J., Borrachero, M. V., & Payá, J. (2018). Olive-stone biomass ash (OBA): An alternative alkaline source for the blast furnace slag activation. Construction and Building Materials, 178, 327-338. doi:10.1016/j.conbuildmat.2018.05.157Fernández-Jiménez, A., Cristelo, N., Miranda, T., & Palomo, Á. (2017). Sustainable alkali activated materials: Precursor and activator derived from industrial wastes. Journal of Cleaner Production, 162, 1200-1209. doi:10.1016/j.jclepro.2017.06.151Fernández-Jiménez, A., Palomo, J. G., & Puertas, F. (1999). Alkali-activated slag mortars. Cement and Concrete Research, 29(8), 1313-1321. doi:10.1016/s0008-8846(99)00154-4Font, A., Soriano, L., Moraes, J. C. B., Tashima, M. M., Monzó, J., Borrachero, M. V., & Payá, J. (2017). A 100% waste-based alkali-activated material by using olive-stone biomass ash (OBA) and blast furnace slag (BFS). Materials Letters, 203, 46-49. doi:10.1016/j.matlet.2017.05.129Font, A., Soriano, L., Reig, L., Tashima, M. M., Borrachero, M. V., Monzó, J., & Payá, J. (2018). Use of residual diatomaceous earth as a silica source in geopolymer production. Materials Letters, 223, 10-13. doi:10.1016/j.matlet.2018.04.010Hu, W., Nie, Q., Huang, B., Shu, X., & He, Q. (2018). Mechanical and microstructural characterization of geopolymers derived from red mud and fly ashes. Journal of Cleaner Production, 186, 799-806. doi:10.1016/j.jclepro.2018.03.086Lee, N. K., & Lee, H. K. (2013). Setting and mechanical properties of alkali-activated fly ash/slag concrete manufactured at room temperature. Construction and Building Materials, 47, 1201-1209. doi:10.1016/j.conbuildmat.2013.05.107Liao, L., Zhao, N., & Xia, Z. (2012). Hydrothermal synthesis of Mg–Al layered double hydroxides (LDHs) from natural brucite and Al(OH)3. Materials Research Bulletin, 47(11), 3897-3901. doi:10.1016/j.materresbull.2012.07.007Luukkonen, T., Abdollahnejad, Z., Yliniemi, J., Kinnunen, P., & Illikainen, M. (2018). Comparison of alkali and silica sources in one-part alkali-activated blast furnace slag mortar. Journal of Cleaner Production, 187, 171-179. doi:10.1016/j.jclepro.2018.03.202Mejía, J. M., Mejía de Gutiérrez, R., & Montes, C. (2016). Rice husk ash and spent diatomaceous earth as a source of silica to fabricate a geopolymeric binary binder. Journal of Cleaner Production, 118, 133-139. doi:10.1016/j.jclepro.2016.01.057Mejía de Gutiérrez, R., Mejía, J. M., & Puertas, F. (2013). Ceniza de cascarilla de arroz como fuente de sílice en sistemas cementicios de ceniza volante y escoria activados alcalinamente. Materiales de Construcción, 63(311), 361-375. doi:10.3989/mc.2013.04712Mellado, A., Catalán, C., Bouzón, N., Borrachero, M. V., Monzó, J. M., & Payá, J. (2014). Carbon footprint of geopolymeric mortar: study of the contribution of the alkaline activating solution and assessment of an alternative route. RSC Adv., 4(45), 23846-23852. doi:10.1039/c4ra03375bMoraes, J. C. B., Font, A., Soriano, L., Akasaki, J. L., Tashima, M. M., Monzó, J., … Payá, J. (2018). New use of sugar cane straw ash in alkali-activated materials: A silica source for the preparation of the alkaline activator. Construction and Building Materials, 171, 611-621. doi:10.1016/j.conbuildmat.2018.03.230Moraes, J. C. B., Tashima, M. M., Akasaki, J. L., Melges, J. L. P., Monzó, J., Borrachero, M. V., … Payá, J. (2017). Effect of sugar cane straw ash (SCSA) as solid precursor and the alkaline activator composition on alkali-activated binders based on blast furnace slag (BFS). Construction and Building Materials, 144, 214-224. doi:10.1016/j.conbuildmat.2017.03.166Nie, Q., Hu, W., Huang, B., Shu, X., & He, Q. (2019). Synergistic utilization of red mud for flue-gas desulfurization and fly ash-based geopolymer preparation. Journal of Hazardous Materials, 369, 503-511. doi:10.1016/j.jhazmat.2019.02.059Passuello, A., Rodríguez, E. D., Hirt, E., Longhi, M., Bernal, S. A., Provis, J. L., & Kirchheim, A. P. (2017). Evaluation of the potential improvement in the environmental footprint of geopolymers using waste-derived activators. Journal of Cleaner Production, 166, 680-689. doi:10.1016/j.jclepro.2017.08.007Pereira, A., Akasaki, J. L., Melges, J. L. P., Tashima, M. M., Soriano, L., Borrachero, M. V., … Payá, J. (2015). Mechanical and durability properties of alkali-activated mortar based on sugarcane bagasse ash and blast furnace slag. Ceramics International, 41(10), 13012-13024. doi:10.1016/j.ceramint.2015.07.001Peys, A., Rahier, H., & Pontikes, Y. (2016). Potassium-rich biomass ashes as activators in metakaolin-based inorganic polymers. Applied Clay Science, 119, 401-409. doi:10.1016/j.clay.2015.11.003Rivera, O. G., Long, W. R., Weiss Jr., C. A., Moser, R. D., Williams, B. A., Torres-Cancel, K., … Allison, P. G. (2016). Effect of elevated temperature on alkali-activated geopolymeric binders compared to portland cement-based binders. Cement and Concrete Research, 90, 43-51. doi:10.1016/j.cemconres.2016.09.013Shirley, R., & Black, L. (2011). Alkali activated solidification/stabilisation of air pollution control residues and co-fired pulverised fuel ash. Journal of Hazardous Materials, 194, 232-242. doi:10.1016/j.jhazmat.2011.07.100Tchakouté, H. K., Rüscher, C. H., Kong, S., Kamseu, E., & Leonelli, C. (2016). Geopolymer binders from metakaolin using sodium waterglass from waste glass and rice husk ash as alternative activators: A comparative study. Construction and Building Materials, 114, 276-289. doi:10.1016/j.conbuildmat.2016.03.184Tippayasam, C., Balyore, P., Thavorniti, P., Kamseu, E., Leonelli, C., Chindaprasirt, P., & Chaysuwan, D. (2016). Potassium alkali concentration and heat treatment affected metakaolin-based geopolymer. Construction and Building Materials, 104, 293-297. doi:10.1016/j.conbuildmat.2015.11.027Torres-Carrasco, M., & Puertas, F. (2015). Waste glass in the geopolymer preparation. Mechanical and microstructural characterisation. Journal of Cleaner Production, 90, 397-408. doi:10.1016/j.jclepro.2014.11.074Turner, L. K., & Collins, F. G. (2013). Carbon dioxide equivalent (CO2-e) emissions: A comparison between geopolymer and OPC cement concrete. 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Effect of nanosilica-based activators on the performance of an alkali-activated fly ash

This paper assesses the effect of the use of an alternative activator based on nanosilica/MOH (M = K+ or Na+) blended solutions on the performance of alkali-activated fly ash binders. Binders produced with commercial silicate activators display a greater degree of reaction, associated with increased contents of geopolymer gel; however, mortars produced with the alternative nanosilica-based activators exhibited lower water demand and reduced permeability, independent of the alkali cation used. Na-based activators promote higher compressive strength compared with K-based activators, along with a refined pore structure, although K-activated samples exhibit reduced water demand. Zeolite type products are the major crystalline phases formed within these binders. A wider range of zeolites is formed when using commercial silicate solutions compared with the alternative activators. These results suggest that there are variations in the availability of Si in the system, and consequently in the alkalinity, depending on the silicate source in the activator, which is important in determining the nanostructure of the geopolymer gel.This study was sponsored by the Ministerio de Ciencia e Innovacion of Spain (Project GEORES MAT2010-19934 and research scholarship BES-2008-002440), European regional development fund (FEDER), and the Universitat Politecnica de Valencia (Spain). The participation of SAB and JLP was funded by the Australian Research Council (ARC), including partial funding through the Particulate Fluids Processing Centre, a Special Research Centre of the ARC. A special acknowledgement is also due to the Centre of Electron Microscopy of the Universitat Politecnica de Valencia and Pedro Garces from the Universidad de Alicante for support in some experiments.Rodriguez Martinez, ED.; Bernal, SA.; Provis, JL.; Paya Bernabeu, JJ.; Monzó Balbuena, JM.; Borrachero Rosado, MV. (2013). Effect of nanosilica-based activators on the performance of an alkali-activated fly ash. Cement and Concrete Composites. 35(1):1-11. doi:10.1016/j.cemconcomp.2012.08.025S11135