Early stage dissolution characteristics of aluminosilicate glasses with blast furnace slag‐ and fly‐ash‐like compositions

Abstract

Supplementary cementitious materials (SCM) have been used by the cement industry for decades to partly replace the portland cement fraction of concrete binders. This is particularly important today in addressing CO2 emissions from the cement manufacturing process. However, defining the reactivity of these mainly aluminosilicate‐based materials and their influence on portland cement hydration chemistry has challenged the research community and has limited SCM replacement levels in cementitious binders. In this study, aluminosilicate glasses as models for blast furnace slag and fly‐ash systems were synthesized and exposed to different activator solutions in a continuously stirred closed system reactor for a period up to 3 hours. Solution compositions were measured from the very first minutes of dissolution and correlated with results from complementary solid surface analysis. Initial Ca concentration maxima in the first 30 minutes of exposure to the activating solution was a common feature in most dissolution profiles with a subsequent rapid decline attributable to Ca‐reincorporation on the reacting surface. Surface‐specific analysis confirmed Ca and Al enrichment at the surface, suggesting the formation of a Ca‐modified aluminosilicate layer, supporting a dissolution‐reprecipitation mechanism for SCM reactivity. Differing chemistries are thought to be responsible for the Ca and Al reintegration on the reacting surface depending on the pH of the solution; near‐neutral conditions favor Ca‐readsorption and surface condensation reactions, whereas alkaline solutions favor Ca‐reintegration via covalently bound phases.

Reactivity of industrial wastes as measured through ICP‐OES: A case study on siliceous Indian biomass ash

“…Figure A illustrates that this silica dissolves to varying extent depending on NaOH molarity (and thus, solution pH). These results indicate the glassy silicate network present in the ash dissolves mainly through hydrolysis, following an asymptotic temporal trend . As might be expected over the time period considered, while minimal Si was dissolved in water, increasing NaOH molarity, and therefore pH, strongly influenced both Si extraction extent and rate.…”

“…It is well understood that alkali‐activation chemistries rely heavily on precursor solubility and dissolution in alkali‐rich solutions . In this study, we demonstrated the utility of a multifaceted characterization approach with the ultimate goal of establishing validity of product chemistry estimation via comparison of dissolution and reaction experiments as measured by ICP‐OES.…”

“…As discussed by Iler, and as observed before and since, amorphous silica displays significant solubility in alkaline media, due to the acidity of typically hydroxylated surface species as well as the propensity for hydrolysis of non‐equilibrium Si‐O bonds in alkaline environments, yielding the formation of silicate ions in addition to the orthosilicic acid monomers present during dissolution in water . The situation becomes more complicated in the presence of other polyvalent metal oxides, such as is the case with most supplementary and alternative cementitious materials …”

Heat‐cured concrete: Improving the early strength and pore structure by activating aluminosilicate internal curing agent with triisopropanolamine

“…Both hydrates had similar Ca, Si, and Al contents, suggesting that the radial shape hydrates developed from the particle shape hydrates, which means that TIPA significantly promoted the formation of hydrates. In view of previous reports, the formation of hydrates could presumably be described as follows. The surface of LWFA was initially smooth and flat.…”

“…LWFA is an aluminosilicate material covered with a dense Si and Al rich glassy phase, and it is often considered to be inert and has no reactive activity at low temperature (ie, the standard‐cured regime) in cement system. Because of the weak molecular migration at low temperature, considerable amounts of dissolved Al 3+ and Fe 3+ ions precipitated on the surface of LWFA rather than forming a complex with TIPA Figure , top right) . Hence, the concentration of Al 3+ and Fe 3+ ions decreased after 1 day.…”