Fly ash-based geopolymers: Effect of slag addition on efflorescence

Abstract

Blended fly ash/blast-furnace slag geopolymers are focused on due to their excellent mechanical and chemical resistant properties. We investigated the effect of slag partial substitution for fly ash on the efflorescence of the resulting geopolymers. The efflorescence of geopolymer binders was inspected and evaluated through leaching tests. The efflorescence deposits on surface of the geopolymer binders were analyzed using XRD and SEM-EDS. The results showed that sodium and calcium cations leached from geopolymer binders reacted with the atmospheric CO₂ and formed the crystal deposits, gaylussite and calcite, in the forms of granular and angular crystal particles. The slag addition led to a refinement of the pore structure of fly ash-based geopolymers, but an increment in the concentration of alkali leaching. The crystal deposits gradually developed in the pore volume of the binders, and finally exceeded the capacity of pore volume. The extent of efflorescence on the surface of specimens increased with the slag substitution. The visible efflorescence is therefore a result of available alkalis and pore sizes and volumes. Higher concentration of available alkalis and smaller pores (and volume) will lead to more intensive efflorescence.

Keywords

geopolymer / efflorescence / pore structure / fly ash / slag

References

[1] Davidovits J. Geopolymers[J]. Journal of Thermal Analysis and Calorimetry, 1991, 37: 1633-1656.

[2] Duxson P, Fernández-Jiménez A, Provis JL, et al. van Deventer. Geopolymer Technology: The Current State of the Art[J]. Journal of Materials Science, 2007, 42: 2917-2933.

[3] Davidovit J. Geopolymer Chemistry and Applications[M], 2008 France: Institut Géopolymére.

[4] McLellan BC, Williams RP, Lay J, et al. Costs and Carbon Emissions for Geopolymer Pastes in Comparison to Ordinary Portland Cement[J]. Journal of Cleaner Production, 2001, 19: 1080-1090.

[5] Zhang Z, Provis JL, Reid A, et al. Geopolymer Foam Concrete: An Emerging Material for Sustainable Construction[J]. Construction and Building Materials, 2014, 56: 113-127.

[6] Duxson P, Lukey GC, Separovic F, et al. Effect of Alkali Cations on Aluminum Incorporation in Geopolymeric Gels[J]. Industrial and Engineering Chemistry Research, 2005, 44: 832-839.

[7] Lloyd RR, Provis JL, an v Deventer JSJ. Pore Solution Composition and Alkali Diffusion in Inorganic Polymer Cement[J]. Cement and Concrete Research., 2010, 40: 1386-1392.

[8] Škvára F, Šmilauer V, Hlavácek P, et al. A Weak Alkali Bond in (N, K)-A-S-H Gels: Evidence from Leaching and Modeling[J]. Ceramicssilikaty., 2012, 56: 374-382.

[9] Škvára F, Kopecký L, Myšková L, et al. Aluminosilicate Polymersinfluence of Elevated Temperatures, Efflorescence[J]. Ceramicssilikaty, 2009, 53: 195-204.

[10] Kani EN, Allahverdi A, Provis JL. Efflorescence Control in Geopolymer Binders Based Natural Pozzolan[J]. Cement and Concrete Composites, 2012, 34: 25-33.

[11] Szklorzová H, Bílek V. Influence of Alkali Ions in the Activator on the Performance of Alkali-activated Mortars[C]. International Symposium on Non-traditional Cement and Concrete, 2008 Brno: Czech Republic.

[12] Duxson P, Provis JL, Lukey GC, et al. 39K NMR of Free Potassium in Gopolymers[J]. Industrial and Engineering Chemistry Research, 2006, 45: 9208-9210.

[13] Puligilla S, Mondal P. Role of Slag in Microstructural Development and Hardening of Fly ash-slag Geopolymer[J]. Cement and Concrete Research, 2013, 43: 70-80.

[14] Provis JL, Myers RJ, White CE, et al. X-ray Microtomography Shows Pore Structure and Tortuosity in Alkali-activated Binders[J]. Cement and Concrete Research, 2012, 42: 855-864.

[15] Yang T, Yao X, Zhang Z, et al. Mechanical Property and Structure of Alkali-activated Fly Ash and Slag Blends[J]. Journal of Sustainable Cement-based Materials, 2012, 1: 167-178.

[16] Ma Y, He J, Ye G. The Pore Structure and Permeability of Alkali Activated Fly Ash[J]. Fuel, 2013, 104: 771-780.

[17] Yang T, Yao X, Zhang Z. Geopolymer Prepared with High-magnesium Nickel Slag: Characterization of Properties and Microstructure[J]. Construction and Building Materials, 2014, 59: 188-194.

[18] Ismail I, Bernal SA, Provis JL, et al. Modification of Phase Evolution in Alkali-activated Blast Furnace Slag by the Incorporation of Fly Ash[J]. Cement and Concrete Composites, 2014, 45: 125-135.

[19] Bernal SA, Provis JL, Walkley B, et al. Gel Nanostructure in Alkaliactivated Binders Based on Slag and Fly Ash, and Effects of Accelerated Carbonation[J]. Cement and Concrete Research, 2013, 53: 127-144.