Designing Precursors for Geopolymer Cements

Abstract

This paper presents a discussion of the ability to design raw materials for use in geopolymers. To provide a “green” material to complement existing cement binders, as well as in the interests of waste beneficiation, various potential means of tailoring geopolymer precursor chemistry and particle behavior are outlined. The opportunities presented by the development of one‐part “just add water” geopolymer formulations are identified as exceeding the potential of the traditional two‐part (solid plus alkaline activator solution) mix design. The key roles played by network‐modifying (alkali and alkaline earth) cations and alumina in rendering glassy phases “ideal” for geopolymerization are discussed, and the potential value of ASTM Class C ashes in synthesis of high‐performance geopolymers becomes evident. This provides a significant step toward the development of international standards for the application of geopolymer binders in the construction industry worldwide, and raises a number of important challenges for researchers in the field of geopolymer and cement technology.

Alkali-activation potential of biomass-coal co-fired fly ash

“…15 content of alkaline earth metals (e.g., Ca 2+ ), which are network modifiers and promote the dissolution of aluminum [18]. However, the impact of the ash composition on the subsequent repolymerization is less clear from these data.…”

“…As a result, the ash with the highest carbon content (C-CA-15) did not form a hardened geopolymer gel at Ms = 0 or 2 (plotted at zero strength) even though it had a slightly higher glassy content than B-CA-4, which formed hardened gels at all Ms values. Also, the higher calcium content of B-CA-4 may have contributed to its higher strength at Ms = 2 (relative to both C-CA-15 and A-FA-0), because a greater concentration of alkaline earth metals such as calcium in the precursor has been shown to increase geopolymer strength [18].…”

Synthesis of stoichiometrically controlled reactive aluminosilicate and calcium-aluminosilicate powders

“…Samples A and B (empirical formulas 2SiO2·Al2O3 and 4SiO2·Al2O3, respectively) were chosen to represent the range of bulk silicon and aluminium content typically found in fly ashes, with A also representing the approximate composition of metakaolin (see Figure 1) [19]. Samples C, D, E and F (empirical formulas 0.800CaO·SiO2·0.078Al2O3, 1.214CaO·SiO2·0.078Al2O3, 0.709CaO·SiO2·0.026Al2O3 and 1.104CaO·SiO2·0.026Al2O3, respectively) were chosen to enable synthesis of binders exhibiting chemistry in regions of the quaternary CaO -Na2O -Al2O3 -SiO2 system which are important for the study of sodium-and aluminium-substituted calcium silicate hydrate gels, the main reaction product present in alkali-activated slag binders [11,20].…”

“…This can be particularly challenging due to the wide variation of chemical and physical characteristics exhibited by commercial geopolymer precursors where a range of chemical reactivity is observed, Postprint of a paper published in Powder Technology, 29(2016): [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]. Version of record is available at http://dx.doi.org/10.1016/j.powtec.2016.04.006 3 meaning it is often difficult to distinguish reactive from inert species.…”

Microstructure and durability of alkali-activated materials as key parameters for standardization

“…Ground granulated blast furnace slag (GGBFS) and fly ash (FA) are currently accepted as attractive precursors for large-scale industrial production of AACs [9], as concretes based on these materials develop high mechanical strengths, and can have more favourable rheological properties and lower water demand, compared with mixes based on calcined clays [10]. AACs containing different ratios of GGBFS and FA have been extensively assessed, and used for large scale structural applications over the past decades.…”