Solution‐Controlled Dissolution of Supplementary Cementitious Material Glasses at pH 13: The Effect of Solution Composition on Glass Dissolution Rates

Abstract

Supplementary cementitious materials (SCMs) are widely used to partially replace portland clinker in blended cements. Reducing clinker contents further without compromising the development of early strength necessitates a better assessment and enhancement of the reactivity of the available SCMs. To this purpose, the reactivity of synthesized calcium aluminosilicate glasses covering a compositional range from blast-furnace slags (BFS) over fly ashes to silica fume was analyzed by dissolution experiments. Initial glass dissolution rates were measured at 20°C and pH 13, and with varying initial concentrations of aqueous Al, Ca, and Si. At pH 13, glass dissolution rates were observed to scale linearly with the glass Ca/(Al + Si) molar ratio. Ca-rich blast-furnace type glass dissolution was shown to be up to one order of magnitude faster than tectosilicate fly ash and silica fume type glass dissolution, supporting different pathways to dissolution. In solutions that are strongly undersaturated with respect to hydrous glass and hydration products, glass dissolution rates are independent of changes in solution undersaturation and aqueous Si activity. In contrast, dissolution rates decrease with aqueous Ca concentration for all glasses and with aqueous Al concentration for tectosilicate-type glasses. The insights gained are instrumental in finding ways to enhance SCM reactivity.

Quantitative Analysis of Phase Assemblage and Chemical Shrinkage of Alkali-Activated Slag

“…(Kulik et al 2003;Lothenbach and Gruskovnjak 2007;Myers et al 2014Myers et al , 2015 follow the previous studies (Myers et al 2015). The thermodynamic simulation assumes that slag dissolves congruently, which is reasonable for aluminosilicate glass (Snellings 2013). The main chemical composition of slag used in this simulation follows Table 2.…”

TC 238-SCM: hydration and microstructure of concrete with SCMs

“…This indicaties that the 29 Si MAS NMR spectra of the alkali-activated slags do not give clear evidence for a preferential dissolution of specific 29 Si sites in the slag. This divergence of views almost certainly arises from the fact that leached layers tend to be formed on glasses in the acidic solutions used for selective dissolution, but not in alkaline solutions as found in cement blends [37,57,71] and supports the use of sub spectra from the original anhydrous material.…”

Assessing, Understanding and Unlocking Supplementary Cementitious Materials

“…While predictions of SCM blended cement hydrate assemblages has greatly benefitted from recent advances in thermodynamic modelling, only very little data on dissolution kinetics of even common SCMs such as blast furnace slag is available. In response, recent simple dissolution experiments have clearly shown that SCM dissolution rates in alkaline solutions are 2-4 orders of magnitude lower than C 3 S and C 2 S [26][27][28]. This strokes well with the generally lower reactivity of SCMs.…”

“…This strokes well with the generally lower reactivity of SCMs. The dissolution experiments showed that SCM reactivity can be rationalized following well-known concepts from glass chemistry such as available reactive surface area and glass polymerization [18,26,29]. Interestingly, dissolution experiments have also shown strong rate dependencies on solution composition, i.e.…”

“…Interestingly, dissolution experiments have also shown strong rate dependencies on solution composition, i.e. pH, solution saturation, and presence of activators or inhibitors such as dissolved Al species [26,30]. These insights are instrumental in better understanding SCM reactivity and can be exploited by engineering solid SCM properties and/or solution composition.…”